Is the 737's autopilot part of the FMS or is it a separate entity? I was watching a tutorial about the FMS and the autopilot in the 737, and I am consfused. I come from a Cessna background, where there is no FMS, there is only the AP (autopilot).

So, is the AP a separate entity being fed info by the FMS and easily overridden by the values you input into the AP (heading, V/S, altitude)? Or is the AP under the FMS, and the FMS has full authority over the AP?

In Boeing terminology, the FMS, Flight Management System, is comprised of:

Flight Management Computer System (FMCS, which is essentially two FMC's, at least on the 737... other jets may have one FMC, or three)
Autopilot
AFDS (Autopilot/Flight Director System - includes the Mode Control Panel used to select autopilot modes, heading, speed, altitude, etc)
Autothrottle
GPS(s)
Inertial Reference Systems (IRS)
Two (in the 737, three in some other jets) CDU's, which are the "Control and Display Units" with a small screen display and alphanumeric keyboards, used by pilots to view, enter, and edit things such as flight routes & performance data. Many such units are now "Multifunction CDU's", or MCDU's, adding ACARS and/or CPDLC capability.

So in their terminology, the FMS is very broad and includes plenty of things, including the autopilot. The FMC, on the other hand, is the computer that stores your route, calculates the aircraft's position (based on inputs from the GPS receiver(s) + the IRS + possibly other sensors), and does all the navigation tasks. One can couple the autopilot to the FMC guidance - select LNAV and/or VNAV - or not.

It's not uncommon to hear or read "FMC" and "FMS" used interchangably, but they are in fact two separate things. The FMS (the system) includes the FMC (the computer) and the autopilot; the autopilot can be coupled to the FMC, but it is always a component of the FMS.

Sometimes you'll see a CDU referred to as "the FMC (or FMS)" since the CDU is the pilot's main interface with the FMC. But they are separate things; you can have a CDU failure with all FMC's still working, and vice versa.

Clear as mud?


In what cases does it make sense to buy a plane before you begin pilot training? I'm halfway through a 10-year plan to pay for pilot training and buy my own plane (or a share of one).  When I was introduced to flying by a friend, he said if he had the chance to do it over again, he would have saved up and bought a plane before he started instruction.

The benefits he mentioned:

Learn in the plane you'll be flying.
Avoid "throwing away" rent money.

What I've seen in most cases, though, is that most people get their license before getting a plane.

Thus my question: when does it make sense to buy a plane before training for your PPL?

I will mention some considerations that were not mentioned above. First of all, it does make sense to buy a plane for training, and it can save you a lot of money on rent but you need to be aware of what you are doing. The positive side is that airplanes do not depreciate as fast as most assets of their kind (it is not unheard of being able to sell an airplane for practically the same amount as you bought it several years ago). However, consider that:

Usually an airplane you want to train in (something sturdy and easy to control, like a C-150) is not an airplane you would like to fly most of the time (traveling in a 150 is not a lot of fun, now a twin Comanche is a different story...).
Insurance costs for a student pilot (even with various restrictions) can nearly negate the advantage of not having to rent.

So, if you would like to buy an airplane to mostly train (and have some fun occasionally) and then sell and buy a 'travel' (or aerobatic) airplane, it can save you money. It is better to get your private first, however, so you can concentrate on initial training (which is a handful) without worrying about the 'pleasures' of plane ownership.


Why aren't planes loaded from both ends? Related to this question about plane loading efficiency, if planes have multiple entrances (generally 6 or more) why are planes not loaded from both ends? I think I've seen it happen sometimes, but the majority of my flights are on 737s and are just loaded from the front entrance.

The aviation industry is already running at near-peak efficiency, performing crucial tasks simultaneously to ensure quick turn-around.  Trying to speed up the boarding process by allowing entrance from both ends would be doable with a large amount of changes to the existing process, in both operations and infrastructure.  However, the result would be horrendous and time- and resource-consuming at worst and comical at best.

Jetways need to be able to reach all points of ingress/egress, where currently, they only reach the forward doors.  Seeing as aircraft nose-in at the gate, to reach the aft doors would require a jetway that goes around the wing (above the wing is even less practical from a design/physics standpoint), effectively creating an even smaller limit to the size of the aircraft that can fit at the terminal since there is now a jetway that needs to reach the rear doors.  As you can see, the space between aircraft is already tight:  Or, you use a simple stairway at the aft door and allow passengers on the tarmac, an already busy place during aircraft turn-around, and we don't need them touching anything en route.  I highly recommend against the latter.

In many instances, during boarding, the rear and/or opposite-side doors are already in use for loading/unloading food and drinks and taking out the trash.  So you'd have to redesign that process.

Humans are generally stupid in large groups.  Southwest notwithstanding, your typical airline assigns seats.  Imagine a passenger entering the rear door with seat 1A.  It doesn't have to be that extreme.  It can be any seat assignment more forward than another passenger coming the opposite direction down the aisle, which has the effect of halting both directions of travel.  Passengers already sit in the wrong seats, or travel with babies, or carry too much luggage (or stow it selfishly).

There have been many studies on efficient boarding methods.  The most efficient algorithm seems to be the Steffen Method, but this method requires someone with an inordinate attention to detail (and willing passengers) to line people up in a specific order.  Taking into account crew resources, the most efficient method is by window-middle-aisle groups, then by random order (i.e. "single-zone"), with typical "zone boarding" least efficient.
EDIT:
There are scenarios where boarding from both ends makes sense and is feasible, e.g. smaller planes with fewer passengers.  On larger aircraft, the problem compounds itself as the number of passengers grows, each "collision" incident affecting that many more people in the queue.  Minimizing collisions requires airlines to throw more resources at the problem, namely personnel to direct traffic.  Ask any CFO - more often than not, human resources is the most significant slice of the operating budget.
In any case, engineering a solution should not entail best-case scenarios; it should be designed for typical-case at best, and more commonly for worst-case.  The human factor is one that cannot be overlooked.  There is no such thing as an idiot-proof system.


Are transponder codes 7701 - 7777 ever used? I understand that blocks of transponder codes are assigned to different area controls. I am curious if the block 7701 to 7777 is in use anywhere? Maybe the emergency code 7700 needs some extra protection?

Yes these codes are used. Only 7700 is used to denote emergencies, and usually only if you aren't in contact with ATC, or can't get their attention(frequency is packed). Codes in this range are allocated according to the National Beacon Assignment Plan in the US. There are other codes that are assigned for various issues, 7777 as mentioned in the comments is assigned, and I've assigned others in that range before, same with the 7600 and 7500 ranges.

If you're already in contact with ATC, and they have you tagged, it is very easy to mark you as an emergency and have it light up on everyone in the facility's scope.


Does terminal control have final say on which runways the towers should use? In areas where there are many airports close to each other under one Class B airspace...

Do nearby airport towers coordinate together with runways to use as to reduce the workload on the terminal control?
Does the terminal control tell them which runways to use?
Is it free-for-all for the towers, and the terminal control just deals with it?

Note that if they all choose the same direction more or less, all takeoffs and landings will be parallel, but airport layout dependent, a non-wind facing runway might be favorable for a certain airport.

No, that's handled by the towered airport itself.  Now approach control is going to know what runways are currently in use at that airport and will direct incoming aircraft to approaches for the runways in use.

Ultimately its up to the pilot in command to use the runway ATC directs or request another runway.


What's the difference between "Nonstop Commercial Air Tour" and "Aerial Photography"? I work for an FBO that has a LOA for Nonstop Commercial Air Tours, which are limited to a 25 statute mile radius of the airport. I was contacted by a man who is a semi-professional photographer who would like to be taken on a flight for the purpose of getting some nice pictures of mountains.

He says that because he is doing aerial photography that he should not be restricted to the 25sm radius per the exemption in 119.1(4)(iii). However, if this is the case, then all of our scenic flights conducted under the LOA would also be exempt, because the passengers always take pictures, and there would be no purpose in having the LOA.

So, what is the line between a Nonstop Commercial Air Tour conducted under a letter of authorization, and aerial photography?

Short answer: as far as I can tell, an air tour implies photography, but photography doesn't imply an air tour. The regulations define various criteria for determining if a flight is an air tour, but there's no 100% clear definition.

First, the regulatory definition of "commercial air tour" is in 14 CFR 110.2:

  Commercial air tour means a flight conducted for compensation or hire in an airplane or helicopter where a purpose of the flight is
  sightseeing. The FAA may consider the following factors in determining
  whether a flight is a commercial air tour: [...]

It's worth reading the "following factors", by the way.

Second, there's no formal definition of "aerial photography". See the Sapp (2007) interpretation (emphasis in the original):

  In a 1989 interpretation, the FAA discussed the meaning of "aerial
  photography" [...]
  the phrase was not defined in the regulations [...]
  "aerial photography" connotes a condition where taking pictures or
  filming is done from the air

Third, the Ragland (2015) interpretation specifically mentions photography as one purpose of an air tour (emphasis mine):

  Specifically, you asked whether §119.l(e)(4) allows persons to conduct
  commercial air tour operations, for purposes of sightseeing and
  photography, without obtaining either a letter of authorization
  (LOA) in accordance with §91.14 7 or a commercial operating
  certificate in accordance with part 119 of the federal aviation
  regulations.

  You assert that the conclusion in a January 5, 2011
  interpretation issued by our office "appears to reinforce the need for
  Operators to apply for a LOA from their local FSDO to conduct
  'sight-seeing tours' within a 25 statute mile limitation under 14 CPR
  91.147." We agree.

Finally, the same interpretation says you can't operate a commercial air tour under the aerial photography exemption:

  We further note that the exception in §119.1(e)(4) for certain "aerial
  work operations," such as banner towing, aerial photography or survey,
  and powerline or pipeline patrol, does not extend to air tour
  operations in which the primary purpose is sightseeing.

So, putting all that together - and remembering that I'm just SGOTI - it appears that:

Air tours within 25SM require an LOA and are assumed to include photography
"Aerial photography" is a separate activity from "sightseeing"
The FAA seems interested in the "primary purpose" of the flight

In your scenario, it sounds like the photographer is asking for a straightforward aerial photography flight: the primary purpose is to take photographs, not to get a tour of an area. And if the photographer actually makes money from their work, that's a strong indicator that they aren't just "sightseeing". But that's just my opinion.


