Why are aircraft tires not pre-spun prior to landing to preserve them?

This has been researched over the years, but it seems that the solutions did not find wide application. The oldest I could find is from 1941 (see page 112 in the September 1941 issue of Popular Science), and there have been several attempts to implement a spin-up turbine. See “Wheels with wings” on NewScientist Blogs or “Spin Wheels Before Landing”, a discussion thread on Eng-Tips forums, for more. The biggest problem seems to be the inertia of the spinning wheel because it makes the aircraft react in funny ways if the pilot wants to correct his approach.

The rough field package on the Cessna Citation 500 uses this technique (for the nose wheel only) to protect the fuselage from debris which could be kicked up by the wheel spinup.


There are a number of reasons why pilot don't use autoland all the time, even if the airport and aircraft are equipped with the right equipment.

To name the two most important ones:

Pilots need to practise their flying technique. If they would always
fly autopilot, they would lose the skills to fly. Skills that they
need when the autopilot does fail. There are phases of flight where
it is better or even required to let the autopilot do its job, but
landing is one the things pilot are allowed to and need to be capable
of doing themselves. Of course autoland needs to be practised as well.
Auto land requires very accurate ILS guidance. Even if the airport is
equipped with calibrated ILS Cat IIIb equipment (required for
autoland), the signals will be degraded by traffic that is operating
near the ILS antennas. Under low visibility circumstances, when
pilots cannot land visually, traffic spacing is increased and ground
vehicles are not allowed anywhere near the ILS antennas to ensure the
best possible signal quality. This is a standard part of the Low
Visibility Procedures (LVP) of all airports. The downside of this is
that the capacity of the airport is reduced. If autoland would be
performed while there is no ILS signal protection, the effects can be
spectacular at best or fatal at worst.

Photo by BFU, incident report here


How often are passenger oxygen masks deployed?

Very, very rare, probably in the range of sinlge digits per 100,000 flights (for major first-world airlines, perhaps higher elsewhere).

I'll try to get you a more numeric answer tomorrow.

Posting an answer now so that I can edit it, evem if the question gets closed between now and then.

"Opinion based", horsefeathers!


That’s going to depend on a lot of things including how well serviced the struts are, what the existing payload on the aircraft is and whether the aircraft is parked on any sort of grade.

I don’t work the A350, but I work other heavy aircraft and I’ve had them “settle” quite a bit when putting on a full fuel load.


Is a recoil start (hand propping) allowed if it isn't mentioned in the aircraft manual?

You didn't say exactly what "allowed" means, e.g. do you mean approved by the manufacturer, or legal in a certain country? But if you're asking is it legal in the US (under FAA regulations), then the answer is yes.

AOPA has a nice article on exactly this question, called Hand propping: A legal primer. It says:

  There is no specific FAA regulation that applies to hand propping an
  airplane, either to prohibit it or to direct how it is to be done

But:

  The FAA contends that hand propping is a two-person operation and has
  expressed this view in the Airplane Flying Handbook (FAA-H-8083-3A)
  under the section titled “Hand propping.” Of course, this publication
  is not regulatory, but the NTSB was surely influenced by it in a 1983
  legal decision. In that case, the FAA sought to suspend a pilot’s
  certificate for being careless or reckless when, while attempting to
  start a VariEze experimental aircraft, it “got away” and ran into a
  parked aircraft.

The NTSB concluded that the pilot had violated 14 CFR 91.13 (careless and reckless operation):

  The board affirmed the administrative law judge’s finding that there
  had been a 91.10 (now 91.13) violation

That means that hand propping itself isn't illegal, but doing it wrongly and against the FAA's general procedures could get you in trouble:

  There have been at least two previously issued NTSB (full board)
  decisions and one subsequent decision that refer to these generally
  accepted procedures and precautions for hand propping. The precedent
  has been set. So, hand proppers beware; if you fail to follow proper
  precautions and the airplane gets away, the FAA might pursue action
  against you for being careless or reckless.


Can an orienteering compass be used in place of a protractor?

From your description you are using the orienteering compass to measure course lines by aligning the side of the compass to the grid lines and using the dial to align with the course. There's no thing inherently wrong with this method, if done properly it will give you an accurate course. Personally I like the protractor better, but it is personal choice. You may have to explain what you're doing to an examiner later, I wouldn't imagine it would be disqualifying though, although you never know, some examiners are sticklers for that kind of thing.

However, before you throw away the protractor I suggest you put one hand behind your back and try to use your orienteering compass to measure a course. You see, at least in the UK you will be tested on your ability to divert, measuring a course using a map while also flying the airplane. That's where that kind of protractor comes into its own, and why I'd recommend you stick with it.


Is it allowed to launch powered paragliders from national parks?

FAA has the following informational web page for Alaska National Parks:
https://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/systemops/fs/alaskan/advisories/parks/

Which has contact information for parks where flight operations are periodically done.  Several of my pilot friends have used park and forest service airstrips with permission, so it is worth asking.  In Alaska, the parks are generally more open to aircraft, than in the lower 48.

There is also an advisory circular, 91-36C.  https://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/systemops/fs/alaskan/advisories/parks/media/ac91-36c.pdf

Some of the lower 48 have strips where permission may be granted, plus forest service has some strips (usually gravel) which permission may be granted to use.  Again, contact the park in question, because they often have local rules which are permissive.

State parks vary. Some states prohibit aircraft of any kind, others permit operations, usually situationally.

Paragliders are just one class of airman who are impacted by park policies. sUAS pilots are also impacted.

Regardless of what you are told verbally, I would only consider ops in a Congress Designated Wilderness with written permission. Those areas have a prohibition of mechanized devices, and that includes hang glider and sUAS activities.


Why does the J58 engine of the SR-71 have a diffuser after the inlet spike?

Generally, a compressor cannot work efficiently at supersonic speed due to the shockwaves, the role of the inlet cone and diffuser is to slow the air below Mach 1. There is a similar need for a ramjet, so that the combustion can occur within the engine and produce thrust.

The cone position and diffuser geometry are adjusted according to the airspeed. The overall shape of the diffuser is diverging.

From Bernoulli's principle, the diffuser decreases velocity and increases pressure according to:

$\frac 1 \rho \; dp = - \mathrm V\;d \mathrm V$ where $\rho$ is air density.

Look at this video: Converging Diverging Nozzles for more details about how pressure and velocity are affected in a nozzle / a diffuser. Here is a summary:

The J58 is turbojet within a ramjet. The forward section of the engine has a complex role. It adapts to a large range of speed (0 to Mach 3.2) and altitude (0 to 85,000 ft), and modifies the airflow to work either as turbojet, or as a ramjet, depending on the airspeed.

Simplified adjustment of the airflow (source).

Actual mechanism used at different airspeed ranges in the J58:

(Source)


It's your money. Spend it on someone you are comfortable with can have a good rapport with.


What can disqualify an airport to be used as an alternate?

As far as Part 91 ops go, paragraph 91.169 is the only IFR alternate requirement to my knowledge.

*Unless otherwise authorized by the Administrator, no person may include an alternate airport in an IFR flight plan unless appropriate weather reports or weather forecasts, or a combination of them, indicate that, at the estimated time of arrival at the alternate airport, the ceiling and visibility at that airport will be at or above the following weather minima:

(1) If an instrument approach procedure has been published in part 97 of this chapter, or a special instrument approach procedure has been issued by the Administrator to the operator, for that airport, the following minima:

(i) For aircraft other than helicopters: The alternate airport minima specified in that procedure, or if none are specified the following standard approach minima:

(A) For a precision approach procedure. Ceiling 600 feet and visibility 2 statute miles.

(B) For a nonprecision approach procedure. Ceiling 800 feet and visibility 2 statute miles.

(ii) For helicopters: Ceiling 200 feet above the minimum for the approach to be flown, and visibility at least 1 statute mile but never less than the minimum visibility for the approach to be flown, and

(2) If no instrument approach procedure has been published in part 97 of this chapter and no special instrument approach procedure has been issued by the Administrator to the operator, for the alternate airport, the ceiling and visibility minima are those allowing descent from the MEA, approach, and landing under basic VFR.*

**If you look in the front of the approach book (DOD or JEPP) it will list the 600/800' limitation for alternate designation.  I guess it's not in the UPT syllabus because the 11-214 (and the DOD for that matter) doesn't honor that specific alternate limitation.  FAR Part 135/121 ops might list other limitations that look like the "RVSM reqd, Wx reporting, GPS only, etc.)

-the queep monster....**


Can a small UAV restart its engine in mid-flight?

Some gliders have pop-up engines to extend range if they cant't catch rising air (known as turbo-sustainers) which start by in-flight windmilling, but I wouldn't count on it with an engine not designed to be started this way. Additionally, if the shutoff was not intentional it seems likely that whatever caused the engine to fail will make it even harder to start in this manner.


Consider that, without any hydrogen, the surface of the wing is coated in aluminum, a material with a sound velocity of 6,300 m/s. It's not the speed of sound on the surface of the wing that matters. It's the speed of sound in the medium it's passing through.

You are proposing a wing coated in hydrogen, but even if that could be made, it would still have to move the surrounding air out of the way. It is the "moving the air out of the way" that creates the mach effects.


Why aren't "radioactive items" allowed on flights?

Radioactive substances are potentially hazardous to people.

It is correct that many radioactive items would be perfectly safe to carry onboard, e.g. a key hanger with an alpha or beta particle emitter cast in acrylic, or a radioactive source for scientific purpose, if that source is properly packaged.

Glowing key hanger containing tritium. Image source: Nite GlowRing

Travelers usually do not carry radioactive items with them. If there is the need or wish to bring a radioactive item along, there is normally no need to have it in the hand luggage. This makes radioactive items different from lithium ion batteries. While potentially hazardous, there is a strong demand for lithium ion batteries on board. Banning them would essentially ban mobile phones and laptops.

Airport security staff as well as airline ground and cabin crew are neither qualified nor equipped to inspect and judge the safety of radioactive items. Opening the safe packaging of radioactive items might be dangerous. An item that cannot be opened cannot be checked if something else is hidden inside.

