When airplane pilots begin a 10 minute wait timer when lightning strikes, is there a geometric reason behind it?

No, because adding candles to candy does not make much sense.
The dimensions are different, so the relative numeric values depend on the choice of units. You could equally state the rule as you have to wait ⅙ of an hour after lighting strike within 5 km (if it's statue miles; 5.5 if nautical) and now the numbers won't match any more.
Besides, it is a 3 mile radius, so the area is about 28 square miles and the numbers never matched to begin with.

The real reason is two-fold:

When there is active storm right over the airfield, somebody could get struck by lightning. Inside aircraft and vehicles is safe, because the lightning will ground through the skin and not get inside, but out on the ramp it wouldn't be. 10 minutes is long enough to consider the storm no longer active.

The storm builds up static charge on the aircraft and vehicles. This is again not a problem for the occupants, because the conductive skin ensure the whole vehicle is at the same potential, but it could cause a static discharge strong enough to hurt someone or set something on fire when touching the vehicle from outside. 10 minutes is considered long enough for these charges to gradually discharge through the wheels to the ground and through the static wicks to the surrounding air.
This would also apply to aircraft that flew near the storm just before landing, but that is normally avoided as storms generate dangerously strong wings.

The 3 mile radius is simply size of typical storm.


What is the maximum altitude allowed to fly a model plane/helicopter in England?

According to the UK CAA, a model aircraft is defined as:

  any ‘Small Unmanned Aircraft (SUA)’ (0-20 kg) used for sporting and
  recreational purposes and a ‘large model aircraft’ is defined as any
  ‘Unmanned Aircraft’ (over 20 kg) used for sporting and recreational
  purposes.

The following rule applies to all "small unmanned aircraft", i.e. up to 20kg:

  (3) The person in charge of a small unmanned aircraft must maintain
  direct, unaided visual contact with the aircraft sufficient to monitor
  its flight path in relation to other aircraft, persons, vehicles,
  vessels and structures for the purpose of avoiding collisions.

The following rule applies between 7kg and 20kg only:

  The person in charge of a small unmanned aircraft which has a mass of
  more than 7 kg excluding its fuel but including any articles or
  equipment installed in or attached to the aircraft at the commencement
  of its flight, must not fly the aircraft:

  (a) in Class A, C, D or E airspace unless the permission of the
  appropriate air traffic control unit has been obtained;

  (b) within an aerodrome traffic zone during the notified hours of
  watch of the air traffic control unit (if any) at that aerodrome
  unless the permission of any such air traffic control unit has been
  obtained; or

  (c) at a height of more than 400 feet above the surface unless it is
  flying in airspace described in sub-paragraph (a) or (b) and in
  accordance with the requirements for that airspace

So in theory, a model aircraft weighing less than 7kg could be flown to any altitude, with the only limitation being the requirement to keep in it sight. From 7kg to 20kg the altitude is 400ft, unless you meet the airspace requirements. In practical terms, the requirement to keep the aircraft in sight "unaided" is the main limitation and that restricts the altitude of smaller models in particular.

If it's over 20kg, the model aircraft is subject to all the regular UK aviation rules but in practice a written exemption is required:

  Large model aircraft having a mass between 20 kg and 150 kg are
  subject to all of the Rules or Articles of the Air Navigation Order.
  As many of these Rules are practically impossible for the model
  operator to meet, the modeller must request a specific written
  Exemption to allow the model to be flown

The CAA homepage for model aircraft is here.


The solution that I needed is the following image:


What are the steep ramps often erected at large airports?

Here in the United States these are called blast fences.  They protect whatever may be behind them from the direct effects of jet blast by directing the blast upwards.


Why would one cylinder on a Continental O-200 run cold at idle?

A: Idle circuit is set too lean and the cold jug is not firing.

B: Intake leak, causing same condition as A.

C: A little of both.

I know that a lot of people will lean out their idle mixture, by adjusting the screw on the carb, to reduce plug fouling with 100LL fuel (since leaning with the cockpit mixture doesn't do anything in the idle range).  You can tell when this has been done because the engine doesn't have the little RPM bump when pulling idle cutoff, and also it may require extra prime to keep running when cold.

Also, please write your questions with a bit of structure and grammar.  That stream of consciousness no-grammar style (that a lot of people use in emails out of laziness) is a total pain to read and interpret.


Why does the ICAO alphabet use "Charlie" for C?

Hard C sounds too much like K.  Ch (Charlie) will not be confused with K (Kilo). And soft C sounds too much like S (Sierra).


There are a several theft-deterrent mechanisms in place.

On small airplanes, most commonly, the door to the airplane itself is usually
locked with a key. (Notice the key cylinder in this picture below the silver door handle:
Prop locks:
Throttle locks:
A lot of airplanes do have an ignition key which you turn to engage the starter.  Of course, as jaytre mentioned, this can be circumvented by hand-propping (which is a very dangerous endeavor for unskilled people who haven't done it before)
You would have to know how to operate the basic systems of the airplane as well as how to fly.
AOPA's Airport Watch Program
Fences and other physical security measures around airports.


If you turned base early, cutting off other traffic, what is the safest way to rejoin downwind?

Interesting, but you're not the first to encounter this situation. I understand from what you say that you were going to wedge in between the no 1 and no 2 traffic already established on final.
Given the circumstances and not time to think about this, the preferred option would be to turn left to rejoin downwind. Assuming no other traffic in the pattern. Then you are turning towards the other traffic. A left turn would have given you a full 270 degree and time to regroup

Should there have been other traffic on the left base then they would be positioned further downwind from your position. You may become a conflict for them then by turning right.  Equally there may have been traffic joining downwind like you did in which case a left turn could become a conflict to them.

This is just assumption. I'm just pointing out the need for full on situational awareness particularly in the circuit. Need to know where all traffic is relative to you.

Finally, I would say it would have been more reassuring for the controller to specify “turn left/right now to rejoin downwind”. If you had made it to final then a missed approach would be the way out and continue rwy heading until advised.


What is the procedure to replace carpets in airliners?

The seats are installed on rails, so they can be easily removed (or moved to a different seat pitch). The bolts are in plain sight (random source for example photo).

The carpets are laid around the rails. I suspect the carpet does not protrude underneath the base board, so they'd only have to remove the seats to get the carpet out.

This is the inside of an airliner with the seats and carpet removed:


What determines in which direction a runway is used?

There are several factors:

Prevailing winds
Neighboring airport traffic patterns
Size of inbound aircraft
Where the aircraft is coming from
Final parking space
Congestion
Fuel status
Weather (thunderstorms)
Noise considerations

At small airports, it is usually just the runway that faces into the wind and can accommodate most of the traffic coming in.

At large airports, the wind dictates which flow is being used (like a "north flow" or "south flow"). From there, aircraft usually are assigned to land on which ever side of the airport their arrival procedure brings them to. Sometimes, it is also decided by which gate/terminal they'll be parking at. Lastly, the available approach procedures can change things if the weather is not good


Why does the Mitsubishi MU–2B have its own SFAR?

Since the MU-2 weighs less than 12,500 lb, a type rating is not required to fly the plane, so pilots only need a multi-engine rating. However, it is a high performance pressurized aircraft that requires more skill to fly. Mitsubishi Heavy Industries asked the FAA to create a type rating requirement for the MU-2, but the FAA decided on creating the SFAR instead, which is more strict than a type rating, especially in the amount of training specifically required.

Research showed that the accident rate of the MU-2 from 2001 to 2005 was not really exceptionally high compared to aircraft of similar size and performance. While the accident rate was higher than some, it was also lower than others. However, the FAA received a lot of pressure to create a rule for the MU-2.

Regardless, the accident rate has gone down significantly since the FAA created new regulations for the plane.


Is the capacity of an airspace sector related to the number of routes it crosses?

Calculating the capacity of an ATC sector is a complex issue, you should not expect to find one single determining factor.

A few obvious factors come to mind:

Lateral extend of the sector (size)
Vertical extend of the sector
Whether or not surveillance is available (RADAR etc.)
The route structure, and whether traffic is forced to follow certain airways or not (free route airspace)
Military areas, their activation frequency and extend
Type of traffic in the sector
Uniformity of traffic in the sector
The actual traffic flow in the sector. Is it mainly an en-route sector where aircraft will enter and leave at the same level, or do a lot of aircraft need to climb/descend within the sector?
ATC staffing. Is the sector manned by a single controller, or by a pair (executive+planner)?
Radio coverage, and whether or not CPDLC is available
Weather - for example, is it an area with frequent thunderstorms?
Runway configurations of any airports covered by the sector, as well as possible noise restrictions

There is no formula that couples all these factors together. In the end, the capacity of an ATC sector is an estimate based on an evaluation of the above (and probably more) factors, experience and trial-and-error. In many cases, it will be an iterative process.


Statistically, how safe are para-motor craft compared to other GA planes?

In the US, there are no records kept nationally, because they fly under FAR Part 103, and are, for the most part, unregulated. Neither para-motors themselves, nor their pilots are required to be certified. Para-motors are not required to be registered. In fact, there is no actual government regulation requiring training of any kind to fly a para-motor. It is recommended, but not actually required.

There is no requirement to report accidents to any governing body, beyond those of the organization (flying club) the pilot may belong to.

Pilot certification -

  At this time, however, pilots of ultralight vehicles are not required by Federal regulation to be certificated.

Aircraft Certification -

  However, the FAA presently has no intent to require certification of these vehicles by Federal regulation.

Aircraft Registration -

  However, registration of ultralight vehicles will not be required by Federal regulation at this time.


Smart skins are at least 20 years old and, like fusion energy, just around the corner since then. The usual concept is to embed optical fibers in the structure and shine laser pulses through them. If the fiber is damaged, it will transmit less light, and by measuring the return time of a very short laser pulse, even the location of the damage can be detected. This concept requires fibers with the same break elongation as the load-carrying material, so they break just when a crack in the structure starts. To detect even small cracks, a lot of fibers must be evenly placed, which is only possible with fiber reinforced plastics. The effort to place a light source and a detector at each end of every fiber has so far prevented a practical application, at least to my knowledge.