How to calculate the zero lift drag coefficient for a wing with data from airfoiltools.com? I'm currently trying to write a script in python that I can use to optimalise a flying wing aircraft. I've run into a problem when trying to use data from airfoiltools.com. I've tried to calculate the zero lift drag coefficient using a value for Cd and Cl found on airfoiltools.com, I used the following equation:
Cd = Cd0 + Cdi
Cd0 = Cd - Cdi -> I then substituted the induced drag coefficent:
Cd0 = Cd - Cl**2/(piARe)
The symbols are:
Cd0 = zero lift drag coefficient
Cd = total drag coefficient (from airfoiltools.com)
Cl = Coefficient of lift (from airfoiltools.com)
AR = The aspect ratio of the wing
e = The oswald efficiency factor
The problem is that this equation gives me a negative value for Cd0, which is not possible for obvious reasons.
Please, does anyone see my mistake here? I'm not formally schooled in aerospace engineering so I don't know all the theory behind these equations, thus I may not understand wether I can or cannot use them in this situation.
Thank you in advance and kind regards,
Remco van Woerkom

Induced drag is only produced when real lift is created. In 2D flow, when only the airfoil drag is given, there is no induced drag even for discrete lift coefficients. 2D flow assumes an infinite aspect ratio which results in zero induced drag.
Your zero lift drag coefficient should be the airfoil drag coefficient at the actual lift coefficient at the wing station when the airplane is in flight. Do this for several stations over span since the lift coefficient varies over span. Plus the contributions of fuselage, tail and whatever is added to the configuration, of course.


Are there Instrument-only airports? Are there airports that in general don’t allow VFR traffic and e.g. don’t even have a VFR chart published and just allow IFR traffic?

No.

Think about what you are asking.

Scenario:

You're a captain at the pointy end.  All your instruments have failed.  Maybe let's add in some extra emergency element for good measure.

You need to land at the nearest usable airfield using little more than the good old Mk1 Eyeball.

Your concept of an "IFR only" airfield can shout "IFR only" down the radio all they like until they are blue in the face.  But in line with the rules of the air, the captain has the ultimate authority, if he's got clear VFR, he'll be landing there as he has no other options.

Keeping the spam-can brigade out of the way of busy airfields is not the job of airfield policy, its the job of airspace policy. And that works perfectly well.

Conclusion:

Even if they might be rarely used on a daily basis, having VFR procedures in place is important whether you are a major airfield or some grass strip.

That way, everyone knows what is expected of everyone else.


What phraseology does ATC use with jet fighter pilots? What do they usually say or ask when the fighter pilot wants to take off, when it's in the air, and what is the reply from the fighter pilot?

This ICAO document lays out the guidelines pretty well in short, in most places military aircraft (of any kind) are treated no different than civilian aircraft and are expected to comply with local regulations which include radio procedures. ATC will clear an F-22 for take off no differently than a Cessna 150 (with perhaps different expected climb rates ;) )

Of course most jurisdictions that belong to countries that have some kind of an Air Force will generally coordinate with them for special types of operations and the organization that controls the airspace expects that anyone wanting to conduct special operations will coordinate with them.

This typically happens in controlled areas like an MOA or for safer operations near a base. I fly quite a bit near a large base and often while transitioning through their airspace its not uncommon to get warnings of high speed or low altitude activity. Either way the aircraft is expected to make radio calls and adhere to any regulations or pre cleared operations.


Why are "counterweights" used in aircraft production? From this question, manufacturers use "counterweight" or "ballast" when producing aircraft. Why is the use of weight necessary? Supposedly aircraft should be made as light as possible, and counterweight is just dead weight without any function.

I presume it is used to balance some centre of gravity, but why would that be necessary? With industrialized factories, components can be engineered to great accuracy, so a case-by-case adjustment to account for manufacturing errors should not be needed.

In the context of aircraft design and maintenance, the terms counterweight and ballast generally have separate and different meanings.

Both concepts involve mass used to balance, dampen, or adjust forces about a rotational axis. While ballast could also be described as a type of counterweight, it is best understood as working within the frame of reference of the entire aircraft since it adjusts the aircraft Center of Gravity (CG). Conversely, counterweights can be understood to work within a frame of reference that is smaller than the aircraft as a whole, such as an engine or a control surface.

I will address each separately.

Counterweights

Counterweights primarily serve three functions in aircraft design: balancing control surfaces, controlling propeller pitch, and balancing crankshafts in piston engines.

Control Surfaces

Counterweights are used to balance control surfaces about the axis of the hinge to avoid potentially dangerous control flutter. This balance is very important. Pilots typically check for counterweight structural security in preflight where able. Mechanics must recheck control surface balance after painting, and painting control surfaces is excluded from the list of preventative maintenance items that an aircraft operator can perform without a mechanics license.

From the A&P Mechanics Airframe Handbook AC65-15A:

  It is this out-of-balance condition that can cause
  a damaging flutter or buffeting of an aircraft and
  therefore must be eliminated. This is best accomplished
  by adding weights either inside or on the
  leading edge of the tabs, ailerons, or in the proper
  location on the balance panels.

The following excerpt from the Cessna 172M IPC shows the elevator counterweights, 23, highlighted in blue:

Propellers

Counterweights are used in some constant speed propeller designs to increase the pitch of the propeller blades. Engine oil pressure is used to overcome the force of the counterweights to move the propeller blades back to fine pitch. In feathering designs, the counterweights assist in moving the blades to the feathered position.

From the A&P Mechanics Powerplant Handbook AC65-12A:

  Propellers, having counterweights attached to the blade clamps,
  utilize centrifugal force derived from the counterweights to increase
  the itch of the blades. The centrifugal force, due to rotation of the
  propeller tends to move the counterweights into the plane of rotation,
  thereby increasing the pitch of the blades.

  Feathering is accomplished by releasing the governor oil
  pressure, allowing the counterweights and feathering spring to feather
  the blades. This is done by pulling the governor pitch control back to
  the limit of its travel. which opens up a port in the governor
  allowing the oil from the propeller to drain back into the engine. The
  time necessary to feather depends upon the size of the oil passage
  from the propeller to the engine, and the force exerted by the spring
  and counterweights.

AC65-12A Fig 7-11:

Crankshafts

Counterweights are used in piston engines for both static and dynamic balancing.

From the A&P Mechanics Powerplant Handbook AC65-12A:

  Crankshaft Balance
  Excessive vibration in an engine not only results
  in fatigue failure of the metal structures, but also
  causes the moving parts to wear rapidly. In some
  instances, excessive vibration is caused by a crankshaft
  which is not balanced. Crankshafts are balanced
  for static balance and dynamic balance.
  A crankshaft is statically balanced when the
  weight of the entire assembly of crankpins, crank
  cheeks, and counterweights is balanced around the
  axis of rotation. When testing the crankshaft for
  static balance, it is placed on two knife edges. If
  the shaft tends to turn toward any one position during
  the test, it is out of static balance.
  A crankshaft is dynamically balanced when all
  the forces created by crankshaft rotation and power
  impulses are balanced within themselves so that little
  or no vibration is produced when the engine is operating.
  To reduce vibration to a minimum during
  engine operation, dynamic dampers are incorporated
  on the crankshaft. A dynamic damper is merely a
  pendulum which is so fastened to the crankshaft that
  it is free to move in a small arc. It is incorporated
  in the counterweight assembly. Some crankshafts
  incorporate two or more of these assemblies, each
  being attached to a different crank cheek. The
  distance the pendulum moves and its vibrating frequency
  correspond to the frequency of the power
  irnpulses pf the engine. When the vibration frequency
  of the crankshaft occurs, the pendulum oscillates
  out of time with the crankshaft vibration, thus
  reducing vibration to a minimum.

  Dynamic Dampers
  The construction of the dynamic damper used in
  one engine consists of a movable slotted-steel counterweight
  attached to the crank cheek. Two spoolshaped
  steel pins extend into the slot and pass
  through oversized holes in the counterweight and
  crank cheek. The difference in the diameter between
  the pins and the holes provides a pendulum
  effect.

From the Continental O-300 overhaul manual:

  C-145 and 0-300 crankshafts have a blade extending from each side of the cheek between No's 1 and 2 crankpins for attachment of dynamic damper counterweights. Each blade has two holes bored through and steel bushed. Slotted counterweights fit over the blades and have holes bored through and bushed to match those of the shaft. Bushings are sized to produce the desired frequency.

The following shows those counterweights on an O-300 crankshaft that is apart for overhaul:

Source: own work

Ballast

Ballast provides a temporary or permanent change to overall aircraft center of gravity. Ballast might be included as a permanent part of an initial or modified design. When I was in flight training we used old aircraft tires filled with concrete as ballast to place the W&B of a U206G near a max gross weight and aft CG configuration for portions of mountain flying training.
I know glider pilots use ballast for adjusting aircraft CG as well.

From the A&P Mechanics General Handbook AC65-9A (this AC is cancelled, but this comes from my old print edition and is still accurate):

  Ballast is used in an aircraft to attain the desired c.g. balance. It is usually located as far aft or as far forward as possible to bring the c.g. within the limits using a minimum amount of weight. Ballast that is installed to compensate for the removal or installation of equipment items and that is to remain in the aircraft for long periods is called permanent ballast. It is generally lead bars or plates bolted to the aircraft structure.

  Temporary ballast, or removable ballast, is used to meet certain loading conditions that may vary from time to time. It generally takes the form of lead shot bags, sand bags, or other weight items that are not permanently installed.


Would a 19,000 ft descent in 6 minutes feel noticably different to passengers? In July 2008 a Qantas 747 suffered decompression at 29,000 ft and the pilots then descended to 10,000 ft in the space of six minutes . More details here : wikipedia.org/.../Qantas_Flight, 30 .