Finally, radioactivity stirs an irrational fear in many (if not most) people.

Given the need to restrict the transport of radioactive material somehow, and the difficulties in controlling it in a more sophisticated manner, the ban of such material from hand luggage seems comprehensible.


What's the advantage of using short wings rather than long wings?

Another reason to have shorter wings on high-speed or maneuverable aircraft deals with the aircraft's aspect ratio, which is the ratio between its length to is breadth/chord. Longer wings (high aspect) bend more under load, and may twist, which causes structural issues. Additionally, aircraft with shorter wings (low aspect) can roll much quicker. This means that a fighter jet with short wings may roll at rates up to 720 degrees/second while a large airliner or cargo plane may roll at 15-60 degrees per second.

A third reason is parasitic drag. From the linked wikipedia article above:

  While high aspect wings create less induced drag, they have greater parasitic drag, (drag due to shape, frontal area, and surface friction). This is because, for an equal wing area, the average chord (length in the direction of wind travel over the wing) is smaller. Due to the effects of Reynolds number, the value of the section drag coefficient is an inverse logarithmic function of the characteristic length of the surface, which means that, even if two wings of the same area are flying at equal speeds and equal angles of attack, the section drag coefficient is slightly higher on the wing with the smaller chord. However, this variation is very small when compared to the variation in induced drag with changing wingspan.
  For example, the section drag coefficient $c_d$; of a NACA 23012 airfoil (at typical lift coefficients) is inversely proportional to chord length to the power 0.129:
   $$ c_d \varpropto \frac{1}{(\text{chord})^{0.129}}.$$

Since parasite drag increases with airspeed, and high aspect wings have higher parasite drag, it makes sense for high-speed aircraft to have the wing that creates less drag at high speeds, and the slower aircraft to have the wing that creates less induced drag. You can see this in a simple graphic of the drag curves:

(Since the induced drag is lower at high speeds anyway, there is little point in minimizing that, rather minimize the type of drag that is a much larger factor at high speeds)


Why have different pattern altitudes for different aircraft?

Several possible reasons.

Speed differences between aircraft classes. Larger jets cruise and land at much faster speeds than single-engine props. Keeping their pattern separate from slower traffic minimizes problems posed by a faster plane entering the pattern behind a slower one.
Noise abatement. A jet, even a smaller private one at near-idle in approach, is loud. Keeping them higher increases the distance and number of thermal strata to shield nearby residents from traffic noise.
Prevailing instrument conditions and relative pilot experience levels. A ceiling below 1000 feet, the small craft pattern altitude, would ground VFR flights and thus drastically reduce the number of small craft in the first place. Jets, turboprops and other larger planes are much more likely to be IFR-capable (plane and pilot) and so they're placed higher because they can deal with clouds in the pattern (the airport, if towered, would likely alter pattern height to clear cloud layers but traffic holding above the clouds would still require an IFR approach).


How can an airplane keep going forward if it has no thrust?

Angle of attack is not equal to pitch angle. Yes you can decompose weight into a forward and a perpendicular component - to airstream! Or you can draw lift relative to airstream.

In this drawing, pitch angle is zero and AoA = 6 deg. Lift now has a forward component relative to gravity.


The CF-100 had a symmetrical NACA 0010 airfoil, which had a Clmax of just under 1.4. according to Airfoil Tools.com (Xfoil).  Is that what you are looking for?


Is there standard ticket data format specification for commercial flight operators?

IATA does have a standard for Boarding Pass Bar Codes that outlines a lot of encoding information and other things. This holds so long as you are not showing up to a Cuban airport in your own plane. There are lots of numbers and codes on boarding passes that mean all kinds of things. Ticketing systems may contain even more information than the boarding pass its self and that is up to the implementation of the system. The effective minimum set of identifying information is likely to be (more or less):

Departure airport code
Arrival airport code
Departure time typically a local time although most aviation things run on Zulu time in practice.
Seat number
Flight number (code share possible)
Date of flight
Passenger Name
Record Locator (Some kind of ID for the information)


What if you approach the VOR station such that your turn OB is not on the holding side?

The picture and your description do not really match. The hold represented is a standard, right-turn holding pattern. It is probably meant as a holding pattern of the missed approach. It is not meant as a holding pattern for before you travel outbound for your procedure turn. Based on the standardized format of IAPs, the right-most triangle is the Final Approach Fix. The left-most triangle is the Intermediate Fix. The VOR is an Initial Approach Fix. If, for some reason, you have to hold above the VOR prior to joining the approach, do so at or above the IAF altitude and intercept the outbound radial by continuing your turn after the outbound leg. I would warn against holding over VORs without ATC providing aircraft separation. VORs are busy airspace.

The IAF will have an altitude associated with it at which you can approach the IAF from any direction and be clear of obstacles. If one is not present, approach the IAF at or above the MSA. If that were not the case, the IAP would have a notation designating the IAP Not Applicable/Available coming from certain directions. For instance, flying from left to right on the picture, ATC would clear you to start the IAP at the IF (which can be designated on the chart as an IF/IAF) instead of the IAF (VOR). Aircraft flying from all other directions would fly to the VOR to start the IAP. The IAF, procedure turn, IF (IF/IAF), and FAF would all have their respective altitudes assigned to them in that order. Your profile view would start with the altitude at which you would need to stay above in order to start your procedure turn. If not, start at your MSA and descend down to the PT altitude.

Something else that comes to mind is checking the sectional and charts for the MSA and whether the IAF is a mandatory fly over fix. If it is not, turning onto the indicated radial in a way to intercept it prior to crossing over the VOR would expedite your IAP. Depending on your speed and original heading, you would start your turn a quarter to a full mile out before reaching the VOR or radial.

Also, “the protected side of a hold“ is a misnomer. There is no such thing. There is a holding-side and a nonholding-side. The entire area around the hold is protected airspace based on the dimensions of the hold. See the following question:
what are the dimensions of the protected space provided by a holding pattern


Is there a database of radio-frequencies for airfields/airports in Europe?

Try https://www.ead.eurocontrol.int/eadcms/eadsite/index.php.html . It is not a database but you have access to all AIPs from members of Eurocontrol .


Controllability and redundancy. Airliners are certified according CFR 14 Part 25, which specifies that upon engine fail the aircraft must still be able to fly and climb: it must have more than one engine.

After an engine has failed, the rudder must be deflected in order to compensate for the asymmetric thrust of the remaining engine. With a V-tail, this means that after engine fail, there is less pitch authority: pitch and yaw surface deflections are coupled. A V-tail has two control surfaces that combine aircraft yaw control and pitch control, which goes well until one of the surfaces hits a stop.

Reduced pitch control due to an engine failure would be unacceptable for an airliner. For a single engine plane with the engine in the centreline, this yaw trim condition would not happen.


Do check rides completed by part 141 schools with self-examining authority count like normal check rides for CFI renewal and gold seal?

No, check rides completed by a part 141 flight school with self-examining authority are not considered to be FAA checkrides for any purposes.

They do not count toward CFI renewal credit for maintaining an 80% 1st-time pass rate, and they do not count toward the requirement to obtain a gold seal CFI certificate.

My source is a direct answer from the chief instructor of a large part 141 flight school who received this information from the local FSDO.


Calculation of temperature correction for altimeter

Finaly i have found the answer the error is on all book that published the equation there is the true equation


When there is a holding pattern assigned by a civilian airports ATC, do military aircraft get first priority over landing?

Do military aircraft get landing priority?

If the government so wishes, yes. ICAO Doc 4444 says:

  7.6.3 Priority for landing

  7.6.3.1 If an aircraft enters an aerodrome traffic circuit without proper authorization, it shall be permitted to land if its actions indicate that it so desires. If circumstances warrant, aircraft which are in contact with the controller may be instructed by the controller to give way so as to remove as soon as possible the hazard introduced by such unauthorized operation. In no case shall permission to land be withheld indefinitely.

  7.6.3.2 In cases of emergency it may be necessary, in the interests of safety, for an aircraft to enter a traffic circuit and effect a landing without proper authorization. Controllers should recognize the possibilities of emergency action and render all assistance possible.

  7.6.3.3 Priority shall be given to:

    a) an aircraft which anticipates being compelled to land because of factors affecting the safe operation of the aircraft (engine failure, shortage of fuel, etc.);

    b) hospital aircraft or aircraft carrying any sick or seriously injured persons requiring urgent medical attention;

    c) aircraft engaged in search and rescue operations; and

    d) other aircraft as may be determined by the appropriate authority

Or c), if by military it's a search and rescue C-130 (for example) wanting to land to refuel and be on alert ASAP.

Now is it wise to put d) ahead of a)? Of course not. So if there is a prioritized government VIP, they will have to wait for the low-on-fuel emergency or the rogue-in-distress (first two paragraphs).

If it's a fighter, say an F-35, why would it land in Heathrow for example among civilian Jumbos? Unless of course it's been coordinated beforehand, or there is an emergency, then yes it will land first.

In the documentary Jetstream, RCAF F/A-18's flew from Canada to KLAX and landed there during heavy traffic, they were treated as normal planes when it came to the sequencing. It was part of their training to manage the complex aircraft in the heavy traffic environment of the civilian world.

You can watch it here. The narrator says (around 3:40):

  In Cold Lake an F-18 coming in to land is top priority, but here you are just another plane in a long queue.


What's the story behind U-2 flying from aircraft carriers?

From Wikipedia (emphasize mine):

At one time, in an effort to extend the U-2's operating range and to eliminate the need for foreign government approval for U-2 operations from USAF bases in foreign countries, it was suggested that the U-2 be operated from aircraft carriers. Three aircraft were converted for carrier operations by the installation of arrester hooks, and carrier-qualified naval aviators were recruited to fly them.
It turned out to be possible to take off and land a U-2 from a carrier. Testing in 1964 with the USS Ranger and in 1969 with the USS America proved the concept. The only operational carrier use occurred in May 1964 when a U-2, operating from USS Ranger, was used to spy on a French atomic test in the Pacific.
In 1969, the larger U-2Rs were flown from the carrier America. The U-2 carrier program is believed to have been halted after 1969.

