Why don’t aircraft have interlocks to prevent high-lift devices from being retracted when doing so would stall the airplane? Most aircraft have high-lift devices on the wings (such as flaps, slats, droops, whatevs) to allow them to take off  and climb out at a reasonable speed instead of having to accelerate to near cruising speed while still on the runway; this enables the aircraft to use shorter runways, but also places it at risk of stalling if these devices are retracted too early in the climb (example).

Given the danger of retracting high-lift devices at too low a speed, why don’t aircraft have interlocks to prevent this from happening?

Most modern airliners have some form or other of mechanism that does exactly that, mostly for the slats (which are more important in stall prevention, anyway).

E.g. on modern Airbusses, there is a Slat Alpha Lock function which prevents slat retraction at high angles of attack, on the Boeings there is a Slat Auto-Gap function extending slats from mid to gapped position at high angles of attack.

Military aircraft often have automatic slat deployment to aid with high angle of attack manoeuvres, and even some vintage aircraft did have aerodynamically activated slat-like devices for stall prevention.

Any sensible reference suggestions welcome for any of these... cannot post mine.

While flaps do slightly reduce stall speed, that is not their primary purpose.  Planes pass quickly through both Vs0 and Vs1 during takeoff or landing, and pilots are too busy to mess with flap settings during those few seconds anyway. The only reason we deliberately fly inside that range is to practice slow flight, stalls and spins, where such an interlock wouldn't be of any benefit.

During takeoff, low flaps may be used to increase lift and thereby shorten the takeoff distance on short runways or get into ground effect sooner on soft runways. In both cases, though, the climb afterward will be slower due to the added drag, so it's only done when necessary and then pulled out at best climb speed, i.e. well above stall speed.

During landing, high flaps are used to increase drag and thereby descend without gaining speed. You're not even close to stall speed until the flare, and raising flaps before then just means you'd land faster--not stall.

OTOH, while the benefit (if any) would be tiny, there is a very real risk that the device would fail somehow, such as preventing flaps from retracting at any speed, which is a serious safety problem. You would need a way to bypass it in such cases, and if you trust the pilot not to stupidly bypass it, then you might as well trust him/her not to stupidly need it in the first place.


Is spin recovery possible in an airliner? During initial flight training a lot of emphasis is placed on stalls and spins and how to recover from them, but is it possible to recover from a fully developed spin in an airliner? Do these large aircraft have enough rudder authority to pull it off?

Has it ever been done? And is it part of the training for specific type ratings? (in a simulator of course)

There were a lot of other mitigating factors in the Colgan Air 3407 crash. Was that one recoverable? It depends. It never should have got to the point of a stall in the first place. It was more preventable than recoverable.

But in answer to your question, again, it depends. Every aircraft in the air can stall and be recovered, if responded to properly. But the plane may very well bend and break if the stall develops too far. Then it may not be recoverable. And most large airliners (or aircraft bigger than a few thousand pounds with multiple engines) aren't designed for the stresses of spins, so they never teach to a full stall. In those types of aircraft a full stall is much more dangerous, and they can be much more difficult to recover from, especially if you break something. Besides, in aircraft like that, you should receive plenty of direct warning long before you reach the point of a stall.

When I was teaching, stalls and spins were one of my favorite subjects for early pilots. Especially in light trainers like the Cessna 150/152s. Those aircraft were always incredibly good at stalls/spins and incredibly forgiving. You can put a Cessna into a hands-off full stall if you trim it right, and it will stop rotating in a spin if you simply let go of it (and have enough altitude). I always taught my students spin recovery from a full spin, even at the Private Pilot level. And usually shortly after teaching them full stalls. I would stall it, make it rotate at least 3 or 4 times, and have them recover the spin. Then have them do it themselves. I never had to worry about my students not knowing how to recover from an unintentional stall/spin. By the time my students were learning to fly multis, I was teaching them more stall recognition and avoidance than recovery. Recovery is essentially the same in all aircraft. You just have to be sure to not reach that point.

There's only one thing you really need with any aircraft in a stall/spin, and that's altitude. Unfortunately, takeoffs and landings are the most likely places for you to get behind the aircraft and let it unintentionally stall/spin. That's why you learn how to recognize them very early in your pilot training. You can't spin without a stall first, and just about any airplane will give you fair warning before you stall it. The trick is recognizing the situation before it becomes serious.

Big airplanes of the jet types have what is called stick shakers to warn pilots of an approaching stall and a stick pusher to initiate a recovery. In training with jets most pilots do 100% of there training in simulators and then make three takeoff's and landings in the airplane.

T tail airplanes may not be able to recover from stalls if the airplane get into a deep stall because airflow over the tail is blocked by the airplane and the elevator becomes ineffective.


Can I get a FAA medical certificate and apply in an Indian airline? I am an Indian, and was wondering if I could get an FAA medical certificate and apply in an Indian based airline.

Is there a problem if I do that? Should I get the DGCA medical certificate itself?

Well Air India is hiring qualified pilots here. The advertisement says you need a medical certificate issued by the DGCA. There is no mention of accepting an FAA certificate.

I'm not completely sure how it works in India but usually you need to get a medical certificate from the country in which the airline is based (or to be specific, the country in which the aircraft is registered). I'm not aware of any exceptions to this rule except for temporary operations, but I stand to be corrected.

According to my knowledge, To be employed by an Indian airliner you have to get a DGCA medical Certificate.


For how long can an Embraer E195 airplane glide at malfunction? E195 specs:

Maximum Takeoff Weight 52,290 kg
Max Cruise Speed M 0.82
Cruise altitude: 35000 feet

Assume the weather condition is perfect (no clouds or gust winds). Also assume this airplane is fully loaded and just reached cruising altitude at its max speed. There and then, both jet motors immediately stops due to malfunction. No fire or anything, they just stop.

Given this scenario; will this aircraft be able to "glide" downwards for an emergency landing, or will it just drop dead and head for the earth? If it won't glide, how long will it take until it reaches the ground for impact?

(Reason for asking: me, being horribly scared of flying, just took a trip with this exact plane model, and I could not get the above thoughts out of my mind)

It's a rather 'clean' plane. Its maximum L/D is, probably, at least 14. (The table shows cruise L/Ds. The L/Dmax is probably much higher in all cases...) Properly handled, and from 35000ft, it might glide for more than 140 kms...

From https://en.wikipedia.org/wiki/Lift-to-drag_ratio :

Of course it will glide, and for many miles. The single engine plane that I flew would glide 9 times its altitude, and big commercial planes will glide even further.

As one relevant example, the Gimli Glider:  From Wikipedia:

https://en.wikipedia.org/wiki/Gimli_Glider

-Skip


Lockerbie bombing - amount of debris (confusing numbers) As mentioned on Pan Am Flight 103:

  ... In total 4 million pieces of wreckage were collected and registered on
  computer files. More than 10,000 pieces of debris were retrieved,
  tagged and entered into a computer tracking system.

This is a bit confusing, at least to me. So which one is the actual number? Or if both sentences are correct, what is the difference between them?

Pieces of wreckage implies a large 'section' of plane, whereas debris suggests miscellaneous smaller items and bits of metal etc.

I agree it's potentially confusing, however, and likely arises from two people editing the same section without adjusting the context.

I'd say that 4 substantial sections of plane were found, along with a large amount of smaller debris scattered around, totalling around 10,000 pieces.


What are the consequences of throttling up past 100% of N1? The B737 is probably my favorite aircraft and I'm always sure to never throttle past 100% of N1. I was told the aircraft is pretty much totaled if you take N1 past 100% but you can eke out that extra power for emergency purposes. Is that true? What are the consequences of exceeding 100% N1?

And what numbers should I be paying attention to for takeoff in a 737?

The consequences are always explained in the flight manual. It has graphs which specify what you should do if you exceed the speed, temperature, etc., by how much and for how long. For example (this is for FJ33-5A):

Note that the 100% mark is, in a sense, arbitrary. It does not necessarily mean the absolute max (even the 'normal' max), as can be seen from the example. (I don't know how it is for CFM56). This happens for several reasons; typically, the 100% value corresponds to a fixed RPM number for the whole family of engines. As the engine undergoes modifications, the permissible RPM may increase (or, in some cases, decrease), yet the 100% RPM number is usually not changed, moving the red line instead. In some cases, a civil engine is installed on a military aircraft, and is then allowed to run at, say, 108%, at the cost of much reduced lifespan and service intervals.

Sorry, could be wrong here, but given the thermo-resilience of the materials most engines are made from are essentially exceeded by overclocking for to long, the thermo-residue buildup eventually end up melting the engine; this is why there is redundancy built into the MCT for engine outage scenarios etc.


Can you identify this aircraft photographed during solar eclipse 8/21/2017? The following sequence of shots was taken about 9.5 minutes before the start of the eclipse, 1:12pm EST.

Shooting in burst mode off of a tripod - all 3 shots taken within 1 second. Burst mode is 14 frames per second, so it's reasonable to assume that these 3 photos were taken 1/14sec apart.

Exif:
Camera: Canon EOS1DX
Lens: Sigma 150-600mm Contemporary.
1/8000s, f/29, ISO 100, focal length 600mm. No filter.

First image: the aircraft is seen above the sun - no contrails.
Second image: completely different trajectory and a contrail (?)
3rd image: the aircraft is gone.

Zoomed in:

Based on the second picture and the list of US military jet, I would guess F-22 Raptor, and since this kind of aircraft usually fly by 2, the jet in the first picture is maybe a second F-22.

As for the timing of the shots, the trail we see in the second pic not appearing in the 3rd is telling me they were shot with at least a couple of seconds interval. That would also explain why each jet appears only in one pic.

The first plane that came into my head after seeing these pictures was the F-117 Nighthawk:

However, this object pictured could easily be something else (maybe not even a plane) due to the low quality of the object and its speed, so no answer will be 100% accurate.


What is this unusual leading edge flap on a B737-200? On this video of Air North's gravel runway-equipped B737-200, there's what appears to be a small leading-edge flap (Krueger flap?) inboard of the engine.  Refer to the screen shot below.  What is this?

Addendum

Notice in the video (and screen shot) that this device shows itself while no other flaps are extended.

