How can engine positioning affect flutter tendency? I understand that moving the engines towards the wingtips would increase flutter tendency, but are there any other positioning options which could affect flutter?

How about moving the engine position forward, or backward on the wing. What about the twist of the wings, & the set angle of attack on the ground. Do these have to be considered when positioning an engine on the wings of the airplane?

Also, what about rear mounted engines. What should be considered here to reduce flutter tendencies of the stabilizers?

To better understand what flutter is, see the structure as a mass-spring system like a spring pendulum that has a damper attached to it. The aerodynamic forces both make the spring stiffer and dampen the movement. Crucially, they will act with a delay to the motion of the spring pendulum. Since we are dealing with oscillatory phenomena here, this delay causes a phase shift. The amount of damping increases with dynamic pressure and the phase shift angle decreases with flight speed.
Things start to get interesting when the phase shift angle approaches π. Now the damper will not work against the movement of the spring pendulum but will support it. Instead of reducing the amplitude of the movement, it will increase it - damping will become negative*. Flutter happens.
There are several ways to shift that point outside of the flight envelope:

Reduce the mass or inertia of the mass-spring system: Now the eigenfrequency of the system will be higher, so the phase shift will approach π at a higher speed. Moving the engines closer to the fuselage will increase the bending eigenfrequency of the wing, so any flutter that involves wing bending will be shifted to higher speeds. A typical case would be the flutter resulting from the coupling of the fast-period mode with the wing bending mode in swept-back flying wings.

Make the spring stiffer: This again raises the eigenfrequency of the spring, so a stiffer structure will shift the flutter speed up. This is no panacea, however: When the Rockwell Commander 112 was developed, flight test revealed flutter of the horizontal tail. A professor from Kansas recommended stiffening of the tail spar and was so convinced that this would cure the flutter that he joined the next test flight, only to crash with the aircraft. As it turned out, the stiffening shifted the flutter speed up such that the forces involved broke the spar while flutter was non-destructive with the softer spar at a lower speed (like in this video).

Change the Eigenmode of the spring: If the motion of the bending wing will at the same time add a torsion moment which twists the wing, resulting in a lower local angle of attack and, consequently, lower lift on the up-moving part of the cycle and vice versa, the aerodynamic damping can be increased. By shifting the engines forward, the engine mass will introduce such a torsion moment into the wing. Of course, when placed further outboard, the engine mass will cause a larger torsion angle with the same torsion moment, so shifting the engines out towards the wingtips makes this more effective.

Shift the resonance speed below minimum flight speed: This might sound silly, but works sometimes: When flying fast enough, the phase shift can be small enough to turn aerodynamic damping back into the positive region, and the plane will not flutter with that particular flutter mode. But it might still flutter at a harmonic …

Generally, to achieve positive damping, the center of gravity of a part should be ahead of its elastic axis. In the case of control surfaces, their center of gravity should be in or ahead of their hinge line. That is the reason for balancing masses!

* to be precise: As long as damping retards the motion, the damping term is mathematically negative and turns positive when it starts to support it.


How to decide the diameter of a propeller and number of propellers needed in a UAV I am designing? I want to design a turboprop aircraft. I know all the design parameters such as lift, thrust, weight etc at a given flight stage. I want to know what the size of the propeller should be.

There is an analytical process for selecting a propeller, but in the most straightforward cases it begins first with the selection of the engine. The propeller choice then can be made almost immediately.
Since you state that the plane will be driven by a turboprop, you have greatly narrowed down the propeller possibilities, and once you have selected a horsepower requirement for your turboprop engine, you have automatically narrowed down the propeller choice even further. Then, once you have selected a particular turboprop engine from a specific manufacturer, your propeller choices are narrowed down to just a couple of possibilities.
Just about the only design choice remaining after you select, for example, a PT-6 with a certain shaft horsepower output specification, will be the prop diameter needed to achieve the correct ground clearance for the engine installation, which may (for example) dictate four blades to absorb the engine power for a small diameter blade disc rather than three blades for a larger diameter disc.
Note also that no prop manufacturer is going to design for you a custom prop from scratch unless you can guarantee the purchase of tens of thousands of propellers of that custom design, and the design process will require years to go from an empty CAD file to a certificated prop being bolted onto an engine.
From an engineering practicality standpoint, your best bet would be to select the engine and then choose the most commonly-used prop in current manufacture with the longest production run and the greatest number of units in the installed base.


Can a private pilot fly commercial-type aircraft? Lets say that a private pilot owns a large commercial-type aircraft like the B777. Can he fly such a plane for himself as a private plane?

Your certificate level determines the type of operations you can conduct*, not the type of airplanes you can fly.  The types of airplanes you can fly are determined by your category, class and type ratings.

If you have a Private Pilot certificate with an instrument rating (not sure if this is required, but you'll want it either way) and an airplane multi-engine land category and class and a B777 type rating, then yes, that person can operate the aircraft privately.

He will also need an SIC and he will only be able to collect the pro-rata share of operating expenses from people he carries.  He will also want to be careful in who he lets on his plane to avoid operations that are regulated under 14 CFR 119.

An example of such a pilot is John Travolta, who has a private pilot certificate with the following ratings:

PRIVATE PILOT
  AIRPLANE SINGLE ENGINE LAND
  AIRPLANE MULTIENGINE LAND
  INSTRUMENT AIRPLANE

Type Ratings:
P/B-707 P/B-720 P/CE-500    P/CL-600    P/EA-500S
P/G-1159    P/HS-125    P/LR-JET

Limits:
ENGLISH PROFICIENT.
AUTHORIZED EXPERIMENTAL AIRCRAFT: SO-G2.
B-707 SIC PRIVILEGES ONLY.
CE-500 (VFR ONLY).

* Private pilots may only collect pro-rata operating expenses, Commercial pilots may be paid to act as PIC and ATPs may act as PIC in 14 CFR 121 operations.


What to do when pneumatic air cycle kit stops working mid-flight on Boeing 737-800? If you are flying a B738 at FL390, and one PACK (pneumatic air cycle kit) becomes inoperable, do you have to descend to FL250? If so, do you need to divert for fuel?

Different airlines may have different policies, but I think what my airline uses is probably pretty standard in this regard: no, you can continue at FL 390.

The limitation of not exceeding FL 250 on one pack comes from the MEL, which is a pre-takeoff document.  If the pack is known to be inoperative before takeoff, then the flight has to be planned at an altitude no greater than FL250, which means that the fuel planning has to account for the burn rate at the lower altitude.  However, when a system fails after you are airborne, the controlling document is NOT the MEL, but the QRH (i.e. your non-normal checklist for pack failure).  The QRH from Boeing does NOT direct you to descent to FL 250 for a single failed pack, for exactly the reason you allude to in the question -- you might very possibly have to divert due to the higher-than-planned fuel burn.

So in the case of a pack failure at FL 390, you can continue that flight at FL 390 as planned, but all subsequent flights until the pack is repaired have to be conducted at or below FL 250.

Some airlines may have a different policy, but that's the basic answer from Boeing's documents and philosophy.  Also, fuel permitting, some pilots might descend from FL390 to something a bit lower if they thought that the remaining pack might have an issue, just to provide a bit of cushion in case it does decide to stop working.  Packs fail rarely enough, though, that the risk of the second one failing on the same flight is pretty remote -- which is probably why Boeing is okay with continuing at the high altitude for the one flight, even though if you'll have to fly several more flights before getting repairs, they want the risk minimized for the others.  Risk management.


What is the descent rate in emergency situations? I fly a plane at 40000 feet. There is a sudden depressurization; what is the maximum vertical speed I can keep to come back at a proper altitude?
Is this speed different for different emergency situations? (Engine stopping/fire/general emergency).

Are there any numerical maximum values in different scenarios for, for example, a A320 or a B737?

(wikimedia.org) Part of a Boeing 747-400's autopilot control panel.

Maximum rate climbs and descents are achieved by using a speed climb/descent mode, where the pitch (nose up/down) controls a selected speed. The button FLCH (flight level change) activates such mode (shown above). Each manufacturer has its own name for it, but it's the same functionality. On an Airbus it is activated by pulling the altitude selector knob (Airbus calls it open climb/descent).

In level change climb, the thrust levers are engaged at the maximum thrust for a climb, the autopilot then controls the plane's nose to hold the selected speed. For maximum climb rate, a low speed (ideally Vy) achieves that, i.e., all of the climb thrust minus what's needed for the low speed is used for climbing.

For descents, the reverse is true -- fastest forward speed possible and idle thrust -- combined with the speed brakes. The plane will nose-down to achieve that speed. The rate of descent will be very steep initially, then it will ease off to hold the speed. Speed brakes add drag, so to achieve the same speed the aircraft will nose down more, resulting in a faster descent rate.

As the plane descends into the thicker atmosphere, the descent rate will again start to decrease -- as the plane will be producing more lift and drag. So we can't pinpoint an exact value, but 6,000-7,000 feet per minute is not uncommon.

Once a rate of descent is achieved, whether it's 1,000 fpm or 8,000 fpm, the g-force on the passengers will be 1 g, as there will be no acceleration in the vertical.

(YouTube) A Boeing 777 flight crew demonstrating such procedure.

A lower altitude is selected
FLCH is pressed
The thrust levers are idled -- by hand is quicker than the auto flight system (this does not disconnect the auto thrust)
The speed brakes lever is deployed
A faster speed is selected -- the maximum allowable indicated airspeed increases as the plane descends into the warmer air where the local speed of sound is faster (thereby allowing a faster true airspeed, up to a limit).

The above applies for a rapid decompression, other scenarios would likely require a descent, but not that steeply.


Where can we use conditional clearance? Besides Line up conditional clearance in a PREPARATION FOR TAKE-OFF situation, where else can we use conditional clearance (on an apron, taxiway, etc.)?

Conditional clearances can be issued for any stage of flight, but are usually not as they increase risk outside of the areas that you have listed.
In the en route environment a controller can issue conditional climb instructions for example:
SIA1223 at DOGET climb to FL340
BAW2283 passing FL250 track direct DROGO
I have never issued a clearance like that and some contries have made them not available in their regulations. But they do exist in other phases of flight.