Other techniques send clearly defined "pings" through the material and detect the propagation of the sound wave with a number of microphones. By comparing the measured signal with a reference signal, damage can be detected in metal structures as well. This technique needs some processing power, but is easily within the scope of modern microcontrollers. However, outside noise will interfere with the measurement, so it needs well defined conditions to be effective.

The downside would be more mass, investment and operator training. Generally, more advanced techniques for structural health checks have been steadily introduced in the last 80 years. Given the high cost of maintenance today, I expect that deployed damage detection technology will continue to advance, with a healthy time gap to what is possible in the laboratory. So there is some truth to those BAe claims, but I would hardly call it revolutionary.

Even more advanced are concepts of self-healing structures which contain capsules of a two-component resin. When the structure breaks, the capsules break as well and the freed resin helps to mend the crack.

If you ask me, the mass of those microcapsules would be better invested if it carries load right from the start, so the structure will tolerate higher loads and more load cycles. But I guess those research grants need to be spent somehow, and marketing departments need to write about revolutionary discoveries on a regular basis.


Which airports in Ireland use Surface Movement Radar?

The wording of this IAA information implies that it's Dublin only:

  The IAA also operate an Advanced Surface Movement Guidance and Control
  System (ASMGCS), which facilitates the safe movement of aircraft and
  airport vehicles at Dublin Airport, even during poor visibility
  conditions. The ASMGCS incorporates Surface Movement Radar,
  Multilateration and ADS-B.

There's a similar comment in this document. And the AIP entry for Dublin mentions surface radar in the obstacles list, but the entries for Cork and Shannon (the next busiest airports) don't.


Structural design software for airplanes

There are many package available for structural analysis, but I know that NASTRAN/PATRAN are used extensively in aerospace engineering.

The software was originally developed for NASA in the sixties and has been expanded with a suite of problem solvers for various structural problems including fatigue and acoustics.


How did this Vampire's takeoff damage the runway so much?

Partly it's that the Vamp's tail pipe is only a foot above the surface, angled toward it, so with most jets that wouldn't happen quite as easily.  Plus it looks to me like the airport operator cut corners with a really cheap driveway quality paving job with an asphalt layer only an inch or two thick.


Variable versus fixed costs in the airline industry

I’ll address your second question first.

I'm fundamentally confused about the distinction between fixed and variable costs.

Simply put, variable costs are ones that go away if you cancel a flight (or, more likely, a pair of out-and-back flights) while fixed costs are ones you still have to pay.
A challenge is that many “fixed” costs are actually step-variable costs. For instance, if you cancel enough flights, you might be able to reduce how many aircraft or gates you need. But with the black and white dichotomy given, we classify those as fixed.

Landing fees (ATC, runways, taxiways, parking at stand or apron for a certain time (e.g. 2 hours), use of gates / fingers / terminal for disembarking).
Surcharges or rebates in addition of landing fees (for noise, peak-hour operations)
Passenger charges
Overflight fees

If you don’t land, there is no landing fee, so that’s variable. Ditto for gate fees, noise fees, peak-hour fees, passenger fees and overflight fees.
Space to park an unused plane isn’t usually an issue when it’s just one or two flights canceled; that will be included in some other fixed cost.

Lounges fees.
Scheduling coordination.
Administrative cost (managing/issuing tickets, etc.)

These are fixed (or step-variable), since canceling one or two flights won’t meaningfully change them.


Why don't we see diverging nozzles or diffusers?

The basic answer is that pressure differential at the exit isn't what you want for thrust.  You want the exhaust stream to have velocity.  If it exits the nozzle with excess pressure, that extra pressure essentially gets converted into plume size (see the underexpanded streams on rocket first stages at high altitudes as an example).

This is why subsonic nozzles converge, and supersonic nozzles converge to a Mach 1 throat and then diverge.


What was the purpose of the "tail prop" on the Ilyushin Il-62 and why was it necessary?

Are you asking about the rear support wheel? It is for supporting the aircraft and avoiding tilt on the ground.

Image from wikimedia commons. Autor:M Radzi Desa

As the aircraft had four engines in the aft, the cg would've been aft too; so they added a tail prop to prevent tilt on ground.

Interestingly, this doesn't seen to be unique for Il-62. Another aircraft with rear mounted engine, Sud Aviation Caravelle, has something similar to this.

Image from wikimedia commons. Author: Eduard Marmet


If you make up your own IFR waypoints, how does ATC know where they are?

Yes, you can define your own waypoints. When we use the waypoint identifiers that are published ATC knows where the waypoint is. That's because we're using the same database they are which contains the Lat/Lon location for each of the waypoints in the database.

When we create our own waypoints, ATC doesn't know anything about them. So we just have to give them the waypoint in a form they can interpret.

Almost all FMS provide the capability for pilot-defined waypoints. They can be entered in the form of Lat/Lon, Place/Bearing/Distance (PBD), or Place/Bearing-Place/Bearing (PBX). Once created, the system assigns a short ID to be used in the flight plan leg list. Usually something starting with LLxx, PBxx, PXxx where xx is a 2 digit number. Some GPS navigators just have one pilot-defined list of WPTxx.

While these identifiers work well in your FMS or GPS, they don't help ATC. You have to give ATC the actual position reference in the Route section of your flight plan. The most common formats would be:

Latitude/Longitude can be entered in either decimal deg or in deg min format. A decimal point is used for decimal degrees. An apostrophe is used for deg min. Use NSEW to identify directions.  They can be either prefix or suffix.  Be consistent.  For example:

N28.52W83.68  or  83.68W28.52N  or  N28'51'W83'40'

Place Bearing Distance and Place-Bearing/Place-Bearing waypoints start with a known database waypoint - typically a VOR - but any fix in the database will work. Examples:

ATL/162/18 to identify Atlanta VOR, 162 deg, 18 NM.

ORL70/MLB348 is the intersection of the Orlando VOR radial 070 and Melbourne VOR radial 348.


How big is the influence of color on the stability of the boundary layer?

Technically, yes. Practically, no.

Boundary layer stability

You are right that boundary layer stability depends on viscosity, but it depends much more on the pressure gradient. Accelerating flow exhibits extreme stability: Even if there is movement orthogonal to the flow direction (due to Tollmien-Schlichting waves), their speed becomes an ever smaller fraction of flow speed in accelerating flow. This kind of flow is always found right after the stagnation point, when the suction area over the mid section of the wing accelerates flow into it.

Conversely, decelerating flow has lower stability: Now any crossflow becomes relatively stronger simply because flow speed is decreasing. This kind of flow is found aft of the suction peak, when the flow has to manage the long and arduous pressure rise to the trailing edge. It does not take long, and transition into turbulent flow happens.

On the Concorde at high angle of attack, lift was created by a strong vortex. The boundary layer became turbulent right after the leading edge.

In cruise, the flow would hit the leading edge at a small angle, so the speed distribution over the wing was less peaky. The long chord length and high flow speed would still cause an early transition, however, so most of the wing had turbulent flow. Indeed, cooling the wing would lengthen the laminar portion, and heating would shorten it, but the difference in friction drag would be small when looking at the full picture.

Air temperature over the wing

In supersonic flow you always have both a temperature boundary layer and a viscous boundary layer. Air is heated when compressed and cools when it expands, and in supersonic flow these effects become too large to be ignored. Also, friction in the boundary layer heats up the air near the wing's surface.

The stagnation temperature increase at Mach 2 is 173°C. The leading edge temperature can be expected to be around 120°C (standard atmosphere air temperature being at -56°C in FL 600). Past the stagnation point, the flow accelerates into a suction field in which air temperature drops below its ambient value. At the bottom of the boundary layer, however, the temperature stays almost as high as at the stagnation point due to frictional heating. In a turbulent boundary layer on a flat plate the frictional effect would increase temperature by 152°C. Without the pressure distribution over the wing I cannot give a value for the absolute temperature, though.

Due to heat transfer with the wing, the air is cooled over much of the wing in the vicinity of the wing's surface. A dark coating will add a few degrees and result in a higher equilibrium temperature over much of the wing. A hotter boundary layer is thicker due to the expansion of air with temperature and will have higher viscosity. The most simple explanation why viscosity increases with temperature is that the mean molecular velocities, which are directly related to temperature, facilitate more transfer of shear forces between molecules. However, when it comes to wall friction, the effect of lower density with temperature outweighs the increase in viscosity, and wall friction is lower in a hotter boundary layer.

Thus, a heated boundary layer shows earlier transition and lower friction drag. The dark paint should actually help to lower the friction losses, and since the influence of temperature on the transition point is small, the change in friction due to lower density at the wall should dominate.

Maximum wing temperature

The maximum speed of the Concorde was limited by the stagnation temperature of air. If we assume that a switch from white to dark blue paint increases the equilibrium temperature of the wing leading edge by 10°C (which is not unreasonable), this increase could be compensated by a reduction of the maximum flight Mach number from 2.0 to 1.94. A restriction of the Pepsi Concorde to Mach 1.7 seems to me to be the result of extreme (and unreasonable) caution.

My verdict

I did not run the numbers, but I would expect that a different paint job would not change wing temperature much. At the leading edge and over much of the wing it adds a little to aerodynamic heating. A warmer wing would translate into less friction, but the difference is extremely small.

On the ground, in the absence of the strong convective heat transfer during supersonic flight, the temperature difference between white and dark wings is much more pronounced (in the order of 30°C to 50°C), and in this case a white wing is very effective in keeping the fuel temperature down and avoiding gas bubbles in the fuel line.


Would the "AOA Disagree" light be the only way 737 MAX pilots could detect malfunctioning AoA sensors?

If there was an AOA gauge, then looking at that could have told him there was a problem without an AOA disagree light.

