Does an engine that combines an air-breathing rocket and non-air-breathing rocket exist? Does a rocket engine that combines air-breathing and non-air-breathing modes exist?

The advantage would be it would have to carry a smaller tank and less oxygen, leaving more room for payload on a weight basis.

There's a very recent claim for an engine called Fenris, which claims to be a no-moving-parts "rocket" that uses ambient air for its oxidizer.

On the face, that sounds like a ramjet, but the claims made by the inventors appear (to me) to be investor bait, rather than anything that could actually be true.  Video on the entry page at the inventor's web site shows a burn more like that of a poorly designed torch, than a rocket or jet.

As noted in comments, there is also the SABRE engine concept -- this is not yet a working engine, as far as I know, but will/would be a hydrogen-fueled turbo-ramjet which uses the liquid hydrogen to liquefy intake air while in jet mod, for use as oxidizer when it switches to rocket mode.  The intent is for use as a spaceplane-to-orbit.

The concept of a launch system combining an airbreathing 1st stage and a nonairbreathing 2nd stage is as old as the X-1 rocket plane carried aloft by a modified B-29
bomber, and carries on a tradition which includes the B-52/X-15 pair and today's Virgin Knight/SpaceShip 2.

This approach has the advantage of weight savings for these reasons:

  Less carried oxidizer, more payload
  Lighter structural requirement from lower "max Q" aerodynamic stresses
         as a result of launching from a higher altitude

However, the vast majority of energy required for an orbital launch (or beyond)  comes from the 90 to over 20,000 (geosynchronous orbit) miles of remaining vertical lift and acceleration to 18,000 mph outside the atmosphere, clearly the realm of the (non airbreathing) rocket.

Any mechanism for breathing air, while viable as a 1st stage, becomes dead weight for the remainder of the flight.  This approach can be replaced with a rocket 1st stage for heavy lifters, such as the Saturn V, the Space Shuttle, and Falcon lineage.  (Note the Shuttle did not need those big wings to bring payload to orbit either, but lowered cost by returning the main engines for re-use).

For aircraft, airbreathing rams, turbochargers, and centrifugal or axial compressors are the most cost effective way to increase power.  Used in conjunction with lifting wings, they increase payload carrying capacity and range through greater efficiency.  Since jets use excess air in proportion to fuel for combustion, more power can be generated by adding more fuel to the airflow.  These "after burners" can be used to increase thrust significantly, but are less efficient.

While turbojets could be considered "airbreathing rockets", the very air they breathe becomes a drag/friction heat impediment at hypersonic speeds.

Research could continue with use of very cold fuels such as liquid hydrogen or a hybridized air/LOX intake in order to increase the density of fuel/air intake charge of a jet, but manufacturing LOX while in flight for rocket propulsion may be beyond reality.

See LACE and SABRE for more information.


What aircraft is in The Do’s music video? There is a band call The Do, in one of their videos there is a plane with a strange configuration of turbines, it looks like a version of a 747.

You can find the video on Youtube "The Dø - Despair, Hangover & Ecstasy"

Does anyone know what plane it is?

This looks like G-BDXJ, a modified 747 that was also featured in James Bond Casino Royale as well as other movies.

Edit: The linked wikipedia page confirms this:

  It was used as a prop in the music video of The Dø song "Despair, Hangover & Ecstasy"

It is indeed a modified 747, based at Duxford and parked next to the "Top Gear" test track.


Is there currently a measurable shortage of pilots? Is there a clearly identifiable and measurable pilot shortage right now? If so, is it a shortage of pilots or of captains, i.e. more experienced pilots? Are airlines changing any personnel rules - like time to go from first officer to captain - that would imply there is a pilot shortage?

If any shortage is for captains couldn't airlines 'upgrade' first officers to fill the places? But presumably that would create a shortage of FOs in turn.

Here in the US (because this varies around the world) some sources do say there is a pilot shortage. There are many reasons that have been cited for the decrease in pilots here in the states. But the main points seem to be,

Rising Costs of training
FAA upping the required hours (250 -1500) for a full ATP ticket
Lower conversion from military pilots (there was a time when many of the commercial pilots out there were former service pilots)
Lower Salary Prospects: its no mystery that pilots don't make what they once did nor get the perks they once did.

Another factor that effects this once you are in the industry is the fact that "seniority" does not transfer over from airline to airline. Generally this is not an issue if you work for someone like American or Delta who have plenty of jobs and steady routes. But if you are captain at NotSoWellEstablishedAir and they go belly up you will most likely join one of the others lower in the ranks if not at the bottom.

Another thing that is worth mentioning is that it may be more advantageous for a pilot to remain a very senior first officer instead of becoming a very junior captain. You may have more power over your route choice, time off, and general schedule as a senior first officer than as a newly minted captain. For some pilots, like those who may be trying to start a family this may be seen as an advantage.

As for the shortage over seas (outside the US) that stems from different issues. First and foremost many countries have seen great and more importantly fast economic prosperity which has allowed them to get into the aviation game. A game traditionally filled with high costs and heavy regulations. As such many newly wealthy nations have been able to enter the aviation world much faster than their regulations and training programs can keep up with. The FAA is almost 60 years old with aviation regulations dating back to the 30's with the CAA. There are even some american issued pilots licensed signed by the Wrights them selves from the very early days. Other countries simply don't have the history of growing with aviation like the US and similar countries have had. Thus they have all these new planes but no one to fly them and no well established programs and regulations to create the pilots. In turn they are forced to import trained, certified pilots from elsewhere.

I'll put it this way: There wouldn't be a pilot shortage if the pay was right and regulators would stop putting in place roadblocks to professional airline pilot training like the asinine 1500 hour rule for first officers.

The saddest thing about this nation's corps of professional pilots is that it's a profession of people who absolutely love what they do and are exploited and treated as wage slaves by company brass who know this.

At this point, though, things are beginning to change in the USA.  The airlines are faced with a glut of senior captains over 65 now and forced to take mandatory retirement.  With typical starting salaries for regional FOs being about \$18-\$22k based upon a realistic calculation of pay, being on duty for 14-16 hours a day, and forced to live in crowded apartments with several other pilots, it's no wonder that people pursuing a career as a professional pilot have dwindled.  This in contrast with the rising demand for pilots has created a situation where the airlines have no choice but to act.  Salaries are being increased, and many airlines are adopting their own flight training programs where they cover the costs to train promising candidates in exchange for a mandatory employment contract for an agreed upon length of time (usually about 7 or so years).


Do we fly full size aircraft with video game style joysticks? Are there planes with electronic joysticks as shown below?

RC airplanes are incredibly effective at using this technique. For actual planes it would remove the need for rudder pedals and a stick along with potentially being easier to get used to.

Are thumb controlled sticks used in aviation? or is there a reason to why they aren't used?

They are used, they are just bigger joy sticks than used for RC flying.

A current example is the Airbus A320 (and related family) of passenger aircraft.  A short video of the joystick in action(called "side stick", start at about 1 minute in).  There is no direct mechanical linkage between the stick and the flight controls.

(For the A330, but basically the same).

For more detail, you can download this (slightly out of date, but with enough information to be useful) Flight Controls lesson for the A320 here.

  I am more curious about thumb controlled flying as you could control
  everything from what essentially looks like a video game controller.

@Rory Alsop noted that ...

  ... even video game controllers are terrible for this. The bigger the stick the better fine control you have over it. This is why for flight
  sims for PC's and consoles, keen players buy proper joysticks -
  otherwise they are twitchy and hard to handle

Video game controllers require two hands, have poor sensory feedback (as compared to a stick type controller) and are not as ergonomically effective as a multi-axis stick.  Also, there are some "push buttons" on a control stick that allow moving a finger or a thumb to activate other functions, like the "take control" button in the side stick(For swapping control between left seat and right seat pilots).  On some sticks you'll also have the "push to talk button" for the radio, as has been done for decades.  It's an efficient use of the hand, without having to move the hand for multiple tasks.

Joy sticks and control yokes are traditional for full size aircraft for very functional reasons going back to the dawn of flight.  All of the pre-WWII aircraft were controlled by direct mechanical linkage. the is moving the stick or control column for and aft pulled on cable that moved the elevator up and down.   Moving the stick or wheel (yoke) side to side caused one aileron to go up and the other down. The ruder pedals were on a toggle or t bar connected to the rudder cables and directly moved the rudder left and right. The larger the plane the larger and more stressful the movements were as the aerodynamic forces on the controls (back pressure) increases with the aircraft's size and speed. This is the original reason multi engine bombers and cargo planes started having co-pilots.  In bad weather it might take the strength of 2 men to handle the controls. By WWII planes were so large and fast that hydraulically boosted controls were needed.  Think of these like the power steering or brakes on your car. Large movements were needed to open and close the valves and allow the hydraulic fluid to flow and move the controls. The first production aircraft that did not have a mechanical connection between the pilot ant the control surfaces was the General Dynamics F-16 (1979 - present).  The F-16 is a side stick "fly by wire" design were the pilot tells the computer what he wants to do, and the quad redundant digital computers figure out what control surfaces need to move to achieve this.  It also prevents maneuvers that would exceed certain safety parameters.  Since planes are durable and stay in service for decades, familiar patterns of instrumentation and controls last for decades with few changes.


Is excess fuel leaking normal during take off of a B737? When we look over this video

it's noted that some fuel is coming off from the left wing during the rotate. This is the position of the fuel vent within the wing, of course, 'leaking' due to new vertical and horizontal forces combined which, in turn, force fluids backwards and outwards in a swept wing, so not exactly a fuel dump procedure as published. My question is: is normal or correct for an airliner to have such an excess of fuel causing it to reach the fuel vent until it spills during take off? Shouldn't this wing carry less fuel?

