Does temperature affect dynamic pressure? Taking off on a cold day (5°C), it can take 10 seconds to reach rotation speed but on a hot day (40°C) degrees it will take longer to reach the same speed.

Is this due to the dynamic pressure? How does temperature affect it?

Yes, temperature affects dynamic pressure by affecting air density: it reduces with increasing temperature.

Dynamic pressure q $ = ½ \cdot \rho \cdot V^2 $

The molar form of the ideal gas law: pressure p = $\rho \cdot R \cdot T$, with R = gas constant and T in degree K

$$\rho = \frac{p}{R \cdot T} \tag{1}$$

Eliminate $\rho$ from dynamic pressure:

$$q = \frac{p}{2R \cdot T} \cdot V^2 \tag{2}$$

From (2) we can see that if temperature increases, dynamic pressure decreases linearly. In a deleted answer @xxavier mentions correctly that Indicated Air Speed is a measure of dynamic pressure, so let’s compare the two situations. 5°C = 292K, 40°C = 327K, TO true airspeed on a cold day = $V_c$, on a hot day = $V_h$

$$ \frac{p}{2R \cdot 292} \cdot V_c^2 = \frac{p}{2R \cdot 327} \cdot V_h^2$$

$$ V_h^2 = \frac{327}{292} \cdot V_c^2 => V_h = \sqrt{\frac{327}{292}} \cdot V_c  $$

$$ V_h = 1.058 V_c \tag{3}$$

So to reach the same IAS, TAS must be 6% higher. But there are more ways that dynamic pressure affects time to reach rotation IAS:

The propeller thrust is proportional to air density: simple momentum theory models thrust as $T = C_T \cdot ½ \rho A \cdot (\Omega R)^2$. Again density $\rho$ which decreases linearly with temperature according to (1). Propeller thrust reduces with factor (292/327), integrated over time until $V_h$ is reached. 11% less thrust to reach a 6% higher velocity.
The engine has less dense air to operate with. From this site:

  When your engine is not equipped with a turbo- or supercharger it will also suffer from the less dense air. Each intake stroke (which is by volume) will contain less air molecules and thus less power can be developed by the engine (due to the fixed fuel / air ratio).

So yes, dynamic pressure plays a role, but the real underlying cause is the less dense air everywhere. Also in the dynamic pressure.

Notes:

All above comparisons at equal static pressure $p$.
$V_c$ and $V_h$ are actual true airspeeds, not indicated speeds.

"where is this temperature"(ground, air, water, space), what is the medium(dirt vs asphalt vs rock vs mountain vs altitude vs clouds vs sun vs rain vs tides vs waves vs saltwater vs freshwater etc etc" and by "dynamic" what is the driving force?(propeller, impeller, turbo jet, ram jet, lifting body, wing loaded lofting body, rocket, hydrofoil, etc etc). Yes of course higher temperature equals greater pressure in a vacuum but there are "inversions" in physical reality where in fact pressure will drop as temperature increases and vice versa. Since a presume by "dynamic pressure" the question pertains to an object with a given forward velocity of some specified medium many right answers would suffice provided there is actual experience and pertinent physical data observed, collected, houses, studied etc none of which is presented here.

"Start with an instrument that can measure pressure" by way of example and go from there.


Is it possible for a plane to use cameras and screens instead of a clear windshield? I was just wondering: is it possible to have a commercial plane with no cockpit windshield, just external cameras and video screens?

The question come in my mind after reading the nth occurrence of laser in pilot's eyes. Moreover, a structure without windscreen is surely lighter: when there are not passenger, we avoid to put windows! Which are the limits and the opportunities to this solution?

With "ever" I don't mean "in centuries" but in 30/40 years.

It's entirely possible to do this now, it's simply not a good idea. The drawbacks to safety outweigh the benefits of doing so. If you have no cockpit windows an electrical or systems failure would leave pilots totally blind, without any references whatsoever. The "mark I eyeball" works in a wide variety of conditions and does not require electrical power of any kind. Plus, there's usually 4 of them in the cockpit, and chances are at least one of them will work.

Technically possible but not very comfortable. As a first step, windowless passenger aircraft could be attempted. In crowded Indian buses with windows being swamped by opaque advertising material it is very disconcerting not knowing where you have reached. Passenger experiences can be taken as a starting point. Also the experience of astronauts could be considered....


Are there any airlines that fly a route that has an arrival time earlier than its departure time? Imagine the scenario where an airline flys a short 30 minute route which crosses a timezone going west. They could theoretically leave at 00:15 (local) and arrive at 23:45 local the previous day. I'm wondering if there are any airlines which fly such a route.

P.S. I'm specifically interested in how the airline allows booking such a flight and the UI that is presented, but am leaving this question more general for any flights that do this.

P.P.S. If someone could help with the tags for this question, it'd be much appreciated.

I found such a route for you. KATL (Atlanta) to KHSV (Huntsville, AL) is a 57 minute hop from the Eastern time zone to the Central time zone. It appears how you would expect:

I like JQ129 from Auckland (AKL) to Rarotonga (RAR). You arrive 19 hours before you depart.


Is it normal to instruct an aircraft to squawk VFR if it goes around on an IFR visual approach? A pilot is flying IFR on a visual approach to a towered airport.  He elects to go around due to gusting winds and notifies the tower. The tower then asks his intentions. He replies that he would still like to land. The tower instructs: "Squawk VFR and enter a left downwind for runway 5."

Is the instruction to squawk VFR proper?

No, that scenario does not sound normal to me. For one thing, a visual approach is an IFR procedure. Instructing the crew to change to a VFR squawk makes it sound like the controller is suddenly treating the flight as a VFR flight, which makes no sense. A controller is never allowed to just cancel IFR; going from IFR to VFR must always be explicitly requested by the crew ("cancelling my IFR flight"). We are not even allowed to suggest a flight to change to VFR, the idea has to come from the pilot.

Besides, it makes no sense that the controller would change the squawk code of a (presumably) already identified flight to a non-discreet code (1200/7000) since radar identification would then be lost and it would be impossibly to continue to provide radar service.

If the example you provide is a real one, there is obviously a reason for the controller doing what they did, however, based on the limited information you give here, it is hard to see what the reason would be. Maybe if we knew the whole picture, it would make more sense.

Since you were on an IFR visual approach and have "gone around" after your 1st landing attempt, and are in the landing pattern curcuit, weather permitting, why not do what the tower says?

There may be different procedures for IFR approaches and go arounds. They may have slotted you to "fit in" for left downwind for runway 5 VFR.  Switching (to 1200) and landing seems to get it done.  Unless you leave the landing pattern or do not follow their instructions, there does not seem to be any harm.


Is trimming for constant speed equal to trimming for constant angle of attack? My understanding of trim:
When you say you have trimmed an aircraft for a constant speed, say 100 mph, you are actually trimming the horizontal stabilizer so that there are no forces on stick (or tail down force is balanced with nose weight) at that speed. To do that you either control the horizontal stabilizer/trim tabs until no force is felt on the stick.

My question is, (if my understanding is right), can I say that we are trimming for constant angle of attack instead of speed (and the constant angle of attack is represented in form of speed). By trimming the aircraft, aren't we making the aircraft fly  at constant angle of attack?

If so, can I make these following statements about trim: (ignoring the things like propeller blast etc..,)

When you are cruising in a trimmed condition and decrease( or increase) the engine power, the aircraft will pitch down (or up) until it finds the old angle of attack where all the forces are balanced and the trim is reestablished.
When you are cruising and closed (or opened) the throttle completely, the aircraft will descent (or climb) at the same trimmed angle of attack.

Short answer: Yes

Generally you are right. You are trimming the aircraft for a point on its polar, and that point is reached at a specific angle of attack.

You say yourself we should neglect secondary effects like the propeller blast, and under this condition you are right. Trimming means to set the distribution of lift between wing and tail surface, and this directly sets the angle of attack.

Now the more elaborate part of the answer

You trim the aircraft for a specific dynamic pressure, that is the product of air density and flight speed. If you slightly change your question from "trimming for constant speed" to "trimming for constant indicated speed", you gain precision and the answer is still yes. With a change in altitude you will also affect the Reynolds number the aircraft flies at, and the same polar point is reached at a slightly higher angle of attack the lower the Reynolds number gets when the aircraft climbs into colder air.

In turns the lift demand is increased. Not changing trim during a turn will let the aircraft speed up to increase lift at an unchanged angle of attack. That is why you pull more when turning - you want to increase the angle of attack, so speed can stay constant. When speeding up, you again change the Reynolds number and indirectly also the angle of attack, but this effect is very small.

When you change the power setting, you add energy to the aircraft at a different rate. Thrust becomes bigger and is counteracted by the sum of drag and the component of weight which acts in parallel to the thrust vector. Now the vertical component of weight is reduced, and so is your need for lift - but ever so slightly. This effect by itself means you will fly at a slightly smaller speed which will also very slightly affect the angle of attack. But since you did not change trim, the distribution of lift between wing and tail is unchanged, so the angle of attack is the same, save for a minuscule Reynolds number effect.

Increasing thrust will also increase the prop blast over the tail surfaces, making them more effective and slightly changing the balance of the aircraft. Depending on the direction of tail lift, the result is an increase or a decrease in angle of attack, but this is precisely the effect you wanted us to disregard.

Another secondary effect is a constant loss of weight as the engine burns fuel. This makes the aircraft lighter, so it requires less lift and a smaller angle of attack over time to remain at the same speed. Since you trimmed a specific polar point, the aircraft would need to slow down in order to stay at this polar point at its lower weight. But the lower weight also creates less drag, so instead of slowing down the aircraft will climb. Now the reduced density will require more angle of attack and will reduce engine output so in the end the same angle of attack is maintained at a higher altitude but a slightly lower indicated airspeed.