It'd be better than the AOA disagree light too. If the same mechanic maintained both AOA probes or their signals were sent through the same wire harness bundle, they could both agree on the wrong answer.


How do you know if an aircraft engine has a supercharger?

As Bianfable has pointed out, the C-130 Hercules does not have a supercharger or a turbocharger. No turbine-powered aircraft have them. Turbine engines do not need these forced-induction chargers since turbine engines compress the intake air themselves. It would be impractical to design a supercharger or turbocharger for them.
The easiest way to know if a piston-engined aircraft has a supercharger or a turbocharger is to check the aircraft’s POH. If one is not handy, you can look at the aircraft engine itself.
An engine with a supercharger will have an accessory belt (usually wider than the other accessory belts) attached to the crankshaft or flywheel. In older aircraft (WWII, Korean War, etc), the supercharger will be less obvious. These may even be chain or gear-driven. The application of superchargers in this case would be for large, powerful engines.
An engine with a turbocharger will have the exhaust manifolds converge down to one pipe. That pipe will feed into the exhaust turbine of the turbocharger. Although, the exhaust turbine might not be readily visible, the housing for the compressor impeller should be more obvious and may obscure the turbine. What would be more obvious would be the additional manifold piping and ducting.
If neither of the above are accessible, just look at the model name of the aircraft. Most modern small General Aviation aircraft manufacturers will want to advertise that their model is turbocharged. A manifold pressure gauge that goes beyond 30 inches of Mercury may be an indicator as well.


Do stunt jets use laser distance meters to align with one another to maintain formations?

No they don't. They rely on visual cues. Basically each pilot aligns features. For example, it could be the wingtip of the plane next to him/her to a letter or feature on another plane.

(YouTube) POV; the drawn circle is merely an illustration.

And they all follow the lead's commands via radio. As when to turn, when to pull, for how long (based on the tone of the voice), etc.

As a team gains experience, they start to bring the distance closer. Not usually noticeable by the crowd.

Source: Blue Angels: A Year in the Life


What were the 20 airspace classes in the US before 1993?

I don't claim to have a definitive answer, but started listing the airspace I recall memorizing or seeing on charts.  So here's my current list:

Continental control
positive control area
Air defense identification zone
Oceanic control area (may not be USA)
terminal control area
airport surveillance area
tower control area
transition area
control zone
uncontrolled airspace
Military operational area
prohibited
restricted
alert area
warning area
caution area (1943 aeronautical chart)
danger area (1943 aeronautical chart)
airways
airport traffic area
national park
wildlife refuge
fire control area (became restricted as I recall)
special use area
laser demonstrations
blast area (later warning area, now TFR)
controlled airspace


Were cabin lights really consuming that much power back in 2006?

Thunderstorms normally mean icing conditions, which necessitates anti-ice, both through bleed air and electrical systems.

I can see this going a few ways:

Pilot is (for instance) at high altitude and really does need the additional bit of power to cross above the thunderstorm.
Pilot has flown aircraft type where this is a legitimate problem and figures 'why not?' for safety sake.
Could be something about motion sickness in the storm, since closing your eyes can be an effective countermeasure. Perhaps dimming the lights goes along the same lines.


Calculate resultant force from pressure distribution?

I don't know exactly you maths background, so i'll start using it for the sake of expressing it generally, and in the second part i'll try to simplify things.
Making use of the definition of pressure p as force F per Area A.
Mathematically, the shortest answer would be to integrate the (local) pressure over the surface, including the normal vector:
$\vec F = \int_{A} p* \vec n dA$
some notes on the symbols:
pressure p is not directional, it is defined as pressing perpendicularly on the surface. Using $\vec n dA$ as "directionalized" surface area element, the normal vector $\vec n$ perpendicular to the surface would take care of the direction of in which the pressure is exercised. Note that the normal vector is "normalized" to the length of 1, so to preserve the pressure.
F as resulting force has a direction, making it a vector.
In real life (as in your diagrams) the distributions usually aren't known analytically, but just as a table of values. So you would discretize the above surface integral into segments of finite area, and then calculate the forces for each element, and at the end sum everyting up.
So I tried running a basic example: airfoil discretized in 5 segments (i through v), suction side pressure = 1bar (abs), pressure side 2 bar(abs),
ran the calculation "p * n * deltaA " and the summation in the Table below.
The force units are "kPond" = 10 N, as result of choosing pressures in bar and surface area in cm^2.

Interpretation of the Result: We get a aero force of
10N in positive x direction: 10N of Drag, and
50N in positive y direction: 50N of Lift.
Total aero Force is 50.99N in the direction of the vector [1,5]
Additional notes:
If you want to get more precise:
the finer the discretization, the more precise your result will be, or you can increase the order of your numerical integration..
https://en.wikipedia.org/wiki/Numerical_integration
hope that helps! have fun integrating..


What is the relationship between fuel mixture and RPM in a reciprocating engine?

I assume you are referring to a fixed pitch propeller because a constant speed propeller will always hold the same speed as the governor automatically changes the blade angle.

Just like any piston motor there is an optimal mixture. Richer or leaner results in lower power. Planes are set up to run rich at full rich mixture so leaning during cruise or descent will produce more optimal power which will affect rpm slightly in a fixed pitch application. Excess fuel displaces oxygen which decreases power flighty.


How is wind direction reported (blowing from or blowing to)?

As far as METARs are considered, the wind direction gives the direction from which the wind is coming. From METAR definitions:

Wind Direction.
The direction, in tens of degrees, from which the wind is blowing with reference to true north.

So, Wind 270 shows that the wind is coming from west.
The reporting in ATIS and tower is the same, only difference being that the reference is magnetic north, while it is true north for METAR.


Propeller Efficiency calculation different by two methods

Defining "useful" as moving the plane forwards, the rate at which useful work can be done is equal to whatever power which has been imparted to the fluid, i.e thrust x velocity at disc. This is propeller power. The rate at which useful work is done which is equal to whatever power which has gone into actually making the plane move forward, i.e thrust x freestream velocity (since freestream velocity and airspeed are interchangeable depending on the frame of reference). This is propulsive power

Consequently there are two different measures of efficiency, the propulsive efficiency which is a measure of how efficiently the plane uses the propeller power and the propeller efficiency which is a measure of how efficiently the propeller uses shaft power. The equation on the MIT webpage is for propulsive efficiency but you want to know how efficiently your shaft power (2π x torque x RPS) was used, therefore you have to calculate propeller efficiency so you don't use that equation.


Why should some piston engines not be run lean of peak?

Considering piston engines in general there's a few reasons not to run "lean of peak", but the arguments I'm aware of all fall into three broad categories:

Poor Instrumentation
Most folks advocating Lean-of-Peak engine operation will also tell you that you need a good engine monitor (with Exhaust Gas Temperature (EGT) and Cylinder Head Temperature (CHT) probes for each cylinder) so you can ensure that all your cylinders are operating within safe temperature limits.
Manufacturer CHT/EGT systems are often "single-probe". On the IO-360 in your Cessna example that leaves you with a 3 cylinder blind spot in your monitoring, and the potential risk of damaging your engine based on the incomplete information you have.
Uneven mixture distribution
Some engines simply can't run lean of peak because of uneven mixture distribution: Either the engine will get rough as some cylinders "miss", or you'll have some cylinders lean of peak EGT and at a safe cylinder head temperature while others are redlining their CHT and potentially causing damage to your engine.
This sort of uneven mixture distribution happens frequently in carbureted engines, but there are many injected engines which also have poor fuel distribution & significant variation in mixture between cylinders (This is where GAMIJectors makes their money - by providing balanced injectors to even out fuel distribution).
"In Case Something Breaks"
Hypothetical scenario: you are cruising at 8000 feet, you've leaned for cruise, and your mixture control suddenly fails in such a way that your engine is stuck at the current mixture setting.  All the airports within your endurance range are roughly at sea level.
An engine running lean of peak may begin to run rough as you descend for landing (the mixture becomes too lean to support combustion).  An engine running rich of peak may continue to run acceptably through the descent. (The mixture may transition into "the red box zone" where operation at high power settings are dangerous, but you'll theoretically be reducing power for your descent, so the chance of doing damage to your engine isn't that high unless you have to perform a go-around or other high-power maneuver.

A prohibition on Lean-of-Peak operation in your POH is probably historically based on #1 or #2 above -- the manufacturer doesn't want to advise you to do something that might damage your engine.  Running Rich-of-Peak is conservative operating guidance, where the downside is slightly increased fuel consumption and the possibility of fouling a spark plug (which is not likely at normal operating power settings) versus the downside of potential engine damage from improper Lean-of-Peak operation.


How does the in flight entertainment system works?

I found a resource specifically for Emirates, so I'll try to explain it with respect to Emirates, though various other Airlines would use more or less the same principle.

  Emirates uses Panasonic Avionics IFE (In Flight Entertainment) system.
  They have the 3000i which is older generation of IFE system on older
  aircrafts and the latest version ex2 on new aircrafts. Media licensing
  is managed, I believe, by the IFE provider via links to the major
  studios. In this tie up, the media is encrypted and stored in portable
  media loaders for the airline to update on the aircrafts. As the media
  is encrypted so the studio doesn't have much objection in giving away
  the rights to air the movies on board rather quickly.

  The Portable media loaders use optical connection for faster data transfer to
  minimize the loading time.

  The Main Aircraft Interface (AI) Server is nothing but a small
  computer which is generally called a LRU (Line Replaceable Unit) a
  small box which controls the entire IFE system of the aircraft the
  back end software can either be windows 95 or Linux depending on the
  type of system. 3000i uses windows. The movies are stored on other
  LRUs which are generally an array of Digital Data Servers or Media
  Servers (MS) or in lay mans terms Hard Drives! These are connected in
  a LAN network and ethernet IP addressing is used in the entire
  aircraft system.

