How can opening of a door on small plane cause a drop in altitude?

In an unpressurized plane the door opening is less of an issue than in a pressurized plane but there are still some issues it presents. Its common for planes to have multiple latching mechanisms to try to prevent this from happening. In some cases they system is not perfect like this AD issued for the DA40 relating to the doors coming off in flight (due to improper closing it appears). Being able to run with out a door or open it in flight is even key for things like para-trooping and skydiving

Depending on the orientation of the door the biggest issue I would foresee is the door shearing off and damaging part of the empennage. This could a have serious if not potentially fatal impact on the plane.

Physically speaking the open door will create drag on the plane which may have been related to the decent you felt. It could also have been an inadvertent reaction by the pilot to the possibly loud noise.

On somewhat of a side note, most aircraft doors are oriented in such a way that the airflow will more or less push them shut (on small GA planes/non pressurized planes). Thus most doors open forwards like the ones on many pipers

Or vertically up so gravity will close them (note the baggage hatch). I would assume this is intentional but it may just be coincidence as that is also how car doors open. Along the opening lines, it is standard emergency procedure in small airplanes to unlatch the door before a forced landing incase the accident mangles the door locks.

For what its worth some planes are even flown with the hatch open most the time (pictured on the ground here but flown in the same config)

Here is a nice article written by a pilot about why it would be very hard (basically impossible) to do on a pressurized plane.


What happened with the YF-16 prototypes?

Some of them are in museums, YF-16 was a technology exploration and didn’t commit to production.

YF-16

72-1567 – Virginia Air and Space Center, Hampton, Virginia
72-1568 – Rome ADC

YF-16A (Full-Scale Development)

75-0745 – Used as a traveling exhibit, on loan from the National Museum of the United States Air Force, Wright-Patterson AFB, Ohio
75-0746 – Pylon-mounted gate guard, McEntire Air National Guard Base, South Carolina
75-0748 – Cadet Area Quadrangle, U.S. Air Force Academy, Colorado
75-0750 – Experimental Aircraft Display Hangar, National Museum of the United States Air Force, Wright-Patterson AFB, Ohio

YF-16B (FSD)

75-0751 – under restoration at the Air Force Flight Center Museum, Edwards AFB, California.
75-0752 – Frontiers of Flight Museum, Dallas, Texas


While I'm not sure about the condition of the aircraft, there are uses for a non-flight worthy aircraft in a carrier deck. For example, the crash and salvage team can train salvaging the aircraft, or the sailors can train craning the aircraft abroad the deck.

For example, in the image below, U.S. Navy sailors use a crash and salvage crane to lift a non-functional McDonnell Douglas F/A-18 Hornet during flight deck drills aboard the aircraft carrier USS Ronald Reagan (CVN-76).

By U.S. Navy photo by Mass Communication Specialist 3rd Class Jonathan Nelson - This Image was released by the United States Navy with the ID 150415-N-WO404-124 (next).This tag does not indicate the copyright status of the attached work. A normal copyright tag is still required. See Commons:Licensing for more information.

It may also be used for firefighting and damage control training, as can be seen in the image below.

Sailors assigned to the crash and salvage crew on USS George H.W. Bush (CVN 77) spray foam on an F/A-18 Hornet training aircraft during a firefighting drill; image from warbirdsnews.com, credited to USN

The article notes:

  Since active jets are precious assets, they use specially-prepared training airframes, like grounded F-18 Hornets ... these former frontline fighters are often antiquated models of current equipment or planes that have been damaged beyond the point of repair. These days the trainers are usually represented by earlier models of the F-18 whose variant has been retired, ... (they serve) as training aids for firefighting and crash retrieval and salvage operations, letting crews hone their skills using real world items, without risking damage to expensive operational flyers


Do helicopters carry radar equipment? Is so, where is it placed and what type is used?

Most helicopter don't carry radar; there is no need for it.

In civil helicopters radar is typically used for weather detection. In most use cases there is not real need for it because helicopters are usually operating under daytime Visual Flight Rules (VFR) and are staying away from clouds. For maritime helicopters that are used in search and rescue operations or off-shore operations on oil-rigs, weather is often installed. The typical location is in a radome in the nose of the helicopter. Examples are the Honeywell Primus 660 or Rockwell Collins RTA-4100

Military helicopters use radar for detecting objects. Depending on the nature of the mission the helicopter is designed for, the radar is underneath (usually for navy operation, providing sea surface detection capabilities, see for example the navy version of the NH90) or on top of the rotor (to look over obstacles such a hills / trees  and provide fire control to their missiles). An example is the AN/APG-78 longbow fire control radar.


Will I have to redo flight time for switching to a new CFI?

You will not need to repeat the hours. I flew with two different instructors during my training due to my first one heading off to the airlines and it was not an issue, as a matter of fact its pretty common. The FAA considers flight time, flight time. Once you logged the hours they are yours for the rest of your life.

However the new instructor will most likely have you repeat some of the stuff you went over with the first CFI just to see where your skills are at. If you only have 4 hours under your belt is likely you have just done turns, climbs, decents, and possibly stalls so switching instructors will be no issue. It takes a fair bit of time to build a rhythm with an instructor anyway.

Just some advice, if you are at a flight school that has a few others to pick from its worth it to ask them what their intentions are. Most instructors are there to build hours towards ATP then its off to the airlines. You should ask instructors how many hours they have left if they are going to ATP out, the more hours they have the longer they will be around. This will help you prevent the situation where you have to change instructors again.


drag force relationship with cube of speed?

You seem to be confusing force (thrust or drag) with energy (under which concept work and power comes). Don't. You'll be spared much grief.
Work done is force times distance.
$$ W = Fs $$
Power is work done divided by time
$$ P = W/t $$
When you double velocity, force quadruples. As does work.
$$ W_\text{new} = 4Fs = 4W $$
Time halves as well, with the following effect on power.
$$ P_\text{new} = 4W/0.5t = 8P $$


Can IPA be used as a FSII with MoGas, particularly with a Peterson STC?

Oxygenates, which includes alcohol, are not allowed in gasoline used in aircraft even with a special type certificate, not even airplanes certified to use MoGas. MTBE is the one oxygenate that is approved.

Gasoline sized hydrocarbons do not need freeze protection. Up to 1% anhydrous IPA (from a sealed bottle) can be used to clear an acute moisture issue, but the fuel should be consumed asap, IPA should not be a regular blend additive and certainly not be stored after adding to the tank.

The reason alcohol is not allowed is that it creates more far more problems than it solves. Alcohol is strongly attracted to water which helps IPA absorb small amounts of free moisture from the fuel system but it will also absorb moisture from humid air. A very small amount of which (1-2% moisture to total gasoline) will cause the alcohol to separate from the hydrocarbon portion creating an aqueous layer that at low altitudes will cause erratic power surges or completely stop the engine and at higher altitudes is insufficient to prevent ice in the fuel lines.

Meanwhile the octane rating of the remaining hydrocarbon mix will be severely degraded as alcohol containing gasoline is reliant on the alcohol as an anti-detonation additive.
Adding more alcohol to overcome the moisture issue by brute force will reduce the usable energy of the fuel. (joules per kg, alcohol has only 0.6 times the energy of petroleum per Kg) Up to 5% alcohol improves burn efficiency slightly more than it reduces specific energy, plateaus at about 10%, then the reduced energy outweighs any improved efficiency. Of course weight matters to aircraft.

If the plane is stored for a few months, the separated aqueous layer can cause substantial corrosion and schmoo in the system. I wish I had taken pictures of the tank and carburetor of the motorcycle I just rebuilt after sitting in a garage for a year to show what happens with gasohol, and on the flip side I have zero alcohol gasoline that can sit for years.

  NOTICE: Isopropyl alcohol in amounts not to exceed 1% by volume can be
  added only to aviation fuel(not automotive fuel) to prevent ice
  formation in fuel lines and tanks. Although  approved  for use  in
  Lycoming  engines,  do  not  use  isopropyl alcohol in the aircraft
  fuel systems unless approved by the aircraft manufacturer.

Source PDF from Lycoming, which also specifies oxygenates shall be limited to 1%.


What is the teardrop-shaped appendage on the T-6 Texan?

It is the RDF antenna 'bullet' (or teardrop, actually) fairing. This image shows the (loop) antenna itself.

Source: mission4today.com

Initailly, RDF antennas were circular loops mounted above or below the fuselage.

"Earhart-electra 10" by Originally uploaded by w:User:Logawi - Transferred from en.wikipedia, description page is/was here.. Licensed under Public Domain via Commons.

Later loop antenna designs were enclosed in an aerodynamic, teardrop-shaped fairing.

Source: airpages.ru


What is physics explanation for minimum sink rate airspeed?

From first principle, assuming the airplane is a point mass, no wind, small angle of attack, and thrust acts in-line with drag:

$$T-D-W\sin \gamma=m\dot{V}$$

where $T$ is thrust, $D$ is drag, $\gamma$ is angle of climb, $m$ is mass of the airplane, $W=mg$ is weight, $V$ is airspeed/forward speed (assuming no wind).

In a total power off scenario, $T=0$, and assuming steady-state, $\dot{V}=0$:

$$\sin \gamma = -\frac{D}{W}$$

The rate of climb ($\dot{z}$), which is the negative of sink rate, is related to angle of climb by: $\dot{z}=V\sin \gamma$. Therefore, we have:

$$\dot{z}=-\frac{DV}{W}=-\frac{P_R}{W}$$

Therefore, for minimum rate of descent, we would like the minimum power required ($P_R$).

Note: for minimum glide slope, it corresponds to $L/D_{max}$, but not for minimum rate of descent.


Are all US fighter/combat aircraft constantly armed, even just in training?

As a general rule, unless you are going to use ordnance e.g. training, alert status, or war, you are not going to have it loaded on the jet.  It's just another risk to personnel or equipment out on the line, in hangars, etc.  Aircraft returning with live ordnance are disarmed and unloaded after shutdown and the weapons defused and returned to the bomb farms on base or magazines aboard ship.