It also provides the following resources:
http://www.kristinhillartist.com/FishHawk_article.html
https://theaviationist.com/2015/06/28/u-2-carrier-operations-story/


FAA Commercial Pilot Knowledge Test: Sign Question

This sign is a taxiway ending marker.  I retrieved this graphic from the CFI Notebook Website.


Why does Canada recommend a minimum rate of climb for ultralights of 300 ft/min?

When you fly gliders you discover it's quite common to run into air that's descending at 1-200 fpm, or "sink" in soaring-talk.  Descending air next to a thermal, or air descending due to downsloping terrain.  It's a lot more than that at times, but a couple hundred fpm is typical.

On a day where there's any convection (with rising air, there is always equivalent descending air adjacent to it) you are in sink quite a lot.  A 300 fpm ROC provides a reasonable assurance that you will be still able to climb while in most (but certainly not all) conditions of descending air, barely.

If you have an ultralight that can only climb 100 fpm, this might be fine on a smooth day with stable air, if you're patient.  If there is any vertical motion in the air however, you have a problem.  The minimum climb rate requirement is an attempt by the regulator to ensure that that average ultralight buyer will have a machine that won't kill him because it couldn't even out-climb a bit of subsiding air at the end of the runway.


It looks to me like the source site you quoted is unreliable or at least not current, e.g. it gives results for codes QQQ and ZZZ too, but they haven't been assigned by IATA. The actual IATA code for Mena (ICAO: KMEZ) seems to be MZX.

Anyway, there's no particular reason why XXX, ZZZ or any other specific combination should be assigned; they just haven't been used yet. There's also no reason why IATA should assign a code to every airport: the US alone has over 5,000 public airports but only 500 or so have air carrier service.


If the push was accidentally started with the brakes on, what will happen since these towbars don't have shearpins?

While it isn't desirable to try to push an airplane with the brakes set, nothing much happens if you try. Nothing moves, and the tow bar is so strong in straight compression/tension that it isn't likely to be damaged.

Problems are much more likely once momentum and moving tugs/airplanes get involved; that is when a sudden brake application is more likely to "break a towbar" (actually, a shear pin or coupling -- designed to let go before you damage the aircraft landing gear). But even that is a side-to-side failure mode, rather than pure compression.

To answer the edit to the question about "without shear pins": pushing straight back, same, nothing happens. If the aircraft applies brakes while being turned and the towbar can't break, then either the tug gets slammed to a halt, or else something gets damaged - probably at or near the point where the towbar connects to the aircraft. (Or possibly both happen.) That's bad... aircraft out of service, seriously expensive repairs, etc. Which is why shear pins ARE used in towbars. Repairing damaged towbars is far cheaper that repairing damaged aircraft.


What is an accurate expression to calculate IAS as a function of TAS?

You might look at Ed William's aviation formulary.

http://www.edwilliams.org/avform.htm#Mach

From there:

> The airspeed indicator measures the differential pressure, DP, between
> the pitot tube and the static port, the resulting indicated airspeed
> (IAS), when corrected for calibration and installation error is called
> "calibrated airspeed" (CAS).
>
> For low-speed (M<0.3) airplanes the true airspeed can be obtained from
> CAS and the density altitude, DA.
>
>   TAS = CAS*(rho_0/rho)^0.5=CAS/(1-6.8755856*10^-6 * DA)^2.127940
> (DA<36,089.24ft)  Roughly, TAS increases by 1.5% per 1000ft.

Note that you can go from TAS to CAS, but you will need help getting to IAS, specifically the instrument error for that AS indicator in that aircraft.


What is the background of the maximum altitude formula?

The formula can be derived equaling the weight ($W$) of an airplane with the maximum lift ($L$) generated by its wings. I'm not aware of any special name for it.

$$ W = L \\
m\cdot g= \frac{\rho_{min}}{2}\cdot V^2\cdot S\cdot c_{L,max}$$

Substituting the aircraft's speed with an expression containing the Mach number ($a$ is the local speed of sound),
$$V=Mach \cdot a$$
and solving for the density you get the formula in Peter's answer:

$$\rho_{min} = \frac{2\cdot m\cdot g}{(Mach^2 \cdot c_L)_{max}\cdot a^2\cdot S}$$

At high speeds the maximum lift coefficient is not constant. That's the reason why the Mach number and the maximum lift coefficient are written together in one term: $(Mach^2\cdot c_L)_{max}$. In order to fly as high as possible this term has to be maximized.

With supercritical airfoils you generate less drag and can therefore fly at higher Mach numbers, increasing this term.

I don't think the value 0.4 is a physical limit. Probably it is just an empirical value which takes many real-world constraints into account (if there is a physical limitation I'd be glad to read an answer explaining it). If you calculate $(Mach^2\cdot c_L)_{max}$ using U-2's data you get indeed a value close to it.


A friend sent me this. Thanks for the answers.

Gull-wing by Werner Siemens, Germany 1847.


How do thrust reversers in high-bypass turbofan engines counteract initial thrust?

There are several ways to describe thrust, which amount to the same thing. Very broadly, it's described by Newton's third law: if A moves forward, B moves backward with equal momentum. On a closer level, it comes from pressure differences across the surface of a body. Even closer, you'd be looking at viscosity and velocity, laminar and turbulent flow, boundary layers, analytical equations.

But all these ways come to the same result: if one, applied correctly, predicts result X, the rest can't predict an opposite result. In the most basic view, the reverser's thrust comes from pushing air forward. As long as the ultimate result is air being accelerated in some direction, however it happens, the thrust will be in the opposite direction.

If you want to get into the mechanics (which isn't quite necessary), the exhaust produces high pressure between the engine and the thrust reverser. This pressure acts on the thrust reverser's inner surface. The resulting backwards push is indeed greater than the fan's forward thrust.


Why do airplanes not have manual transmission?

Aircraft have fixed gears (when they have gears at all)! However in a sense a variable-pitch propeller can be considered analogous to transmission in a car and it was manual in some aircraft.

The power transmitted by propeller is, within some reasonable range, proportional to its rotation rate. And so is, again within some reasonable range, the power produced by the engine. So for slow planes a fixed pitch propeller with connected by fixed gear does a decent job. As you open the throttle, the engine speed increases, so does the propeller and that's exactly what it needs to do to transmit the power. Simpler aircraft have no gears at all and propeller is mounted directly on the engine shaft, higher power engines often have 2:1 reduction gear as the engine rpm would be too high for a propeller.

Now at higher speed, the apparent propeller pitch is reduced as the air is already moving, so it would spin faster and faster and eventually too fast for the engine. To counter this, faster propeller-driven aircraft have variable pitch propeller. As speed increases, it is set to higher angle of attack (coarser) so it keeps delivering power without increasing rpm.

Early variable pitch propellers had manually controlled pitch, but quite quickly constant speed propellers were developed (many WWII aircraft had them already) where a weight-on-spring controls the propeller pitch so that constant rpm is maintained. The manually controlled units required a lot of attention and the constant-speed system is rather simple, so manual pitch control was quickly abandoned.

And that is kind of equivalent to perfect variable gear transmission. The pilot still has a throttle lever and a propeller pitch lever and selects power and rpm independently. Higher rpm allow higher power, but don't require it, so landing is usually done with low power, but max rpm so the engine reacts quickly if power is added (does not need to spin up). During cruise some more moderate value is selected (according to manufacturer recommendation) to reduce wear of the engine.

Turboprop engines always have constant-speed propellers, because in a turbine engine the difference between turbine speed at idle and at full power is not actually that big. Again the rpm limits maximum power, so landing is done with low power, but high rpm and the engine reacts quickly when power is added.

Last the turbojet/turbofan engines just turn the turbines and compressors as they need. It's not much different from the fixed propeller really, though the jet engines now usually have variable guide vanes in the stator (that are just linked to rpm).


What is the cause of cracking and corrosion in Trent 1000 engines?

The problem is sulfidation corrosion, according to this article:
https://airinsight.com/rolls-royce-trent-1000-corrosion-issues/

Turbine blades are made of metal, and they suffer temperatures and forces so high that they are usually 'grown' from a single metal christal. A single blade can cost as much as a luxury car.

The problems also seem to be related. Corrosion leaves a little pit, which turns in to a crack due to the cyclic loads.


What are magnetrons installed on aircraft used for?

The magnetron is a high-powered vacuum tube, that works as self-excited microwave oscillator. They are used mainly in radar transmitters as either pulsed or cw oscillators at frequencies. In (civil) aircraft, they are mostly used in weather radars.

They have relatively simple construction but have been replaced in almost all aircraft due to their disadvantages:

They can usually work only on a constructively fixed frequency.
They have poor reliability.
They have high power consumption and have noise issues.
They have finite life, considerably lesser than solid state devices.

Most of the aircraft operating today use solid state devices in their Radars. It may be still used in some older aircraft and helicopters, but they are becoming increasingly rare.

Weather radars are regularly used by pilots to detect the weather conditions in front of them. According to Airbus Flight Operations Briefing Notes: Optimum Use of the Weather Radar The weather radar only detects:

Rainfall
Wet hail and wet turbulence
Ice crystals, dry hail and dry snow. However, these three elements give small reflections compared to water droplets.

It does not detect clouds, fog or clear air turbulence.

Most of the aircraft in the list were designed 25+ years ago and have (mostly) switched over to solid state devices. Aircrafts are rarely used after 30 years as maintenance becomes expensive.

However magnetrons are still used in some aircraft due to their simple construction and high power output. For example, the WU-880 Radar Receiver Transmitter Antenna in Honeywell Primus 880 radar used in Falcon 2000EX uses magnetron.

Note: Almost all commercial aircraft use convection ovens to heat food (they won't have aluminum foils if they microwave ovens were being used); however, microwave ovens are available for aircraft and are used in some executive aircraft.


Why do (almost) all military transports have high wings and civilian transports low wings?

For military transport aircraft:

Wings further off the ground will mean that the engines will also be further off the ground, reducing the risk of foreign object damage.
You can move vehicles under the wing, and taxi across smaller taxiways.
The fuselage can be closer to ground, facilitating transport.
No wing spar crossing the cargo floor.

