What is the future of manufacturer independent jet engine maintenance repair and overhaul (MRO) services?

Background:
These days, Rolls-Royce is not any more in the business of selling engines, but selling thrust. The engines send telemetry data to four centers, the biggest one in Derby, in Great Britain, where every engine is under surveillance. An inspection can be scheduled at or spare parts can be directed to the right destination even before the pilots or the airline know that one of their engines has a problem.

By now, 80% of Rolls-Royce engines are sold at a loss which is recouped by a hourly fee paid under the TotalCare (.pdf!) program, and that center in Derby is monitoring maybe 4000 of them at the same time. Rolls-Royce has accumulated a treasure of engine operations data, which enables it to consult airlines on best practices. This makes it very hard for a third party to steal maintenance business from Rolls-Royce. All maintenance cost is covered by the TotalCare fee which now accounts for more than half of Rolls-Royce's revenue.

Other engine manufacturers have begun to copy this approach, and both Airbus and Boeing now offer similar programs for airframe surveillance and maintenance to their customers.

I wonder how Air France KLM can get at the data from the engines. My impression is that Rolls-Royce is in a different position, and third parties cannot compete on an equal basis. Airlines can rent out their shop capacity to others, but the specific business model of Rolls-Royce is directly coupled to them being the manufacturer of those engines and owner of the data it creates.


If you are referencing the manuals found here the procedures look pretty standard to me. Granted they involve some thing specific to the plane they are generally what one would find. Pages 2-19 through 2-23 seems to cover the start up procedure and it looks pretty standard. Make sure ground unit is connected, check fuel flow, check engine is open, start, check RMP (provides some trouble shooting for RPM issues as well). It also goes on to say left engine first for odd flights and right engine first for even flights to keep the wear some what in line. There are a lot of "Note" sections but you are talking about one of if not the highest performance aircraft ever made so these are to be expected.


Are old illegal air transfer methods still feasible today?

Yes, it is possible to fly "under the radar".

The type of radio waves that are used by radar and similar equipment to track aircraft generally travel in straight lines. This means that, because of the curvature of the Earth, radars have blind spots at low altitudes when you are sufficiently far from the radar. See the top illustration (not to scale):

While radar coverage today is no doubt much better than it was during World War II, much airborne surveillance today (SSR, ADS, etc.) relies on cooperative targets - which means that tracking an aircraft is a two way communication; the radar sends out a request, and the aircraft replies. The pilot could easily turn off airborne surveillance equipment, thus becoming invisible to secondary radars, ADS and so on, but would still be visible on primary radars, which work by sending out a radio pulse which is reflected off the surface of an aircraft. My point is, primary radar coverage is limited, with more and more primary radars being phased out and replaced by secondary radars, so there are definitely plenty of areas where, if you fly low enough, you can avoid radar detection.


Do Cargo flights carry anyone other than the crew?

Yes, cargo aircraft are like other aircraft in that there is generally at least a jump seat available. Especially larger aircraft will also have additional jump seats, a lavatory, and a galley. This area can be used for relief crew, or other crew that are just deadheading.

There are exceptions though. The upper deck of the 747 is larger than just the cockpit, even on the cargo versions. There is more room in the back for additional crew. The An-124 and An-225 also have additional space for crew behind the cockpit. The extra crew can be loadmasters, navigators, mechanics, or other functions that can make it easier to operate in and out of airports with less services available.

Here is the upper deck of a 747-400F:


Departure and arrival fix loading via FAA website

The FAA has a graphical display of forecast arrivals by arrival fix for airports in the Airport Arrival Demand Chart. Choose a time interval, airport, and select "arrival fix." If you look at what it's doing through a network inspector, you'll see it's fetching JSON data, if you're looking for programmatic access.

That page only shows arrivals, not departures though.


In an emergency near a remote island is it better to land resulting in the airport closing or ditch in the water?

In general, it's a bad decision to ditch if there's an alternative, even a gear-up landing (Sully ditched in the Hudson because the alternatives were much worse: virtually certain total loss on board, plus significant ground casualties due to dense population).  The safety of the crew, passengers (if present), and people on the ground is the first concern of a captain or PIC.  Ditching seldom ends well, and often results in 100% fatalities, because even with a perfect ditch, rescuers often can't reach the aircraft quickly.

For a sufficiently remote location that incoming flights may not be able to return or divert (like the example, Easter Island), there may be an option to land alongside the runway (potentially a better choice for gear-up anyway, in a location without a large fire crew, since grass is less likely to start a fire than tarmac), both for safety and to keep the runway open.


How is crew resource management trained?

CRM training which I have been exposed to consists of lecture/videos to cover principles and expand on them with techniques.  There may be some classroom exercises.  However, due to the way that most training is conducted, the "classroom" is usually small numbers.  The application of CRM is in the simulator (SIM), where evaluation of techniques can be provided as the techniques are applied in routine and not-so-routine training scenarios.  Debrief is normally instructor(s) on team, after the SIM session(s).

For the training I get, CRM is pretty effectively integrated into recurrent SIM training.

For ab inito and primary training, the CRM training is similar, with classroom/video training.  Flight schools and academies will have larger class sizes and normally have quite a bit of depth in their training. I recently reviewed a 4 credit hour university course on CRM.

A friend who is a pilot, and also an Emergency Medicine Physician, (and with graduate and undergraduate degrees in Human Factors and Industrial Engineering) has been applying CRM to the hospital emergency department operations, and the military has similar efforts.

CRM has been around for a long time, although there were cultural impediments to it's widespread integration in the aviation context.  Much of that continues to change over the last 20 years.  I expect that CRM will expand into areas such as varying personality styles and other team techniques in the future. An example is some of the people style recognition and skills as developed by Robert Bolton, PhD and Dorthy Grover Bolton.

To summarize, the method of teaching is dependent upon the venue.  In many areas of aviation, CRM is integrated into recurrent training and critiqued on observed operations.  In initial training, the introduction of CRM is largely dependent upon the style of instruction, and whether that instruction is individualized or team based.


How to use airport panel information on sectional chart?

In addition to @JWalters's answer:
L-2F, 3B is one group, and it refers to the "Enroute Low Chart Number(s) and Panel Identification",$^1$ that is:

L-2F, and
L-3B.

Since you are aware of the L-2F, here's the L-3B:

Source: skyvector.com

$^1$ Interagency Air Committee (IAC) Specifications, IAC 8, faa.gov, § 3.1.5.2.7


How are procedures for curved-runway operations different from those for straight runways?

I know that KAVX has quite a hump in the middle of the runway which does not allow for departing aircraft to see all the way down the runway, and I'd imagine that the procedures are the same as they would be for Elk City Airport. The Facilities Directory/Chart Supplement for KAVX says:

PILOTS CANNOT SEE ACFT ON OPPOSITE ENDS OF RWY DUE TO GRADIENT, MUST ANNC TAKING ACT RWY ON UNICOM PRIOR TO DEP

Essentially, communicate your intentions on the common traffic frequency. Where you are taxiing, what runway you are using and when you're about to take off. Also be vigilant watching for traffic that may be using the opposing runway.
On a curved runway, Your main concern is that someone else would be approaching or using the opposite runway while you are using the other end. This is even recommended in the Chart Supplement for Elk City, which says

LAND RY 14 TKOF RY 35 WHEN WIND CONDITIONS ALLOW

As far as actually taking off on a runway that is not straight, you'd need to take into consideration obstacles around the runway environment. In the case of Elk City, I'd hold off on rotating until after the bend so that I can climb straight out and get above tree level prior to making a turn.  It appears as though that is in line with the Chart Supplement instructions, as landing RWY14 would give you the longest length to land and start to slow before you had to make the turn, and taking off on RWY35 would have you turning prior to rotation speed (or at least shortly thereafter).


Coded RAREPs (Radar Weather Reports) and SDs (Storm Detections) may still be used to exchange data between radar stations, but for human users they seem to have been superseded by visual displays that provide a more human-friendly visualization of the same information, such as at http://www.aviationweather.gov/radar.  The PHAK you linked to (published in 2008) is likely out of date on this.  (But this is the most recent PHAK available.)

From http://weatherjackwilliams.com/answers-weather-radar/ :

  The NWS Aviation Weather Center (AWC) doesn’t have any links to the
  coded SD/ROB reports, but does link to the Radar Summary chart, which
  is complied from these  reports.

This information is also incorporated into a standard weather briefing for a particular flight plan.  The DUAT system used to provide an "SD (Radar Weather Reports)" section in its briefings, but DUAT is no longer available.  DUATS instead has a section titled "Radar Summaries" in its briefings.


How can I calculate distance based on altitude and glideslope angle?

Since the 1 in 60 rule of thumb yields a solution of 300 feet for every NM from the touchdown point for a 3 degree slope, use 320 feet for a 3.2 degree slope.  So 670ft, gives you a nadgers whisker over 2 nm.

To be a little more precise, 2.09375 nm ($\frac{670}{320}$)


You wont find a single source for any of these things but you can find some of the info form fairly reliable sources:

The NTSB publishes accident data by type and year but this is only for US accidents or accidents involving US aircraft that they can investigate overseas.
The FAA allows you to lookup by make and model and would allow to get some info on registered aircraft but again only for the US.
ICAO also lists their final reports online which give a more global picture of whats going on but you will still need to combine all the data. They also offer some rolled up stats.

All of these sources generally can get spotty before the 80's for a few reasons. A lot of those reports only existed on paper and are still being digitized so results are intermittent. Official governing bodies started at different times around the globe and even paper reporting took time to standardize, accidents that pre-date that may have gotten lost in the mix.


What is the distance between RLLS lights?