  The data is distributed over Optical fiber in first phase and over
  normal ethernet network to the specific seats. The interface is done
  via Ethernet Switches which intelligently routes the data from the
  Media server to the Area Distribution box to the Seat Electronic box
  and finally to the Smart Display.

Using a central dedicated computer instead of individual computers on different seats is preferred as it is less costly. Also, the IFE is connected to Aircraft's Main IFE cpomputer, and not the Aircraft's main computer, so by hacking it all you get is the files (IFE files), not the aircraft data, though the moving map system data might be first dumped into the IFE system from the Airplane's main computer


How are IAS to CAS conversions calculated?

There are instrument errors in the airspeed indicator system, which consists, but is not limited to the air speed indicator, a pitot port (which senses ram air pressure) and a static port (provides ambient air pressure for airspeed and for altimeter and VSI instruments).

Because there are errors in the indicated airspeed, each manufacturer is required to measure airspeed and then provides data of indicated vs calibrated airspeed data.  This used to be a much bigger deal when flights were conducted by dead reckoning, and reliable airspeeds were more directly beneficial to the flight planning and enroute process.

Today, other instruments provide more accurate effective ground speed data.  For example, a low cost GPS can have greater accuracy in measuring effective ground speed than radar, and rivals lidar systems costing much more money.

Nevertheless, manufacturers still provide CAS / IAS tables.

Oh the instruments used to determining CAS?  Often supplemental pitot probes, which are on extended booms in front of the aircraft.

To a lesser degree GPS/IMU, radar and lidar may play a role in some testing, but these instruments do not actually measure airspeed, where as an extended boom pitot will measure ram air pressure, ideally outside any airframe and power plant perturbations.

Finally, a pilot may translate, using manufacturer provided CAS / IAS conversion tables, IAS to CAS when CAS figures are needed.  But CAS figures are not calculated, they are empirical.


What is the main materials of the windshield? And how do they function in bird strike?

Here is an example of the latest and greatest.

http://www.ppgaerospace.com/getmedia/926cb26f-e047-477d-b604-62d079f494bc/B787_TD_FINAL.pdf.aspx?ext=.pdf

You will notice that instead of multiple glass laminations separated by plastic interlayers of traditional aircraft windshields, the 787's windshields are basically two thick layers of acrylic plastic (plexiglas) as the main structural element, with interlayers to separate them and just a single outer layer is high strength glass.   This would provide superior birdstrike resistance while the glass outer layer maintains a hard outer surface that won't scratch easily.


What does the actual path of air within a turbojet engine look like?

(Source) Image shows CFD simulation for a jet engine carried out by Northern Arizona University.

Pretty much as your illustration, but more turbulent and not as many complete turns.

Let's take one rotor disk at a time.

Each blade on each disk is like a wing. Air is rushing in at it. And it, is moving down on the air (or up from the other side). Giving the blade an angle of attack.

In a wing, air is pushed down.

So, one disk will push down on the air on one side, up the other, left and right top and bottom—the stator disk will straighten it out for the following rotor. And so on, i.e., a stepping swirl.

If the stator reversed the flow, it will be an immense angle of attack for the receiving rotor, i.e., the rotor will stall. So, a stepping swirl makes more sense.

While a propeller, an axial compressor, and a turbine are different in what they do, I don't see why the shape of the corkscrew of the propeller I asked about here—would change for any rotating disk carrying airfoil blades—

(Source)

—except in magnitude and thermodynamic properties.

To complement the earlier CFD image, here are two more:

(Original image) Three stage transonic compressor.

(Source) Analysis of Rotor-Stator-Interaction and Blade-to-Blade Measurements in a Two Stage Axial Flow Compressor


Why are there double hinge lines on the rudders of the Grumman C-2?

The double hinged rudder is also a Dehavilland Canada feature on most of its larger designs like the Caribou/Buffalo/Dash 7/Dash 8, where maximum yaw power for a given surface area was a design priority (especially if there are height or other limitations that prevent you from adding more area by going up; in the C-2's case, they also added more surfaces as well to limit height, an obvious issue on a carrier, and the same reason the Constellation had 3 tails).
It improves yaw power for a given overall surface area by allowing the rudder to operate at a larger net angle before significant flow separation, by allowing the airflow to make 2 smaller changes in direction vs one larger change in direction for the same overall displacement.
It's not quite as complicated as it looks.  The trailing edge segment is effectively a giant anti-servo tab and is simply geared to the vertical fin by a push rod.  The actuation system only has to drive the forward segment.  The extra parts and complexity are in the second set of hinges and the actuating rod.  In the C-2 pics you can see the gearing rod attachments in the little blisters. On the DeHavilland Canada products, the gearing rod is hidden at the base of the rudder.


Can a pulse jet be used on a light GA aircraft?

In principle yes. But some details will turn most potential operators off.

Noise is the obvious first one. You might not mind, but cockpit noise and vibration in operation will certainly put an unacceptable stress on the pilot. Just think how you will communicate with ATC or with a co-pilot. Also, your choice of airports to operate from will be rather restricted.

Vibration also means that you need to ruggedise the airframe. This will certainly eat up some of the mass benefits of the pulse jet, but is hard to quantify.

Now fuel consumption: The AS-014 would consume 350 g of fuel per hour for every Newton of thrust. Compare this to the 60 g/Nh of a modern turbofan. The additional fuel will eat up the remaining mass advantage once you desire to fly for more than just a few minutes.

Next will be take-off distance. Unless you use a catapult, you will need a long runway. The pulse jet has limited static thrust, so your initial acceleration will be poor. At the high end of the speed envelope, though, thrust should be plentiful.

Cooling, however, is no problem. Just expose the pulse jet to the elements and you are all set.

To summarise: Yes, a pulsejet is a possible power source for a GA airplane, but is a poor choice for a multitude of reasons. It makes more sense in an unmanned, one-way application.


Guidelines for using a constant speed/adjustable pitch propeller

why would anyone want to mess with the pitch of the propeller ?

A propeller runs at its highest efficiency when used at a particular combination of forward speed and RPM. By changing pitch, you change this combination, so the best efficiency can be shifted over a range of airspeeds.

For the physical background please consult this answer.

  This implies that the lower RPM will result in lower thrust ( true? )

Yes, lower than maximum thrust. If you need less than maximum thrust, a lower RPM is sensible to reduce engine wear. Reduce RPM only if the remaining prop speed can still absorb the power; in other words, make sure the RPM is high enough to allow the engine to run at the speed needed for the desired power. But do not control thrust with RPM - this is what the throttle is for.

A piston engine outputs a constant amount of power, regardless of airspeed. This power output grows about linearly with engine RPM. You control this power with the throttle (and measure the power indirectly with the manifold pressure) and use the prop pitch to allow the engine to run fast enough to create the desired power at all. If you run the prop faster by reducing pitch, it will operate at a blade lift coefficient which is lower than that of optimum blade L/D, so you lose efficiency. Also, the engine will run faster and be in the partial-load operational range where it also runs less efficiently. Run the prop slower by increasing pitch and you will slow down the engine so it cannot produce the desired power. Also, now the propeller will run at a higher lift coefficient, efficiency will drop and part of the prop blade might even stall if you increase pitch too much.

As to what is a significant reduction in noise: This is subjective and I advise you to find out for yourself.


When one engine fails in a twin-turbojet aircraft, is there a weight imbalance?

Since your question is specifically on "jets".
We need not worry about the critical engine.

There is one thing to be noted in most of the commercial jets. The engines are placed close to the fuselage in order to reduce the moment arm - mean that should an engine fail, there is a reduced difference in forces,as compared to if an aircraft had engines on the wings tips.

The following are two vital things to be carried out during imbalance due to engine failure:

1) Effective rudder (and aileron) control:

The rudder (and aileron) is used to maintain directional control in flight, acting around the normal axis. An engine failure will yaw (and roll) an aircraft, making the rudder (and aileron) the best control to counteract this.

2)Fuel Balance procedure:

The following procedure is for a Boeing 737 :

Detailed schematic of a B737 Fuel System:

The procedures vary from one aircraft to another. And for a turbo prop aircraft it's a whole new thing involving "critical engine".


What are the advantages of the Riblett airfoil over the Original Pietenpol Airfoil?

Assuming that the same wing chord is used for both, one technical difference between the Pietenpol and the Riblett is the depth of the airfoil.  The Riblett that has been used on the Air Camper is the 612 (or sometimes the 613.5), which makes it 12% (or 13.5%) deep.  With a 60" chord, that's a depth of 7 to 8".  The deepest section of the stock Pietenpol airfoil is only 6-9/32", which makes it roughly a 10.5%.  The offshoot is that a taller spar can be used with the Riblett, and in spar strength the height makes a great deal of difference because the section modulus goes as the square of the height and the section modulus is what determines bending strength.  A taller spar can be made lighter with proper design.  Another useful consequence of using the Riblett is that a deeper wing section allows a larger fuel tank to fit in the space between the spars.  The stock Pietenpol wing centersection can accommodate maybe 10 gallons, but the Riblett should be able to fit more up there.

I've attached a graphic overlay comparison of the Pietenpol airfoil with the Riblett GA30U-612; Piet in red, Riblett in white.  The 613.5 is similar but the differences are a bit more accentuated.

For performance differences, I will defer to both a technical treatise by Mike Shuck (on the airfoil list) and the flight comparison between two very similar Piets conducted several years ago and documented in the BPA Newsletter.  Very similar performance in all flight regimes.


Does drag increase with increasing bypass ratio in turbofan engines?

According to this 1975 NASA report on the effects of turbofan engine bypass ratio, the drag does increase for increasing bypass ratios. In the report, they use the following drag coefficient equation:
$$
C_{D,prop}=C_{D,nacelle}\cdot \frac{A_{nacelle}}{S} = \frac{D_{nacelle}}{\rho_\infty A_{nacelle}} \cdot \frac{A_{nacelle}}{S}
$$
As shown below, the nacelle drag coefficient initially increases for increasing bypass ratio.