What are ATC-side procedures to handle a jammed frequency? A few days ago, I was flying into my base airport in the USA with a control tower, and something/someone was jamming the frequency with what the tower thought was a hot mic after I had established communications and received instructions.

They thought it was us with a hot mic (Spoiler: It wasn't), and they managed to somehow broadcast through the hot mic tying up the frequency.

Luckily, that tower operates on two frequencies, so I changed over to the other one and managed to get back in contact with the tower and continued in to the airport; I made sure they knew that we were not the cause of the frequency jam.  That was clear, since nothing was jammed when we changed to the other frequency, plus the original frequency continued to remain jammed.

When such a situation as I describe above happens, what are the procedures that ATC controllers have to follow, and how did they manage to transmit through the hot mic like they did?

Honestly, there is no guarenteed way we can solve such a problem, and it is extremely frustrating when it happens. A few possible solutions:

The radio transmitter associated with the tower frequency is usually quite powerful, so (at least for nearby aircraft) it may be possible to override the other transmission by simply transmitting normally. AFAIK, the transmitter is actually designed to be more powerful than aircraft transmitters as a safety feature. Sounds like this is what happened in your situation. This is usually only the case for tower frequencies (not ground/approach etc.)

Sometimes there is an obvious alternative frequency you can use, and maybe some of the pilots will try tuning to that frequency. We could also do a call on 121.5 and ask everyone tuned to the tower frequency to check for stuck mic. This wouldn't help for small GA aircraft with only one radio, since they won't be listening to 121.5.

In CPDLC airspace (en-route environment), ATC can send a "CHECK STUCK MIC" message to relevant aircraft.

In the end, the pilot with a stuck mic will usually realise after a while of apparent silence on the frequency.

Here is a recording of a stuck mic causing issues at JFK:


Do seaplanes need to get clearance for takeoff? Do seaplanes need to get clearance for takeoff? Do they have ATC? How do seaplanes get clearance to takeoff?

If the seaplane is operating from a land airport with a control tower AND a water runway, yes.  Or, if the seaplane is operating from a Tower controlled  water-only aerodrome, such as the one along the waterfront in Vancouver BC in Canada, yes also.  Same radio procedures as any other airplane.

Otherwise, no.


How can the zero-lift drag coefficient (parasitic drag) be calculated? Consider a 3-D wing made from an arbitrary airfoil, say a NACA0012 airfoil. The wing has a trapezoidal shape, with a fixed span, root chord, and tip chord. Also, assume that the wing loading is known as well. I am trying to calculate the speed at minimum drag of this wing (assume that there are no other parts of the aircraft, just the wing!) My thought process is as follows:

We know that, to a reasonable degree of accuracy, that there are two types of drag on the wing in steady, level, flight: parasitic drag and lift-induced drag. This can be shown mathematically as:

$$ C_D = C_{D_0} + C_{D_i} = C_{D_0} + \frac{C_L^2}{\pi e AR}$$

Also, assume that the AR and efficiency factor are known. Now, for minimum drag to occur, there has to me a maximum lift to drag ratio. The formula for drag is

$$ D = \frac{1}{2} \rho V^2 S C_D = \frac{1}{2} \rho V^2 S \Big(C_{D_0} + \frac{C_L^2}{\pi e AR}\Big) = \frac{1}{2} \rho V^2 S C_{D_0} + \frac{\rho V^2 S}{2\pi e AR} C_L^2$$

Lift has a similar formula to drag, and in steady, level flight, is equal to the weight of the aircraft. Lift is related to the lift coefficient as $L = \frac{1}{2} \rho V^2 S C_L$. So we solve for the lift coefficient as follows.

$$ C_L = \frac{2L}{\rho V^2 S} = \frac{2W}{\rho V^2 S}$$.

Plugging into our original formula, we obtain

$$ D = \frac{1}{2} \rho V^2 S C_{D_0} + \frac{\rho V^2 S}{2\pi e AR} \cdot \frac{4W^2}{\rho^2 V^4 S^2} = \frac{1}{2} \rho S C_{D_0} V^2  + \frac{2W^2}{\pi e AR \rho S}\frac{1}{V^2}$$

This is great for us, because now we have a relationship between drag and lift, and to find the speed at minimum drag, all we have to do is take the derivative and set it equal to 0. I've done this and the resulting answer comes out to be

$$V_{md} = \Bigg( \frac{4W^2}{\rho^2 S^2 \pi e AR C_{D_0}} \Bigg)^{1/4},$$
where the 'md' stands for minimum drag. My problem arises because I cannot for the life of me figure out how to analytically calculate $C_{D_0}$. It can also be shown that at minimum drag, $C_{D_0} = C_{D_i}$ so that the total drag coefficient becomes $C_D \equiv C_{D_0} + C_{D_i} = 2C_{D_i} = \frac{2C_L^2}{\pi e AR}$, but then we are back to our starting point, which confuses me again.

My last resort was to read some papers that said that there is a method to finding $C_{D_0}$ using the skin friction coefficient, because at subsonic speeds, a large part of the parasitic drag is due to skin friction (and a little due to pressure drag). Anyways, this led me to the formula $C_{D_0} = C_{fe}\frac{S_{wetted}}{S_{ref}},$ where you use an equivalent skin friction and wetted area. Now I don't understand what a wetted surface area is, since in this example we are only dealing with one wing (would it just be twice the regular area??) As you can see, I am greatly confused. How do you find this zero-lift drag, and subsequently the minimum flight speed.

Yes, the wetted area is roughly twice the reference area. Now details depend on how well the reference area captures the exposed area of the wing - dihedral will already increase the wetted area by a factor proportional to the inverse of the cosine of the dihedral angle.

But there is more. Airfoil thickness means that the air has to flow around the airfoil. This displacement effect causes the flow around a thick airfoil to speed up more than around an equivalent but thinner airfoil. The thicker airfoil pushes the air aside and around itself more, causing the flow to accelerate and create more friction than the slower flow around a thinner airfoil. This effect is normally approximated with an additional term in the friction drag formula which is proportional to relative thickness.

Next, the type of boundary layer flow needs to be known. Rough surfaces or high sweep angles will provoke an early transition from laminar to turbulent flow. Read this answer for a more detailed discussion.

Another correction is needed for the Mach number, even in subsonic flow. Of course, once flow becomes transsonic or supersonic, wave drag needs to be added, too.

First you need to calculate the friction coefficient which depends on the Reynolds and Mach numbers of your airfoil flow and the relative mean roughness R:
$$c_f = \frac{\frac{0.43}{log(100/R)^{2.56}}-\frac{1700}{100/R}}{\sqrt{1+0.14\cdot Ma^2}}$$

Next, you approximate airfoil drag as explained above:
$$c_{d0} = c_f\cdot \left(2 + 4\cdot\delta + 120\cdot\left(\frac{1}{\sqrt{1-Ma^2}}\right)^3\cdot\delta^4 - 0.09\cdot Ma^2\right)$$
where $\delta$ is the relative thickness of your airfoil.

The term $\frac{1700}{100/R}$ in the friction drag equation allows for the initially laminar boundary layer. Change the factor 1700 depending on how much laminarity your airfoil offers. This answer shows a graph with the possible range. In the airfoil zero lift drag formula you see first the factor 2 which accounts for the fact that the wing has two sides. To that you add the thickness summand to allow for the displacement effect. The third term with the Prandtl-Glauert factor shows that the formula only works well for Mach < 1, and both the third and fourth term are empirical factors to improve accuracy over Mach.


Are there FAA rules about changing an airport name from Municipal to Regional? Are there any FAA requirements to be met or stipulations for an airport to change its name from Municipal to Regional?

In general there are no strict rules on airport names. This would be more of a marketing decision, and it's up to the owners/operators to decide of the expense of the "rebranding" is worth the benefits.

US regulations do cover international airports, and the Secretary of the Treasury designates the official list of airports. Even then, there are plenty of international airports not on this list, and there are even some airports called "international" with no customs facilities or plans to have them in the near future.


Would diesel (Jet A) cause less pollution than other fuels? Has any research been done on pollution from a aircraft using diesel (Jet A) vs other standard aircraft fuels? Is there a push to use diesel fuels in GA as a viable alternative and if so why or why not? (Ignoring the consideration of the non-availability of Jet A at most GA airports.) Would diesel-powered GA aircraft be considered the "future of green GA flying" or are other technologies such as electric propulsion more likely?

This is a good question which does not have an entirely straightforward answer as the different types of pollution produced and their effects on the environment are still being studied. Also, I know of no actual studies of aero diesel versus avgas versus unleaded avgas pollution in different types of aero engines to base a conclusion off of. I will draw some parallels with auto engines and fuels as they are similar in many ways.

Comparing the efficiency and pollution of a modern aero-diesel engine to the archaic avgas engine technology in most light airplanes is not really a fair comparison because modern aero-diesel engines have computerized electronic fuel injection, and often computerized variable pitch propellers which combine to create the best efficiency for the phase of flight. Old engine technology has no electronically controlled fuel injection (often no fuel injection at all), and often they don't have the gauges installed to inform the pilot how best to lean the engine. A better comparison would be a modern aero-diesel to a modern avgas engine with similar levels of technology, that's something I'd like to see.

There are many different types of pollution, and the different types of engines produce differing amounts. I will list the major types:

CO2: If you look at it from a CO2 perspective then auto diesels are less polluting than auto gasoline engines, which is why in many places across the world people have been moving to diesel. Governments (many in Europe) have in some cases taxes diesel less to make it more attractive. Whether aero-diesel engines produce less CO2 than a comparable technology avgas engines is not certain, as I said I've seen no actual data. Aero-diesel engines are heavier than avgas engines because they are partly made of steel, but they don't need magnetos which saves some weight, but then they are turbocharged which takes weight. Looking at the auto comparison I'd say aero diesels are probably better on CO2
NOx compounds: Nitrogen oxides are linked to asthma and breathing disorders, and diesel engines produce more of these than gasoline engines
Sulphur compounds: These are also linked to asthma and breathing disorders. Jet fuel has higher sulphur content than diesel fuel, and much higher than gasoline/avgas. Sulphur compounds may actually be helping to cool the planet though, as they help form clouds (acidic clouds) which reflect sunlight back into space
Fine Particulate Matter (FPM): particulates are a biggie from an environmental and health perspective these days. Particulates are linked to asthma and breathing disorders, and there is some evidence that black carbon particulates are heating the planet and causing glacier melt at an accelerated rate as they absorb heat. Diesels produce much more particulates than gasoline engines do

There is growing scientific evidence that the health and environmental costs of particulates, nitrogens and sulphur compounds of diesel outweigh the benefits of lower CO2 levels. I know in the UK the government is thinking about a U-turn on their stance on diesels, and many people are looking at going back to gasoline engines.