I'm curious to know if you're in a large aircraft descending at that rate would there be a strong sensation of descent for the passengers? Would the plane be angled downwards in a way that wouldn't normally happen or some other sensation not normally experienced when travelling on large civil aircraft?

I appreciate that in this case the masks were down and there might have been noise/wind associated with the actual incident, so clearly it did feel strange to these passengers, but if the descent was done as a test at that rate would it feel strange?

From the physical side, you can not measure / feel if you are at a constant altitude or if you are ascending / descending with constant speed. What you can feel is the change of speed in any direction, and acceleration acting in an unexpected direction. This causes the usual sensations:

Accelerating / braking on the runway: You are pressed into the seat / belt.
Weird feeling right when the aircraft becomes airborne: The aircraft accelerates upwards, which presses you into the seat with more than 1g. This higher g-force feels strange.
While climbing, the aircraft still accelerates, but the more strange feeling comes from the fact that the force doesn't point down to the floor of the aircraft, but more backwards. Your eyes see that you are sitting upright in the aircraft, but it feels more like lying.
At some point, usually when the flaps are retracted, the climb rate decreases suddenly and it feels as if the aircraft falls. This is because the aircraft accelerated downwards - tough it still climbs, but at lower rate.
Usually, you don't feel much during a coordinated turn. Maybe you feel a little heavier, but when you look out of the window and don't see horizon, this again gives a strange feeling.

Of course, the passengers of that flight did have several sensations. right after the incident, the aircraft for sure has done some unusual movements, plus what the pilots did.

The reference #7 of the Wikipedia article contains this diagram on page 36:

Directly after the incident, the aircraft climbed a little and the speed brakes were deployed (50%) to reduce speed. This was for sure noticeable by the passengers. And I guess the aircraft started to descend faster than usual, so the sensation of "becoming lighter" will have been much stronger/longer than usual.
After this, the aircraft descended with a quite constant rate for several minutes. This doesn't cause the feeling of being lighter. Maybe the attitude was unusual which means gravity doesn't push you vertically into the seat.

Later, when the aircraft reached 10,000ft, it accelerated upwards to stop the descent. At this moment, the passengers felt heavier.

(If you have a closer look, the descending part isn't a perfect straight line. This wasn't a smooth ride, but as said, a constant descent rate doesn't cause a sensation)

Of course, this is just about the sensation of acceleration so far. The passengers for sure have noticed the drop in cabin pressure, drop in temperature, more noise and so on.


Will an Airbus A320 plane go into an unrecoverable nosedive and crash if a single angle of attack sensor fails, like on Lion Air JT610? For example, has an Airbus gone from cruise flight into an automated unrecoverable nose dive until it hit the ground because an AOA sensor failed in flight?

Moreso, are there any cases of an AOA sensor failing on an Airbus, and the plane not crashing?

if a single angle of attack sensor fails

No.

An A320 has three AoA sensors. If one reports a different value to the other two, the avionics will ignore values from that AoA sensor and use the values from the other two.

If two of the three fail and report consistent values - the avionics will believe the third is the odd-one out and unreliable.

If those two both both report a consistent and  overly high AoA then the flight protections will apply a nose-down input in an attempt to restore the AoA to normal values and prevent a stall. this input is averaged with the pilot's inputs.

As I understand it all the following conditions must be met for the AoA protections to be erroneously invoked and cause a nose-down input:

Two AoA sensors fail and
Both report the same value and
The value is one that would cause a stall if true.

According to Airbus' Safety-First magazine:

  In normal law, on a protected aircraft, exceeding the AOA value of the
   α PROT threshold would immediately trigger the
  high AOA protection, thus resulting in a nose down pitch rate ordered by the
  flight control laws. Further increasing the AOA by maintaining full back stick
  would eventually result in reaching the α MAX threshold.

  are there any cases of an AOA sensor failing on an Airbus, and the plane not crashing?

I expect there are many.

There are even cases of two AoA sensors simultaneously failing and the aircraft continuing, after some control problems.

For example this incident  reported by Aviation Week

  German investigators studying the cause of an uncommanded pitch-down of a Lufthansa Airbus A321-200 near Pamplona, Spain, in November 2014, hope to discover the probability of similar events linked to frozen angle-of-attack (AOA) sensors as the investigation continues. In the interim, both the European Aviation Safety Agency (EASA) and Airbus have published directives alerting pilots of the issue and the workarounds.

...

  The captain continued to hold “more than 50%” rearward stick in stable flight for a period, but with help from technicians on the ground, the crew was able to reconfigure the automation into the aircraft’s alternate control law, rather than its normal “direct” law. The action removed the alpha-protection checks and canceled the nose-down input. The aircraft then continued to its destination.

...

  Airbus in early December issued a Flight Operations Transmission and Operations Engineering Bulletin to all A320-family aircraft operators noting that “if two or three AOA probes are blocked at the same angle, an increase of the Mach number may activate high-angle-of-attack protection,” which results in “continuous nose-down pitch rate that may not be stopped with backward sidestick inputs, even in the full backward position.” The recommended fix is to turn off two of the three ADRs, which puts the aircraft in alternative control law, deactivating the high AOA protection.


Does a high-pitching-moment symetrical airfoil exist? I'm looking for a high-pitching-moment symmetrical airfoil.

I understand the Zenith 701 uses a reverse NACA4412 as it has a high pitching moment. This allows for a smaller horizontal tail.

What about a symmetrical high pitching airfoil for the vertical tail?
Wouldn't this reduce the size of the vertical tail?

Does a symmetrical airfoil with a pitching moment exist?

How about one with a high pitching moment?

What you probably look for is a symmetrical tail airfoil which produces high control moments. Since those moments are the product of force and lever arm, placing those control surfaces far from the center of gravity produces high moments.

A symmetrical airfoil will have zero pitching moment around its quarter chord point in attached flow. This is understood as zero pitching moment, since the pitching moment of an isolated surface is per convention defined around its quarter chord point. For a thorough explanation please consult this answer.

If, however, you choose a different reference point for your moment, even the symmetrical airfoil can produce a pitching moment. That effect is used in tail surfaces and for a given geometry, a higher maximum lift coefficient will produce a higher maximum moment. Traditionally, the NACA four-digit range of airfoils starting with a double-zero have been used for tail surfaces, but more modern designs will produce a higher maximum lift and lower minimum drag. A good choice would be the Wortmann FX 71 range of airfoils, like the FX 71-120 or the FX 71-L-150 which can often be found on gliders.


Are the implications of weight and balance for rotary wing aircraft similar to fixed wing aircraft? Original discussion here.

How does weight and balance for rotary wing aircraft work?  Is lateral CG more or less of an issue, or is it comparable to fore/aft CG since the lifting surface is rotating around the aircraft?

What are the major differences compared to fixed wing, if any?

I don't understand your statement since the lifting surface is rotating around the aircraft - not sure where you are going with that.

In general, the principles are the same as for fixed wing.  If the CofG limits are exceeded, it is possible to run out of control authority to the extent that the aircraft becomes uncontrollable.

Many helicopters, I believe any with a tail rotor, have different left/right CofG limits.  The tail rotor opposes the rotation of the fuselage due to torque from the rotor.  Since it does this by producing thrust to the side, there is a "translating tendency" which would cause the helicopter to drift in the direction in which the TR is generating lift.

To counter this, the cyclic neutral position is rigged to the left (CCW rotor) or right (CW rotor) which results in the skid on that side hanging low.  Clearly, there is now less possible movement in the cyclic to that side and therefore, a narrower lateral CofG.

For example, in a helicopter with a counter-clockwise rotating rotor, the fuselage wants to rotate clockwise.  The tail rotor will produce a thrust to the left to counter this and a long lever couple is formed with the main rotor which, if not corrected, would cause the helicopter to drift to the right.

With a perfectly balanced helicopter, in a no wind steady hover, you want the cyclic to be in the centre with no force required from the pilot.  To stop the drift to the right, the cyclic is moved to the left.  To prevent the need for the pilot to do this, the cyclic is rigged so that its neutral position is to the left.  The main rotor thrust vector is now titled to the left which introduces a horizontal component of thrust acting to the left.  This also causes the left skid to hang low.  This is why in most CCW rotor helicopters, the captain sits on the right and in some of these helicopters, solo flight from the left is prohibited.

Since the cyclic is already left of centre, there is less cyclic authority to the left than to the right.  Therefore, the right limit of lateral CofG is less than the left limit.

This could not be achieved by moving the CofG since this would level the fuselage but would not oppose the thrust.

I will never forget the sensation of my first solo lift into the hover after the talking ballast (my instructor) got out and left me to it.  I lifted with the control positions where I was used to them.  Because there was 170lbs less weight in the front left corner, this meant that I started to pitch up and move back.  I was surprised by how much forward and left I had to move the cyclic to counter it.  It felt very odd for a few minutes.


Is there any practical benefit of the Boeing-787 to perform near vertical takeoff? In a promotional video for the Paris 2015 airshow, this video was released promoting the new Boeing 787's near vertical takeoff capability. Whilst highly impressive, I was wondering if there is any practical benefit or advantage of such an aircraft being able to perform this manouevre?
If there is no benefit of being able to climb at this angle of attack, then why was this aircraft designed with such a capability. But if the 787 wasn't designed to intentionally perform this, then does this mean other Boeing aircraft can do this? And if other aircraft can do this, then why hasn't this manouevre been marketed in such a way before?
In other words, why even bother to design an aircraft capable of this, if it serves no real benefit? And why market the aircraft as being able to do so in the first place?

The 787 was not designed to perform such a maneuver. Any jet airliner could do this.
What you need for such a steep climb is a good thrust to weight ratio (or enough excess speed to bleed off during the maneuver). A passenger twin-jet is designed such that it can still climb with at least 2.4% climb gradient after a single engine failure during a takeoff at the maximum takeoff weight (see e.g. this answer). When the aircraft carries no passengers and only enough fuel for a short demonstration flight, it is much lighter than that (source):

Aircraft
Operating Empty Weight
Maximum Takeoff Weight

Boeing 787-9
284,000 lb / 128,850 kg
560,000 lb / 254,011 kg

As you can see, the empty weight of a 787-9 is only about half its maximum takeoff weight. And if both engines are operating, that gives you a lot of excess performance for such a maneuver. At normal weights, the 787 could not perform such a steep climb and there is also no "practical benefit" in doing so since clearing terrain must still be possible after an engine failure, which results in much less climb performance.
Also note that the aircraft was not flying at a high angle of attack. It was flying at high pitch (although not nearly vertical). The angle of attack is the angle between the average chord line of the wings and the relative airflow. When climbing steeply, the angle of attack is therefore not necessarily high.