Approach Lighting Systems (ALS) can have many variations, but each variation will be a combination of certain components.
For example, green runway threshold lights extend across the runway threshold, 5 feet apart (center-to-center), and extend outward 45 feet from the runway’s edge on either side. This line of lights can be up to 10 feet from the landing surface before requiring a waiver.

Centerline lights are rows of 5 lights that span 13.5 feet wide and are usually spaced 100 feet apart extending away from the runway threshold out as far as 3,000 feet in some cases.

Many other lights may be incorporated, including sequenced flashers, runway alignment indicators (RAILS), side row bars, and wing bars.
In general, rows of lights will usually be 100 feet apart for at least the last 1,000 feet, and 200 feet apart beyond that.

For more detail on all of the various types of lighting and specific measurements between each, check out this article on Code 7700.


Could some one explain me with the mathematical relations on how the double bubble fuselage cross section (example A380) is designed.

A380 actually has an elliptical cross section, not double bubble. 'Double bubble' fuselage cross sections (also called double lobe) are usually used in case of aircraft which require specific arrangements for carrying passengers/cargo and in which case using a circular or elliptical fuselage would result in a large wastage of space or because this type of arrangement is cheaper to make. Another reason for this appearance is that some aircraft were extensively modified (for reasons other than the original intentions) resulting in this shape.

The double lobe fuselage aims to reduce the wasted space by having fuselage in two intersecting circles, joined together at the floor. The (relative) size of the circles is determined by the requirements. A good example is the Boeing C-97 Stratofreighter, which was a military transport based on B-29 Superfortress.

Boeing notes:

  ... it had a double-lobe fuselage consisting of two intersecting circular sections, so that the 74-foot-long (23-meter-long) upper deck had a larger diameter.

Image from Boeing.com

The civilian counterpart of the C-97, the Boeing 377 Stratocruiser inherited this shape having a double lobed structure, with 100 passengers on the main deck plus 14 in the lower deck lounge.

Boeing 377 Stratocruiser fuselage cross section; image from tdpri.com

These aircraft were later modified to carry oversized aircraft parts as the Pregnant Guppy, Super Guppy and Mini Guppy, all having the distinctive double lobed design.

Note that most of the double bubble aircraft are for carrying cargo. Contemporary aircraft with a similar arrangement include the Airbus Beluga which again are used for transporting oversized aircraft parts.

Airbus beluga, image from australianaviation.com.au

The Beluga is an example of how specialized requirements required this design. This aircraft was designed because none of the available large transports had enough space to transport the required sub-assemblies. Designing and building a new aircraft for carrying these sub-assemblies (including fuselage sections) would have been prohibitive (only five were made); so Airbus modified an existing aircraft according to requirements.

Another aircraft that acquired this shape as a result of modifications was the Hawker Siddeley Nimrod, which had this shape due the addition of a bottom section to the De Havilland Comet. The lower section had the radar, bomb bay etc, while the upper section had the crew.

Quite a few airliners have utilized this shape in the past, though the shape is not as pronounced. Airline manufacturers, from Boeing to Douglas used them as they are efficient in using space. For example, the Boeing 707 fuselage cross section below shows this design.

707 fuselage cross section; image from forum.justflight.com

Also, as I noted before, the A380 has an elliptical cross section, not double bubble.


Once you launch an ICBM, you're pretty much committed.  Even if there is a self-destruct on the missile (I don't know, nor am I making that claim.  Additionally, I think debris from such an act would be a big concern.).  A bomber also allows you to send something part of the way, and rattle your sabers in the face of the other party without again having committed to the act of the warhead being launched.  You can always recall a bomber without having to worry about a debris field or other unintended consequences.

As to the claim that bombers are particularly vulnerable, there are numerous ways they get around this.  For instance the B-2 employs stealth to get around this.  The B-52 can use standoff weapons to reach out to a target (such as cruise missiles or JASM).  Also, the B-52 can use low altitude routes to avoid radar and detection (if you’ve never seen a B-52 do a low level, I recommend you find a route and observe, it’s something else).  And on top of all that, the aircraft have defensive systems to help them on their missions (chaff, flares, RW gear, etc.).

Also, with a bomber, you can employ different types of weapons that give you a broader range of response options.  You can use bombs of anywhere from a 250lb laser/GPS guided bomb to something much larger.  These delivery mechanisms are generally much more accurate than a TBM (Theatre Ballistic Missile) or even an ICBM (InterContinental Ballistic Missile).  Those systems are generally inertially guided (some have GPS capability), which can lead to a larger CEP (circular error of probability), meaning that it may not hit exactly where you aim.  Those systems rely on a much larger warhead to get the job done than bombs from a bomber.  You don't use a Nuke to swat a mosquito, as a bit of military wisdom goes.  And, even ballistic missiles can be intercepted by systems such as the Patriot, so they are not a panacea against being stopped.


How do you calculate the vertical and horizontal tail volume if you have Vvbar and Vhbar?

The 'bar' volumes are the same volumes but taken with respect to the wing-body aerodynamic centre (AC) rather than CG. This is more convenient because this is a constant reference, whereas CG may move.

The difference between them is only the arm: $\overline{c}(h-h_{n_{wb}})$, which leads to your last expression for $V_H$.

For the yaw motion, the aerodynamic centre of the wing is much less relevant(*), and thus the 'plain' $V_V$ (with respect to CG) is commonly used. This is why you can't find an expression for $\overline{V_V}$.

Nevertheless, if we want to relate it to the same wing-body AC as for $V_H$, we can do it. However, in lateral motion the generic reference is the wing span $b$ rather than the MAC $\overline c$ (as you can see from your first two definitions). Thus $\overline c$ is not eliminated, and we have an uglier expression:

$$\overline{V_V} = V_V + \frac{S_{VT}} S \frac {\overline c} b (h-h_{n_{wb}})$$

(*) It could be related to AC of the body alone (which is typically near the very front of the fuselage), but this is also not very sensible: the wing (and the wing-body interaction) does play a major role. I've never seen $\overline{V_V}$ defined like that for airplanes.


What does "OBJECTIONABLE" indicate on a VFR chart?

It means that the airspace around the airport is still under review after a proposed change.

This article explains it in more detail: http://expertaviator.com/2012/07/31/what-is-an-objectionable-airport/

And here's the official text: Part 157

  §157.7   FAA determinations. (a) The FAA will conduct an aeronautical
  study of an airport proposal and, after consultations with interested
  persons, as appropriate, issue a determination to the proponent and
  advise those concerned of the FAA determination. The FAA will consider
  matters such as the effects the proposed action would have on existing
  or contemplated traffic patterns of neighboring airports; the effects
  the proposed action would have on the existing airspace structure and
  projected programs of the FAA; and the effects that existing or
  proposed manmade objects (on file with the FAA) and natural objects
  within the affected area would have on the airport proposal. While
  determinations consider the effects of the proposed action on the safe
  and efficient use of airspace by aircraft and the safety of persons
  and property on the ground, the determinations are only advisory.
  Except for an objectionable determination, each determination will
  contain a determination-void date to facilitate efficient planning of
  the use of the navigable airspace. A determination does not relieve
  the proponent of responsibility for compliance with any local law,
  ordinance or regulation, or state or other Federal regulation.
  Aeronautical studies and determinations will not consider
  environmental or land use compatibility impacts.

  (b) An airport determination issued under this part will be one of the
  following:

  (1) No objection.

  (2) Conditional. A conditional determination will identify the
  objectionable aspects of a project or action and specify the
  conditions which must be met and sustained to preclude an
  objectionable determination.

  (3) Objectionable. An objectionable determination will specify the
  FAA's reasons for issuing such a determination.

  (c) Determination void date. All work or action for which notice is
  required by this sub-part must be completed by the determination void
  date. Unless otherwise extended, revised, or terminated, an FAA
  determination becomes invalid on the day specified as the
  determination void date. Interested persons may, at least 15 days in
  advance of the determination void date, petition the FAA official who
  issued the determination to:

  (1) Revise the determination based on new facts that change the basis
  on which it was made; or

  (2) Extend the determination void date. Determinations will be
  furnished to the proponent, aviation officials of the state concerned,
  and, when appropriate, local political bodies and other interested
  persons.


Why aren't the canards used as airbrakes on the Tupolev Tu-144?

A number of things happen when you rotate the canards by 90°, and in no way I see how these could be addressed by

  not too many modifications

1. Transient

Once you land, you need a certain amount of time to rotate the canards. During this time the canards will not produce a perfectly horizontal force, but it will have also a vertical component.
Whether this component will be upwards or downwards it will depend on the rotation direction: rotate them with the leading edge up, and you will have some upward force; downward otherwise.

In both cases this is not ideal:

an upward force will reduce the adherence of the nose wheel, reducing the steering authority
a downward force will increase the load on the wheel, increasing the chance of tire burst and increasing the required size of the strut to sustain said load.

2. Deployed Status

Let's assume for a second that the transient problem can be avoided. Now you have two large surfaces perpendicular to the airflow that create a massive amount of drag. And torque.

You need then to design a structure that is capable of:

keep the canard in place during the flight
rotate the canard by 90°
sustain the drag force during deceleration
sustain the torque during deceleration

You can reduce the torque and drag forces to be transmitted through the mounting by delaying the deployment/rotation of the canards, but that would defeat the purpose or, at the very least, severely limit the usefulness of such a system.

In conclusion, a structure that would fulfill all the listed requirements is

extremely likely to be heavier than equivalent brakes,
more likely to be prone to structural problems due to complexity,
more expensive due to maintenance,

making even less sense in an aviation application.


What is this strange thing under Tu-95 which looks like a horse-fly's eye?

According to this site it is a MAK-UL IR Threat Warning System, an infrared based missile approach warning system. Here is a closer picture:

(picture by Miroslav Gyűrösi)


How can I find out the best time to practice within towered airspace?