These are two leading edge Krueger flap surfaces at each side of the wing, you can see details about them according IPC and AMM documents I found over the internet:

Regarding the Addendum, and why it seems that there is no other flaps deployed, I found a similar topic at Airliner.net Forum. As it is mentioned there, when is no hydraulic pressure, they can be extended by their weight:

  ...it has to do with the shut off valves and the actuators relaxing with no hydraulic pressure on them.

and also:

  ...Pressurize the system and they all move to their present commanded position

and another sidenote:

  ...Someone pulled that Krueger Flap to the fully extended position. When they droop because of no pressure on the system there in the mid positions.

and as final note, this issue is also mentioned in the AMM:

The 737-200 does have Krueger flaps inboard of the engines as seen in this photo

source

It’s hard to really tell, but it looks like the outboard half of the flap is not entirely retracted.


Why did the Avro Vulcan use a delta wing? Why did the Avro Vulcan use a delta wing?

The B52, from the same era, used a swept wing, and had a higher maximum speed.

In the answer to What are the advantages and disadvantages of a delta wing compared to a swept wing?, Peter Kämpf explains that a swept wing is ideal for subsonic airliners.

No one else has built a subsonic delta-wing aircraft since, military or civilian. Why did the designers of the Vulcan make this unusual choice for a subsonic aircraft?

By Ministry of Defence [OGL 3], via Wikimedia Commons

It was obvious to the design team that conventional aircraft could not satisfy the required specification; knowing little about high-speed flight and unable to glean much from the Royal Aircraft Establishment or the US, the team at Avro investigated German Second World War swept wing research.
The team estimated that an otherwise conventional aircraft, with a swept wing of 45°, would have doubled the weight requirement. Realizing that swept wings increase longitudinal stability, the team deleted the tail (empennage) and the supporting fuselage, it thus became a swept-back flying wing with only a rudimentary forward fuselage and a fin (vertical stabilizer) at each wingtip.
The estimated weight was now only 50% over the requirement; a delta shape resulted from reducing the wingspan and maintaining the wing area by filling in the space between the wingtips, which enabled the specification to be met.
— Wikipedia

In short, the team didn't know much about high-speed flight (blame Wikipedia). And to reduce the weight, they eliminated the tail-plane, shortened the span, and filled in the space between the wingtips. Achieving their weight target.
For the same area, a wide wing is lighter to attach, as it requires smaller spread spars.
So, for weight reduction, a delta wing wins against a conventional swept-back wing aircraft. In all, great engineering solution to a big problem, with one downside—
—higher fuel burn at those speeds, limiting the range.
The B-52's were known for loitering in the air for extended durations. Their efficient design requires fewer rendezvous' with the tanker. Unlike the famous Vulcan train.
Some numbers (in kg and km):
        empty weight     MTOW      payload+fuel      range
B-52      83,250        220,000      136,750         7,210
Vulcan    37,144         77,111       39,967         4,171

Maintaining the same wing area; saving weight by reducing the heavy structural elements—the tail-plane, big spars, and wing-span. (Eyeballed the scale, only illustrative.)

Vulcan was built to a specification which gave it a top speed capable of outrunning the fighters of that time. The specs from wiki make it too slow to do that. The Mk 10 used the same engines adopted much later for the Concord. Rumour had it that the last ships off the line were capable of 900mph. In the fifties six Vulcans did an exersize. They flew over the pole and attacked six major US cities. They were not intercepted. After the initial report in the newspapers a D notice made sure that the incident was hushed up. It did appear as a front page feature in the AVRO news, A monthly company newsletter.
Much later the Valkerie was developed in the US. This compensated the nose dive tendency by adding a canard wing on the nose.Later again the B1 was a similar shape. The latest idea is now the blended wing design which like the Vulcan is capable of carrying 50% more than an aircraft with a fuselage. Just in case you missed the point. The initial research was done in the AVRO factory in Chadderton. Tests in a huge tank found the wings suffered fatigue and  fell off. The solution was found when it was suggested that a line of perforations along the breakage line would solve the problem. The toilet paper never ripped along the perforations. Solution Honeycomb sections. Saved lots of weight and was far stronger.


Why are geodesic airframes no longer produced? Why are geodesic airframes no longer produced?  Do they cost more than conventional structures?  Are they not as strong as conventional structures?  I assume it is insufficient cost benefit ratio, but how does that work out?

  Wellingtons under construction. Photo: Royal Air Force

Geodesic (sometimes also spelled geodetic) designs were used in aviation as early as 1909, in the Schütte-Lanz SL1 airship. It had a wooden structure with fabric covering, and Professor Johann Schütte, the scientific head of this design, used the most efficient method conceivable. However, planning the shape of all structural members was an enormous amount of work, and stretching an existing ship by inserting a new section was almost impossible. For those reasons, the late Schütte-Lanz airships used aluminum frames with conventional design, just like Zeppelin did from the beginning. Diagonal wire bracing was used to take up shear loads.

Geodesic frames are good in transferring both bending and shear loads. This is helpful when the aerodynamic covering is not stiff enough to contribute any shear stiffness, as in the case of fabric covering. However, when the skin is made from the same material as the frame, it can carry shear loads and a geodesic frame would not improve matters. Now it is better to carry longitudinal loads in longerons and shear in the skin.

But geodesic constructions are not dead. CAD makes the design effort manageable, and in some cases they give a weight advantage. Look at the casing of the EJ200 engine: It uses a geodesic reinforcement to make the casing light and strong and to prevent harmful vibrations. In the end, a jet engine casing is a big pressure vessel and needs to be strong, stiff and light.

photo by Julian Herzog, CC-BY

They ARE still produced. See for example the EU research project from 2013 here: http://www.transport-research.info/project/advanced-lattice-structures-composite-airframes


What is the best way to retrieve (and transmit) location (GPS) of plane in real time? What are some of the best ways to retrieve and transmit the location of a plane I am in, real time.

To speak in realistic terms, I'm currently training for my private pilot's license and as such am spending a lot of time in various planes I do not own / have decision powers over. How could I share my current location with someone in a remote location while in the air without physically modifying the aircraft.

There are a couple of ideas that have come to mind, but my understand of the solutions or challenges are not complete:

There are websites like flightradar24.com, but the aircraft I'm in often don't show up. That being said, a flight I took yesterday DID show up, but was not terribly accurate. Perhaps that is because I filed a flight plan and / or used flight following (which would put me on the radar tied to my tail number).
I could use a simple app like "Find my Friends" on the iPhone. I realize this is crude, but it could work. That being said, I don't know how well cell phones transmit above the ground.
Some other portable device. That device would need to transmit real time in some way and there would need to be some way to look up that transmission.

Any information on this would be appreciated!

UPDATE:
I'm talking about general aviation here. Speeds <= 120 kts altitude typically <=  5,500

There are a few consumer-facing easy-to-obtain devices that you could use for this, although they don't quite transmit in real-time (they'll transmit updates down to every 2 minutes).  Spot and inReach are aimed at more casual users, and Spidertracks offers real-time tracking that might be considered targeting more of the commercial or "prosumer" market, but they still transmit updates every 1-2 minutes.

They all work in a similar fashion: rather than some kind of ground-based radar, they utilize a combination of GPS to calculate your location and use the Iridium Satellite communications network to transmit it (so it doesn't rely on cellular signals and has global coverage), they transmit on an interval you decide to a website that your interested party could monitor.  This is the key difference from other answers that use an app on a device: even if the app is linked to a real-time tracking service like Map my Tracks, your phone or tablet will still be relying on the cellular network (which you're technically not supposed to be using in flight), and even if it does work, it could be intermittent. These devices link into the Iridium Satellite network for global coverage.

The three devices are: Spot Satellite Communicator and the DeLorme (now owned by Garmin) inReach, and Spidertracks.

This isn't a free service, there is a monthly fee for using the devices.

Spot is around USD$150

inReach is around USD$350

Spidertracks start at USD$1000

In July 2016 ($USD)

inReach: Allows tracking updates every 10+ minutes ($15/month) or the 99/month package allows for updates every 2+ minutes.

Spot: 50/year allows 5, 10, 15... minute tracking update intervals or $150/year: 2.5+ minute tracking updates.

Spidertracks has various plans, basically you pay by reporting point the range is $0.05 - $0.13 per reporting point.

DeLorme inReach:

Spot Satellite Personal Tracker:

Spidertracks

Example of the web interface from Spidertracks for real-time tracking

You should consider aquiring an ADS-B transmitter. This is the new standard, growing rapidly, and it's what lets you be visible in sites like flightradar24 or others.

AFAIK, it uses your transponder in mode S to broadcast (to air AND ground) a bunch of information, like aircraft position, speed, altitude, heading, ...etc.

It is already used by most commercial airliners, small jets, and even piston driven aircrafts, and is considered the technology to be used in the near future, in respect of the FANS-1/A specification.


Are pilots legally required to verbally declare an emergency to invoke §91.3(b)'s deviation authorization? Related:Do you have to explain what your emergency is?

I am aware that pilots are required to declare an emergency and inform ATC of as much information as possible during IFR flight due to this rule:

  §91.183    IFR communications.

  Unless otherwise authorized by ATC, the
  pilot in command of each aircraft operated under IFR in controlled
  airspace must ensure that a continuous watch is maintained on the
  appropriate frequency and must report the following as soon as
  possible—

  (a) The time and altitude of passing each designated reporting point,
  or the reporting points specified by ATC, except that while the
  aircraft is under radar control, only the passing of those reporting
  points specifically requested by ATC need be reported;

  (b) Any unforecast weather conditions encountered; and

  (c) Any other information relating to the safety of flight.

Is there any rule that requires the declaration of a VFR emergency for it to be legally valid for the purpose of rule deviation?

My assumption is no because a 2-way radio is not even required in all locations.

The short answer is no, there is no specific requirement for VFR flights to state an emergency, however you may be expected to explain yourself and your actions once you reach the ground.

  My assumption is no because a 2-way radio is not even required in all
  locations.

To expand on this you don't need a radio on board for VFR flight (FAA FAR 91.205) so they would have a legally contradicting issue if they required you to announce when you don't have a radio. As mentioned by Ron in the question you linked the rule is "Aviate, Navigate, Communicate" If you are too busy with the first two that is far more important.