What is the significance of the "date designation expires" on a temporary airman certificate?

"date designation expires"

Assuming your temporary certificate is issued in the United States.

Is the date that the Designated Examiner's designation expires (assuming it was a "Designated Examiner" who issued the temporary certificate).

A Designated examiner's authority has to be periodically renewed.

This is not the date your temporary certificate expires, which is 120 days from issuance.


How to do blade element momentum theory analysis for different geometries of airfoil, e.g. NACA airfoils?

The only difference would be the lift and drag coefficients used.  You'd need those to be specific to the airfoil(s) you choose.  Momentum theory is otherwise not sensitive to the airfoil shape.
Given the same lift and drag, momentum theory will give you the same induced velocity.


What is this aircraft parked in Oceanside Municipal Airport?

Most likely an ERCO Ercoupe. BTW, this tail configuration is called H-tail.
Note the similar-looking Max Holste MH.52, but with the noticeably smaller dihedral angle.


What are all the US airports where E4 "extensions" change to E2 and become part of a larger E2 "surface area" when the tower closes for the night?

With these 21 airports,  the airspace definitions are written so that the E4 "extensions" change to E2 and become part of a larger E2 "surface area" - which also includes the airspace that was Class D during the daytime -- when the tower closes for the night.

The page number references are for the FAA's "Airspace Designations and Reporting Points" document, FAA JO 7400.11C.  The page numbers listed are for the E4 airspace designation, the E2 airspace designation, and Class D airspace designation.

KENA or PAEN
AAL AK Kenai, AK
Kenai Municipal Airport
E-158, E-7, D-5
KGCK
ACE KS Garden City, KS
Garden City Regional Airport
E-159, E-17, D-7
KJEF
ACE MO Jefferson City, MO
Jefferson City Memorial Airport
E-162, E-21, D-11
KNHK
AEA MD Patuxent River, MD.
Patuxent River NAS (Trapnell Field)
E-165, E-28-29, D-15
KITH
AEA NY Ithaca, NY
Ithaca Tompkins Regional Airport, Ithaca
E-167, E-30-31, D-19
KPOU
AEA NY Poughkeepsie, NY
Dutchess County Airport, Poughkeepsie
E-167, E-32, D-19-20
KCXY
AEA PA Harrisburg, Capital City Airport, PA
Capital City Airport, Harrisburg
E-169, E-35, D-22
KLNS
AEA PA Lancaster, PA
Lancaster Airport
E-170, E-35, D-23-24
KRDG
AEA PA Reading, PA
Reading Regional/Carl A. Spaatz Field, Reading
E-170, E-36, D-24
KUNV
AEA PA State College, PA
University Park
E-171, E-35, D-25
KIPT
AEA PA Williamsport, PA
Williamsport-Lycoming County Airport
E-171, E-37, D-24
KLYH
AEA VA Lynchburg, VA
Lynchburg Regional-Preston Glenn Field Airport
E-172, E-38-39, D-26
KNTU
AEA VA Oceana NAS, VA
Oceana NAS (Apollo Soucek Field)
E-172, E39-40, D-28
KAPN
AGL MI Alpena, MI
Alpena County Regional Airport
MI E-176, E-45, D-36
KMKG
AGL MI Muskegon, MI
Muskegon County Airport
E-177-178, E-48, D-39
KRST **
AGL MN Rochester, MN
Rochester International Airport
E-178, E-54, D-41
KSTC **
AGL MN St. Cloud, MN
St. Cloud Regional Airport
E-178, E-54-55, D-41
KGFK
AGL ND Grand Forks, ND
Grand Forks International Airport
E-179, E-56-57, D-42-43
KILN **
AGL OH Wilmington, OH
Wilmington, Wilmington Air Park
E-181, E-59, D-46
KRAP **
AGL SD Rapid City, SD
Rapid City Regional Airport
E-181, E-61, D-47
KPRC
AWP AZ Prescott, AZ
Ernest A. Love Field
E-210, E-129, D-140

** means that in these 4 cases, no limit on the effective hours is given for the E4 airspace - apparently it is simply assumed that the E4 will be superseded by the E2 whenever the E2 is in effect.

Among airports with part-time control towers and with E4 "extensions", the style of airspace designation that is much more common over the nation as a whole is for the E4 airspace to be in effect 24/7, and for only the Class D airspace to change to E2 when the tower closes for the night.  Here's an example of such a designation:

KMFR
ANM OR Medford, OR
Rogue Valley International-Medford Airport
E-189, E-80-81, D-64

Note that there is no way to tell one style of designation from the other just by looking at the sectional chart or the Airport/ Facility Directory.  Perhaps this may be taken as a hint that the distinction rarely matters in actual practice.

Note the uneven distribution of the airports in the list above among states and regions.  For some reason, in some regions such as the northeast, the style of airspace designation that we're discussing here is actually more common than the style that we see at KMFR.

To understand why the distinction between the two styles of airspace designation might matter, at least in theory, to pilots flying at first light before the tower is open for the day, including ultralight flight, aerobatic practice, non-recreational sUAS (drone) activities, and possibly now that the FAA is implementing some new regulatory changes, recreational sUAS (e.g. RC model airplane) activities, see the first two links below.  Whether this distinction has ever yet mattered in actual practice is an open question-- perhaps in actual practice the airspace in these extensions is simply treated as E4 airspace 24/7 in relation to FARs 91.303c, 103.17, and 107.41.  Nonetheless, pilots of such aircraft would undoubtedly hope that this unusual style of airspace designation is avoided in the future.

It is interesting to note that on the FAA's LAANC map for authorization for sUAS (drone, model airplane) flight, these projecting E4 extensions that change to E2 when the tower is closed at the 21 airports listed above are NOT covered by the grid squares that indicate the areas where pre-authorization is required.  This supports the idea that these extensions are simply treated as E4 airspace 24/7, at least in relation to FAR 107.41.

Unlike what is implied by the actual language of FAR's 91.303c and 9.155c, it seems unlikely that the distinction between the two different styles of airspace designation has ever mattered in actual practice to a pilot seeking to obtain a Special VFR clearance, or planning to fly beneath a cloud ceiling below 1000' AGL without obtaining a Special VFR clearance.  See the third and fourth link below for more.

For more, see these related question or answers:

Which parts of class E airspace can an ultralight (part 103) fly in without prior ATC authorization?
What is the primary reason that the non-towered airports KACV and KTLV have E4 extensions to E2 airspace?
In actual practice, do ARTC Center personnel generally follow the rule that a SVFR clearance may be granted in E2 airspace but not E4 airspace? (US)
In the US, is there much variation among the various ARTC Centers as to where a SVFR clearance may be granted?
Does an SVFR clearance extend to Echo surface extensions?
Does an SVFR clearance extend to Echo surface extensions?
Does FAR 91.155c apply to class E surface extensions?


What degree of elevator deflection is required to takeoff?

It depends. Mostly on two parameters:

What is the position of the center of gravity? A more forward position would require a bigger downforce at the tail, so deflection angles would be bigger. On the 777-200, c.g. positions from 14% to 44% of MAC are allowed.
What is the trim setting of the stabilizer? Depending on the setting, more or less deflection is needed to set the whole horizontal tail to the right downforce for rotation.

Further parameters are flap settings, take-off mass, rotation speed and desired rate of rotation, but the first two are the most important.

Since I do not have the official Pilot's Operating Handbook for the Boeing 777, the virtual version has to do. Sadly, it contains very little information. The more seedy corners of the internet have maybe more substantial content, but here you are on your own.

The Boeing 777 has a computer based weight and balance system, called Accuload, which will compute the proper take-off trim setting, therefore, no discrete values can be given. With the recommended trim setting, the pilot will apply forward pressure on the control column until roatation speed ($v_R$), relaxing control forces to neutral for smooth rotation.

If you would take off with the trim setting for cruise, the elevator would need to be deflected by approx. -10° (trailing edge up) in a simulation with typical parameters. Please note that this is not the regular take-off procedure, and the actual deflection angles are much smaller.


We really shouldn't speculate, but it does not look like a panel piece for a door or window. Aside from two small warning lights on some models there shouldn't be very much.

This is very much speculation: Aside from the deep inset, which looks like it could have housed a CRT monitor, there are two holes for square aviation-style switches, and two holes, perhaps for backlighting, above it. The left hole looks very similar to an SD card slot.

Then again, it could have come from a boat or anything.


Do helicopter rotor tips regularly go supersonic?

The "wop wop", usually known as blade slap, is heard when the tip of the blade passes through the vortex created by the previous one.

It can be avoided.  The most common flight regime when this happens is a shallow descent but still with quite a lot of power - e.g. fast and shallow.  The vortex starts to move down as soon as it leaves the tip of the blade so in level flight, the following blade passes over it.  In a shallow descent with high pitch angle, the following blade can literally "slap" into the previous vortex.  The vortices of the two blades now interact and can cause local, transient supersonic flow.  To avoid it, simply lower the pitch to establish a more positive descent or pull back on the cyclic to increase disc loading and flatten the attitude.

The blade tips do not go supersonic.  In fact, in nearly all helicopter designs, the rotor rotates within a very narrow range of speeds, typically between 90% and 110% of the normal speed.  In most flight regimes, the rotor is rotating at 100%, +/- a few percent, whether you are climbing, descending or cruising.  Only during auto-rotation and aggressive manoeuvring does the range vary by 10% or more.  It depends on the type of helicopter but absolute limits would be something like 85% (panic time, risk of complete stall) and 115% (smaller panic, risk of damage to the machine, especially in the tail rotor drive shaft).

In normal operations, and design aims to achieve this, the rotor tips do not go supersonic since when they do, there is a sudden and large decrease in performance with more power required, higher blade loads, vibration and noise.

Think about a helicopter flying forwards.  The advancing blade at its most perpendicular position experiences a relative airflow which is equal (ignoring all kinds of minor side effects) to the forward speed plus the speed of the blade.  The retreating blade is experiencing a relative airflow equal to the speed of the blade minus the speed of the helicopter.