This is an interesting question. I believe that both of your statements are wrong though.

"Trimming for constant speed" is technically not possible, as the trim itself has nothing to do with the speed. As you probably know, you have to adjust both throttle and trim to have the plane fly level at a constant speed. Trim only controls your elevator (neglecting the other two trims that larger aircraft usually have as well). When you "trim for constant speed", you usually adjust your power setting while keeping the plane flying at a certain altitude. Then (or even while you adjust your speed) you trim the plane to take work of your arms ;)

Once you're flying at a constant speed, you can say that the angle of attack remains the same when you're not descending/ascending. No comes the tricky part though:

You're saying that the aircraft will find a balanced condition again - which is right. Yet you have decreased the power, thus you've changed one force. Because of that, the other forces must change as well to balance each other out. The angle of attack will thus NOT be the same when the throttle is different.
Again, when closing the throttle, the aircraft will find a new balanced condition, and again, the angle of attack will change.

Another interesting question is: When you are flying at a trimmed condition and decrease the throttle, then after a while increase it back to the original setting, will the aircraft return to level flight? - The answer is yes, but no ;) Yes, because now all forces are back to the original condition, thus the airplane must have the same attitude. No, because by descending, the air density will change, thus resistance of the air becomes bigger which enforces a bigger force or resistance on the plane messing up the balance again.


Why do commercial pilots always engage reverse thrust even if it is not necessary? Most of the time the usage of reverse thrust is not needed. I wonder if it's an authority (e.g. FAA) requirement to land safely.

Obviously, in bad weather conditions or when the runway is contaminated, the brakes might not work as effectively and thus R/T may be required to land safely. However, in most of other situations the aircraft can brake OK. Given that it would probably be more efficient to land without using R/T, why don't airlines routinely do so?

The correct answer is, habit patterns.

If your habit, as a pilot, is to ALWAYS select reverse thrust, you'll do so reliably even when the weather is bad, you're fighting gusty crosswinds, and there is whatever else going on. On the other hand, if you sometimes do & sometimes don't select reverse thrust, that habit pattern isn't there to back you up when you have the proverbial "dark & stormy night" and getting into reverse thrust right away may be the difference between staying on the runway or running off the end.

For example, if I'm landing a fairly light aircraft on a 12,000' dry runway in DEN with a little headwind, it is entirely possible to leave the thrust reversers stowed, roll out with the speed brakes deployed, tap the brakes slightly, and exit on the last high speed taxiway at a normal taxi speed.  And I'd burn less fuel and make less noise doing that.  But at my carrier, I'm not allowed to, because it's considered that the habit pattern of always deploying the T/R is so important that it's worth it to burn that extra gas even when it isn't strictly necessary, so that on the day when it's vital, the habit pattern to grab the T/R's right after touchdown is strong.

I don't think that this is an OpSpec (i.e. FAA) requirement, at least for the aircraft that I fly, but I'm quite certain that it is a requirement in our books, so my supposition is that it's a company requirement.  If that assumption is correct, then other companies might choose to do differently (and I recall one early morning arrival into Frankfort on a Lufthansa A-320 that used NO reverse thrust, but some heavy braking instead -- presumably to reduce noise at that hour of the morning).  The fact that safety is so important, though, probably drives plenty of operators to make the same choice that our carrier does: build the habit of ALWAYS using reverse thrust -- even though that means sometimes using it when it isn't necessary.

How can we say that it's not necessary?

I'd say that the reason I use reverse more then brakes is that it's my airline procedure and Airbus says that too!

Use of brakes to slow down airplane after high speed landing is not good for tyre's health. So what we do normally is slow down the airplane by thrust reversers till 40-60 knots and then we use brakes.


For large jets, what is the primary means of slowing down after landing? I understand that a large(r) commercial jet slows down after landing using the following methods:

Wheel brakes
Reverse thrust
Spoilers/flaps/airbrakes

What is the effectiveness of each compared to the others? What if one of the first 2 fails? Can an airliner usually be stopped without using wheel brakes or without using reverse thrust?

And what if the runway is slick because of rain, snow or ice? Does that change the equation?

The brakes are much more effective than anything else, at least for the jet I have experience in (EMB-145).

Our landing performance data typically assumes full braking application, spoilers deployed and no reverse thrust.  The airplane will most certainly stop without using reverse thrust, just not as fast.  I never tried not using the brakes, and if I were to I would want a light airplane and a very long runway.

As Lnafziger pointed out in the comments, the brakes are part of redundant systems so that they are always available.  In the EMB-145, the brakes were serviced by two independent* hydraulic systems. The inboard brakes were on one system while the outboards were on the other for a total of four wheels each with big carbon fiber brakes.

To address the comments on slick runways, assuming braking action allows an attempt to land in the first place, you have to be careful. With reverse thrust alone you may not be able to maintain the runway centerline and directional control may become difficult through uneven deployment of the reversers and other factors.  In this scenario the spoilers are helpful to increase traction and brake effectiveness.  In short, if the runway is slick then the only way I'm attempting a no-wheel-brake landing is after declaring an emergency.

Finally, to address the question in the title, the wheel brakes are always the primary means of slowing the airplane.

*You could transfer fluid between our systems through the parking brake.

I have landed at Cabinda and Angola.
I have made many landings there. They can be tricky, but local pilots use CPP, reverse thrust and wheel braking.

One pilot has mentioned that disc pads are very expensive, so you want to wear them down as little as possible.

The same pilot mentioned that reverse thrust can also damage engines, no matter whether CPP or jet engines.

I am still flying cessna's.


Do pilots adjust the aircraft's flight path to allow for the curvature of the Earth? If an airliner is flying at approximately 500-600mph, it seems to me that there would need to be a significant adjustment for altitude so as to not fly off into space.

Wikipedia says that there's an 8 inch drop for every mile because of the Earth's curvature. But, I've never heard of any airliner adjusting for the curvature. Also, shouldn't aircraft have to adjust somehow for the Earth's rotation because it varies depending on the latitude?

Aircraft altitude is measured (inferred) by atmospheric pressure. The aircraft is usually flown at an altitude that maintains constant ambient pressure (by pilot or autopilot, as the case may be). Changes in local barometric pressure (provided by air traffic control) are used to recalibrate the aircraft altimeter.  As long as the aircraft is flown at a constant ambient pressure (hence constant altitude), it will be following the earth's curvature (as the atmosphere is attached to the spherical earth and has same properties at same distance from the center, in an ideal case) as the altitude is measured from the surface, which is curved, and not a plane.

Assuming we are flying "on the front side of the power curve"--

For a given power setting, there is only one angle-of-attack that will allow a given aircraft to maintain a constant altitude.

For a given angle-of-attack, there is only one power setting that will allow a given aircraft to maintain a constant altitude.

So your question is essentially, "is the required angle-of-attack, or power setting, different than it would be if the earth were flat?"

The answer is "yes-- very very slightly."

If your question is also meant to ask "is this something that a pilot must consciously take into account?", the answer is certainly "no".  Having a few pounds of dust accumulate in the nooks and crannies of the aircraft would probably make more difference to the required angle-of-attack or power setting than the fact that the earth is round rather than flat.

Likewise for effects due to the spin of the earth and its surrounding atmosphere.

If your question is also meant to ask whether an ARHS reference system or other similar system must specifically take into account the curvature of the earth to remember which way is "level" on a flight covering a long distance or whether this is automatically corrected for by other built-in functions of the system-- that is a much more complicated question but the answer is generally the latter.  The same is generally true about remembering which way is "level" over a long duration of time, as the earth rotates about its axis.

For self-contained inertial navigation systems that operate completely independently of any GPS-derived position information, the answer is quite different: in this case effects related to the spherical shape of the earth, and effects related to its rotation about its axis, are very important.


What happens if a student busts Dallas Fort Worth bravo airspace? What would happen if a student busts a corner, exceeds the floor of Bravo airspace by 500 feet then descends after one minute?

The pilot is on the frequency of a Golf airport heading towards a Delta controlled airspace, both within the Bravo 30 nm veil.

Does the Bravo tower have a way of knowing the aircraft involved?

Just to make it perfectly clear:

If you accidentally enter a controlled airspace without clearance, as soon as you realise what has happened, the first thing you do is contact the responsible ATC unit! Period.

Panicking, initiating a rapid descend to leave the airspace or simply pretending it didn't happen is extremely bad airmanship, and will surely get you in trouble if you get caught. On the other hand, admitting you made an honest mistake and asking ATC what the best solution is might still get you in trouble in some countries, but it is definitely the safest solution for everyone.

Depending on the exact details of the airspace infringement, it may be extremely dangerous if you try to solve the problem on your own. By suddenly descending to leave the airspace, you risk colliding with traffic below you. If the airspace in question is of a military kind, turning a blind eye to your mistake and maintaining radio silence will potentially result in a visit from some aircraft with a lot more weapons than yours.

Anyone can get lost and make mistakes. If you do, ATC is there to help you - not to punish you for an honest mistake. Make use of that help!

As for procedures about which forms need to be filed after an incident like this, I will leave it to someone with knowledge about FAA specific procedures to answer.

You can read more about Airspace Infringements at SKYbrary.

Well, it depends.  Controlled traffic around these satellite airports would be on the Class Bravo's approach frequency.  If you were in that category and contacted approach and they had given you flight following or assigned a transponder code to you, then yes, they would know it was you and be able to track your aircraft down, if they were so inclined to investigate.  Also if you were in contact with the tower at the class D airport and they had previously located you, then it's possible you could be notified about that.

Yes, theoretically you could get in trouble for that.

Now uncontrolled traffic squaking VFR would be more difficult to identify.  ATC may note the radar return which violated the controlled airspace and track it to its destination, but further pursuit would probably be wasted effort.