EDIT: To help explain exactly what I am talking about, we are looking for a very thin trail of fuel coming from the fuel vent of the left wing. This vent is located under the wing and a little ahead the (left) aileron. We are not talking about a vortex from the engine vortex generators or from the flap edges. ;)

This:

This other video shows the same with much more detail:

No it is not normal. It can happen if the wing tanks are fully filled, typically for long trips or when the airline is tankering fuel to airports where fuel is more expensive. When cold fuel warms up it expands. With full tanks, the fuel has to go somewhere and it flows through the vent channels and will end up in the surge / vent tanks in the wing tips. From here the fuel can flow back into wing tanks (when there is space again) through a check valve.

 Boeing 737 fuel vent system. Source: Aeronautics guide

There is a little NACA duct at the underside of each wingtip (about a meter from the tip) in the surge tank. That ensures a positive pressure in the surge tank and through the vent channels in the fuel tanks. This help the fuel pumps, reduces evaporation of the fuel and prevents a vacuum when the fuel is being used.

source: www.b737.org.uk

If the wing tanks are overfilled, this is where the fuel will come out.

source: the aviation forum: user Keithnewsome

During the take-off the fuel tanks are changing their shape a little bit because the wing is flexing up. This may slightly reduce the volume of the tanks so if they are fully filled you will see a fuel trail spilling from the fuel vents at take-off.

Another situation where this may occur is at zero-gravity. I have seen this many times during parabolic flights with a Cessna Citation. At zero gravity the fuel will start to fly around in the tank and it will find its way to the exit (the vents at the wing tip) resulting in an impressive cloud of fuel from the wingtips. Whilst it looks like a big cloud, it is actually very little fuel that is lost.

In the video, you see the fuel trail starting below the wing (at 1:28), a couple of seconds into the 0-G part of the flight.

What you see is not actually fuel. It is the vortex coming off an engine strake in which some water vapour in the air condenses. You can see more of that phenomenon in this answer.


Why don't most military transports use modern commercial engines? Why don't most military transports use modern commercial engines?

More specifically planes like C-17, the Antonov's use older less powerful engines while modern efficient and powerful engines are available in the commercial sector.

Some do; the C-17 you mention uses the Pratt & Whitney PW2000 which is also used on the Boeing 757. The USAF and USN also fly the C-40 which is the military variant of the 737 and carries the same engines.

Generally the answer is that military aircraft are built on spec for the military which is a bit different than the way the civilian market works. Civilian builders shop a design around to airlines to get some deposits then build the airframes (the notable exception being the 747 which was largely the idea of Pan-Am CEO Juan Trippe). This often causes there to be new aircraft every few years on the civilian side as Boeing needs to stay in business... On the contrary the military will put out a request for designs to meet their needs, evaluate the submissions and chose what is to be built. They can do this as often or as little as they so please (or as budget allows). If there is no active conflict or need for new tech then the military will keep flying what they have. Many military aircraft have cutting edge tech from the era they were designed in, they may however be dated by todays standards.

Much like the FAA here in the US the various military branches have their own certification programs and regulations thus upgrading and bringing in new gear may require something to be approved this can unfortunately stifle new technology being included due to high time and cost of approval. Similarly military requirements may be different, while a civilian airframe may suffice they may have takeoff length requirements or something similar that necessitate more thrust than their civilian counterpart thus variances in outfitting may occur.

There are several reasons, although all of them can be reduced to a single one: they have different requirements:

Military aircraft are most of part of their life on idle, in a hangar. We do not want to use military aircraft; we only use them when there is a conflict. That kills any economical trade-off of fuel savings for example.
Mission of military aircraft is extremely different. No discussion about fighters as they are flying at higher Mach number (where commercial airplanes engines are not useful), concerning transport aircraft the commercial one are optimized for fuel saving that creates an expensive engine that is amortized with fuel savings along the life of the airplane and transport military airplane fly very often.
There are requirements from military aircraft not satisfied by commercial engines, like for example, being able to land in sand or bumpy terrain. Engines from military aircraft are protected against that.

Saying that, there are some commonalities that engine manufacturers try to achieve, but that can be found at component level (i.e. having the same turbine for some stages).


Why is the autopilot called "George?" The autopilot of an airplane is frequently referred to as "George" (for example, in this answer). When did this nickname enter common usage, and what is its origin? Please cite sources if possible!

The first "practical" autopilot was invented by George DeBeeson (the patent can be found here, updated here) - This seems to be the most likely reason for the informal name "George" for the autopilot system on aircraft.

Autopilots are also sometimes called "Otto" (as in Otto the Autopilot from Airplane!, and our very own chat bot, but this seems to be less common than "George".

The term "George" as a reference to autopilots originated in the RAF in WWII.  It is a reference to the aircraft's "owner" King George.  Also, at the time, there was a popular radio show referenced in an earlier answer that may have reinforced the use of "George". I have spoken to a number of British WWII pilots. Everyone assumed it was a reference to King George.  None of these pilots were aware of the name of the inventor of the earliest autopilot.  They were, however, aware of the name Sperry.


What job opportunities are there for low time pilots in Malaysia? Does a new pilot who has just obtained ATPL license has job opportunities?

When I search at pilot job offered on Internet, they mostly required more than 3,500+ flying hours. What I knew about those who obtained ATPL license have flying hours aroun 1500 hours. It mostly includes aviation academy training used turboprop engine plane and they are very light weight. The jobs ads require those pilot who have flown aircraft more than 40,000 lbs.

Will a new pilot get an opportunity to get such a job? How does new pilot get their job under these kind of conditions?

Malaysia I suspect would be very similar to where i started working a few years back in Africa. In countries (continent) like that you really need to be there if you are a low timer. Hanging around the airports and meet people who could help you with finding your first opportunity forget about sending CV's from miles away hoping for an opportunity, key here is to be pro active and make yourself known locally....


How did aircraft in WW2 navigate to the carrier? How did aircraft in WW2 navigate to the carrier after their mission? I was thinking of something like a beacon installed in the carrier but wouldn't it reveal the location of the carrier itself?

You are correct. US carriers did indeed have a homing beacon that enabled aircraft to find them.

The carrier transmitting units were called YE or YG, and the receiving units in the planes were designated ZB, and called "Zeebies". The transmitters consisted of rotating "superfrequency" beacons that broadcast different morse letters in different directions that could be decoded by the ZB units, but sounded like static to ordinary listeners. They were installed on all US carriers in WW2.

Here is an excellent summary of the system and its history. More information can be found here and here, and History SE already has a question about it.

The British also had a similar system, installed on a carrier in 1936 and used through the war.

Sources also indicate that the Japanese employed a radio homing system (Hirohito's War by Francis Pike), but I have been unable to locate any details.

American carriers were fitted with a line-of-sight radio homing system, but Japanese aviators were probably limited to old-fashioned dead reckoning, since Japan was less advanced in electronics than the U.S.


Is this paragraph about the dihedral effect in the FAA's Glider Flying Handbook correct? I've been reading the FAA's Glider Flying Handbook, 2013 (FAA-H-8083-13A). In chapter 3 ("Aerodynamics of Flight"), the book is discussing stability. On page 3-12, it states:

  Dihedral is the upward angle of the wings from a horizontal (front/rear view) axis of the plane. As a glider flies along and encounters turbulence, the dihedral provides positive lateral stability by providing more lift for the lower wing and reducing the lift on the raised wing. As one wing lowers, it becomes closer to perpendicular to the surface and level. Because it is closer to level and perpendicular to the weight force, the lift produced directly opposes the force of weight. This must be instantly compared to the higher and now more canted wing referenced to the force of weight. The higher wing's lift relative to the force of weight is now less because of the vector angle. This imbalance of lift causes the lower wing to rise as the higher descends until lift equalizes, resulting in level flight.

That doesn't sound right to me.

This paragraph says that there's more lift on the lowered wing and less lift on the raised wing. That's not true, is it? The amount of lift only depends on a wing's airspeed and angle of attack, not on the wing's bank angle.

The paragraph then explains that the lowered wing produces more upward lift than the raised wing. I think this is true, but it's not relevant, because upward lift isn't the only lift which contributes to rolling moment. Rolling moment depends on the total lift (and the direction of the lift).

All in all, I think that dihedral can't produce a stabilizing rolling moment in the way that the book says that it does. Any stabilizing effect must come from a difference in airspeed or angle of attack between the two wings.

Is the book's description of dihedral correct?

No, the explanation is not correct.

Tanner, you are right when you say that lift does not depend on bank angle. Lift is caused by a pressure difference, and pressure can only act perpendicularly to a surface. Therefore, the lift on each wing and its lever arm to the center of gravity won't change with bank and no "correcting" rolling moment is created.

Instead, what does happen is a side force from the wing's bank angle which will accelerate the airplane sideways. This in turn will result in a sideslip condition, and only now will a dihedral effect show up: By changing the angle of attack on each side differently, the sideslip in combination with dihedral will create a correcting rolling moment.

As you correctly observe, a stabilising effect can only come from a difference in angle of attack between both wings, and that only occurs in a sideslip.

Yes, it is correct.  Consider an airplane with a positive 5° dihedral to its wings.  If the lift the airfoils generate is perpendicular to its span line, this means that in level flight the lifting force parallel to the plane’s vertical axis is L*cos(5°) for both wings.  If the airplane is rolled 30° to the left, then the lift generated by the left wing parallel to the force of gravity is L * cos(25°) whereas the lift generated by the right wing is L*cos(35°).  This imbalance in lift causes a moment about the plane’s CG, causing it to roll back level and providing both a positive lateral static and dynamic stability.


Does lift equal weight in a climb? This subject keeps coming up in the discussions and questions such as this one, which asks if lift equals weight in level flight. Good answers there, pointing out that upwards force has many sources. But also some that need clarification.

It is also mentioned at several places on this Aviation SE site, in question & comments, that lift always equals weight if the aeroplane is not accelerating upwards or downwards, since only an acceleration requires extra force according to Newton.
With zero wind, lift is always defined as the force perpendicular to the flight path, but gravity does not tilt with the aircraft axes. My question therefore is also about the sum of all vertical forces: in a steady climb, is the total upwards vertical force from all sources (wing, tail, engines, fuselage) larger than, or equal to the weight of the aircraft.

If larger: please quantify.
If equal: please explain why.