What was the Space Shuttle's glide ratio? The Space Shuttles glided to a landing in the atmosphere after reentry. They were not good gliders, aerodynamically speaking, so their glide slope angle was rather steep.

What was the glide ratio of the Space Shuttles in this phase of flight?

As far as I know the space shuttle is no longer in use.  However, the glide ratios (more than one in different configurations) can be found on the Wikipedia page: Space Shuttle Wikipedia page.  There it states that “The orbiter's maximum glide ratio/lift-to-drag ratio varies considerably with speed, ranging from 1:1 at hypersonic speeds, 2:1 at supersonic speeds and reaching 4.5:1 at subsonic speeds during approach and landing.”


Why is Cessna 172 POH performance chart based on Pressure Altitude and Temperature instead of Density Altitude? While calculating takeoff distance for Cessna 172, POH need to be used. POH charts has pressure altitude and temperature and then distance for those two known parameters.

Does this mean if we have pressure altitude and temperature then we don't have to worry about density altitude in our calculation? Why would we want to calculate density altitude if we only need to know pressure altitude and temperature?

I have analyzed this information before, and this is what the chart looks like with one line for each weight category if you convert the temperature and pressure altitudes to density altitudes and then chart that vs. the takeoff distance:

You can see that I have drawn a sort of best-fit line for this information.  I did not add humidity as a factor because the manufacturer's charts had no relevant data.

Clearly, the trend from the manufacturer's data, when converted to density altitude, does not appear perfectly linear if you follow the data points they jump up and then start lower again in chunks of similar density altitude.

The greatest variation here is about 400 feet from the highest point in any of those clusters to the lowest point in the same cluster. That would be the yellow line around 8,000 ft of density altitude.

To answer your question, maybe they didn't use density altitude in the POH because their data appears to be irregular.

With that small margin of error here, I am comfortable using these best-fit lines to quickly calculate my data because I wouldn't make a go descision for a takeoff with a calculated distance anywhere near being within 400 feet of acceptable runway length.


Can an F-16 land on an aircraft carrier, at all? Looking at the F-16 again, I noticed the tailhook which it seems to have. I know the F-16 is not designed to land on any aircraft carrier, however, if it was between ditching in the ocean and attempting to land on a carrier. During wartime or any emergency; if the F-16 found itself over an ocean and needed to land, and there was a friendly carrier nearby. Could it be done?

For this we assume an unmodified F-16, any of the F-16 variants are candidates for this thought experiment. However, I assume the lighter F-16A (I assume they all have the hook, even the early block A variants?) is better, since it has less mass which needs to come to a full stop?

I understand that this will probably be speculation at best, I'm just curious. Forgive me. If someone happens to know the figures of maximum load on the F-16 tail hook versus what would roughly be required, that would be awesome. However, I'm also taking just educated guesses.

My own layman efforts towards an answer, limited to mostly just identifying some obvious issues:

Is the F-16 tail hook even compatible with the arrest system an aircraft carrier uses? Perhaps it wouldn't catch the arrestor cable at all.

If it does catch it, perhaps it is not designed for that kind of abuse, and would tear straight off the airframe if this was attempted.

For carrier landings, the aircraft will typically from what I understand not flare and make hard landings which really beats the undercarriage. I'm not so concerned with the undercarriage breaking, it would be better to recover an F-16 with broken undercarriage than losing it to the ocean.

However, if the undercarriage does break, it might prevent the hook from catching the cable at the correct angle. Even if it does grab the cable, perhaps the aircraft with broken undercarriage would risk sliding off the side of the deck.

From what I understand, there are no barriers on modern Nimitz carriers any longer. Hence they will not be considered as an option. Perhaps a barrier could catch an F-16 but I'm more curious about the properties of the hook, undercarriage, and other issues with landing on a carrier.

I know landing on a carrier is hard, so what is it that makes it so hard for an F-16?

The hook is for emergency use at airports that have Runway Arrestor Systems.  Lots of non-naval fighters have arrestor hooks for that purpose.

Now, there is nothing stopping someone from landing an F-16 or any other fighter on a carrier deck and using its arrestor system, which works the same way.  The main issues are the proficiency required to do it and the ability of the airframe to take it.

A carrier landing isn't really a landing; you more or less descend into the ocean and the deck gets in the way.  So the airplane needs a pilot trained to do that sort of thing, and an airframe that can do it repeatedly, that is, land with a descent rate of >500 fpm, a "hard landing" for a normal airplane, without developing cracks here and there and everywhere after a few dozen times.

No doubt that in theory, you could take a carrier qualified pilot, check him/her out in the F-16, and that pilot could shoot traps onto a deck with the F-16 using the hook (launching it is another matter in the absence of catapult link).  But they wouldn't be able to do a lot of them before the airframe would be toast.


How is Reynolds Number derived and used? Reynolds number is the ratio between inertial forces and viscous forces according to wikipedia. However, I still do not understand its derivation process and how to, for example, calculate the Reynolds Number for a cylinder in large pond of water with the water moving in a direction with speed v.

You can derive the Reynolds number by non-dimensionalization of the Navier-Stokes momentum equation: Wiki link

The choice of reference length and velocity is somewhat arbitrary: usually they are chosen so that they represent "fundamental" dimensions of the study case, e.g.:

For a cylinder in a flow: freestream velocity and cylinder diameter
For a pipe: mean velocity and inner diameter
For a flat plate: freestream velocity and distance from leading edge

In the end of the day, it is a matter of conventions, but what you choose must be physically relevant (e.g. you cannot choose the plate thickness) in a way that, increasing either of them, you go from laminar to turbulent flow. Once the choice of the above pair (length, velocity) is standardized, you can define a critical Reynolds number, which marks the boundary from laminar to turbulent flow (actually, a range of it because of the complex behaviour of fluids during laminar-turbulent transition).


How do stealth aircraft get ATC? I believe that all aircraft must be controlled under ATC's instructions to fly safely especially when take-off and landing. And, most ATC instructions are conducted by ground radar which controllers use.

But I know that the stealth aircraft (including B-2, F-22 etc.) aren't captured on radar display owing to their stealth ability. If so, how does a controller give instructions like radar vectors to stealth aircraft?

I know that there's are primary and secondary target when using radar, and the controller must use primary target to vector aircraft. I guess stealth aircraft can be captured by secondary radar but not primary target.

The concept of ATC is based on primary radar targets, secondary radar targets and radio communication being used to determine the position of aircraft and establish separation.

The concept of stealth aircraft is to reduce production of primary radar targets and being able to turn off transponders to disable secondary radar targets being visible. Stealth aircraft also do not communicate on frequencies during tactical missions, they are designed and meant to reduce radio emission to enable the stealth features.

If they are not on a tactical mission and stealth is not required, they will simply turn on their transponders and communicate with ATC on the required frequencies.


Did the Germans ever use captured Allied aircraft against the Allies? I have noticed that during WWII the Germans captured quite a few P-47s, P-51s, Spitfires, and other Allied aircraft. I know that they tested them extensively but wanted to know if they ever used them against Allied aircraft.

Not sure about the Germans, but the Italians used a P-38 (from the site 12 O'Clock High):

The piece about the P-38 captured by the Regia Aeronautica is
extremely correct (at last, I was sick of reading accounts or
questions mutuated from the complete fantasy of Martin Caidin...! ),
except for one detail: the plane shot down on August 11, 1943 by Col.
Angelo Tondi with the P-38 wasn't a B-24 but a B-17 instead...

and later on the same post:

This is extracted from the diary of 2nd Lt. James Franklin Boston:
"August 11, 1943-Mission to Terni, Italy 06:00. Carried 6000 lbs.
demos. (demolition bombs). Flak moderate. Coming back 60 miles from
Italy intercepted by ME-109 and captured P-38 with enemy flier flying
it. Nobody fired at first, thinking it friendly. Saw it slip in a
formation from behind and shoot down a B-17. Everybody fired at it
then including myself but my gun jammed. 20mm shell came by my head
while I was looking through astrodome and went into No. 2 engine. P-38
was not shot down."


What closed-cockpit biplane is this model modelled after? What closed-cockpit biplane is this model modelled after?

(wikimedia.org)

Beechcraft Model 17 Staggerwing first flew in 1932. It flew air races, served in WW2, and served as a civilian transport. One of its rare features is the lower wing being ahead of the top wing.

  The Model 17's unusual negative stagger wing configuration (the upper wing staggered behind the lower) and unique shape maximized pilot visibility while negligibly reducing interference between the wings.


Could compressor stalls be caused by air in supercritical conditions? It is likely that in compressors of jet engines appear conditions that cause the intaken air to become supercritical, cf Is the air in a jet engine supercritical? .
Is it possible that supercriticality of the fluid (air) is one of the causes for compressor stalls or compressor surge ?

The answer to your question:

  Is it possible that supercriticality of the fluid (air) is one of the causes for compressor stalls or compressor surge ?

...is definitely no.

Stall is caused by an excessive angle of attack of the incoming air, relative to the blade. It can happen on the first stage (first row of rotating blades), where the pressure is no where near high enough to be supercritical. Surge occurs when the stall is very severe, so it’s the same phenomenon, just worse.

While the likelihood of a stall occurring is determined by measuring the total pressure distortion across the compressor face, it is the angle of attack that is the critical factor. Regions of low total pressure indicate the flow is likely to be turbulent in these regions, and therefore the angle of attack is not steady, and can exceed the ability of the air to follow the surface of the blade. Once it separates, it becomes turbulent, which means the blade does not perform its function of compressing it well. This is a big problem, as the compressor is trying to get the air to flow “uphill”. Stall generally starts as a phenomenon involving a few blades on one or more stages. It can then develop and cover a large section of the compressor. If the axial velocity of the flow through the compressor starts to vary, faster and slower, then faster again, it is called surge. The engine “chugs”.