If you did this, just make a mental note of what happened, what caused it, and vow not to go down that path again.  Most likely nothing will come out of this.  Save for major, intentional tresspass of these types of controlled airspace or violations which result in an incident or accident, the authorities will just note that it occurred and won't wast the time or effort on further investigation.

TFRs are another story altogether.  Violate those and you can expect an airborne visit from a couple of nice young men flying F-16s who will have instructions to follow them and land at a nearby airport.  Police will most Likely arrest you there.  Expect to spend the day chatting with a couple of nice people from Homeland Security before being released and receive a letter from the FAA informing you that they are revoking your pilot's license.


Why is the mammatus cloud formation so dangerous? I have read and heard that the mammatus cloud formation presents a danger to aircraft and is often associated with funnel clouds and tornadoes. How is it formed and why is it dangerous?

Source: Wikipedia

Nobody knows exactly how mammatus clouds are formed, it's been studied and there are several theories about it but none are accepted. They are most often seen below anvil clouds, ie cumulonimbus clouds with extremely powerful updrafts. One thing that the theories all agree on is that where they are formed on the underside of cumulonimbus clouds there are huge shifts in temperature, moisture and pressure within a short space of time. Although these clouds can form under other types of cloud they are mostly seen under the most powerful of storms.

So why are they dangerous?

They are usually made of ice: ice accretion is dangerous, especially for light aircraft without de-icing systems
They are almost always associated with severe low level wind shear. Wind shear is sudden changes in wind direction which is dangerous for aircraft. You can suddenly find that a 30kt headwind is a 30kt tailwind so you've lost 60kt of airspeed, this is especially dangerous during takeoff and landing
They are almost always associated with severe convective activity, ie very strong updrafts and downdrafts which are dangerous for aircraft. You could get sucked up thousands of feet or pushed down as well, and there's be nothing you could do about it
They are almost always associated with severe turbulence which is also dangerous for aircraft. Severe turbulence is at best extremely uncomfortable, at worst can cause a loss of structural integrity

So mammatus clouds are usually an excellent sign of an area to be avoided.

Based on the fact that mammatus clouds are associated with crazy air currents, it would very easily throw an airplane out of control.


Can a Private pilot fly a company aircraft for business purposes if he is not being paid? I understand that if you are carrying passengers and getting paid, then you have to have a commercial license.

What about this scenario? I have a PPL (Private Pilot License).  My friend owns a company that owns a plane.  If I fly him and/or his employees around, and am not being paid for the time and just doing out of the goodness of my heart, is that okay?

I'd say you'd be on thin ice with this. The principle is that private pilots cannot be compensated for their flying, with very few exceptions. That doesn't necessarily mean getting paid to fly, it can mean having the expenses of the flight given to you in some way.

Say you take 3 friends on a trip, and your friends pay all the costs. You'd be in violation of FAR 61.113 because you haven't paid your share, in other words you've received compensation. You need to pay 1/4 of the costs of the trip.

In another case you are going on a business trip and decide to fly yourself and your employer pays all the expenses. This is legit because flying is incidental and not the purpose of the trip.

In the case you are stating you have no reason to be flying the airplane other than the flight itself, therefore flying for free means you are receiving compensation and a violation of FAR 61.113.

Note other countries may vary, the UK is extremely similar to the US on this, as are most European countries, I can't speak for anywhere else.

The privelages of a CPL are it allows you to fly an aircraft CARRYING PASSENGERS OR PROPERTY FOR COMPENSATION OR HIRE under specific circumstances governed under 119.1 of the FARs.  The FARs do, however, allow a private pilot to fly for compensation or hire, only if the flight is incidental to the pilot’s employment and it does not carry passengers or property for compensation or hire.  See FAR 61.113.
The other requirement here is that you the pilot are required to pay no less than a pro rata share of the aircraft’s operating expenses eg fuel, oil, parking fees, etc.

Be careful, as well, to conform with the terms of AC 120-12 when discussing this in order to comply with the FAA’s rules concerning holding out for common carriage, as this can get you into trouble very quick if you don’t


How complete is our understanding of lift? I'm currently studying for my PPL and one of the accepted textbooks contains the following disclaimer at the end of the Principles of Flight section on lift:

  It is important to note that the forgoing explanation of lift, and its reliance on Bernoulli's theorem, is very much the 'classical' theory of lift production and the one on which the exam questions are usually based. There are differences of opinion amongst scientists on the subject....[snip]

The same book previously also describes the venturi theory which NASA discredits.

Additionally, one of my previous CFI's told me that during a previous successful job interview he had been asked to explain lift and had merely responded with "Which theory would you like me to cover?"

On the contrary - we must have an excellent understand of some components because of the way we're able to design and build such stable (and unstable when we want) aircraft. Plus, I see some absolutely incredible mathematics described on this website which seek to accurately answer complex questions.

So, my question isn't how is lift generated -it's how complete is our understanding? Which bits are still in dispute, and which bits are fully accepted?

Short answer: Yes, our understanding of lift is complete, but solving the equations for some practical cases needs more resources than what is technically sensible.

Lift is a matter of definition

First of all, lift is only one part of the aerodynamic forces. It is the component normal to the direction of airflow. Since the aircraft will distort the local flow around itself, this direction is taken ideally at an infinite distance where the air is undisturbed.

The other component is, of course, drag. It is defined as the part of the aerodynamic forces parallel to the direction of airflow.

The aerodynamic forces are the sum of all local pressures, which act orthogonally on the local surface of the airplane, and the shear forces, which act parallel to the local surface.

When aerodynamics was researched first, electric fields were new and exciting, and the same equations which help to calculate electromagnetic forces could be used to calculate aerodynamic forces. Therefore, abstract concepts like sources or sinks were used to explain aerodynamics. This made it not easier to understand, and many authors tried to find simpler explanations. Unfortunately, they were mostly too simple and not correct, but the next generation of authors would mostly copy what had been written before, so the wrong concepts were still bandied about.

To get to the bottom of it, it might help to look at lift at a molecular level:

Every air molecule is in a dynamic equilibrium between inertial, pressure and viscous effects:

Inertial means that the mass of the particle wants to travel on as before and needs force to be convinced otherwise.
Pressure means that air particles oscillate all the time and bounce into other air particles. The more bouncing, the more force they exert on their surroundings.
Viscosity means that air molecules, because of this oscillation, tend to assume the speed and direction of their neighbors.

All three contributions are well understood, and with the Navier-Stokes equations they can be completely mathematically expressed. What is still improving is our ability to solve these equations, and in turbulent flow the characteristic length required to capture all effects is so small that it is practically impossible to solve those equations fully with finite time and resources.

Flow over the upper side of the wing

Now to the airflow: When a wing approaches at subsonic speed, the low pressure area over its upper surface will suck in air ahead of it. See it this way: Above and downstream of a packet of air we have less bouncing of molecules (= less pressure), and now the undiminished bouncing of the air below and upstream of that packet will push its air molecules upwards and towards that wing. The packet of air will rise and accelerate towards the wing and be sucked into that low pressure area. Due to the acceleration, the packet will be stretched lengthwise and its pressure drops in sync with it picking up speed. Spreading happens in flow direction - the packet is distorted and stretched lengthwise, but contracts in the direction orthogonally to the flow. Once there, it will "see" that the wing below it curves away from its path of travel, and if that path would remain unchanged, a vacuum between the wing and our packet of air would form. Reluctantly (because it has mass and, therefore, inertia), the packet will change course and follow the wing's contour. This requires even lower pressure, to make the molecules overcome their inertia and change direction. This fast-flowing, low-pressure air will in turn suck in new air ahead and below of it, will go on to decelerate and regain its old pressure over the rear half of the wing, and will flow off with its new flow direction.

Note that lift can only happen if the upper contour of the wing will slope downwards and away from the initial path of the air flowing around the wing's leading edge. This could either be camber or angle of attack - both will have the same effect. Since camber allows for a gradual change of the contour, it is more efficient than angle of attack.

Flow over the lower side of the wing

A packet of air which ends up below the wing will experience less uplift and acceleration, and in the convex part of highly cambered airfoils it will experience a compression. It also has to change its flow path, because the cambered and/or inclined wing will push the air below it downwards, creating more pressure and more bouncing from above for our packet below the wing. When both packets arrive at the trailing edge, they will have picked up some downward speed.

Behind the wing, both packets will continue along their downward path for a while due to inertia and push other air below them down and sideways. Above them, this air, having been pushed sideways before, will now fill the space above our two packets. Macroscopically, this looks like two big vortices. But the air in these vortices cannot act on the wing anymore, so it will not affect drag or lift. See here for more on that effect, including pretty pictures.

Lift can be explained in several, equivalent ways

Following the picture of a pressure field outlined above, lift is the difference of pressure between upper and lower surface of the wing. The molecules will bounce against the wing skin more at the lower side than at the upper side, and the difference is lift.

Or you look at the macroscopic picture: A certain mass of air has been accelerated downwards by the wing, and this required a force to act on that air. This force is what keeps the aircraft up in the air: Lift.

If you look at the wing as a black box and only pay attention to the impulse of the inflowing and outflowing air, the wing will change the impulse by adding a downward component. The reaction force of this impulse change is lift.

Either way, you will arrive at the same result. By the way: Most of the directional change happens in the forward part of the airfoil, not at the trailing edge!

Supersonic flow

When the aircraft moves faster than pressure changes propagate through air, the changes in pressure are no longer smooth, but sudden. The aircraft will push the air molecules aside, producing a compression shock. Behind the shock front pressure, temperature and density are higher than ahead of it, and the increase is proportional to the local change in flow direction. The incremental pressure change $\delta p$ due to the aircraft hitting air with an incremental angle of $\delta\vartheta$, expressed in terms of the undisturbed flow with the index $\infty$, is proportional to the change in the streamlines:
$$\delta p = -\frac{\rho_{\infty}\cdot v^2_{\infty}}{\sqrt{Ma^2_{\infty} - 1}}\cdot\delta\vartheta$$

Gas pressure on a molecular level is the number and severity of particle collisions. The air molecules experience more collisions on the downstream side of the shock, since air pressure is higher there. The average  direction of the additional collisions is indeed orthogonal to the shock, because it is the boundary between blissfully unaware molecules at ambient pressure ahead of the shock and their bruised brethren downstream which have just crossed that boundary. Once a molecule has passed the shock, the collisions are coming again equally from all sides and its speed does not change any more.