Addition
An answer.

It depends on exactly how you define "lift" and "weight". You might say intuitively that lift is all the forces acting on the aircraft in the upward direction, like this:

In this case, lift must equal weight, otherwise the aircraft would be accelerating. That is, it's rate of climb would be changing.

But it's more usual to define lift this way:

Here, lift and weight are equal in magnitude, but in different directions. Of course lift doesn't need to be equal in magnitude: it can be adjusted by the angle of attack. But let's suppose lift is equal to weight and see what happens.

Let's do all our calculations with Earth as the frame of reference1. It's useful to decompose lift into a sum of vertical and horizontal components so we can analyze the horizontal forces and the vertical forces separately:

Comparing the vertical component of lift with weight, we can see they are not equal:

Considering only the vertical forces drawn here, there is a net downward force on the aircraft. So why then is the rate of climb not decreasing?

A similar transformation happens to thrust. In a climb, thrust provides an additional upwards component. And of course we must also consider drag. Point being in a steady climb, lift (by the conventional definition) is not equal to weight, but the sum of all the vertical components of lift, thrust, and drag do equal weight.

Let's add an arbitrary amount of drag, and enough thrust to balance the vertical forces.

Now the vertical forces are balanced, but the horizontal forces must also be balanced if we want stable flight. Adding all the horizontal forces in my drawing, there's a net force to the left. So this aircraft may be maintaining a steady rate of climb at this instant, but it's losing speed and probably headed for a stall.

Remember, we initially set lift equal in magnitude to weight, and this is what happens. Without changing the direction or magnitude of lift, there's no solution that results in stable flight.

Therefore, a climbing aircraft requires less lift. To maintain this direction and velocity, this pilot must reduce lift by reducing the angle of attack, and increase thrust such that the vectors add to zero and there's no net force on the aircraft. Reducing lift will also reduce drag.

1 Any other frame of reference could work. For example we could use the aircraft as the frame of reference, which would mean lift is always up, but weight would change direction.

Since a climb is produced by either Lift or Thrust, a clever answer to this question would be that Lift always exceeds Weight since, in both Propeller and Jet airplanes, Thrust is the result of Lift produced by spinning blades.
Otherwise, it appears that the answer to this question depends on who you ask and how the climb is flown.
If you ask a Pilot (like myself), they will tell you what they were told during flight training - that to climb, you increase lift. Since, in level flight vertical Lift equals Weight, this means that, in a climb, vertical Lift must be greater than Weight. As explained by one of the premiere flight training schools "To get a plane to climb, we need to create more lift than weight. Pilots typically do this by pitching up and adding power." [Embry-Riddle Aeronautical University, "Aerodynamics", p. 8] Similarly, according to the FAA "When an airplane enters a climb, excess lift must be developed to overcome the weight or gravity. This requirement to develop more lift results in more induced drag, which either results in decreased airspeed and/or an increased power setting to maintain a minimum airspeed in the climb." [Airplane Flying Handbook (FAA-H-8083-3B), p. 3-16]
If you ask an Aeronautical Engineer, you will likely get an entirely different answer. The formula which appears in several engineering sources indicates that, in a climb, vertical Lift equals Weight X Sine(Climb Angle). Since the Sine is always less than 1 in a climb, vertical Lift is always less than Weight in a climb. This is consistent with the general physics equation stating that, in order to move up an incline, Thrust must be increased by Weight X Sine(Incline Angle). The combined result of these equations is that as the Angle of Climb increases, the burden of maintaining altitude is shifted from Lift to Thrust.
Before attempting to address this apparent inconsistency, I should better define the scope of the question. For example, both Pilot and Engineer would agree that, to maintain speed in a very steep climb, Thrust is the dominant force and vertical Lift is less than Weight. In fact, for most general aviation aircraft, this is likely true whenever the Climb Angle exceeds 25 degrees. Instead, we are limiting our discussion to climbs with a maximum Climb Angle equal to the best Climb Angle (Vx) for the airplane. Further within this range is a climb which has a lower Climb Angle, but which produces the maximum Climb Speed (Vy). Finally, there is the "cruise climb", which has a lower Climb Angle and Climb Speed, but which allows you to maintain a higher forward speed.
My opinion is that it is likely that both answers are correct: whether vertical Lift exceeds Gravity in a climb depends on how you fly the climb. There are a couple of reasons. First, the engineering equation could be limited to a certain type of climb. It does not rule out the possibility that a Pilot could also climb by simply increasing Lift. Second, the data indicates that it should take less Thrust to climb by increasing Lift, than by using Thrust alone.  Consider that, in a typical aircraft, for an aircraft in level flight, the Lift force produced by the wings far exceeds the Thrust force produced by the engine.  For example, on a Cessna 172P that weighs 2400 lbs and is travelling at 120 mph in level flight, the wings are producing 2400 lbs of lift, while the propeller is only producing 285 lbs of thrust. Thus, it seems that you can climb more quickly and efficiently by simply adding a few degrees to the Angle of Attack and adding a little Thrust to compensate for the increase in Induced Drag.
I am working on some vector-based examples to (hopefully) illustrate a stable climb in which Lift exceeds Gravity. So, until that is done, don't count this as my final answer.
[Note that this response has been rewritten a couple of times, so some of the excellent responses to my original post(s) may not make as much sense as they once did.]


Is TCAS II required in the US? I would like to know if, in addition to any MEL requirements, there is any regulation or requirement about having an operational TCAS II while operating in US airspace?

TCAS II is required for most airline flights. This is not a requirement for certification, and the TCAS may or may not be on the MEL. However, most flights under part 121 (scheduled airline service, as well as some freight) require TCAS II.

As noted in FAR 121.356, "Turbine-powered airplane of more than 33,000 pounds maximum certificated takeoff weight" must be operated with equipment that meets a list of standards, but is essentially equivalent to just requiring TCAS II. Smaller aircraft with 10-30 seats can use TCAS-I.

No.  It's not required in the United States.  There is nothing in Part 25 of the regulations.  However, if you install one it should comply with this AC.

www.faa.gov/documentLibrary/media/Advisory_Circular/20-151B.pdf


Why would seaplanes use a curved takeoff run? I came across this interesting factoid in another SE Aviation answer (How flat does a runway need to be?):

  seaplanes often use a curved takeoff run.

I'm trying to imagine why but cannot come up with a good reason.

Does anyone know why?

Years ago now I gave a fair amount of instruction for seaplane ratings. I remember it quite fondly as seaplanes combine the fun of flying with aspects of the fun of boating. There were three conditions in which we used curved takeoff runs.

The most frequent curved takeoffs were on rivers, which tend to not run in a straight line, and even for those portions of a river that do, there may be rapids to stay clear of, so following the bend of a river or weaving between rapids was not unusual. In my case, the rivers were the McKenzie and Willamette, both in Oregon, USA. If you're ever in Eugene, Oregon, go down to Skinner's Butte Park on the Willamette River. On the upstream end of the park is the Ferry Street bridge. On the downstream end is the Washington-Jefferson bridge. In the 1970s we used to operate on the water between them, avoiding the rapids. We stored the airplane for a time on the Skinner's Butte Park shore line. That was legal and safe back then.

The next most frequent usage of curved takeoffs was to get off ponds that were not wide enough to allow a straight line takeoff. However, you can do it taking off in a curve along the perimeter of the pond. If you ever happen to fly over Daniels Field alongside Interstate 5 about 20 miles north of Eugene, Oregon, you'll see a lake/pond alongside the runway with a small island in the middle. There is no straight line you can draw on that pond that comfortably gives you room for takeoff, but you can circle the island and get into the air without difficulty.

The third circumstance we didn't have to use often was when we had to run across our own wake to be able to get up on the step on glassy water. For example, Waldo Lake in the Oregon Cascades is at 5,400 feet elevation. A J-3 cub with an 85 horse engine and with two people on board simply cannot get up on the step when the surface of the lake is a dead calm. However, if you get going in a curved path, you can get up on the step when you run across your own wake. Once you're on the step, you can then put the airplane up on one float and get enough airspeed to take off. Just as a matter of information, seaplane operation on Waldo Lake is now prohibited.

The waves are running separate from the wind. When the plane has pick up enough out of the water it turns into the wind.


Have there been any cases of collision/airprox of small drones with manned aircraft? Small civilian mini-drones such as the DJI Phantom or professional surveying drones are becoming increasingly widespread, raising concerns about the potential collision/airprox with manned aircraft (especially GA where flight altitude is typically relatively low).

Have there been actual cases of collision and/or dangerous airprox reported so far? What were the consequences?

CASA (Australia's aviation authorities) has a report on an airprox between a crop duster and a surveying mini-drone:

ATSB incident report

Within US airspace, no such thing has occurred. The FAA has regulations for UAV flight that keep them away from any potential collision in controlled airspace.

Way back in 2011, there was a collision between a military UAV and a C130 in Afghanistan.


Do I understand the rules of logging cross-country time as a Safety Pilot correctly? Let's say there is a private pilot ("primary pilot") practicing instrument training under the hood and a private pilot who is a Safety Pilot, and the flight involves a landing at an airport more than 50 nm away in VFR conditions.  I want to see if I have this right:

The primary pilot can log instrument time and cross country time, but not PIC time.
The Safety Pilot can log PIC time, but not cross country time or instrument time.
If flying a high-performance and complex airplane, both the primary pilot and Safety Pilot must have a complex and high-performance rating.
The symbiotic benefit of this system is that the primary pilot gets instrument time and the Safety Pilot gets PIC time, both at half price if they split the cost of flying.

According to FAA regulations, do I have this right?