Simplest answer: Call the tower. Or ask instructors/schools in the area if the controllers care when you arrive and want to practice. Usually if you arrive during the busiest time, you'll likely be accommodated as best as they can, but there's a chance you could be told to just do a full-stop taxi-back operation if that helps out or told to go fly around elsewhere for a bit.

It depends on what airport you're thinking about going to. If you want to go to ATL, well, you'll be vectored in a gap, and told go as fast as you can for as long as you can, and be told to land(or if you go around, expect a long delay to find a new gap). If it's just a general aviation airport, anytime is fine.


What is a typical ratio of airline pilots to aircraft?

A Google search shows United Airlines has 709 aircraft and 12505 pilots for a ratio of 17.6 : 1.

If an aircraft was operated 100% of the time, a month's activity (720 hrs) would need 7 pilots pulling 100 hr/month duties, so it's an interesting related question why they need twice this amount. Perhaps there's significant variation in the hours worked by pilots - not all want to work 100 hrs/month, or can be efficiently scheduled to do so because of their home locations etc.


What improvements did Airbus make as a result of the Air France 447 accident?

The official report has a section headed

5 - CHANGES MADE FOLLOWING THE ACCIDENT
...
5.2 Airbus
Review of the “Unreliable speed indication” procedure
Flight Operations Telex (FOT) of 9 September 2009 recommending, at the next recurrent
training course, a session on the simulator at high altitude in normal and alternate law
including:

Manual aeroplane handling,
Carrying out the UNRELIABLE SPEED INDICATION / ADR CHECK PROC procedure.

Most of the changes were carried out by other parties, Air France, EASA, etc.

If the stall warning didn't stop, but instead changed into an even more ominous "you're now tumbling down at less than 60 KIAS" warning.

Opinion: If the computers have decided they don't know what the heck is happening, it's probably a bad idea for them to make something up at random to shout at the crew. If the computers always know best, they should just probably shut-up, activate the cockpit wrist-restraints and fly the plane.

it might not be out of order for the airplane to announce that it is now very much possible to stall the plane by pulling up (in actual words).

Wild guess: Maybe this would help but not when the PF is already ignoring stall warnings and determinedly pulling up almost continuously. Generally less is more when the crew are likely to be confused and overwhelmed. There's probably a hundred things you can more easily accidentally do when you are flying in alternate law and when you are in alternate law you may not have time to patiently wait and listen whilst the computers enumerate them all to you.

the unlinked nature of the sidesticks was a big part of the problem; are there good reasons to leave them unlinked in future designs?

So that the pilots can engage in wrestling matches? Yes, it seems there needs to be an even clearer indication of conflicting inputs but I'm not sure if mechanical feedback is necessarily the best method. Pilots are already supposed to be trained and tested on clear handover of control.


Why a higher compressor pressure ratio results in higher Thrust and lower TSFC?

Because the constant pressure lines are diverging with increasing enthalpy.

Have a look at the right most diagram.
The two lines are constant pressure lines, with the higher line indicating the higher pressure, and as you can see, they are diverging.

1 is the beginning of the cycle, thus at ambient temperature

From 1 to 2, we increase the temperature, and go to a higher pressure in the compressor. This will cost some energy, which is delivered by the turbine.

From 2 to 3 we increase the Temperature at the the same pressure by adding energy.

From 3 to 4, we decrease the temperature and pressure in the turbine (and use some of the extracted energy to drive the turbine)

From 4 to 1, we use the energy in the flow to propel us, and we go back to ambient temperature.

In principle we could also skip the higher pressure, and simply go from 1 to 4 and back to 1 (which is just heating air, and propelling yourself by the heat.)

But by moving to a higher pressure, we can take advantage of the divergent pressure lines. This yields us a benefit because the distance 3-4 is larger than 2-1. This means that if we use the turbine to drive the compressor, we gain some 'free' energy.

Source

Following OSUZorba's comment:

To illustrate the point of the 'free energy', look at the image below, here two extra stations are added the inlet, which isn't that important for now, and the nozzle. Note that the vertical distances of the compressor and the turbine are equal (they have to be, because one drives the other), thus
$$ \begin{aligned}P_{comp}  = P_{turb}  &\Rightarrow \Delta T_{comp} = \Delta T_{turb} \\ &\Rightarrow (T_3 - T_2) = (T_4 - T_5) \end{aligned}$$

But because of the divergent nature of the lines, we have some extra energy left. We use the nozzle to optimally expand the high pressure, high temperature flow and extract the 'extra' energy.

Source


Why don't aircraft have DME that can automatically convert the slant range to ground range?

There's no accurate and simple way to know the height above the station in order to do the calculation with the existing equipment. Altitude is not an indicator as the DME station may be above sea level. If your airplane is at 15,000ft and the station is at sea level you'll get one answer, if the station is at 10,000ft you'd get a completely different result, and mistakes could compromise safety.

The only way your proposed system would work is if the DME device had a complete database of every station height and altimeter readings, which would require upgrading the DME devices at great expense. I don't think anyone is interested in that when you can have GPS for a lot less money.


Considering that these systems are tested against drones, then the answer is yes. The limitations on what is too small to engage for any particular system are likely classified.


Are the holes inside the engine nacelle used for uniform intake of air?

They are for reducing noise emissions. According to Wikipedia,

  Liners are applied on the internal walls of the engine nacelle, both in the intake and by-pass ducts, and use Helmholtz resonance principle for the dissipation of incident acoustic energy.

The Helmholtz principle (Wikipedia again) can be watched (or rather heard) when blowing over a bottle which produces a sound.

  Helmholtz resonators are also used to build acoustic liners for reducing the noise of aircraft engines, for example. These acoustic liners are made of two components:
  a simple sheet of metal (or other material) perforated with little holes spaced out in a regular or irregular pattern; this is called a resistive sheet;
  a series of so-called honeycomb cavities (holes with a honeycomb shape, but in fact only their volume matters).

  Such acoustic liners are used in most of today's aircraft engines. The
  perforated sheet is usually visible from inside or outside the
  airplane; the honeycomb is just under it. The thickness of the
  perforated sheet is of importance, as shown above. Sometimes there are
  two layers of liners; they are then called "2-DOF liners" (DOF meaning
  Degrees Of Freedom), as opposed to "single DOF liners".
  (Wikipedia)


How do I choose the correct NACA airfoil for my requirements?

So you know your wing planform and look for the right airfoil.

You need to be more specific with your requirements, and yes, NACA airfoils will most likely not be the best choice. But since there is plenty of literature on them, they are a good start.

Please answer those questions first:

What is the maximum airfoil thickness you can afford? A thicker airfoil makes for a lighter wing with more internal volume for flaps and fuel. However, if you want to operate your design at high subsonic speeds, thickness needs to be controlled.
What is the lowest cruise lift coefficient and the highest lift coefficient for a clean wing and with flaps down? Does your design need flaps at all?
If the aircraft is small: What Reynolds number is flown at which lift coefficient?
What is the desired stall behaviour? Docile (as preferred for training aircraft) or snappy (as preferred for aerobatic aircraft)?
What construction technique is used for the wing? Wooden frame and fabric? All metal with countersunk or exposed rivets? To be built on a jig or on a flat table? Composite, in a mold or positive over a foam core? All of them have subtle consequences for airfoil selection.

Generally, you look at all requirements and then select or design the airfoil according to the desired pressure distribution at different angles of attack and Mach numbers. Once you tell us more, I can become more specific.


First airplane to use a flight simulator?

According to the Oakland Aviation Museum the first known was a simulator to learn to fly the Antoinette monoplane, although they don't provide any references for this, so I can't say that is entirely true.

The link trainer is the best known trainer and they were built in 1927 by Edwin Albert Link. They were used to train Army Air Corp pilots for instrument training in all weather conditions. The link trainer continued to be the sought after training device in WWII as well training almost all US Air Force Pilots.Link

If I find more information I will update my answer as best as possible.

I know typically answers on Wikipedia aren't the best but this one is littered with references that would take entirely to long to search out for ones self.


How do I calculate FPNM for standard take-off minimums?

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

-20°   0°   20°    40°

760   695   555   560

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

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

-20°   0°   20°   ?°   40°

685   620   625  565  496

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

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

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

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

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

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

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

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

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


Why does the speed tape on the Lockheed U-2 go the opposite way?

In essence, you are correct.
It was a conscious decision to do it that way:
- when the nose pitches up, you're "pitching" toward the slower airspeed on the tape...
- and you're pitching toward the higher altitude on the altitude tape.

My question:  why do most aircraft have the higher speed near the top of the tape?  Is it "just because the altitude tape does it that way"?  Or is there a better reason.

Having flown the U-2 with the glass cockpit for over 10 years, it is intuitive and is "normal" for me to see that.


Why is it more difficult for ATC to manage a larger airliner?

They must leave a greater amount of time in between landings/take-offs as the size of the aircraft increases due to wake turbulance

There were historically 3 classes of aircraft for the purpose of wake turbulance classification

H (Heavy) aircraft types of 136 000 kg (300 000 lb) or more;
M (Medium) aircraft types less than 136 000 kg (300 000 lb) and more than 7 000 kg (15 500 lb); and
L (Light) aircraft types of 7 000 kg (15 500 lb) or less.

With the introduction of the A380-800, where it is near MTOW, a fourth category has been added

Super Heavy for Airbus A380-800 with a maximum take-off mass in the order of 560 000 kg

How much time must be left? Well that depends, for an A380:

Arriving Aircraft

  MEDIUM aircraft behind an A380-800 aircraft — 3 minutes;
  LIGHT aircraft behind an A380-800 aircraft — 4 minutes.