Why do modern airliners have windscreens which open? I'm sure it must be nice for pilots on a hot day to pop open their windscreen while waiting on the tarmac, but is there a good engineering or safety need for them? There must be a significant amount of cost and time effort in making a windscreen both openable and safe. If the pilots really need some fresh air, they're usually pretty close to the passenger door.

I can imagine there were valid historic reasons for having them: when planes were smaller and instrumentation not so sophisticated, you might literally want to take a proper look at your propellers spinning before setting out. But why do we persist with them?

737 Max with both its cockpit windows open source

Airbus A380 with open window source

Not all modern aircraft have windows that can be opened. The Boeing 747 for example does not.

On the Boeing 737, the windows can be opened for two reasons:

Emergency Evacuation: When the aircraft needs to be evacuated, there is always a way to escape from the flight deck without going through the cabin. On the Boeing 737, this is accomplished through the windows. From the 737 NG FCOMv2 (1.40.30):

  The flight deck number two windows can be opened on the ground or in flight and
  can be used for emergency evacuation. To open the window, depress the trigger
  and turn the handle back and inboard. After the window moves inboard, move it
  back until it locks in the open position.

  [...]

  Flight Deck Window Emergency Egress

  If the flight deck number two windows must be used for emergency egress, use
  the following procedure:

  open the window
  open the escape strap compartment (above and aft of window)
  pull on the escape strap to ensure it is securely attached
  throw the strap out the window
  sit on the window sill with upper body outside
  exit in accordance with the following illustration.

  CAUTION: Ensure the escape strap is securely fastened to the airplane.

Aircraft without windows that can be opened, have an escape hatch in the ceiling. You can see the 747 escape hatch in the following image from the FCOM:

Smoke or Fumes Removal: If there is a fire in or near the cockpit that cannot be easily extinguished (e.g. fire in the electronics behind the screens), the smoke has to be removed in order to continue to fly the aircraft. This can be accomplished by opening a window. From the 737 NG QRH (8.19):

  Smoke or fumes source is confirmed to be on the
  flight deck:

  Caution! Window should not be
  opened unless the source is
  confirmed to be on the flight
  deck.

  Establish normal holding speed. High
  airspeed may prevent opening the window.

  Open the first officer’s sliding window.

On aircraft where the windows cannot be opened, there is a dedicated system to evacuate the smoke, e.g. from the Boeing 747-400 QRH (8.43):

  Smoke or fumes persists or is severe and the smoke or fumes source is determined to be on the flight deck:

  Pull the smoke evacuation handle. Pulling the smoke evacuation handle when smoke or fumes source is not on the flight deck may bring the smoke or fumes into the flight deck.


How to increase payload capacity of plane? Keeping thrust, wing span, weight (of plane) constant, can we increase the payload capacity (nearly 50% more)? Adding payload to plane, it decreases thrust/weight ratio, how does it affect the control over plane?

I'm not sure what you mean by 'payload capacity'.  Airplanes have what's termed a 'useful load' which is the maximum combined weight of the passengers, baggage and cargo, and useable fuel.

If you wanted to increase useful load, you would have to make the airframe and all systems aboard the airplane which constitute useful load lighter.  This does have the adverse effect of making the structure weaker, lighter engines generally are less powerful so you have less thrust, and removal of mission systems reduces aircraft capability.  Manufacturers strive to address these things and improve them over time with more rigid aluminum alloys or composites for increased strength to weight ratio, higher thrust to weight ratio engines with better fuel efficiency and lighter mission systems.

How an increase in weight affects aircraft performance not only depends on how heavy the airplane is but where the center of ends up being located.  On a conventional airplane a forward CG produces better stability but requires more lift from the wings, resulting in decreased performance.  An airplane with a more aft CG offers better performance, but is more unstable, particularly during high alpha operations such as slow flight.   The maximum takeoff weight of the airplane was established during preliminary design studies and verified during flight testing so that it cannot exceed the load limits of the airframe and offer the required performance over a wide range of potential operating conditions.

Aircraft are, on occasion, approved via a Supplemental Type Certificate (STC), to increase their useful load, if the OEM or third party vendor can demonstrate that the mod can still operate safely and fulfill the regulatory requirements.

At any rate, the heavier the airplane is, the more lift it needs to fly, which means more drag, which means more thrust, which means greater fuel burn.  This is why the airlines are so miserly in issuing out the bare minimum gas to meet federal Part 121 and company SOP requirements for their flights.  The fuel saved doing this saves the company millions of dollars annually.


Which pressure mode of operation has the most stress on aircraft frame So I am want to know which mode of pressurization has the most demand on the airframe

Isobaric mode

constant - differential mode

unpressurized

I hope to get an answer because I have an exam and need to know
Thank you very much

Isobaric mode causes the most stress if you keep the cabin pressure and climb higher and higher. (Because the delta pressure and thus the forces become higher and higher)
That's why at high altitudes the isobaric mode is no longer used and the cabin pressurization switches to constant differential pressure instead, which limits the maximum stress.
And unpressurized, well that is not really stressing the hull at all


How much fuel does it take to start/land an aircraft, compared to normal flight? I'm wondering how bad it is to fly a short distance, such as ~50km, with a big airplane. How much less fuel does it take to fly at high altitudes compared to low? And how much of the fuel is spent on start/landing? Flying between continents is never a problem, but if a politician flies a shorter distance all hell breaks loose.

The fuel consumption or fuel burn rate is dependent on the aircraft type, size, engine configuration, cruise altitude, temperature, thrust setting and other factors.

In general: The larger the aircraft, the less economic do short flights become due to weight/size and fuel burn on takeoff/climb.

Here are some values I found for the CRJ2, the source may not be entire citable:

  Approximate total burn pounds / hour

  Taxi: 700 (Both engines and APU)
  Takeoff: 6000-7000 (depending on temperature, elevation, reduced/full thrust, etc)
  Climb: 6000-3500 (reducing as as altitude increases)
  Cruise: 2500-3000 (depending on altitude/weight/etc... subtract 500 for long range, add 500 for high speed)
  Holding: 1800-2400 (depending on altitude/speed)
  Normal descent: 1500
  Idle descent: 600
  Approach: 2000 (fully configured)

(Source: www.airliners.net - Author: Flyf15)

You can also read the following related questions to understand how altitude affects fuel efficiency:
Why do jet engines get better fuel efficiency at high altitudes?
How does flight duration affect the hourly fuel consumption in heavy aircraft?


What would happen if a pilot tried to land with a tailwind? What if a pilot was forced to land in a tailwind? Would this be possible and what is the maximum tailwind an aircraft can handle?

Your landing rollout will be longer, your groundspeed will be faster and you will stress the brakes more than a landing with less tailwind.  The same can be said for choosing calm winds over a headwind.

The jet I flew and many others have a limitation for maximum tailwind of 10 kts and it isn't unheard of to request an opposite direction landing (e.g. with a tailwind) if the tailwind is acceptable, the runway is long, and there is no conflicting traffic when it is convenient for the operation.

If you were forced to make a landing with a tailwind exceeding your limitations then the situation is probably an emergency and you'll want a longer than normal runway.  There is an increased threat of a brake fire, but in an emergency ARFF will be following you down the runway and they'll take care of it.  The tailwind landing only really becomes a problem if the runway isn't long enough (overrun) or if the tailwind is so strong that the maximum wheel speed is exceeded (loss of directional control or worse).


Are there any hybrid electric planes? Are there any hybrid planes (planned), or would this be impossible because we don't have big enough batteries?

There are experimental electric planes. Some are promising enough that they might end up useful as trainers and private GA flown for the love of flying.

Long-range electric will not work. The electric equivalent of the Breguet equation is R=L/D*E/W*n/g, where E is stored energy and n is propulsive efficiency. For a 100% efficient L/D=20 aircraft that is 100% battery with 250 Wh/kg cycle depth, that's 20*250*3600*1/9.8=1.8*10^6 meters, or 990 nmi. This is the hard limit. With 80% efficient props and real world factors, you can expect 5-8 nmi for each % takeoff weight dedicated to batteries.

Hybrid aircraft are, even on paper, only moderately interesting. Aircraft throttle in cruise at 45-75% for GA, 70-90% for small jets, and 80%-95% for long-haul widebodies. This is due to the engines "self-throttling" in a way - power and fuel consumption reduce due to lower air density as you climb.

So major airliners have nothing to gain from going hybrid, they can only shrink their engines by 5-10% with a hybrid system. This is very different from cars, which run duty cycles as low as 10%.

And there are no start-stops or regenerative braking to recover energy in flight. More precisely, aircraft already use regenerative braking - by pitching up or deploying flaps, speed gets traded for lift. So that braking energy is already being harvested, and stored as altitude (potential energy).

Smaller propeller aircraft could replace up to 30% of their power, so it's less cut and dry. However, when you want full throttle, you often want it for a while, like in climb. The only way for a non-plug-in hybrid to save energy is to use a lighter/smaller engine, and it's difficult to shrink enough to offset the hybrid system's weight.

A plug-in hybrid could benefit from the lower cost of electricity vs avgas, but fuel averages to less than a third of private flying expenses. Pure electrics have a shot at making flying more accessible through simplicity. With no fuel, very simple and reliable engines, it makes sense to relax the rules, like is done for ultralights. Hybrids have all the complexity of a piston-engined plane and then some.

The hybrid route makes sense for cars. The only safety-critical parts of a car are steering and brakes. Engine power is almost arbitrary, most hardware is just nice to have, and there's the universal failsafe of pulling over. In a plane, things need to work. Two systems that both have to work to fly safely is a complication and will likely increase costs.

Alternately, either system needs to supply takeoff thrust on its own. That could work in the 19-seater class, if the authorities accept a hybrid "twin"-engine single prop as sufficient redundancy. But there's a lot of "ifs" in this.