As background, see this question for a general explanation of how safety pilots can log time. Also have a look at the Gebhart (2009) interpretation for the cross-country part (and see this question too).
Note that the two key things to keep in mind in these logging scenarios are:

Acting as PIC and logging PIC time are two different things
You have to be very clear about who is the acting PIC for the flight

With all that in mind (and referring to 14 CFR 61.51):
The primary pilot can log instrument time and cross country time, but not PIC time
The primary pilot can log all three. Whether they're the acting PIC or not, they can still log PIC time as the sole manipulator of the controls (61.51(e)(i)). They can also log instrument time while they're under the hood (61.51(g)) and cross country time.
The Safety Pilot can log PIC time, but not cross country time or instrument time
If the safety pilot is acting as PIC then that's correct. They can log PIC time because they're acting as PIC "of an aircraft for which more than one pilot is required under [...] the regulations under which the flight is conducted" (61.51(e)(iii)). If the safety pilot is not acting as PIC then they can log SIC time.
But either way, the safety pilot may not log cross country time (Gebhart). They also can't log instrument time because they were never operating "the aircraft solely by reference to instruments under actual or simulated instrument flight conditions" (61.51(g)).
If flying a high-performance and complex airplane, both the primary pilot and Safety Pilot must have a complex and high-performance rating
Only the acting PIC requires those endorsements (not ratings), per 61.31(e) and (f). So if only one of the two pilots on board has them, that's the only pilot who can act as PIC.
If only the primary pilot has the endorsements the flight can still go ahead because a safety pilot isn't required to have them. However, the safety pilot couldn't act as PIC and could only log SIC time.
If only the safety pilot has the endorsements the primary pilot can still log PIC time because you don't need the endorsements to log PIC time. But the safety pilot must act as PIC.
The symbiotic benefit of this system is that the primary pilot gets instrument time and the Safety Pilot gets PIC time, both at half price if they split the cost of flying
Essentially, yes. Typical practice is for the pilots to agree that the safety pilot will act as PIC, and they split the costs 50/50 (61.113(c)). That way they can both log PIC time - which is valuable for further ratings - while only paying 50% of the costs. This question has more information on cost-sharing.
And thanks to JScarry for pointing out that if the safety pilot has BasicMed rather than a regular medical, they must act as PIC. See this question for more details.
Whatever you do please be sure that both pilots do know and understand who is acting PIC for the flight. That person has the final responsibility if something goes wrong. Knowing who's acting PIC is important to prevent things like a safety pilot without a complex endorsement agreeing to act as PIC in a complex aircraft, because "I'm just a safety pilot". You might also have insurance or flying club rules on who can act as PIC.

In your scenario:

Let's say there is a private pilot ("primary pilot") practicing instrument training under the hood and a private pilot who is a Safety Pilot, and the flight involves a landing at an airport more than 50 nm away in VFR conditions. I want to see if I have this right:

The primary pilot logs PIC time as long as they are the sole manipulator of the flight controls, instrument time as long as they are under the hood, and cross country time as long as he flight is made between airports more than 50 nautical miles away from each other.
The safety pilot logs PIC time as long as the primary pilot is under the hood and cross country time as long as the primary pilot is under the during the flight between airports greater than 50 miles apart. No instrument time.
Any pilot logging PIC must be properly certificated and rated. Although, a safety pilot with a private pilot certificate only can log SIC.
The pilots can split the costs or not. It’s up to them at that point. But, if they split the costs, it must be evenly.


What is the longest range single-pilot certified (FAA and/or EASA) business jet? I suspect the single-pilot business jet with the longest range is the SyberJet SJ30x:

NBAA IFR Range with 100 nm Alternate
M 0.76 (1 pilot + 2 passengers; passenger/pilot at 90 kg each)
2,575 nmi (4,769 km).

But I am not sure; also, there are many negative reviews regarding SyberJet company and its aircraft of which, by the way, only a dozen have been produced for now. Are there any single-pilot certified jet with longer range in comparison with SyberJet SJ30x?

There aren't any civilian, current-production jets that come close to the range of the SJ30 for single pilot operations based on my research, although one or two turboprops have comparable ranges. I consulted Aviation Week's "Business Airplane's 2012" and the only other light jets listed with a long range are the Embraer Phenom 300 with a range of 1,954 nm, and the Cessna Citation CJ4 with a range of 1,913 nm.  The Cessna CJ3 comes in at a respectable 1,869 nm. The PC-24, which is still undergoing certification in 2016, is listed here with an NBAA range of 1,950 nm. All of these are (or will be) single-pilot certified in at least one cockpit configuration, to my knowledge.

Is there any reason you're restricting this to jets and not turboprops? (Speed is one of the biggest differences between the two categories.) The King Air 350IER has a range of 2,239 nm.  Several other turboprops have ranges that are comparable to average light business jets, like the PC-12 NG which has a  range of 1,544 nm.

Here's a graph of my own making to show these statistics:

For any readers unfamiliar with the restrictions regarding FAA approval for single-pilot operations, here's a good source: http://www.flyingmag.com/single-pilot-jets . The biggest stipulation is that transport category aircraft (12,500+ lb MTOW or not commuter category) are assumed to be two-pilot aircraft.

Note:  all ranges listed here except the PC-24's range are NBAA IFR max fuel ranges w/ 100 nm alternate as listed in Aviation Week's "Business Airplanes 2012"

Cessna Citation 501sp Eagle II, spx. has a 1,987 NM range.


Why does the Boeing 737 have 5 x the passenger fatalities of the Airbus 320? I thought I'd compare the accident rates of these two similar, competing, very successful aircraft.

                    737     A320

Introduced          1968    1988
Number Built        8104    6171
Accidents/Incidents  329      60
Hull Loss Accidents  154      23
Fatalities          4287     782

These figures are from the respective Wikipedia pages. I assume they have not been the subject of edit-war falsification by fanboys of planemakers.

I wondered what might be the reason for the 737 seeming a much less safe plane.

The 737 design is 20 years older?

But it's still in production, so 1988...current 737s can be built with many of the same safety features found in an A320 produced the same year. Were 3,500 of those fatalities in the first 20 years?

There are lots more older less-safe 737s being flown by corner-cutting budget airlines in third-world kleptocracies?

Are there that many 40-year old 737s in the hands of incompetent airlines?

The 8,104 737s have, on average, flown many times more cycles than the 6,171 A320s?

But they address the same market, why would their usage differ so markedly?

The 737s have, together, flown many times more passenger-miles than the A320s?

See above. Plus I imagine older 737s have mostly been retired.

My speculation doesn't seem very convincing to me. Is there a better explanation supported by reputable studies?

For one, the early 737s had a design flaw which allowed the rudder to reach a hard-over position, and get stuck there. Boeing initially dragged their feet in rectifying this, so it took a number of accidents before this design flaw was corrected. This is a major contributor to the high number of fatalities in the early operational years.

To have a more meaningful comparison, I would suggest to compare the fatalities per year, so the status in operational procedures can be excluded as a factor. As others have pointed out, this should give a more equal basis for a comparison.

If you look at fatalities per year, beginning in 2000, these numbers emerge:

Now you need to factor in the number of flight hours per type per year, which I do not have available. But I would expect that the low fatality rate in the early 2000s is more due to the small number of A320s around. But if we just compare the 737 NG with the A320, this advantage is reversed, and still the A320 comes out slightly ahead.

But thankfully, there are very few accidents for each type per year, so the statistical base is too low for a meaningful comparison. If we want to draw any conclusions, it could be that the A320 is indeed a safer aircraft, but the certainty of this conclusion is very low, being based on a very small number of accidents.

A320 has triple redundancy in systems like AOA and radio altimeter/ autoland vs Boeing double radio altimeter/ autoland and single aoa channel. Design philosophy and cost savings approach seems more safety oriented on the airbus.


If my parachute fails to open, why should I aim for land rather than water? I was watching these 'what if' parachute failure videos on YouTube and everywhere they say do not choose water over land. Why should we not choose water and what happens if we land in water?

One such video:

If your parachute fails to open entirely you are almost certainly extremely dead no matter where you land, however occasionally people do survive. A partial failure of a chute is much more survivable. You will be coming down much faster than you would with a good chute, and you are going to get injured, probably badly. Think broken legs and arms with neck or back trauma. You may sustain a concussion as well, and you will certainly go into shock.

If you come down in the water you will be injured and unable to keep yourself afloat, and it will be much harder to rescue you. On land help will be much closer and, and as @RonBeyer says in comments, you can't drown on land.

Land has features which may help you survive: trees, vegetation, hay bales, crops, snow, and many other things may cushion your impact enough to make the difference between life and death. Water is the same wherever you go, and doesn't have nearly enough give to cushion an impact.

If you see a large water body around you, direct yourself to that.

Carry something which can cause a large concussive force just as you're about to impact. Say you're about to hit the water, you lob in object X which causes a large boom. The concussive force of the blast pushes you back and cushions you using the water as a "sofa" of sorts. You have to time this perfectly though, too soon and you miss it, too late and you get caught in it yourself. You can always try practicing by jumping from a low enough bridge into the water and trying, have enough health insurance and you'll be fine.


Is Vy closer to Vbg with a variable pitch prop My experience with fixed pitch props is that Vy is generally higher than Vbg due to engine efficiency issues. If I set my prop pitch so optimal engine rpm is at Vbg, will Vy = Vbg?

Too long for a comment:

My POH does not show Vbg, only the 'normal' V's listed below, and even then only some of these are indicated on the Airspeed Indicator with the Green, Yellow, Red color bands. How would you determine Vbg? Experimentally?

VA,  Maneuvering Speed is the maximum speed at which you many use abrupt control travel.

VFE,  Maximum Flap Extension Speed is the highest speed permissible with wing flaps in a prescribed extended position.

VNO,  Maximum Structural Cruising Speed is the speed that should not be exceeded except in smooth air, then only with caution.

VNe,  Never Exceed Speed is the speed limit that may not be exceeded at any time.

VS,  Stalling Speed or the minimum steady flight speed at which the airplane is controllable.

VSO,  Stalling Speed or the minimum steady flight speed at which the airplane is controllable in the landing configuration at the most forward center of gravity.

VX,  Best Angle-of-Climb Speed is the speed which results in the greatest gain of altitude in a given horizontal distance.

VY,  Best Rate-of-Climb Speed is the speed which results in the greatest gain in a given time.