The biggest polluter with avgas is the lead though, in the form of Tetra Ethyl Lead (TEL) which is extremely toxic and very expensive to deal with. Unfortunately, without the lead avgas engines can rip themselves apart because of detonation at high density altitudes. This is an edge case to be honest, most light aircraft will never be in that situation, but it is potentially deadly in enough cases that you can't just get the lead out (pun intended). The lead makes avgas much more expensive than Jet fuel, which is one of the drivers behind aero-diesel; it's cost, not environmental benefits which make it attractive.


How many aircraft can an ATCo control simultaneously, on procedural and radar service? Aispace is separated in sectors, and each one has its own frequency. What's the airspace capacity for procedural and radar services, for a single sector?

There's probably not a specific number.   The answer will probably end up being "however many can do and maintain separation." Some sectors will include more complex maneuvering (more than one airport, several different approaches, both commercial and GA aircraft) so the airspace would have to be broken up into many smaller sectors with fewer aircraft in each to reduce workload. Whereas if you're talking about en-route, where the aircraft are not doing a lot of maneuvering the controller can probably deal with several times as many planes. If you think of arrivals at a busy airport, the airspace is broken into several different controllers, whereas often one guy in the tower is doing all of the landing clearances. That means he controls every single inbound flight whereas the approach controller is only juggling the portion that approach through his airspace. The workload per plane for the tower on landing is much lower since the approach controller will pass aircraft to him to him separated and already on ILS or with a visual on the runway. So all he is responsidle for is is making sure the runway is clear for each landing. In most situations tower only talks to the arrivals twice. Once to give clearance and then to pass them on to ground.


How to perform a "first principle" performance calculation? I am a PhD student on flight dynamics and control. This week I was given an assignment to do some research on methods of aircraft performance calculation. After some search on the Internet, I found that traditional methods depended on tabulated data on the airplane flight manual (APM), and about a decade ago, both Boeing and Airbus started to do performance calculation using "first principle" method.

I read on an Advisory Circular document that provides a definiton of this method:

  A calculation using basic parameters such as lift, drag, power or thrust, etc. with the equations of motion. (AC No: 25.1581-1, Change 1.)

And an Airbus document gives some explanation on this method:

  The next step in the performance calculation process, referred to as OCTOPUS (Operational and Certified Takeoff and landing Universal Software), not only offers the same advantages as TLC but also drastically changes the performance calculation method. It is no longer based on pre-computed data, but uses the “first principle” mode that allows a real on-time computation to benefit from a higher takeoff weight. Instead of smoothed pre-computed performance results, the OCTOPUS performance database contains all the airplane and engine characteristics, enabling performance computation based on physics equations. In addition, OCTOPUS introduces a new and improved takeoff chart format, with its use of multi-configurations and influences. ("Getting to Grips with Aircraft Performance", Airbus)

However, I have not found any paper or report on this topic. Is there anybody out there who could help by offering some details of this method, or, providing some references?

The equations of motion are the easy part. In essence, you look at all forces affecting the aircraft (lift, thrust, drag, weight) and balance them with proper control settings (elevator, throttle) and accelerations (if thrust > drag, the forward acceleration is (thrust - drag)/mass).

This you repeat over and over, one timestep at a time. The next timestep sees the aircraft at a new speed, which you get by multiplying the forward acceleration with time, and altitude if the climb speed is nonzero. The new, changed mass is the old mass minus the fuel consumed during the last timestep. And so on. This involves coordinate translations as some forces are defined in the aerodynamic and others in the airplane coordinate system. NASA Langley has published an open source software which does exactly that (LaRCsim).

For very high precision you can even model the inertias and calculate which aileron deflection is needed to arrive at a desired roll rate in the next timestep, but even without that you will get very precise data if the forces are correct.

The hard part is to arrive at the correct forces. We have had several questions here asking for the aerodynamic data of modern airliners, and every time the answer was: They are kept secret. You need to do your own analysis, and it is the same with engine data. Older methods relied on tabulated data, but in order to calculate conditions outside of the validity of the table they need to calculate the forces analytically. To get an idea what parameters need to be considered, look at this answer about the Boeing SCAP module.

However, even some crude assumptions can get you very close to the real result.


What is a "Major Airline"? Which airlines can be designated as "major"? what difference between them and other airlines?
What qualities airline should have to be "major"?
I can't find any proper description, but I heard about it a lot from aviation news.

Unofficial Terminology

In the United States, the unofficial term Major Airline is likely based on various official FAA and DOT terms. I cannot speak to use of the term outside the United States, but it may be similar, if used at all. This answer will address use in the context of US law and FAA regulations.

If a definition of Major Airline is to be faithful to official sources, that definition could be one such as the following from BusinessDictionary.com:

  US designation for an air carrier with annual operating revenue of more than one billion dollars, such as American, Northwest, and United Airlines. Also called major carrier.

However, as voretaq7 pointed out, the term Major Airline can be used to refer to the traditional "Legacy Carriers"—as opposed to newer start up carriers, the "Regionals", or low cost carriers. The terms are sometimes used interchangeably.

Official Terminology

The official terminology from which Major Airline is likely derived has a regulatory basis in 14 CFR 241, Section 4, "Air Carrier Groupings". This section describes the basis for grouping of Large Certificated Air Carriers, and defines the various groups. The following gives the criteria for assessing the level of operations (note that the nature of operations is assessed separately):

  (a) All large certificated air carriers1 are placed into three basic air carrier groupings based upon their level of operations and the nature of these operations. In order to determine the level of operations, total operating revenues for a twelve-month period are used. The following operating revenue ranges are used to establish air carrier groupings:

 Carrier Group      Total Annual Operating Revenues
 I                  0-$100,000,000
 II                 $100,000,001-$1,000,000,000
 III             $1,000,000,001 +

The DOT's Bureau of Transportation Statistics provides the following similar, but simplified, definition of Major Carrier Group:

  Major Carrier Group: Air carrier groups with annual operating revenues exceeding $1,000,000,000.

Answer

Thus, to answer your question as to what is required for a US "airline" to be designated as "Major" in an official capacity, the "airline" must:

Be a Large Certificated Air Carrier (see definition below), and
Have a reported annual revenue of more than $1,000,000,000.

Definitions

The following are definitions as given in 14 CFR 241, Section 3, "Definitions":

1Large Certificated Air Carrier:

  An air carrier2 holding a certificate issued under 49 U.S.C. 41102, as amended, that: (1) Operates aircraft designed to have a maximum passenger capacity of more than 60 seats or a maximum payload capacity of more than 18,000 pounds; or (2) conducts operations where one or both terminals of a flight stage are outside the 50 states of the United States, the District of Columbia, the Commonwealth of Puerto Rico and the U.S. Virgin Islands.

2Air Carrier:

  Any citizen of the United States who undertakes, whether directly or indirectly or by a lease or any other arrangement, to engage in air transportation3.

3 Air transportation:

  The carriage by aircraft of persons, property, or mail.


What are the advantages of using DC electric power over AC, as e.g. done in the EMB 135/145? In this question I can see the advantages of using AC electric power over DC in large aircraft. However, Embraer decided to produce a "DC aircraft": the ERJ 135/145.
What are the advantages of such a DC power system over the more commonly used AC one?

Now, DC is easier to produce than AC and easily to inverted to AC
To produce AC of a specific frequency, you will need one of below

An engine that rotates at a fixed rate.
A variable transmission box that normalizes the rotation rate.
Produce DC somehow then invert it to AC.

Method #1 is used by most American GE diesel locomotives. As a result, when the locomotive is providing AC power to the train cars, the engine needs to run at a fixed rpm, hence can not run at full rpm and full output. For this reason, a lot of other countries have switched to DC bus for train cars, essentially switched to method #3 (e.g. China uses DC600V for the train bus and it is inverted to 220V/380V 3-phase within each car).
Method #2 I believe is used by most airplanes, because fixing the engine at a certain RPM is simply not possible. The variable transmission is certainly not zero weight and is pretty complex and is certainly a point of failure. It seems like some airplane designs are switching to method #3 as well. They didn't switch to #3 earlier simply because aviation industry relatively is slow on new technology (so is the space industry).
Method #3 is basically what everyone else chooses since the beginning of this century, when semiconductor finally makes it cheap and simple and efficient to invert DC to AC. From small gasoline generators and home air conditioning, to electric cars and trains and ships, whenever the frequency of the power generator doesn't match the consumer, using DC and semiconductor power electronics to bridge the gap is the simple choice.
Most avionics are electronics, and most electronics runs on low voltage DC
Except the gyro, the CRT display, and environment control, everything else runs on DC internally. If you use an AC bus, then every device needs its own converter for it's internal working DC requirement. If you need a converter for each device anyway, then why not a DC-DC one and it's lighter and smaller and possibly cheaper?
Changing voltage used to be easier for AC than DC, now it's sort of the other way.
Before semiconductor, the only efficient way of converting voltage is via a transformer, hence AC. But transformers are heavy, which is why aviation uses 400Hz instead of 50/60Hz: transformers for higher frequencies are lighter and smaller. With modern semiconductor power electronics, you can basically convert DC voltages with near-zero weight, which is certainly desirable for airplanes. Also, semiconductor are made from sand, a lot cheaper than copper that makes a transformer.
DC-DC voltage conversion is more robust than AC-AC
An AC power transformer converts the voltage at a fixed ratio, so when the input side's voltage or frequency fluctuates, it propagates to the output, potentially affecting the downstream devices. DC-DC converters and DC-AC converters outputs at a fixed spec, so the input fluctuations are isolated from the output. This additional protection is certainly desirable for the aviation industry where safety, reliability and fault tolerance are the top of concerns.