In a zero-weight scenario, some military aircraft (fighters, naval) could benefit from a hybrid system, as they have excess power like cars do. That's where reality hits: for given output, electric motors are lighter than car engines, but much heavier than aircraft jet engines. Since they're not lighter, there's nothing to be gained.


What determines the maximum speeds for a particular aircraft? Aircraft have three different maximum airspeeds:

VMO (maximum operating speed) - the maximum speed that the aircraft is allowed to reach during normal operations.
VNE (never exceed speed) - the speed that should never be exceeded during operation, even in an emergency, as flying at speeds higher than this could damage the aircraft.
VD (diving speed) - the fastest they got it to fly during testing.

What part(s) and/or characteristic(s) of the aircraft determine the values of these three maximum speeds?  Is it that the plane's engines are incapable of pushing it through the air any faster?  Would the wings snap off from excessive aerodynamic loads if it flew faster?  Is it something else entirely?

There are various physical things that will limit the top speed of an aircraft. Which one you will hit first depends on the airframe in question but here are some things you may encounter (aircraft dependent):

Drag will generally counter your thrust which will limit the speed you can achieve in level flight and is often the practical limiting factor on aircraft that actually fly. Level flight is important to note as you can gain a huge amount of speed if you simply enter a dive.
For propellor driven aircraft there are some practical speed limits because of the propellors.
At some point flutter will become a problem and you may literally shake the wings off the plane.
Around the speed of sound (mach 1) you are going to have all sorts of interesting things going on if you are pushing a subsonic optimized airframe to such speeds.
Ultimately, if you still have your engines and wings heat becomes the real problem. The Concorde pumped fuel through the nose to use a coolant in the mach flight regime and was in part speed limited by nose temperature. For manned flight this becomes the limiting factor at the extreme end of the envelope and aircraft like the SR-71 had a very physically demanding environment.


Which simulator is appropriate to learn the minimum to land an airliner? If one has zero flight training, but wants to learn the basics, so that they might be able to land an airbus in a Helios 522 type scenario (or any double pilot incapacitation for that matter), what would be the best simulator to learn on and what specifically would be best to learn (basically how to communicate with ATC and perform an auto-land).

I am fully aware that it takes thousands of hours of training to learn to fly and do not expect to be some sort of pilot after just using a simulator. Basically the premise of the question relates to increasing chances of survivability in-case of such an emergency and there being no other experienced people on-board (even if the increase is only by a few percentage points:)

Edit: Also, if the flight crew were all incapacitated, how would one enter the cockpit?

The simple answer is: none.

Flying an airliner (never mind the difficulties of getting into a locked cockpit) is not just a matter of wrestling with some controls. And, unfortunately, you would indeed need to be "some sort of pilot" to do that, including "just" being able to "communicate with ATC and perform an auto-land".

Even if you were a qualified pilot of a different aircraft, you'd be staring at a sparkling ocean of "what the hell do these do" buttons, lights, knobs, switches, levers and other controls.

You might as well ask what kind of simulator would prepare you for playing first violin with the Vienna Philharmonic orchestra, or taking charge of a nuclear power station.

They are just not things that can be done without much study and training, without which you literally wouldn't even know what you are looking at.

This is quite sad, because I for one would be quite happy to be known as that person who stepped in and saved the day when the pilot/first violin/nuclear power station chief engineer was suddenly incapacitated.


What is the top altitude of the class delta KEDC? It looks like it's not depicted on the VFR sectional chart Can someone tell me what I'm missing? I usually see a [-#] that denotes the airspace above a class delta. I believe KEDC (Austin Executive) is a class delta based on the chart supplement.

Attached is the VFR sectional from vfrmap.com:

This looks odd to me.

The supplement (3 Jan 2019) does indicate class D operations:

  AIRSPACE: CLASS D svc 1200–0400Z‡ other times CLASS E.

But the current (August 2018) Airspace Designations and Reporting Points doesn't list class D airspace for it, only class E.  This matches the sectional shown.

When I look at another part-time airport (like Drake Field/FYV), the airspace is listed both as class D and class E as expected, and the height of the class D is given.

Perhaps something needs to be updated?

UPDATE
Yes, looks like the control tower opened at KEDC Feb 2018.  It should eventually be charted.  Until then, NOTAMS...

  KEDC NOTAM:

  !EDC 01/001 EDC AIRSPACE CLASS G SFC AREA CHANGED TO CLASS
  D 1901031200-PERM

And the update section of the supplement.

  8 Nov 2018 No Major Changes.

  3 Jan 2019 Add AUSTIN, TX Class D: That airspace extending upward from the
  surface to and including 3,000 feet MSL within a 4.1-mile radius of
  Austin Executive Airport, excluding the Austin Class C airspace. This
  Class D airspace area is effective during the specific dates and times
  established in advance by a Notice to Airmen. Revise AUSTIN, TX Class
  E: That airspace extending upward from 700 feet above the surface
  within a 14-mile radius of 30º17´55″ N, 97º42´06″W ....

I don't know why the airspace change is marked as Jan 2019 when the tower opened in Feb.


How to calculate best glide speed at a 30 degree bank? The Best Glide speed is the indicated airspeed that guarantees the maximum glide distance during an engine out scenario.  However, the landing straight ahead option after an engine failure may not be the best option especially if there is nothing but houses in front of you after an engine failure.  Sometimes turning back towards the field may be the best option.
The Best Glide speed is actually tied to a best Lift/Drag ratio for a specific angle of attack.  When in a banked turn, the pilot must increase the angle of attack to avoid a spiral dive.  So this implies that the best glide speed would increase during a banked turn in order to maintain the best L/D angle of attack.  My question is how would one calculate the Best Glide speed for an aircraft in a 30 degree bank based off the POH listed Best Glide at Gross Weight (I do realize best glide varies with weight).

During a turn the load factor increases. This increases the apparent weight. Thus, during a turn, the best glide speed is selected according to the weight times the load factor.
The load factor at 30 degrees bank is $$n=\frac{1}{\cos{\theta}} \approx 1.2$$
The best glide speed is thus the best glide speed for a weight that is 1.2 times your actual weight. This will be proportional to the square root of the load factor.
$$V_{opt,\theta}= \sqrt{\frac{1}{\cos{\theta}}} V_{opt,0^\circ}$$


Is there a regulation against having uncaged dogs or other animals as passengers on private aircraft? There is flight club at our field and this discussion came up.  A regulation cited would settle the matter.

It appears that the answer is "there is no such regulation". For example, from AOPA's Flying with Family:

  Airlines require that any animal on board be confined to an animal carrier at all times. Although there are no such requirements for general aviation aircraft, it is always better to err on the side of safety and keep them in a carrier.


Would a laser dazzler be militarily useful? I saw Why don't combat aircraft have rear-facing *laser* weapons? pop up in the Hot Questions list and that motivated me to join here and ask this question.

Weapons that blind are banned. But what if they merely dazzle?

I'm imagining a little box with a laser pen in it - like those that so trouble landing pilots when wielded by foolish people on the ground. The box can point the laser around the sky and switch it on or off. It's a relatively cheap unit. It's probably controlled from an air defence computer that is looking at radar, IFF etc, that tells it where to point. If a hostile aircraft arrives, dazzle it.

Of course, the first thing the hostile aircraft will do is shoot up the box. (So you wouldn't want to be a human defender pointing a laser pen.) But if the boxes are cheap enough, you could scatter a hundred or so around any base you were trying to defend, and target an attacker with just one box at a time. When it gets blown up, use another box.

Without fancy radar, IFF etc (you may have no aircraft so you want to dazzle all of them) you could put a camera and image recogniser in each box.

If it all goes wrong and points at a friendly aircraft or even a human on the ground, probably no harm will come. But it seems it would make it much harder for an aircraft flown by a human to attack a target. It could work against drones, too, even relatively high-flying ones.

Would it work?

Would such a system be legal? Practical? Has anyone deployed one? Is anyone working on one?

Such a system already exists (in a way) and is in place to warn pilots who improperly enter the DC SFRA area. Im not sure it "dazzles" but it is what you describe and could be extended to do so. You can see an example of it running here.


What do those writings mean that are on the landing gear doors? I've been watching carrier videos a lot these days and I notice these writings. What do these writings means? I didn't upload all of them, most of the time there are location names and sometimes person names. What is written on those doors? This says UK, this F-18 belongs to US, this is a screen image from a video that was recorded in Naval Air Station Whidbey Island

For a US Navy jet, it is usually the plane captain (who is responsible for checking the plane and making sure it's flight ready) on the landing gear door.

In the image above, the plane captain's rank abbreviation (AE2) and name are on the first line and hometown is underneath.


How accurate is the barometric altimeter in the Tu-154? If the Smolensk disaster was to be traced down to a single decision (other than attempting landing in the first place), it would probably be the choice of radio altimeter to control altitude over a very unfortuitously shaped terrain (a wide valley, with steep slopes). This made the airplane to descend to 80 meters above the bottom of the valley, instead of 80 meters above the runway located 60 meters higher.

Someone mapped the black box recordings of the navigator's altitude readouts to speed and terrain profile, interpreting them as barometric altimeter readouts and it came out as an unreasonably bumpy ride (the orange line). I tried to follow up with mapping these same readouts at the same intervals, but relative to ground surface - treating them as radio-altimeter readouts - and it follows the blue line; judge for yourself which can depict a large passenger plane trajectory more accurately.

An unbiased comparison would include both advantages and disadvantages of the two types of altimeters. In this specific case (unknown, uneven profile terrain) the one main disadvantage of the radio altimeter is obvious: it doesn't provide accurate information about altitude of the airplane relative to the runway. I wonder though, what redeeming properties does it have - what are the advantages (if any) of using a radio altimeter over a barometric altimeter during landing - any inherent flaws of the barometric altimeter, like accuracy, reaction speed, or such, in which one type excels over the other?