Can a wing generate lift in excess of its aircraft's weight? "For a plane or bird to fly, its wings must produce enough lift to equal its weight. "

I got that excerpt from "https://www.sciencelearn.org.nz/resources/300-wings-and-lift".

My questions:
(1) Can an aircraft wing create lift that is greater than the weight of the aircraft?
(2) If the answer to question (1) is yes, then what happens in such a situation?

Yes, otherwise airplanes would be unable to go upwards into the sky.

If you have an aircraft with 20 tons of cargo, and the total weight of the aircraft, including cargo, is 60 tons, then clearly the wings are capable of producing 60 tons of lift. If you fly the same plane without cargo, then that's not going to affect the amount of lift the wings can produce. So clearly there are situations where the wings can produce more lift than the weight of the aircraft.

Something else that shows that aircraft must be sometimes operating below their maximum lift is that when an airplane takes off or lands, it's not moving at its maximum speed. Since lift increases with speed, that means that its lift is significantly crippled. If an airplane has enough lift to fly at runway speeds, then it has more than enough lift to fly at cruising speed.

In addition, an aircraft is going to need a margin to climb,  turn (one of the reasons airplanes bank when turning is that the lifting force of the wings can then be applied to centripetal force, aka turning the aircraft), etc. Tell any pilot that you want them to fly a plane with a maximum lift equal to, or only slightly above, the weight of the plane, and unless they have a death wish they'll be running the other way.


Can commercial pilot get paid for introductory flights with their own customers? Can a pilot with their commercial certificate look for their own customers, rent an airplane, and get paid to do introductory flights?

If yes, where in the FARs does it talk about it?

There are three parts to your question and the answer to all three is no. And there isn’t one specific place in the FARs that says you can’t do this, but reading Parts 91 and 135 along with appropriate ACs and Legal Opinions of the FAA leads most pilots to realize that they can’t do this.
§91.147   Passenger carrying flights for compensation or hire. contains a list of requirements that you must satisfy as well.

If you look for customers it is considered 'holding out' and according to AC 120-12A ‘A carrier becomes a common carrier when it "holds itself out" to the public, or to a segment of the public, as willing to furnish transportation within the limits of its facilities to any person who wants it.’ And if you are a common carrier, then for this type of operation, you must have a Part 135 certificate.

As a commercial pilot, you can be paid to fly someone in their airplane. Lots of commercial pilots do this. However, if you provide the plane then you are acting as a Part 135 operation and you can’t do it.

Getting paid is also not allowed. Since you can‘t do parts one and two of your question, you are acting under your Private Pilot certificate for the flight. At most, you can split the immediate expenses i.e. fuel, landing fees, etc. Even that is a bit dicey since you won’t have a ‘common purpose’ with the person you are flying. In other words, without holding out for customers, you wouldn’t have been making the flight anyway.

Not part of the question, but there are lots of things you can do with a commercial pilot’s license:

Corporate Pilot, Charter Pilot, Contract Pilot (for a private owner), Freight/Cargo Pilot, Ferry Pilot, Banner towing Pilot, Sight-Seeing/Tour Pilot, Agricultural Pilot/Crop Duster, Skydiver Pilot, Photographer Pilot, Airshow Pilot, Demo Pilot (aircraft sales), Medical Evacuation Pilot, Humanitarian/Charity Pilot, News/Traffic Pilot, Pipeline Patrol Pilot, National Defense or Border Patrol Pilot, Firefighting or Forestry Pilot.

Depends.  If the commercial pilot in question is not a Certified Flight Instructor, he/she cannot sign off on dual instruction time for a student pilot and said student pilot cannot log that flight time in their logbook. - see FAR 61.181-189.

Now if a commercial pilot appropriately rated for the category and class of aircraft, or with a type rating, with a current Class I or Class II Medical certificate takes a passenger up for compensation or hire on an introductory flight, they may do so.  But it cannot count for instruction time.


How do I calculate the required heading for an aircraft carrier with an angled deck to sail into the wind? The natural wind is from 360 degrees at 10 knots. The desired relative wind down the angled deck is 10 degrees left of the ship’s heading at 30 knots.

What heading and speed must the carrier go?

A carrier heading of 010 degrees at a speed of 20 knots would give you an acceptable solution.  You could perform some vector addition to compute the resultant wind and perhaps optimize this somewhat, but in reality the winds are generally not constant enough to make minor adjustments worth chasing.

Even if the winds were calm and the ship was making all 30 knots the crosswind component is almost negligible, and well within limits for any carrier based aircraft.  This happens a lot.  There is a bigger negative effect from  turbulence caused by the island structure when the ship has to make wind than any effect of increased crosswind.

Let’s suppose that the runway is angled by 10º to the left. To start with, let’s assume there is no wind, and that we wish 30 kts of relative wind parallel to the runway. The speed of the carrier (with any heading) will be 30 kts/cos 10º = 30,46 kts.

Now, we have a wind with a speed of 10 knots in relation to the sea. We change the heading of the carrier in order to take the maximum advantage of that wind, so that it may be parallel to the runway. So the carrier steers to a heading exactly 10º to the right of the wind direction. Now we have too much wind, 30 + 10 = 40 kts, and we should reduce the ship’s speed in proportion to that excess of 40/30. In other words, the carrier should steam at 30,46 x 30/40 = 22,85 kts.

Hence, the carrier should have a heading of 10º to the right of the north, and a speed of 22,85 kts...


An airplane has an engine that pushes its flight. What force pushes a glider to fly? An airplane has an engine that pushes its flight. What force pushes a glider to fly?  Is it gravity? I think the flight of a glider is driven by gravity, but some people disagree with me. They say gravity acts vertical, it has no component in the horizontal direction. Am I wrong?

Please note that this question is not specifically asking about what (thrust-like) force acts opposite to the drag vector.  The direction of a glider's flight path as viewed from the earth may not necessarily be opposite to the direction of the drag vector-- for example, the glider may be travelling horizontally over the ground at constant altitude, or may be rising straight up in ridge lift or wave lift-- and this question may be construed as asking what force is pushing the glider along the direction of the flight path as viewed from the surface of the earth.

Airplanes do not fly because of their engines. Airplanes and gliders both fly because their wings turn thrust into lift and drag.

That simplistic answer, of course, just begs the question "how can you generate thrust without an engine?"

A glider is constantly trading altitude (potential energy) for airspeed (kinetic energy). Energy over time equals force, which in this case we call thrust. Airplanes do the same thing when descending. Both can also trade energy in the opposite direction, but only briefly until the wings stall.

The big difference is that an airplane can also turn fuel (chemical energy) into thrust, which allows sustained level or climbing flight. Gliders don't have that option.

Momentum and inertia.

The others (gravity, lift, drag) are not sources of energy, but they do modify the forces of energy.  The actual forces involved are momentum and inertia.


Under 3rd Class Medical Reform, When Do I Need To See My Doctor? Lets say I'm a 35 year old pilot who just had a medical renewed so that it doesn't expire until 2021. 3rd class medical reform (although not law yet) requires that I visit my regular physician once every 4 years.

When do I need to see my doctor?

Anytime prior to the expiration of my 3rd class medical?
Do I surrender my 3rd class medical and go to the doctor immediately (after regulations pass of course)?
Do I go to my doctor in 2020? 2019?
Do I wait until my 3rd class medical expires (or within a month or two)?
4 years after the expiration of my 3rd class medical?

And a bonus question:

Does the 4 year clock start ticking when my medical expires, when regulations are enacted, or some other time?

114th Congress Senate Bill 571 - Pilots Bill of Rights 2

The FAA hasn't written the regs yet so who knows. All that has happened is congress has told the FAA to write the refs

Personally I think it's foolish to use your personal doc. You're waving all your HIPPA rights and obligating your personal doc to report anything to the FAA without your consent.

-Robert


When the angle of attack is increased does the air flowing below it slow down So the air above the wing flows faster. So it creates low pressure above the wing. The air flow below the wing, is it slowed down by the increased angle of attack or does it stay the same? So is the higher pressure on the bottom of the wing relatively higher then the bottom or does the airflow on the bottom slow down beucase if the increased angle of attack?

In high alpha flight it is not uncommon to have compression below the wing, which would increase the pressure, and act in concert with the Bernoulli Effect on the top of the wing.  The effect on the underside of the wing could also correctly be called a form of Bernoulli Effect.

There need not be any compression on the underside for there to be lift on the top side of the wing.  However in higher angles of attack there is compression, which supplements the lift.

This is an old Bernoulli explanation of how wings work that is miss-leading or just plain wrong. The air is not moving, the wing is. So to answer your question, since the air is not moving.. it can't slow down.

As the wing moves forward, the air is compressed under the wing and decompressed above it. That difference in pressure causes lift. The angle of attack changes the relative amounts of each till you reach a point where the air becomes turbulent above the wing. At that point the lift becomes erratic and drag goes through the roof.

A simple analogy can be demonstrated by taking sand or talcum powder and sprinkling it over a table or sheet of cardboard or whatever. Then take a cardboard cut-out of the cross section of a wing and sliding it flat across the sand in the normal wing like direction. The sand under the wing will clump together and form a line of sand along the bottom side of the wing. The sand above the wing will be moved away from the wing leaving a void above the wing.

Now, of course, air is not like sand, and hates a vacuum, and will rush back in to fill the void above the wing. However in order to do so it is "stretched" forming low pressure above the wing. Similarly the air under the wing tries to get out of the way and equalize itself, but in the meantime it is compressed and has a higher pressure.

It is this difference in pressure that causes a net force up through the wing to provide lift.


What does "speed checked" mean? Here is a Scenario:

PF: Flaps one.
PM: Speed Checked, Flaps one.

What does that mean and why do they have to say "speed checked" every time?

Because there is a maximum deployment speed for things like flaps, gear extension (and sometimes retraction). Exceeding these speeds and using those devices can cause damage to control surfaces or other equipment. The speed check is there so that when the PF calls for flaps, the PM remembers to check the speed before performing the action.

Some companies mandate that the PM verbalise "Speed checked", but it's utterly useless verbiage.