If the blades rotate so fast that the tips are supersonic, then the main lift generating part of the retreating blade, the outer two thirds of the span, would experience such a low airspeed, for some of the span it will even be negative, that the blades will stall causing a catastrophic roll into that side.  It is this phenomenon which ultimately limits the rotational speed of the blades and the maximum speed of the helicopter.

Let's look at the R22 as an example.  The following figures are approximate.

The rotor tip speed is about 670 fps (feet per second).  The speed of sound at ground level on a standard day is about 1100 fps.  The R22 is flying at close to VNE, let's say 100kts which is about 170 fps.

The tip on the advancing side, at it's fastest, is therefore flying relative to the airflow at 840 fps and on the retreating side, at it's slowest, at 500 fps.

The blade length is about 11 feet, so the middle portion of the blade on the retreating side is only flying at 190 fps (half of 670 minus the airspeed).  When you get to about 4 feet out from the blade root, it's now only 50 fps and not much further in from that, becomes zero, then negative.

Remember that lift is proportional to the square of the speed.  You can now see the huge discrepancy between lift on either side as airspeed increases.

To answer your question directly, the R22 would need to fly at 530 fps to approach supersonic tip speed which equates to about 330 kts which it can't get anywhere near achieving.

PS.  The R22 POH speaks in Imperial measures.  When I get some time, I'll redo the figures in metric which I, and most of the world, prefer.


Can a handgun shot take down a commercial airliner?

shooting at it with a handgun

That's really going to depend on the handgun.

James Bond carries a Walther PPK - this is a .32 calibre popgun with rather limited use outside of a small office. Direct hits on people are usually survivable unless you take a round in the heart or brain. Chances of even hitting an airliner during takeoff or approach are zero - it simply doesn't have the range, and that tiny subsonic projectile will get deflected by the aircraft's wake.

Skipping the middle range and going straight for the hand-cannons, we might get somewhere with a Desert Eagle or a Smith & Wesson 500. Remember the posters for the first Terminator movie? The one where The Ah-nuld is wearing sunglasses and holding up some light artillery? These are bigger. At close range, both guns can crack an aluminum engine block1 and are one-shot kills on most things smaller than a rhino. Hitting an approaching widebody isn't all that difficult - it's coming toward you, the angle isn't changing, and it's a rather big target.

But aircraft are large, complex systems with a lot of redundancy, so in order to actually take it down we have to hit something critical. Hitting a 767 right in the nose will destroy the weather radar and (maybe, if it has enough energy left) poke a 1/2 inch hole in the forward bulkhead. No one will notice. The flight-deck windows are rather strong, apparently a police sniper tried to take out a hijacker on the flight deck way back in the 1970s and the rifle round (far more powerful) just pock-marked the window. Several hostages were promptly shot as a result.

The best shot (ha!) is the engines. They don't like ingesting bits of metal but just hitting the fan won't do much. You would have to get very lucky to get the round into the engine itself, where it will promptly do a lot of very expensive damage.

But even if one engine literally goes boom it still won't crash the plane. Pilots practice for an engine failure on takeoff all the time, and an engine failure on landing is almost a non-event.

Hydraulic lines for control surfaces are certainly sensitive, but they are well buried in the structure and there are several independent systems. You won't get them all.

So, in conclusion, handguns are sufficiently ineffective at bringing down large aircraft that we really don't need to be concerned about them. There's a reason air forces around the world prefer missiles or 20mm cannon2 for this sort of thing. Geese, however, are quite effective if released in sufficient numbers along the takeoff path. Rather noisy though - you won't hide 500 of them anywhere near an airport without someone noticing.

Internet legends of a .50 cal being able to kill a truck refer to the MUCH larger .50 BMG round, available in explosive and armour-piercing and rightfully categorized as a first-class military weapon.
The projectile's the size of your thumb, and the gun fires 6,000 rounds per minute. It'll do your plane like a chainsaw.


What is the required cloud clearance in G airspace when there are clouds just above in class E airspace?

KDKK is under a Class E shelf starting at 700 ft AGL (Magenta vignette around the airport).  If the airport elevation starts at 692’ MSL, the Class E shelf will begin at 1392 ft MSL.  Therefore operation at 1800 ft MSL above KDKK will put you in Class E airspace and subject to the VFR weather minimums of 3 sm visibility and 1000 ft above / 500 ft below / 2000 ft lateral cloud clearances.

As the the second question, clear of clouds means remain in a position outside of clouds and a flightpath which will not place you in immediate risk of entering a cloud.


What happens in a turbine high-temp combustion?

The biggest limiter of hot section temperatures in aviation gas turbines is moving hot section parts subject high stress loads under high temperatures and do so for very long periods of time.  Even the best nickel cobalt superalloys cannot maintain acceptable yield strengths past about 2000°F.  Some additional solutions have utilized to achieve even higher TIT levels such as novel single crystal casting techniques for the rotor buckets as well as using bleed compressor air to envelop the surface of the buckets to protect them against the high temperature exhaust gases.  Some military engines can operate with TITs as high as 2600-2700°F.  Another proposed option has been to manufacture the buckets, stators and hot section casings out of carbon composites, which hold the promise of increasing TITs as high as 4000°F.  However carbon composite blades are susceptible to oxidation before reaching these temps, making it difficult to realize this.  General Electric Aircraft Engines may be on the cusp of solving thes problems; if they do, a composite gas core would offer a quantum leap in power and efficiency.


Is it possible to obtain a PPL after having a brain surgery?

According to AOPA's medical guru on their discussion board (members only, or I would link to an example) it is possible to get a medical certificate following a tumor removal but only after a 5-year wait and a battery of tests.

But having said that, medical issues are very individual and the FAA's AME guidance suggests that one year is enough in some cases. In the end the only way to get a definite answer is to find a good AME who can review your case in detail and advise you. Note that standard advice is to schedule a consultation first, rather than go straight for the actual flight medical.

Disclaimer: I'm not a doctor or AME and I have no idea how brains work :-)


What is implied about altitude and the VDP by this Visual Flight Segment arrow in the profile view example in the Aeronautical Chart User's Guide?

This is extracted from the RNAV (GPS) RWY 23 of WESTERN NEBRASKA RGNL/WILLIAM B HEILIG FIELD (BFF) in Scottsbluff, Nebraska.

A VDP (Visual Descent Point) is only used in conjunction with an MDA (Minimum Descent Altitude). Do not mistake this for a DA (Decision Altitude). If visual contact with the runway environment is not made once a pilot reaches MDA, the pilot must continue at the same altitude on the approach course until reaching the MAP (Missed Approach Point). The VDP is the point along the course where a normal descent has been calculated as possible using normal procedures and maneuvers. It is a recommended point where the pilot should make the decision to go missed once reaching the MAP. That means that even though the pilot has decided to go missed, they will continue to fly past the VDP, straight and level, until the MAP. The key word here is “recommended”.

At a DA, if the pilot has not made visual contact with the ground, the pilot is required to decide to go missed. In most cases, that means the pilot would initiate the missed approach procedure immediately before reaching the DA. Since there are two DAs for the LNAV/VNAV, depending on if the local altimeter setting is available, there are two distances to the MAP. This is conditional upon the pilot maintaining glideslope all the way from the FAF (Final Approach Fix).

In this case, upon making visual contact with the ground, the pilot can choose to make a Visual Approach. There is no altitude requirement unless specifically charted. Cloud clearance and visual obstacle clearance must be maintained.

According to the users guide, it appears a pilot on the approach can fly visually past the point of decision if they have broken free from the clouds.

The Aeronautical Chart Users Guide states...

  Visual Flight Path
  Instrument approach procedures, including Copter approach procedures, that terminate or have missed approaches prior to the airport, and are authorized to proceed visual, shall depict the visual segment by the dashed line symbol from the missed approach point to the airport. The note “Fly visual” (“Proceed visually” on Copter procedures) along with the bearing and distance shall be shown leadered to the visual flight path.
  RNAV charts sometimes have visual flight for LNAV/VNAV minima which do not start at the missed approach point. An additional note indicating “LNAV/VNAV” will be placed above the note.

Furthermore the AIM 5-4-5-l states...

  l. In isolated cases, an IAP may contain a published visual flight path. These procedures are annotated “Fly Visual to Airport” or “Fly Visual.” A dashed arrow indicating the visual flight path will be included in the profile and plan views with an approximate heading and distance to the end of the runway.

  The depicted ground track associated with the “Fly Visual to Airport” segment should be flown as a “Dead Reckoning” course. When executing the “Fly Visual to Airport” segment, the flight visibility must not be less than that prescribed in the IAP; the pilot must remain clear of clouds and proceed to the airport maintaining visual contact with the ground. Altitude on the visual flight path is at the discretion of the pilot, and it is the responsibility of the pilot to visually acquire and avoid obstacles in the “Fly Visual to Airport” segment.
  Missed approach obstacle clearance is assured only if the missed approach is commenced at the published MAP. Before initiating an IAP that contains a “Fly Visual to Airport” segment, the pilot should have preplanned climb out options based on aircraft performance and terrain features. Obstacle clearance is the responsibility of the pilot when the approach is continued beyond the MAP.

  Note: The FAA Administrator retains the authority to approve instrument approach procedures where the pilot may not necessarily have one of the visual references specified in 14 CFR §91.175 and related rules. It is not a function of procedure design to ensure compliance with §91.175. The annotation “Fly Visual to Airport” provides relief from §91.175 requirements that the pilot have distinctly visible and identifiable visual references prior to descent below MDA/DA.

My reasoning for saying the VDP is recommended and not required is that the VDP is found in the AIM.