Departing Aircraft

  3 minutes should be applied for a LIGHT or MEDIUM aircraft and 2 minutes for a non-A380-800 HEAVY aircraft taking off behind an A380-800 aircraft when the aircraft are using:

  the same runway;
  parallel runways separated by less than 760 m (2 500 ft);
  crossing runways if the projected flight path of the second aircraft will cross the projected flight path of the first aircraft at the same altitude or less than 300 m (1000 ft) below;
  parallel runways separated by 760 m (2 500 ft) or more, if the projected flight path of the second aircraft will cross the projected flight path of the first aircraft at the same altitude or less than 300 m (1 000 ft) below.

Source for timings: http://www.skybrary.aero/index.php/Airbus_A380_Wake_Vortex_Guidance


Subpart E (Powerplant) of Part 23 (AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES) has quite a few regulations regarding fuel system operation. In particular, section 23.995, "Fuel Flow".

However, I could not see in there a regulation requiring no fuel to flow in the off position, but given the safety implications of that not occurring, I would fully expect that is a requirement that needs to be demonstrated.

It appears to exist in Part 33 (AIRWORTHINESS STANDARDS: AIRCRAFT ENGINES), subpart E (Design and Construction; Turbine Aircraft Engines) section 33.75 "Safety Analysis". This states:

  The applicant must analyze the engine, including the control system, to assess the likely consequences of all failures that can reasonably be expected to occur.... The safety analysis must also include, but not be limited to, investigation of the following: (vii) complete inability to shutdown the engine.

I don't expect there are any regulations defining how it needs to be designed to do this - but rather regulations saying what it needs to do, and the way of achieving it is left up to the designer.


Why don't modern jet engines use forced exhaust mixing?

Source: wikimedia.org

They're back. Above is the General Electric Passport. Entry into service was 2018.

  Its core cowling, exhaust cone and mixer are made in ox-ox composites, with inorganic high-temperature-tolerant resins and oxide ceramics CMCs to withstand 1,000°C without deformation, saving weight and allowing complex molding.

The above hints at the hotter exhausts of the newer (since the mixers disappeared) engines, and that CMCs were the solution.

For the turbine inlet temperature, below is the trend:

Source: researchgate.net

From the respective flight manuals, an A380's max continuous EGT (Exhaust Gas Temperature) is 970°C, while it's 580°C for the older MD-80 (both don't have mixers, but it shows the trend). While you can bleed-cool turbine blades, there must have been no gain in cooling a mixer with bleed or they would have done it (bleed takes away from a combustor's efficiency, and at some point overall gains turn into losses).

Related: Why did Boeing remove the engine chevrons on the 777-X?


How to convert an EASA CPL(H) to FAA CPL Rotorcraft With a Helicopter Class Rating?

I just saw somebody try to do this. They had an EASA CPL(H) and a FAA PPL(H). The DPE needed to have a letter, sent from EASA to the FAA in Omaha, Verified, and then a copy sent to the pilot. This letter is EASA confirming the logbook entries attained in Europe were legitimate. This letter is only valid for six months. Despite getting the necessary flight training from a FAA certified CFI, as per the appropriate requirements, without this letter a DPE can’t administer a practical exam.

You need to pass the FAA practical to get any FAA certificate. Written test requirements vary.


Why aren't thermal analysis of propeller done?

As a propeller turns through the air at subsonic speeds, the dynamics of creating the pressure distributions in the air surrounding the propeller blade can be accurately modeled as being isothermal (no significant and persistent temperature gradients are created) and adiabatic (no significant net heat transfer from one location to another occurs within the flow field).
This means that the thermodynamic state of the air coming into the propeller disc is almost exactly the same as its state when exiting it, and for this reason there is no significant thermodynamic analysis needed to successfully account for the behavior of a propeller as long as it is subsonic.


In general, food for commercial coach passengers is made on the ground and then stored on the plane in special refridgerators, until it is time to eat.
The food is then heated in convection ovens and served. Sometimes there are special occasions for higher class seats/airliners.

Safety standards and space constraints mean your food’s made on the ground, near the airport. Big boys like LSG Sky Chefs produce 15,000 bread rolls every hour (24hrs a day, 365 days/yr), and 30,000 sandwiches a day.
As a rule of thumb, food is prepared 10hrs before it gets eaten. Those “Made Fresh!” stickers are there to mock you. It’s not ready-to-eat by any means at this stage; generally, chicken is cooked 60% of the way, and steak 30% to done, with the final phase occurring onboard. Once cooked, it gets blast-chilled in special fridges -- in a not-quite-frozen-but-not-edible state, your food awaits transfer to the tarmac.
Flight on time? Food on the plane? Time to finish the prep-work. Contrary to what most people think, planes generally don’t have microwaves. Your little tray makes its way into a convection oven for about 20min. Convection ovens have a fan (which pushes hot air onto the food) that's both faster and means a lower cooking temp.

https://www.thrillist.com/travel/nation/airline-meals-how-your-airplane-food-is-made-thrillist-nation


Why bother having different engine options on one aircraft?

When Lockheed built their L-1011 TriStar, they had one engine option, the Rolls-Royce RB211. RR did not deliver in time, and that has been attributed to the airplane's demise.

Although the TriStar's design schedule closely followed that of its competitor, Douglas beat Lockheed to market by a year due to delays in powerplant development.

So, having more than one engine option lowers the risk of a new airplane launch, and this has the benefit of allowing the airlines to pick their favorite.
Having one engine option on the other hand, like with the Boeing 777-300ER and the 777-200LR/F, allows cheaper certification, but it frustrates the customers:

Even if the 777X programme is successful, the sole-source deal has left some customers frustrated. Boeing argues that it chose the GE90 as the best engine for the 777X programme after its own rigorous competition. But as one airline executive says: "Our response is we'd rather run our own competition."
He adds the suspicion that Boeing decided to take the benefits of the engine choice competition for itself rather than let it accrue to the customer. Also, by eliminating a choice of engines, the company saved the costs of certifying more than one of them, he points out.

Back to your points: Your final conclusion is right, the performance difference is not a factor. For the second point, airlines get maintenance deals, so they like to stick with the manufacturer they already have business with. Getting discounts is easier when there is competition.

Related and interesting: How much would it cost for a large airline to switch engine manufacturer for their planes?


How will a variable pitch propeller move during takeoff?

What happens is the prop at idle will be at the maximum fine pitch limit.  The prop control is set to Max RPM for take-off (it uses variation in pitch to regulate RPM) so the prop governor is set up to regulate engine rpm at redline once there is sufficient power to spin it that fast.

You add throttle to take off.  The engine increases in speed, with the prop blades still in full fine pitch, until it gets to redline RPM, which is also the governor setting.  When the RPM gets there, the governor now acts to keep the RPM from going any higher.  It starts to move the blades to make the blade pitch more coarse to add load to the engine, and does so until the RPM stabilizes at the Max RPM governor setting.  As you keep adding throttle, increasing torque, the governor will increase blade angle more, whatever is required to keep the RPM at the governor setting.  Also, as you start to move, the forward speed starts to unload the propeller by reducing angle of attack, and the blades will coarsen further as required.

The governor doesn't know or care what the blade angle is; it's just a flyweight device like on an old steam engine and all it knows is "speed too high, do this, speed too low, do that". All the prop control does is apply a preload to a spring that determines the speed at which the flyweights will do their thing.

So yes the propeller will move toward coarse pitch because it's already fully fine and the governor has to move it more coarse to limit RPM in that situation.

If you shove the throttle in quickly, causing the RPM to rise very quickly, there may be a slight lag in the governor's response and the prop will overspeed momentarily a little bit (enough to create a noticeable EAAAOOOOWWW sound as RPM passes redline a bit and then slows down as it recovers to the governor setting).

The question is poorly worded.  It should be referring to "constant speed" governed propellers, not variable pitch, which is manually operated and quite rare (way too much work).  And the statement "best angle of attack" really means "angle of attack required to load the engine such that RPM is stablized at the Max RPM setting" (normally redline RPM for takeoff).  And this will always be more coarse from full fine pitch.


What can I do if my carb-heat cable breaks in-flight?

Well, this depends a little on your situation.

In all cases your goal is get on the ground in a controlled manner that leaves the pilot, passengers, and airframe intact - so obviously you'll be heading for the nearest airport (and if you can get in contact with ATC and explain your situation doing so would be a really good idea).

No signs of carb ice (yet).

If you're flying in conditions conducive to carburetor icing but don't yet have signs of icing there are a few things you can do to help prevent it from forming:

Seek a warmer/drier altitude
There's a wonderful diagram I'm sure everyone has seen that gives an idea of the probability of carb ice. If you can find an altitude where the temperature/dew point spread is less conducive to carb ice formation fly there until you can land.
Lean the mixture (as practical) to limit evaporative cooling from the fuel vaporizing.
This can limit the temperature drop in the carburetor, and if it's only a few degrees of difference between ice and no ice it might help.
Avoid low-power operation (<60% power).
A partially closed throttle plate is more likely to pick up ice (there is a greater pressure drop across the throttle plate which means a greater temperature drop).
"Clear" the engine periodically by opening & closing the throttle.
This helps ensure the throttle plate does not freeze in place, and can dislodge any small ice patches before they become a more serious problem.

  I think this would qualify as an "urgency" situation (pan-pan), per this answer.
  If you can get in contact with ATC don't hesitate to let them know that.

Signs of carb ice are apparent.

If you do have signs of carb icing you can do all of the things above too, but how effective they are may vary.

As xpda noted adjusting the mixture can help (typically carb ice makes the engine run over-rich).
In extreme cases wide-open throttle and an aggressively leaned mixture may keep the engine producing power (and will reduce the pressure drop across the throttle plate, possibly bringing the carb temperature up enough that the ice will melt off).