Reasons why most commercial transport jets don't have it:

Many are converted passenger jets.
They are mainly pallet loaded, less vehicles and bulky objects.
They normally use prepared airports, which military jets cannot assume they will.
They often loaded from a side door, and it makes little difference I think if you go up one meter or three meters.

  but then why do civilian aeroplanes hate this design?

Airlines don't 'hate' this design, look at the BAe146 Quiet Trader for instance. It's just not that many commercial aircraft from which cargo jets are derived are built this way.

  Except in the erstwhile USSR, I haven't really seen high-winged military aircraft being used as civilian airliners (Boeing 737 size and beyond), though I can't think of any reasons why not.

Military jets are very expensive to operate and the east block Antonov 124 probably satisfy the most demand. There are a few commercial C130 (L100) around though. It's also not like the US airforce will give us C-5 Galaxy to a commercial company to do whatever it wants with it.


If the Captain's screens are out, does he switch seats with the co-pilot?

If the plane is on final approach and the pilot flying loses his displays the co-pilot (who is also rated to fly the aircraft) may take over. Perhaps more importantly the system is built to avoid this. The "screens" you mention are independent and both (2 screens per side) are capable of displaying the primary instrumentation/information, a situation where both fail simultaneously and completely is rare.

All screens in the cockpit are generally visible from both seats, any pilot who was a former flight instructor (and many likely were) has plenty of experience viewing instrumentation from the opposing seat. Flying and landing like this should be of little issue.

In good weather to land an airplane the most important instrument is the airspeed indicator (and perhaps angle of attack indicator if you have one). With that in mind the pilot flying may continue the approach if the backup instruments are still working and in view, that is after all why they are there.

Some airline operational specs may have specific procedures for this as well but as far as I know the FAA does not really have anything to say on the matter.


What are the differences between top and bottom mounted airbrakes?

Since airbrakes are frequently used during landing, putting them underneath the fuselage could create a ground clearance problem.

Putting brakes on the top only would create a pitch-up tendency when they are deployed. This is countered automatically by the Fly-By-Wire flight controls, so no correction is necessary for the pilot.


Rotation direction for adjacent propellers, how do different arrangements compare?

Initially during A400M development (when the project was still called FLA), all propellers were supposed to spin in the same direction. The reason for this was the objective to use a single engine in order to minimise logistics costs.

Windtunnel tests soon revealed that the prop wash would create asymmetric flow on the wing, causing uncontrollable rolling moments in low speed flight. Only two options allowed to remedy this:

Use of counter-rotating propellers, like on the Progress D-27 powering the An-70.
Use of two variations of the same engine with opposite direction of rotation.

Counter-rotation resulted in heavier propellers and gearboxes, so it was decided to go with the second option. The exact direction of rotation for each engine was then determined in further wind tunnel tests, with low-speed handling and maximum lift coefficient the determining objectives.


On a bypass engine does the bypass air travel faster or slower than core air?

The simple way to think of it is the bypass engine is kind of part way between a pure jet and a turboprop.   In a nutshell, the pure jet moves a little bit of air a lot; the turboprop's propeller moves a lot of air a little, relatively.  In other words, small mass at high velocity vs large mass at low velocity, to get the same push.

A bypass jet engine is somewhere in between.  It's just a fixed pitch non-geared turboprop with 30 or 40 blades, in a shroud, instead of 3 or 4 variable pitch blades in the open (geared turbofans get even closer to the "fixed pitch turboprop" thing).

The package of air being accelerated is smaller than a propeller, but much larger than a pure jet, so fan's exhaust velocity is also in between; faster than the wash of a propeller, slower than the exhaust of the core.


Why are cockpit voice recorders limited to 2 hours recording?

Aviation manufacturers generally design the equipment to comply with legal requirements. Under FAA two hours is what is required by law.

14 CFR  121.359–Operating Requirements:  Domestic,  Flag,  and Supplemental  Operations–Cockpit  Voice  Recorders
(i)  By  April  7,  2012, all  turbine  engine-powered  airplanes  subject to  this  section  that are manufactured  before  April  7, 2010, must  have  a  cockpit  voice  recorder  installed that  also—
(1)  Meets  the  requirements  of  §23.1457(d)(6)  or  §25.1457(d)(6)  of  this  chapter, as  applicable;
(2)  Retains  at  least  the  last  2 hours  of  recorded  information using  a  recorder  that  meets  the standards  of  TSO-C123a,  or  later  revision;  and
(3)  Is  operated  continuously  from  the  use  of  the  checklist  before  the  flight  to completion of  the final checklist at the  end  of  the  flight.
(4)  If  transport  category,  meets  the  requirements  in §25.1457(a)(3),  (a)(4),  and  (a)(5) of this chapter.
[The following section has the same requirements for aircraft manufactured after April 7, 2010.]

The flight data recorder is required to retain 15 hours worth of data.
FAA allows pilots to erase anything on the CVR recorded 30 min (in some cases 15 min) prior. This is probably something that was negotiated between the NTSB and the pilots union to protect the pilots' privacy.  Since it's written into the statute that way I assume modern digital CVR'S must have a function to erase everything but the last 30 min. (@OSUZorba there's that word again)

14 CFR  121.359 (f)  In  complying  with this  section, an approved  cockpit  voice  recorder  having  an  erasure feature  may  be  used, so that  at  any  time  during  the  operation of  the  recorder, information recorded more than  30  minutes  earlier  may  be erased  or  otherwise obliterated.

This was most likely in response to the 1979 incident that occurred on TWA flight 841 where the pilot was accused of improperly extending flaps during cruise but had erased the CVR when they landed,  so they had no proof. At the time CVR's were still fairly new and pilots balked at having their conversations recorded for privacy reasons, so it was common practice to erase it after each flight. There is still some concern over privacy issues since in some situations the recording can open the pilot up to legal liability.
There are really only a handful of cases where a longer recording would have been useful, most of which involved pilot incapacitation. In 2014 EASA proposed extending the requirement. The European Cockpit Association, which represents pilots released a position paper .pdf stating that they would only support the extension if there were also systems in place to ensure that only the pertinent portions could be used and any other conversation could not be leaked to the public or used in jurisdictions where there are no legal requirements to maintain pilots' privacy.

ECA  stresses  the  following:

Pilots  submit  to such  recording  under  the  strict  condition  that  the  CVR  data is  to be  used exclusively by  accident  investigation authorities in  the  context  of  their  safety  investigations.  Pilots  are  one of  the few  professions  that  agree  to  being  recorded  at  their  workplace  and  the  consequent  infringement  of their  privacy

National  and  European  legislators  recognise  the  need  to  protect  CVR  recordings  (Reg.  996/2010). However,  despite  various  legal  provisions  at  EU  and  national  level,  as  well  as  best  practices  in many  airlines,  CVR  data  or  their  transcripts  have  too  often  leaked  to  the  public  and  media , exposing  data  with  private  and  personal  content  –  sometimes  the  last  minutes  of  the  crews’  lives  – to  a  wide  audience,  generating  speculation,  interpretations  and  apportioning  blame  –  in  a  way  that may  be  far  removed  from  what  actually  happened,  what  contributed  to  the accident  and why.

This  inappropriate  use  and  distribution  of  sensitive  CVR  data  beyond  accident  investigation agencies  negatively  affects  Just  Culture  and  the  safety  improvement  efforts  in  Europe.  Extending CVR duration would increase the  quantity  of  data  available for  misuse  significantly.

Leaking  of  CVR  data  results  in speculation that  increases  the  pressure on  accident  investigators,  on the  judiciary  to  act  quickly  to  hold  accountable those  ‘responsible’,  and  on  other  authorities  or  public figures  to  come  up  with  quick  answers,  rather  than  waiting  for  the  Final  Report  to  be  published  and generating  mature  safety  improvements.

Increasing  CVR  duration  would  also  increase  the  data  that  is  potentially  available  to  the  airline management.  While   many  companies  in  Europe  have  internal  procedures  –  and  sometimes agreements  with  the  pilot  representatives  –  in  place  to  ensure  sensitive  data  is  not  misused,  this  is not  the  case  for  all  companies.  Hence,  an  increased  recording  time  –  combined  with  very  powerful digital  storing  facilities  and  the  possibility  to  cross-check  CVR  and  FDM  data  –  would  also  increase the  scope  for  (un)intentional  (ab)use  of  such  data  by  company  management  for  other  than  safety purposes  (e.g.  any  form  of  disciplinary  measures).  Although  this  would  not  be  in  line  with  EU legislation,  not  all  airlines  are  as exemplary  as  some,  and not  all  legislation is adequately  enforced.

Increasing  CVR  duration  on  European aircraft  also increases  the  risk  of  CVR  data being  used  –  and potentially  made  public  –  by  non-European  authorities,  which  are  not  bound  by  EU  legislation  and the  protections  contained  therein.  This  is  the  case  especially  for  long-haul  operations  (at  which  an increase  of  the  recording  time  is  actually  aimed)  where  the  majority  of  the  flight  is  outside  Europe.  If an  accident  happens  outside  Europe,  the  national  safety  and  judicial  authorities  will  be  entitled  to seize  the  CVR  and  will  be  bound  by  their  own  local  laws,  by  local  political  considerations,  and general  public  pressure.  –  This  would be  an  unintended  –  but  very  real  –  consequence  that  must  be taken  into  account.


Where can I find a flight log archive for commercial flights?

Under the Freedom of Information Act you can request these records from the FAA. Please read more about doing so here:
http://www.faa.gov/foia/foia_request/


What is the effect of a taildragger on P-factor?

By inclined, do you mean that the conventional (taildragger) landing gear configuration angles the propeller? If that is in fact your question, know that the propeller is not “inclined” in flight any more than a tricycle landing gear aircraft. Straight and level is basically (very roughly) the same between the P-40 and the SR-22. And, P-factor is only induced when the aircraft has sufficient forward motion. At very low airspeeds, there is hardly any P-factor.