What is the difference between a cold-stream thrust reverser and a conventional one? What is the difference between a cold-stream thrust reverser and a conventional one? It seems that all engines emit hot air, due to the combustion process.

Turbofan engines don't push all air through the combustion chamber. Instead part of it runs along the sides.

This bypass region is where the (cold) air stream is redirected from to create the reverse thrust.


Why do older airplanes have the wing curved upward like a 787? I was just wondering one day about because the 787 uses a wing flex to reduce wing tip vortex, but back in World War 2 they didn't know about wing tip vortex, so then why would it be curved upwards?

You can see in the middle picture the wing is curved upwards. I see this on a lot of commercial airplanes too like the Boeing 737

You are confusing 2 concepts here, dihedral and winglets. What you are showing in the picture is dihedral, which is not a curvature but an angle positive from the horizontal. This angle helps improve lateral (roll) stability in flight. This is nothing new, almost all commercial jets have dihedral. Winglets improve efficiency. A Boeing 787 has both.


Why would pilots get special cups? This Reddit post shows a picture of a disposable cup that is labeled specifically for use by pilots only:

Is that seriously a thing? If so, why? There's some explanation in that discussion thread about fitting cup holders more tightly, but it doesn't sound like a plausible explanation to me, since the cup holder should be designed to hold the cup properly, not the other way around.

The answer is pretty simple...

It is because those cups have matching lids that won't fit the passenger cups. Lids are used on the flight deck to keep the liquid inside from spilling on the (ever increasing) electronics, especially those located in the center console between the pilots (which house the radios in a lot of airplanes).

So some airlines have made a policy of any cup going into the cockpit must have a lid, and these cups specifically have lids.


What makes fast decompression so dangerous for the fuselage? There have been flight accidents which involved structural failure after fast decompression of the cabin, like
BOAC Flight 781.

I'm  thinking about how decompression can destabilize or destroy the structure of a fuselage;

I would think that a hole pinched into the cabin wall of 1 cm diameter will just cause slow decompression over minutes.

I got the impression that creating a larger hole, like removing a door, can potentially cause severe failure of the fuselage in other places than the hole.

If that is the case: what makes a hole large enough to be dangerous?
And what is the mechanism making a large hole dangerous?

Or is it that the structural failure comes first, and decompression is just a salient symptom of it?

Often it's the structural failure that results in decompression.

The comet (the aircraft in your example) was vulnerable to fatigue cracking that would propagate throughout the fuselage and compromise the structural integrity. Nowadays the fuselage is designed to stop such cracks from reaching further than the next spar and planes are retired when the number of cycles has reached the design limit.

There are factors to take into account when the vessel decompresses. If portions of the vessel are closed off from each other, then the pressure difference between those sections can exceed the tolerance of the divider and cause damage. This caused the floor to collapse when the cargo door blew off in Turkish Airlines Flight 981.


At what point does an aircraft need a new type certificate vs a STC? First post. Yes, I did search but this specific question has not been asked before. This answer is close, however:

How does a mechanic determine if a repair or alteration requires a Supplemental Type Certificate?

I do not own an aircraft and do not have a PPL. BUT, I love the Piaggio P180.  This question pertains to the difference between getting a new Type Certificate and getting a STC (Supplemental Type Certificate). So, which of these alterations would require a new TC of the aircraft vs a STC?

Lengthening or shortening the fuselage?
Changing the engine(s) from say piston to turbine or turbine to electric fans?
Adding extra components to the airframe, like batteries, controllers, etc. to make a hybrid aircraft?
Changing the wings to newer ones from another certified aircraft (re-winging)?
Changing the landing gear to a newer model with higher load capabilities?
Expanding the fuselage diameter by 10%?

Would implementing one of these changes require STCs or after a certain number of alterations, does the FAA require a new TC?

I'm really trying to understand when STCs are used and when the FAA requires a new Type Certificate.

Since this is an aircraft for personal use, is under 19,000lbs gross weight, and less than 19 seats it will fall under Part 23.

If you don't plan on selling "kits" to do these modifications, then an STC is not required. STC's are only for modifications intended for sale to aircraft for installation by an A&P mechanic. STC's are required not for the kit itself, but for each aircraft type (and sometimes variant) that it is to be installed on. This is why the STC process can be very expensive.

You would not need an entirely new type certificate either, again which would be required if you were doing these modifications as a business for sale as another aircraft type, or if the original manufacturer modified the aircraft in some significant way.

What you would need in almost all the cases you described above is an FAA Form 337, which describes "major repair & alterations to airframe or power plant". This document will require you (and your A&P) to make detailed descriptions and drawings of the modification and submit it to an FSDO. The FSDO will review the modifications and approve or disapprove of the changes. It is advisable to work with the FSDO from the beginning, not the end.

  So, which of these alterations would require a new TC of the aircraft vs a STC?

  Lengthening or shortening the fuselage?
  Changing the engine(s) from say piston to turbine or turbine to electric fans?
  Adding extra components to the airframe, like batteries, controllers, etc. to make a hybrid aircraft?
  Changing the wings to newer ones from another certified aircraft (re-winging)?
  Changing the landing gear to a newer model with higher load capabilities?
  Expanding the fuselage diameter by 10%?

None of them require a new TC or STC, however your first question would probably be difficult at best. The second question doesn't make a lot of sense for the Piaggio since it already has turbine engines, and there are no electric fans of the size that would be required. Changing the wing or modifying the landing gear are pretty common things, usually in the form of STOL kits or FOD deflectors. Some of them would require extensive testing from the FAA before issuing the airworthiness paperwork.

The last one though will nearly be impossible. It would be a lot cheaper to just buy an aircraft that fit your needs, like the Pilatus PC-24 than try to make that modification.


Why do large turbofans generally have many more LP turbine stages than HP turbine stages? In almost every large turbofan I see, the LP turbine stages outnumber the HP turbine stages by a factor of at least 2. Here's a photo of the RR Trent 900:

The Trent 900 (like most Rolls-Royce turbofans) is a 3-spool turbofan, rather than a 2-spool. But even here, my observation holds. There are far more LP turbine stages than the middle or high pressure stages.

Why is this?

Because the LP turbine extracts power for the fan, which requires the most power. The HP and IP turbine only extract power for their connected compressors - the LP turbine extracts power for the fan and the LP compressor. The fan does work on all airflow through the engine, the compressors only on a fraction (10:1 for a high bypass like the Trent 1000). The fan produces up to 75% of the thrust of the engine.

From this presentation: the cross section of the Trent 1000. It shows that the LP, IP and HP rotors have different rotational speeds, but does not list them. Another (older) presentation lists them as 3600. 6800 and 10200 RPM. Rotational speed goes down as the volume of the mass stream goes up.

An old textbook of mine gives the power P extracted from a turbine stage as:

$$ P = \dot{m} \cdot u \cdot v_{ax} \cdot [tan (\alpha_2) + tan (\alpha_3)]$$

with

$\dot{m}$ = mass flow [kg/s]
u = tangential blade velocity [m/s]
v$_{ax}$ = axial gas velocity [m/s]
$\alpha_2$ and $\alpha_3$ angles according to the figure below.

So the tangential speed of the turbine blade is in the equation for power extraction, which is composed of rotational velocity and blade radius. The faster the turbine turns, the more power can be extracted per stage, and the fewer stages required. Why then does rotational velocity go down with pressure? (HP = 10,200; IP = 6,800).

The reason is the constructional limits of the turbine. As the gas stream expands, the turbine blades become larger and are mounted at a greater axial distance, which results in greater centrifugal forces which are proportional to blade mass, rotational speed and distance from the axis. In order to limit centrifugal forces, the rotational velocity of the rotor is reduced: each subsequent stage turns at a lower RPM. Notice that a lower RPM can be compensated by mounting the blade further away from the rotational axis.

The LP rotor of an un-geared engine runs at the same rotational velocity as the fan. Its optimal RPM for the turbine may be higher, and that can be accommodated by the geared fan. As the bypass ratio gets higher, the LP turbine will be extracting a higher fraction of total power from the airstream - turboprops and turboshafts have a gearbox in between the LP shaft and the propeller/rotor, and the high bypass fan approaches the relative dimensions of a propeller...


Do Freon gas leaks occur in Airplane conditioning systems as well? I was just reading about Aircraft Conditiong Systems and found that, the A.C. mechanism begins with compressor in the engine. Do these compressor also work the way in which AC/Refrigerator's compressor do? If they do, then Freon Gas Leaks should be something happening atleast once in a long period .. They are pretty common with household Air conditioning system.So, does this happens? I have never really heard of something like this happening to an aircraft..

Large aircraft use air conditioning packs (air-cycle machines) which uses only air, compressors and heat exchangers to cool/heat the air. There is no freon involved.


What is the minimum speed a glider can thermal at? What is the minimum speed a glider can thermal (climb)at, typically, in terms of Vs over a dark field on a warm summer day?

Is it 1.1Vs, 1.2Vs, or 1.3Vs, etc,?

I do a lot of soaring and you thermal at min sink +/-, which is normally just few knots above stall, around 1.1 Vs.  The slower you can go the better (smaller circle) and sometimes going below min sink is worthwhile if it lets you core the thermal better, but your ability to do this can be limited by the glider's particular stall characteristics and your own flying skills.

On gliders with docile stall behaviour you can pretty much circle on the edge of the stall buffet.  A glider that breaks sharply with not a lot of warning, and wants to roll off, you need to leave more margin lest you enter a spin while above someone else and you might thermal at min sink or a little above.

The Schweizer 1-26 has very docile stall behaviour with a very strong pre-stall buffet that starts well before the stall break, and you can thermal a 1-26 right in the buffet range, shuddering and shaking as you go around.

BTW the best thermals come from lighter brown fields, that are dry.  Moisture in the ground makes it store heat and this tends to move the thermal activity to later in the day, and makes it milder.  Spring time after a very dry winter with little residual snow cover to moisten the earth when it melts will yield boomer conditions on good soaring days.