In many light singles your alternate air is the carb heat box, but if you have an alternate air source for the engine besides carb heat that may be worth trying as well (especially if it's in the engine compartment or heated cabin).

  Carburetor icing with carb heat inoperative is a bona-fide emergency.
  I can't imagine not making a mayday call in this case. Best-case scenario you wind up making an uneventful landing with fire trucks waiting to greet you ; Worst-case scenario you wind up landing somewhere that's not an airport, but at least someone knows where you are.


Lindbergh's panel-- Ryan NYP-- what is this instrument and how was it useful?

Its an Inclinometer which provided pitch and roll information

  In the early 1920's, the US Government contracted Rieker Instruments
  Company to produce bubble style pitch and roll indicators for the fast
  emerging aircraft market.

  One of the most famous inclinometer fluid filled vial type
  installations - if not the most famous - was the use of a pair of
  Rieker glass tube instruments on the panel of the Ryan NYP "The Spirit
  of St. Louis".  In 1927 Charles Lindbergh chose the lightweight Rieker
  P-1057 Degree Inclinometer to give him climb and descent angle
  information.

(source)

This was useful to the Spirit of Saint Louis as it had effectively no forward visibility with the exception of the periscope. He may have also chosen this in the interest of weight as it would be much lighter than an early gyroscopic instrument.


What is the difference between MMEL and MEL?

The Master Minimum Equipment List is issued by the manufacturer with the approval of the regulator and can be considered a "global" document you might say.  The manufacturer will work hard to build the mathematical case to make the requirements as broad and flexible as it can. It's an ongoing process, and as the type is introduced and matures, the OEM will continue to increase the scope of the MMEL, because each new item added improves Dispatch Reliability (because more more and more components and subsystems can be inop without needing to be fixed right away).
The MMEL is the foundation for the Minimum Equipment List that the airline uses.  The MEL is an in-house document created by the airline and approved by the local authority.  It'll be based on the MMEL but may have additional limitations imposed by the local authority as it deems necessary for that operation.
It's similar to the Maintenance Program. The OEM will issue a Maintenance Program for a given aircraft type, but each airline will have its own variations by negotiation with its local authority.


Can pilots hear their passengers clapping on touchdown?

In my 10 years of flying 747s on international flights, there was no way we would know of passenger reactions upon landing unless one of the cabin staff told us, and that was rare.


What is the difference between fail-safe and fail-soft?

Fail-safe does not necessarily imply that the system will continue operating after a fail. If the system stops operating but does not create a dangerous situation, it is still fail-safe. A non-essential service on board an aircraft such as the entertainment system can be fail-safe if it just stops operating because a fuse blows. If upon a failure the fuse does not blow and as a result the system catches fire after a short-circuit, it is not fail-safe.

Fail-soft does indeed mean that after a failure, essential services are still functional, although in aviation context this is mostly referred to as graceful degradation. A fly-by-wire system such as on board the A320 is fail soft:

If all flight computers are functioning, the system flies with normal law active, providing protections against getting into unsafe regions of the flight envelope.
Upon certain detected failures, the system switches to alternate law, still with some protections in place.
Upon further failures, the system switches to direct law: no more flight envelope protections, just surface deflection proportional to stick deflection.

So this flight computer system is fail-soft and fail safe. The electronic flight control system as a whole is fail safe: if all flight computers are lost, the system has hydro-mechanical connections from pedals to the rudder and from the trim wheel to the stabiliser.

Hydraulic systems require special attention regarding fail-safety, since a stuck servo valve can command a constant velocity: the actuator runs into one of its stops and has a hard-over failure. An elevator that is stuck in full up deflection is not safe, so the pitch control system needs to make provisions for fail-safety if this fault occurs. For instance by allowing left and right elevators to normally work in unison, but uncoupling them after a detection of a hard-over failure. The working elevator can then be commanded to full opposite position, making the elevator system fail-safe but not fail-soft: pitch command must now be done with the stabiliser trim. One elevator stuck in the mid position would be fail-safe, and control with the other elevator provides graceful degradation.

The flight control system on board an F-16 is fail-operational: upon a system failure, full system function continues, no degradation. It is triple redundant, meaning there are four systems on board that carry out the same function, while only one is required. The four systems function independently, and a monitoring system determines if all four outputs are within a pre-determined range. If three are and one is not, this system is switched off and the other three continue. This can happen once more, but if there are only two systems operational the voting system would not know which of the two has failed.


Why was Concorde never sold as a private business jet?

Private business jets have a few requirements:

Operational costs must be within budget. The concorde is pretty expensive to run as demonstrated by the high ticketprices you had to pay for a trip on one of them. Fuel is only part of that costs; maintenance is a pretty big part of that as well.
Be able to land and take off close to where the CEO has his meeting. This means making use of small airfields with their short runways and noise restrictions. Concorde needed a lot of runway and was not a quiet plane.
Account for airfields sometimes not having fuel available or the fuel being too expensive. This may mean doing the roundtrip on a single tank or doing another short hop to an airfield with fuel.

Business jets would also mostly operate on a domestic scale. Doing mostly short hops where the concorde would not even reach supersonic cruise altitude before it's over the destination. While plenty of business jets can easily do 0.75 mach which is already 3/4 the speed of sound.


It means that no Procedure Turn is required/expected if arriving within the sector defined by the 297 and 020 radials (inclusive) of DBL. The grey bars are a way of denoting the boundaries of the No PT sector (the entire pie section between the radials) without obstructing too much of the other details. That's why the bars are bordered on the north side of the two airways.
The Jepps wording seems to generate quite a lot of confusion because of the practice of including the words "Via Airway".  I found a message thread here that might help a bit.  Just remember that if confronted with something like this on a check ride and are confused, express your confusion to ATC and ask for clarification rather than blunder into a wrong move.


How thick is the skin of an aircraft like the Airbus A350 or Boeing B777?

From whats written here

  f100 skin is 1.0 - 1.4mm

  b747 skin is 1.8 - 2.2mm

  a320 skin is about 1.1mm

According this article on the 757

  ...Although Boeing specified that the skin in that area of the
  fuselage must be 0.039in (0.99mm) thick...

Some interesting info here as well.


What are the correct fixes for the MAX's pitch control systems?

The Max's problems had nothing to do with stall. The larger more forward nacelles caused shifts in the aerodynamic neutral point, only discovered during testing, that had an effect similar to shifting the center of gravity aft, and if you were holding a certain amount of stick force, say in a turn, keeping that stick force in would cause to nose to drift up unexpectedly.  This happened in certain configurations and speeds.  It was as if a whole bunch of passengers suddenly moved aft in a group and you were holding 15 pounds of back pressure and suddenly that back pressure would make the nose rise when you didn't actually change anything you were doing, and you would have to ease off some of the back pressure to compensate.

The behaviour in itself did not prevent the airplane from being certified if pilots were trained to recognize it.  But it was enough of a deviation from the other '37s behaviour that it put the common type certification at risk.  This results in a very expensive supplemental training burden on Boeing's customers.  MCAS was a software bandaid that used the trim system to make the airplane's behaviour mimic other 737s in the particular regimes where this was happening.

Boeing used an even stranger software bandaid on the 787-8, where the FBW system actively runs the normally dormant outboard ailerons to fix a wing vibration problem.  In the age of FBW this isn't all that controversial.

Anyway, there was a very fatal defect in the architecture of the system where it took data from only one AOA vane, because whoever did the system safety analysis decided that the failure mode where the system malfuntions due to defective AOA input was a low criticality failure (I think it was only classed as Major, not Hazardous or Catastophic).  It was classed as being equivalent to a stab trim runaway and depended on the HSTAB QRH procedure to deal with.

This allowed a mathematical risk justification for taking a signal from only one AOA vane.  This helps with system dispatch reliability, because if you have dual inputs and must have both, that's "anti-redundant" from a dispatch reliability perspective (two inputs are half as reliable as one).  Changing the system to have only one input doubles your dispatch reliability and if it's considered not that big a deal safety wise, it makes sense to do so. That's the main motivation for doing that single input architecture even though it was only more or less wiring and software differences.

The alternative to MCAS would have been physical redesign, maybe moving the operating CG forward which would have required a larger tail, or some other physical change, maybe something to the nacelles that would spoil the lift they were creating, that would've driven costs up and made the airplane way less saleable, and it would probably have killed the program.

In any case, notwithstanding all the other cockroaches that have scurried out from under the rug as it was lifted in the investigation, if Boeing had taken signals from both AOAs and lived with the need to put up with dispatch delays caused by having dual inputs where both must be present, none of this whole fiasco would have happened and it would be merrily doing its thing.  The safety analysis that was used to justify a single AOA input (and the FAA's failure to catch it) is at the root of all of it, in my opinion (having participated in supporting roles in similar crises with another OEM over the years).  Too bad really.


Is there a way, by which an airline or ATC would be alerted, if both pilots are asleep or incapacitated?

No there isn't. The only indication ATC has is if the pilot doesn't respond to radio calls but that can also be because of other issues like a radio malfunction.

There is not much ATC could do anyway if pilots are non-responsive.


Why are the largest civilian aircraft not adapted for military use?