In a conventional (tail-dragger) landing gear aircraft, once you are above the customary taxiing speed (the sufficient airspeed mentioned earlier), you pitch the nose forward. This raises the tail. In effect, you eliminate the “incline” in question. You are, at that point, almost flying the aircraft as if it had tricycle landing gear.

The conventional landing gear was the norm in those days. And, they were more conducive to landings on unimproved runway surfaces. Although, the conventional gear is more advantageous on non-hardened surfaces. Its biggest disadvantage is its difficulty in steering at low speeds. The lack of a steerable nose wheel means you must rely on differential braking only at low speeds and the rudder at medium to high taxi speeds.

This leaves you prone to what is called ground loops. A ground-loop is caused by the center of gravity being positioned behind the point of lateral rotation (the main landing gear in this case). Any over use of differential braking or miscalculation of the leverage applied by the long leverage arm of the rudder can cause the aircraft to violently and uncontrollably spin around. Think of trying to steer your car while driving at high speeds in reverse.

The old adage is that you have to fly a taildragger from the moment you leave the hangar till the time you park it to put it away. Tail-draggers require you to be a lot more adept on the rudder.

It also leaves you vulnerable to prop strikes due to nothing stopping the nose from over-pitching. Something very easy to do by applying the brakes too hard during roll out from landing.


How is human waste taken care of on commerical aircraft?

Human waste from the lavatories is collected on-board and later disposed of at the airport after landing.

(Image Source: WikiMedia Commons - Author: Mnts)

Check out this related question here on Aviation.SE:
Where does my pee go when I flush at 35,000 ft?


What main landing gear actuator does the Boeing 777-300ER have?

The Boeing 777-300ER is the only variant of the 777, which has a Semi-Levered Gear. From the 777 FCOM (v2 14.20.3 Landing Gear - System Description):

Semi-Levered Gear
[777-300ER]
The semi-levered gear consists of an additional hydraulic actuator that connects the forward end of each main gear truck to the shock strut. During takeoff, the actuator locks to restrict rotation of the main gear truck and allow takeoff rotation about the aft wheel axle, thereby improving airplane performance capability. During landing, the actuator is unlocked to permit rotation of the main gear truck and provide additional damping.

The 777-300 and 777-300ER are both equally long at $ 73.86 \, \mathrm{m} $, which is about $ 10 \, \mathrm{m} $ longer than the -200 variants. Due to the higher risk of tailstrikes, both variants are equipped with a Tail Skid:

Tail Skid
[777-300 and 777-300ER]
The airplane is equipped with a tail skid system. The tail skid extends for takeoff and landing and retracts during flight. It helps protect the pressurized part of the airplane from contact with the runway. The tail skid uses the main lading gear actuation system.
The EICAS advisory message TAIL SKID is displayed when the tail skid is not in the correct position.

The -300ER however has a MTOW (maximum takeoff weight) of $ 352 \, \mathrm{t} $ compared to only $ 299 \, \mathrm{t} $ for the -300, which increases the risk of a tail strike during takeoff rotation.
This Boeing article explains it as follows:

The Boeing 777-300ER's new semi-levered landing gear system has performed flawlessly during the flight-test program. The unique gear, which is manufactured by Goodrich Corp., allows the airplane to rotate early by shifting the center of rotation from the main axle to aft axle of the three-axle landing gear truck. As the airplane rotates, the nose is allowed to rise higher earlier.

You can see the difference here:

(image source: airliners.net and youtube.com)


When calculating the lift coefficient,should I use only the lift provided by wings, or also the net upward forces of the entire aircraft?

If you want the lift for the whole airplane, of course you add the contributions for each part. While the fuselage might indeed contribute a positive lift, its presence will lower the lift of the wing. In the end, all parts of the aircraft will stick together when it flies and need to create just enough lift to keep its mass airborne, so it makes sense to look at the sum of all parts.

Since the wing will dominate lift, it is common for first-order calculations to consider the wing only. However, if you have data for all parts, you should include all their contributions, too, for a more precise result.


What causes the distinct sounds of a jet engine?

There are several dimensions to the answer on this topic.  First, consider that different flight profiles (TO, approach power, final approach power, etc) will have different engine acoustic signatures.  The sound output from a jet or turbofan is not linear with power, rather it changes with power level, and resulting flows and RPMs. Second, consider that the polar acoustic radiation is different for the aircraft. Nose down vs nose up, banked, etc. and consider that these radiation patterns are changing with respect to power. These are the primary noise factors.

Secondary noise factors include APU operation, and airframe noise. The airframe noise is greatest with airspeed which impacts boundary turbulence energy, and then with gear extension, and flap/slat/spoiler extension and slips.

To this complexity add airspeed, and aircraft configuration.

Different engines have decidedly different spectral content, and some are quite characteristic.

The bulk of the engine noise is exhaust turbulence, and quite specifically the differential of the exhaust velocity and the ambient flow.  This is why turbofan engines are much more quiet, because they have a more gradual gradient between the ambient flow, and the jet flow.

Whines are often forward directed radiation and are largely acoustics from the intake, and most specifically from fans on turbofan engines.

There is a plethora of literature on A320 engine whine and solutions with different engines.

There are also some specific airframe noises.  For example, the same aircraft, the A320 has some open vents on the lower wings, and the addition of vortex generators has been shown to reduce this noise substantially (up to 11db, which would be perceived as half the noise, and is a more than 99% acoustic energy reduction.  Some A320 aircraft can be heard from 30 miles away.

To address your questions, the roar is mostly engine noise.  The whine is also engine noise, but can sometimes, on some aircraft be port or acoustic flutter noise.  The buzz noise is normally airframe or to a much lesser degree airframe and engine interactions.

Apart from civil aviation there has been a lot of work done, and thousands of papers written on acoustic signatures of aircraft. There are various sensors equipped with correlation software which will classify aircraft in the air, from the ground. Aerospace contractors work hard to reduce the signatures of every aircraft from large transport to fighters. Civil aviation responds to different threats, which are the public complaining about noise associated with airports near cities.


How is maximum payload determined in the payload-range diagram?

Aircraft also have a Maximum Zero-Fuel Weight (MZFW). This defines the aircraft's maximum weight without any fuel loaded. A large aircraft certainly would not be able to fly with only 10lb of fuel on board,
so structures like the fuselage are designed to carry a lower payload.

For example, the Boeing 777F freighter has a maximum takeoff weight of 347,814kg. The type certificate lists the MZFW as 248,115kg, which leaves almost 100,000kg for fuel out of the max fuel capacity of 145,538kg. This is a large increase from the passenger version (777-200LR), which has a MZFW of 209,106kg with only slightly lower MTOW.

See also: What are different types of weights of an aircraft?


How can an up-lifting tail have normal force direction and gradient when generating UP force?

Let me break it down in sections. It's rather long I'm afraid.
1. Tail lift direction
Consider the following diagram of a wing-body and tail combination, with a non-pitching aircraft in steady-state. Let's assume that a true wingbody mean aerodynamic centre ($h_{n_{wb}}\overline{c}$) exists and therefore the pitching moment does not vary with AOA at that point.

Image ref: Etkins, Dynamics of Flight
The pitching moment for the whole aircraft about every point must be zero. Let's pick the point of CG ($h\overline{c}$) to sum our moments, since it also corresponds to the point of rotation for a free-body (this equation can be found in Etkins, Dynamics of Flight, but its derivation is simple and you should be able to deduce it from first principle):
$$C_m = C_{m_{ac_{wb}}} + C_L(h-h_{n_{wb}}) - \frac{\overline{l}_t S_t}{\overline{c} S} C_{L_t} = 0$$
where $C_m$ is the total pitching moment, $C_{m_{ac_{wb}}}$ is the wingbody pitching moment coefficient about the MAC, $C_L$ is the total lift coefficient (wingbody + tail), $C_{L_t}$ is the tail lift coefficient normalized over the tail surface area ($S_t$), $\overline{l}_t$ is the distance from the tail MAC to the wing MAC, and $\overline{c}$ is the wing reference chord.
The sign of the tail lift, $C_{L_t}$, to make the above hold can be either positive or negative, depending on the relative contribution of each of preceding terms. Note two facts:

For a positively cambered wing, $C_{m_{ac_{wb}}}$ is typically negative.
$C_L$ is positive for 1G flight.

Consider some extremes:

If the CG is way ahead of the wing MAC ($h \ll h_{n_{WB}}$), then the second term will be very negative, and $C_{L_t}$ must be negative to compensate. That is, negative tail lift.

If the CG is behind the wing MAC ($h > h_{n_{WB}}$), and $C_L$ is very large, then $C_{L_t}$ must be positive to compensate. That is, positive tail lift.
Furthermore, if the CG is behind the wing MAC, then there will always be an AOA above which the trimmed tail lift becomes positive, assuming stall does not occur.