Firstly, the PF should already have checked the speed before asking for the next flap setting.

Secondly, pilots have a history of simply saying "Speed checked", but not actually checking anything. All part of the ritual of PF says Flaps x, I say "Speed checked" and move the Flap Lever.


Does rolling or yawing affect the angle of attack? If I'm on final in windy conditions and I need excessive rolling and yawing movements to stay on centerline and say, my pitch stays constant - does rolling or yawing change my AOA such that I could stall?

No that's not how it works.  You shouldn't need "yawing" movements on final before the landing flare.  That implies that you are using rudder to push the nose left or right to keep the runway sight picture where you want it, a very bad practice.

Never use rudder to stay aligned with the runway, except in the landing flare.  Other than that, only use rudder to keep the ball centered, or to side slip to lose altitude.  At all times, unless you are side slipping on purpose, use coordinated banked turns to stay aligned with the runway prior to the flare.

The rolling movements should be just those movements required to make coordinated banked turns to adjust heading to stay on centerline, or to get back on centerline.  Maybe 20 degrees of bank. Ball centered as much as you can keep it centered in bumps.

Moderate banked turns in a descent with ball centered create zero risk of stalling if speed is attended to.  Stall/spin accidents happen when pilots try to shove the nose with rudder to point it at the runway, causing uncoordinated flight, on top of sloppy speed control, so that if they get too slow, with the airplane slipping or skidding, when it stalls it flicks over the inside wing and down you go on your ride to oblivion.

If you are keeping bank angles within reason, ball centered, and speed on the proper approach speed, you won't stall the plane and normal control inputs will not get you close to stalling the plane. And with any modern plane, if you do stall it but the ball is centered, you won't depart in a spin and you can recover instantly.  Coordinated ball centered flight is the most critical item after speed control.

Roll on one side usually increase (depending on the aircraft type) the amount of the airflow AOA one wing  (locally), but it will decrease the other half of aircraft (the other side wing)because of the helix movement, if the rates of those rolls are higher. But important thing is to have enough speed for bank angle (this is starting of the stall process) If bank angle is big  you need for higher speed than level wing. The answer is NO. But momentarily will be increasing then settling down if you have trim a/c.


What is the coordinate system used in an Aircraft? I know that from nose to tail the aircraft is divided by STA (station). At least for Boeing and Airbus this is the case but I am not familiar with other manufacturers.  However, there is also two other dimensions that give every location of an aircraft an identifiable point location. It's obviously not x,y,z.  What is this coordinate system and approximately what does one unit along each access mean in terms of inches or centimeters?

Stations (STA), generally Fuselage Stations (FS), designate location along the length of the aircraft, increasing from nose to tail. Generally station 0 is somewhere in front of the airplane. One reason for this is that if the airplane grows longer, there still won't be any negative stations, and sections of the plane keep their station numbers. FS 100 can also be placed at an important location (looks like the firewall below).

Water lines (WL) designate location in the height of the aircraft, from ground up. You can probably guess by now that these are holdovers from the marine industry. Like the stations, water line 0 is generally a bit below the aircraft, possibly to have WL 100 at the center of the fuselage, or WL 0 could be at the bottom of the fuselage.

Butt lines (BL) designate location left/right on the aircraft, generally centered in the middle.

While the main system is based on the whole airplane, different parts (like the wings) have their own system of STA, WL, and BL.

The stations are generally in whatever unit is being used for the aircraft. In the US, this is inches.

See this link for an example and further explanation.

For a picture similar to the one below but with more detail, see here.

To my knowledge there isn't a coordinate system to describe locations on an aircraft airframe.  Measurements along the longitudinal axis of the aircraft exist for center of gravity measurements.  These measurements are made as an "arm" measurement from a standard arbitrary point, known as the datum.  Specific measurement locations are "stations".  There is no real need as far as I know to have a measurements in the other 2 axis.

For locating components for maintenance purposes, my experience of technical manuals usually describe locations verbally, such as "the flap actuator can be located forward of the inboard flap rail".

My experience is mainly with light piston aircraft and corporate jets, it could be different with larger aircraft.


Why do many commercial aircraft have a red circle on the wing? Many commercial aircraft operated by japanese airlines like JAL and ANA have a red circle on the wing. Look:

Source: Airliners.net
And on this ANA plane, also:

Source: Airliners.net
Why do they have that red circle there?

That would be the Japanese sun symbol which also appears on that nation's flag. You can also see that symbol on the tail of that JAL 777 on top.

Same as the Japanese Flag:

May be another example:

Emirates airline:

and the flag of the United Arab Emirates:


What's the use of so much torque on propellers? (This question is closely related to this question)

A typical Cessna 172 has a 180 hp engine, with a max. rotational velocity of 2700 RPM. Even small 1 hp electrical motors can achieve that RPM, and therefore, I guess the rest of the power is converted into torque.

What's the use of so much torque, and what happens if there is less torque at the same RPM - i.e.

Can an electric motor perform similar to the Lycoming IO-360 with the same max. RPM, but with just half the torque of the latter?

Even small 1 hp electrical motors can achieve that RPM

Yes, but can it sustain that RPM when something tries to stop it, that is the question. 1 hp combustion engines can get to 2700 rpm as well, but you cannot attach a propeller to it, stick it in the air, and expect it to maintain the RPM. It takes a lot of torque to create aerodynamic thrust.

It is a fact that electric motors are way better at producing torque than combustion engines. An electric motor produces almost maximum torque at the get-go, with the rotor standing still. The combustion engine needs to make RPM in order to make torque. This article compares electric motors with combustion engines for powering a hydraulic pump: a 20 hp electric motor can do the job that a 50 hp combustion engine can do.

Electric motor:

Combustion engine: intermittent torque means torque pulse from combustion.

But wait, is that even possible? Power is power, kilowatt is kilowatt, and it should not matter which engine we use to generate the kilowatts, they should all equate to equal amounts says the first law of thermodynamics, the conservation of energy. But it does matter, since with a combustion engine torque is a function of RPM. So increase RPM, and power increases due to increased RPM and increased torque. At lower RPM the combustion engine may simply lack the torque to speed up, while the electric motor has an almost flat torque curve.

This same happens with outboard motors, when comparing 2-stroke with 4-stroke. 2-stroke has way more torque at lower revs, the 4-stroke may have the same horsepower but may never get to the high revs because it lacks the ability to get the boat planing.

But I digress. To get back to your questions:

  What's the use of so much torque, and what happens if there is less torque at the same RPM

To keep the output shaft at this RPM while the propeller is pushing all that air backwards. That requires a serious amount of torque. If there is less torque at the same RPM, there will be less thrust produced and the aeroplane won't fly as fast.

  Can an electric motor perform similar to the Lycoming IO-360 with the same max. RPM, but with just half the torque of the latter?

Well, the surprising thing is that a horsepower is not a horsepower. Part of the problem lies in the horsepower output functions, so maybe an electric motor with a lower hp rating can be used. But one thing is very clear: at the RPM of the propeller, a certain torque is required at a certain speed to keep the propeller turning. This amount of torque will always be the same, no matter what kind of engine produces it.

It all depends on the propeller one can use:

The prop should rotate at as much RPM as possible because force is proportional to speed squared and one want a small PropPhiW as possible (the AOA required by the prop-speed / airspeed geometry). Lower PropPhiW means increased efficiency.
The prop's tips should rotate below the speed of sound, or else massive additional frictional forces (-> lift/drag goes into the cellar)
The prop's AOA0 (the difference betw. set PropAOA - PropPhiW) should be at the max. lift/drag point (most often around 4-6°).

To get that prop rotating one needs torque in the first place, enough to bring the prop into the high efficiency region (low PropPhiW) speedwise and into the maximum lift/drag region (AOA0).

Having a lot of torque makes the setup easier, one has more choices, but one certainly needs an excel-sheet to analyze it fully, operating outside the optimal costs a lot of efficiency.


Do stealth designs have canard configuration? Do stealth-focused aircraft have canard configuration? I believe canards have a negative impact on the radar cross section.

So far, no operational stealth aircraft has had a canard wing as the canards do affect the radar cross section.

However, a few experimental and under development under development aircraft have canards, like the Chengdu J-20.

"J20 2" by V587wiki - Own work. Licensed under CC0 via Commons.

The Sukoi PAK-FA, on the other hand uses movable Leading Edge Root eXtensions(LERX), which are much more stealthy and are shown drooping down in the following figure.

Source: defenceindustrydaily.com

There are a few major drawbacks with the traditional canard designs:

Planform alignment Most of the canards are in aircraft for stability and aerodynamics requirements an as such are not amenable to planform alignment, as their characteristics are sensitive to their shapes and sizes. For example, compare the planform alignment in case of F-22 and Eurofighter Typhoon.

Source: forum.keypublishing.com

Some low observable aircraft, like the Boeing X-36 did  have planform alignment, it is simply that it is difficult to achieve.

"McDonnell Douglas X-36 planform" by NASA/Dryden Flight Research Center - http://www.dfrc.nasa.gov/gallery/photo/X-36/HTML/EC97-44165-151.html. Licensed under Public Domain via Commons.

Canard Angle Most (not all) of the canards have an anhedral or dihedral due to aerodynamics requirements, which means that they are not in the same plane as the wing and reflect radar waves in other directions, increasing RCS. The following image shows the (mis)alignment of canards with the aircraft.

Source: forum.keypublishing.com

More reflecting surfaces Having canards basically means there are two extra surfaces to reflect the radio waves and increase RCS.
Interaction with fuselage and wings The diffracted (radio) waves from the canards can impact on the wings and fuselage and get reflected back, which can increase the radar cross section.

Canards can be stealthy. There is a very interesting Oregon State University lecture given by Dr. Paul Bevilaqua about the F-35 that actually shows a canard fighter.

The point here is that you use computer models to optimize radar return, especially to the front but also to the rear. A fighter that doesn't look optimized might still be.