Im not sure where they are pulling the quotes but this NASA presentation on emergencies sums it up well.

  “…an intent of 91.3 is to ensure the PIC will handle the emergency in
  a manner necessary to save lives and not be worried about regulatory
  compliance.”

  “I’ve never seen a pilot violated for deviating from a
  regulation when that pilot has either declared an emergency OR has
  stipulated in ANY written response to the FAA that an emergency
  existed at the time of the deviation.”

This article has some interesting points from a lawyers perspective on the situation,

  Madsen defended a case for a pilot who deviated from an assigned
  altitude due to extreme turbulence while flying a Cessna 150. The
  pilot had dropped his handheld mic, so he couldn't initially
  communicate his situation. He stabilized the airplane and was about
  600 feet off his altitude when ATC called him. At that point he was
  able to find the mic and he told the controller what had happened.
  "It's unrealistic in some situations to communicate your emergency
  before you secure the aircraft," Madsen said. "You want to control the
  aircraft first." Madsen said the case was ultimately dismissed, but he
  felt it would have been much easier to defend had the pilot declared
  his emergency.

Here we can see that ultimately the pilot was in the right and while he should have declared, there was no legal grounds that required it.

On some level you are at the mercy of the FAA with this one and its clearly a case by case basis (as is everything in aviation) and the lawyer in the above article goes on to say

  Some FAA field offices take the wording very seriously. Such was the
  case with the Cessna 150 pilot who deviated from his altitude. "They
  questioned why he didn't state an emergency and call out mayday, and
  they took great issue with the fact that he didn't use the accepted
  terms," Madsen said.

Again the case was ultimately dismissed whether or not they were happy about that.

First of all, FAA regulations are not laws, they are regulations. Federal laws are made by members of Congress elected by the people of the several states. Regulations are issued by executive-appointed bureaucrats. The word "legal" or "legally" is properly used when speaking of laws, not regulations. Violations of regulations are usually what are called "civil violations," and have nothing to do with "illegality" which normally refers to criminal actions.

When Washington bureaucrats discuss regulations they do not use the words "legal" or "illegal" for the reasons stated above. They use terms such as "compliant" or "non-compliance". Non-compliance with an FAA regulation has nothing to with "legality". I know there are a lot of people who fantasize about controlling every time a pilot wipes their butt and throwing them in jail for any imagined act of willfulness, but so far that has not happened, so please do not refer to FAA regulations as though they were laws.

As for your question, pilots are required to declare an emergency only if the circumstances permit it.

A pilot can deviate from ATC instructions any time they determine that it is required for safety. Notifying ATC of a deviation is purely secondary to the primary goal of preserving the aircraft and avoiding crashing.

If a pilot deviates from an instruction in a way that is of concern to ATC, then an explanation can be demanded by certain appropriate officials at the discretion of those officials. If they find the pilot's explanation unsatisfactory or indicative of poor judgement, they can revoke the pilot's license.


ATC interruptions, when is it okay/overlooked? Having recently completed my first solo flight, the tower gave me my taxi instructions, and then congratulated me, as my instructor was hanging out in the tower with the controllers at the time.

It's relatively busy airspace, so there were quite a few pilots on frequency, and multiple landing at the same time. However, before I could repeat/confirm my taxi instructions, a half dozen other pilots got on frequency congratulating me as the "new-blood". Seeing as this took about 30 seconds, it delayed my taxi readback, and potentially delayed other pilots approaching.

Controllers were fine with it, so it seemed, but I would assume that in certain situations this could be considered abuse of airport communications. Are there any guidelines for when the tower has to / should report such incidents, or is it merely up to the towers discretion?

It didn't prove any large issue in my case, other than a delayed taxi, but I'm wondering where the "line" would be drawn.

Since you have not stated any jurisdiction in your question, I am basing this answer on the EU, which is what I am familiar with. Rules in many other parts of the world are going to be similar if not nearly identical.
Regulation EU 376/2014 lays down rules on the reporting, analysis and follow-up of occurrences in civil aviation. On the list of Mandatory Reporting you will find:

(v)   communication-related occurrences;

which I think, among the possible categories, would be the best fit for the kind of event you describe. However, it is not detailed further what is encompassed by this category, so whether something like what you describe falls under mandatory reporting, I don't know for sure. In theory, rules were violated (unrelated chatter on the radio is, quite simply, not allowed). In practise, it doesn't sound like any harm was done.
In any case, there is also Voluntary Reporting, which is designed to capture

(a)  details of occurrences that may not be captured by the mandatory reporting system;
(b)  other safety-related information which is perceived by the reporter as an actual or potential hazard to aviation safety.

The rules concerning reporting can be quite difficult to comprehend; my general advice (and what I have learned at school) is: if in doubt, file a report. If you feel the safe environment was in any way compromised, you should report it. Remember, the aim of a report is not to appoint blame, but rather to improve safety. I know from experience that it might be difficult to report something done by someone you know, since it might feel like you are pointing fingers or ratting someone out, but the truth is that the reason aviation is so safe, is because the people who work with aviation takes safety seriously, and reports violations.
As for whether the controller is going to report your situation, I doubt it - they is the one who initiated in the first place after all. But again, if you feel safety was violated, please write a report. Your writing today may save lives tomorrow.

ATC communication priority on "Tower" Frequency:

If you were flying in the US:

ATC
Aircraft exceeding 31.44m in length (103ft, 2inch)
All of the smaller aircraft
On-ground vehicles

In all of the EU Airports:

ATC
Aircraft (No matter what size or load they are carrying)
All other On-Ground Vehicles

In your Case, If you were flying in Europe You should have been fine. There is no such rule about aircraft priorities in the EU airspace.


What are the advantages of the angled flight deck layout used by some aircraft carriers? I've been flying aircraft carrier approaches in a flight simulator lately and noticed that the carrier has an interesting layout. I have an image below where the landing runway is in red and the takeoff runway is in blue.

I can understand the takeoff runway - taking off into the wind with the catapult so that you can get enough air flowing to take off. The part that confuses me is the position of the landing runway. It is at a slight angle to the direction of the carrier's motion, meaning that when I fly the approach I have to aim to the right of the carrier and let it move underneath me. It seems to me as though this would just complicate an already difficult procedure, particularly in rough weather conditions.

Why not just take off and land in the same direction? As far as I am aware the aircraft only take off forward of the jet blast shields i.e. at the tail of the blue arrow. This would leave plenty of room on the carrier for landing. The only time I can think this would be a problem would be when a pilot needs to abort the landing and quickly take off again when there is another jet waiting to take off ahead of him, though this would assume that aircraft were taking off at the same time as others were landing (I have no idea if this actually happens).

It would be great if someone could shed some light onto why aircraft carriers have this layout - I'm not a pilot, just been playing around in simulator.

This kind of layout is called the angled flight deck (also called 'skewed' or 'canted' deck) and was first used by Royal Navy. There are a number of advantages to this layout compared to using the same direction of landing and takeoffs:

It allows concurrent landings and takeoffs.
By having an angled deck, the aircraft which fail to connect (with the arrestor cables) during landing can go around and try again without risk of damage to other (parked and taking off) aircraft).

The main reason for the emergence of angled deck was the introduction of jet aircraft in naval operations, which due to their weight and high speeds required most of the deck available to complete an arrested landing. Also, in case of missed wires, it was possible to use a barrier in case of propeller aircraft, which was not possible in case of jet aircraft. According to Rear Admiral Dennis Campbell, the inventor of angled deck,:

  But with the advent of the heavier faster jets, it soon became obvious that the dimensions of the carrier's deck would impose a limit to the standard of aircraft that could be operated. The inevitable increase in weight and landing speed of the jets would make it impracticable to retain the existing combination of arrester wires/barriers/and deck park without a drastic reallocation of the deck space required to absorb the much longer pull-out of the wires.

Prior to the application of the angled deck, this caused significant problems and requirement of complex machinery to overcome.

  Ark sister ship and predecessor, the Eagle, was equipped with sixteen arrester wires and three different types of barrier (together with all their several hydraulic machines), and all this gear could only just cope with the first generation for (straight wing) jets.  No way would such a layout be good enough for the newer types.

The solution was to skew the flight deck by about 10 degrees (the HMS Ark Royal first had the flight deck angled by 5 degrees, which was then increased to 10) and use it for landing. This lead to:

  The saving in arrester gear units and barriers – Ark needed only four wires and one (emergency only) barrier.  The reduction in weight and the extra space that this conferred enabled more mess-decks to be fitted in, thus reducing congestion in living spaces.
  Since landing accidents would obviously be far less frequent, fewer aircraft and spare parts would be needed so costs would be greatly reduced.
  Similarly, death and injuries to aircrew and deck handlers could be kept to a minimum – with a big boost to confidence and morale, not to mention the saving in training costs.
  As experience was gained of the new scheme, less obvious advantages came to light.  New areas of parking, (abaft the island for instance); an added flexibility in the relative wind speed and direction, easier and faster deck handling, less wear and tear on the command, etc.

Perhaps surprisingly, though the USN has adopted this system in its supercarriers, the RN dropped it later on.

I'd prefer to avoid bumping into any of the catapults' pits so angling your landing through the superstructure sounds just peachy, regardless of how many super-steep-angled Chuck Yeager landings in mountain foothills you've ever approached (old timer instructors will grey your hair QUICKLY!)


Do aerodynamic forces and moments change aircraft pitch and yaw in the same way? Several questions on the Aviation SE site have dealt with the question: can the rudder alone turn the aircraft:

This one, which was marked a duplicate of
this one, which was itself marked as a duplicate of
this question, with a skilful and detailed answer.

So we know in triplicate that the rudder alone can turn an aircraft. Not very comfortably due to the side forces, wrong way lean, different airspeeds on inside & outside wing etc, that is why the normal way to turn is to bank.
However, the following has been posted in the comments (partial quotes only due to length):

Yaw does not cause aircraft turn. It only causes yaw. Yaw is not turn.
Lift, pointed in a direction other than perpendicular to the horizon, is what creates turn. Nothing else.
With no other yaw force on the aircraft, if you have right rudder, that does create a leftwards force, but it also creates a right yaw (sideslip) which itself creates a rightwards force that opposes the leftwards force from the rudder.
It works in exactly the same way as it does in pitch. The elevator pulls the tail down and, because it's behind the CG, creates a nose up pitching moment (torque). Lift on the wings lifts the aircraft up, and because it's also (generally) behind the CG it produces a Nose down pitching moment. Because the moment arm of the elevator is so much longer the torques balance, but the Up force from wings is much larger than the down force from the elevator and the aircraft is able to fly. The force from the rudder, and the force from the sideslip angle of the fuselage act in the same way.
The nose of the aircraft does not "turn" away from the "direction the pilot ... " it only "yaws" away, and it only yaws away until the sideslip angle reaches the point where equilibrium occurs.