There are several angles to this question, so I'll try to address what I think is important. My so-far short career has so far involved working almost exclusively with 747 derivatives, so I don't have as much to say about the A380, but I'll touch on it as I can.
In summary, the decision to modify a commercial aircraft for military use comes down to cost, schedule, performance, and politics. The platform needs to be the right one for the mission, be available in time to execute the mission, be worth the money for its capabilities, and be politically appealing. These four factors are best addressed on a case-by-case basis. The 747 has a much longer and more storied history than the A380, and I am not aware of any thoughts to militarize the latter; however, the 747 has been adapted for military use in several circumstances and there have been even more preliminary studies about doing so that never made it to production. So here is a brief summary of those programs. Hopefully looking at each will satisfy your curiosity and give a picture that answers the question.
Civil Reserve Air Fleet
Adapting an aircraft for military use does not necessarily involve modifying it in any way. The United States has the Civil Reserve Air Fleet (CRAF), a program through which domestic airlines pledge the availability of some of their aircraft to the Department of Defense "to augment the Air Mobility Command's long-range intertheater C-5s and C-17s during periods of increased airlift needs." Currently, none of these aircraft is permanently modified. Perhaps the interior of a passenger model gets reconfigured for a CRAF flight, but they are the same airplanes that members of the public fly on regularly. Back when Delta and United flew 747s, nearly all of them were available to the CRAF; now it is only 747 freighters that are available. The cost-schedule-performance analysis of this setup is favorable. The DOD only pays for the airplanes when it needs them, and is legally allowed to use them any time it needs them. Airlines get compensated at above-market rates when their aircraft are used. And unless you need to land on an austere runway, fly through contested airspace, perform an airdrop, or load/unload extremely quickly on the ground, a 747 can do almost anything that a C-5 or C-17 can, and usually more efficiently.
However, in the late 1980s and early 1990s, about two dozen early-model 747s were structurally modified specifically to support the CRAF, including N739PA:

The fuselage structure of N739PA differed from the majority of Boeing 747 aircraft in that it had been modified to carry special purpose freight containers on the main deck, in place of seats...The effect of this modification on the structure of the fuselage was mainly to replace the existing main deck floor beams with beams of more substantial cross-section than those generally found in passenger carrying Boeing 747 aircraft. A large side loading door, generally known as the CRAF door, was also incorporated on the left side of the main deck aft of the wing.

The CRAF door can be clearly seen in this photo:

Again, the analysis is favorable. The modifications were relatively simple structural ones and the DOD paid an ongoing subsidy to operators of these aircraft to offset the cost of the extra weight, which was much less expensive than maintaining a fleet of military-only aircraft of comparable capability.
I do not know what capabilities there are for NATO or other European countries to press civilian aircraft into service, but they do not seem extensive. This is where I think you'd most likely see an A380 used in a defense role.
Airborne Aircraft Carrier
Here's a fun one that didn't make it very far. The idea was to use a 747 as a flying platform for the launch, recovery, and refueling of small fighter aircraft:

Boeing's report sung the praises of this idea, of course, but my feeling is that it was something of a solution in need of a problem. The USAF had experimented with the idea before and found it to be technically feasible but operationally difficult, which was likely again the case here. Although the proposed schedule was favorable, the performance would not have matched a mission, and the cost of putting the system together and deploying it would likely have been huge.
Advanced Tanker Cargo Aircraft
The 747 was indeed converted for use as a refueling tanker, albeit in small numbers. The KC-10 won over a 747 variant mainly due to lower costs and better overall performance. The KC-10 could operate out of smaller airfields and had an all-new boom, as opposed to the 747 contender's barely-modified KC-135 boom with poorer handling qualities and less clearance away from the aircraft. There were a few other technical aspects favorable to the KC-10 as well, not to mention the inherent ongoing cost savings of flying a trijet over a quad.  Additionally, McDonnell Douglas at the time was in need of a lifeline for the DC-10 program and thus applied more political pressure. It should also be noted that the 747-based tanker design was better suited operationally for refueling long-range bombers and transports than fighters. As the other answers and some comments point out, an enormous tanker has some inherent deficiencies when directly supporting combat operations. My opinion is that Boeing focused too much on the long-range mission when trying to sell their solution, but this might be the best example of the 747's size as a direct and insurmountable detriment, whereas in most of its other military roles its size is its greatest benefit.
Despite the US not adopting the 747 solution, Iran purchased a couple of them, and at least  one still flies:

For Iran, the cost-schedule-performance triangle was beneficial. My guess is that Boeing offered a discount to Iran to get some tankers operationally deployed to help boost their case with the USAF, they were available almost immediately, and Iran's military operations were more concentrated and less reliant on situations that would put such enormous links in peril.
And just because it's interesting, it was the very first 747, RA001, that was modified to test this refueling concept, as seen here:

RA001 still boasts most of that equipment (the boom is long gone, though), but it should be noted that there were no modifications to the fuel system to allow it to pass fuel—the hardware was for testing tanker-receiver contacts and boom dynamics only. You can see RA001 up close for yourself at The Museum of Flight. And if you do stop by, say hi—I'm one of the volunteers on the restoration crew for this airplane.
Cruise Missile Carrier Aircraft
Another interesting one that never made it past the drawing board, although it got farther along than it usually gets credit for. The idea was patented by Boeing during the B-1 program as a way to supplement that aircraft and ease the B-52 into retirement.

It was eventually canceled in favor of the B-2 and upgrades to the B-52. History has questioned that decision, but at the time costs were deemed too high given commitments to the aforementioned platforms, and the considerable performance was still not found to fit well into the contemporary operational concept.
E-4
The E-4 was the first 747 derivative to enter military service. There is not much to say about it technically that Wikipedia doesn't, but it is worthwhile to note that, in the view of the Air Force, having four engines is a must on this type of platform. In the early 1970s, there wasn't much by way of twins, so that was taken care of at the time of aquisition. Redundancy and survivability are primary design drivers, so although its systems could probably have been transferred to a smaller, cheaper airframe, there is no way to match the mission assurance of four engines. Along with that, it would be tough to find a way to generate enough electricity on the airplane to power all its systems without four engines. Additionally, the first two airframes were offered to the government at a discount due to their being built for a canceled order.
Non-Developmental Airlift Aircraft
More a case study than anything, this might actually be the best example for how cost, schedule, and performance are balanced. I highly encourage you to read this retrospective:

...[the NDAA] was originally developed in the early nineties due to poor cost and schedule performance during phase two...of the C-17 acquisition. Forty C-17s were being built for phase two; and due to problems, alternatives were sought with respect to the remaining 80 aircraft. Attempting to leverage commercial industry, the NDAA promised a low-cost alternative to the DOD acquisition process. However, since this was an alternative for the C-17, DOD stipulated that the NDAA would have to be a jumbo cargo aircraft capable of carrying outsize cargo. The NDAA study focused on a minimally modified Boeing 747 cargo aircraft. These “minimal” modifications included hardened decks and a flipup nose and ramp system for ease of straight-in loading versus the sidemounted-cargo-door style loading of the commercial industry. Consequently, the price for the NDAA alternative increased from under \$150 to about \$200 million per aircraft. Nevertheless, after examining several options, the most cost-effective solution was an 86/30 mix of C-17 and NDAA aircraft. This mix, however, did not allow for a full strategic brigade airdrop nor was it optimized for tactical airlift requirements and lesser regional contingencies in support of peace enforcement scenarios. These requirements were better met by the military-specific C-17. Ultimately, the Defense Acquisition Board decided to procure the fleet of 120 C-17s and no NDAA.

Airborne Laser
The YAL-1 ultimately suffered from cost, schedule, and performance problems. The idea was to fly around a huge laser that could heat up and destroy ballistic missiles from afar. The 747 platform was chosen because it was the only airframe large enough to contain the huge tanks of chemicals needed to generate a laser strong enough to have any effect. But after almost two decades and more than five billion dollars, it still needed a laser many times more powerful to be operationally viable, so it was canceled. One prototype flew for over 10 years, but was unfortunately scrapped.

VC-25A
The VC-25A is generally what people think of as Air Force One, although technically that designation applies to any USAF aircraft with the president onboard. Again, the number of engines was a major design driver, and in this case the size and iconography of the 747 helped it tremendously. The DC-10 was competed as an alternative, although it never was a serious contender and was reportedly only included to get Boeing to lower its price. As with the E-4, survivability, redundancy, and power requirements support a four-engine airplane; the floor space of a 747 also supports a lot of functions that couldn't otherwise coexist. Even by the time the VC-25A was introduced, the 747 had an enduring and recognizable preeminence in the history of aviation and Unites States prestige that the government found attractive to its branding as the president travels the world. Commonality with the E-4 airframe was also a consideration. In this case, politics and performance played an outsized role in selection of the aiframe, with cost and schedule secondary. Obviously there was much willingness to spend the big money and wait some extra time to fulfill all the requirements.
VC-25B
Once again, we have power and redundancy requirements driving the selection of the airframe for the next presidential aircraft. There was some early talk about perhaps pursuing an A380 option, but politics quickly put that idea to bed in favor of the 747-8. The VC-25B will have modifications similar to those of the VC-25A, and will probably look similar:

The program has been much in the news due to cost, schedule, performance, and politics, but is overall proceeding with similar priorities as the VC-25A program did.
Conclusions
I count about 30 747 airframes that have been modified and flown for military purposes. Obviously that's not a huge number, but it is actually fairly respectable for an aircraft of its era, although 707 variants are clearly more ubiquitous (it's important to note, however, that the C-135 family is not a derivative of the 707). Nowadays, with the KC-46 and P-8 leading the way, commercial derivatives are becoming more attractive to the armed forces. But with production of the 747 winding down, we are unlikely to see any more variants beyond the VC-25B: parts will become more difficult to obtain and the labor force skilled with the airframe will dry up. The 747's size and capabilities have both helped and hindered it along the way, and it warrants a case-by-case look at each program to see how cost, schedule, performance, and politics have played a role. The A380 is a somewhat different case, being more recent and less revolutionary in its era than the 747. It has not found a military mission that cannot be accomplished with smaller, cheaper airplanes, and it has no history of modification to help it win over the decision-makers. I am doubtful that we'll ever see it take on a military role.  A lot more could be said about any of my examples and the overall picture, but I hope I've dispelled the idea that the 747 is not used militarily, and I hope I've provided some insight as to why it is not used more.