  AIM 5-4-5
  h. The Visual Descent Point (VDP), identified by the symbol (V), is a defined point on the final approach course of a nonprecision straight-in approach procedure from which a stabilized visual descent from the MDA to the runway touchdown point may be commenced. The pilot should not descend below the MDA prior to reaching the VDP. The VDP will be identified by DME or RNAV along-track distance to the MAP. The VDP distance is based on the lowest MDA published on the IAP and harmonized with the angle of the visual glide slope indicator (VGSI) (if installed) or the procedure VDA (if no VGSI is installed). A VDP may not be published under certain circumstances which may result in a destabilized descent between the MDA and the runway touchdown point. Such circumstances include an obstacle penetrating the visual surface between the MDA and runway threshold, lack of distance measuring capability, or the procedure design prevents a VDP to be identified.

  VGSI systems may be used as a visual aid to the pilot to determine if the aircraft is in a position to make a stabilized descent from the MDA. When the visibility is close to minimums, the VGSI may not be visible at the VDP due to its location beyond the MAP.
  Pilots not equipped to receive the VDP should fly the approach procedure as though no VDP had been provided.
  On a straight-in nonprecision IAP, descent below the MDA between the VDP and the MAP may be inadvisable or impossible. Aircraft speed, height above the runway, descent rate, amount of turn, and runway length are some of the factors which must be considered by the pilot to determine if a safe descent and landing can be accomplished.


Can airflow reverse over the flight surfaces of a uav in high wind conditions

It is possible, but only if there were a very sudden and dramatic change that the aircraft was unable to overcome.  However, it would be only temporary.

If the airflow direction was actually reversed the control surfaces would likely be blown to a full deflection position one way or the other depending on which side of neutral they were.

Otherwise, the aircraft would still move forward at 25kts relative to the moving airmass, with the additive effect of the wind giving it 60kts of ground speed.


Is it possible to determine the mass flow rate through the engine of MiG-21 during its various cruise Mach no. operations?

The mass flow is approximately $20 \ldots 100~kg/s$.
You can try to calculate it yourself using thermodynamic equations (see for example NASA Resources, MIT Resources or dedicated books).

Although the (idealized) calculations are not very difficult, please note that you will have to make a lot of assumptions concerning the efficiency of the turbojet components (particularly intake, compressor, combustion chamber, turbine and nozzle), since this data is not published by engine/airplane manufacturers. Some variables that are usually available are the thrust, the total compressor pressure ratio and maybe the (approximate) geometry of the intake and the nozzle.
Also, you are asking for supersonic calculations, which are more complex than the subsonic ones -- including the assumptions.


Why would a pilot ask the tower to turn the VASI off?

It could have been a flight instructor with a student that was becoming too reliant on the VASI's slope information for visual approaches to landing, and he wanted to force the student to do without.


There is transfer of control -- "I have the aircraft" / "You have the aircraft."  Then there is intervening -- which may or may not involve a transfer of control... directing "you're getting slow, ADD POWER NOW" may be a more effective example of intervening than taking control, depending on the phase of flight & other circumstances.  (It's easier for a First Officer to intervene with a directive "add power" or "go around" than than for him to take the aircraft!)  And then there is what was shown in the video, which looks like neither of the above -- simply crew duties as @Lnafziger commented. The captain there didn't take over control (yet -- the video ends before he takes over to taxi), they simply both pushed forward on the control column -- put weight on the nosewheel for better steering, perhaps.  Looked perfectly normal & expected.

To answer the question as asked ("Under what circumstances should the pilot not flying intervene without asking for aircraft control?"), there are plenty of times when intervening without taking control could be appropriate -- the directive callout ("ADD POWER!"), or correcting an aircraft system or Flight Management Computer setting, for example.  There are also a smaller set of times when "I have the aircraft!" is appropriate: a disoriented pilot is about to fly into an unusual attitude, or a pilot is incapacitated in a phase of flight where there is no time for "hey, are you okay?" to differentiate between distracted & incapacitated.  The captain always has the prerogative to take over, although there are plenty of times when something else is a better choice -- directing "go around" instead of taking the aircraft at low altitude to try & salvage a bad landing, for instance.  Particularly in cases of incapacitation, the FO also has that option, but realistically, he may have more explaining to do than the captain would have if roles were reversed.

In a pure training situation (initial formation flying in the military comes to mind), there are times when control may transfer back & forth... the student flies as far as he can, starts to get out of position, the instructor takes the aircraft, puts it back into position, the student is given control again, etc.  But that's not really the sort of scenario you'd see in airline operations.  There might be times the pilot-monitoring captain (i.e. he is the pilot not-flying on the FO's leg) might take over the FMC programming rather than talking the FO through the necessary changes -- sometimes it's just better to do it & explain what you're doing rather than talk through each entry and button press.  But that's again not really the same as "I have the aircraft."

With qualified crews in the airline world, it just isn't all that common that a situation arises where one pilot has to assume control outside of the normal transfers (i.e. the normal transfer to the captain on landing if he has the only nosewheel steering tiller).

And, as noted in the comments, every transfer, both expected and unexpected, needs to be verbalized by both pilots: "I have the aircraft."  "You have the aircraft."


To what extent is the HOST system still in use?

From this news article dated April 30, 2015:

  "As of today, Host is history," FAA Administrator Michael Huerta declared during a press conference.

From the latest NextGen report dated June 2016:

  In March 2015, the 20 planned ERAM sites achieved operational readiness, which signified the full commissioning of ERAM into the NAS and allowed the FAA to begin decommissioning the legacy HOST system.

So, it is fully out, it is not available as back-up, and no ATC system uses Host.


Why do pilots wait for a positive rate to put the gear up, When V1 means “commit to takeoff”?

V1 is the speed at which you are committed to take-off, it doesn't mean you are off the ground. You can't retract the gear at V1 because you are still rolling on it heading down the runway.

Vr is the speed at which you rotate the nose up to get into the air. Again you are still rolling down the runway with your nose in the air, you can't retract your wheels if you are using them.

V2 is the speed at which you are able to climb with one engine inoperative. It doesn't mean you are in the air yet, you can't retract the gear.

And just because the main gear come off the ground doesn't mean a gust won't push you back down, so usually you leave it down until you are reasonably assured that you won't touch again. It's a lot gentler on the aircraft if you touch the wheels than if you rub the skin off the aircraft. Positive rate is pretty much the only indication of this since there is a little bit of a lag in the VSI, by the time it shows positive rate you are far enough off the ground that you really don't need to worry about touching again.

  Shouldn’t it be retracted as soon as they see a difference in altitude?

The best indication is not the altimeter, it is the VSI. It reacts faster than the altimeter.

For GA aircraft, a lot of pilots won't retract the gear until "there isn't any runway left". This means that taking off on an 8,000 foot runway, they would be airborne by the 1500 foot mark and leave the gear down in case the engine fails they can just put it back down again.

What you really don't want to happen is for the gear to be retracted prematurely. When you are rolling down the runway you get "light on your feet" and the gear retraction mechanism can pull the gear up before the aircraft is ready to fly. The squat switches may be unloaded so they won't stop the system. Best thing to do is to wait for the positive rate, verify visually and then retract. Personally I leave it down until I'm 500' below pattern or no more runway left.


Are Ground Crew Airline or Airport Personnel?

Ground crew are typically employed by a handling agency, which is a company dedicated to performing ground handling of aircraft (exactly the things you describe).

Some airports have several different handling agencies. Have you ever noticed, when waiting for your luggage to arrive at an airport, that there are several different help desks to choose from, depending on your airline? Those are the different handling agencies at that airport.

At a given airport, a certain airline will typically have a contract with just one handling agency. Sometimes, airlines have their own handling agencies. The exact structure can vary.

Smaller airports often do not have third party handling agencies, but instead offer handling services directly to the airlines. In such cases, the ground crew is employed directly by the airport, and could also have other tasks, for example as airport fire fighters.


How to reduce the noise of the supersonic passage(bang)?

Most supersonic aircraft have points where the cross-section suddenly changes, such as the fuselage nose, the wing root leading edge or the wing trailing edge. The points of sudden change produce sharp changes in air pressure, i.e. loud sonic booms. Concorde was one example.

By designing the plane's cross-section to vary smoothly from end to end, the handful of points of major change are replaced by many more points of minor change. The booms are thus reduced in loudness and spread out in time, making them less intrusive.

Other factors which help include overall aerodynamic efficiency, light weight and high cruise altitude. A small, carefully-profiled and aerodynamically modern high-flying aircraft can thus be a lot quieter.


Do you ever get to practice ejecting out of a plane as a fighter pilot?

Air forces use special training rigs rather than real ejection seats. Example video

Plenty of pilots have survived ejection (Wikipedia says "As of 20 June 2011 ... the number of lives saved by Martin-Baker products was 7,402 from 93 air forces")
The types of injury are illustrated by this example

The ejection seat has been responsible for saving the lives of thousands of pilots around the world since its introduction in the late 1940s. Typical survival rates quoted in the literature vary from 80–97%.
It is generally accepted that radiographic evidence of vertebral fracture can be found in 30%–70% of aircrew after ejection

The reason real ejection seats are not used is almost certainly the high risk of injury. Ejecting clear from a high speed jet requires a lot of acceleration.


Do you get separate certificates for CFI and CFII?

No.  Under ratings on the backside of the Flight Instructor certificate, it should say:

FLIGHT INSTRUCTOR

AIRPLANE SINGLE ENGINE, INSTRUMENT AIRPLANE.

This is a CFI, CFII Flight Instructor Certificate, assuming you did your training in the United States under the FAA’s system.

You should see the same ratings on your temp certificate as well.


Why does the B-52 outboard engine nacelle have a sharp change in shape?

The B-52 was build in different versions (A-H) and the engines and their installation differ between these version1.

The image in the question most likely shows the engine configuration of a B-52H.

The following drawings suggest that this also changed the inlet design2.

There seem to be different engine-designations depending on the application. For the B-52H, JT3Ds (TF33-P-3) were used3.

Pictures of the TF33-P-3 inlet show they are symmetrical. (While the question is focused at the outboard engine-inlet, this question can only be answered taking the other engine and the placement relative to the wing into account as well).