The gist of all this is that the aircraft would behave in yaw in the same way as in pitch: rudder deflection only causes an angle of sideslip, not a continuous turn in heading. That would conflict with the earlier questions posted above.
So the question is: does yaw really behave exactly like pitch? Does deflecting the rudder only cause a greater angle of sideslip but no flight path change?

Of course will yaw also change direction if we define this as a change in the flight path. But it does so much less efficiently than banking.

Yaw creates a side force on the fuselage and fins which accelerates the aircraft sideways. This does change the resulting flight path, but the amount of side force is small due to the low aspect ratio of the fuselage. The lift-to-drag ratio of the fuselage is poor, so another change to the aircraft's vector is a deceleration if the increased drag is not compensated by more thrust.

Banking also creates a side force (when seen in the geocentric reference system), but now the wing is responsible for that force. Its lift-to-drag ratio is much better than that of the fuselage, therefore, the amount of side force is much higher and less drag is created. By first banking and then pulling more than 1g, the pilot changes the flight path much more effectively while maintaining altitude.

So the answer is yes, yaw behaves the same way as pitch. Only the wing and elevator are replaced by the fuselage and fins, with all changes to the magnitude of the forces this causes. The only difference is that pitch is needed to adjust lift, and changing the pitch attitude will change the speed of the aircraft or the load factor. Flying in a sideslip with no adjustment for the side force by a corresponding bank angle will continuously accelerate the aircraft sideways and will result in a uncoordinated turn. Now the sideways load factor (which is zero in coordinated flight) will be nonzero while in the longitudinal motion the normal size of the load factor is one (and be different from one when pitch is changed).

EDIT:

@TomMcW has contributed a practical example in the comments. Consider a crosswind landing with a glider or motor glider where crabbing is your only option to fly a straight approach over ground. Right before touchdown you should then step on the rudder to align the aircraft with the runway so the tires can touch down without moving sideways. Now consider that you stepped on the rudder too early and the aircraft floats along the runway with a sideslip angle. You will drift leewards, right? That is exactly the change in flight path I am talking about.

In crabbed flight the aircraft flies without sideslip. The fuselage with its forward center of pressure position destabilises the aircraft in yaw and the vertical tail adds the required stability. Both create no side force in crabbed flight. Now you want to align the fuselage with the runway and step on the rudder: The tail swings the aircraft around into a sideslip until the fuselage points into the desired direction. Now opposite rudder must be applied briefly to stop the yawing motion and then returned to a position between neutral and the initial deflection in order to trim the new sideslip. Note that this works exactly in the same way as the elevator when a new angle of attack is trimmed!

In the sideslip condition both the fuselage and the vertical tail will create a side force in the same direction. The side force of the fuselage is higher because its center of pressure is closer to the center of gravity than that of the tail, and in order to reach an equilibrium, both must point to the same side. This combined side force accelerates the aircraft sideways such that a speed component is added which reduces the sideslip condition. Since the aircraft is trimmed for a specific sideslip, the changing balance of moments with a change in sideslip will yaw the aircraft further so that the trimmed sideslip angle is restored.

Why is that? Remember that the rudder is deflected. This creates a camber in the vertical tail which moves its zero-sideforce angle of sideslip away from the sideslip angle of zero to a negative angle (for example, right rudder deflection will shift the zero-sideforce sideslip angle on the tail to a left sideslip value). Any change in sideslip will, therefore, bring a relatively larger change in side force at the tail which changes the balance of yawing moments such that the old sideslip is restored. Note again how similar this is to static longitudinal stability.

This means that the aircraft must maintain a slow yawing motion in order to keep the sideslip constant. The side force causes a reduction in sideslip and the yawing motion is a result of the sideslip-maintaining tendency of the vertical tail.

And, no, yaw is not a moment. Please let's all use an agreed version of English.

First of all, by Yaw, I mean the torque or moment created by the lift produced by the vertical stabilizer and rudder when at a sideslip angle, acting on the aircraft through a moment arm between the CG and the rudder.
This Yaw, itself, exclusive of analyzing the total sum of all other aerodynamic forces on the total surface of the aircraft, does NOT cause the aircraft heading to continuously change.

F=ma !!!!

Unless the total lateral force (parallel with the wings) is non- zero, the aircraft will remain on a constant heading. Yaw, (by definition) is nothing more than the condition that the aircraft Heading is not aligned with the relative wind. PERIOD.

Depressing the rudder, does cause a Yaw. But it also causes Lateral Lift to the side.  It is this Lift which can potentially cause the aircraft to turn.  But it will ONLY cause a turn if the sum of all other lateral Lift is insufficient to balance out and compensate for the Lift created by the rudder deflection. The sideslip generated by the rudder (THIS IS THE YAW) also generates Lift, and it is in the opposite direction from the Lift generate by the rudder Lift. Which direction the aircraft turns in is determined by the total Lateral Lift produced by not just the rudder, but by all aircraft surfaces, including the side of the Fuselage as a result of the sideslip.

The point is that it is not the Yaw which causes the turn, as Yaw is a torque. It is the Lift. Lift Is a force

Yaw is torque, and can only produce rotational acceleration, which can only change attitude, and the equilibrium sideslip angle. Absent a non-zero total lateral force, it cannot change direction of motion. It will just change the angle of the fuselage to the relative wind, (sideslip). As the sideslip increases, the torque from the rudder deflection decreases, and the opposing torque frm the sideslip increases, until they reach equilibrium. At that point, the sideslip angle stops increasing.

IF at this point of equilibrium, the total lateral (sideways) force is non-zero, then the aircraft will turn.

As a thought experiment, imagine a side thruster on the nose of the aircraft pointing to the left, that puts out 100 pounds of thrust, let's say, 5 feet forward of the aircraft CG. This would produce the exact same right Yaw as a rightwards rudder deflection at the tail, that produced 50 pounds of leftwards force on the tail, 10 feet behind the CG. Clearly, the aircraft is not going to turn in the same direction at the same rate of turn in these two scenarios. Why Not? you might say - the yaw is the same!  Both are producing an identical amount of Yaw (500 ft-lbs) in the same direction (clockwise)! But obviously, they do not.  This is because, absent consideration of the forces produced by the fuselage due to the sideslip, the rocket thruster is pushing the aircraft to the right, and it will turn right, the rudder is pushing the aircraft to the left, and, (Absent consideration of sideslip forces),  it would turn left.

It is difficult to understand this because any aircraft has a fuselage, with significant sideslip forces, and these distort the effect of the issue, but if you imagine an aerodynamic body that consists of a flat plate and a rudder, so that there is no sideslip force, then imagine what would happen if you deflect the rudder. Why, the entire body would just spin around the yaw axis until the rudder is once again streamlined in the relative wind, and there would be no turn created at all.


What is the difference between a POH and an AFM? Some aircraft come with a Pilot Operating Handbook and some come with an Aircraft Flight Manual.  Why the different name, and is there a difference between them?

Both a POH and an AFM meet the "Operating Limitations" requirement in the ARROW acronym.

The difference between the two is mainly in length and content: an AFM is usually a thinner document, satisfying the requirements of FAR 23.1581 and not much else, while a POH contains these required items plus other information like system diagrams (The contents & format of a POH are standardized in GAMA's Specification 1).

Parts of the POH (like the Limitations section) are FAA-Approved, and serve as the AFM, and both documents are typically associated with a specific airframe (by serial number).

A better explanation might be this:
The AFM is a regulatory document (it's contents are prescribed under the section of the regulations the aircraft was certificated under - Part 23, Part 25, etc). The POH is a GAMA-defined document whose contents meet the regulatory requirements of an AFM, and present other information in a standardized way so that a pilot can go from a Cessna to a Piper to a Mooney to a Socata and browse the book to learn about the airplane they're about to fly with all the information presented the same way no matter who the manufacturer is.

The other two types of documents you may encounter are an "Owner's Manual" (which usually goes along with a thinner AFM & provides some of the information found in the newer-style POH) and a Pilot Information Manual (PIM) which is a "generic" version of the POH which many pilots buy so they can study the procedures without removing the regulatory document from the aircraft.

Chapter 9 of the Pilot's Handbook of Aeronautical Knowledge talks a little about the differences between the two documents (and a whole lot of other flight documents).

The POH is the official book of rules for that specific serial number airplane.  The AFM is the unofficial/generic one for a type of airplane that may or may not match the one it's in.  On occasion you'll run into a book labeled "AFM" that is in fact actually the "POH" (often due to an STC requirement).


4 Boeing 707 for $50,000. Is that possible? I'm helping a friend with an article on some issues in my country, mostly related to corruption. His English isn't very good, so here I go

One of the cases he's analyzing is the sale of 4 Boeing-707 airplanes for $50,000 . These airplanes couldn't fly but according to public information, they had their avionics, each of them has 4 working (not suitable for flying) Pratt & Whitney JT3D engines and one of them had a working intelligence/surveillance system (this was a very complex subject and now government says they'll try to keep this for training). Airplanes were for military use, both passengers and cargo.

Even considering selling them for scrap or replacement parts, is $50,000 a realistic price? For example, is there a place I can find prices for the parts, eg engines, landing gear and such?

EDIT: this is in Argentina, newspaper article (in Spanish).

Some data translated from article:

Approximate cruising speed: 977 km / h
Service ceiling: 11,000 meters
Approximate range: 8690 km
Empty weight: 62,500 kg
Load capacity: 94,000 pounds
Maximum operating weight: 335,600 pounds
It could carry up to 180 passengers

They are four-engine jet aircraft, Boeing brand.