Does engine failure shut off the auto-pilot?

No, there is no necessary connection between the autopilot and an engine failing on any aircraft that I'm aware of -- which is far from all of them!  If you're in an idle descent, one motor failing wouldn't really change the flight characteristics of the aircraft, so in that case there's no great need to get rid of the autopilot.  Also, once you have everything trimmed up (i.e. rudder trim in to balance the asymmetric thrust), it's nice to put the autopilot on to let it keep the wings level & hold altitude for you while the pilots sort out everything that comes next -- checklists, ATC coordination, choosing where you'll land, etc.

What DOES come off almost immediately after engine failure, at least on the 737, is the Autothrottle.  It will sense that the thrust and throttle position are mismatched, and rather than moving the good throttle around when you may not be ready to compensate with the rudder, it disengages.  I'm not certain if that is universally true; the 777 computers are crazy smart, and they may actually leave the A/T engaged in that sort of a scenario (while the A/P flies the rudder for you).

The basic challenge that you mention, an autopilot that will hold altitude even when the thrust is insufficient to maintain airspeed, is a scenario that's not limited to an engine failure.  The automation will have some set of rules as far as when to hold, when to go into reversion modes, and so forth.  And if you get caught in the wrong spot, the automation can bite you.  In the 737, for instance, if you're in altitude hold or glideslope capture, the autopilot will hold that no matter how badly the speed decays. (Stall while on glide path, or follow the speed cursor into the dirt short of the runway... damned if you do, damned if you don't!)  On the other hand, if you're in a vertical speed mode or a VNAV climb or descent, there are speed reversions that will change your flightpath rather than accepting a speed above or below safe limits. If everything has been set up correctly and the Autothrottle is engaged (or the pilot is setting the power appropriately), then everything works really well.  But if enough things go wrong and you aren't paying attention... well, that's when bad things can happen.


How can a VTOL aircraft control yaw while hovering?

In case of F-35, the yaw control during hover (and transition to forward flight) is provided by the Three-bearing swivel module (3BSM), which forma a part of the Rolls Royce Lift System. As Lokheed Martin notes:

  Two roll ducts supplied by engine fan air provide roll control. Yaw control is through swivel nozzle yaw. Pitch control is effected via Lift Fan/engine thrust split.

From codeonemagazine

  The three-bearing swivel nozzle, 3BSN, design uses three segments of the engine exhaust duct cut on an angle and joined by two airtight circular bearings. ... The forward and aft segments always stay aligned with one another in the rotational axis. The center segment rotates through 180 degrees relative to them. The third bearing is on the back of the engine aft of the turbine stage and provides the ability to swivel the nozzle thrust axis in yaw at any pitch angle.

Consider the nozzle in VTOL position, like below:

By Tosaka - Made by uploader (ref:見森昭編　『タービン・エンジン』　社団法人日本航空技術協会、2008年3月1日第1版第1刷発行、ISBN 9784902151329, 1), CC BY 3.0, Link

If we hold the aft two segments and rotate only the first one, it is obvious the rear segments will rotate along the engine axis, producing yaw by virtue of its position at the rear. There is a slight associated loss in lift produced, but the Digital Flight Control System can easily compensate for it.

Of course, this method of controlling yaw in hover is specific to F-35. In case of Harrier, the reaction control system had 'puffers' at the tail to provide yaw control.

Reaction control system, showing pipes and nozzles for engine HP bleed air.; image from harrier.org.uk

  In addition to the vectoring engine nozzles, the Harrier also requires a method of controlling its attitude during jet-borne flight, when the normal aerodynamic surfaces are ineffective. To this end, a system of reaction control nozzles in the nose (blowing down), wingtips (blowing up and down) and tail (down and lateral blowing) are fitted to the aircraft.


Helicopter Basics: How does lead-lag of blades actually help in compensating for increase/decrease in speed due to flapping?

Blade flapping is simply the action of the tilting of the rotor disc; the blade's tip is following a particular path attached to a hub that is rigidly fixed on its vertical axis. The blade flaps up and down because its incidence/pitch is being continuously varied (or not if the stick is centered) by the swash plate.  The limits of the rotor disc's tilt range is, beyond the swash plate limits, ultimately the blade flapping travel limits.  Articulating rotors can handle this, but on a two blade teetering rotor, achieving those limits is called "Mast Bumping" and is a fatal condition.

For lead lag, the issue is you need to allow for that motion on an articulating rotor helicopter because Coriolis force makes a blade want to speed up as it flaps up relative to the other blades (actually, moving off perpendicular to the mast's axis).  When it flaps up, its center of mass moves closer to the hub than a blade on the other side that is closer to perpendicular to the mast, which makes it want to speed up, like a figure skater pulling arms in while spinning.  The lead/lag hinge provides the necessary compliance to accommodate the speeding up and slowing down tendency of the blade as its center of mass moves closer and farther from the mast as it rotates while moving up and down, so it doesn't force the rotor hub to absorb the forces.  The lead/lag damper is there to resist sudden movements of this lead/lag action that can be caused by sharp ground contact, which can lead to ground resonance.

On a teetering rotor system, you don't need lead lag hinges because you have the geometry of the teetering hinge, which is the blade flapping hinge for both blades on a single flapping axis.  The up flapping blade moves away from the hub because the hinge is above the blade axis (called an under slung hub) and this keeps the CG from moving closer to the hub significantly, eliminating most of the Coriolis forces, or reducing them to a level can be absorbed by the rotor head and blades.


Yes. During and after WW2 several aircraft were converted to serve as "Dumbo" aircraft, dropping boats or rafts near people in distress. Other models were used as well, but the B-17 were among the most prominent. Most were retired when the helicopter gradually took over rescue operations.


What are (wing area)/(weight) ratio in birds and airplanes?

From 'The Simple Science of Flight', by Henk Tennekes, MIT Press

https://mitpress-request.mit.edu/sites/default/files/titles/content/9780262513135_sch_0001.pdf


LPV, LNAV/VNAV, and Baro VNAV are considered to be an 'Approach with Vertical Guidance (APV)'. These types of approaches are differentiated from 'Precision' approaches (ILS, PAR, etc.) in the FAA AIM (Section 5-4-5, Paragraph 7):

  (b) Approach with Vertical Guidance (APV). An instrument approach based on a navigation system that is not required to meet the precision approach standards of ICAO Annex 10 but provides course and glidepath deviation information. For example, Baro−VNAV, LDA with glidepath, LNAV/VNAV and LPV are APV approaches.


How much is a swashplate system more energy efficient than a fixed blade system for the same load

The question does not really make sense: a helicopter is a kind of aircraft, a drone is a mode of how a vehicle is controlled.
I can rip the seats and controls out of a helicopter and put some clever software, some cameras, and some transmitters inside, and boom: I have a drone that can carry exactly as much as it could before – probably even more because humans and safety systems are heavy, and we got rid of both of those.
In fact, that's exactly what some companies are doing. The Northrop-Grumman MQ-8C Fire Scout is literally just a Bell 407 with some added electronics and software. And while this particular drone is designed for combat, there are others which are designed for cargo delivery. For example, two uncrewed Kaman K-MAX were deployed to Afghanistan already in 2011.
Here is a video about the Office of Naval Research's Autonomous Aerial Cargo/Utility System AACUS program. The goal of this program is to have a software/hardware package that can be installed in any helicopter to make it fully autonomous. There is no reason you couldn't install it in a Mil Mi-26, for example.
So, in short: by turning an existing helicopter into a drone, a drone can by definition lift just as much as a helicopter. By designing a helicopter specifically as a drone, you could potentially lift even more, because you can get rid of all the weight for the cockpit, seats, life support, safety systems, controls, etc. You could also remove a lot of redundancy, if you consider occasional crashes acceptable when no humans are on board.


Is "lower pressurization" the correct term for the 787 Dreamliner?

The terminology is confusing. When you say lower or higher, it is better to clarify the reference.

Boeing 787 has a higher cabin pressure compared to the legacy airliners.

The best way to say it is that it is pressurized to (or has) a lower cabin altitude compared to other airliners.


May a helicopter fly at night with only strobe lights?

In the US FAR §91.209   Aircraft lights. applies

No person may:
(a) During the period from sunset to sunrise… (1) Operate an aircraft
unless it has lighted position lights;
…
(b) Operate an aircraft that is equipped with an anticollision light
system, unless it has lighted anticollision lights.

There are no exceptions. A couple of thoughts though. It can be pretty dark on the ground and still not be after sunset. I live in the shadow of a mountain and the sun goes down at my house 15 minutes before sunset.
It is possible that they just forgot. Most pilots who have strobes turn them on all the time (an exception would be in clouds or fog) so they would be on.
It is also possible that they were on, but because of the position of the helicopter, you just didn’t see them.
The beacon (referred to in the FAR as anti-collision light system) does not have to be just red. Lots of them are red in back and white in front, so you may have seen just the forward facing light.
This StackExchange Post has more details on lighting.


What are static discharges for on an airliner?

It is difficult to tell by the picture, but they look like static wicks. See this question.


Crew members each have their own approach to this but in general on the long haul routes, as a pilot you have at least 24h layover, so you can catchup on some sleep, walk outside for a bit (depending on the local time) and then sleep some more so you're fit for the next flight back home. At home you have a couple of days off to recover from the trip.

On the very long flights 13h+ the pilots are with at least 4 so you can do a quick nap on board as well.

As a passenger I cope with the jetlag by looking at the arrival time, do I arrive in the morning I will try to sleep on the plane, will I arrive in the afternoon the I will try to stay awake and go to bed early. By doing so I wake up easily next morning and do not feel jetlagged.


Are the first solo flights by a student pilot more dangerous?