At the symmetry-plane the TF33-P-3 inlet-section extends further than the rest of the inlet-lip.

I would guess that there are multiple reasons and considerations which led to this design. Three of which will most likely have been:

Basic aerodynamic considerations like stagnation-point and pressure distribution will prefer a sharp/point nose over a flat area. Especially since the air needs to be diverted from the engine-pylon.
The cruise speed of the B-52H is Mach 0.914 which means the nose could also be some kind of anti-shock-body reducing wave-drag by applying the area-rule.
The nose between the two engines prevents aerodynamic interaction of the two engines, for example during cross-wind operation.

The negative aspects of placing two jet-engines close to each other were also discussed in another SE-question with respect to commercial airliners.

[1]:www.airpowerstrategy.com/
[2]:http://www.afwing.com/
[3]:en.wikipedia.org/wiki/Pratt_%26_Whitney_JT3D
[4]:www.globalsecurity.org/wmd/systems/b-52.htm


Is it normal practice to use 25 degrees of flaps when taking off at max weight in a PA-28-181?

The PA-28-181 POH I have read says to set first stage of flap (10 degrees) for a normal takeoff, and 2 stages (25 degrees) for a short or soft field takeoff. I've flown PA-28s quite a bit and I've never heard any suggestion of using 25 degrees for a normal takeoff. At maximum weight on a hot day at sea level 5,503ft should be plenty at 10 degrees, even if you are at 4000 ft pressure altitude it should still be sufficient, so I see no reason to set 25 degrees.

Setting 25 degrees for takeoff increases lift at the cost of drag, and risk as you are closer to performance limits. An engine failure on takeoff with 25 degrees of flap will give you less time to get the nose down, and stall characteristics are harsher with more flap.

If the runway was shorter I would see 25 degrees as good advice. There are plenty of light aircraft pilots who don't do performance calculations before they fly, drilling 25 degrees of flap when heavy into them may just save their bacon on a hot day on a short airfield.


What would happen if a plane lost half of its weight instantly?

In steady flight, the lift $L$ generated by the wings equals the loaded weight so that there is no vertical acceleration.  Thus, the lift just before the bomb is dropped is
$$
L = m_1g =  245\,250 \;\textrm{N}
$$
where  $m_1=25\,000$ kg is the loaded mass and $g=9.81$ m/s$^2$ is the acceleration due to gravity.

In the time interval just after the $10\,000$ kg bomb is dropped, the lift remains the same until the lift is reduced to again balance the new mass of $m_2=15\,000$ kg. During that transient period, the Lancaster will accelerate upwards at
$$
a = \frac{L-m_2g}{m_2} = \left(\frac{m_1-m_2}{m_2}\right)g
$$
which works out as an upward acceleration of two-thirds of a "gee":
$$
\frac{a}{g} = \frac{m_1-m_2}{m_2} = \frac{2}{3}
$$

As @sanchises pointed out, the steady increase in the upward velocity results in a decrease in the angle of attack, so that the aircraft will again settle in a steady climb.


Do Federal Regulations really require compliance with all crewmember instructions?

I found an overview from a lawyer on what "interfering" actually means. The short version is that there's no regulation or law that says "you must obey all instructions". Instead, they say "you must not interfere" and that's interpreted very broadly.

She based the article on one regulation and one law:

14 CFR 121.580 (see also 91.11 and 135.120)

  No person may assault, threaten, intimidate, or interfere with a crewmember in the performance of the crewmember's duties aboard an aircraft being operated under this part.

49 USC 46504

  An individual on an aircraft in the special aircraft jurisdiction of the United States who, by assaulting or intimidating a flight crew member or flight attendant of the aircraft, interferes with the performance of the duties of the member or attendant or lessens the ability of the member or attendant to perform those duties, or attempts or conspires to do such an act, shall be fined under title 18, imprisoned for not more than 20 years, or both. However, if a dangerous weapon is used in assaulting or intimidating the member or attendant, the individual shall be imprisoned for any term of years or for life.

The lawyer's analysis is that not following an instruction would be a violation of the regulations (civil penalty). If you go further and physically interfere with a crewmember that would be assault (criminal penalty).

When it comes to instructions specifically, she says that "interference" can be interpreted very broadly (emphasis mine):

  Almost any offensive or disruptive behavior that distracts the crew
  can be considered interference, such as:

  [...]

  disobeying repeated requests to sit down, return to your seat, or turn off an electronic device

Her basic advice is to follow all instructions if possible and never touch a crewmember:

  Any time you disobey a crewmember’s instructions, you run the risk of violating federal law. But civil penalties and criminal prosecutions usually result only when passengers repeatedly ignore, argue with, or disobey flight attendants; or when they act out in a way that is dangerous.

You can see the FAA's enforcement statistics on this, by the way. Interestingly, it seems that the number of cases fell sharply in 2005 and has been trending down since then.


Unofficial Terminology

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

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

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

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

Official Terminology

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

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

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

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

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

Answer

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

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

Definitions

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

1Large Certificated Air Carrier:

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

2Air Carrier:

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

3 Air transportation:

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


If you are asking “When did the Cessna 172s adopt the modern 6-pack layout, the answer is 1968. You can verify this by looking at for sale pictures. All of the 1968 panels have the normal 6-pack layout while very few of the 1967 do. The revised layout in the 1967s is obviously not from the factory. They aren’t completely lined up like in your picture for a few more years. If you care to know when, browse through some for sale listings.

Cessna 172 - 1967

Cessna 172 - 1968

Also,I have a copy of the 1967 Owner’s manual and it shows the old layout like in the first picture.


What are the failure mode(s) for flying cars in case of power loss?

As I am closely working on some of these projects, I think I can answer.

Let me start from:

  if the power fails

this is a rather extreme situation, since everyone is including emergency functionality in case the batteries get below a charge guard level, triggering an emergency landing (still powered).

So to have the "power fails" scenario that your phrasing suggests, you would need a sudden fire or failure of all the battery packs installed on the craft.

What's more likely is that one of the engines will fail, but that's less critical, since all these crafts will have 8 engines as a minimum exactly for this scenario. And once again, this will trigger a powered emergency landing.

Nevertheless, you are right in assuming that these crafts can't autorotate, and some projects are evaluating/have evaluated the inclusion of emergency parachutes similar to the ones seen on some general aviation fixed wing aircraft.


What are the differences in design considerations for ground attack and air dominance aircraft?

One thing to note is that 'pure' air dominance fighter or ground attack aircraft is not being developed anymore. Most of the combat aircraft developed recently/under development are multirole (or 'omnirole') aircraft.

In case of air dominance (or air superiority) fighters, which have the task of eliminating enemy air defense system especially fighters and securing aerial control for operation of friendly forces without harassment, the following are important design objectives:

High thrust to weight ratio, as it helps in maneuvers.
Stealth, as the enemy can't shoot what he/she can't see.
High maneuverability, for close combat situations and evasion.
High weapons load, as it enables engagement of a large number of enemy aircraft at once.
A good range, as it is better to engage enemy aircraft in their area rather than in friendly territory.
A powerful radar to track and engage enemy aircraft, as it enables them to shoot first.
Communication links to transfer data between the aircraft and between the AEWACS aircraft, as most of the aircraft today operate in an integrated battlefield.
Speed is also a very important parameter.

In case of ground support (or attack) aircraft, whose primary task is the destruction of enemy logistics and/or support for ground troops under fire, the designers look for similar yet a bit different set of characteristics.

Ruggedness, as the aircraft should be able take some amount of punishment and return home.
High endurance and Time on Target, as the ground troops may require support for an extended period of time, with corresponding weapons load.
Communication links between aircraft and ground troops for obvious reasons.
Precision targeting systems for situations where friendlies are in close contact with the enemy troops.
Ability to operate from forward operating bases is desirable.

Most of the present generation aircraft carry out their ground support duties using precision weaponry rather than any fundamental design decisions. Though there are still trade-offs, as in any aircraft design.

The weapon load of stealth aircraft is lesser their non-stealthy counterparts as external weapons carriage increases the radar signature of the aircraft.
For ground attack aircraft, a high subsonic speed is more than enough unlike the supersonic air dominance fighters.
Low altitude maneuverability is important for ground attack aircraft for quick ingress and egress from the combat area.

One aspect of aircraft design is that combat aircraft optimized for high altitude operations can face higher stresses when operating in lower altitudes (i.e. near ground). For example, when USAF switched B-52s from high altitude bombing role to low altitude penetration tactics, it caused increased stress in the airframe.


What tests are done on aircraft wings for testing the effects of lightning?

Almost all the tests done on aircraft wings can easily be categorized in one of the areas you mentioned.

The only remaining thing I can think is bending an aircraft's wing. It is stated on BBC as:

  Many modern passenger jets can flex their wings nearly 90 degrees in a test rig.

For B787, it is reported:

  During the test, the wings on the 787 were flexed upward
  “approximately 25 feet” which equates to 150 percent of the most
  extreme forces the airplane is ever expected to encounter during
  normal operation. The test is used to demonstrate a safety margin for
  the design and is part of the certification process to show the
  airplane can withstand extreme forces.

This video shows (also this one) how much force a wing can take before breaking.

OP asked about tests for lightning effects. Lightning commonly strikes the nose, wingtips, engine cowlings, and tip of the vertical tail. Hence, wings are not the only parts of an airplane which needs to be protected against lightning.

To avoid reinventing the wheel, please see the following questions:

How is an on ground lightning strike test conducted?
What happens when an airplane gets struck by lightning?


Can I convert an FAA medical certificate to a Canadian one without visiting an AME?

You cannot convert an FAA medical certificate directly into a Transport Canada medical certificate. However, you can obtain the Transport Canada medical certificate on the basis of the original or certified copies of FAA medical examination reports by submitting them directly to the Civil Aviation Medicine Branch of Transport Canada, Headquarters in Ottawa for processing and assessment. If they are deemed acceptable, the certificate would be issued in Canada without having to start the process with a Canadian AME. For more information, see Transport Canada Advisory Circular (AC) No. 401-001, "Application Guidelines for Aeroplane FAA to TCCA Licence Conversion Agreement".