Primary function: Transport of passengers and cargo, as the case may be.
Wing type: low implantation. Undercarriage: type retractable tricycle with 10 armed wheels. They have four Pratt & Whitney engines (turbines).
Length: 44 meters. Span: 47 meters. Tail height: 13 meters.

3 of the airplanes were bought by an US company specialized in airplanes' instrumental and parts, 1 was bought by a local party.

Its surely possibly and there are a few things I can think of off hand,

Missing Log Books: generally speaking if an aircraft is missing its log books you need to do quite a bit of tear down and rework on it to make it airworthy once again. In many cases the cost of this far out weighs the cost of a logbook/airworth plane so not always done. As such this can severely drive down the price of the aircraft making it close to worthless. In line with this, without the log books you can not sell any of the parts for replacement either. With out the ability to properly tag the part they are only worth their weight in scrap. Considering they seem unflyable and are fairly large to chop up and ship scrapping it can also become a costly maneuver.
The tax man...: Airplanes (and all manner of vehicles) often change hands for strange dollar amounts due to various tax regulations. That does not look like the case here but it does happen.
Simply Outdated: keep in mind the 707 is a fairly old plane by anyones standards these days. While it may have avionics chances are they are no newer than when it was parked there to collect dust, like it or not the best LORAN C unit in the world may have cost a fortune to install back then but is worth next to nothing now.

These things dont exactly go up for sale all that often but here is a pretty nice one listed for 6.2 Million and here is reference to one listed for only 700K. Please keep in mind that there are countless variables for this kind of thing that could drive the price both up and down drastically.

I would recommend you do this for either scrap, or, if you have time and money, a worthy airliner. As a person who collects jets (Like, old De Havilland Comets), I would pay you in the 10-100 millions to get one. Just an FYI, museums would love on of these for display. I sould a DC 3 to a museum and got shy of 1 million, and it cost me 20k in modern money.


Is it okay to take off with weight more than the POH max gross weight? I wonder if I could take off with weight more than the gross weight stated in the POH of my aircraft as long as I take off with a higher speed?

I think I have done it once by mistake.

Can you take off over gross weight? Yes, it's possible on any airplane, dependent on how far over the weight limit you are, the density altitude, how much runway you have, what obstacles are in the area and other factors. It's very easy to go above gross in a Cessna 152 with full fuel and 2 passengers, and probably happens more often than people realize or own up to. That doesn't make it a good idea, which is why pilots are trained to do weight and balance plus performance calculations before every flight.

Besides the safety angle, taking off over gross weight could land you in trouble with the FAA even if nothing goes wrong, you can lose your ticket for that. If there was an incident your insurance may not cover damage or litigation costs.

You should not do that; see the example of the Colt Richter who crashed his plane after overloading it.

https://www.ktuu.com/content/news/New-information-sheds-light-on-how-pilot-died-in-Willow-Lake-crash-489634791.html

http://www.ktva.com/story/38687378/witnesses-describe-pilots-takeoff-struggle-before-fatal-crash


Why do control towers have tilted glass panels? Almost all control towers I've seen have tilted glass panels:

Amsterdam-Schiphol tower (EHAM), source.

What is the reason behind this choice?
How is the tilt angle determined?

I'm pretty sure that has to do with reflections especially at night.

If you have ever stood between two mirriors you will understand the infinity mirror.

Light bounces back and forwards between the mirrors so when you look into them it appears like the scene goes on forever.

Window glass reflects a certain amount of light, like a mirror. In a control tower, where windows are all around you, if the surfaces of the windows are parallel you get that infinite mirror effect.

During daylight hours this can be seen as glare, but at night when you are trying to see that navigation light on Flight 594 amid a sea of runway and taxi-way lights, having your vision further confused by a myriad of reflections from the back window would be a bad thing. Further, since the room is a glass box, light can bounce all the way round the room. It would be quite possible to look off to your right and think so you see an unidentified aircraft approaching, but be actually seeing some truck's lights on the hill a couple of miles away over your right shoulder.

Tilting the windows outwards means the reflection angle is towards the ceiling, which is generally painted black, and the effect goes away.

Further, tilting out means you can no longer see your own reflection, or reflections from other lit workstations in the window. Ever tried looking out of a window at night into the dark and only see your own ugly mug staring back at you, then tried to move your head to the side to see around yourself. LOL

Of course, for all this to work, the ceiling should be dark.

A few other reasons include, less affected by rain, fewer refraction effects, and external reflections. Bonus feature, less greenhouse effect and AC bills. Downside... darn hard to clean.

Machicolations ;-)

I'm not building control towers, but I think one reason would be to allow for better viewing of what happens on the ground near the tower.

It may not be needed so much with an airport control tower as a railroad control tower (and most are using screens anyway), but there is also the comfort for passengers that a control tower looks like what they expect: Up there there are people looking down on the airport and making sure we are all safe.

If the windows were vertical or slanted upwards, it would look "wrong", and signal that the people in the tower weren't interested in little me on the ground.


Is there a height limit to national airspace? Given the following facts:

satellites can operate at an altitude of 200km without triggering frontier violation incident
aircraft can trigger diplomatic protestations if they cross a frontier at an altitude of few kilometers
there is a gap between high altitude and space

There must be a altitude or height limit between national and international airspace. If so, what is this limit?

As it stands, that 'border' between FL600 and above is undefined, and unregulated.

  There is no international agreement on the vertical limit of
  state sovereignty. Today, the need to settle this gap in the law is
  growing in importance.

  More and more states are developing their own domestic
  space launch capability. Few of these new space powers will be
  able to freely access space, or utilize the most efficient launch
  azimuths, if neighboring states can claim sovereignty up to even
  62 miles (100 kilometers). They will have even more difficulty
  returning objects to Earth if the boundary is set at that altitude.
  Even the United States and Russia are facing limitations on their
  ability to freely access space. Setting a low vertical limit on state
  sovereignty will ensure all states have equal access to space.

  Dean N. Reinhardt, The Vertical Limit of State Sovereignty, (2007)

and

  Vertical Sovereign Territory.

  Interestingly, there is no international law (or agreement) defining the vertical boundary of a nation’s sovereign territory/airspace (the boundary between outer space which is not subject to national jurisdiction and national airspace). Obviously, there is a “white” unregulated area that should be defined, not at least from national security concerns. Presently the airspace between FL 600 and up to the border between the earth’s atmosphere and outer space (generally an altitude of approximately 100 km (62 mi) (the Kármán line)) is not regulated.

  H. Bertil Nordin, U-2 and the Vertical Boundary of Sovereign Territory, (2017)

No, there is no defined height limit to national airspace, but there is an upper speed limit to national airspace, or should we say, an interlock between speed and altitude.

Any aircraft that must generate net downlift in order to not gain altitude can be safely to be orbiting rather than flying.

And for all practical purposes, all orbital flight is considered to take place in international airspace (or in cases where the altitude is so high that the atmosphere is truly neglible, you may prefer to call it international spacespace.)

The higher the altitude and thus the further from the earth's gravitational center, the lower the speed required for a body to be considered to be orbiting rather than flying, and thus safely beyond the limits of any national airspace.


If all fighter jets become stealthy, how will they fight each other in the future? In dogfights? I came across this question on dogfight-capable fighter jets still being made. If all aircraft become so stealthy, how will they fight each other? Only in dogfights, I presume. Or am I wrong?

Table of contents

  Future focii
  Short answer - Important: stealth, sensors (radar & IR), data fusion, networking, long-range weapons. Unimportant: dogfighting with guns.
  Future counter-detection and counter-measures - Important: RF and IR stealth, lasers, hard-kill defenses
  How will stealth fighters fight each other? - including THE MOST IMPORTANT LESSON
  Busting myths

  Myth: Stealth aircraft can't use radars / radars reveal your location - LPI radar
  Myth: IR sensors render stealth obsolete - IR range is short; shorter than radar range against nonstealthy a/c, but greater than radar range against stealthy a/c
  Myth: US lags behind Russia/Europe in IR tech - US had less need (better radars); US has very good IR tech
  Myth: Stealth makes you invisible to radar  - very hard to see, not invisible
  Myth: Stealth is obsolete / a hoax / just marketing - vastly reduced detection range; more efficient jamming; dictate engagements
  Myth: WWII/low-freq radars make stealth obsolete / an F-117 was shot down with this one simple trick - Low-freq radars have limited use; F-117 story is untrue.
  Myth: most combat is WVR dogfighting - not since the 1960s
  Myth: Guns are primary weapons. F-4's were massacred by obsolete MiG-21s in Vietnam because they didn't have guns.

  F-4 guns myth - the F-4s did just fine
  Welcome to the BVR missile era - where missiles take all the credit, and you usually don't see your enemy

  Resources - for modern air combat
  Glossary

As aircraft become stealthier, we'll rely more on the following:

Non-radio sensing

IR search and track (IRST)
Optical sensing
(EO/IR are/can be combined into essentially an EO/IR telescope. Future designs will use multiple bands (MWIR, SWIR, color HDTV), have wider fields of view
Mid-future: laser tracking and targeting.
High-powered lasers (100s of kW) for fighters won't debut for decades, but in the meantime they could obtain very high quality bearing, range, speed, and altitude information.

Networking and data fusion

Highly integrated aircraft sensors
Off-board targeting
Eg, a very stealthy sensor platform feeding targeting info to less stealthy (even non-stealthy) launch platforms.

Advanced radars

Multi-band or broadband radars (integrated mid/high-frequency capabilities)
More powerful AESA radars
Better processing
Multi-static arrays to detect side-aspect radar returns.
Side-looking radars.
Again, VLO a/c are not equally stealthy in all directions. They are least detectable from the front aspect.
For instance, the F-22 was to be upgraded with cheek-mounted, side-looking radars, but these were cancelled to reduce cost.

Even better stealth

Short answer

Detection ranges will shrink (against other LO fighters). IR sensors may become the primary means of detection. Fighters may cruise at low subsonic speeds to delay detection.

Radar will still remain the primary sensor for years to come (at least 2 decades, the minimum time for adversaries to field large numbers of LO a/c).

Stealth remains essential.