If the surface curves away from the local flow direction, the air produces an expansion fan which re-sets the old pressure and density values when the air flows again in its original direction.

Pure supersonic lift is only a matter of the angle of incidence, and any local curvature of the wing will not change overall lift (but increase drag). Now the total aerodynamic force is normal to the wing, and drag will become proportional to the angle of incidence. In hypersonic flow you will get good results with the venerable impact theory first formulated by Isaac Newton.

Separated flow

This happens when the air molecules are no longer able to follow the contour of the aircraft. Instead, you get a chaotic, oscillating flow pattern which is very hard to compute exactly. This is really the only part of aerodynamics which cannot be predicted precisely, even though the effects are well understood. Separated flow will produce lift, too, but less than attached flow. In delta wings, this separation is produced on purpose to create what is called vortex lift.

The principles of aerodynamics and fluid dynamics are what you would call "well understood."

The ambiguity is around what so-called "lift" is, which can be a nebulous concept. For example, if you drop a piece of paper it will drift slowly to the ground, essentially a form of gliding; this same air resistance is the basic force keeping a plane aloft. Would you consider this "lift"? Once you get into these arguments about semantics, things get vague.

Just as one example of the craziness, the FAA test, the same one you are taking, requires you to know the "four forces of flight" in which the so-called "lift" is the force that keeps the aircraft aloft. The only problem is that you can compute lift by equations that are in every book on aerodynamics and if you actually do this (like I did) you will find that the force generated is nowhere near enough to keep a plane in the sky. If "lift" were the force keeping a plane up, it would fall like a rock, so the FAA guidelines are simply completely wrong. It's just a huge semantic hairball that is not going to go away anytime soon.

The worst part of it is that EVERY pilot (or wannabe pilot) I have ever known thinks they know exactly what "lift" is and, even worse, their beliefs generally fall into one of 5 or 6 different categories with contradictory principles. This leads to huge arguments whenever the subject comes up. After 15 years of this, I just try to stay out of it, other than to tell the beginners not to make the same mistake (like I am telling you now).


If a twin-engine airplane's propellers both rotate in the same direction, do they still produce a left-turning tendency? If an airplane with two propellers has both propellers with the same rotation direction (say, both the propellers rotate counter-clockwise as seen from nose to the tail), will  be the four left-turning tendencies still be generated?

Yes, for the most part.

Definitely P-factor will still exist and provide a yaw torque in the expected direction.  This is why twin-engined aircraft have a "critical engine".
Engine torque will still produce a roll torque in the expected direction.
Gyroscopic precession will still produce a yaw torque in the expected direction when the aircraft pitches.
The yaw torque from the spiralling slipsteam interacting with the vertical fin-- which is normally quite significant in conventional single-engine aircraft-- is the one effect that may be be greatly reduced in a twin-engine airplane of the usual configuration, since the fin is not located in a strong part of the circulation behind either prop.

No, because they turn on different axis which does not coincide with the longitudinal axis of the airplane. Having two propellers turning the same way on the same axis, it would enforce the effect.


Could you encode data in a Black Box ping? Black boxes put out a sonar ping at about 32kHz. From what I've read, depending on sea conditions the ping will be audible at the surface out to about 16 km, leaving a search area of around 1024 square km.
By adding a little complexity to the ping circuit, you could encode within it the last received GPS position of the box, before it hits the water. With average sea depth and average sink angles of less than 45° that information would cut the search area down to about 10 square km.
Is there some reason this tech is not used, or is it still in the rigorous testing pipeline these devices must go through?

Current underwater locator beacons (ULBs) have a detection range of only a few km. 16 km would be under exceptionally favourable conditions. So in most cases the GPS data would not be of any additional help. It might tell you where the aircraft was before it hit the water, not exactly where the debris ended up after falling through several Km of water.

An advantage of current ULBs is their extreme simplicity and small size. There's no need for external data-feed and power connections. There are no issues of openings in the casing for waterproof connectors that also need to withstand the g-forces and pressures expected to be endured by a ULB. They are easy to test regularly and relatively easy to maintain.

From what I have read, current proposals for improvements to ULBs mostly focus on

increase duration from 30 days to 90 days
increase range by changing frequency from 37.5 kHz to ~10KHz

There are trade-offs here - longer duration means bigger batteries. changing the frequency may make it harder to distinguish from other sources of sound in the ocean.

An interesting 2011 dissertation describes the difficulties involved  and discusses modulating the beacon signal to include data.

Main reason those signals can be distinguished for what they are is because they have a specific signature. If the signals were to change all the time because you mix in extra information, they'd be impossible to recognise and thus useless.
Combined with the short range of the signal (inevitable consequence of the need to be low power, anything more would mean heavier equipment and/or shorter lifespan), there's just no benefit.


Could modern unmodified Airbus aircraft be used for zero-G flight? ESA operates a mostly-stock A310 for their zero-G science flights, which doesn't have the flight envelope protection of more modern planes. Even then, a third pilot is required to monitor warnings to sort out the ones normally encountered in the parabolic maneuvers from unusual ones. If this aircraft were replaced with a modern Airbus (newer than A300/A310), would it be possible to fly these parabolic maneuvers without going into alternate law or doing other modifications to the control system?

According to this source and this source, the relevant A320 control laws (CLAWS) limitations are:

Normal load factor limitation in clean configuration down to -1g
Nose down pitch attitude down to -15deg
High Speed Protection (HSP) to prevent exceeding VD/MD

The problematic one would be the pitch attitude limiting. Since the pitch attitude will keep decreasing at zero G, the limiting function will pull the aircraft up and increase the load factor after some point. This could limit the time in zero G below the requirement.

Given the constraints and objective, more analysis would be needed to ascertain whether aircraft in Normal Mode is acceptable.

Actually not really. For one there are the protections in the software - but you must also take into account the cabin also needs to be a little modified to be usable for these kind of flighs. And possibly you'd also need to "tune" the fuel, lubrication and other related systems also...


Why is there no "reverse sensing" on a horizontal situation indicator (HSI)? When we use this awesome instrument for navigation (not only for ILS/LOC), it is said that there is no reverse sensing (except for back course thing). I kind of understand why pilots are confused when we use conventional VOR, and now I want to know why there is no reverse sensing? How does it work? Can anyone help me out?

Essentially because you turn the instrument upside down and read it normally.

On the back-course, the signals are reversed. That is a property of the ILS signal. When using traditional ILS/LOC instrument, the needle moves right when it senses more of the right signal, but since the signal is now on the left, you get reverse sensing.

On the HSI, the needle still moves right when it senses more of the right relative to the arrow when it senses more of the right signal. However, the needle points in the selected heading and is rotated with compass. So when you fly a back-course, you dial the normal course of the ILS and since you actually fly opposite direction, the arrow points down and right relative to it is left. And you get normal sensing.

For VOR, the situation is similar. In VOR, the needle moves normally if you are flying the heading selected and it moves in reverse if you are flying the opposite heading. And when you are flying the opposite heading, the HSI arrow points down, reverting the sensing back to normal.

I guess what the OP means is that why there is no "reverse sensing" switch on the instrument. The answer being rather simple - to avoid the pilots making a mistake when they forget to flip the switch to the correct position.

You can always flip the OBS 180 degrees to make that change. I like to think of the HSI as always sensing "positively". You're just tracking the wrong side.

The instrument always tells you the relative position to the VOR course / localizer, it is up to the pilot to manipulate the plane to the desired position. It's reverse tracking, not reverse sensing. The instrument tells you your deviation from the selected course, it has been and will be doing that all the time. If your selected course is 180 degrees off, following the rules of geometry, you'll naturally end up switching left and right.

It is worth noting that the autopilots have an "reverse course tracking" switch:

If you want an instrument which tells you how to fly to intercept the course, it is called a Flight Director.


Depth and range for FDR/CVR black box detection What is the maximum depth range of a FDR underwater, at which it is able to be detected by receivers?

I want to know the maximum range of ULB pinger locator if it's submerged.

The maximum range if it's transmitting on 37.5kHz is usually between 1 and 2 kilometers in poor conditions and around 4 to 5 kilometers in normal conditions and up to 6 or 7 in good conditions. The range depends on the frequency it's transmitting but the ULB's work on 37.5kHz.


Do pilots breathe the same air as passengers? Do pilots breathe the same quality of air as passengers ?
(i.e. identical parameters: same O2, CO2 and O3 levels, same temperature, same humidity, etc.)

Do pilots breath the same air as passengers (shared air) ?
(i.e. the air a passenger exhales will be inhaled by the pilot [or vice verca], which also means that smoke in the cabin will inevitably end up in the cockpit)

In General, Yes.

As your image already shows, the same air is distributed throughout the cabin and the flight deck. For example, in the 737 NG FCOMv2 2.30.4 (Air Systems - Air Conditioning Description) it says:

  Since the flight deck requires only a fraction of the air supply provided by the left
  pack, most of the left pack air output is mixed with the right pack supply and
  routed to the passenger cabin.

So on the 737, the left pack supplies air to the flight deck and the cabin, the right pack only to the cabin (in normal operations).