What fail safe protections exist to prevent non-plug type cabin doors opening in flight? Increasingly, modern types do not use plug doors to save complexity and weight.

As far as I know, the doors automatic/manual interlock only controls whether the slide inflates when the door is opened.  The doors have electrically powered locks and EICAS alerts to show unlocked doors.

However, anything electrical can and does fail.  What fail safe protections are in place to prevent non-plug doors from being opened in flight?

I am not sure about all aircraft types, but on the 777 cabin pressure is still used to positively lock the door into position in flight. When the door is open, the door is in a slightly raised position. As the door is closed, rollers on the door are lowered into tracks on the door frame. The tracks are curved slightly outwards, so to open the door the it most be moved slightly inward, which is impossible even with a slight amount of cabin pressure. The actual pressure load on the door is carried through the stops, which are inboard on the door and outboard on the frame. Once loaded with the pressure, these stops would also have a tremendous amount of friction preventing the door from sliding upward. Note the vent door near the top of the door in the picture below, this door is attached to the latching mechanism and it opens in the first movement of the handle, again preventing the door from unlatching if the cabin is pressurized.

Refer to this picture of the 777 door, to see the rollers, tracks and stops (Source).

I believe the 777 design is very similar to the Airbus design. There is a very good video showing the operation of Airbus doors on YouTube, here. It shows how the door must be lifted above the stops, before it can open outward. If you watch closely you can see the move slight inboard before lifting. This is a quote from the A340 maintenance manual: The lifting arms of the lifting shaft (which support the passenger door in roller fittings attached to the door frame) move the passenger door a small distance into the cabin and then upwards."

Note, some people (including Airbus and Boeing) still consider these doors plug designs since pressure still loads the door against the stops. For example, Boeing specifically states the 777 doors are plug type doors.


How can a glider pilot add sport pilot privileges? If I understand the rules correctly, if one already has a Private Pilot rating, then one has Sport Pilot privileges but will need an endorsement for a new category/class of aircraft. What if one has a Private Glider rating? Would that person be able to fly a Sport Pilot power aircraft with just an endorsement?

The short answer is no. You can get student pilot privileges with only a CFI endorsement for a new Category and Class. You would not have Sport Pilot privileges, though. The regs for Sport Pilot certificate holders would be that you need endorsements from two different CFIs and file an application with the FAA for each Category and Class.

Although 61.303 and 61.321 can be confusing, they both make mention of category and class. A sport cert does not have Cat & Class. For Sport Pilot privileges you have to have a training endorsement from one instructor and a proficiency check endorsement from a second instructor before the FAA will issue you a Cat & Class endorsement.

  61.321 How do I obtain privileges to operate an additional category or class of light-sport aircraft?

  If you hold a sport pilot certificate and seek to operate an additional category or class of light-sport aircraft, you must—

  (a) Receive a logbook endorsement from the authorized instructor who trained you on the applicable aeronautical knowledge areas specified in §61.309 and areas of operation specified in §61.311. The endorsement certifies you have met the aeronautical knowledge and flight proficiency requirements for the additional light-sport aircraft privilege you seek;

  (b) Successfully complete a proficiency check from an authorized instructor other than the instructor who trained you on the aeronautical knowledge areas and areas of operation specified in §§61.309 and 61.311 for the additional light-sport aircraft privilege you seek;

  (c) Complete an application for those privileges on a form and in a manner acceptable to the FAA and present this application to the authorized instructor who conducted the proficiency check specified in paragraph (b) of this section; and

  (d) Receive a logbook endorsement from the instructor who conducted the proficiency check specified in paragraph (b) of this section certifying you are proficient in the applicable areas of operation and aeronautical knowledge areas, and that you are authorized for the additional category and class light-sport aircraft privilege.

Private, Sport, Recreational, Commercial, etc. are all separate certificates. You can have multiple category and class ratings on each. If you have a Private certificate already, you will not need to get another certificate for any further non-commercial privileges. All you need to add a different Category or Class is an endorsement showing appropriate training and a Checkride. You will retain Private Privelages for any Category and Class listed on your certificate. Glider is a separate Category to any powered aircraft.

  61.63 Additional aircraft ratings (other than for ratings at the airline transport pilot certification level).

  (a) General. For an additional aircraft rating on a pilot certificate, other than for an airline transport pilot certificate, a person must meet the requirements of this section appropriate to the additional aircraft rating sought.

  (b) Additional aircraft category rating. A person who applies to add a category rating to a pilot certificate:

  (1) Must complete the training and have the applicable aeronautical experience.

  (2) Must have a logbook or training record endorsement from an authorized instructor attesting that the person was found competent in the appropriate aeronautical knowledge areas and proficient in the appropriate areas of operation.

  (3) Must pass the practical test.

  (4) Need not take an additional knowledge test, provided the applicant holds an airplane, rotorcraft, powered-lift, weight-shift-control aircraft, powered parachute, or airship rating at that pilot certificate level.

  (c) Additional aircraft class rating. A person who applies for an additional class rating on a pilot certificate:

  (1) Must have a logbook or training record endorsement from an authorized instructor attesting that the person was found competent in the appropriate aeronautical knowledge areas and proficient in the appropriate areas of operation.

  (2) Must pass the practical test.

  (3) Need not meet the specified training time requirements prescribed by this part that apply to the pilot certificate for the aircraft class rating sought; unless, the person only holds a lighter-than-air category rating with a balloon class rating and is seeking an airship class rating, then that person must receive the specified training time requirements and possess the appropriate aeronautical experience.

  (4) Need not take an additional knowledge test, provided the applicant holds an airplane, rotorcraft, powered-lift, weight-shift-control aircraft, powered parachute, or airship rating at that pilot certificate level.

For instance, I have a Private Cert for Airplane Single Engine Land. I also have Rotorcraft Helicopter hours. I can not solo a helicopter without an endorsement from my instructor. Essentially, giving me Student Pilot privileges for helicopters without a student pilot license (minus the Class B restriction). I would need a Checkride to add Rotorcraft Helicopter to my Private Cert.


Why was the Iraqi airspace closed on 12 Mar 2020? I was onboard BA105 on March 12, 2020 (London LHR to Dubai DXB), which was rerouted (I hope this is the correct term) to fly over Egypt. See the inflight map photo below:

Close to arrival, the crew informed us that we had changed course because of an Iraqi airspace closure, bit didn't give any additional info.

How would I find out more details about what happened (I couldn't find anything through a basic online search)?

The diversion was roughly 3 hours into the flight (based on FlightAware), at about 0000 UTC (the 13th).

At "12 MAR 22:50", i.e. about an hour before, the US issued the following NOTAM (notice to airmen):

  Those persons described in paragraph a (applicability) below are prohibited from operating in the Baghdad flight information region (FIR) (ORBB) at all altitudes due to heightened militia activities and increased tensions in Iraq, which present an inadvertent risk to U.S. civil aviation operations due to the potential for miscalculation or mis-identification. [converted case from all caps; emphasis added]

KICZ A0036/20 (PDF)

Note: "Those persons" refers to "U.S. air carriers and commercial operators". It's likely the UK issued a similar NOTAM.

Such communication – and the solution (reroute, return, land*) – will typically be sent from BA's ops to the plane via datalink (ACARS).

* Interestingly, the same flight turned around and landed at Istanbul on the 11th, followed by IST–DXB two hours later. This suggests on the 12th (your flight) they planned for this contingency and loaded enough fuel. The longer (Big Dipper) route adds an additional 580 NM (1,100 km) – not accounting for the increase in the air distance due to turning across/into the jet stream.

For how to find out generally, here I used EASA's Conflict Zone Information Bulletin.


Does a windmilling propeller create more drag than a stopped propeller in an engine out scenario? For this question lets assume that we are talking about a fixed pitch propeller and not a variable pitch propeller.  I do understand that variable pitch props should be feathered during an engine failure.

The main rationale for this question is this statement that I found in a pilot forum:

  I've been doing some research on something I hard from my old chief CFI a couple years back, but I'm not finding much on it. He is the only person I've heard this from, and any CFI, DPE, ect. I've talked about this to since have not heard of it. That being that when you have an engine failure more than several thousand ft. with a non-full-feathering prop, that you should pitch up and decrease airspeed, sometimes to an intentional stall, to stop the rotation of the prop/engine. (Of course, only after you have attempted to restart.) The reason being that you will see a greater gain in glide distance by reducing the drag created by forcing thee air to turn over the engine. He claimed that while you would most likely be off of Vl/d for a short amount of time, thus not gliding in the most efficient manner, that is outweighed by the decrease in drag. (As I said, do this only with several thousand feet and plenty of time.) He claimed that in the case of something such as a 172, doing this procedure at, say 10,000ft, you would gain several more miles of glide distance.

So what I am asking for is if indeed a windmilling prop has more drag than a stopped prop and if so would it be beneficial to follow the advice in the pilot forum?

I would not follow the advice in the forum. While the reasoning that a windmilling prop does create more drag is sound, I have seen no empirical evidence that says how much it actually translates to in Feet Per Minute. The only studies I have seen have been inconclusive on the subject, and say there's a number of factors that you can't really control in that situation. The prop isn't that big compared to the airplane itself, so if a spinning one has 30% more drag (just a guess, as I said I've seen no actual numbers) it isn't going to make you plummet out of the sky.

What I would recommend is following the engine failure procedure in the POH of your particular aircraft. The advice to slow the airplane to try and get the prop to stop has a number of flaws:

Distraction from critical tasks: Slowing the airplane until the prop stops is taking your focus away from finding a field to land in, ensuring your passengers are briefed and strapped in, making a mayday call and attempting to restart the engine. You'll be busy enough!
Low airspeed danger: Slowing enough to stop the prop may require a very low airspeed, and you could have a stall/spin excursion, which is far more dangerous than a glide landing
Drag curve: flying very slow to get the prop to stop will put you below best glide speed, which is where you get your best glide ratio. Below best glide speed you start to develop a high rate of descent, so by the time you get the prop stopped you have lost hundreds of extra feet. You could lose more altitude than you would potentially save, and waste valuable time doing it
The chances are good that you couldn't change the prop behavior anyway: if your crankshaft has broken the prop's going to spin no matter what you do, if you've thrown a rod it's going to stop and you couldn't get it to windmill if you flew at mach 1

Doing some math puts this into perspective. Say an airplane's engine-out rate of descent with a spinning prop is 1000, and with a still prop it's 900 fpm. In a glide from 3000ft that buys you an extra 20 seconds, but it probably takes a lot more than 20 seconds to slow enough to stop the prop and then regain a stable airspeed.