2. Neutral point
Neutral point ($h_n\overline{c}$) is the longitudinal position at which the aircraft does not experience any pitching moment with a variation in AOA or $C_L$ (in another word, NP = MAC of the aircraft). If the CG is ahead of the NP, the aircraft will experience a pitch down moment with increasing lift (statically stable); and vice versa for unstable.
I will cite the following result, once again from Etkins (but simplified):
$$h_n = h_{n_{wb}} + \frac{a_1}{a} \frac{\overline{l}_t S_t}{\overline{c} S} \left ( 1 - \frac{\partial \epsilon}{\partial \alpha} \right )$$
where $a=\frac{\partial C_{L}}{\partial \alpha}$ is the total lift slope of the aircraft, $a_1=\frac{\partial C_{L_t}}{\partial \alpha_t}$ is the isolated lift slope of the tail, $\epsilon$ is downwash from the wing on the tail.
Note that the second term is always positive. Therefore, the CG can be behind the wing MAC, yet ahead of the NP.
3. Elevator hinge moment and stick force
For a reversible aircraft where the column is directly connected with an elevator, stick force gradient is directly conferred by the aerodynamic hinge moment on the elevator (let's assume there is no down-spring or bob-weight for simplicity).
For a non-cambered tail, there are two main contributions:

Hinge moment due to flow incidence ($b_1$)
Hinge moment due to elevator deflection ($b_2$)
Hinge moment due to trim tab ($b_3$)

You are right to point out that if a tail is lifting, and its flow incidence increases with aircraft AOA, then there will be increasingly TE up HM on the elevator, which would imply instability. However, static stability ensures that there is increasing TE up elevator needed to trim for increasing AOA, which will add TE down HM on the elevator.
The details are more nuanced than the above, and it will involve airspeed since HM is squared to airspeed, but it can be shown that the stick force reversal only happens when the CG is aft of the stick-free neutral point ($h_n^{'} \overline{c}$), and not at neutral point:
$$h_n^{'} = h_n - \frac{b_1}{b_2}K$$
where $K$ is a positive constant that is a function of the aircraft geometry (I've simplified from eqn 2.6.13 from Etkins). As you can see, if $b_2$ (HM due to elevator deflection) overpowers $b_1$ (HM due to flow incidence on tail), then we pretty much recover the NP. Down-spring and anti-servo tabs are some methods to increase the $b_2$ artificially.
More specifically, please consult the following figure, adapted from Bromfield, Factors affecting the apparent longitudinal stick-free static stability of a typical high-wing light aeroplane and Etkins, Dynamics of Flight:

In the graph, $\delta_t$ is the trim tab deflection.
Observations:

The first two curves are with the tab always set to 0 incidence against the elevator. The movement of the CG purely shifts the stick force vs. V curve up and down. When the CG is aft of the stick-free neutral point ($h>h_n^{'}$), any steady-state speed would require a pull force (despite the stick may be forward of neutral if the CG is still ahead of the neutral point!)

The last two curves are with the tab set for a trim speed ($V_{trim}$). Now, when the CG is aft of the stick-free neutral point, the stick force gradient also goes unstable! What effectively happens when the CG coincides with the stick-free neutral point is that the hinge moment contribution from the elevator+tab cancels that from the tail AOA; therefore, zero steady-state force is needed to hold any particular elevator/stick position.

Either way, whether the tail is lifting doesn't dictate the stability of the stick force vs. airspeed.


How to convert IAS/CAS to TAS up to Mach 3?

For higher airspeeds, TAS is always calculated based on the Mach number:
$$
\mathrm{TAS} = M \cdot a_0 \sqrt{\frac{T}{T_0}}
$$
where $ a_0 $ is the speed of sound at ground level ($ a_0 \approx 661 \, \mathrm{kt} $) and $ T_0 = 288.15 \, \mathrm{K} $ is the temperature at ground level. This formula is just based on the fact that the speed of sound in air is proportional to the square-root of the temperature.

How to calculate the Mach Number

Now, we need to distinguish between subsonic and supersonic flow. The pitot tube will give you the ratio of impact pressure $ q $ and static pressure $ p $. From this ratio, you calculate the the Mach number:

subsonic flow:
$$
M = \sqrt{5 \left( (q/p)^{5/7} - 1 \right)}
$$
supersonic flow:
$$
M \approx 0.8813 \sqrt{\frac{q}{p} \left( 1 - \frac{1}{7 M^2} \right)^{5/2}}
$$
This equation needs to be solved iteratively.

The following plot shows the Mach Number as a function of the $ p / q $ ratio (red for subsonic flow, blue for supersonic flow):

Calculate the True Air Speed

Now that we have the Mach number, we need to calculate the TAS using the formula from above. The last missing piece is the static air temperature $ T $, which can be calculated from the measured total air temperature $ T_\mathrm{tot} $:

$$
T = \frac{T_\mathrm{tot}}{1 + M^2 / 5}
$$

This gives the final answer:

Unfortunately, there is no easy way to calculate this based on KIAS as an input. You will need the ratio $ q / p $ and the temperature $ T_\mathrm{tot} $ as measured by the aircraft.


What does the condition lever in turboprops control?

Shamelessly quoting from Skybrary: (emphasys mine)

  A Condition Lever is a pilot actuated control which is located within
  the throttle quadrant of a turboprop engine equipped aircraft. It is
  utilised to control some functions of both the propeller and the
  engine. These functions vary from installation to installation.

  Functions of the condition lever can include any of the following:

  Fuel cut-off.
  Propeller feathering.
  Propeller un-feathering.
  Low idle/high idle selection.
  Propeller speed control.


Do Blue Angels jets have a snap-to-angle feature in their control sticks?

Short answer: No.

Long answer: No way!

This would be a feature which pilots would never accept and for good reasons.
There are many instances where you want to fly at a slight angle to exactly horizontal or vertical to make corrections. Just think of flying an approach with crosswind.

The designers have made the cockpit glazing transparent to enable the pilot to check and adjust his/her attitude, and this feature works really well. There is no need to add something which will be in the way of proper flying at some times.

What you do find sometimes on small aircraft with manual controls, however, is a trailing edge modification which helps with centering the rudder and/or the ailerons. See below for an example: This is the tail of the Klemm 35, and the rudder has two narrow strips which are deflected slightly to the left and the right, respectively. This increases the force gradient over deflection for the first few degrees when the rudder is moved away from its centered position.

Klemm 35 tail detail (own work)


How to avoid getting trapped on top VFR?

By regulation you just have to be sure that the conditions at destination allow you to maintain VFR clearance from cloud for your descent.  Pretty much all you have to go on is the TAF for the area of your destination.  If there isn't a TAF for an airport within say 20 or 30 miles from destination that would be a problem for me.

Assuming a TAF is available, you technically could go if the forecast was for broken cloud below you, hoping for a large enough hole to get down (basically a hole at least 4000 feet across, with you in the middle of it).  But that's taking a bit of a risk.

It would be imprudent to go with anything more than scattered cloud in the TAF at any level below you at the time of your planned arrival.  And even scattered cloud in late afternoon is pushing it.  On top of that you are continuously monitoring the METAR at destination for detrimental changes, and you also have a planned alternate that has better forecast conditions than your destination.

One of the more important factors to keep in mind on a trip like that is the temperature/dew point spread at destination (which will determine the cloud base if there is enough humidity), and the time of day.  When I was bush flying in Northern Ontario many many years ago, with many hours spent scud running under low cloud, the dew point spread was the most important bit of weather information and a tighter spread was more acceptable in the morning than in the afternoon.

A morning trip, with a decent temp/dew point spread that makes unexpected cloud formation below your level unlikely with temperatures naturally destined to increase until early afternoon, is lot safer than an afternoon trip where the spread will be decreasing and more-than-forecast cloud formation at a level below you is more likely.

Personally, I would never do VFROTT because I'd be biting my nails the whole time worrying about the engine quitting (I've had a mechanical engine failure) and being forced to descend through a cloud layer and then trying to find a landing area underneath it, if there was a decent ceiling.

And there's the rub; you not only have to come up with good weather margins, you have to have iron clad confidence in your engine if you're doing it in a single (which lots of single-engine IFR pilots do - me not so much).


Why doesn't the air force order more F-22's?

Aside from Juan's point about the F-22 being fairly outdated by now (it's an 80's era design), it is also not possible to just restart production of it.

First, it would cost ~$10Bn to simply get to a place where you can produce the an F-22 again. That doesn't include the actual cost of a single plane, just the money required to re-equip factories, train workers, produce a new engine since the old one is end-of-life, etc. Source

This estimate is assuming that the project was left off in the state Lockheed claimed it was. There is reason to believe that some of the tooling for the F-22 no longer exists at all. Source

Finally, the F-35 program has, in my opinion, shown that there is not so much to be saved by re-using components if the overall process is not efficient.


Why is the magneto drop check done at 1700 RPM?

According to this article from the New Zealand CAA:

  The particular rpm setting at which the check is done is not very
  important for the purposes of the check, but other engine handling
  considerations will usually mean a recommendation from the engine or
  aircraft manufacturer for an rpm setting from the low end of the
  cruise power range. From the magneto checking point of view, the
  important aspect is that the check on any particular aircraft should
  be done consistently at the same rpm, so that any trend can be
  monitored. There is little to be gained, for example, in comparing
  today’s 150 rpm drop at 2000 rpm with yesterday’s 100 rpm drop at 1700
  rpm

And this Lycoming service instruction mentions a range of 1800-2000RPM:

  Aircraft that are equipped with fixed pitch propellers, or not
  equipped with a manifold pressure gage, may check magneto drop-off
  with the engine operating at approximately 1800 RPM (2000 RPM
  maximum).

Obviously you should always follow the procedure and the RPM settings in the aircraft's POH, but those quotes suggest that getting the RPM exactly right isn't essential. However, the comment about consistency implies that the RPM drops will be different depending on your starting RPM, so if you don't use the POH settings then you have no way to know if what you're seeing is acceptable or not.

As for why 1700RPM and not some other value, I assume it's a setting that the engine manufacturer decides is high enough to put a realistic load on the engine but not so high that you could overheat it during the run-up checks. Or, as GdD suggested, it could be to avoid overloading the brakes. But I'm not an engine expert, and someone else might be able to give you a better explanation.


Are thrust levers synchronized by default when pushed/pulled?

On a non-FADEC engine (older airplanes - not this one) where the thrust levers are connected to the engine fuel control units with a cable circuit or a teleflex cable, you have to manually adjust each lever to wherever it has to go to achieve a given N1 (fan speed), and this can result in small variations in position of each lever when all engines are at the same power setting.  On takeoff on a non-FADEC, you move the thrust levers until power is reasonably close to take off thrust, call "set thrust", and the non-flying pilot tweaks each lever to synchronize all 2 or 4 N1 values to the takeoff bug setting on the N1 indicators.  With mechanical controls, the thrust levers may or may not be perfectly aligned when the engines themselves are in synch (there are limits to the misalignment allowed).

On a FADEC aircraft like the 380 in the video, the engines are managed by computers, and the thrust levers are just electrical input devices.  At the bottom of each lever there are Rotary Variable Displacement Transducers (RVDTs), that tell each engine's FADEC computer where the thrust lever is.  The FADEC will manage the N1 and if all 4 levers are at the same position, each FADEC will achieve the same N1 (within the tolerance of the RVDT's signal).