DATA FUSION and NETWORKING become hugely important; large forces must fight as seamless units. Remote targeting will become more common. Very, very stealthy sensors (eg, F-22 successor) may pass targeting info to less stealthy shooters (eg, F-22, F-35, F-15, missile truck with VLRAAMs)

Future AAMs will feature datalinks and multimode seekers (eg, IR, RF, and laser), improving counter-measure resistance. Many AAMs already have datalinks---shooter guides the missile until the missile's own seeker acquires the target. Advanced propulsion systems debut (multi-pulse motors, ducted-rocket/ramrockets, scramjets), yielding longer range, higher speed, imrpoved kinematics.

Defenses will improve, requiring deeper magazines (smaller weapons and/or larger internal payload bays).

Space, weight, power, and cooling requirements go up. Aircraft grow larger.

Dogfighting will remain rare. Short-range, maneuvering combat will remain unsurvivable with the advent of reliable, high-performance, high Pk, HOBS missiles and helmet-mounted cueing systems. Also, lasers don't miss. (See Myth: guns below.)

5th gen fighters (F-22, F-35) will thoroughly dominate over 4th gen fighters (F-15, Su-35, Typhoon).

Regarding counter-detection and counter-measures

Fighters will better hide their RF and IR signature. See: engine exhaust troughs on F-117, B-2, YF-23, and 6th gen fighter concepts. See: AETD, ADVENT, and F135 upgrades. Tails may disappear.

EW (eg, jamming) will remain important (See: Myth: Stealth a/c can't use radar).

DIRCM (directed IR countermeasures, an IR laser to jam/kill missile IR seekers) will protect fighters and bombers. Already slated for the F-35.

Hard-kill missile defenses will debut (likely small anti-missile missiles in near-term; anti-missile lasers 20+ years hence). Today, we rely primarily on soft-kill defenses, like jamming and decoys.

Answering the question: how will stealth fighters fight each other?

With better sensors and better stealth.

With mid- to long-range missile shots, but mid-range detection (eg, networked, off-board targeting).

With more lethal weapons (faster/short fight time, improved terminal kinematics, less spoofable sensors).

And with better defenses.

In other words, not unimaginably different from how the F-22 sometimes fights today -- a variation on 5th gen combat. Why? [See note.]

Because stealth hasn't changed the most critical component of aerial combat since WWI: SA -- situational awareness -- obtain SA and deny it to your enemy.

THIS IS BY FAR THE MOST IMPORTANT LESSON IN THIS ENTIRE POST. If you learn nothing else, learn this: SA and OODA.

Then do exactly this:

Watch F-18/22/35 pilot and TOPGUN instructor LtCol Chip Berke discuss 5th gen combat.
Go to the resources at the bottom of this post.

Read CSBA's Trends in Air to Air Combat: Implications for Future Air Superiority (or listen to the 1hr presentation) to see how modern air combat is actually fought.
Read The Radar Game to find out why SA (and stealth) is so important.
Read the Gulf War Air Power Survey. Short, concentrated glimpse into modern air wars.

Learn to fly a fighter.

Seriously. Go pick up FSX or DCS and learn. There's a vibrant community to help you out if you get stuck. (You only fly the F-16 in FSX, but it has a dynamic campaign. DCS has far more pilotable a/c. Both are VERY realistic.)
You'll quickly learn that flying the plane takes a lot more effort and is a lot harder than you imagine. You'll spend much of your time flying the plane (or crashing), not actually fighting... which makes sense because it's the same in real life. (The F-14 has two crew for a reason.) You'll quickly appreciate the luxuries of modern conveniences (like auto-trim). "Data-fusion" and "networking" will start to mean something. SA will become the difference between life and respawn.
You'll also learn that dogfighting is very dangerous. You'll rely more on your AMRAAMs than you guns (once you learn to use the radar ;)). You'll resent the Russian IR AAMs, which don't show up on your radar warning receiver. You'll learn the F-16 is not nearly as agile at medium altitude as headlines led you to believe... especially not when loaded with weapons, fuel, and sensors.

To give you a snippet of The Radar Game:

In most victories, the target isn't aware they're being shot at. SA was determinant.
The most successful aces don't engage in gladiatorial 1v1 dogfights -- more like hit-n-run.
Points 1 and 2 apply from WWI to the present day.
Reaction times are measured in seconds, a function of detection range and closing speed. Radar increases your reaction time; stealth decreases your enemy's reaction time.

[Note well: 5th gen platforms already operate differently from their predecessors ("speed is life")].

[Note: it goes w/o saying my prognostications are opinions. Although I'm confident in my predictions -- which are vague but reflect longstanding trends and realistic S&T developments -- I don't pretend certainty.]

[Note: timeframe is near- to mid-future.]

Addressing myths

Myth: Stealth aircraft can't use radars / turning on radars instantly reveals your location

Low-probability of intercept functionality allow you to use your radar without being detected you. Principals of operation include using wider-frequency bandwidth (wideband), frequency hopping, using a frequency-modulated continuous-wave signal, using only the minimum power required for the task, and pulse compression. Wiki has a good summary. AESA radars are particularly suitable because of their thin, pencil-like beams and minimal side-lobes.

Here's a Naval Postgraduate School thesis on the detection and jamming of LPI radars.

This is similar to how LO a/c communicate without being detected. The F-35 is equipped with MADL - multifunction advanced datalink - a stealthy, secure, minimum power, high data rate, line of sight comms system.

Myth: IR sensors render stealth obsolete

Bodies heat up when moving through air.

Vid: F-16 seen through an F-35's EODAS

Vid: F-15E in IR.

IR sensors do not see as far as radar (contrary to other answers here).

Against 4th gen fighters (non-stealthy platforms):

IRST detection range is typically measured in low-dozens of miles.
The F-15's radar ranges out to 100 nmi
The F-22's radar ranges out to 150 nmi
The E-3 Sentry's radar ranges out to 400 nmi

For reference, the F-14's optical (not IR) system could ID and track bombers out to 50 nmi. Perhaps 15-25 nmi for fighters. (Some IR bands are less readily  absorbed by the air than visible light.)

The PIRATE IRST may detect a VLO fighter (with RF and some IR reduction) from these ranges (CSBA):

Altitude  | Mach | Stag temp | Ambient | Contrast | Detection range
==========|======|===========|=========|==========|================
45,000 ft | 1.8  |  85 C     | -56 C   | 141 K    | 150 nmi
45,000 ft | 0.8  | -28 C     | -56 C   |  28 K    |  48 nmi
45,000 ft | 0.5  | -45 C     | -56 C   |  17 K    |

(150 nmi figure assumes no afterburner, ie supercruise.)

While IR is harder than radar to jam at long range, it can't estimate target range as easily.

Myth: US lags behind Russia/Europe in IR tech

Again, IR sensors don't see as far as radar, but they are harder to jam from long range. Historically, NATO fielded better radars and jammers than the Soviets, who therefore couldn't rely as heavily on their radars. So the Russians added IRST capabilities to augment their radars.

Remember also that the US flies dozens of AWACS that usually detect enemy a/c long before even an F-15's radar. So IRST wasn't as critical for US fighters.

The F-22 has a space reservation for IR sensors, but that upgrade was cut to reduce costs.

The F-14 received an EOST relatively early because its main targets were large, Soviet bombers, which are easier to detect.

The US eventually added IRST to late-block F-16's, Super Hornets, and of course the F-35, which fields the most complete IR sensor suite of any fighter. The F-35 has a stealthy, built-in IRST that doubles as a targeting pod. (Demo.) Its DAS also allows pilots to see in a complete sphere (4 pi steradian) around the a/c, even through the floor and headrest (no blindspots); its primary function is missile approach and warning.

The F-35 is an important example here because it'll soon comprise the backbone of NATO aviation for decades. Some 3,400 F-35s are slated for production, more than all F-15s, Super Hornets, Rafales, Gripens, Eurofighters, and Su-27s produced to date combined.

(Btw, if you're skeptical about the F-35 -- kinematics (speed, dogfighting v. F-16), range, stealth, weapons (gun), software, cost -- I'll direct you to these two..comments on kinematics, this compendium, and this community. (To start, a fully loaded F-35 with 5k lbs weapons accelerates like a clean F-16 and points its nose like a Hornet.) If you're still skeptical, I can start another 30,000 character post.)

Myth: Stealth makes you invisible to radar

Not quite.

Stealth vastly reduces your RCS, but does not completely erase it.

VLO a/c are much, much harder to detect and track. Active radar detection range goes with RCS1/4. So a 10x reduction in RCS roughly halves detection range. [See radar equation.]

For example, an F-22 or F-35 has an RCS of 0.0001 m2. A clean [unarmed] F-16 has an X-band RCS of about 2 m2. The F-22/35 will be detected at 12-22x shorter ranges than the F-15/16---effectively under 5-10 miles when using a fighter-class radar. That's almost close enough to see [see note] and certainly within IRST range.

Platform | RCS m^2 | 1/range | Detection range
=========|=========|=========|==================
 F-15    | 25      |  1.0    | 100.
Su-27    | 15      |  1.1    |  88.
 F-16C   |  1.2    |  2.1    |  47.
 F-18    |  1      |  2.2    |  45.
Rafale   |  1      |  2.2    |  45.
Typhoon  |   .5    |  2.6    |  38.
Bird     |   .01   |  7.1    |  14.
Insect   |   .001  | 13      |   8.0
 F-22    |   .0001 | 22      |   4.5
 F-35    |   .0001 | 22      |   4.5

(RCS values are ballpark figures for clean aircraft. External stores greatly increase RCS. A typical F-16 loadout for permissive environments (eg, ISIS, COIN) includes 2x 370 gal fuel tanks, 2x 2000 lb JDAMs (or equivalent), 2x AMRAAMs, 1x Sniper targeting pod. 2x AMRAAMs, 2x AIM-9s, a nav pod (eg LANTIRN), and an ECM pod may be added in more challenging environments. Like this. Not like this. Exception: F-22 and F-35, which carry their stores internally in high threat environments.)

[Note that visual range is theoretically up to 20 miles. But in 99.9% of real life cases it's <5 miles. Often just 2-4 miles.]

Note that once loaded with fuel and weapons, the F-16 and F-15 have much larger RCS values, so will be detected from even further out.

Also, while we no longer use large faceted designs (see: F-117) thanks to modern computing, we still shape our a/c to direct radar energy in certain directions away from the transmitter -- mostly to the sides and above -- in narrow lobes or "spikes."