Since $\frac{A_{nacelle}}{S}$ also increases with bypass ratio, the propulsion system drag will increase as well. So drag is closely related to the frontal area of the engine.

(images taken from report linked above)


What could cause an irregular climbing pattern on takeoff?

The brief period of leveling off is not unique to the flight on that day. Looking at track logs for previous days, it always levels off at around 7,000 feet for some period.
As Terry commented, this is most likely to deal with the congested airspace. Other routes coming into and out of the London area probably pass through the same space, and keeping flights departing Stansted at a lower altitude prevents them from interfering with other traffic.
Looking at a standard departure chart, there is a warning box:

WARNING
Due to interaction with other routes, do not climb above 5000 until instructed by ATC.

This looks to be the route followed by this flight, at least to the DETLING VOR, so it would be expected that ATC will need to limit the flight's climb until clear of other traffic.


Twist optimization for a low speed aircraft

Is a twist even necessary for my model?

Yes, with that amount of taper I would recommend twist. Those 4° look rather low on first sight. The tapered wing will produce induced loads on the outer wing due to the amount of suction of the deep inner wing.  Below is a plot of where flow separation starts for different sweep angles and aspect ratios (source):

I would classify your wing as a high taper wing (second from top, right column). Without twist it will start to stall from the tip. My recommendation is to use 0.7 taper even if that means higher root bending moments. With 0.7 taper and the same stall angle of the inner and outer wing airfoil, 2° of twist are usually sufficient.

  Twist optimizes drag reduction and lift distribution for a single aoa in non-elliptical planforms. Should this angle be the aoa for the Cl I get for my cruise speed?

Yes.

  Also how would my planes angle of incidence depend on the twist that I select?

Proportionally to the lift loss on the outer wing with increasing twist, the whole wing needs more angle of attack for the same lift. You will, however, need many degrees of twist before the wing's incidence will increase by more than one degree.


Is it possible to design a GA plane with a 5' -10' wing span?

They can, its just not a very efficient size for one that needs to cary people. The simple answer is that everything comes with a trade off, there are plenty of planes with small wing spans like this one, and this one and some planes that don't have wings at all... But smaller wing spans means a thicker wing, at some point you will run into a drag issue, a roll stability issue or both.

When it comes to aircraft people tend to be concerned with efficiency as air travel has always been about going far, fast, and for a similar cost to what you can on another means of transport. As such efficient designs win out over novel ones or ones that provide some means of limited added benefit.

On any note most of the supporting infrastructure has been designed for planes with substantial wing spans so aircraft width in the GA market is not really a huge issue. Saying a narrower wing is "way more useful" depends on your use case.


This is also know in Europe as an Enroute Instrument Rating or EIR, which allows flights under Instrument Flight Rules in the cruise phase, but not for departure or approach. It is based on EASA FCL 825

  FCL.825 En-route Instrument Rating (EIR)

  (a) Privileges and conditions.

  (1) The privileges of the holder of an en-route instrument rating (EIR) are to
  conduct flights by day under IFR or in IMC in the en-route phase of flight, with
  any aeroplane for which a class or type rating is held.

The curriculum to obtain an EIR is lower than for a full Instrument Rating (IR), especially the number of hours for theoretical and practical instructions have been lowered:

  (2) instrument flight instruction.
  (i) The instrument flight instruction for a single-engine EIR shall include at
  least 15 hours of flight time by reference to instruments.

As GdD has pointed out in his answer, this is not the same as the UK CAA IMC Rating. See his answer for more information on this.


Has there ever been a seaplane with retractable pontoons?

There have been a couple of examples- the Blackburn B-20, for example, had a retractable pontoon below the hull (and retractable wing floats), though it was an one-off experimental aircraft with a single flight to its credit.

Blackburn B20, image from dinger.byethost5.com

As a more widespread example, the Consolidated PBY Catalina's wing floats were retracted electrically after takeoff.

Catalina's retractable wing float; image from navy.memorieshop.com

Retractable floats have been used in other aircraft too- like the Grumman G21A Goose and the SL-12C amphibian. Some designs like the Kawanishi E15K featured retractable floats, which were later removed due to issues.

A little more digging reveals that the German Ursinus Gotha WD 10 Fighter Seaplane had retractable floats quite early- during WWI!. However, I doubt it counts as the aircraft never went past taxiing stage.

Ursinus WD 10 fighter seaplane, image from 1000aircraftphotos.com


Why are taildraggers considered more rugged than tricycle?

To expand/clarify upon the other answer, bush planes and the like use tail wheels because imagine if when landing on a rough runway, your little tiny nose wheel hit a rock.  That could be catastrophic.  However, on a taildragger, the big main landing gear can go over some obstacles, and the little wheel on the back won't pose a big problem with small rocks and such.  The little wheel will just bump over the obstacle, instead of possibly skidding on it and throwing the whole plane off.  Effectively, the plane is dragging the tail wheel over the obstacle vs. pushing the tail wheel into the obstacle.  So, that's why I think that tail draggers are preferred for a rough surface.

Feel free to correct me if I'm wrong... I've never really flown a plane in my life.  I'm just an enthusiast.


How do modern helicopters tackle Vortex Ring State?

Helicopter driver here.

I am not aware of any technical features which can prevent it.  Quite simply, the disc must accelerate air downwards to generate lift.  If the helicopter descends into that downward accelerating air, it is recycled through the disc resulting in a catastrophic loss of lift.

The preventative measures are:

Be aware of the flight conditions under which vortex ring state may occur.
Do not fly into these conditions.
Be able to recongise the symptoms of vortex ring state.
Understand, and be practised in, the correct recovery technique, which is most often fly in any direction away from the vortex.

I am not an aerodynamics engineer but I doubt that there is a physical solution to this - and if there was, it would likely have been implemented by now.


What turbine blade alloy did the Jendrassik Cs-1 use?

Jendrassik's own patent from 1939 does not go in-depth into the alloys. However, for the turbine blade legs he mentions "austenitic [stainless] steel" as preferable (see PDF page 3).

From that era, a Swiss patent from 1937 on the materials of gas turbine parts also discusses austenitic steel, in particular (translated from German):

  Alloy of an austenitic steel containing 25 to 35% of chromium, 25 to 35% of at least one of austenite-forming metal [e.g. nickel], 1 to 4% of titanium and 0.3 to 0.8 (preferably 0.4 to 0.6%) containing carbon, optionally up to 3% silicon and up to 10% molybdenum.

It is close to the composition of the 316 stainless steel (source), which has a mechanical maximum temperature of 590°C (source).


What is required to fly privately from a region with high levels of the ebola virus (Nigeria) to the UK?

You'll be on a flight plan. You'll have to clear customs at a designated airport and file the appropriate paperwork. More info here:

Notification of Flights

If you notify the border agency it will make recommendations if they think your flight poses a risk. There is only screening at Gatwick and Heathrow.

Ebola Specific Information


Does a lean mixture result in a higher cylinder temperature for a given power setting?

To oversimplify, you could say it's because when you are rich of peak you are getting temperature reduction from too much fuel.  When lean of peak you are getting temperature reduction from too much air.  Watch this guy's youtube video seminars.  They are a treasure.


How much, generally speaking, does it cost to learn how to fly?

Assuming a regular private pilot's license (i.e. not sport/recreation), a part 61 instructor, and a rented aircraft, then you need to budget for the following:

Aircraft rental (this usually includes oil and fuel)
Instructor time (air and ground)
Materials (books, DVDs, charts, fuel tester etc.) as recommended by your instructor
Headset
Third-class medical
Insurance
Written test fee
Examiner's fee for the actual test

If we assume the aircraft costs \$120/hr wet (i.e. including oil and fuel), an instructor costs \$40/hr and you need 50 hours to be ready for the test (40 is the minimum required) then you can do a calculation like this:

35 flying hours with instructor: \$5600
15 flying hours solo: \$1800
15 hours ground school (instructor's time): \$600
Materials: \$500
Headset: \$500
Third-class medical: \$150
Renter's insurance: \$700 (per year)
Written test fee: \$150
DPE test fee: \$400 (plus \$120 rental for the aircraft)
Total: \$10,520

You can play around with these numbers, there's a lot of variation and research is obviously important. But the single largest cost will be the number of flying hours you need, so anything you can do to reduce that time is worthwhile and the simplest - but unfortunately not the easiest - way to do it is to fly as much as possible, i.e. several times a week. Given weather and other factors, you should probably even plan to fly more than you actually can on paper: a bunch of flights will certainly be cancelled.

You can also train in the most 'minimal' aircraft you can find: a two-seater aircraft without a glass panel could be \$50/hr cheaper than a four-seater with a G1000. Unless you have a very clear idea about what sort of flying you'll do in the longer term there's no point in paying for anything that isn't directly required for the private pilot's test.


Why were german pilots more successful on the eastern front than the western front?

Several factors.  The ones you mentioned, plus the different purpose of most of the Soviet aircraft and the longer flight career of German pilots on the Eastern Front.  Beyond that was the fact that, early in the war, the Germans enjoyed near-complete air superiority (reinforced by their superiority in other factors).

As you note, at the beginning, most of the Soviet aircraft were inferior to the German ones; some of them were ten or even fifteen year old designs (or even older -- one squadron, known as the "Night Witches", flew biplanes into 1943), while the Germans flew new designs, either late pre-War or fresh off the drawing board.  The newer aircraft were faster, more robust against damage, carried heavier loads and more/larger guns.  This aircraft design deficit was reduced and possibly even reversed later in the war, but by then the Germans were on the defensive, being pushed back week by week.

The German pilots, at least early in the war, were far better trained -- theirs was the best air force on Earth in 1940 (though they started to run out of good pilots later in the war, because they had a far smaller population to draw replacements from and were resource limited in building aircraft, both for combat and for training).