Air from the cabin is also reused in the recirculation system:

  The recirculation fan system reduces the air conditioning system pack load and the
  engine bleed air demand. Air from the passenger cabin and electrical equipment
  bay is drawn to the forward cargo bay where it is filtered and recirculated to the
  mix manifold. The fan is driven by an AC motor. The fan operates with the recirc
  fan switch in AUTO except with both packs on and one or both in HIGH.

This implies, air previously exhaled by a passenger could make its way into the flight deck, but it is filtered first. In case of smoke in the cabin, the recirculation system would be switched off. However, during normal operations, the left pack supplies the flight deck directly:

(source: 737 NG FCOMv2 2.30.4)

All air quality parameters you mentioned should be identical or very similar for the flight deck and the cabin, except for temperature. Most aircraft allow separate temperatures for different zones. E.g. the 737 again:

  There are three zones: flight deck, forward cabin and aft cabin. Desired zone
  temperature is set by adjusting the individual Temperature Selectors. The selector
  range is approximately 65°F (18°C) to 85°F (30°C).
  The packs produce an air temperature that satisfies the zone which requires the

Temperature Selectors in the 737 overhead panel:

(source: 737 NG FCOMv2 2.30.4)

The details will of course depend on the exact aircraft model!

No, they do not. The pilots in the flight deck zone receive 100% fresh conditioned air directly from the left pack. The rest of the conditioned left pack air will be collected in the mix manifold for distribution for passengers. Recirculation fans will recirculate cabin air back to the mix manifold. Since the F/D isn't receiving air from the mix manifold, they aren't receiving recirculated, stale cabin air.


What are the SOPs following an overweight landing? Modern commercial aircraft are certified to be able to land at any weight providing that the runway is long enough.  The "overweight landing" QRH procedures for the 734 and A320 are correspondingly quite short, referencing mainly the approach reference and target speeds and adjusting for wet/contaminated surfaces.

This video (which by the way, deserves repeated watching - there is just so much to look at, e.g. the vortexes high above the wings and from the flap outboard trailing edges) unfortunately is clipped from shortly after the emergency response crews arrive until the aircraft vacates under its own power.

This made me curious as to how the decision to taxi clear is made.  Are there QRH/SOPs for this, either the operator or the airport?

My guess is that the fire fighters will check the bogies for any sign of fire and, coupled with the crew checking EICAS and the wheel and tyre temperatures and pressures, make a joint agreement that it is safe to vacate.

Following vacating, would the QRH/SOP be to stop when clear and allow extra time for cooling (which could be a long time) or taxi to the stand?

Wouldn't taxiing to the stand increase the risk of a fire starting even if there was none after it had stopped on the runway?

And that video, oh, watch it again.

The answer very much depends on the operator and type of aircraft (or rather its manufacturer).

First of all, overweight landing would normally be performed for the following scenarios:

Medical emergency on board that requires prompt medical attention
Any fire/smoke that cannot be extinguished/ventilated
QRH dictating "Land at the nearest suitable airport"
Any situation where safety might become further degraded by prolonged flight

It's hard to list all the situations here, and most of the time the Captain will have to make a decision whether to do an overweight landing or not.

Having made the decision to perform an overweight landing, the crew needs to take into consideration the following items:

Runway length available - landing at significantly higher weight than MLW increases landing distance substantially
Missed approach climb gradient - this might be a problem at airports with high terrain nearby
Reduced landing flap - normal landing flap speeds at higher than MLW might be too close to Vfe (maximum speed for the selected flap setting)
Required brake cooling - if heavy braking is required to stop within the required landing distance available, then it's best to vacate the runway and have fire services check the brakes and tires. Fuse plugs might have melted and tires might have deflated. Subject to all clear from the fire services, aircraft might taxi to the stand, have the chocks set and wait there with brake released for a while.
Overweight autoland is normally not recommended, as the autopilots are not certified for this.

After an overweight landing, an inspection is required by engineers to make sure there are is no structural damage on the aircraft, particularly its landing gear and the skin. According to my knowledge, the overweight landing inspection is just a bit more thorough walkaround by the engineer, provided the overweight landing wasn't a hard landing. If it was a hard and and overweight landing combined, the aircraft is likely grounded for a while, as more detailed inspection is required.

All Part 25 (FAR 25, CS 25) aircraft are certified to be able to land with sink rate of 600 ft/min (10 ft/s) at MLW and 360 ft/min (6ft/s) at MTOW, so unless you do a particularly poor landing when overweight, there should be no structural damage, even when landing straight away after a takeoff at MTOW.

The whole aircraft would be checked for structural damage, and the runway would be inspected as well.


In a flat spin, does the F-16 use its rudder deflection against the rotation for recovering? If the H-tail is used in recovery from the flat spin, is the rudder used for stopping the yaw or beta of the F-16?

I know that it is surely used for inverted flat spin, but I believe that the rudder is blanked by the H-tails in upright spin and is not effective.

It is not possible to have the rudder deflection because the huge amount of AOA and control law take that in consideration and cancel (fadeaway) the pilot rudder inputs.Activating the MPO the slabs moved  max in order to get the nose down to lower AOA and after that we can get responses from the rudder .https://www.flightglobal.com/f-16-spin-recovery-technique-invented/15027.article


What is the airplane with the best flying characteristics? I'm reading Stick and Rudder by Wolfgang Langewiesche, and in Chapter 7 titled, "What the Airplane Wants to Do" he discusses stability. In discussing it, he says that no plane yet built is completely "well-behaved" and that the plane closest to perfection is Fred E. Weick's Ercoupe.

It's been over 50 years since this book was written. Have aircraft flying characteristics improved? How much have they improved? And what airplanes have we built that have the best flying characteristics (which are the "best-behaved")?

First, let's get a little perspective
Stick and Rudder was written in the early days of aviation. To a modern reader, things were really weird back in the early days of aviation.

For a while, air traffic control was a guy sitting in lawn chair next to the runway waving a big flag that said "GO".
Parts on the plane just failed.  Planes would crash on their way back from bombing Hitler, a truck full of mechanics would come out to bolt on some (hopefully) new parts, and then they'd take back off in the crashed airplane to go bomb Hitler some more.
One time, the Allies bombed Switzerland by mistake. This was a world where more than one airplane could miss not only a target, but the entire country.

The kinds of things that went on in those days as a matter of routine would send any modern-day NTSB investigator into full-blown panic attacks.
What I'm getting at here is that it's a mistake to judge Stick and Rudder by modern standards.  This is not the equivalent of brain surgery.  You have to think of this as a surgeon just trying to get other surgeons to wash their hands with soap before they operate.
Now on to your questions

Have aircraft flying characteristics improved?

Yes. One example out of many:  Cuffed wings.

How much have they improved?

Enough that Wolfgang didn't need to write a second book.

And what airplanes have we built that have the best flying characteristics (which are the "best-behaved")?

An Airbus flying in Normal Law.
There's a section in Stick and Rudder (page 160 in some editions) where Wolfgang says that a "foolproof" airplane is one in which the controls have been restricted so that the pilot is mechanically incapable of pulling the airplane to an angle of attack which will result in a stall.  Guess what?  A pilot flying in normal law can yank on elevator all day long and not stall that Airbus.
An Airbus in normal law automatically trims itself.
An Airbus in normal law automatically increases power on the engines if a pilot pulls the airplane into a high angle of attack.
Some people might hesitate to put words in a dead man's mouth, but he's not here, so I'll go for it:  The best behaved airplane according to Wolfgang would be a modern-day Airbus airliner.

Flying characterisctics have improved as engineers have learned more about aerodynamics. Like adding wing dihedral to make the plane self centering.  Better stall characteristics.

How much?  Tons! Enough so so that manufacturers could dream of a plane in every garage for homeowners.

Which best?  Cessna Cardinal after getting past the initial year jitters. Sweet handling, pretty fast, good on fuel, easy to land.


Is a firm landing an indication of the pilot inexperience? In a commercial airplane, when a landing has been a bit firm, a passenger may think it was not perfect, or maybe performed by an inexperienced pilot.

(Source)

A perfect landing is seen by passengers as one where the contact with the runway is almost imperceptible. Is that true? are there other technical or regulatory explanations?

First of all, the landing should be in the touchdown zone. Often I see pilots try to achieve a very smooth landing but floating far out of the touchdown zone before touching terra firma. Then they have to brake hard and taxi of at the far end. There are no points for landing outside the touchdown zone, even if it is the smoothest landing imaginable. In many overruns, landing late is a contributing factor.

A good landing is in the touchdown zone, firm enough to quickly spin up the wheels (and prevent wear by smearing rubber over hundreds of feet), and not so hard that it bounces up again. In calm winds, that can be very smooth, cross wind and wet / contaminated runways require a bit more of firm landing.

Hard landings1 can occur due to turbulence (wind shifts), upslope of the runway or when the air density above the runway is lower due to heating (typically in calm winds, with sun heating the runway surface)

So a hard landing is not necessarily an indication of pilot inexperience. However, some of the hardest landing I have ever experienced were when I joined in a training flight where new airline pilots were practicing landings in a Boeing 737 for the first time after their simulator training. I wouldn't be surprised if the runway was dented :-)

1Hard landing is used as a colloquial term here, not in the context of EASA CS 25 §473. See this answer for that context.

I think that the landing has more to do with pilot preference.The pilot is supposed to land within a "touchdown zone" (as mentioned above) and how hard the landing is really just depends on what the pilot prefers. (most of the time anyway...) When pilots try to make light landings for the passengers they end often end up outside their preferred comfort zone and end up landing wrong anyway.
Based on that info I believe that a firm landing isn't a sign of pilot inexperience.


Where can I find the best site to learn aircraft design on a small scale? I am undergraduate student still trying to figure out a lot about Aerodynamics and aircraft design. I am learning how to design rc planes.

So the thing I know the weight of my plane which is between 700 gm to 1000 gm and velocity which is 13 m/s.