Are there non-economic barriers to a 1000 passenger aircraft? I know the number 1000 is just an arbitrary number that happens to have some zeros in it, but is there any non-economic obstacle to making a 1000 passenger aircraft?

Also, assume normal-ish space-per-passenger constraints, so 1087 people on a 747 isn't really a 1000-passenger aircraft.

If money is no object, and we ignore terminal constraints, then no, there isn't. The A380 already supports 850 passengers in a single-class layout, and Airbus has plans to make a stretched version (the wings are designed to give room to stretch the fuselage without needing too much redesign). 1000 passengers isn't really that much of a stretch; we can basically get there now. The issue is that economic obstacles are very real obstacles to building planes; no one has a need for a 1000-person plane on any route (the A380 isn't even used today with max capacity, it's used to give lots of space to first-class passengers with a bit over 500 passengers).

There are certainly at least two airfields out there that would be able to handle a 1000-passenger A380; unfortunately, neither is a commercial airport (the two are Edwards AFB and the Shuttle Landing Facility; the SLF has a 15,000 foot runway that's 300 feet wide, while Edwards has a similarly-sized paved runway). However, if operation is uneconomical, you won't see anyone building a plane to do it.

As aircraft get larger, it becomes more difficult to make them strong enough. For example, a two-story building does not move much, but the top of a skyscraper will sway back and forth by about a yard in the wind. Aircraft have the same problem. With super materials, like carbon fiber, it would probably be possible to build an aircraft big enough to hold 1000 passengers, but would require a range of new designs and innovations, so there is a "barrier" in the sense that the builder would have to come up with a whole new set of innovative designs. All of these new designs would then have to be tested, which would be laborious. You may remember the tedious testing process for the 787 "dreamliner" that went on for years, even though it was a relatively standard design. A giant aircraft would have a testing regime that would make the 787's look like a piece of cake.

Airbus has announced that they have a potential design for a stretch 380 that could accommodate 1000 passengers.

From a practicality point of view, 1000-passenger planes would not work without changing the gate arrangements at the airport because loading and unloading would take too long. You would need to have 3 gates, 3 doors and 3 ramps all in operation simultaneously to load and unload the aircraft in a time-efficient manner. Since airport terminals are designed to have only one gate per aircraft, you would have to redesign all the airports in the world to accommodate a gigantic aircraft with a triple gate. Starting to see the problems?

Another problem is that runways might not be long enough. The larger the aircraft, the longer the runway must be. A 747-400 has a rejected takeoff distance of around 12000 feet if there is a reverser failure. Usually 747s will not operate on any runway shorter than 7000 feet and that is pushing it. If they have an RTO on a 7000-foot runway, it could result in multiple fatalities. With a giant aircraft, you might need a 12000 foot runway or something like that at least, so it would be difficult to operate the aircraft.


On a modern Aircraft like the A320 or B737, is it possible to disable computer interference with the control inputs of the pilots? One more question due to the recent and unfortunate events in the case of the second ever B737 Max 8 crash.

As far as I know, the first of the two crashes was caused by the MCAS System, that overwrite the inputs of the pilots as a faulty reading of an angle of attack sensor indicated a stall (that was not actually happening).

Knowing (rather, having an idea of) what a difficult time pilots have in such situations I wonder if it is at all possible to stop the aircraft from executing such maneuvers.

I know that on an Airbus A320, there is different flight laws. While during "Normal Law" all the various protections the A320 has are active (Stall protection, overspeed protection, bank protection with all their proper names and so on), they are not active in "Direct Law". There are two more levels between "Normal" and "Direct" (namely "Alternate" and "Abnormal Alternate"), but let's ignore them for this question.

I have never flown an A320 in real life and lack the training any A320 pilot goes through, but in the Simulators I have flown (not talking FSX here!) you could "exit" out of "Normal Law" by turning off the flight computers on the overhead, like the ELAC, FAC and SEC, and go into alternate or even "Direct Law".

So the question is: is this actually possible on a real A320 as well? And is there a similar method on a B737 (Max 8)?

For A320 it is possible also in the real aircraft. The problem with disabling flight control computers is that it also disables associated control surfaces. If you disable all five computers, you disable all surfaces and the aircraft goes in to "Mechanical backup" mode, which leaves pilot only the control of the trimmable horizontal stabilizer (ie. pitch trim) and rudder. Wide bodies are similar, although they have more redundant flight control computer architecture.

The correct procedure to override normal law in Airbuses is to switch two ADRs off, which forces controls to alternate law. This disables most of the protections leaving only load factor protection. All control surfaces would still be operating with automatic pitch trim. This would be used only in undue protection activation.

The more correct answer is that it is possible to disable the computer control on the Boeing 737 Max 8, but in order to avoid a crash you may have only 40 seconds in which to do so -- including the crucial first step of diagnosing the problem (which in the first accident was not obvious: a single faulty sensor indicating a stall that was not actually happening).

The pilot can optionally turn off the automatic stabilizer inputs from MCAS, an auto-stabilising feature intended only for a flight state outside the normal flight envelope (because, the B737 being aerodynamically unstable, a software routine was designed so that it would feel and behave in that situation the same as an aircraft that is aerodynamically stable).

But the pilot has first to correctly determin whether the aircraft is outside the normal flight envelope, in circumstances where he cannot rely on what his flight instruments are reporting.

If the aircraft is outside the normal flight envelope, and inherently unstable, disabling the MCAS system would be a bad idea.


Cockpit vs Flight Deck? Is there a distinction between a cockpit and a flight deck on an aircraft, or are the terms interchangeable?

Boeing refers to the flight deck The new Flight-Deck Displays and Airbus refers to the cockpit Passenger Aircraft>Cockpits

Based on this image,

would the B-2 be described as having a cockpit or a flight deck, or is there not enough information in this image?

They refer to the same thing, but there is some separation between the terms, especially in the military. A cockpit is a hole with a seat that you strap into for the entire flight. A flight deck is a larger version of a cockpit, where you can at least leave your seat and walk behind it.

The traditional nautical term "cockpit" referred to a fairly small steering station at the top of the ship. Boeing introduced the term "Flight deck" post-WWII for their larger aircraft, to indicate the difference, and it has spread somewhat. A heavy's flight deck is still a cockpit, and can be referred to as such, but a "pointy's" (jet fighter) cockpit is very unlikely to be called a flight deck in speech.

In general and civil aviation, the terms are pretty much interchangeable. Still, a Ultralight Aircraft's cockpit is not a flight deck, so there is a strong connotation of a flight deck actually being a deck.

The B-2 has a flight deck, so do some fighters like the Su-34. Both can be called a cockpit as well. Basically, solo or tandem seating with entry through the canopy = "cockpit". Side-by-side seating with side door or bottom hatch entry = either "flight deck" or "cockpit".

This distinction is largely English-specific. Powered flight was being concurrently developed in France and Russia, and many languages ended up following their convention ("Piloting post/cabin" and "Crew cabin" respectively), where no term distinction was ever created.

Some organizations prefer one term in their style guide, while others prefer the other. There is no substantive difference between them that I've ever encountered.


Which airlines allow you to gain hours with them by paying them As a fresh grduated pilot is there any airline that you can pay them to fly with them without a salary just to build hours?

There are pay to fly services, however regulations require a minimum number of hours before you can do any kind of part 121 or part 135 work. So while you can get some extra hours in Jets by paying them that way or turbo props or whatever else you’re looking for, it’s not recommended. Probably the best starting gate once you have a commercial pilot certificate is just doing flight instruction work until you gain the required 1500 hours.  After that you should have offers for most of the regional carriers to work for them as a first officer.

None. It doesn't work that way. Airlines have employees, not volunteers or indentured servants flying their aircraft, and the law requires that employees be paid. Not always paid very much, but "flying for free" doesn't exist at any airline I've ever heard of. And I wouldn't want to ride on any that had such a program.


How do the vortices of a fixed wing and horizontal stabilizer interact? What interaction of vortices between the fixed wing and horizontal stabilizer?

How do the vortices affect the flow of the horizontal stabilizer upon leaving the wing?

when will the downwash effort affect the flow, apart from not having clean-flow?

Does the downwash decrease dynamic pressure the reduce the lift?

Does the Airflow be affected after leaving the wing?

The vortices coming off the ends of the wing are outside the width of the stabilator or stabilizer/elevator, thus there would be little interaction.

In my plane for example, the wings are 35 feet 6 inches wide, the stabilator only 11 feet 10 inches.
Thus the end of the wing is 17.25 feet from centerline, the end of the stabilator at 5.9 feet, thus 11+ feet of clearance.


Why does the F-111 sometimes squirt a giant fire plume behind it? (NOT afterburners!) As seen in multiple pictures:

First, this one, it appears the aircraft is spraying copious amounts of fuel into the exhaust!

Surely this provides no thrust, not in the way an afterburner (which the F-111 has!) does.

Is it perhaps as an alternative to flares for anti IR missiles? It seems logical, but I don't think so, because I've seen it on takeoff too!

At any rate, it is QUITE badass!

EDIT: YouTube video!

EDIT: Can any other aircraft perform this?

The F-111 has, like many aircraft, a fuel dump port so it can get rid of a lot of heavy fuel rather quickly. Most aircraft have the dump ports on the wings, the F-111 designers put it in the tail between the engines. End result is if you dump fuel and briefly light the afterburner you will ignite the liquid fuel in your wake creating a rather spectacular trail of fire.

Aerodynamically it's completely useless, financially it's very expensive, you'd only do it in combat if you were suicidal as it greatly increases your IR signature right where you don't want it, but at an airshow it does look totally badass, especially as the afterburner is adding a lot of noise at the same time.

I would expect any pilot who does a dump-and-burn outside of an airshow (or an emergency) will have his own tail set on fire by the air wing's commanding officer.

The SR-71 had a similar issue - it leaked like a sieve on the ground. Rotating for takeoff would occasionally set fire to the JP-7 on the runway leaving a burning trail behind it much like the Road Runner.

Reply to the video:
watch the takeoff section carefully. You can clearly see the afterburners come on before the fuel dump starts.