Further, the German aircraft that the aces flew were dedicated fighters, designed from the ground up to destroy other aircraft in the air.  The BF-109 and Focke-Wulfe 190 were superb airplanes for the day.  The Soviets, on the other hand, especially early in the war, had a heavy preponderance of ground attack aircraft, and their primary mission was to destroy German armor, infantry, and supplies.  This made them sitting ducks for the German fighters and fighter pilots.  Further, there were lots and lots of those differently tasked and outdated Soviet airplanes -- the Soviet Union had more than twice the population of Germany and tens of times the landmass and resources; that gave them the ability to do the air equivalent of "human wave" attacks, which would still succeed even after a "turkey shoot" by the Germans.

Because of the disparity in pilots and aircraft, the German pilots lasted a great deal longer on the Eastern Front, where they weren't flying against the elite of nations larger than their, who hadn't had a decade or more with no powered aircraft and who had P-38s, P-47s, and P-51s, Hurricanes and Spitfires to pit against their aircraft.  The Western Front pilots had a strong tendency not to come home, even in the early years of the War, and much more so after the Normandy invasion.

Additionally, especially after the first winter of the Russian invasion, German pilots stayed on the line until they were physically incapable of flying -- either dead, or seriously injured (loss of eyes or limbs, for instance), or shot down behind lines and captured.  As noted in comments, also, there was a tactical difference, with German squadron leaders often flying without any thought for defense, trusting their mates to protect them while they simply destroyed as many enemy aircraft as possible, and this worked better against the relatively less experienced pilots in the Soviet forces.


There is not much gained by the third dimension for your use case. In GA you generally want to avoid any active weather. Why make it more complicated?

can't go over it (performance limited)
can't go under it (microbursts can kill you)

=> only way is to go around it and therefore no need for that 3D information.


What creates most drag during flight: fuselage or wings?

It's the wings. Most of the time.

Best L/D is reached when the induced drag is equal to the non-lift-related drag. Induced drag is a byproduct of lift creation, and that is predominantly done by the wings. Therefore, induced drag (physically a backward tilt of the lift vector away from the direction in which lift is defined) is produced by the wing.

For the remaining drag you can do a very rough estimation based on wetted surface and friction drag. Here the wing again produces a substantial fraction which must be added to its induced drag.

For racing aircraft like the Supermarine S.6A (which won the Schneider Cup back in 1931), the fuselage, struts and the floats did produce almost all drag at high speed. This would be a clear exception to the answer given above. However, even with this aircraft, at low speed (during take-off and landing) the wing would most likely create at least half of the drag force.

On the Dornier Seastar (your first example) the thrust line is chosen so high in order to move the propellers and turbine intakes away from possible splashes of water. The resulting pitch moment is trimmed away with proper elevator deflection. In your second example a lot of drag is created by the many bracing wires. At low speed the wing will produce most of the drag while at high speed the drag line will move down when the unfaired pilot (and wheels, engine and tank) and the many wires will create most of the drag.


Why does this Strikemaster have a textured leading edge?

The leading edges are roughened to improve the stall characteristics. Typically vortex generators are used for this purpose nowadays.

  The 5 and the 5a were used by the RAF for pilot training and the nose strakes were fitted to improve the spinning characteristics - the leading edges of the wings had a roughened paint finish to improve the stall characteristics. The 5s with the tip tanks (I'm not sure if 5b is an official or 'unofficial' designation) were used by the RAF for nav training and didn't have the nose strakes (not sure about the roughened wing leading edges) I don't know if it was because the tip tanks themselves improved spin handling or if it was because they weren't flown by studes for spin training.

(source: User "Fritag" at www.britmodeller.com)

  The rough grey coating on the wing of the aircraft was applied in order to break up the smooth airflow and give an early indication of the onset of a stall as the T5's original clean wing design gave the pilot little prior warning.

source: all-aero.com / RAF Museum

  A great deal of work has been put into stalling, spinning and
  stall-warning over the years of Jet Provost and Strikemaster
  development. This has led to all sorts of devices, like
  inverted-aerofoil tailplane, fences under intakes, strakes round the
  nose, roughened outboard leading-edges and little "eyebrow slats" at
  the wing roots. Of all these devices, the Strikemaster requires only
  the "eyebrow slats" to give it that precious smooth spin, a tidy g
  break in the stall and a distinct stall warning.

source: Flight International 12 October 1972 500-501

  At first it was forecast that the T.5 would take the place of the T.4
  on certain roles such as high altitude training. Unfortunately the
  majority of T.4s had to be taken out of RAF service much earlier than
  anticipated so the T.5 had to take on more responsibilities. As a
  result, the RAF decided to update its fleet of Jet Provosts with new
  avionics suites, spin strakes, and roughened leading wing edges in
  1973.

source: Jet provost heaven


Why do jet planes with multiple engines have separate throttle levers for each engine?

All multi-engine airplanes, whether jet or prop driven have separate throttle controls for each engine. There are good reasons for this:

If there is a problem with one engine you can separately control it for troubleshooting purposes
If one engine isn't developing the right amount of power you can independently increase the other engine(s) to compensate
If you have a control failure of some kind you can use differential thrust to steer the airplane, this has been done more than once, the example that comes immediately to mind is United 232


Are tritium runway lights widespread in remote areas?

I think it's a major headache to heave radioactive material in remote areas. Soviet union used RTG for lighthouses. A lot of countries were worried about that. You can find articles on the internet. So probably it's not very good idea due to threats.


What good reference books for aviation (ATC & AOC) systems are there?

I'd start with the Global Operational Data Link Document published by ICAO.

It covers pretty much everything data link.  What it doesn't cover, you'll find in the referenced documents.


How universal are air traffic control systems, training and practices?

This question is analogous to asking, for example, how universal are law enforcement  systems, training and practices. At the highest levels you may find similarities driven by things like EU regulations, to pick one, but as you dive deeper into the implementation of those three things, you will find differences, from minor to wildly diverging. Police officers and air traffic controllers may receive very similar basic training, but once they move off from there and into the field, things can and will change dramatically.

The same explanation holds for commercial pilots. A pilot flying cargo in Alaska on Cessna 185's, for example, will be trained in and execute procedures and practices completely different than a commercial pilot flying Britten-Norman Islanders on puddle jumping routes in the Caribbean.

Bottom line is it is challenging to answer this question without context, i.e. two countries you wish to compare.


What is the reference used when measuring flight speed?

Speed of a plane is actually measured in a number of different ways, and relative to different things. Here is a summary of the different types:

Indicated Airspeed (IAS). This is the number shown on the instrument that measures airspeed, and isn't really relative to anything.
Rectified Airspeed (RAS) or Calibrated Air Speed (CAS) This is IAS corrected for known errors in the instrument and the measurement system.
True Air Speed This is the speed relative to the air around the aircraft; usually found by correcting the RAS for pressure and some other errors.
Ground Speed This is the speed relative to the ground, or a fixed point on the earth ('imaginary grid). Its the vector addition of the True Airspeed (and direction) plus the wind speed (and direction). In olden days this was estimated from the Airspeed and the wind velocity, or through dead reckoning navigation, but now it is trivially found from GPS or other navigation aids.

Planes use different ones of these for different purposes. Measurements relative to the fixed stars are not generally useful until you are in the realm of space travel.


How to realistically model propeller static thrust?

This basically depends on the prop loading and RPM. If you are not satisfied with the momentum disk theory based results then the next step would be to use blade element theory based calculation.

If I were you I would certainly run few test cases with a known propeller geometry by scaling the propeller. One of the easiest way I can think of doing this is to use QPROP from Prof. Mark Drela at MIT. This is a free software and on top of this it is a command line program which is very well suited for this kind of an activity because all the parameters could be changed on the go, preferably via a bash or python script.

HTH


How to calculate the location of C.G. A.C. & N.P. in static longitudinal stability?

Why assume the c.g. is aft of the a.c. and the tail is providing positive lift?

Maybe the two authors were sick and tired of that old meme that positive longitudinal stability requires negative lift on the tail. This is simply not true and never was, still it is believed like some religion.

What is true is that more static stability needs less tail lift, and many aircraft have so much stability built in that their tail lift is always negative. But with modern flight control systems this negative lift means more drag than necessary. Back in the old days, when the pilot wanted to let go of the stick or yoke in order to read a map or take a leak, a tail downforce was the best way to make sure the aircraft would behave. Still, low and sometimes missing roll stability meant that the pilot could never take his eyes off the horizon (real or artificial) for more than a short while.

  Why not sum the moments assuming the c.g. is in front of the a.c. for calculating neutral point?

The position of the center of gravity relative to the wing's aerodynamic center has no significance for stability — all what counts is the center of gravity position relative to the overall aerodynamic center, fuselage and tail effects included. A smaller tail means that for the same stability the tail lift has to be lower, and most aircraft have the smallest tail surfaces that their designers could fit.


Can a super land without flaps/spoilers?

Even the largest commercial airliners are able to land without flaps, since flap failures do happen occasionally. See a report here where an A380 landed with no flaps. This was at the Auckland, New Zealand airport, where the runway is 3,635 m (11,926 ft) long.

The pilots have checklists to follow in the event of issues with flaps, which include information about what speeds they should fly with what amounts of flaps. They simply land at a higher than normal speed. The brakes can end up getting hotter than normal, so they may have to stop and let them cool or have them inspected by emergency services. The tires are designed to deflate with fusible plugs before high temperatures would cause them to blow.

Aircraft are also tested to make sure they can reject a takeoff at high weights (higher than normal landing weights) using no thrust reversers. Here is a video of the 747-8 doing this test.