I just know the basics that is the lift formula and other fundamentals. I want to know how to design a nice fuselage for my plane and also how to keep balance in my plane. I seriously need help and also there are courses where you learn all this, but they ask for heavy cash.

It's not a website, but it's totally worth buying: Dan Raymer's Simplified Aircraft Design for Homebuilders (ISBN 10: 0972239707  ISBN 13: 9780972239707) is applicable to RC aircraft and has the best ratio of comprehensive coverage to beginner-friendliness of any resource I know.

13 meters per second calculates out to around 30 mph.
At 1 kilogram, you should have no problem whatsoever
getting it in the air.  Models at this weight generally land at around 8 to 15 mph and are capable of around 50+ mph at full throttle.  I would start by looking at classic airplane designs like the Piper Cub.

One of the best sources of more info would be your
local hobby shop.

Bob


Why is the F-35B's elevator not in neutral position when in vertical flight mode? I was watching videos of F-35B taking off and landing vertically on ships when I realized that when transitioning from horizontal to vertical flight mode (I don't know the exact vocabulary to describe that), the horizontal elevator moves to "stick pushed full forward" position. The elevator is also put in that unusual position when transitioning from taxiing to a vertical takeoff. I know that the elevator position is not significant in vertical flight as attitude is controlled via non-aerodynamics means. Thus I wonder why this control surface is then put in that position for that flight phase instead of staying in its previous position or in a more neutral position.
I'm even more confused as this behaviors doesn't seems to be reproduced on other VTOL fighters such as the AV-8B or the Yak-141.

In this video you can see it better I think:

I drew on a screenshot of the video from the side where you can see the air moving under the aircraft.
Compare this to the Fig. 1 in the paper linked by "Anonymous Person" here in the comment section of your question: http://ltces.dem.ist.utl.pt/lxlaser/lxlaser2016/finalworks2016/papers/03.2_3_366paper.pdf
As you can see angling the tailerons down significantly widens the gap between the leading edge of the tailerons and the trailing edge of the wings which allows air to be pulled along with the exhaust gases (drawn in blue). The paper calls this "entrainment".

Again I drew on another screenshot of the video and illustrated possible air currents that can freely move around the airframe: aft of the exhaust duct and to the left and right of the vertical stabilizers. As you can see the flaps are also extended which helps guide the air around the wings. There probably is a similar airflow around the front section of the fuselage where the wings are not blocking the flow and the fan is pushing the air down.
In a vertical descent or climb the tailerons also create less aerodynamic drag in this configuration than in a leveled attitude so the pitch inducing effects due to the large surfaces at the rear are reduced.
It could also be beneficial to angle the tailerons trailing edge down for a vertical landing or a short takeoff to increase the lift at the rear end by blocking the escape path for air trapped under the rear end of the aircraft. Essentially preventing the cushion of air to escape at least when in ground effect.

Vertical flight needs the big panel behind the canopy open, to admit air to the LiftFan® that it otherwise covers.  While that's open, in the transition to horizontal forward flight it would pitch the nose up.  The deflected elevators might compensate for that, although the downward-vectored thrust at the rear of the airplane compensates more effectively during slow forward flight (as shown in the video in Anonymous Person's comment.)

The AV-8B lacks such a speed-brake-like protrusion, so it needs no elevator deflection to compensate.

The Yak-141 has what looks like a smaller panel. Photos of it hovering show no elevator deflection, but the far-aft flaps are strongly deflected, perhaps for the same purpose.


How can an airliner make up for time lost? If a plane has been delayed at the origin how does it make up for the lost time? Does the pilot need any special permission from ATC to increase the speed so that it can cover the lost time or has the pilot the power to make such kind of decisions?

That's a common scenario, that you're pushing off the gate late and would like to make up time.  There are a number of ways that making up time can happen, although how much of that the pilot can affect doesn't often amount to a huge impact.

The flight is scheduled for whatever length of time, gate-to-gate.  This accounts for the sorts of delays that the planners foresee when they're building the schedule: it's winter, so the aircraft may need to be de-iced.  It's a busy time of day, so they plan on a slower taxi than simply driving out to the runway & taking off.  The flight is usually scheduled around a moderately worst-case headwind/(lack of) tailwind.  And so for the 1+00 (in the air) flight, you might be scheduled for 1+30 gate-to-gate.

And if some of the negative factors don't materialize, then you'll under-fly the schedule, which is nice.  Maybe the delay at the gate caused you to miss the "morning rush hour" and you did get to taxi right out, no line or delay, and take off.  There's no precipitation, so no delay for de-icing.  The tailwinds are better than average today, so instead of 1+00, your flight will only be 0+55 in the air.  All good things!

But none of that is really under the pilot's control.

The two places that the pilot can most affect things are, going faster, and getting shortcuts.  Going faster essentially means using more gas, and sometimes guys are willing to do that... the high-school tour group is in danger of missing their connecting flight & being stranded in the hub for the night, let's go fast & get them there!  Another version of going fast is flying at a more "speed efficient" altitude, usually around FL290 or FL300.  If winds are all the same, you'll generally get more speed there because your maximum indicated airspeed (Vmo) and limiting Mach number (Mmo) are very close around that altitude.  The tradeoff is, however, that you are burning more gas by doing this compared to going higher.

If you have the gas to burn, this can typically work.

Also, you can request shortcuts.  Depending on the filed route and what's going on in the airspace, this may get significant savings.  From the West Coast to DFW or IAH, you're typically routed around the north or south side of White Sands.  But, if it's Saturday night and the restricted area is cold (not in use), then you may be cleared direct right through it & save some significant time.  Of course, requesting shortcuts also saves gas (unless it takes you off a wind-optimized route -- rare but possible), so there's no real reason not to do it on every leg.

ATC may or may not cooperate with your plans.  If the restricted area is hot, then you don't get the shortcut through it.  If you're inbound to a busy terminal area (DFW, LAX, IAH, BOS, etc) then ATC probably has a sequence in mind, and they won't approve anything that changes the orderly flow of aircraft into the arrival.  In fact, they may assign you a speed in order to fit the sequence together.

Other than that sort of planning, though, they typically don't mind if you fly fast, and if they aren't too busy, ATC usually approves requests for shortcuts that don't have you driving through restricted areas (or other special use airspace).

How much time can you make up as a pilot?  If you really want to burn the gas, you might make up 5-10 minutes by going fast on a typical 1-2 hour flight, but those extra minutes are getting pretty expensive when you do that.  Shortcuts may give you another 5 minutes or so, in the best case.  (Longer flights tend to be more direct, as a % of the time, so you can't get the bigger & bigger time savings on the longer flights with shortcuts as you do with speed, compared to the short flights.)

But when a pilot tells you that he's going to make up 20 minutes off the planned flying time, most of that will probably be already baked in (tailwinds, no delays, etc) rather than things that he's doing differently than he otherwise would.  (It's still a nice line on the PA, though.)

And some days, none of the above works the way you hope, and the late flight doesn't get any earlier, or even gets later, despite your best efforts.  Speed, time, and distance can just be a bear, sometimes!

On some planes (airplus, sorry no reference) there is a “sprint mode” that uses more fuel but goes faster.    Airlines may therefore decide to time their flights not using the “sprint mode”, so as to save fuel costs, but be willing to use it if they are running late.

Flights are also timed so that can keep to timings even if the wind is in the “wrong” direction,  therefore often a flight can go faster than the planners assumed.


What happens if a helicopter engine fails at 20,000 feet? A fixed wing aircraft is able to glide in case of an engine failure and potentially land safely.

What would happen if a helicopter engine fails at high altitude?

Is it possibly to land it safely?

Yes. See the Wikipedia's article on autorotation!, which mentions a real-world example of the case you are describing:

  The longest autorotation in history was performed by Jean Boulet in 1972 when he reached a record altitude of 12,440 m (40,814 ft) in an Aérospatiale Lama. Because of a −63 °C (−81.4 °F) temperature at that altitude, as soon as he reduced power the engine flamed out and could not be restarted. By using autorotation he was able to land the aircraft safely.

The biggest concern here is the disk loading of the helicopter's rotor - the greater the disk loading (the mass of the aircraft related to the rotor's area) the worse the autorotation capabilities. See this Google Books link for an in-depth discussion of the autorotation capabilities of different aircraft based on their characteristics.

The weight of the very rotor also plays a significant role here - the heavier the rotor, the more kinetic energy it stores, and the greater the probability of a successful entry into the autorotation state. See the Osprey's design, for example - it has light propellers on each wing which are practically unable to autorotate because of their small mass.

As you can see, the aforementioned helicopter - Aérospatiale Lama - is a light aircraft which is geared towards high altitudes - it has three propeller blades, which translates to low disk loading, and sufficiently heavy blades to allow easy entry and execution of the autorotation stage.

When a helicopters engine fails, it would start falling until Auto rotation kicks in.

  Whether this happens and the pilot shuts off the engine or in the case of actual engine failure, once the engine drops below a certain number of revolutions per minute, relative to the rotor RPM rate, a special clutch mechanism, called a freewheeling unit, disengages the engine from the main rotor automatically.  This allows the main rotor to spin without resistance from the engine.


Is the commonly assumed UFO (flying saucer) design aerodynamically efficient? Is this design, a circular disc (or flying saucer) slightly humped on the top and bottom aerodynamically efficient? And if, we are able to use it for commercial purposes , would they give a better efficiency than existing aircraft?

This article states that this would be a better design. Is this true?

They use the concept of VTOL thats vertical Take off and Landing. Click here to know more about VTOL

Regarding the efficiency, well I think no one can give a 100% perfect information on this because, we do not know the fuel used, the engineering behind the structure. There are a lot of factors affecting efficiency like :
Materials, Fuel, Type of Engine, Weight etc. So aerodynamics alone cannot judge the efficiency of the aerovehicle.
Thanks!