For takeoff, to make it easy, there is a detent for each lever at the Takeoff Go-Around setting (TOGA) that you can feel as you move them up (a little roller drops into a depression on a cam profile on the lever's arc of rotation).  There is another detent for climb power as well (CL) to avoid having to fuss with lever settings during the departure. When in the TOGA or CLIMB detent, the FADEC computer takes care of setting its engine's computed takeoff or climb power automatically.  So on a FADEC engine, when you take off, you just push the levers until you feel each one click into its TOGA detent, call "set thrust", and the non flying pilot just looks at the N1 indications to confirm they are all at TOGA thrust, without having to tweak the thrust levers (on the RJ I used to touch the levers below the handles as the PF was pushing them up with my finger and thumb to feel for myself that the levers clicked into the detents, although it wasn't really necessary).

At settings other than TOGA or CLIMB thrust however, they tend to work like mechanical thrust levers, where if one lever is at a different position it will have a different N1 value, so at intermediate power settings or on approach you have to individually align the levers, so you end up moving them as together as best you can and fine tuning as required.

What the pilot in the video is doing is synching the levers for taxi because when he pushed the levers up he didn't push them evenly and it looks like the outer ones were a little farther ahead than the inner ones.  Not that big a deal for taxi; he's just being a perfectionist.


If Boeing used two sensors instead of one simultaneously, wouldn’t they be in the same position today?

The problem is that there is no redundancy in the sensor input. The quote from the article is:

  This original version of MCAS, according to two people familiar with the details, was activated only if two distinct sensors indicated such an extreme maneuver: a high angle of attack and a high G-force.

So on the original design, MCAS activation required two sensors detecting an input over a certain threshold, and in itself this creates protection against false positives.

There are two major failure modes for sub-systems:

Zero output, where the sub-system simply stops outputting a signal.
Hard-Over failure, where the sub-system outputs a false positive. This is what happened with the AoA sensor in the two MCAS disasters.

With the original design, if one sensor would go hard-over, MCAS would not activate and the system would be protected against a single failure. But in the certified config, the activating input was not checked against any signal and MCAS repeatedly activated.

Further notes on the AoA sensors, from the final accident report page 45:

There are two AoA indicators on the B737Max, and only one was used for MCAS input.
There was an AOA disagree detection installed - as an option which Lion Air had not selected at the time of the accident:

  Accordingly, the software activated the AOA DISAGREE alert only if an airline opted for the AOA indicator. At the time of the accident, Boeing advised that the AOA indicator has been selected by approximately 20% of airlines.

  When the discrepancy between the AOA display requirements and the software was identified, Boeing determined that the absence of the AOA DISAGREE alert did not adversely impact aircraft safety or operation. Accordingly, Boeing concluded that the existing functionality was acceptable until the originally intended functionality could be implemented in a display system software upgrade, scheduled for the third quarter of 2020.

  Lion Air did not select the optional AOA indicator feature on the PFD of their 737- 8 (MAX) aircraft. As a result, the AOA DISAGREE did not appear on PK-LQP aircraft, even though the necessary conditions were met.

The safety analysis of the certified system has proven to be fatally incorrect, and this is what is so baffling. A single mode of failure was allowed to activate a flight critical system, by the most experienced aerospace company on earth. Plus: the incorrect safety analysis was accepted by the aviation authority whose function it is to protect us, the passengers.


What were the U.S. Air Force's first 2-crew fighter planes?

The first two-crew fighter aircraft to enter service with the US Air Force was the Lockheed F-94 Starfire.

Source: Wikipedia Public Domain

The aircraft's first flight was on April 16, 1949 and entered service in May of 1950.


What is the standard temperature used in this true altitude equation?

Standard temperatures are based on the Standard atmosphere. A lapse rate, dry or wet depending on your environment, is used determine the standard temperature for a given altitude relative to the standard sea level temperature. The post, How does one calculate true altitude? may help you out here.


How are performance classes for helicopters/rotorcraft defined?

Multi-engine helicopters have 3 Performance Classes defined at certification that is related to single engine performance and how this affects follow-on risks following an engine failure.

Class 1 helicopters have massive reserve power and can continue flight on one engine.  They have engines that are way larger than necessary for normal operation and normally operate at a fraction of their power potential until called upon to do it all.  Risks following engine failure are low.

Class 2 helicopters have somewhat less reserve power, and can continue flight temporarily on one engine, but not indefinitely.  Risk factors are higher.

Class 3 helicopters have little reserve power and are generally forced down when one engine fails, although at a much gentler descent rate than an autorotation. Risk factors are highest.

I was looking for a link that provides a good detailed description but haven't had much luck.


What Height Atc radar reads from pilot selection

The altitude reported by the mode C of the transponder is based on the standard altimeter setting (29.92 in the United States)


The terminology is a combination of history and "trustworthiness" (for lack of a better term).

Historically, primary radar was invented first. So it makes sense that this would be called "primary" and another scheme invented later would be called "secondary".

ATC systems like to ensure that the data they are working with is trustworthy. Primary radar systems are based only on the reflected radar signals. If you get a reflection, you know there is something there, whether or not it has a transponder (or indeed, whether or not it is an aircraft). This is a certainly a key point in military radar systems, and ATC radar was derived directly from military radar.

With secondary radar (transponder) operation, there is no guarantee that the transponder isn't lying (whether deliberately or unintentionally). A faulty transponder could certainly report false locations to the ATC system. Or, you can probably imagine scenarios where a false location might be deliberately returned.

ATC systems take both the primary and secondary location information for an aircraft, and correlate them to represent one aircraft in the sky. They don't report the exact same physical location, so there is a degree of fuzziness in the system to account for that. If the two reported locations drift too far apart, you get an uncorrelated track. Sometimes, if two aircraft cross each other's track in certain ways, the ATC system can get confused and associate the wrong primary radar blip with the wrong transponder report. The controllers have procedures to deal with and correct these kinds of problems.

So, primary radar is primary because it (a) came first, and (b) is the most trustworthy source of aircraft location information. Secondary "radar" (which, as you point out, is not really radar) is called such because it is integrated within the primary radar system.

More generally, the various technologies for locating and identifying aircraft in airspace are collectively called "surveillance". Examples of ATC surveillance are primary radar, transponders, multilateration, ACARS position reports, and other technologies.


The gust envelope is four lines overlaid on the flight envelope, usually the plus/minus of maximum gust at design cruising speed (Vc) and half maximum gust at maximum speed (Vd) as required by the certifying authority. This is usually +-50ft/sec (15.2m/sec) and +-25ft/sec (7.6m/sec).

n is the normal acceleration in a sharp edged gust
K is the tailplane gust alleviation factor. In a canard this is an aggravation factor.
u is the airplane mass ratio

The source contains examples of how the lines are calculated. The following information (defined) is required:


When did the FAA begin offering added-rating tests for flight instructors?

Could you decode your abbreviations for us. I just took all of the tests and I am not familiar with those abbreviations.

Just to clarify for those who are not familiar with the knowledge tests. You need to take the Fundamentals of Instruction knowledge test (FOI) for all of the instructor certificates. You can take the Basic Ground Instructor (BGI) test, Advanced Ground Instructor (AGI), and Instrument Ground Instructor (IGI) if you want to get a Ground instructor certificate. To get your CFI certificate you need to take the Flight Instructor Airplane (FIA) test. CFII requires the AIF. There are separate tests for Sport Pilot Instructors.

If you are adding a rating to an existing certificate, you can take an abbreviated version of the test, e.g. if you already have your CFI Airplane, then you can take the add-on test for gliders and only have to answer 25 questions rather than 100, and the questions will focus on glider operations assuming you already know the rest of the stuff.

Once you have any instructor certificate, you never have to take the Fundamentals of Instruction test again.

I don’t know when the short tests started, but if you look at Order 8080.6D which was published in 2003, you can see that short tests were available then. Since you had your CFI in 2009, you had the option of taking an abbreviated test for your CFII.


How can leading edge separation bubbles be prevented?

The velocity-jump at $\simeq 0.5c$ is due to a laminar separation bubble.

But you ask two different things here:

Prevent leading edge separation

A leading edge separation may happen as the laminar separation bubble progresses forward for higher angles of attack and is more common in thin airfoils. A way to suppress this is by the use of roughness elements, a trip or vortex generators. You can experiment with this using Xfoil and fixing the transition location at the point (or in a distance before this point) that you assumed that you have a roughness element for example. Otherwise try modifying the geometry with Xfoil's inverse design routines and if you're seriously into this read these Low Reynolds
Number Airfoil Design Lecture Notes provided by Selig.

Increase aerodynamic efficiency ($L/D$)

Increasing $L/D$ for a specified angle of attack for these kind of airfoils and for the low-Reynolds regime, means in general to reduce the velocity-jump of the laminar separation bubble. If I am correct, Selig's airfoils are already an improved version of similar NACA airfoils for low-Re. To do this you should again consult the aforementioned notes.

Are you sure that the spike on $c_p$ plot before the suction peak is not a paneling issue? It seems unphysical. Have you tried refining your airfoil? I do not capture this with the same analysis using Xfoil with 200 panels.

A rule of thumb is that the shape parameter ($H_k$) of the boundary layer at a laminar separation bubble is around 4. You can see from the following plot that you have a laminar separation bubble around $0.5c$ on the upper surface. Not in the leading edge though.


When doing "bunts", it's about the oil, not the fuel. The airframe doesn't care; it's in a ballistic arc and is completely unloaded, like some trash you launched into a neighbor's yard with your Yard-A-Pult.
Overall, the main risk is of a temporary drop in engine oil pressure when oil in the sump turns to globs and floats around, potentially unporting the oil pump suction pickup at the bottom of the sump.
The effects of this are less severe in a carbureted engine because the engine will also quit temporarily while this is happening (the carb will flood), and without the torque related forces acting on the main bearings, it's unlikely to do damage to the main bearings for the couple of seconds you can sustain the bunt.
Oil pressure loss is more likely to happen if you push too hard and go negative G. All the garbage that was on the floor, and is now on the ceiling of the cabin, also tells you that the oil in the engine is up against the top of the sump and running backwards through the drain path into the main crankcase, and the oil pickup is sucking air for sure.
If the engine is fuel injected, the risk of doing real bearing damage is higher; it'll still produce power during the time you can sustain the maneuver (until fuel in the lines is consumed if the fuel in the tanks unports, which will take longer than you can sustain the bunt) and if the oil pressure drops while it's making power, that's a very bad thing, as it's likely the main bearings will achieve metal to metal contact, and it's downhill from there.
If I was an FBO who learned that my renters were doing zero G bunts in my planes, I'd probably be not too happy about it.