One way is to see what the following NASA links have to say about it and possibly using the calculator they have at the bottom of either page.
https://www.grc.nasa.gov/WWW/K-12/airplane/viscosity.html

The similarity parameter for viscosity is the Reynolds number. The Reynolds number expresses the ratio of inertial forces to viscous forces. From a detailed analysis of the momentum conservation equation, the inertial forces are characterized by the product of the density $\rho$ times the velocity $V$ times the gradient of the velocity $dV/dx$. The viscous forces are characterized by the viscosity coefficient $\mu$ times the second gradient of the velocity $d^2V/dx^2$. The Reynolds number $Re$ then becomes:
$$Re = (\rho \cdot V \cdot dV/dx) / (\mu \cdot d^2V/dx^2)$$
$$Re = (\rho \cdot V \cdot L) / \mu$$
where $L$ is some characteristic length of the problem.

and

The dynamic viscosity coefficient divided by the density is called the kinematic viscosity and given the Greek symbol $\nu$
$$\nu = \mu / \rho$$
$$Re = V \cdot L / \nu$$
The units of $\nu$ are length^2/sec.

https://www.grc.nasa.gov/WWW/K-12/airplane/reynolds.html

The Reynolds number expresses the ratio of inertial (resistant to change or motion) forces to viscous (heavy and gluey) forces.


Can an aircraft have a lifting fuselage that only generates lift at certain speeds?

I think you are looking at this backwards...  (at least for a utilitarian passenger type aircraft)
First, such a design is most certainly possible, but it would create more problems than it would solve.  Wings don't need extra help producing lift at cruise speeds, that is when they are most efficient.  Instead, wings can use a little extra help at slower speeds, which is why they are typically equipped with lift enhancing features like flaps and slats.
Second, producing lift creates induced drag.  You want the fuselage to be as streamlined as possible to produce the least amount of drag at higher cruise speeds, not more.  And if your lifting fuselage is fully stalled at all other phases of flight it will be producing MASSIVE amounts of drag.
This full-stall drag penalty would create significant performance problems in all other phases of flight that would likely cancel out any small efficiencies at cruise speed, such as redesigned wings, more powerful engines, etc.  I don't see anything to be gained by such an idea.
And finally, what makes you say that we are 20 years away from a blended wing body design being able to fly?  There have been all kinds of designs built and flown in the last century, I don't think there are any technological hurdles to this type of aircraft.


What material is used for the floor panels in the main cabin for Boeing 747-400?

This illustration is earlier than a -400. Later ones might differ. There are two types: the normal one has aluminum skins bonded to a PVC core, for galleys/hold it is titanium skin bonded to a PVC core with greater strength/corrosion resistance.

747 cutaway view

Later a honeycomb sandwich was used, apparently two cross plied glass-epoxy prepreg skins bonded to phenolic coated nomex honeycomb core using an epoxy film adjesive. From:

  Handbook of Adhesives and Sealants: volume 1, 2005


Where to find the LSA exporting requirements from the USA?

Go to Appendix 2 of AC 21-2, and select Saudi Arabia from the drop down menu.

For example:

  It will be the responsibility of the Saudi Arabian importer to ensure that the nationality and registration marks are properly displayed on the aircraft prior to departure from the exporter's base and to ensure that the necessary flight documents are installed and carried in the aircraft during the delivery flight.

The full document lists all the requirements, too many to copy and paste here. For the regulations, that would be Title 14, Code of Federal Regulations (14 CFR) part 21, subpart L (.pdf).


Can there be more than one airway with the same name in the world?

No.

From ICAO SARPs Annex 11 'Air Traffic Services' Appendix 1:

  3.1.3 A basic designator assigned to one route shall not
  be assigned to any other route.

And to clarify what is meant by designator for the ATS routes (airways): a designator is a letter followed by 1 to 3 digits (1 to 999). In your case the L602 is the designator. The preceding U (for Upper) is a supplementary letter.

RE Is UL602 still part of the L602 airway or are they two separate airways?

They are the same route (lateral path), but not necessarily have the same navaids/waypoints:

The lower ATS route may require an extra VOR, for example, to compensate for the low altitude line-of-sight limitation.
It may also have extra waypoints for joining the SIDs and STARs to the airway (on/off ramp highway analogy). This is more applicable to the example given since it's an RNAV-only ATS route (see letter L below).

Bonus: The current letters for the designators are:

A, B, G, R (regional non-RNAV)
L, M, N, P (regional RNAV)
H, J, V, W (non-regional non-RNAV)
Q, T, Y, Z (non-regional RNAV)

A regional ATS route is usually one that passes through more than 1 FIR.


What emergency situation can pilots encounter in gliders/non-powered aircraft?

The number one emergency in a glider is a tow rope break at low altitude, less than 200 feet above the ground with no appreciable headwind. Below 200 feet, the proper technique is to land straight ahead, which usually means landing off airport.

Between 200ft and 500ft, it is possible to make a U-turn back to the runway, and land in the opposite direction in which you took off.  The main hazard with this kind of landing is landing with a tailwind, and once the wheel touches the ground, the flight controls operate in the reverse direction.

Above 500 feet, it is possible to fly an abbreviated pattern and land on the runway you took off from.

Add 50 feet of altitude for each 10 knots of headwind.

Some other tow emergencies are inability to release to tow rope, in which case the tow pilot needs to release the rope on his end; engine failure of the tow-plane; and a double tow rope release failure, which means the glider needs physically break the tow rope (it has a pre-determined breaking strength of 80-200% of the weight of the glider) or to land behind the tow-plane.

You can also run out of altitude and have to land in a field, which is called an "off airport landing." Someone has to come and get you with a trailer, and you disassemble the glider and drive it away. One hazard is the off airport landing in a field, and the farmer comes out with his shotgun.

Other hazards are flying into the clouds or into severe turbulence, which can happen when the glider pilot is flying "wave," a kind of lift generated by strong winds in proximity to
 mountains.

When thermaling, you are flying very tight steep turns, often with other sailplanes who are also trying to gain altitude. Everyone is supposed to fly the thermal in the same direction, and there is the hazard of colliding with other gliders.

Reference: FAA Glider Flying Handbook - Abnormal and Emergency Procedures


The following describes reverse-flow, free-turbine type gas turbine engines such as the Pratt & Whitney Canada PT6 series of turbo-prop engines that I am familiar with. There are also geared turboprop engines such as the Garrett models; I am not very familiar with these.

The Beechcraft systems description for one of the PT6 models provides the following:

  The PT6 engine has a three stage axial, single stage
  centrifugal compressor, driven by a single stage reaction
  turbine. The power turbine, counter-rotating with the compressor turbine, drives the output shaft. Both the compressor turbine and the power
  turbine are located in the approximate center of the engine
  with their shafts extending in opposite directions. Being a
  reverse flow engine, the ram air supply enters the lower
  portion of the nacelle and is drawn in through the aft
  protective screens. The air is then routed into the
  compressor. After it is compressed, it is forced into the
  combustion chamber, and mixed with fuel that is
  sprayed in through nozzles mounted around the gas
  generator case. Two spark igniter plugs are used to start combustion. After
  combustion, the exhaust passes through the compressor
  turbine and two stages of power turbine and is routed through
  two exhaust ports near the front of the engine. A fuel control system schedules fuel flow to maintain the power
  set by the gas generator power lever. Propeller speed within
  the governing range remains constant at any selected
  propeller control lever position through the action of a
  propeller governor, except in the beta range where the
  maximum propeller speed is controlled by the pneumatic
  section of the propeller governor.

  The accessory drive at the aft end of the engine provides
  power to drive the fuel pumps, fuel control, the oil pumps, the starter-generator,
  and the tachometer transmitter.

  The reduction gearbox forward of the power turbine provides
  gearing for the propeller and drives the propeller tachometer
  transmitter, the propeller overspeed governor, and the
  propeller governor.

The following diagram depicts airflow through the compressor stages, the combustion chamber, the power turbines, and the exhaust section. The propeller bolts on the front of the engine at the output shaft (left side in the diagram).

The following diagram depicts the various compressor and turbine stages. Note the physical disconnect between the gas generator and power generator turbines. This is why these types of engines are called "free-turbines": the power turbine (and by extension the propellor) can spin freely from the gas generator section.


What is the wire running from the CG to the tail?

Sounds like an HF antenna. It absolutely isn't structural, as neither of those aircraft needs guy-wires for structural stability. (You'd also expect to see it on every example, not just some, if it were required that way.)

This article provides a lengthy discussion of HF antennae, for those interested in going deeper into the subject.

This thread has a related discussion of why not all HF antennae are of the long-wire type. Essentially, newer designs often replace the long wires.


What do solo pilots do between reporting points on longer flights?

The short answer is that you keep checking everything in the aircraft is doing what it should. For light piston GA operations, one common acronym for en route checks is FREDA. Here are some things that could be included (pilots often use their own checklists for things like this):

Fuel. How much have I burned? Is my navigation log up to date? Have I burned the amount I expected? How much longer can I fly for before I have to land? Which airports are within my current range ring? Is it time to switch tanks? Is the aircraft still within weight and balance limits? Is the airport where I planned to refuel still the right place to go?
Radios. Do I have all my radios set to correct and useful frequencies? How am I going to identify my next waypoint? Do I need to tune and identify a new VOR? Have things been suspiciously silent for a while? Should I file a PIREP? Do I need to tell ATC I need a deviation for weather? What's the latest weather information from ADS-B or another source? Can I guess which frequency ATC is going to hand me off to next? Did ATC ask me to report at a certain time or place?
Engine. Are all temperatures, pressures, gauges etc. showing the values I expect? Have I leaned the mixture properly? Are the exhaust gas temperatures correct? Is manifold pressure correct for this altitude? Has anything changed unexpectedly since the last time I checked them? If the engine dies right now, where am I going to land?
DI to compass. Reset the directional indicator to match the wet compass, to avoid gyroscopic precession errors.
Altitude. Is this altitude correct for my current heading? Is this the altitude I was assigned? If I lose comms now, what altitude should I fly at? Do I know what terrain is below me? What's ADS-B showing me right now? Any potential traffic conflicts? If I encounter icing here, will I descend, climb, or turn around? Is the autopilot correctly configured? Have I entered the current altimeter setting in all the instruments?