What is the 0-60mph time of an aircraft carrier catapult?

According to Wikipedia https://en.wikipedia.org/wiki/Aircraft_catapult an American carrier type Kitty Hawk has a catapult capable of accelerating a mass of 35000 kg to 139 knots (71,51 m/s), and the system's stroke is 76 m.
From the terminal speed and the stroke, a simple calculation gives a mean acceleration of 33,64 m/s/s. Hence, and assuming the acceleration constant along the stroke, the time needed to reach 60 mph = 26,81 m/s is
t=v/a => t=26,81/33.64 => t=0,796 seconds...


Is it possible to get permission to fly in the DCA “no drone” area?

Yes. This page comes up on a quick Google search.

Flying an unmanned aircraft within the 15-mile radius inner ring is prohibited without specific FAA authorization.

Experienced Part 107 and public aircraft operators with justification can file your request through the on-line Access Program (AAP) https://waivers.faa.gov


"Gross" and "net" planned runway length for the Haifa airport

Gross and net are not aviation terms for runways. Many runways have extra space on either end to be used as stopways, giving extra stopping distance in case of an overrun.

I'm going to hazard a guess and say that the gross length is the total paved area of the runway and the net length is between the thresholds that is usable for takeoffs and landings.


They use differential breaking. The elevons are split, and can open up both above and below the wing to increase drag on one side, yawing the plane.


Why is extreme cold weather a challenge at airports, since jets operate at extreme cold conditions in flight?

The extreme cold is not an issue so much as the weather that typically accompanies it and the fact that planes are not always designed to be started in extreme cold with out some assistance even if they can run in it. For example so long as the weather is good and the aircraft are equipped, there are plenty of airports in Antarctica

When extreme cold is accompanied by precipitation you can get ice build up on the runway which is quite dangerous. Most airports that are in an area of regular cold weather are equipped in some way to handle this.

Extreme cold temperature that comes with/because of frontal movement may also come with very high winds that can exceed aircraft limits. But high winds can come with warm weather as well so this is not exclusive to the cold.

For piston engines you have an issue of thick oil. When the temperature drops the oil thickens and it becomes hard to start the engine as well as running the risk of engine damage. Piston engines in commercial operations are much less common than they once were so this is less of an issue. However the general aviation fleet is still pretty effected by this issue.

Jet engines do have cold start procedures just like piston engines, there is a good discussion on that here. You can see a neat video of an A320 starting up in -28C conditions here so cold weather starts are not a huge issue.

Most airports have some form of ground crew that operate in the elements. Crew like baggage handlers, aircraft marshaller, and even mechanics may work out on the ramp to get an aircraft loaded and ready to go. This is one instance where sheer cold can be a factor although weather can also make working conditions very tough, even if proper protective gear is available.


Are there any airliner crashes that can be definitively attributed to Mach tuck?

I've never heard of one, but note that the pitch down effect of Mach tuck starts  below Mcrit, and below Mmo for that matter, and airliner trim systems have a "Mach Trim" function to drive the stab to counteract it.

Fortunately, in the speed range of a commercial airliner, the amount of tuck is modest and it's not really a controlability issue, just an increase in trim speed.  Flying manually without Mach Trim, it would just require a manual trim input to keep the nose from dropping.  If the autopilot was on, it would take care of the trim change on its own.

So I would say that an airliner would never encounter a mach tuck condition that could cause loss of control unless it was way above Mmo in the first place, which means it was already out of control for some other reason.


Is it true that the pilot and co-pilot are required to eat different meals?

It is a company specific rule found in the Flight Operations Manual so is airline specific.  There is usually a statement that goes along with it which also says to avoid foods with a higher than typical rate of food poisoning, such as raw fish before and during the Flight.  In the US, the FOM is submitted to, and accepted by the FAA so the procedures become required.


Is jet fuel typically injected before or after the flame holder in an afterburner?

This is what I could find on the matter in my university textbook.

  The fuel spray bar is typically composed of
  one or more rings with distinct fuel injection heads circumferentially distributed around
  the ring. The V-shaped flame holder ring(s) create a fuel–air mixture recirculation region
  in its turbulent wake, which allows for a stable flame front to be established.

Although it does not mention fuel heating explicitly, I would agree with your assumption -- as the mixing of the hot gas and the (colder) fuel of course also evens out temperature differences between the two.

Source: Farokhi (2014), Aircraft Propulsion (p. 199)


When to climb and when to descend when faced with icing?

While there may be guidelines as to whether to climb or descend when you're icing at your current level, individual pilots that I have known varied widely in the specifics of what they would do depending on their experience, their comfort level in icing, the route they were flying, and their experience with that route in bad weather. My take follows.

First, @acpilot's comment gives the general guidelines and is worthy of being an answer, I believe, except that I would be happy with just a couple of degrees above freezing rather than 5°C.

I put in a few hundred hours in Turbo 210s back in the 1970s. The ones I flew had boots on the wings and hot props. As such they were a reasonable machine to handle the icing of the U.S. Pacific Northwest. The things I wanted to know to decide whether to climb or descend included:

what's the rate of the icing
what kind of ice is it, rime ice (the most prevalent) or clear ice (basically freezing rain)
what kind of cloud am I in, is there convective activity
how high can I expect the icing to persist, are there pireps giving the tops
how much distance will I have to fly to either be in the clear, between layers, or get to where the minimum safe altitude is above freezing
what's my climb capability, in other words how heavy am I and how much has my climb capability already been degraded

Even with knowing those things, it's still as much a subjective decision as an objective decision, at least it was for me.

The distinction between rime ice and clear ice is particularly important. Clear ice (basically freezing rain) is the more dangerous, accumulating faster than rime typically and heavier. It always (almost) means there's air greater than 0°C above you, which would favor climbing.

Rime ice is minute drops of super-cooled water (water less than 0°C) that changes to ice when it hits the aircraft. More often than not, rime ice means there's no air above greater than 0°C, unless you happen to be in an inversion. Climbing out of rime icing usually means you've got to get high enough to get clear of clouds or get the temp down to -15°C or so.

Fortunately most icing is rime ice rather than clear ice. The rime usually collects slowly, although it can collect quickly in convective conditions. I once iced up with rime ice in a Cessna 340 in less than a minute to the point that I was having trouble maintaining altitude.

(skyvector)

Much of my T210 flying in bad weather was between Eugene, Oregon and airports in California's central valley (shown above left to right). V23 was the airway from the Eugene VOR to the Medford VOR to the Fort Jones VOR to the Red Bluff VOR and then south into the central valley. The airports were typically above freezing, but the MEAs were in the ice if the weather was bad, and you were guaranteed to get at least some rime ice. The MEA from Medford to Red Bluff was 10,000, and that was where the worst ice was usually encountered, but the MSA dropped rapidly south of Fort Jones.

If southbound from Eugene and approaching Medford you had already picked up more ice than you liked, and the Medford airport was above freezing, you could shoot an approach there and drop the ice before proceeding south of the Siskiyou Mountains. Once the OAT gets above freezing, the ice melts really fast, typically on the order of a minute or less. The windshield clears first. Importantly, for rime ice, the rough surface of the ice smooths quickly, permitting better airflow.

If it appeared icing along V23 was not going to be flyable, we would file over to the coast and go down over the beach so to speak with the attendant low MEAs and more airports, all usually well above freezing.

My point is, a lot of things enter into whether you should climb, descend, go another route, or get on a jet.

A couple of good (IMHO) links (pdf's) to icing information are:

Aircraft icing, noaa.gov
Aircraft icing, aopa.org


Why does wing bending cause wingtip twisting?

I would say it's because the twist in question relates to Mean Aerodynamic Chord, which is always aligned with the longitudinal axis and airflow, and diverges from the airfoil chord line when the wing is swept (it becomes a truncated slice you might say).

Assume a wing that can bend along its spar axis but that has perfect torsional stiffness for our purposes.  When a straight wing is bent up, the incidence of the MAC at any given point, being perpendicular to the bending axis and the same as the airfoil chord, remains the same from root to tip.

On a swept wing that is bent up, the airfoil chord line, perpendicular to the span wise center line (B), also remains untwisted along its bending axis (in our perfectly torsionally stiff wing), but the MAC, which is now different from the airfoil chord line because it's aligned with the longitudinal axis (A), sees a geometric reduction in incidence in proportion to the bend.


Why is cloud base estimation taught in Fahrenheit?

It's not, the source you are looking at is taught in Fahrenheit.

Jeppesen being an American company, I would assume that their teaching material uses units of measurement common in America.
There are many places which have the same formula in Celsius such as the wikipedia entry on Cloud Base among others.
I suspect that pretty much everybody looking to calculate this would understand the difference between Fahrenheit and Celsius and adjust accordingly. That's not to say that errors are impossible, but errors are always possible when calculating anything.


Why is the generator turned back off for starting the second engine on a King Air?

Yes it loads up the battery, but the battery is sized to do this. The generator is not necessarily sized to do this, especially on the ground, so this procedure gets you to take the generator out of the system for each start.

On an Alternator, like on your car, there is a phenomenon known as 'forward-stripping', which is where there is such a demand for current out of the generator that it overloads the rectifiers (that convert the created AC electricity into DC for output). So here, during/after the engine start, there may be a large charge request by the battery which might forward-strip the gen's rectifiers.


Airplane gently rocking its wings during whole flight

I can give you two theories.  One is it's a very very mild case of "overcontrolling" of the autopilot roll servo as it chases a perfectly wings level condition and continuously applies a teeny bit too much left, ooops, then a teeny bit too much right, oops, and back and forth.

The aileron control circuit is cables running to hydraulics at the ailerons, with a spring loaded roller in a curvy V shaped cam device that centers each side of the aileron cable circuit. The breakout force to move the control circuit out of neutral (forcing the roller from the center V of the cam) is fairly high and this can actually be a problem for pilots hand flying at higher speeds where the ailerons are quite snappy - applying enough force to break out the circuit and move the wheel left gives too much, and back the other way... too much... and back and forth you go.  It can be a pain.