Illustration (video). Skunkworks engineer discusses designing stealth. Listen closely.
Screencap:

Placeholder: once detect radar transmitter, stay out of detection range. Because detection range is so short, you have a lot more elbow room than non-stealthy fighters.

No, you're not invisible to radar, but operationally, it's much easier to remain undetected.

Placeholder: B-2 spike management. mission planning.

Myth: Stealth is obsolete / stealth is a hoax / stealth is marketing

LO remains relevant (and very useful) for the same reason armor didn't become obsolete when antitank guided missiles were fielded.

LO also makes jamming far more efficient. Jamming basically hides your aircraft's 25 m2 RCS. If your RCS is only 0.0001 m2, it takes far less power to hide yourself, and your jamming will work at far greater range. Primer: how jamming works.

LO technologies drastically reduce detection ranges and warning times. Sensors that work well against stealthy aircraft would work far better against non-stealthy aircraft.

What's the alternative to stealth? No stealth? Make our aircraft easier to detect and track?

All future combat a/c designs must consider signature reduction going forward---at the very least some signature reduction, if not outright VLO designs---camouflaged tanks are always more desirable than this (or this):

Myth: WWII radars / low-frequency radars make stealth obsolete / an F-117 was shot down by an 1960s radar with simple modifications

First, the F-117 story is untrue. The Serbs claimed they made simple modifications to their old Soviet radars, allowing them to easily spot the F-117s. But Zoltán Dani, the Serbian commander who shot down the F-117 in Kosovo, later admitted on national TV that he never modified the radars, merely used the lowest frequency setting. He explained that he fabricated his story for propaganda. Others alleged he did it to take [more] credit for shooting down the F-117.

Also, NATO jamming support was unavailable the night the F-117 was shot down. Dani was aware, so he turned his radars on a third time without relocating, which allowed him to obtain the fateful radar lock.

But more importantly (and accurately) the F-117 was shot down because of lazy mission planning by the US. The F-117 flew the same route night after night at roughly the same hours. So the Serbs moved their radars directly beneath the anticipated flight path. After a number of attempts were made over several nights, they finally got a lock at just 8 mi (13 km) when the bomb bay doors opened. The F-117 doesn't have a radar warning receiver---the pilot never knew he was directly overflying a SAM radar site (doable, but still ill-advised for any stealth fighter). He only ejected because he visually spotted the missile heading for him.

People forget the F-117 is an old design. It entered service in 1983, just five years after the F-16 and nine years after the F-14. Back then, we didn't know how to integrate radars and other apertures into the skin without compromising its low signature.

To be clear, a kill is a kill, and Dani deserves credit. People also forget that the Serbian forces were motivated, competent, and well-trained---measurably more so than Saddam's air defenses. The Serbs performed much better than the Iraqis and learned much from the lessons of Desert Storm.

The F-117 was only shot down once in its entire career, despite regularly flying into some of the most heavily defended airspace in the world, a feat no other platform could perform without massive support (expensive!)...

...or massive losses (save the B-2, F-22, F-35). Stealth alone allowed the F-117 to survive. Even F-15s and Su-35s would have been shot down in droves if we sent them on the same missions alone. (Image source)

Second, low-frequency radars have several drawbacks:

extremely large and power hungry, suitable only for ground-based platforms, not fighters. Some are vehicle-based, but as so large, they're only semi-mobile
require large apertures to function, owing to their long wavelengths
easiest to spoof
easy to detect from long range
detection range is grossly over-advertised
resolution is terrible (on the order of kilometers), making them unsuitable for targeting.
the most straightforward countermeasure to low-freq radars is to make aircraft larger. So VLO bombers (large a/c) are far less detectable by low-freq radars

(Principal: long wavelengths approach the feature size on aircraft, like tails, so shaping is less effective in redirecting radar returns)

all the above make them easy targets for long-range weapons like cruise missiles.
for all the above reasons, they're usually used as early warning radars or to cue higher-frequency radars.

High frequency radars are suitable for targeting, are more jam resistant, and are smaller/lighter. That's why fighters are optimised for stealth at higher frequencies.

Analogy: you can hear a fly buzzing around your room somewhere (detection), but you must see it to swat it (higher resolution sensor for weapons quality track). You can use your ears to cue your eyes, but you'll never hit it with your eyes closed.

(Lo-freq on left, hi-freq on right. SMSgt Mac, elementsofpower.blogspot.com)

Myth: WVR combat / dogfighting is the primary arena of aerial combat

First, WVR combat =/= dogfighting =/= guns.

Second...

Myth: Guns are the primary weapons of aerial combat. F-4's were massacred by obsolete MiG-21s in Vietnam because they didn't have guns.

Common F-4 myth

When Vietnam started, USAF and Navy F-4's claimed just a 2:1 kill/loss ratio. Here commentators often blamed malfunctioning missiles and lack of a gun.

So the USAF added a gun to the F-4, but their K/L remained at 2:1.

In contrast, the Navy began a new program to better train pilots how to use their missiles. They also trained the maintenance crews how to properly handle and maintain their missiles. They did not add a gun.

By war's end, the "sluggish" Navy F-4's claimed a 12:1 K/L ratio against its more maneuverable adversaries like the "agile" MiG-21.

That training program? It became TOPGUN. (Source.)

Welcome to the BVR missile era

The last fighter v. fighter guns kill was in 1989, an Iranian F-4E shooting down an Iraqi Su-22 (CSBA). The F-35's gun is largely for air to ground.

The vast majority of kills over the last 40 years were achieved with missiles:

(Global, fixed-wing v fixed wing. "Other" includes things like CFIT and flying into your own drop tanks. CSBA. See pg 24, pg 36 of 76). Annotation.

In the 1960s, guns still dominated. Most gun kills were achieved by Israelis; they used guns exclusively because no one would sell them missiles.

However, by the 1970s, missiles accounted for more kills than guns.

Even in Vietnam, the AIM-7 Sparrow missile accounted for more kills than any other weapon.

North Vietnam also favored missiles for the balance of its air to air kills, especially as the war progressed.

By Desert Storm, most shots were fired from BVR. Few air to air engagements required any significant maneuvering at all. Only two air to air guns kills were claimed: A-10s vs helos. In another engagement, a helo was destroyed by a laser-guided bomb. In other words, "A2A" bombs killed nearly as many a/c as guns in the Gulf War. Iraq also lost 3 a/c to CFIT.

And yes, we make supremely better missiles today.

Early AAMs were more akin to guided cannon shells: narrow field of view, short range, and low maneuverability; often only chased a target in front of them (tail chase).

Modern AAMs (HOBS, LOAL) have comparatively stupendous ranges: a modern SRAAM (188 lb AIM-9X Sidewinder) has roughly the range of the original AIM-7 Sparrow (a much larger 500 lb MRAAM); and the new AIM-120D AMRAAM (335 lb MRAAM) has nearly the range of the legendary AIM-54 Phoenix (1000 lb LRAAM).

You will not easily outrun a Mach 3 missile pulling 50 g's with a 200° field of view. Why turn 720° when you can shoot almost directly behind you? (video of AIM-9X testing, 2000). (Realistically, some level of maneuverability is required for good shots, but far less than for a guns solution.) More videos, gifs, gfys, and MICA.

Reliability. In ODS: shot 28 AIM-7s at BVR, 22 hit the target or fireball; 10x more reliable than AIM-7s in Vietnam.

Essentially, missiles are now far better dogfighters than fighters.

But the best dogfighting weapon by far is neither gun nor missile: it's a wingman. Fighters don't fly alone. When you dogfight, A) you rapidly bleed speed and altitude, and B) your SA evaporates because you can't afford to focus on anything else except the guy you're turning with. You're effectively a sitting duck and blind, an easy target for anyone outside the fight.

Dogfighting is extremely dangerous. Two modern fighters are liable to both die in a dogfight, ie a kill/loss ratio of 1:1.

I know of no pilot who prefers dogfighting over taking BVR shots.

Dogfighting may not be dead. But it sure is on life support.

Resources

CSBA: Trends in Air-to-Air Combat: Implications for Future Air Superiority --- essential reading
The Radar Game --- Radar and stealth primer. Requisite reading.
RadarTutorial.eu --- radar tutorial. How radars work. Very useful explanations. Explains some of the limitations/necessities of targeting/guidance.
Gulf War Air Power Survey (GWAPS) --- how the Gulf War air campaign was fought (these are some of my notes; the entire report is ~3500 pg).
War with Iraq: Critical Lessons --- General Glosson's book on the war (he orchestrated and designed the campaign) and "explains the deeper strategy and thinking behind the air campaign"
A great selection of books on ODS.
Air Warfare in the Missile Age by Lon Nordeen. Covers every major conflict from 1965 to 2003.
Modern aerial warfare and doctrine.
RCS values on Global Security. Note that the F-35 values were estimates from early in the JSF program, before any production airframes were built. After the F-35 had been built, flown, and tested, officials from the test program (including a pilot) went on record saying the F-35 was actually stealthier than the F-22.
Resources I most frequently recommend

Glossary:

1

AAM - air to air missile
a/c - aircraft
Allied Force - NATO bombing of Yugoslavia, Kosovo War
HOBS - high off-boresight - describing very agile missiles with a wide field of view
LOAL - lock-on after launch
ODS - Operation Desert Storm, part of the Gulf War
RCS - radar cross section
RF - radio freq

2

EO - electro-optical ("telescope")
EOST - " "
IRST - IR search and track ("IR telescope")

3

SR - short range
MR - medium range
LR - long range
VLR - very long range

4

BVR - beyond visual range
WVR - within visual range

5

LO - low observable - ("stealth") a broader term, sometimes interchangeable with VLO
VLO - very low observable - ascribed to only "true" stealth platforms - eg, F-117, B-2, F-22, F-35

(30,000 character limit exceeded)

Placeholder: kinematics still matter

Placeholder: Alleged flaw: Dogfights are more common if US fought USSR instead of easy foes. Why would an adversary with better, longer-ranged sensors and weapons want to get closer where he is also more vulnerable? Related: Combat between peers results in dogfights. Most kills during the 80s resulted from the 8-year Iran-Iraq war between pretty evenly matched opponents. Missiles still dominated. Related: Comparison isn't fair; US had better tech. That's the point. Don't want to fight fair. If high-tech produces fantastic victories, then high-tech sounds like a good idea.