After you've worked through all that, it's usually time to go back to the beginning and start again :-)

Of course, there are plenty of other things that pilots are likely to be doing, like having drinks or snacks, taking pictures, admiring the view, listening to music, trying to find their spare headset batteries at the bottom of their flight bag, and so on.

But an IFR flight - or any flight - is never just sitting back between waypoints and waiting for ATC to call. The point of the constant checks is to detect any problems as soon as possible. For example, if you notice the oil pressure dropping gradually, you can take action while you still have engine power; if the first you know about it is that the engine suddenly stops then you have a big problem. Not only have you lost engine power, you're also not mentally 'primed' to deal with the situation and that could turn a tricky situation into a dangerous one.


Virtually any radar in the world can detect and track a stealth aircraft as well as to provide a “kill chain” to direct and guide weapons at it.  The key is at exactly what range they can do this and that’s a function of the radar cross section of the target.  Stealth aircraft typically, depending on the bearing and azimuth a radar illuminates them from have an RCS on the order of a BB pellet; a conventional aircraft eg a SU-27 has an RCS around the size of a two story house.  Certain kinds of radar sets like low frequency radars can detect stealth aircraft much better than X-band radars can but are inferior for miniaturization or for providing weapons guidance, limiting their effective ranges.


Why is the main landing gear of the Cessna Caravan placed so far forward?

You're right, placing the gear more aft would make ground handling much easier and not affect flight stability. But it would make taking off harder.

When the aircraft has accelerated to a speed just below lift-off speed, the wing's angle of attack is too low to create enough lift when that speed is reached, so the pilot will lift the nose while the main gear is still on the ground. This maneuver is called "rotation", and the speed at which the pilot pulls the stick or yoke back to lift up the nose is called rotation speed. By the time the aircraft has the right angle of attack, the lift-off speed is reached and the aircraft takes off.

If the gear is further aft, the downforce on the elevator needed to push the nose up needs to be bigger, and more drag is created during rotation. If the gear is still further aft, the maximum possible downforce at that speed would not be sufficient to get the nose up, and rotation must be delayed. The acceleration up to rotation speed is done with horizontal ground attitude because then the wing creates less lift and also less drag during the take-off run. Therefore, the pilot has to get the nose up to get the plane into the air, or he would need to accelerate to a much higher speed, at which the airplane flies even with its ground attitude. This all helps to minimize the airfield requirements.

To strike the right compromise between ground handling and elevator downforce during rotation, it is recommended to position the main gear along a line from the center of gravity down to the ground which is slanted 10°-15° back. The drawing below shows limits between 6° and 20°, but this is quite a wide range. Details depend on the desired angle of attack at liftoff and the maximum range of the center of gravity.

Side view of the recommended tricycle gear layout (Picture source).


How can we calculate the benefit gained from taping glider wing roots?

The two questions actually concern very different issues.

The second question is easier to answer. Let's take your thought on:

  I've always wondered though how critical this practice is.

It is pretty crucial! If you did not tape the gap between the wing and the aileron, you increase chances of a stall. This is especially true at low speed and large angles of attack, i.e. while thermaling or landing. Then an airflow from the lower side of the wing to the upper side might occur, through the gap, destroying the upper side's airflow. This very certainly leads to a performance penalty but also favors stalls. There have been some prototypes experiencing exactly this loss in performance (I could provide more detailed references if desired). I haven't heard of a stall related to this issue, and it actually might be unlikely to happen because under the described circumstances the transition point from laminar to turbulent flow is rather close to the wing's leading edge anyway. Nonetheless, the possibility of increased stall probability should be considered and, imho, is reason enough to never ever fly without aileron tapes.

The first question can only be answered qualitatively, at least with today's methods. It is effective: the airflow, although transitioned to turbulence by the tape, is definitely less turbulent than without the tape. Any kind of turbulence model will consider the "amount" of perturbation, i.e. larger discontinuities of the surface lead to stronger turbulence, thus more drag. You could fly with only one wing taped and see if you can notice a difference. If you notice rolling or yawing, then that's in favor of the corresponding wing. Honestly speaking, I doubt anything can be noticed if the wing consists of one part only, because the asymmetric drag is so close to the center of gravity (only at wing root). But if the wing is made of multiple parts, that might actually lead to some practical result. I am thinking of, e.g., Schleicher's ASW 28 or ASG 29 that have inner and outer wing parts + winglet, meaning 3 tapes distributed over the half wingspan. However, please check the manual of the glider first, if flying without tapes is permitted by the manufacturer.

And then there is also the noise issue.

Given all this information on the one hand and comparing it to the cost of tape and the time it takes to apply it, there is no reason not to use sealing. (Except, of course, around the canopy. You wouldn't expect what kind of ideas people can come up with)


Can someone identify this warplane silhouette?

This is a B-1B Lancer.

It is a 4 engine (afterburning engines mind you, very rare for a bomber) variable sweep wing bomber, designed during the Cold War to use its terrain-following radar to stay low and fast, weaving between the mountains of Russia to stay below radar to deliver nuclear warheads.

It carries more bombs than the B-52 as well.

Essentially, it is a bomber built like a fighter. It is actually the only swing-wing aircraft in the entire US military right now.

Fun fact: The canards near the nose aren't for control. Because the aircraft is flown by autopilot using terrain-following radar (TFR), weaving into and out of mountains, autopilot makes many quick pitch adjustments. The canards are to cancel out sine waves in the structure of the fuselage.

It can carry a whole lotta' bombs:

24 nuclear bombs, 48 JDAMs, 84 Mk82 bombs, or 48 AGM missiles.

100 were built, 66 remain.

I leave with my current desktop background:


Does any country issue daytime-only commercial licenses?

In Australia you can get a class 1 medical whilst being colour-blind, limited to day VFR. Night flying over here is a separate rating and not incorporated into the PPL/CPL so it is optional - it might limit your job prospects but you can absolutely fly on a CPL here in daytime only.


According to a recent article from the travel blog The Points Guy (whose reporters were at the Paris Air Show and toured the aircraft,)

  [W]hile it has three motors, the aircraft can continue to fly with just the rear motor engaged. If one wing-mounted motor fails, the other will be disabled to maintain stability, and additional electric power can be diverted to the rear motor so the plane can continue its flight.


Where can I get IFR charts for throughout the world?

The primary source for every country would be the countries' Aeronautical Information Publication (AIP). In some cases the AIP is freely accessible, printed copies can be directly obtained from the Civil Aviation Authority (CAA) or commercial companies authorized to distribute these, such as Jeppesen.

In some cases there will be a joint resource for certain areas, e.g.
The IFR charts for European countries can be obtained as digital copies from EAD EUROCONTROL.


What does it mean to "lock on" to a DME ground station?

"Lock-on" just refers to a unit receiving multiple different response signals in response to its interrogation broadcasts, scanning for the signal it's looking for, and when it finds the signal who's encoding matches its channel selection, it starts to process that signal and ignores all others.  It's locked on to that signal.


What is wrong about this interpretation of QFE and QNH?

Your question is quite not clear, you are challenging definitions and use of definitions, but you may start with a misunderstanding:

  QFE = pressure measured by an altimeter which is adjusted to ground
  level (it gives a height of 0 when the airplane is on the ground).

Definitions

To ensure clarity, QFE/QNH:

are reference pressures, not altitudes
are not read/measured by the altimeter, but entered by the pilot in the setting window.
when mentioned in an altitude would be mentioned like, for instance: "I'm flying at 1,000 ft referenced to QFE", and not "my QFE is 1,000 ft".

QFE and QNH are not what the needles of the altimeter indicate, they are only the pressures that are to be entered in the setting window to calibrate the altimeter for common low level flight references.

How is QNH determined

While QFE is a direct measurement of the pressure, where the temperature is ignored, QNH is never measured, it is "retro-computed" from QFE:

Determining QNH requires first to know the local pressure (QFE) at the relevant location (e.g. airfield reference point)
The actual altitude of this location is then converted into a pressure difference, using the ISA model (+1 hPa per 27 ft at low altitude), without taking into consideration the temperature
The offset (which is positive unless the airfield altitude is under sea level) is added to QFE, the result is QNH (hence QNH pressure is usually > QFE pressure)

Said otherwise: QNH is the theoretical pressure value at MSL. but as the temperature wasn't taken into account, and actual distance between isobaric surfaces vary with actual temperature, then the actual pressure at MSL (if it could be measured) would be likely different.

Altimeter readings

After calibration with QFE or QNH value, any change in actual pressure -- that can be due to an actual altitude change, a local temperature change or a local pressure change -- will be sensed by the altimeter, the pressure change being indicated by an altitude change at the ISA rate of -27 ft for each added hPa.

By principle when the altimeter is on an isobaric surface equal to any pressure entered in the window, the value read is zero. As by definition the QFE is the pressure at the airfield level, then if the altimeter is at the airfield, set to QFE, and QFE has been just updated, then it indicates 0 altitude above ground level (AGL).

More generally (I hope this is accurate, else correct me):

Note that the pressure scale on the left has the higher value at the bottom, while the altitude scale on the right has it at the top.

  As you can see this figure says that $h_{QFE}=h_{QNH}+h_e$ which should
  instead be $h_{QNH}=h_{QFE}+h_e$ (the opposite).

You or the book may be correct, depending on the sign of $h_e$. But it's not clear. If this quantity is positive, you are correct.

Remember that QFE and QNH are not altitudes, they are the altimeter reference values. For an airfield above MSL, QFE < QNH and an altimeter reading (h) referenced to QFE ($h_{QFE}$) will be approximately the height above the airfied (AGL) while when referenced to QNH ($h_{QNH}$) it will be approximately the altitude above MSL (AMSL).

Indeed altitude above sea level is larger than height above ground. Possibly in your example above, the author may have $h_e$ as a negative value.