Flying very slow to stop the prop is a potentially dangerous distraction, just set best glide speed and if the prop stops its a bonus.


Why do the two different "ground effect"s used by aircraft and automobiles do opposite things in almost the same conditions? I found How come the ground effect has such a different outcome for wings and cars? and:
I am not allowed to comment as a new user because of some weird rule and I do not know enough to answer the question as I searched the web to find the answer to this.

Everyone is explaining that the two types of "ground effects" have the same name but are two entirely different phenomenons, but no one seems to have answered the question properly, at least that I can understand. It is all well and good saying they are different effects for different purposes but that does not explain why the two opposite effects occur in such similar conditions. I was originally searching for the answer to this question strictly in the context of car design - why the car-context ground-effect sucks the car down using the venturi effect yet having a full teardrop shaped car is meant to be impractical for the reason of creating a lifting air cushion underneath, though someone may think that the curve towards the ground would act as a venturi and suck the car down. The question is: "why do the opposite effects happen in such similar conditions". Venturi effect or air cushion? What decides which occurs?

I think aeroalias' answer sort of explained it but not in a clear and direct way; venturi effect occurs until the venturi is so extreme that the flow is "choked" and the venturi effect ceases to operate and you just have an air cushion? Is that the answer?

edit: This might make it clearer as to what I am asking though it is mainly a rephrasing of what I have already asked:

Why isn't an air cushion formed underneath a car (like with the aircraft) when the underside is curved towards the ground? Does the venturi effect occur when the curve is shallow but an air cushion form when it is steeper and flow is "choked"? I think I understand the basic theory of the car ground effect but what causes the aircraft ground effect and what conditions determine whether upward or downward force is produced?

venturi effect occurs until the venturi is so extreme that the flow is "choked" and the venturi effect ceases to operate and you just have an air cushion? Is that the answer?

No. Neither answer to your linked question talks about venturi effect at all!

In the aircraft case the wing is still far enough above the ground there there is no significant venturi effect at all. The pressure field around the wing is still similar as in free flight, but because the air can't move down behind the wing, the effective angle of attack is decreased, which reduces the induced drag. It does not even increase the lift all that much, reduction of drag is the most significant effect.

In the car case the bottom of the car is much closer to the ground, but the venturi effect is still not the major part. The underside of the car acts as an inverted wing, which creates upward lift. The ground again prevents the, in this case, upwash, this time by preventing other air to fill in and this again reduces the induced drag. The point is again not creating more force, the point is creating the force with less drag, so the car can go faster with the same engine (most racing classes are limited by engine power or cylinder volume).

Also note that venturi effect would be always downward, so if it was true that venturi effect increases until it becomes “choked”, it would pull the aircraft (which has the wings higher, so definitely no choking) down and possibly (depending whether it would be choked under the car) push the car up, the opposite what is observed.


Can a C152 land VFR in Miami International Airport (KMIA)? I know that it is a Class B airspace and VFR aircraft should request clearance at least 1 hour in advance before entering. The question is more related to MIA operations restrictions due to airliners.

It is possible to land with a C152 there, apart from being above VMC weather minimums (3 SM visibility and clear of clouds) and having 2-ways radio and transponder Mode C? How much is the landing fee? How can I gather all the information for GA and light ACFT operations in MIA?

Sure can if your C-152 is equipped with at least a two way VHF radio and a transponder with altitude reporting capability.  And you hold at least a PPL with current medical or are a student pilot with current medical and have a logbook endorsement from a CFI to fly there.

According to the A/FD entry for KMIA, all GA arrivals should file request a clearance at least three hours in advance of their arrival.

As with flying into any Class B airport, you will have to be on top of your game and able to quickly and accurately comply with ATC instructions.  Have all you charts and plates ready to go, especially taxi diagrams and frequencies.  Expect taxiing delays and instructions.  Wake Turbulence avoidance procedures should be used and anticipated.


Do I have to notify someone or file a flight plan for a private flight in the UK? Say I have a private pilot's licence (PPL) and I want to go on a flight, say from Stapleford (ICAO: EGSG) to Damyns Hall Aerodrome (ICAO: EGML). What would be the procedure for the journey i.e. would I have to notify anyone or submit a flight plan to the CAA?

Stapleford and Damyns Hall are both in class G airspace, so there would be no need to file a flight plan or ask permission of anyone to make the flight. The only thing you might need to do is call Damyns Hall in case they are PPR (Prior Permission Required). VFR flights generally don't need any sort of flight plan unless you are going abroad or to the channel islands. If you are going a long distance over water it's advisable as well. If flying into Damyns Hall keep in mind that the London City zone is very close by, so make sure you stay clear of it. The London TMA is at 2,500ft as well.

Both airfields are not controlled, however both have AG radios who try to coordinate flights, you technically don't have to communicate with them but you might not be allowed to use those airfields in the future if you don't use it.


How long can ATC operate for without main power? This question pertains to large towers at large airports. I'm assuming there is backup power in case of a power cut / power failure. But how long does a typical reserve generator / unit supply power for and what happens if it runs out without a main supply back online?

Nearly all generators designed to serve as a backup power source in a safety critical environment (Hospitals, Air Traffic etc) will be designed to run 24/7 "indefinitely" with hot refuelling.

Obviously there will be a real world practical limit to that, but it will be many days if not even weeks potentially depending on the generator.

I suspect there will be huge variation in the type of standby equipment available, pre-loaded fuel and so on depending on the mission. For example, it would be entirely possible to have two generators which can switch over - allowing the other to be serviced and maintained.*

*NB: I don't know if this is an actual "thing", but I'd expect it in certain circumstances, for example, military.


What does this wind symbol mean? At https://www.aviationweather.gov on the Forecasts puldown, then the Aviation Forecasts selection, the chart opens and often shows what looks like a letter R with a tail in the lower right, in different colors.  The legend does show the symbol. What does it indicate?

The Info button (top right) takes you to an explanation site, which in turn links you to

https://www.AviationWeather.gov/metar/symbol

Which explains the Symbol (under the section Fog or special weather) as Thunderstorm


How does the safety record of a Cessna 152 compare to a jetliner in Europe? I have a fear of flight and I'm working on it.

There is an airfield about 40 minutes from me and they offer flying lessons in a Cessna-152 for around 140 euros per hour. Pretty reasonable I think. So, this is my next step. But... I've only ever flown in an A320 / 737. This is because of the (approximate) very low risk of around 1 in 11 million of a fatal incident occurring.

My question is, what is the fatality rate (per million) for flights in a Cessna? I know it will be higher, I just want to know how much.

I did Google and look around, but the stats seem skewed on several sites as they include global incidents, whereas I know Europe is more tightly regulated than some parts of the world. Also, I'm not going to be performing (intentional) aerobatics, so I think we can exclude those cases as well.

I can't give an answer on this, but the reasons why are informative. General aviation as a whole has a higher accident rate than commercial aviation, at least in part because of the many varied missions, some of which are inherently higher risk, like:

Microlights
Homebuilts
Cropdusting

So the statistics aren't going to be very much to go on. Additionally as you mention it varies a lot globally, and there's variations for the type of flying, time of day and other factors. Focusing down on the C152 isn't going to give you a good figure because they are an extremely popular training airplane, which is a higher risk activity.

Basically you want to know what the accident rate is for a European Cessna 152 flown in the day by an instructor pilot for non-training purposes, there just isn't any data source for that. It's going to be pretty low I would imagine.


Who pays for Air Traffic Control services? I imagine certain fees from flight boarding sales are paid to the FAA, but who is responsible for paying fees for passenger flights?

FAA Funding is currently a mix of General Fund(taxes everyone pays) and Airway Trust Fund(ticket taxes and fuel taxes) money. The breakdowns are shown in: https://www.faa.gov/about/office_org/headquarters_offices/apl/aatf/media/AATF_Fact_Sheet.pdf


How do fuel tanks prevent free surface effect? Free Surface Effect is a fancy term that refers to liquids changing their relative orientation within a container, whenever the container is rotated.
So imagine a large plane banking very steeply, at least 30 degrees. If the fuel tanks in the wing were one giant tank, all the fuel would run down to the end of one wing, and in the other wing the fuel would bunch up near the fuselage. This can change the center of mass and might be dangerous.
How is this prevented? Are their baffles in every fuel tank? Are there many individual tanks instead of one or two large ones? What sort of other designs might address this issue?

It's not from banking that makes fuel slosh around when the airplane makes normal coordinated turns, any more than your drink sloshes over the side of your glass, or falls off the tray during a turn.  The fuel doesn't know there's a turn going on.
It's from yawing motions that occur, to the extent that the yaw damper system allows it (very small yaw excursions), or more severely, in the initial moments following an engine failure where big yawing motions occur if the pilot is slow in correcting the asymmetric thrust, and perhaps during landing where yawing actions are done to align with the runway.
In any case, the fuel tanks are just sealed off areas of the wing box structure, with bulkheads formed by the ribs.  The bulkheads will have holes to allow fuel to migrate, so they act like baffles.  In some bulkheads, there may be little one-way flapper valves along the bottom to only allow the fuel to migrate inboard, so once an outer zone of the tank is empty, fuel can't slosh back into it.
At the inboard end of the typical wing tank is a "collector tank" that the engines actually draw from, which is continuously filled to overflowing (the overflow running back into the main tank or sometimes just overflowing an opening around the top within the main tank).  The filling of the collector tank is done by scavenge pumps installed at the tank extremities.