An important addition consideration is realizing is many aircraft historically are destroyed on the ground.

In Operation Desert Storm, of the ~140 Iraqi aircraft destroyed in the way, 105 of them were destroyed on the ground. The largest portion of Iraqi craft destroyed were not brought down in air-to-air combat.

Even in WWII, large numbers of planes were destroyed on the ground.

It is not overly unrealistic to expect that in the future as planes continue to get stealthier that more will be destroyed on ground as compared with in air.


Are transponders required for hot-air balloons in the US when operating within a Mode C Veil? I've taken some people flying recently for fun, and they noticed some hot-air balloons and asked me if they had transponders. In San Diego (Southern California) I often see hot air balloons well within the Mode C Veil (a 30 NM radius circle surrounding from a Class B airport). Do hot-air balloons need transponders when they are within the Mode C Veil?

I've gotten this question enough times to look up the regulations and answer my own question :)

14 CFR 91.215 lays it out quite nicely.  Particularly section B(3):

  (3) Notwithstanding paragraph (b)(2) of this section, any aircraft
  which was not originally certificated with an engine-driven electrical
  system or which has not subsequently been certified with such a system
  installed, balloon or glider may conduct operations in the airspace
  within 30 nautical miles of an airport listed in appendix D, section 1
  of this part provided such operations are conducted -

  (i) Outside any Class A, Class B, or Class C airspace area; and

  (ii) Below the altitude of the ceiling of a Class B or Class C
  airspace area designated for an airport or 10,000 feet MSL, whichever
  is lower; and

Where I see the balloons is definitely outside of the Class B airspace and below 10,000 feet MSL, so the answer is, no, they don't need a transponder.

When do I need to get a transponder?

Within the UK FIR, Mode S Enhanced (EHS) has been mandatory for all aircraft flying IFR as GAT within notified Mode S airspace since 31 Mar 05 (with a 2-year transition period until 31 March 2007), as per AIC 49/2005 (YLO 171).

The carriage of a Mode S Elementary (ELS) transponder within remaining UK airspace has been mandated by 31 Mar 2008. It is likely that there will be a 2-year transition period until 31 March 2010, to allow for any implementation difficulties.

Within other European Mode S implementing states, the target for Mode S (EHS and ELS) implementation is 31 March 2008, with no exemption period!

  What is Eurocae ED115?

  ED115 is the agreed technical standard for LAST Mode S transponders.


What is the maximum rate of descent in an instrument approach? What is the maximum rate of descent approved in an instrument approach procedure non-precision? Basically what is the maximum rate of descent (Fpm) that I use during the approach?

ICAO Doc 8168 stipulates that for a non-CDFA non-precision approach, the aircraft should not exceed 15% gradient when descending from FAF to MDA.

  1.7.4 Stepdown descent
  The third technique involves an expeditious descent and is described as “descend immediately to not below the
  minimum stepdown fix altitude/height or MDA/H, as appropriate”. This technique is acceptable as long as the achieved
  descent gradient remains less than 15 per cent and the missed approach is initiated at or before the MAPt. Careful
  attention to altitude control is required with this technique due to the high rates of descent before reaching the MDA/H
  and, thereafter, because of the increased time of exposure to obstacles at the minimum descent altitude.

If the Descent Gradient exceeds 400 ft per nm, the approach will be designated a circling approach, even if the course is straight-in.


Why is vertical take-off restricted to lighter weight aircraft? Vertical take off is a big advantage, but why it is only limited to low weight?

For example, fixed wing like An225 can lift more than hundred tonnes of payload, while the biggest helicopter is 25 tonnes. Why there is no effort to build a helicopter can lift 50 - 100 tonnes. What limits them? Economic or technical problem? I guess it is a technical problem because even the heaviest helicopter is just an experiment, but what is it?

Essentially it comes down to supersonic rotor tips

With a plane, in theory you can make it pretty much as big as you like - as long as you have strong/light enough materials, and can keep adding power, an aeroplane design scales pretty well. Bigger wing = more lift. As long as you can make the wing bigger without it breaking, and as long as you can add enough power to overcome the extra drag, there aren't many fixed limits

With a helicopter, we're limited by the rotor tips: once they go supersonic, they cause a lot of problems.

So how does a helicopter produce lift? By using rotors to push air down within a kind of circle. To add more lift we can do (essentially) three things.

Make the rotor spin faster, so it pushes more air down in the circle it already uses. Obviously this makes the tips spin faster, so we can only do it to a certain extent. We've already hit this limit.
Make the rotor blades longer, so they push a bigger circle of air. Again, though, due to the nature of a circular blade, the outside of a blade is moving faster than the inside. For a certain rotor speed, there's a fixed limit to how large the blades can be. Again, we've already hit this limit
Add more blades, so there are more blades producing lift. This works to an extent (hence why smaller helicopters may have two rotor blades, but larger ones have 4, 5 or more. Again, though, this doesn't scale indefinitely - each rotor interferes with the next, you can't just keep adding more

There are other slight modifications we can make, such as the airfoil of the rotor, but they don't add significant gains

So, basically, we've hit the limit of what we can lift with a single rotor, The only real way to add more lift now is to add more rotors: doing that would be far less efficient than simply using an aeroplane.

Which brings me to the final point - helicopters are very inefficient and pretty slow... We simply don't need, except in a few niche circumstances, to carry more weight with them.

In addition to the power-to-weight ratio - already aptly described above - I bluntly strike at the economic reasons and cite that bean-counters look at the cost-per-takeoff and shake their head.


Why can't an airplane stall at zero G? You may be surprised to find out that an airplane can stall at any attitude if the critical angle of attack is exceeded, but it cannot stall at 0 G.

This quote found in the April 2014 issue of Flying magazine, but it seems counterintuitive to me.

Why can't an airplane stall at 0G?

At 0 G the plane does not need to generate any lift, therefore there is no critical angle past which the airfoil cannot generate the lift required.

In addition, a sustained 0 G maneuver is a parabolic arc, which means that in theory your flight path should keep your angle of attack at zero the entire time (in a theoretical, symmetrical airfoiled aicraft). You can't stall because your AoA is constantly 0 degrees and cannot exceed the critical angle.

Aircraft is flying in the air by 1 G force that resist the gravity of earth and keep the aircraft stay airborne. So if we lose this lifting force that is generated by the differential pressure between the upper and lower side of the wings, in this case the weight force, it will overcomes the lift and will pull that weight of aircraft to the downward.

So the zero G means the weight will be a little bit more than of lift, And eventually the zero G will account as weightlessness but it will be moving toward the centre of gravity (the earth). Why? because we are still flying at the atmosphere environments.


How does Bernoulli's principle contribute in lifting airplane? I have searched if any explanation that bind Bernoulli's principle in lifting airplane. There is one here which receive many appreciations, but still did not answer the question. So far, it was taught, explained, or mentioned in any aerodynamic or airplane principle, but never bound the Bernoulli's formula to the lift formula. As we know, there are pressure conservation as below:
$$\mathrm{P}_{1}+\frac{1}{2} \rho \mathrm{V}_{1}^{2}+\rho \mathrm{gh}_{1}=\mathrm{P}_{2}+\frac{1}{2} \rho \mathrm{V}_{2}^{2}+\rho \mathrm{gh}_{2}$$

Due to height is considered are same below and above the wing (the different are very small), then the third part of the equation will cancel one each other. Then left only part one and part two of each side of the equation. As the velocity above (considered as V1) is said will be different below the wing which wind is faster in above, then pressure above the wing will be lower, which will lift the wing. Thats is commonly taught in every explanation. Then, the

$$V_{2}=\sqrt{\frac{2\left(P_{1}-P_{2}\right)-\rho V_{1}^{2}}{\rho}}$$
Meanwhile, lifting formula is expressed as below:
$$L=\frac{1}{2} \rho v^{2} S C_{L}$$
V here is the airplane velocity, which is the wind hit the airfoil. Thence, V=V2 of the Bernoulli's equation above. V1 that hit upper side of the airfoils/wing, which is said faster than below, is unknown.

So, where is the Bernoulli's principle contributes in this case? How actually we calculate the lift force of an airplane?

If I understand correctly you want to know how to get from the first formula to the second one. If that is the case, the answer is simple: you don't :)

The lift formula is a simplified one, which considers the wing as a whole. It doesn't use velocities on different points of the wing, it uses the speed of the airplane. All the factors such as profile, wing shape, etc are included in the lift coefficient. This formula is useful when you already know the behavior of the wing in different situations (the behavior is determined in wind-tunnel tests or with numerical methods).

The Bernoulli equation is defined between 2 points in a flow field. It has limitations, mainly that it's valid only for incompressible flow, so only valid for low airspeeds. As you noted accurately, the height term is usually ignored, but it's more to do with the low density of air than the size, as for water or mercury it would make a large difference even with small lengths.

So the equation you derived (apart from rho being at the wrong place, it should be p/rho)  is accurate between any 2 points in the flow field. Lift is caused by the pressure difference between the two sides of the airfoil, so if you wanted to calculate the lift, you would need to evaluate pressures at all points on the upper and lower side of the airfoil. As the Bernoulli equation states, where the flow speeds up, the pressure drops, and this is the upper side of the airfoil. See picture from wikipedia, the bottom streamline is almost straight, so its shorter than the curved one on the top. Because of continuity, so the air that flows in from the left side must flow out at the right, the upper flow must get there at the same time. But because that line is curved, air has to go faster to get there at the same time. Faster flow = lower pressure.

So you can use the Bernoulli principle to estimate the pressure at every point, provided you know the speed at the given point. Once you do that, you get pressure distributions over the airfoil, something like this:

Note that these distributions are not calculated by hand, but rather with some CFD code, or measured in wind tunnels. Once you have the distribution, it can be summed to get the total forces. To make life easier, engineers measured all these forces as a function of altitude, speed (Re number) and angle of attack, and made it available for you as a CL-alpha curve. Then the lift equation is a similarity law essentially, where you turn the non-dimensional pressure distribution, eg the CL into actual force that you can use to calculate.