Are there commercial airplanes that are still flyable without any electricity?

Are there any still commercial airplanes in use that are still steerable with complete loss of all electric systems? Do some commercial airplanes still have mechanical backup steering mechanisms?

Yes and Yes.

On most(*) Airbus aircrafts,

  In case of a complete loss of electrical flight control signals, the aircraft can be temporarily controlled by mechanical mode.

This is called MECHANICAL BACKUP and is the lowest level of control law (after Normal, Alternate and Direct Laws)

The aircraft can be steered:

  Pitch control is achieved through the horizontal stabilizer by using the manual trim wheel.
  Lateral control is accomplished using the rudder pedals.

The pilots are notified with:

  A red MAN PITCH TRIM ONLY warning appears on the PFD.

But:

  Both controls require hydraulic power.

This means that if the aircraft looses BOTH electrical and hydraulic power, is no more controllable.

Usually there are pressurised hydraulic reservoirs that allow to have a minimum of hydraulic power even if there is total loss of electrical power, but if there is substantial damage to the aircraft that has severed the hydraulic lines, this is no more applicable.

(*): beyond the A320. Functionalities vary in the following manner: (emphasys mine)

  Primary Flight controls:

  Back-up Control Logical evolution of A320 / A340 / A340-600 family:

  Full Fly-By-Wire, with a “Back-up” as an additional precaution to keep control of the aircraft during temporary loss of:

  all Primary Flight Control computers
  all Electrical power supply

  A320 : full FBW controls, mechanical Back-up (Pitch Trim & Rudder)

  A340/A330 : like A320, additional Yaw Damper to improve Dutch Roll
  damping even in Back-up mode (BYDU with hydraulic micro generator)

  A340-600 : like A340 for pitch, Rudder becomes fully Electrical (BPS + BCM : Back-up Power Supply + Control Module)

  A380 : like A340-600 for Yaw control + BPS+BCM also power:

  Electrical Pitch Back-Up (elevators) linked to side-stick
  Electrical Roll Back-Up (ailerons) linked to side-stick
  Pitch Trim (Wheel is replaced by Switches)

For the A380, in particular:

  Active Stability Control functions:

  All levels of control laws (Normal, Alternate, “Direct” and even Back-up) include a Yaw and Pitch damping function


How to balance the cargo on a plane with the wings further aft?

Yes, the wing is positioned so that the center of lift is near the center of gravity. The MD-80 is very tail heavy due to the aft mounting of the engines. I have actually personally seen the nose of an MD-80 lifted off the ground by a jet bridge, and it didn't even hurt the door that was supporting the weight.

This chart is from the MD-80 weight and balance manual, which can be found on google. You can see that the center of gravity (CG) must be within -2.8% to 33.4% of the Mean Aerodynamic Chord (MAC) which is an approximation of average wing chord. So basically the CG must be in the forward 1/3 of the average wing chord, typically the center of lift is around 25% of chord. On the MD-80 the leading edge of the MAC is at body station 885.547, which is behind the actual LE of the wing at the fuselage.

The reason you want to place the CG near the center of lift is to create the smallest pitch moment possible between the CG and CL. The pitching moment created by the difference in the CG and CL location must be reacted out by the horizontal stabilizer. The more moment, the larger the stabilizer must be and the more inefficient the aircraft. Here is an illustration (stolen from this question How does a commercial airliner measure its weight/mass?):

Here is the picture of the MD-80 doing the wheelie:


What questions should I expect during an EASA skill test?

Goodness, the best not guess, since the amount of information an ATPL candidate must master is just massive. Could be anything from the smallest detail to broad concepts. Anything to make you uncomfortable and see if you are willing to admit that you might not yet know everything, or whether are you the kind of guy who takes the best guess and hopes it's the right one...

For your sake I hope all goes well, and for everybody elses, I hope you know everything needed to become a safe professional airline pilot. Godspeed.


Why do jet nozzles close at different rates?

The nozzle position is automatically adjusted according to the current engine state to maintain optimal exit flow conditions at the end of the nozzle.

The difference in nozzle actuation you are referring to is caused by a slight difference in activation time of the afterburner between the engines.

Please see the following Aviation Stack Exchange question and answer(s) for more information on the purpose of the nozzle:
Why are adjustable area jet engine nozzles mostly limited to military use?


Why does the Convair 990 produce this howling sound during landing?

What you hear at 0:11-0:12 is just the sound of the engines being reduced to idle thrust, and the doppler effect as the aircraft passes your position.

I have heard that sound hundreds(maybe thousands) of times. It is very normal, and sounds just like all jets of that generation.

Here are more examples:

Skymaster DC-8-63F Landing

707 ! Touch & Go, Depature, Landing.

Boeing 707 Landing - Smokey!


What is the smiley face sensor at the stern of the F-4 Phantom?

Your daughter is right as explained here:

  The 'bug-eyed' face of the parabrake door mounting the two
  rear-hemisphere radar warning antennas.

So they do detect other airplanes and probably the smiles of their pilots too as they are getting close to the phantom.


Do low-cost airlines make more profit than luxury airlines?

It is hard to say for sure - profits will always be relative and in many cases not clear to anyone without advanced economics/accounting qualifications. However, there are a number of differences in terms of customer experience and service that can make a lot of difference to profit. Examples might be:

Crew size - it usually states that the crew on a no frills airline
are there for customer safety rather than service - on a legacy
carrier they are (technically) there for both so there are more of
them
What's included - rather than charging separately for things like
seat selection, baggage and meals, a 'frilly' (as opposed to 'no
frills) carrier will bundle them together, earning less than an
airline that charges them separately. Note - BA and a few other
airlines do charge separately for seat selection
Operating efficiency - a no frills aircraft typically spends less
time on the ground being turned around, so this expensive asset is
utilised with a higher percentage air time
Seat pitch - a smaller seat pitch means two or three additional rows
of seats in an aircraft - so greater profits per flight
Less straightforward pricing models - in many cases, a 'low cost'
airline charges more for a ticket than a standard airline, hiding
behind clever yielding of fare and additional costs added on later in
the booking process. In the travel industry I have seen time and
again people being fooled by the term 'low-cost airline'

I am sure there are many more. The operational efficiency of individual aircraft can be quickly worn away when a 'frilly' airline is required to compete with a 'no frills' on a similar route. Also, some 'flag carrying' airlines, which tend to make much greater use of joint ventures and codeshare agreements than no frills airlines, sometimes fly routes because it is a requirement of a larger deal - and if that is not very profitable (or even loss-making) it can drag down overall profit.


What airfoil is used on the MQ-1B Predator's wing?

The MQ-1B uses three different airfoils: Drela GW-19, GW-25 and GW-27, created by Dr. Mark Drela (one of the creators of the XFOIL software) and proprietary to General Atomics.

The airfoils used on the MQ-1B (Drela GW-19, GW-25, GW-27, created by Dr. Mark Drela) are proprietary material of General Atomics. Dr. Drela personally stated on a hobbyist remote-control drone forum that a scale model should use an SD7032 wing (similar shape to a NACA 3510), while the full-scale MQ-1B airfoils "...have LOTS of top surface camber."

"Fixed-Wing UAV Airframe Design and Validation", Bachelor's Thesis of Timothy Brown, University of Queensland


What is the sink rate of a glider during a roll?

As always, it depends. Besides the steady-state drag sources of lift creation and friction, you need to look at the drag created by roll acceleration and manoeuvring, including adverse yaw.

If the glider starts the roll at a bank angle which is sufficient to reach a steady roll rate by the time it rolls through 0°, the roll acceleration term becomes zero. However, now you have deflected ailerons and a deflected rudder to counter adverse yaw, which all add their own drag. How much depends on the roll rate and the needed deflection.

On top, now the local incidence of the wing shows a discontinuity at the spanwise station where the ailerons begin. This will create a less than optimum lift distribution over span, so the induced drag of the rolling glider is higher than that of the same glider in a steady glide. Again, the magnitude depends on the roll rate, and the aileron placement and deflection angle.

I would not be surprised if the sink rate in a brisk roll increases by 50% over that in a steady glide at the same speed, even with zero sideslip. If adverse yaw is not properly countered by the rudder, the additional drag from the resulting sideslip angle can easily double the sink rate.


What's the preferred approach for a passenger jet?

I'll give the answer from an ATC perspective. A visual approach is the most preferred approach, since we can get aircraft to follow each other, and don't have to worry as greatly about aircraft getting too close. The rules say we can compress under certain conditions to 2.5 miles on ILS or radar separation approaches, but timing wise, for the runway to be clear, you can often need less separation between aircraft to maximize its usage. With the visual approach, you're vectoring to keep aircraft closer so they can see each other and follow in closely to each other to the runway.

In most ATC facilities, the Tower decides what runway to use, and the approach control calls the type of approach generally on offer(this can vary depending on facilities and how they agree to run things). A pilot can always request a different approach... they might be delayed, sometimes significantly if they insist on something way out of the loop.


What are the ANT and ADF modes on an NDB receiver?

ANT mode improves the audio reception when listening to a station's morse code identifier or whatever else is being broadcast.  Normally the directional needle gets parked at 3 o'clock when in ANT.  NDBs can also have other broadcasts besides station ident, like ATIS or AWOS weather data, etc., and in some cases use of ANT may make the difference between making out what is being said, or not.  It may also improve AM radio audio reception, but not sure.  I've used the ADF to listen to music back in the day, but never had to go to the trouble to switch to ANT to hear it.
Here's a link to a KR 87 manual.