What are the printouts/paperwork a captain does at the check-in desk? While flying American out of Chicago yesterday I noticed that when the captain arrived he went to the check-in desk and first read the monitor of a computer there for a minute or two, then he printed out a one or two page document from a dot matrix printer at the desk. Then for several minutes he made notations on the printout with a pen. Finally, he printed out a much longer document, maybe five or six pages long, folded it up, then went down the jet bridge together with the FO who arrived just as he was finishing up with the printouts.

Can an ATP, ideally an ATP who flies with American, tell me what exactly those two different printouts were and what notations he would have been making on the first one?

The paperwork he was looking at is the dispatch release.  This paperwork will have

Crew names
Fuel information
Filed route of flight
Alternates as needed
Current weather
Forecast weather at destination and alternates
NOTAMS for departure, destination, alternates, navaids and anything along the route of flight.
Deferred MEL items

There are also probably a few things I'm forgetting at the moment.

When the captain gets the release the first thing to do is make sure it is  for you -- correct crew names and airplane.  You'll check the route of flight and make sure it will work (weather) and evaluate the ordered fuel.  You'll review the destination weather, see if an alternate is needed and make sure a suitable one was filed.  You'll also check departure weather and make sure a takeoff alternate is specified if needed.  If the paperwork isn't right, you call your dispatcher, otherwise you sign it and take it down to the airplane.

The one-page item the captain got may have been a pre-departure clearance.  These are generally available via ACARS but can be printed if needed at a terminal.  They could also be other information such as ground delay programs or ground stop information that affects the flight.


Sukhoi Superjet 100 avionics The Sukhoi Superjet 100 features flight control system with characteristics copied from Airbus. Side-sticks, same control laws. But does it actually use any of the hardware or software from Airbus (under license), or is it an independent development based on detailed descriptions of the behaviour?

characteristics copied from Airbus

More precisely, copied from the package developed for Airbus by Thales.

  Thales pioneered the development and certification of FBW technology on modern aircraft, starting with the Airbus wide-body A310 in 1983 followed by the A320 family (...)

To that regard, from an official brochure (PDF), the SSJ100's avionics are also provided by Thales. As for the flight control system, it's been developed by Liebherr (cockpit controls, computers, and mechanical components). (Cropped page below showing who has done what.)

Liebherr (headquartered in Bulle, Switzerland) has an official video about it on YouTube. Where the narrator says:

  (...) Liebherr supplies the entire flight control systems from the various controls in the cockpit, to the rudder of the plane. More clearly, the aerospace equipment manufacturer designed joysticks, or here more properly called side stick controllers, in-flight computers, brake levers, pedals, and slats and flaps activation systems for the Russian regional jet (...)


Why are the outboard Krueger Flaps retracted before the others on the B747? In this video, I noticed that the outboard Krueger Flaps on this Boeing 747 were retracted while the middle and inner sets remained extended (refer to 3:22 - 3:30 in the video).  My questions are:

Why the staggered retraction?
Does each leading-edge flap configuration have its own unique setting on the pilot's flap-control lever?
On approach, are the leading-edge flaps extended in a reverse staggered order?

Please note that I have already reviewed the below Aviation SE questions (and their answers):

What are the benefits of using Krueger Flaps?
Is it possible to takeoff without flaps extended?
Is the A320 family allowed to take off with the flaps retracted?
If flaps are used on takeoff, when should they be retracted?

But I haven't found anything related to how flaps (leading- or trailing-edge) might be extended or retracted in a staggered fashion like this.

This is from memory and applies to 747-100/200 aircraft, which I last flew in 1999. The video shows, I think, a -400. However, to the best of my knowledge, it has the same flap settings.

The flap selection handle detents and resulting device positions are:

0° — leading and trailing edge retracted
1° — leading edge inboard of the engines extended, trailing edge up
5° — all leading edge extended, trailing edge 5°
10° — all leading edge extended, trailing edge 10°
20° — all leading edge extended, trailing edge 20°
30° — all leading edge extended, trailing edge 30°

At least one carrier, TWA, but maybe others, ordered aircraft with additional setting. I seem to remember 15° and 40°, but the above was the 'standard'.

  Why the staggered retraction?

On takeoff, it's all about changing the wing from a low-speed wind to a high-speed wing. Normal takeoff flap setting for the -100/200 was 10°. I think it's 20° for the -400 but I never flew them. As you retract the flaps (both leading and trailing edge), the minimum safe airspeed increases approximately 20 knots for each decrease in flap extension. That gave you a safe bank angle of 15°. Add 10 more knots and you could, as I remember, bank 30°.

So, in the video the airplane is accelerating, and flaps are being retracted in stages as it reaches the minimum safe airspeed for that stage.

I'm not knowledgeable enough to authoritatively explain why, if you want to change part of a swept wing to a lower-lift wing while leaving part of it as a higher-lift wing, you need to make the change to lower-lift from outboard to inboard, but I do know, at least I think, that you must avoid the possibility of the outboard wing stalling while the inboard is still flying. You need to retain outboard aileron control as long as possible. Thus, retract the outboard leading edge devices before the inboard devices.

  Does each leading-edge flap configuration have its own unique setting on the pilot's flap-control lever?

No, the leading edge flaps do not have a separate selection. They're tied to the trailing edge flap setting. Note that flaps 1° doesn't actually put any trailing edge flaps down (although I seem to remember it took them out of the retract position and moved them backwards, but I may be wrong), but extends only two of the four leading edge flap sections.

  On approach, are the leading-edge flaps extended in a reverse staggered order?

Yes. On approach you're slowing, and you must not slow below the minimum safe speed for your flap setting. Those speeds will be lower than the respective takeoff speeds because you're lighter. I just looked up the fuel for a -400 that I have on my weight and balance web page, and it shows 359415 max fuel. Thus it's not unreasonable that you might be as much as 340000 lbs lighter than at takeoff and the minimum safe airspeed for a given flap setting could conceivably be in the range of 40 to 50 knots slower than at takeoff.

For those interested in more detail about the -400 leading edge devices, go to this incident report detailing an un-commanded retraction of the leading edge devices inboard of the engines. The single paragraph that most caught my attention is:

  The serious incident involved the un-commanded retraction of the automatic
  Group ‘A’ leading edge flaps on rotation for a period of about 23 seconds.
  Subsequent to the initiation of the retraction of the Group ‘A’ leading edge flaps, the aircrew was faced with unexpected stall warnings. The pilot flying was able to prevent the aircraft from stalling, with support from the other crew members and to keep the aircraft flying until the leading edge flaps re-extended and normal performance capability returned.


Can I shoot any approach at an uncontrolled airport in VMC without any clearance? I am in IFR Flight plan to an uncontrolled airport. I find out that the weather is well above VFR limit, and hence canceled IFR flight plan. But I want to shoot an approach (with safety pilot) for my currency. In this case, can I still shoot any approach to the uncontrolled airport in VMC without any clearance?

You would have to cancel your IFR flight plan with ATC, fly the duration of the flight and the approach by VFR, but, yes, you could.

Many people fly practice approaches at untowered airports by announcing their intentions over the CTAF.  This can be difficult to do at beehive airports with a lot of GA traffic going into and out of them, but it’s possible.  I’ve done it plenty of time without incident.


Why am I seeing extremely high L/D ratio of (e.g. L/D = 90) in my 2D airfoil analysis? Can anyone explain/justify why, using the 'Theory of Wing Sections' by ABBOTT the lift/drag ratios seem so high. For example, I'm doing an analysis of the NACA0012 airfoil and using their experimental data on pg462/463 at 8 degrees CL is roughly 0.9 and CD is roughly 0.001 giving a lift/drag ratio of 90. This seems incredibly high since as far as I'm aware lift/drag ratios go up to 70 to 75 practically from answers I've seen on here. My problem is that my CFD analysis also gives these high lift/drag ratios but I just didn't think it was possible.
Thanks in advance to anyone who can help!

The difference is that one figure looks at 2D flow around an isolated airfoil, where L/D ratios of up to 200 can be reached, while the other figure is for the 3D flow around a whole airplane, warts and all. The additional sources of drag which are absent in 2D flow around airfoils are:

Induced drag. This will double the total drag right at the polar point of best L/D.
Fuselage and tail drag. Of course isolated airfoils only have their own surface where friction drag occurs, but all the non-lifting parts on whole airplanes will bring D up without helping L.
Lift loss at the tips. L/D for airfoils uses the pressure distribution and maybe a drag rake at the windtunnel center section, so no tip effects will tarnish the result, but the outer wings of airplanes will have reduced lift relative to the local surface and drag because of tip effects and to improve stall behavior.
Trim drag: The tail can very well add a downforce to balance the lengthwise lift distribution with the location of the center of gravity. Now extra lift has to be produced by the wing, and both, downforce at the tail and extra lift on the wing, will produce more drag.


What is the difference between flap load relief protection and overspeed protection? What is the difference between flap load relief protection and overspeed protection?

According to this document/study guide

  Flap Load Relief – on the 757 and a few 767s, if the flaps are at 30
  and Flaps 30 speed is exceeded, the flaps automatically retract to 25.
  On most 767s, if the flaps are at 25 or 30 and the placard airspeed is
  exceeded, the flaps automatically retract to 20. The flaps will
  automatically re-extend when airspeed is reduced. If the Flap Load
  Relief fails to operate when it should, the Trailing Edge light will
  illuminate and the FLAP LD RELIEF EICAS message will display

So flap load relief is a system that specifically protects the flaps. This is the result of accelerating to higher speeds.

Overspeed is a more general term and the actual speed that defines overspeed may vary with configuration, the 767/757 has a warning for that

  Overspeed Warning – Master Warning, EICAS message, discrete light and
  siren when airspeed exceeds Vmo/Mmo.

It appears that overspeed protection is a function of the auto throttles.


What happens if you take off with a direct tailwind? What happens if you take off with a direct tailwind?

Given how few bounding criteria you have in your question, the general result is

For fixed wing aircraft: your ground speed will be significantly
higher than if you'd taken off heading into the same wind, and thus
you'll tend to use up more runway before lifting off.

Example: with a take off speed of 100 kts, going into or downwind is the difference between 90 knots or 110 knots ground speed before reaching take off speed when the wind down the runway is 10 knots.  This difference becomes more pronounced as wind speed increases; it's a differential of 2 x wind speed.