The autopilot servo is basically a little electric winch connected into the aileron cable circuit, doing the same thing the pilot does. It could be that something in the electronic control loop, or mechanically within the servo, can cause this back and forth oscillation on some airplanes, sometimes.  It may be related to wear and backlash within the autopilot servo.

The other theory is it's more or less something similar, but in the yaw mode with the yaw damper not able to fully dampen out a dutch roll mode because the amplitude was within the yaw damper's sensitivity band. Dutch roll is rolling due to yaw, which in swept wing jets is very strong, such that it can set up continuous self energizing oscillation.  It could also be related to wear and backlash in the yaw damper actuator, which is a pair of electric linear actuators (little electric screw jacks), in the push rods going to the rudder hydraulics.

If you saw the wing tip just going straight up and down, it's mostly likely the first theory.  If you could see the winglet moving in a little circle (indicating rolling and yawing), it's more likely the second theory.

I can really only theorize because the issue was never fully explored on the RJ program as this phenomenon was random, very minor and not dangerous, and was never complained about by operators because only someone sitting near the wings that can look straight out at the winglet ever notices it.  It was never bad enough to get anyone sick for example, at least on the RJ fleet.


Can the Landing gear be lowered when system A hydraulic pressure is lost in Boeing 737?

Normal gear extension is by the A system; alternate gear extension is by manually releasing the up-locks, allowing the gear to free-fall into place. There is no provision for any other alternate gear extension beyond that, such as via the B or Standby hydraulic systems, electrics, pneumatics, or otherwise.


How do I find out the fuel consumption of the PT6A for a lightly loaded aircraft?

You need to obtain the specific fuel consumption (SFC) for the particular dash number of PT6 (scroll down to the bottom for the chart with the data). For example, the -67A turboshaft is down around .47 lb/hp/hr, close to piston engine territory, but most are between .5 and .6 lb/hp/hr.
So pick the dash number of engine applicable to the airplane you want to compare, note its SFC, and now all you have to do is calculate the HP required of a given aircraft at a given weight to cruise at a given speed, and that you should be able to interpolate from the airplane AFM/Operating Manual's cruise performance and power required chart data, working out the HP required to cruise at Speed X, and Weight Y.
Once you work out the required HP, and you know that engine's SFC, you're there.


Mi-2 was almost entirely produced in Poland, on PZL-Świdnik. That production officially ended in 1992.

Since then, a few new modifications/prototypes may have been produced, according to various sources, but they were almost certainly retrofits of the existing airframes.

In 2012, it was announced that production of a modernised Mi-2A would start in China, but I could not find any confirmation that it actually happened. Frankly, I see no good reason why it would. Generally, any announcement of plans from Russia in the last 30 years should be treated with extreme caution and not considered valid without confirmation.


FX stands for Franz Xaver, Professor Wortmann's given names.

The next two digits stand for the year this airfoil has been designed. Add '19' in front and you have the full year.

Then may follow one or two optional letters which specify a dedicated use, but they can be missing for general purpose airfoils. For example, the 'L' in FX 71-L-150/30 stands for "Leitwerk" which in German is the name for the combination of the horizontal and vertical tail surfaces.

The next three digits denote the relative thickness times one thousand. So the "150" in FX 71-L-150/30 tells us that this airfoil is 15% thick.

The last digits are again optional and denote the relative flap chord in cases of control surfaces, this times in percent. The FX 71-L-150/30 is optimized for a 30% chord control surface.

Reference: Stuttgarter Profilkatalog ISBN 3-528-08464-2, 1981.


Why do we have to do an alternate brake check during preliminary cockpit preparation?

On the old system the switching between the normal braking using the green circuit  to the alternate braking using the yellow circuit is done by an automatic switching valve pressure dependant (Automatic selector).The alternate system being very little used, it happened the valve did not switch from green to yellow when loosing the green circuit

please refer to the old system here below

http://www.a320dp.com/A320_DP/landing-gear/images/braking-schematic-d.jpg

On the new system the alternate brake is activated by a specific computer(ABCU) decision and is automatically tested by the computer at power up as soon as the hydraulic pressures are available, please refer here below to the new circuit

https://m.facebook.com/A320Theory/posts/normal-brakingnormal-braking-is-obtained-when-the-green-hydraulic-pressure-is-av/790898894383508/

Hope this has been useful and explains why it was very important to do the testing on the old system


How to measure the Aircraft cabin air quality?

A few years ago, the Australian Civil Aviation Safety Authority convened an  Expert Panel on Aircraft Air Quality.

From page 138 of the report they discuss the available monitoring devices. From my brief readthrough, there were no real monitoring devices for this purpose at the time (2009) however research was being conducted.


No, you can’t get an ATPL online.
Your first step would be converting your FAA PPL to an EASA PPL. You will then need to add Instrument, Commercial Single-Engine, Commercial Multi-Engine, Multi-Crew Commercial and frozen ATP ratings. All of that will require ground instruction, flight instruction, written tests and checkrides. Then you will need to build time until 1500 hours to get your ATPL unfrozen. There are some differences in process and terminology between FAA and EASA, of course, but the end result will require roughly the same skills and experience because both systems have to meet the same ICAO standards.
COVID-19 has not changed the requirements to get a license, just the feasibility of actually meeting them. Many flight schools are closed, those that are open may not be accepting foreign students, and you may not be able to get there at all due to border restrictions.


What modifications are required for automotive fuel STC?

For most engines it would require a hardened valve seat.

The reason why lead is required for aviation engines is that the value seats are not hardened and the lead in the gas helps prevent "micro-welding" that can occur on a valve seat.  Micro-welding happens when the valves are hot and the the valve is pressed against the valve seat; the valve will start to weld to the seat before it is torn away when the valve opens.  This causes a jagged edge at the valve seat which causes a bad valve seal.  Old engines relied on the lead in the gas to prevent this. When the automotive industry switched to unleaded gas, the engine makers had to use valve seats out of hardened materials that were more resistant against heat.

The lead is also a great octane booster although many airplane engines can use octanes lower than 100.  In automotive fuels today ethanol is used to boost octane and that has its own host of problems since ethanol is very corrosive.  So before you switch to automotive fuels you need to make sure you engine and fuel system can handle the ethanol.

For a discussion of micro welding among mechanics check this link out.

EDIT:  After doing more research I discovered that Lycoming has always used hardened valve seats so the modifications on a Lycoming engine would be very minimal.  However, most Continental engines do not have hardened seats and major modifications would be required.

Lycoming has a good article on the use of unleaded fuel in the their engines here.  Notice however that Lycoming states that ethanol CANNOT be used in their engines.  In the US at least it is getting very hard to find fuel that does not contain ethanol.


If the EPU (Emergency Power Unit) on a modern fighter jet fails, will the aircraft drop out of the sky?

How Are Modern Fighter Aircraft Controlled?

The F16 was the first US military aircraft to be designed around the revolutionary fly-by-wire concept.  This meant there were no direct mechanical linkages between the cockpit and major control surfaces, and that all pilot input was electronically carried to the hydraulic system via wire.  However, since the F16 burst into the scene, there have been further major advancements in aircraft systems design.  Late Gen 4 aircraft, such as the F/A 18 Super Hornet, are designed around a concept now called control-by-wire.  Control-by-wire aircraft not only have removed mechanical linkages to the hydraulic system, but now the pilot is only a voting member.  This means that all input is received by a computer bank that then computes what it thinks the pilot is intending to do, and then autonomously operates the control surfaces to achieve the effect.  This means that Gen 4 aircraft rely heavily on both computer integrity (and there are plenty of self-healing backups), and the power required to run those systems.

Power Failure

If there was a catastrophic total electrical failure and the only remaining power supply was the battery, the only option is for the pilot to restart a generator.  In the event that the engines were operating and all power generation was destroyed, the aircraft would only be flyable for the duration which the battery could provide power to the aircraft--that's a very limited duration.

Possible other scenarios could include a dual-engine failure. In this instance, the aircraft may be able to fly fast enough to generate enough airflow down the turbine to turn the generator and perform an airstart, but this would only be useful in a dual engine failure, and only if there was enough altitude and airspeed to trade to make it a realistic option.  Otherwise, the battery would probably be used to power the APU, and attempt a relight.  Again, if both engines relit and the generators (including the APU) failed to produce power, then the aircraft would not be flyable.

But what about the RAT?

Although currently in limited use on some trainer aircraft like the T-45, modern fighter aircraft do not use a RAT.

So what usually happens in a total electrical failure?

If the aircrew cannot get a generator back online then they eject.


How can I find out how much a passenger window of a Boeing 737 costs?

This page has declared values for part shipments, including one with the 140N2139-4, which is the assembly containing the seal, mid pane, and outer pane for the 737 NG. The declared value is 24,562 INR which is currently about 375 USD. A shipment of 20 also listed has a lower unit price.

For searching purposes GKN has part numbers in their catalog. You typically have to ask for a quote from suppliers.


Is there a rule of thumb for spacing between jet engines?

Placing the engines farther out is mainly done for bending relief in the wing. Given that the Stratolaunch needs to keep its center wing clear of fuselages and engine nacelles, the engines are out enough already. Moving them farther out would create more thrust asymmetry once one engine fails.

Airliners with a central fuselage are different. We have an answer here discussing optimum engine placement. Why they should not be combined in one nacelle is explained here.


Which one is considered the departure time of a commercial flight?

The scheduled time is the EOBT. Flights that depart within 15 minutes of it are considered on-time.
Standard taxi times for each airport are included in the scheduled flight time.


Why was this commercial plane highly delayed mid-flight?

If you look at the details, you’ll see the aircraft left the gate at 9:37, but only took off at 10:47.

They probably received notice of the issue in MUC pointed out by Machavity while taxiing to the runway (and then asked to park somewhere waiting for the airport to be ready for them). No sense returning to the gate for a delay like this which is expected to be relatively short.