The correct answer is no. A ufo with its circular shape has trouble traveling through the air. It struggles to travel through the air like a city bus, which  gets 2-6mpg. Depending on the amount of thrust this object has depends whether it can lift up into the air. But it would not be efficient because of the amount of fuel it needs to consume to pass through the air, its kind of like a flying city bus not really very aerodynamic and is terrible in efficiency. If this was powered by human technology it would not be efficient considering if its made by humans, if it was made by aliens then maybe it would be efficient, but that information we do not know and probably never find out in our lifetime and we don't even know if aliens exist. You also have to consider the design of this certain ufo. This shape cannot develop lift and runs fully on thrust, which also decreases its efficiency because of gravity pushing down on the flying object. Imagine an airliner without wings and how much efficiency you loose without the wings.Wind tunnel test for a circular shape. If a ufo was so efficient it would have been used on our current airliners. Now lets go into problems with a ufo being an airliner.

Its round circular shape would have trouble fitting into modern day terminals
Much thrust needed for vertical takeoff and landings
Not much room to store fuel
It would be very difficult for pilots to fly this object compared to modern day airliners
Airports would be redesigned for these objects which costs billions of dollars
Only has one engine to push the object instead of generally 2 on an airliner
Lots of weight the one engine needs to lift
One engine would be very difficult to do maintenance work on
The amount of money needed to be invested into this type of airliner
No horizontal or vertical stabilizer
Cost even more than the Concorde for maintenance
The costs to buy one of these would be 5x the price of a regular airliner
Amount of gas needed would be more than the Concorde
Amount of money needed to invest in this kind of technology, which doesn't even exist yet
No airline would want this because of the price
The whole ufo would generate lift, but that technology already exists and that's called a blended wing body, which is more of the focus towards future airliner and already has lots of money invested into it, and investing in a ufo would be too much money considering the amount invested blended wing body designs.

So I hope those 16 reasons helped explain why it would not be more efficient  than a modern day airliner and why it can't go into service. So the article was false for efficiency and other reasons.


Is it a common airline practice to base T/O speeds on the actual T/O weight when an assumed temp thrust is used? Let's say the current outside air temp is 15 C and you have decided to use 50 C as the today's assumed temperature for your takeoff. In this case, use of the T/O weight the assumed temp thrust supports gives you the balanced V1.

But our company rules are to use the T/O speeds of the "acutual" T/O weight instead of those that the T/O weight the assumed temp thrust applied provides. I assume this rule has been made to give a greater safety margin for a runway overrun in the event of a possible rejected takeoff at the expense of decreased obstacle clearance, since use of the actual takeoff weight invariably brings lower V1, Vr, and V2 speed than when the T/O weight of the assumed temp thrust is used. My question is: is it a common practice among commericial airlines to use the actual T/O weight instead of the assumed temp T/O weight?

You determine the t/o thrust as a function of t/o weight and runway length
Once the t/o thrust is determined you can select the assumed temperature on the thrust limit page on the CDU.

V1 is not the target primary parameter, it is a consequence of the calculation, on modern FMS your calculated value is cross checked with a range calculated by the FMS, that is your calculation could be rejected by the installed FMS unless you may force your value on some models.

A minimum rate of climb is necessary with a speed of V2+10, and at worst V2 with engine failure.

Backward of this Vr is computed.


What is the minimum size of a ramjet? Having recently learned that 155 mm ramjet artillery shells are now a thing, I wonder how much ramjet engines can be miniaturized. Could we see ramjet tank shells? Man-portable recoilless guns? Shotgun shells? Rifle bullets? For less martial applications, could we see micro-ramjet engines for small drones, similarly to micro-jet engines? (Whether or not it would actually sell if built is out of the scope of the question, let's simply imagine that there is a market for ramjet-powered microdrones.)

Given current (or near-future) manufacturing techniques, what would be the limiting factor for ramjet miniaturization? What would be the performances for the smallest engines, and how difficult/expensive would it be to make them? Are there theoretical physical limits to the minimal size of a ramjet engine?

Note: this ramjet-assisted shell is probably using solid fuel, but limitations for liquid fueled ramjet specifically are also relevant.

Ramjets could be miniaturized, but at some point, air viscosity and boundary layer thickness will make it impossible for them to work. Simply put, the intake hole will get so small that air will find it easier to flow around the whole thing and ignore all of its complicated inner structure.

In more technical terms, as the intake shrinks, intake velocity will approach an asymptotic limit regardless of flight velocity due to boundary layer friction, and for very small intakes, the air mass flow will be insufficient to sustain fuel combustion. That point seems to be somewhere in the centimeter range, but an engine becomes increasingly less useful as it approaches this point. Manufacturing parts this size isn't a problem even now.

Ramjet shells can help long-range artillery, but ramjet tank shells would not be effective in combat.

The figure of merit for tank rounds is their high-density penetrator's sectional energy at the target. Discarded sabot rounds are more effective at delivering this than any kind of engine internal to the projectile. Combat ranges are short enough to preserve the velocity.

If you had to use some sort of engine for a tank projectile, it would be a rocket. The reason is easiest to explain in numbers. At a range of 7.5 km with average 1.5 km/s velocity and a 10 kg round, to get 500 m/s of delta-V, you need 10 g = 1 kN of thrust (engine), plus 50 seconds of impulse (fuel). We'll ignore engine mass for the first approximation.

A rocket with TWR=50 and ISP=250 seconds will weigh 100 kg / 50 = 2 kg for the engine + 10 kg * 50/250 = 2 kg for the fuel, for 4 kg total.
A ramjet with TWR=5 and ISP=1000 seconds will weigh 100/5 = 20 kg for the engine + 10 kg * 50/1000 = 0.5 kg for the fuel, for 20.5 kg total.

Simply put, when flight time is this short, a heavy engine like a ramjet doesn't pay for the minute amount of fuel (or rather oxidizer) mass it saves vs a light and powerful rocket.

This applies to all combat applications within visual range: rockets are better, and guns are better still if you can afford the launcher weight. Beyond visual range, rockets or hybrid gun/rockets take over, and past 100 miles, air-breathing engines become viable.

Well, physical lab-size prototypes, based upon a variety of factors, would suggest 40mm, perhaps 18.5mm (12 gauge) as a practical testbed minimum bore diameter. There has also been some 50/12.7mm work, perhaps smaller if the gyrojet is considered.
Theoretical limits are speculative, because designs would vary. There are atom stacked electric motors.
External projectile scram power presents itself as a variation on a theme for smaller bore projectiles, using the projectile itself as the solid fuel. Like a self destruct mechanism, it dissolves down range.
Powered vehicles get into the size/payload/altitude/range issue very quickly, along with acceleration and thermal survival of payload at ram/scram velocities.
50 year time-frame? Centimeters and grams.
22nd century? Molecular.
Best guess.


How do I calculate FPNM for standard take-off minimums? I have trouble understanding and calculating FPNM for standard take-off minimums.

As I understand, the formula is: (Ground speed)/60 * FPNM = FPM

Let's say the ODP says:

  565' per NM to 2800, or 1000-3 with minimum climb of 370' per NM to
  2800, or 1500-3 for climb in visual conditions

With a Cessna 172S, could you let me know whether the aircraft is able to meet this requirement? Here is the rate of climb chart:

You don’t specify an altitude in your question, so let’s start with 2000' and the requirement to climb at 565' per NM and assume you have the airspeed at 73 kts. Then the performance table says

-20°   0°   20°    40°

760   695   555   560

So you meet the requirement for all temperatures up to almost 40°.

At 4000' you will make it at 20° but to see what the maximum temperature would be you need to interpolate.

-20°   0°   20°   ?°   40°

685   620   625  565  496

There are lots of ways to do the arithmetic, one way is with percentages.
The difference between 625 and 496 is 129. The difference between 625 and 565 is 60. So 565 is 60/129 (47%) of the way between the two. Our unknown temperature is also 47% of the way between 20° and 40°.

The difference in temperature is 20°. 47% of that difference is 9.4°. We went from left to right in calculating the percent difference so we do the same thing for temperature and add 9.4° to 20° to get 29.4°.

So as long as the temperature is less than 29.4° and you maintain an airspeed of 73 kts indicated, you can meet the climb gradient.

If you are at an altitude in between one on the table then you would need to do two interpolations. One at the lower altitude and one at the higher.

In the real world, and not on an FAA test, just use the next higher altitude and temperature.

Note that the table is based on pressure altitude, so set your altimeter to 29.92 to get the pressure altitude of the field.

Also note that if your airspeed is faster than in the table, you will be climbing too slow to make the numbers. This is also a no wind table. If you are climbing with a tail wind you will not meet the climb rate per nautical mile.

And finally, the climb can be to an altitude that is fairly high above the field elevation. If you look at the chart you will see that performance drops off with altitude. In your example if the field is sea level, then you will need to climb 2800' at 565 fpnm. Don’t use the sea level numbers since you are climbing through the 2000' level. Use the 2000' numbers to be safe.

My home field is at 212' MSL and one of the departures has a minimum climb of 320' per NM to 3000'. I’d use the 4000' row to decide whether I could make the departure.

If your takeoff speed is 60 knots, and you're climbing at 500 feet per minute, then you are climbing at 500 feet per nautical mile,  yes? Extrapolate from there.


Does taxiing time gets considered in a pilot's flying hours? Basically the title. This could be referenced to US or European rules.

In the US, taxi time can be logged. 14 CFR 61.51 says the pilot must log (emphasis mine):

  Total flight time or lesson time.

And 14 CFR 1.1 says (emphasis mine):

  Flight time means:

  (1) Pilot time that commences when an aircraft moves under its own
  power for the purpose of flight and ends when the aircraft comes to
  rest after landing; or

  (2) For a glider without self-launch capability, pilot time that
  commences when the glider is towed for the purpose of flight and ends
  when the glider comes to rest after landing.