With a long enough runway it won't matter in terms of "taking off before running out of runway."  On a short field it may matter a great deal.
For Rotary Wing aircraft: you may need a bit more power to hover when
lifting off with a tail wind.  The FAA has this guidance:

  Headwinds are the most desirable as they contribute to the greatest
  increase in performance. {snip} When taking off into a headwind,
  effective trans lational lift is achieved earlier, resulting in more
  lift and a steeper climb angle. When taking off with a tailwind, more
  distance is required to accelerate through translational lift.

For a variety of aircraft types, if the tail wind is high enough your manual will recommend against/prohibit down wind takeoffs, but that varies enough between models and types that a general answer can't encompass all of the variations.


What is the format specification for Avidyne R9 flight data? The Avidyne R9 records flight data five times per second and can export it for later analysis.

I'm interested in parsing this data and exporting it to Google Earth / X-Plane for visualization.  Cirrusreports already does this, so I know it's possible.  It would be easier, though, if there was a spec already out there.

Is there a specification for the Avidyne R9 flight data file format available, preferably online?

According to section 12-4 of the Release 9 Pilot's Guide, data logs are saved as a simple .csv file that can imported into any spreadsheet software (like Microsoft Excel) for analysis.

There are many free tools that can covert Excel files to KML for Google Earth, ie: http://www.earthpoint.us/exceltokml.aspx


Can i create a home built aircraft with this engine? http://www.chiefaircraft.com/da-100.html
Would this engine work for a homebuilt ultralight aircraft? I am still in the research phase, so i don't know what the weight of the aircraft will be, but I would like to know what a good prop size and max weight that it will be able to fly.

It's a 100cc engine, and it's in the Radio Control section of that web site. It's an engine for model aircraft.

I suppose, technically, that's a home-built aircraft, but you're not going to sit in it!


Why does an ADIRU 1 failure disable all functions of the A330/340’s GPWS - even those not requiring ADIRU data? Among the many (many many) aircraft systems degraded or rendered unavailable to the flightcrew of QF72 as a result of a partial intermittent ADIRU 1 (Air Data / Inertial Reference Unit 1) failure, the aircraft’s GPWS was rendered totally inoperative (all emphasis mine):

0440 [. . . . .] NAV GPWS FAULT [. . . . .] The GPWS required ADIRU parameters such as true track angle, computed airspeed, true airspeed and roll attitude, and it was only connected to ADIRU 1. A problem with ADIRU 1 resulted in a loss of the GPWS function.  [ATSB Transport Safety Report AO-2008-070, page 48 (page 68 of the PDF file of the report).]
In addition to the potential for a pitch-down command, other known effects associated with the data-spike failure mode on the A330/A340 included:
[...]

unavailability of some other aircraft systems, depending on the ADIRU involved. For example, in cases where ADIRU 1 was affected, the ground proximity warning system (GPWS) was no longer available.  [Page 200/220.]

It makes sense that those GPWS functions requiring ADIRU input would be rendered inoperative by a loss of ADR/IR data;1 for instance, excessive-descent-rate protection and terrain-ahead avoidance both require pressure altitude (to calculate the aircraft’s descent rate, in the former’s case, and to determine whether the aircraft has enough altitude to safely clear rising terrain ahead, for the latter), an ADR parameter, while bank-angle protection requires roll attitude, an IR parameter.
However, not all GPWS functions require ADR or IR input; for instance, of the GPWS’s original functions, most (dangerously low height above terrain when not configured for landing; excessive terrain-closure rate; loss of height after takeoff) require only radioaltimeter data2 (plus, for the first, aircraft-configuration data), which is unaffected by even a complete loss of all air and inertial data.
So why does a loss of air-data and inertial inputs disable even the functions of the A330/340’s GPWS not requiring said inputs?

1: Although this raises the obvious question as to why such a safety-critical system as the GPWS was connected to only a single ADIRU, with no ability to switch its inputs to a different source should ADIRU 1 fail.
2: The very factor that makes the radioaltimeter inferior to the baroaltimeter for most purposes (its measuring height above the variably-high ground, rather than altitude above mean sea level) makes it ideally-suited for the GPWS basic functions (as we are interested in not colliding with the ground, rather than with mean sea level; indeed, in some cases, the ground is located below mean sea level).

You wrote:

  (...) the GPWS's original functions (...) require only radioaltimeter data (...)

That's wrong. The basic GPWS needs barometric data alongside the RA.$^{[1][2]}$ (Not talking enhanced functions of EGPWS here, rather the most basic modes 1–3, and mode 4 needs airspeed/Mach with RA.)

The A340's GPWS computer (EGPWC) takes this barometric info (vertical speed) from ADIRS 1 (schematic), if that's failed, so would the basic GPWS.

$^1$: GPWS patent from 1970
$^2$: Aircraft Instrumentation and Systems (page 342 snippet below)

Note: Computing the height time derivative ($\dot h$) is not as easy as using V/S, you need high sampling rate and a perfect radar lock that won't be fooled by say trees or uneven ground reflecting the signal away. In France, some airports use radar reflectors on masts to fool the RA into thinking the ground is flat:

  Source: lustublog.com (in French)


Why is the delta wing naturally stable in pitch? Any thoughts on why the delta wings are naturally more stable in pitch, so they don't require any tail surface? What's the physics behind this?

This is a very good question, as it shows some of the misunderstandings regarding "tailless" aircraft.  With deltas, one can consider them as blended wing/tails.

The function of a horizontal tail surface is pitch control.  The back of a delta is certainly large enough to do this. So much so, that now one can design
a forward canard to go with it.  This plane should pass the horizontal drop test (nose must go down).

Notice that birds, wanting more straight wing lift,
"unblend" a little and also have a fan tail.  Delta's do not generate as much lift as a comparable straight wing.

So designers can work with what they need, particularly with desired speed range.  Faster, the wings can pull in a little, as with the FB-111 swing wing.


Grand Canyon flying minimum altitudes I'm looking to visit the Grand Canyon this September. I fly an open-cockpit two-seater gyroplane - a Magni M16. Its ceiling is around 13k' and I'm not wild about trying to reach the top end of that. I'm confused by the SVFR rules on the special Grand Canyon chart and would appreciate some clarification.
If I look at the chart on Skyvector, I can see the allowed corridors and the SVFR area fine. Looks like in the east it's more restricted and for the Native American areas, you have to be above 14.5k' to fly over them (which rules them out for me anyway) but that I can use the Dragon and Fossil Canyon corridors down to 10.5k', which should work. The rest of the area I need to be at least 10k', at least over the Supai and Diamond Creek sectors.

So far so comprehensible. However, in the west, you have to avoid The Sanup tribal area below 8k' but then the rest of the area is either the same or higher than that! Do I have that correct? Looks like I could depart from 1G4 and fly due east over the Sanup area at 8k', then turn north and provided I followed the edge of the Pearce Ferry sector, I could stay at 8k' all the way to the Bar 10 airport 1Z1. Is my interpretation correct?

Thanks for any help and guidance, especially from anyone who's done this in a low power open-cockpit craft.

The rules for operations in the Grand Canyon Special Flight Rules Area (SFRA) are governed under 14 CFR Part 93, Subpart U.

Please review these rules here and all applicable GCSFRA NOTAMS prior to departure.  Also perform your performance calculations for the predicted density altitude on the day of your flight to verify your aircraft will be capable of ascending to at least 9500 ft MSL, else it may not be legally or physically possible to make the flight.

For an eastbound flight like that departing 1G4, I’d recommend a takeoff and climb to 9500 ft MSL (eastbound VFR altitude which meets the minimum requirements of both the Pearce Ferry and Diamond Creek sectors of the GCSFRA) prior to overflying the Pearce Ferry sector enroute for 1Z1.  Be advised for both fixed wing and rotor wing aircraft over the northern sections of the Pearce Ferry and Diamond Creek sectors.  Commence your descent into 1Z1 only once clear of the northern edge of the Diamond Creek sector.

Aside from the legal aspects, keep in mind that you are going to be flying over some pretty rugged country out there.  Have a plan of action should an engine failure or other inflight emergency occur enroute, requiring you to set the aircraft down somewhere.


Can reverse-thrust be used to push back from the gate? Crazy idea, I know.  But instead of pushing back a passenger plane using a vehicle connected to the front wheel, what if I turn on the reverse-thrust and rev up the engine?  My logic is if it can slow down the plane during the landing, it can certainly roll the plane from a dead stop having it go backwards to clear the gate.  Would that be possible in terms of laws of physics?

It has been done before but is generally frowned upon due to high fuel consumption, equipment FOD caused by debris kicked up by the fan exhaust and intake suction dangers.  It is just simpler and safer to connect a powered tug and give the aircraft a pushback.

But yes, you can pushback using thrust reversers.


Why does the Aurora D8 have vents on the bottom of its fuselage? The Aurora D8 is a concept of an experimental aircraft (not an actual aircraft for now), described in this site. It's discussed in this question here on Aviation.SX.

I was watching the embedded video on the website I linked to, and it seems to show a couple of (intake?) vents on the bottom of the fuselage. You can even see this in the freeze-frame before playing the video.

What could these be used for? Do they suck in air for use in the engine? In the cabin? Elsewhere?

If you're talking about the dark spots here...

...then those are the tires of the main landing gear. This is the same approach used by the Boeing 737 — as discussed in another question here.

By skipping main landing gear bay doors, the aircraft's total weight is reduced. An aerodynamicist could provide a more confident answer, but the impact of the exposed wheels to the airflow would be relatively minor and not impact drag meaningfully.


What airport has this walkway over a taxiway? I saw this image posted in another question. What airport is this?

This image was taken at London Gatwick. The bridge connects two portions of the North Terminal, right next to where the North Terminal is labeled on this map:

London Gatwick claims to be the first airport to have such a feature. As can be seen in the photo, it is the largest in the world, high enough for a 747 to pass underneath.

This is not the only airport to have such a feature, though. Denver International also has a bridge (picture) over the taxiway connecting the terminal building with Concourse A. This one is not as high as the bridge at Gatwick and can't clear anything larger than a 737.