A possible alternative (though probably not here) is they they had an issue right after gate departure which triggered a maintenance request. It happened to me once on some regional airliner which had an issue just when they spooled up the engines (or just after a few meters, don’t remember). Immediately powered down and had some part of the engine changed (or maybe just a filter or something similar) while we were waiting, took about an hour or so.


How can an Airbus Beluga fly only with two engines and use short runways?

This airplane is based on the Airbus A300-600. The maximum take-off weight of the aircraft is 155 tonne as published in the wikipedia. In addition, the the manufacturer has published the Aircraft Characteristics for the base aircraft.

If we assume that the aircraft low-aerodynamic aerodynamic characteristics has not been changed for the take-off phase (which the runway length depends highly on the aircraft lift and the engine power, and considering that the wing which contributes to the lift has not been changed and engines remained the same), then we can estimate the runway length for take-off and landing from that "Aircraft Characteristics" documents.

For the aicraft at its max take-off weight, in Sea/level, the required take-off runway length is predicted as 1800 m:

For the landing, the maximum landing weight is 140 tonne. Based on the document, the landing field length is 1554 m.

It should be mentioned that these aircraft are used for transportation of another aircraft sub-assemglies, which are large and light structures, such as wing, fuselage plugs, and tails. For this reason, the take-off and landing weight will be far lower from the above mentioned values, which permits them to operate on shorter runways.


How does wing bending relief of an a340 compared to an a330 allow it to carry 30t more fuel in a center section of nearly identical wings?

Short answer: they lied, it's 12, not 30 tonnes extra carrying capacity on the A340 due to being a quad.

How does an wing-mounted engine provide extra payload?

The weight (force) of the engine times the distance to the wing root is a torque (force * distance) that bends the wing down. The farther out the engine, the bigger this torque.

This downward torque reduces the upward torque (from the lift) experienced by the wing. You can think of it as the lift force from the spanwise aerodynamic center $y_{MAC}$ to the wing root -- more on that in a bit. So, if the plane is wing-limited (structurally), any extra bending relief will allow more weight to be lifted.

It was also why the 707 had better payload compared to the Vickers VC10 (its 4 engines are tail-mounted). The wings had to be built stronger (heavier), which ate into the payload (vc10.net).

  That is one of the reasons that especially the Standard VC10 is more expensive to operate than a 707, its structure is slightly heavier for the same number of passengers (25,7% of MTOW as opposed to 24,6% for the 707).

Does it really account for 30 tonnes?

No. It turns out Airbus was lying. But it does account for some.

The lying part first. According to John Leahy -- an Airbus exec of 33 years -- from a Jan 2018 interview on leehamnews.com (good thing you asked in 2018):

  The 330 was intentionally being held down in takeoff weight and performance because they didn’t want it to overlap the 340.

So, how much was engines and how much was being held back?

The A330 (and A340) like many jet-liners gain MTOW as they fly more. Small steps at first after design validations, then big steps after modifications. So in order to have a fair comparison, we need to go back in time.

The quoted reference is from 1991, but the A330 entry-into-service (EIS) MTOW was not 30 tonnes below the A340. That figure was based on the 1986 MTOWs of 204 and 232 tonnes for the A330 and A340 respectively (flightglobal.com).

(Graph: Airbus) A330-300 MTOW increase over the years. Note that the neo starts at where the ceo left -- at 242 with further development to reach 251 tonnes as announced in March 2018 (leehamnews.com).

As you see, the A330's EIS MTOW was 212 tonnes (a 20-tonne gap, not 30). Without major modifications it reached 217 (a 15-tonne gap, not 30).

Are the 15 tonnes due to the outboard engines?

Yes. First, back to the $y_{MAC}$. See: Where is the lateral position of the aerodynamic center?

Calculating it for the A330 based on its available plan view and ignoring the Yehudi gave me an 8.9 m figure (from wing root). Taking into account the complex shape would, I believe, move it farther inboard, giving the engines an even bigger edge -- so we are okay there.

The engine stations are at 6.4 and 16.5 m from the wing root. And the engines weigh 6.16 (Trent 700 on the A330) and 3.99 (CFM56-5C on the A340) tonnes.

With those figures, the A330 engines provide a downward torque (bending relief) of 39.4g kNm (per side). The more spread out A340 engines (but also each ~2 tonnes lighter) provide 91.4g kNm (per side).

By taking into account the 8.9 m $y_{MAC}$ and the higher 217-tonne MTOW, my results are:

11.67 tonnes of the 15-tonne gap are indeed due to being a twin and not a quad. The remaining 3.33 tonnes are likely due to my lenient $y_{MAC}$ -- moving it more inboard gives the engines more credit.

If you are wondering about the original 204-tonne figure, then they held back 16.3 tonnes (72.6g kNm per side). So the original statement should have been an approximately 12 tonne extra carrying capacity, not 28 (or 30) -- but they didn't want to hurt the A340 sales.

This was a lot of fun, and it's nice to see how the A330 EIS final gain (13 tonnes from 204) is close to my estimate.

Original 3-view drawings:
- https://commons.wikimedia.org/wiki/File:A330FAMILYv1.1.png
- https://commons.wikimedia.org/wiki/File:A340FAMILYv1.1.png


Do fighter jets use elevators as ailerons?

Yes.  The airplane’s flight control computer can command a roll using all primary and secondary control surfaces, including differential actuation of the tailplane as Blue Angels #6 demonstrates during a preflight check.


Can anyone identify the plane in this old photo?

It's probably a Stinson Junior. Built in the late 1920s and early 1930s.


Why is the flight duration of the same flight different in different months?

Jet stream is a stream of air flowing around the Earth from West to East at high altitude. With wind speed averaging more than 100+ km/h, it has a tremendous effect on a plane's ground speed.

The pattern, strength and location of the stream is constantly changing. For example, during the (Northern Hemisphere) winter the stream generally strengthens, and during the summer it generally weakens. With modern technology such as weather satellites and data fusion from thousands of weather stations around the world, the stream is fairly predictable.

The effect is more pronounced on long flights because these flights stay in high altitude much longer.


Is it possible that meteor could strike a commercial airliner?

Yes, it is possible, however unlikely!

The final report into the downing of MH17 investigated the possibility that the aeroplane was hit by "meteor or space debris"

  In section 3.5 a number of scenarios are analysed that relate to the possible source or sources of the object that perforated the aeroplane. These include meteor and space debris.

It was concluded that

  The chance of a meteor striking an aeroplane was calculated as being one event in 59,000 to 77,000 years. This value was obtained from the University of Pittsburgh's Department of Geology and Planetary Science and was originally part of the NTSB's investigation into the 1996 accident to TWA flight 800 (see NTSB Report AAR-00/03, dated 23 August 2000)


What operational aspects of Alphabet's Wing drone delivery service will be the same as that of an airline?

Under FAR Part 117, only certified "air carriers" are allowed to sell "aviation services" to the general public. Certification means that the FAA has determined the proposed operations, whatever they may be, will be reasonably safe.

FAR Part 121 covers most scheduled air carriers, which are commonly called "airlines". These are the only air carriers that the media knows about, so it's understandable that they'd conflate the two.

FAR Part 135 covers unscheduled and very small scheduled air carriers. I suspect this is where Google Wing would fall, but I haven't seen anything definitive so far.


On what principle(s) do aircraft smoke detectors work?

The typical aircraft smoke detector works using optical sensing which exploits the Tyndall light scattering effect.

From Boeing:

(Source)

An LED illuminates a sample of air while a light sensor, which is not in line-of-sight with the LED, looks at the same sample of air. If enough light is scattered by smoke particles then the detector will signal an alarm.


Why do jet engines sometimes spit out flames after ingesting birds?

As RedGrittyBrick has commented, what happened in that video is a compressor surge. This is not really an engine fire, but a temporary backfire. To understand what is happening, look at this diagram of a turbine engine:

The air is compressed in the front of the engine, fuel is injected and ignited, and then everything flows out the turbine section and the exhaust nozzle. The only thing supporting the compression at the front of the engine is the rotation of the compressor blades. There are many different things that could cause the compression to fail. In the event of a bird strike, these blades can be damaged.

When that happens, there is highly compressed air in the combustion section, and there is no longer enough compression to prevent it from exiting the front of the engine. This causes the air to exit both the front and rear of the engine. The disruption in air flow happens too quickly for the engine control systems to react. This means the engine is still pumping enough fuel to run the engine at normal thrust, but there is no longer enough air flow to burn all that fuel in the combustion section. The result is that the fuel burns through the turbine and exhaust section of the engine, and behind the engine.

Once this compressed air has exited the engine, it will generally recover. The engine is not on fire, so once the excess fuel burns away, the flames are no longer visible. However, if the problem is still present (and damage from a bird strike would not go away), then the engine surges over and over until it is shut down or set to a lower, more stable power setting.

So this is not so much a safety feature as physics taking over, and there is no real fire of immediate danger to the airplane. The engine system will automatically shut down the engine if it senses there is anything potentially very dangerous or that completely prevents the engine from running. While compressor surges can eventually damage the engine, it's not really a catastrophic event, and it is up to the pilots to assess the situation and shut the engine down if necessary. Reducing power to idle may sometimes be sufficient to stop the surges.

During a compressor surge, the flames are confined within the engine. There should be nothing to burn here besides fuel, so cutting off fuel will stop the fire. Actual engine fires are generally caused by flammable fluids leaking into hot areas around the engine, or the hot engine gases escaping from the air flow sections into surrounding systems. There are detection systems to alert the pilots of this situation, and the engine area is designed to contain a fire until the pilots can use the fire extinguishing systems to put such a fire out or at least get the plane back on the ground.


What are the names of the forces acting upon the side of a vessel?

As we engineers are extremely boring people, and given the fact that a name seems not to be available, we generally refer to them simply as "side forces".

Or, at least, I never encountered a different term on any of the textbooks that I have read.