There is no evidence to back the claim that the first solo ride of the student is more dangerous compared to the later ones.
US NIH conducted a study on the accidents with solo pilots, which doesn't indicate that first-time solo fliers are any more prone to accident than others. Aircraft accidents with student pilots flying solo: analysis of 390 cases by  Sjir Uitdewilligen and Alexander Johan de Voogt analyzed NTSB probable cause reports of 390 crashes that occurred in the period 2001 – 2005, concluding that,

Student pilots flying solo show fewer injuries and fatalities compared to general instructional flights while in our sample first-time solo student pilots did not feature any fatalities.

Note that this gives only the injuries and not the times the students got into accidents per se. Out of a total of 3811 accidents involving student pilots, 390 occurred while they were flying solo and around 50 involved first-time student solo pilots. Actually, student pilots themselves are prone to less accidents compared to others. From Comparative Analysis of Accident and Non-Accident Pilots by David C. Ison:

Most accidents (49.1%) were conducted with individuals holding a private pilot certificate. Second in incidence were commercial pilots (28.2%), followed by Airline Transport Pilots (ATPs) (13.7%), and student pilots (5.7%)
Considering that 20% of pilots hold a student certificate, these individuals have a disproportionally low accident occurrence.

The report also gives some additional insight into the reason the first-time solo fliers have lesser injuries:

... first-time solo pilots are commonly confined to the airport and practice their takeoff and landings. Such operations may result in accidents, but they will occur near to the ground with a lower risk of a fatality

The report also gives some data about higher experienced student pilots sustaining more injuries, though nothing conclusive, noting that,

... in 25 cases, student pilots were reported to have more than 100 and up to 322 h of flight experience. In the dataset, these pilots were significantly more often injured than students with less hours of flight experience.

It has to be noted that as the hours logged gets more, the students get into more demanding flights which may be reason for this increase in injuries.


Why would it not be OK to replace a map light bulb with an LED?

White LED spectra contains quite a bit of blue range wavelength, which is bad for night vision.  Red light is much better.
The eyes have cone receptors for day time and rod receptors for night vision.  The rods contain rhodopsin, which enables night vision.  It takes about 1/2 hour for enough to build up to have full night vision.
Exposure to shorter wavelengths quickly breaks down rhodopsin, which is why blue light is to be avoided.
Natural sunlight is strong in blue (and UV) spectra.  Incandescent tungsten filaments have much less blue/green spectra, and a lot more orange/red.  So it may be a bit "old school" to shun LEDs.
Newer OLEDs have spectra closer to candles and incandescent.
One interesting measure is how much the light suppresses melatonin, which helps one sleep.  Newer OLEDs were found to be only fractional of blue light, so it would be important to be sure any replacement map light is appropriate for the task.


What is the "A/B AUTO EXT" button for in a Falcon 7X?

It's the arming switch for Air Brake Auto Extend on landing.  The airplane has speed brakes (often called Flight Spoilers) the pilot can operate manually for glide path control.  This mode extends them automatically as lift dumpers after touchdown.


Why are we still putting lead in our fuel?

There is nothing "special" about an aircraft engine that requires lead in the fuel -- Engines don't much care about the lead in tetraethyl lead, nor do they much care for it (it gets everywhere, fouling sparkplugs and contaminating the oil). What they care about is the octane (anti-knock) rating of the fuel.

Many "low performance" aircraft engines run just fine on unleaded fuels with a lower octane rating (among them the Lycoming O-320 and O-360 family that power a good chunk of the GA fleet), but high-performance aircraft engines (e.g. the IO-520 you'll find in Beech Bonanzas) require a 100 octane fuel. The approved specification for 100 octane aviation gasoline (ASTM D910) lists tetraethyl lead as the octane booster of choice.

It's also worth noting that some of the octane boosting techniques used in automotive gasoline are not acceptable for aircraft engines (the most common in the US being the addition of ethanol, which has two undesirable effects: reducing the energy content of the fuel, and damaging aviation fuel system seals and other components).

So why do we still make 100LL, and why don't we offer the other unleaded options at every airport?

Aviation gasoline is a minuscule slice of the gasoline market, so it doesn't make sense to have 5 tanks with 5 different grades of fuel at every airport:
All aircraft engines will run on 100LL, so 100LL (leaded) aviation gasoline is still produced because it is a "single fuel" solution to piston aviation's needs.

If leaded avgas were to disappear tomorrow the engines that require it would be left without an approved fuel, which would result in those aircraft being grounded until such time as an alternative fuel could be developed or the engine manufacturers develop a procedure for derating the engines (operating them at reduced power). For obvious reasons neither of these options is attractive, particularly to folks who own higher-power engines which were presumably purchased for the performance...

Changing the avgas specification is quite a bit of work - it requires ensuring that the new fuel is a "drop-in replacement" for 100LL -- one which can be mixed with 100LL in any proportion, and will work correctly in any engine designed for 100LL fuel.
The FAA is working with engine manufacturers and major fuel producers on a program which will result in such a specification (a Google search for unleaded avgas transition also produces useful results), and hopefully a universal unleaded aviation fuel specification and one or more products will come out of those efforts.


Determining total engine life in relation to SMOH/SFOH

2000 is common but that depends on the engine. The official TBO is what ever the TC/manufacture states, here is the list for of the Lycomings published by Lycoming and here is the continental list. These are manufacturer recommended TBO's and are presumably based on data and tests they have run but they are in the end an estimate and usually reflect a relatively cautious value.

The "actual" TBO is a somewhat subjective number that no one can give you. Internet data and general collaboration can help you get a picture of what to expect for a given airframe/engine combination but individual units must be handled on a case by case basis. When assessing any aircraft its good to look for statements like "generally makes it to TBO" or "this aircraft had a lot of engine issues" or "oh man that turbo charger made that a finicky power plant" then come to your own conclusion. Forums, message boards, and old APOA articles can be your friend on these matters. Oil analysis and compression testing is the best objective way to measure engine health and a good pre-buy is important for that. Some people say "if it ain't makin' metal keep on flying it"


How do I keep my home address private following new aircraft registration?

The 'usual' alternative is to have the aircraft owned by a legal entity like an LLC or trust of some kind (trusts are also used by foreigners who own N-reg aircraft). But that only adds a layer of obfuscation: if someone really wants to know who owns the aircraft then they can dig into the LLC or trust ownership details. That information is usually also public although it's at the state level not federal level.

The best thing here is to talk to an attorney in your state, preferably one with aviation experience. He can tell you what legal entities might fit your needs, as well as the pros, cons and costs of each one.


Has anyone built an aircraft with a flat ring wing?

George Kitchen patented a design and half-built a biplane. It was completed by Cedric Lee and Tilghman Richards in 1911 but failed to fly. Richards went on to develop a series of increasingly successful Lee-Richards annular monoplanes before the outbreak of WWI.
This was a serious and promising design, having been wind-tunnel tested by the National Physics Laboratory in the UK during development. Kitchen and Richards understood that the strange shape would create vortices which trailed back over the rear part of the wing, and they used these to help impart stability. The monoplanes were indeed all safe and stable in flight (although the first was tail-heavy), a rare characteristic in those days. Pilots included Gordon England, Gordon Bell and NS Percival.


How to best recover from an excessive descent?

Sideslips at high G and/or high speed aren't a good idea structurally.

Absent a G meter, airspeed and judging G load is all you've got.  If I found myself going straight down at 100 kt, I would try to keep the speed below maneuvering speed, 128 kt, but if I felt I was applying too much force and risked an accelerated stall, I would let it go faster and if the air was smooth I'd let it go up to Vne if necessary.

And in a really extreme case, if the choice was exceeding Vne or maybe pulling the wings off, I'd take my chances exceeding Vne.  If you have to exceed a parameter, it's safer to go too fast than to pull too hard, because there is ample safety margin for flutter, and you know how much you are going over.

Of course, without a meter, with G load it's all judgement.  The yield G limit for normal category is 3.8, so what can be really useful is go with your instructor and practice 60 degree banked level turns to become familiar with the sensation of 2Gs, which will at least give you a reference point.  Even better if you can get a ride in an aerobatic airplane and learn what 4 Gs feels like and try to stay below that when the time comes.

The other big thing is knowing whether you are in a dive inverted or right side up.  This is a problem for pilots who get flipped over by wake turbulence and end of upside down in a 45 degree dive, and instinctively pull right around in a split S through 90 degrees and rip the wings off.  In an inverted dive most airplanes will accelerate past Vne in a heartbeat.

If you are in an inverted dive like that you have to roll the plane right side up before pulling out.  Recognizing it takes training and professional pilots often get upset training in aerobatic aircraft to develop the correct reactions.


What is the difference between a navigation database and an airport mapping database?

Navigation databases are typically targeted at FMS based systems, usually using the ARINC-424 standard.  These are ASCII database files that describe aspects such as approach procedures, flight plans, spacing, etc.  It would also provide basic runway information such as heading and altitude of touchdown points - enough to navigate but not enough to paint a completely pretty picture.
By contrast Airport Mapping Databases provide a detailed layout of the entire airport in question - runways, taxiways, vertical structures such as buildings, etc.  The industry standard is ARINC-816 for the databases themselves, but the content is based on DO-272's parameters.  They are usually installed into systems with displays, e.g. Electronic Flight Bags (EFBs) - this may include Class 2 EFBs that are simply iPads for ground-only operation.
Moving maps of this type provide situational awareness, especially when coupled with Cockpit Display of Traffic Information (CDTI) and its associated applications utilizing ADS-B/TIS-B: these provide awareness as to other aircraft that might be in the vicinity, threat level, etc.
Side note: additional CDTI applications that utilize ADS-B are enumerated in DO-317.  These include airborne procedures, e.g. decreased spacing for in-trail procedures (ITP).