Note that in reality, general aviation pilots (I don't know about airline pilots) usually just log whatever is on the Hobbs meter, which may include some time sitting still on the ramp doing post-startup checks, setting up avionics etc. That might not be strictly correct per the regulations, but absolutely no one cares.

This question is closely related.

My instructor always taught me to "test the brakes" immediately upon startup, therefore moving the aircraft under it's own power (and stopping again) so that technically, the hobbs time is an accurate loggable time.. Also a good habit to get into regarding testing brakes before getting distracted with the checklist and having the plane move itself accidentally while you're head down..


What has been done to provide security for remote wireless updating of in-aircraft software components? Is it true that in the latest generation of Boeing aircraft some software components / Electronic Flight Bag data can be pushed to the flight remotely via a Wireless link?

If so, what sort of safeguards are in place to preserve the integrity of such an update? How does the aircraft authenticate that the data sent is indeed legitimate?

I'm curious to know the details. e.g. Are these conventional Ethernet networks over which the update gets pushed at the airport end? Is the final wireless transmission done by a COTS WiFi router? Does the update travel via the internet from (say) Boeing till the airport?

Boeing claims in this document:

  The 787 uses wireless (802.11 b/g) technology while at the gate to
  transfer maintenance data and update the Electronic Flight Bag (EFB).
  This is referred to as “e- Enabling” and it will allow airlines flying
  the 787 to operate more efficiently.

So, yes, they use a regular WLAN connection for transmitting data while on the ground.

The document continues:

  Upon weight on wheels the 787 attempts to authenticate specific ground
  access points. Information regarding the key configuration
  requirements and how the 787 authentication occurs requires the
  signing of a PIA.

I interpret PIA as Proprietary Information Agreement, a form of secrecy agreement. Boeing uses security through obscurity to safeguard the integrity of the connection.

If you want to know more, Boeing advises to contact 787terminalwireless@boeing.com. However, I doubt they will talk to you or me unless we are airport representatives with a credible need to know.

In theory, they are just transmitting data, not code updates to the aircraft. So, the worst-case scenario would be that somebody would replace a chart with fake chart or something like that, which would be a nuisance but should not affect the safety of the flight.

As a matter of routine, any radio link should be considered an inherently insecure mode of communication, because it is open, unlike wire connections which can be physically isolated and secured against intercept.

Of course, if there is a bug or weakness in their system somewhere, it might be possible for a hacker to "pierce the veil" and somehow modify a live system. Whether that is possible or not depends entirely on the system architecture and implementation details of the software in question. Without knowing this (highly proprietary) information it is impossible to know whether such a weakness exists.

The official guidance on practices is contained in various FAA circulars, notably FAA advisory circular (AC) 20-153.

Here is a paper describing the general security situation: FAA Aircraft Systems Security.

Only the 787 is able to load actual flight system modules remotely, I believe, although as mentioned above many aircraft can wirelessly retrieve flight bag info. How Boeing verifies that a module is valid before loading I do not know, but in all likelihood they use a cryptographic certificate. If this is the case, then a hacker would either have to steal the cryptographic keys from Boeing, or find a bug in how they were using the certificate, in able to introduce a false module to the aircraft.


How much pollution is created by an airplane taking off? I read on a site that a 747 taking off emits the same amount of air pollution in the first 5 miles or so as 3000 cars. This seems extreme (accepting that the cars will be average).

Are there any more precise comparisons for 2 or 4 engine aircraft?

To provide more detail, let's look at some actual numbers. Without knowing where you got this information, the term "air pollution" is especially vague. But let's see what we can do. I'll compare CO (carbon monoxide) emissions since I could find that for both cars and jet engines.

The new 747-8 uses the GEnx-2B67 engine. The older 747-400 has a few engine options, one of which is the CF6-80C2B5F. Emissions information about these engines is available from EASA tests, and available for the GEnx and CF6. More info about the tests is here.

Based on that information the two engines have the following CO emissions at takeoff, reported as grams per kg of fuel burned:

CF6: .05 g/kg CO
GEnx: .17 g/kg CO

The fuel burn rates at takeoff for the engines are reported as:

CF6: 2.685 kg/s fuel
GEnx: 2.451 kg/s fuel

To find a value of comparison for cars, the EPA standards are here, in units of g/mi. Let's assume that we are using a recent model year, certified to the ULEV (Ultra-Low Emission Vehicles) standard.

ULEV: 1.7 g/mi CO

Now we need a way to compare these values. Let's use your initial value of 5 miles as the comparison distance. The jet engines will remain at takeoff thrust over these 5 miles, and the cars will meet the ULEV standard.

So how long will it take the 747 to cover those 5 miles? Let's look at the whole takeoff run, from a complete stop. This means that it will take about 40 seconds to cover the first mile down the runway. After that, lets assume it averages 160 knots, or 185 mph, over the next 4 miles. This means it will take 78 seconds to cover the rest of the distance, for a total of 118 seconds.

Computing the emissions for the takeoff:

CF6:

$$\begin{align*}
2.685\,\mathrm{kg/s} \times 0.05\,\mathrm{g/kg} &= 0.13\,\mathrm{g/s}\text{ CO}\\
0.13\,\mathrm{g/s}\times 118\,\mathrm{s} &= 15.84\,\mathrm{g} \text{ CO per engine}\\
15.84\,\mathrm{g}\times 4\text{ engines} &= 63.4\,\mathrm{g}\text{  CO per takeoff.}\end{align*}$$

GEnx:

$$\begin{align*}
2.451\,\mathrm{kg/s} \times 0.17\,\mathrm{g/kg} &= 0.42\,\mathrm{g/s}\text{ CO}\\
0.42\,\mathrm{g/s}\times 118\,\mathrm{s} &= 49.17\,\mathrm{g}\text{ CO per engine}\\
49.17\,\mathrm{g}\times 4\text{ engines} &= 196.7\,\mathrm{g}\text{ CO per takeoff.}\end{align*}$$

The car will be easier to compute:

$$5\,\mathrm{mi}\times 1.7\,\mathrm{g/mi} = 8.5\,\mathrm{g}\text{ CO per car.}$$

The 747-400 holds 416 people, and the 747-8 holds 467 (3-class configuration). Let's assume each car will carry 4 people.

$$\begin{align*}
416/4 &= 104\text{ cars}\\
467/4 &= 116.75\text{ cars.}
\end{align*}$$

We'll split the difference between cramming the three extra people into other cars and adding another car, and just leave it as 116.75 cars. Totaling the emissions from all cars:

$$\begin{align*}
104\text{ cars}\times 8.5\,\mathrm{g/car} &= 884\,\mathrm{g}\text{ CO}\\
116.75\text{ cars}\times 8.5\,\mathrm{g/car} &= 992\,\mathrm{g}\text{ CO.}\end{align*}$$

So comparing the 747 and the cars:

747-400: 63.4 g CO
104 cars: 884 g CO
747-8: 197 g CO
116.75 cars: 992 g CO

So a 747-400 is equivalent to about 7.5 cars, and a 747-8 is equivalent to 23.2 cars, comparing the takeoff run with average vehicle emissions.

I found this pretty surprising. It would be more fair to compare a takeoff with a drag race or a 0-60 test on the cars, which is probably not what the emissions test requires.

If anyone has more info or sees an issue with this please let me know.

Uff way to complicated .

747-400 fully loaded 160t of fuel (can take more fuel). 160.000 x 0.87 (fuel index) 140.000 liters approx.

140.000 L / 50 (average tank full per car)= 2800 tank fulls

140.000 gives probably 12 to 14 k nautical miles.

One car filled up 2800 times = about 2 million km. At about 7l/100 km.

This has nothing to do with mile per pax etc. As rarely do aircraft fly fully loaded or even with pax as many cargo aircraft in the air as well.

Just thought I make it a little bit more easy to imagine.


Is fuel moved around during flight on a passenger or cargo plane? If so why? Is fuel moved around during flight on a passenger or cargo plane? If so why? Is balance an issue?

Maybe

This is dependent on the air frame and varies from plane to plane and not all planes have capability of moving fuel although most large planes do. The Concorde moved fuel all over the place from its 13 tanks to cool the nose cone as well as trim the aircraft. It was perhaps one of the most complex implementations of such a system and kept the flight engineer quite busy.

(source)

Here is a layout of how it was used to control trim.

(source)

For any of this to be possible the aircraft must be equipped with cross-feed abilities. On larger planes this is fairly common, in case of a single side leak the cross feed valve is usually kept shut but since engines can have slight variances in fuel burn the pilots may need to cross feed every so often to balance the plane out. There is a nice overview on 737 fuel systems here.

(source)

In small, often single engine aircraft fuel management is generally left up to the pilot. There are often multiple tanks which can be individually selected and must be rotated in flight every so often (30 min usually). Since some planes are prevented from drawing from "both" tanks, the switch has a lot to do with not running a tank dry in flight.

This article overviews weight and balance fairly well. Often times quantity of fuel is more important than location. Most modern airliners store the fuel fairly close to the CG (in the wings or belly for that matter). The Concorde's unique delta wing design led to a fairly different use case than your run of the mill jet.

Some of the balance issue is solved within the tank using baffles which keep the fuel from sloshing around too much but allow it to flow freely around a fairly large tank when need be.

You can find the full text of the FAA's book on fuel systems here.

Here is a neat video of how to actually cross feed fuel.

Yes, fuel is moved around during flight in an airplane.

As the plane flies and burns fuel, the fuel level in the tanks will lower.

If you consider the elevation of fuel within the tank as a Y-axis value, then gradually as flight progresses that value of Y will decrease. So yes. Fuel moves around during flight.

If the fuel tank is symmetrically distributed about the aircraft in the X-axis then balance would not be an issue as it is moving in value only in the Y axis