Reply to about half the comments:
Highly unlikely they designed it to do this. The F-111 was one of the earlier swing-wing planes, that meant that you can't put much on the wings. And as the bigger tank is in the fuselage anyway, someone would have looked at the space between the engines and thought it was just right for a dump pipe. The flame effect was probably discovered later.

The "Dump and Burn" as it was called here in Australia was used for 'effect' at air shows and for 'promoting' the Air Force as a great place to be.

The 'effect' was really quite spectacular. And frightening to those who saw it for the first time, like here in Brisbane, resulting in many phone calls to the police of a OFO sighting.

As used by some American pilots in SVN on missions to light up the area they were flying through too, for a better idea of just how close to the ground they were.


Fighter YO-YO counter measure? In a dogfight ("A" Scenario), aircraft "A" is being shot at by aircraft "B". In order to lead aircraft "A", "B" must turn inside "A" and will soon overshoot if "B" does not perform a defensive maneuver. "A" can force an overshoot and then turn into "B" for a shot.

("B" Scenario) To prevent "B" from overshooting, it is common practice for it to perform a YO-YO (quick climb then dive) which absorbs energy and increases the flight path which will help keep it behind "A".

In the second scenario, what options does the lead aircraft have to gain the advantage over an enemy behind it that likly is about to perform a YO-YO?

my artwork

Sort of amusing F-16s were used here, instead of older vintage aircraft.  One must realize those little turns would involve high Gs that may incapacitate the pilots.  Also, any "yo-yo" would bleed off a lot of energy and make B an easy target for wingman of A.

One "oldie but goodie" would be for A and its wingman (person) to weave and have B turn right into the wingman's line.  This is the value of teamwork.

However, these days, more realisticly, you need to dodge the opponents missile, which can be very tough.  Stealth and shoot now rule.  But old methods should still be studied.

In the second scenario, one on one, aircraft A would also try to "yo-yo", and they wind up in "a rolling scissors".  The aircraft with more power to weight and better turning rate prevails.  For identical aircraft, it would be pilot skill.  But for modern aircraft with missiles and partners, this type of turning engagement would be very rare.

Col John Boyd was a masterful genius who developed many concepts of aerial warfare, including the concept of specific excess power, to compare dog fighting capabilities, the OODA loop, and wrote the first USAF manual on fighter tactics, the Aerial Attack Study.  See page 72, procedures for countering high speed Yo-Yo, and page 84 for the low speed.

An excellent biography, by Robert Coram, covers his life.

  He was dubbed "Forty Second Boyd" for his standing bet as an instructor pilot that beginning from a position of disadvantage, he could defeat any opposing pilot in air combat maneuvering in less than 40 seconds.

He’s buried in the National cemetery, Arlington, VA.


What does this symbol on this Aerodrome Chart mean? Does anyone know what this symbol on aerodrome charts is?

It is the Aerodrome Reference Point, ARP.

As per ICAO annex 14 vol 1, chapter 2.2:

  2.2 Aerodrome reference point

  2.2.1 An aerodrome reference point shall be established for an aerodrome.

  2.2.2 The aerodrome reference point shall be located near the initial or planned geometric centre of the aerodrome and
  shall normally remain where first established.

  2.2.3 The position of the aerodrome reference point shall be measured and reported to the aeronautical information
  services authority in degrees, minutes and seconds.

The FAA likes to use the term "Airport Reference Point"

Please see the Jeppesen AWM introduction - airport chart legend (pdf). Chart on page two has the symbol with refrence number 17, and on page three this is explained as:

  17 — The geographical location of the Airport Reference Point (ARP) is depicted when known.

The circumscribed cross icon in SACAA charts appears to be a non-descript icon for a radionavigational beacon. The type is not indicated; could be VOR, TACAN or NDB.

They seem to be more common on "sectional" charts than for AFDs; the AFDs I've checked on the SACAA website show FAA/ICAO-style nav beacon types. Compare this Airspace Infringement Hotspot chart for the Cape Town Intl. area with the AFD for the same airport: the beacon's location, but not type, is marked in the wider map, while the more specific symbol for the VOR station is used on the AFD.

This is opposite FAA norms, where the sectional chart (intended to be used from the air to get into and out of airports) shows the specific beacon type with frequency info, while they're usually only shown on the AFD if they're somewhere in the airport that you can taxi to (making them an obstacle you should avoid while moving around the airport), and even then, they're typically displayed as a "black box" indicating a building. The beacon icon on FAA AFDs is usually only for rotating lights.


Are an aircraft's nuts and bolts generally either all Imperial or all Metric, or can they be mixed? This is a low-tech question, but I was wondering about the distribution of imperial vs metric hardware on aircraft.

When current commercial aircraft land at major airports, a mechanic will know which set of wrenches to grab. Still, I wonder is everything metric, or are some commercial aircraft still imperial? Could an engine or some subsystem use one kind of hardware on a plane that mostly uses the other?

What about at a more remote airport visited by a wider variety and vintage of aircraft? Would a mechanic need to go up and check before deciding which toolbox to use?

Found in this comment under this answer

Why not mixed? If the airframe is manufactured in a "metric" country but the engine is from the US, you will find metric nuts and bolts behind the firewall (and on the engine mount) but Imperial on the engine.

If I remember correctly, the Robin DR-300 and DR-400 that towed me many times had just that mixture. Lycoming engine and French airframe.

In a nut shell, all measurements are moving to metric so older air craft like the C-130 is all in feet and inches and weights are in kgs. So the trim sheet has to be converted to this. However the newer aircraft like the C-17 and aA-400 are in lbs and meters and again anything loaded has to be converted to the trim sheets. To be honest its not hard to convert between the different airframes.
The Concorde was made using both metric and imperial as it was a joint British-French build. It all fit together perfectly.


How can I calculate QNH from QFE? Can someone please explain in simple terms how to work out your QNH from QFE?

For example, you take off at 0' but leave the circuit, what do you set the altimeter to? How do you know the QNH?

In metric:

1 milibar is approximately equal to 30 feet.  This calculation is therefore also approximate but is good for airfield elevations to several hundred feet since we round to the nearest millibar.

Divide the airfield altitude in feet by 30 to get the number of millibars above MSL. Add this to the QFE to get QNH or subtract it from QNH to get QFE.

For example, the airfield elevation is 200 feet.  Dividing by 30 gives us 6.66r.  The QFE is 1023. Add 6.66 to get 1029.66 and round up to 1030 millibars, which is the QNH.

  In imperial:

1 inch mercury is approximately equal to 900 feet.  This calculation is therefore also approximate but is good for airfield elevations to several hundred feet since we round to the nearest hundredth inches.

Divide the airfield altitude in feet by 900 to get the number of inches above MSL. Add this to the QFE to get QNH or subtract it from QNH to get QFE.

For example, the airfield elevation is 300 feet.  Diving by 900 gives us 0.33r.  The QFE is 30.12. Add 0.33 to get 30.45 which is the QNH.

If the airfield elevation is below sea level, subtract rather than add and vice versa.

From google of 'how to calculate QNH from QFE:
Divide airport altitude (in feet) by 30 feet. Add resultant number of millibars onto the QFE that you are given. Then you have QNH.


Are those devices allowed on a flight which create their own WiFi signals? I am going from Canada to Mexico but I don't want to be dependent on in-flight entertainment. Thus I got seagate wireless plus so I can stream to my iPad. I couldn't find any policies I can use this device during flight or not. At very least I am trying to determine if it is worth asking the flight company?

No, the rules are about any transmitter or receiver, regardless of whether it comes under the specific category of phone/tablet/laptop etc

If anything your device is worse as it transmits at a higher power and range than a receiver.

The airlines will be primed to say No. But you will hardly be the only one on board with an iPad so it's unlikely anyone will notice. Turn it off if the plane suddenly pitches nose-down at the beginning of your movie.

However, I question the need. I have a 32Gb iPad and there's absolutely no way I can watch a full load of video on my entire vacation, never mind the flight at each end.


How does fuel efficiency depend on wing configuration? Which of the following wing configurations is the most fuel-efficient?

The largest losses on a wing usually occur at the tip, where high pressure air flows around the end from the underside to the top side. This can be minimised by making the wing longer and thinner, or tapering it so the tip is smaller. You can also add winglets to reduce tip losses, but they're tricky to get right.

If you fly near the speed of sound, you get shockwaves that cause a lot of extra drag. You can slightly raise the point where they become a problem by sweeping the wing, and wing sweep also helps to reduce the drag when you are supersonic - but supersonic is never an efficient choice.

Drag is proportional to speed squared, so if you just want to fly for as long as possible, it's most efficient to fly slowly. However if you want to cover distance it's more efficient to fly really high where the air is thin.

You can put all this together to get an airliner, with a long, thin, highly tapered wing (and winglets), flying so high that the air is only just dense enough to support it, and just below the speed that shockwaves cause extra drag.

You ask about wing position, and there is some interference drag where two surfaces meet. It is minimised by making the angle between the two surfaces as large as possible. Thus a mid-wing is slightly more efficient than other designs, but it's a relatively small effect. Wing position is usually determined by the undercarriage design and the pilot's field of view.

Straight wing, look at sail planes ;)

Short story long: the wing configuration itself has not so much of an influence, the position close to zero. It's about the aspect ratio: higher aspect ratio gives you a better glide ratio, thus reducing the power needed. Less power = less fuel consumption (at a given engine efficiency) = better total efficiency. You can also build an inefficient straight wing, let's say one with a quadratic planform.

Problem: large swep back angles (and particularly deltas) compromise aspect ratio geometrically - a 60° delta has given aspect ratio of 2:1 and also high swep back wings bear troubles. You can't build them too long without the position of center of lift becoming too far aft (you might attach them farther up front, but this is limited by the plane's nose... have a look at the B-52's wing attachement position for example). So for a high aspect ratio you need low or no swep back wings.

Yes, such planes are usually rather slow. But, while slightly off topic but related, there is another formula saying twice the speed = four times the energy (or so). This bears the bad news that speed is inherently inefficient anyway...