(yes, I'm asking for a biased comparison; one with focus on superiority of one of the other. I realize both have their correct applications, both have strengths and weaknesses, applications where one or the other is better. Here I'm specifically asking for one side of this argument; half of the full image; look at it not as "why is A better than B" but "which traits of A are better than B")

A barometric altimeter is required to meet certain operational standards for use in an aircraft under instrument flight rules. We talked a little about this in another question with references to the relevant FAA requirements for the instrument.
I'm certain there's an equivalent in the Polish regulations, and while I don't know where you'd find it I would bet it's broadly similar in its requirements.

A radio/RADAR altimeter is typically accurate to within 20 feet within its operating range (typically <= 2,500 feet AGL). There are varying TSOs for radio altimeters, so you'd have to look up the standard a specific unit was built to in order to get exact numbers.

One of the core issues underlying this accident which you highlighted in your question is that a barometric altimeter and a radio altimeter are two different devices, measuring two different things, so it's not really reasonable to compare them.

Barometric altimeters measure altitude above a standard reference (usually sea level) by using a known/standard pressure lapse rate (~1 in.Hg per 1,000 feet) and measuring the difference in pressure at the instrument.

The readings given by a barometric altimeter are affected by weather conditions (mainly temperature), so the displayed altitude may be 'incorrect' (relative to say GPS altitude above mean sea level).
The readings given by a barometric altimeter are not affected by the local terrain, so peaks, valleys, and tall buildings won't change what it shows.

Radio altimeters measure the distance to whatever radio-wave-reflecting object is below the unit (typically "the ground" - whatever terrain happens to be under you) by detecting how long it takes a radio pulse to be reflected back.

The radio altimeter reading is not affected by weather conditions (temperature) as these don't affect the pulse reflection time.
The radio altimeter is affected by local terrain (peaks, valleys, etc.) as this changes the distance the radio pulse has to travel.
The radio altimeter reading is affected by any object that reflects radio waves (buildings, other aircraft passing below you).
The radio altimeter reading may be affected by "slant range error" just like DME, (in practical terms this is less of an issue for radio altimeters: The radio altimeter points "straight down" so the slant range error is generally small unless the aircraft's pitch or roll attitude is extreme).

So to directly answer your question, barometric and radio altimeters aren't comparable in the way you're asking: Because they measure two different things it's not possible to say one is "superior" to the other. They are different tools, serving different purposes: It's incumbent on the pilot to be aware of the limitations of whichever tool they happen to be using at the time (and to ensure that they've selected the correct tool for the task at hand).


What has been done to provide security for remote wireless updating of in-aircraft software components? Is it true that in the latest generation of Boeing aircraft some software components / Electronic Flight Bag data can be pushed to the flight remotely via a Wireless link?

If so, what sort of safeguards are in place to preserve the integrity of such an update? How does the aircraft authenticate that the data sent is indeed legitimate?

I'm curious to know the details. e.g. Are these conventional Ethernet networks over which the update gets pushed at the airport end? Is the final wireless transmission done by a COTS WiFi router? Does the update travel via the internet from (say) Boeing till the airport?

Boeing claims in this document:

  The 787 uses wireless (802.11 b/g) technology while at the gate to
  transfer maintenance data and update the Electronic Flight Bag (EFB).
  This is referred to as “e- Enabling” and it will allow airlines flying
  the 787 to operate more efficiently.

So, yes, they use a regular WLAN connection for transmitting data while on the ground.

The document continues:

  Upon weight on wheels the 787 attempts to authenticate specific ground
  access points. Information regarding the key configuration
  requirements and how the 787 authentication occurs requires the
  signing of a PIA.

I interpret PIA as Proprietary Information Agreement, a form of secrecy agreement. Boeing uses security through obscurity to safeguard the integrity of the connection.

If you want to know more, Boeing advises to contact 787terminalwireless@boeing.com. However, I doubt they will talk to you or me unless we are airport representatives with a credible need to know.


How do pitch attitude, airspeed and sink rate come into play in a rapid descent or a dive? So, I have a hypothetical aircraft that needs to get from FL350 to 10,000' as quickly as possible.

What is the difference in sink rate between a 'standard' airliner rapid descent (idle thrust, extended spoilers, and nose slightly down) vs. having the flight crew simply point the nose down below the horizon as far as they care to?
How does the airspeed build-up over time differ between a 'standard' rapid descent vs. a dive?
For a rapid descent, what nose-down pitch would be typical?

Airspeed control is the difference. In a rapid descent, airspeed is controlled and the pilots will keep it below $v_D$, the maximum dive speed for which the aircraft is certified. For a modern airliner, this is somewhere around Mach 0.9.

In a dive with "nose down as far as they care to" (I read this as 90°), airspeed is not controlled, but an outcome of the situation. The airliner will go supersonic. It is possible to recover it from a short dive, but will incur damage to the aircraft (e.g. the pilots will need to lower the landing gear to increase drag, but lose the gear doors in the process).

If the pilots would only care to put the nose down to the point where they not exceed $v_D$, we are back at a rapid descent. They could lower the gear in order to increase the sink speed, and circle to increase drag further. Circling needs more lift (proportional to the inverse of the cosine of the bank angle), so more lift-induced drag is produced. To maximize drag, the pilots should fly at the maximum permissible load factor (which is rather low at maximum dive speed due to gust loads).

If we assume the L/D of the airliner to be 5 with gear and spoilers deployed, the pitch attitude would be between -11° and -12° and the sink speed would be between 50 and 60 m/s (10,000 to 12,000 ft/min). The bank angle would be between 45° and 60° and the plane would be violently shaken by buffeting.

Going any steeper than that would only be attempted by pilots with suicidal leanings. Flying like described above is scary enough already.


Why do helicopter operations avoid IFR? In almost any airplane commercial operation, unless you’re doing something very short haul daytime ops, an Instrument Rating is all but required with airplanes(it’s even in the FARs). Generally the weather won’t stay nice enough for you not to use it, and most airlines and other commercial operations will avoid VFR all together, leaving VFR mostly for recreational pilots. In helicopters however it seems much different. Even in professional  settings like news services, 135s Helicopter operations, and even essential services like fire rescue,  will try and stay VFR at all costs, and will avoid flying if the weather is not VFR, even if they have an Instrument Rated helicopter pilot. VFR has a lot of limitations that would have a large chance of losing money for a helicopter service. Why is IFR so much more taboo and/or dangerous in helicopters compared to airplanes?

Helicopters do not avoid IFR. They will, however, try to avoid IMC for safety reasons. The same is true for airplanes in the same weight class. Just because the pilot is IFR rated and the aircraft is IFR certified, it does not mean they will always fly IFR, whether they are fixed or rotary wing. Light aircraft in general don’t do well in extreme IMC, whether they are fixed or rotary wing. And, many of the same FARs in Parts 61, 91, 119, 135, 136 and 137 that would require an instrument rating apply almost the same to rotary-wing as they do to fixed-wing.
The main difference between fixed and rotary wing would be their environments of operation. Altitude would be a major factor. The majority of airspace below 1200-1500 feet AGL is uncontrolled airspace. You can not get an IFR clearance unless you are in controlled airspace. Since Part 91.119(d) allows helicopters to operate at reduced altitudes and distances from persons or property, they will specifically be used in applications not conducive to IFR flight.
If a helicopter were to fly IFR,they would be restricted to at least an altitude of 1,000 feet above the highest obstacle within a horizontal distance of 4 nautical miles from the course to be flown by Part 91.177. This would greatly reduce the usability of helicopters. The increased restrictions of IFR flight means that there is much more opportunity to make money in VFR flight with a reduction of risk.

§91.119 Minimum safe altitudes: General.
(d) Helicopters, powered parachutes, and weight-shift-control aircraft. If the operation is conducted without hazard to persons or property on the surface—
(1) A helicopter may be operated at less than the minimums prescribed in paragraph (b) or (c) of this section, provided each person operating the helicopter complies with any routes or altitudes specifically prescribed for helicopters by the FAA; and
(2) A powered parachute or weight-shift-control aircraft may be operated at less than the minimums prescribed in paragraph (c) of this section.

As far as your assertion that commercial fixed wing operations are almost exclusively IFR, that is not a completely true statement. While I will agree with you that may apply to Part 121 operations. That is not necessarily the case for all other operations. Many commercial operations depend exclusively on flying VFR.


Are there any situations in which drones may legaly fly higher than 400ft? FAA FAR 107 states, "The maximum allowable altitude is 400 feet above
  the ground, and higher if your drone remains within 400 feet of a
  structure."

Are there any exceptions to this rule that would allow a drone to be flown at a much higher altitude than 400ft AGL or within 400ft proximity of a tall structure?

source

As they say with any regulation, there’s a waiver for everything.  If you do wish to operate your sUAS at or above 400’ AGL, you are advised to contact the local FSDO in your area.  Protocol varies from area to area, but you will be required to file an request with local ATC with the dates, times and areas you intend to operate in so NOTAMS can be issued.


Why don’t airliners have temporary liveries? For buses, it’s quite common to have plastic foil with advertisements on them, but I’ve never seen that on an aircraft. Looking at how aggressively some airlines try to save money, they probably already came up with the idea to sell the space on the side of their aircraft for advertisement purposes – so why did they not do it? Is there any technical reason to not have temporary liveries?

They do have temporary liveries. This is very common in wet lease operators, where an aircraft is flown for an airline during a peak period or when their planes are down for maintenance. Airlines want customers to feel they are getting the brand-name product they are paying for; they don't want customers to board a generic white jet.

An airplane will be painted and decals applied only for several months. Just like motor vehicles, 3M makes aircraft film wraps, including models specifically for short-term use.

It is also common to have a livery for a special event, say the Olympics. You can expect ANA's jet for the 2020 Tokyo Olympics to be returned to normal shortly after the Olympics are over. You can see Lufthansa and Egyptair dressed their planes up for the World Cup. Egyptair's photographic livery can only be done by printing onto a decal.

This video shows Alaska Airlines paint essentially an ad for Disneyland and the Cars movie franchise. They paint the simpler parts like the clouds and the large solid areas, but at 1:28 you can see them apply decals of the characters' faces. They say it took 29 days to paint. This is another video where they're simply applying a decal to advertise another movie.

So, no, there is no technical reason not to have a temporary livery and such schemes are done regularly. It's merely an issue of marketing and customer impressions.


Who was the oldest pilot ever so far? Based on any historical records, who has been the oldest pilot ever? "Pilot", I mean, somebody who managed to take off, return to the airport and land without  help. That much is probably not possible without training; would still be interesting to know if this pilot had a valid or maybe expired license.

Cole Kugel, 105

  Born March 14, 1902, Cole Kugel, a resident of Longmont, Colorado, USA is the oldest qualified pilot. He was born one year before the legendary Wright Brothers took to the skies, and has been flying ever since. Kugel earned his pilot's license in 1945 and flew in 2007 for the last time, aged 105, piloting in the company of local veterinarian Lynn Ferguson in his beloved 1976 Cessna 182.

http://www.guinnessworldrecords.com/records-1000/oldest-qualified-pilot/

2005 Photo: Daily Times-Call | Hunter McRae


Why do larger aircraft need two or more static ports? Some background information:
"Static pressure is the measurement of the ambient barometric pressure at the aircraft’s CURRENT location AND CURRENT Altitude.
The Static Port is located in a position on the aircraft that will not be affected by air flow as the aircraft moves through the air. This is typically on the side of the fuselage but can also be on the back side of the Pitot Tube or any other number of locations, it varies by the aircraft. Again smaller aircraft will typically have one Static Port, larger aircraft with redundant systems will have two."

After reading through that paragraph, I am wondering as to why smaller aircraft typically have one static port, whilst larger aircraft have two or potentially more static ports.

Your quote already answers your question:

  larger aircraft with redundant systems will have two.

The key is redundancy. You want to have at least two independent systems to measure altitude and airspeed so if one fails, the other still provides good data. Of course redundancy is also a good thing in a small aircraft, but it always comes at a cost: complexity. With larger aircraft the added complexity and therefore maintenance cost does not make such a large difference any more therefore tipping the balance in favor of redundancy.

For passenger airliners with potentially hundreds of people on board, safety is far more important. They usually have even more than two static ports. E.g. the Boeing 737:

  Air Data

  The pitot static system is comprised of three separate pitot probes and six flush
  static ports. Two pitot probes and four static ports interface with the air data
  modules. The remaining auxiliary pitot probe and alternate static ports provide
  pitot and static pressure to the standby instruments. The auxiliary pitot probe is
  located on the first officer’s side of the airplane.

  The air data modules convert pneumatic pressure to electrical signals and send
  these data to the ADIRUs. Each pitot air data module is connected to its on–side
  pitot probe; there is no cross connection. The air data module connected to the
  Captain’s pitot probe sends information to the left ADIRU, while the air data
  module connected to the First Officer’s pitot probe sends information to the right
  ADIRU. The remaining air data modules are located at the balance centers of the
  Captain’s and First Officer’s static ports. The air data module connected to the
  Captain’s static ports sends information to the left ADIRU, while the air data
  module connected to the First Officer’s static ports sends information to the right ADIRU.

(Boeing 737 NG FCOMv2 10.20.13 Flight Instruments, Displays - EFIS/Map System Description, emphasis mine)

This results in three independent measurements of altitude and airspeed:

Captain's side
First Officer's side
Standby Instruments


How does the attitude and heading reference (AHRS) work on Boeing 737 aircraft? I would like to know how the AHRS work on Boeing 737 aircraft. If this aircraft (like every the other ones I guess) has an Inertial Reference System (IRS), composed of 3 accelerometers and 3 gyroscopes, what elements compose its AHRS?
3 accelerometers and 3 gyroscopes as well?

The 737 does not have a separate AHRS. Those functions are simply outputs from the two IRS's.

(Source) 737 IRS panel.

ATT (attitude) mode selects the AHRS-only output of the IRS.


Why close isolation valve and APU bleed air for engine fire? For engine fire, the reason to close the packs (affected side) is to prevent smoke from filling up the cabin? But why the Isolation Valve and APU Bleed Air need to be closed too?

Closing the isolation & APU bleed valves keeps hot bleed air away from areas near the engine that may have damaged bleed air ducting. Closing the Pack valve causes the other pack to switch to high flow, making up for some of the lost output of the affected-side's pack. The steps are together in the checklist because it's all on the same overhead panel, even though the reasons differ.


Can you be a monocular airline pilot in Europe? I know this question has been asked before but it was for the US and I would like to know about Europe.

I was born with no vision in my left eye, and I have always wanted to become a commercial airline pilot, I have very good vision in my right eye. I just want to know if I could do it in Europe and if I would have any restrictions on my medical like not being able to fly internationally or fly big planes like the a380, and if it’s possible to become a captain. Or if it’s possible to get it without a soda, and would there be any differences. Or can you get a soda in Europe like the us.

UK CAA says

  EASA MED.B.070 (e) states that “Applicants for a Class 1 medical certificate shall be required to have normal fields of vision and normal binocular function”.

Therefore, you will unfortunately have to move out of the EU to become an airline pilot.


What CPU does the F-16 use? I've read that the "F-16", without it being specified what version, uses the 1750A CPU, it is on the list here, although without a citation: https://en.wikipedia.org/wiki/MIL-STD-1750A

However, surely this can't be right for more modern F-16's?

I'm curious what CPU the F-16A, C, E, and IN uses.

Perhaps even the more modern F-16's still retain the 1750A for some "legacy" features, but have a more modern "front end" CPU to handle the more modern features?

MIL-STD-1760A is simply the standard that a processor must conform to, and is not an actual model of CPU.
There are actually a lot of independent computers in a military aircraft, each with specific responsibilities. They are usually linked up via networks, typically over MIL-STD-1553 busses for older platforms. The radar has its own processor(s) and architecture(s), as does the flight control module, the fire control module, the navigation system, the munition controllers (sometimes one per weapon station/pylon), the display controller, the mission computer, et cetera. All of these come from different OEMs, and therefore use a variety of hardware. The different subsystems present and their exact functionalities depend on the design and requirements. A subsystem may itself be composed of multiple computers within their own network, independent of the main aircraft networks.
The F-16 uses Raytheon's Modular Mission Computer (MMC) for its mission computer, with the following specs:

The first generation, the MMC3000 relied on MIPS R3500, a 32-bit chip processors with 110,000 transistors and running at 12 MHz. We found this chip on the end of the 1990s HP9000 computers. The computer had 4 MB of memory RAM.
The MMC5000, the second generation of the F-16 computer, still relied on a chip MIPS, a RM5260 who was noticeably faster (with a 133 MHz to 150 MHz clock frequency) and above all it is a 64-bit chip. The memory was more than doubled, with 10 MB available.
The MMC7000 that equips the more modern F-16, including all F-16 Europeans who benefited from the MLU (mid-life Update) modernisation, has always that 10 MB of memory but its RM7000A processor, designed in the early 2000s, works between 300 and 400 MHz.
Source: http://www.4erevolution.com/en/ordinateur-de-bord-f-16/

I highlighted the mission computer because I think of the mission computer/controller/processor (exact terminology depends on the platform) as the brains of a military aircraft. They tend to be the bus controller of the main aircraft network, aggregating inputs from other subsystems and computing/providing information to the pilot to help them carry out their mission.

To the second part of your question, I assume you mean faster or more powerful CPUs when you talk about modern CPUs. Modern here depends on context. CPUs used In aircraft will never need the type of clock speeds or memory capacity you see in consumer computers, for a few reasons. Firstly, there is actually a lot of processing capacity distributed over the various subsystems - the need for a single powerful chip only arises when you demand that a single chip do everything. Secondly, when the requirements of subsystems are as specific as they as in military platforms, the software can be very compact and efficient, unlike consumer software (which require a lot more code for things like architecture adaptors, multi-tasking logic, and thousands of device drivers) - you trade off unnecessary flexibility in return for reliability and efficiency.
The multi-functional displays of military aircraft (and also commercial ones) focus on conveying the necessary information in a clear and concise manner. The rendering requirements are actually quite primitive compared to modern 3D games - it can get by with less processing power than a computer from the 1990s.

EDIT: Elaborated answer, following user3528438's comment.


Why isn't there a single start button for all systems on aircraft? Why is it that airliners and aircraft do not have a single start button for all systems?

On TV etc., I noticed that pilots pressing buttons above and below forward and sideways, mostly above though, switching on button after button, switch after Switch.

Why not:

have single start button for all systems where a computer does all the check lists?
is because they need to do checklists hence the switches?

Good question, actually the history of aviation teach us that: any technology on board is robust and capable to not crash or reboot for nothing. Behaviour you can see sometimes on brand new technologies. So everything which is on board is ten years old technology.

In the same time, the pilot needs to be able to switch off or on some systems if they are failing, if you automated all the sequence it start to be difficult to know if the pilot has the real control of the system.

It is only matter of safety and control. Because we already know that we are capable to automatically take off, fly and land UAVs. Why not in an airliner? Because safety. It has to be proven for a long time to convince safety agencies to make the step forward.


Does airspeed affect the critical angle of attack on an airfoil? I understand that the critical angle of attack is mostly affected by the shape of the airfoil.  However does the airspeed of the airfoil or the density of the air affect the critical angle of attack?  I would think that the airspeed or air density would affect the laminar flow properties and could change the critical angle of attack of that airfoil, perhaps only slightly.

Yes, through the Reynolds number

The Reynolds Number is a function of airspeed and is used to predict the transition from laminar to turbuluent flow:

$$
{Re} = \frac{\rho v L}{\mu} = \frac{v L}{\nu}
$$

The critical angle of attack is affected by the separation of the boundary layer, which, in turn, depends on the laminar or turbulent qualities of said layer.

Do note that the Reynolds number of the layer is not the same as the Reynolds of the wing, although they are related.

EDIT: to visualize the efect, see for example the following graph (thanks @MikeY)

Quite a bit of experimental work on low airspeed performance was done by Selig et al. at the UIUC, and their website maintains a significant catalogue of airfoil datapoints.

Another resource worth checking is Airfoiltools,  which provides graphed Xfoil polars for an extensive seleciton of airfoils. Do keep in mind Xfoil´s prediction of flow separation points is numerical and therefore may not converge with reality at all points.