Can a helicopter operate continuously in a small, enclosed, sealed environment? Many years ago I had an interesting discussion with a friend (while drinking). We were discussing what would happen if a helicopter was placed into a sphere of some size (slightly larger than the helicopter, a few times larger than the helicopter, etc.). Assume the sphere is filled with air at standard temperature and pressure, and there is standard 1G gravity pulling in one direction.

Can the helicopter maintain flight?

I believe it might, for a very short time, until the air starts circulating in a (relatively) stable manner, causing the "natural flow" of air to be already descending when it encounters the rotor disc, therefore reducing lift to nearly nothing.

I'm curious what an expert might think. If this is off-topic, mark it as such and I'll delete the question. Adding more useful tags I don't know about might also be helpful. :)

A helicopter develops lift by accelerating air downwards through its rotors.  This relies on the air above the rotors being slow enough for the rotors to accelerate that air enough to provide sufficient lift. When hovering in still air, the incoming air has zero velocity relative to the helicopter. While of course the air is conserved, in a large volume of air, the downwash is able to diffuse much more, and much of it does not immediately circulate back up above the helicopter.

If the helicopter were enclosed in a sphere, the smaller the sphere, the less the air would be able to diffuse. The downwash would circulate back to the top of the sphere, where the rotors would take that air in again. The rotors would be less effective at accelerating the air that is coming in with significant velocity, just as a propeller develops less thrust with increasing forward speed. Successful hover would depend on the helicopter being able to develop lift at a rate of circulation where the air can slow down enough for the rotors to be effective.

This seems like a experiment manageable enough that someone could try it at home...


Which computer controls auto thrust on an Airbus A320? An Airbus A320 has seven computers that control flight surfaces:
two ELAC, three SEC, two FAC, and two AP (autopilot) computers.

Is there an separate computer that controls auto thrust, or is this controlled through one of the above?

More specifically on your question:

See diagram below:

In the autothrust mode (A/THR function active), the FMGC computes the thrust, which is limited to the value corresponding to the thrust lever position (unless the alpha-floor mode is activated).

  So as you can see computers/controllers that control the A/THR are:

  FCU
  FMGC/S
  EIU or EEC
  FADEC
  ADR

The **speed or Mach target may be:

  ‐ Selected on the FCU by the flight crew

  ‐ Managed by the FMGC.

EPR mode is the normal mode to control the thrust. The required EPR is set by controlling the fuel flow.

DSC-70-35-20 P 1/2

The FADEC has two mode of power setting, EPR and N1 modes.
The FADEC computes the command EPR as a function of :

‐ Thrust Lever Angle (TLA)

‐ Altitude

‐ Mach number

‐ Ambient temperature

‐ Air inlet total temperature (T2) ‐ Service bleed.

Arming conditions of the A/THR are numerous. The following is a list of the most important ones:

‐ One FMGC operative

‐ One FAC operative

‐ Two ADIRS operative

‐ Two FADECs operative

‐ One channel of the FCU operative

‐ One LGCIU operative

‐ A/THR is not manually disabled (instinctive disconnect pb has not been pressed for more than 15 s).

  So to summarise:
  FMGS computes the THR and the FADEC computes EPR and through EIU/EEC and ECU commands the fuel flow to the engines in order
  to give the desired EPR.


Were stub wings on early flying boats designed or able to exploit ground-effect lift? I came across a link to the Dornier Do X, and the Boeing 314 Clipper in another question, both aircraft have similar short wings/floats low on the fuselage, described in one wikipedia article as "stub wings"

Were these stub wings designed to exploit ground effect to aid take of and landing (or could that have been an unintended advantage)? Or is the ground effect of these small wings likely to be irrelevant relative to the full size wings.

The wikipedia articles linked imply their main function was for stability in the water and use as landing stages for embarkation. But they seem reminiscent of the wings of some ground effect aircraft or ekranoplans such as the A-90 Orlyonok

In the early 1920s ground effect was not as well studied as today, so it was not considered during development. These stub wings, mostly called sponsons, were meant for roll stabilization on the water, so they were aerodynamically shaped buoyancy aides. Dornier had studied the optimum hull shape in the early 1920s with water tunnel tests, and the result was the flat-bottomed Dornier hull with sponsons.

The sponsons were mounted with significant incidence, not only to provide some more lift in flight, but mainly to reduce spray when sailing through choppy water at high speed.

From a 1925 Russian memorandum on hydroaviation, about the Dornier Wal, a 1922 flying boat design using sponsons:

  The distinctive feature of this aircraft was two protrusions on each
  side of the hull (so-called "gills") instead of under-wing floats
  providing lateral stability. Thanks to its flat bottom, the airplane
  could if necessary take off from snow or ice.

Other manufacturers of that time used outriggers, called under-wing floats in the citation above. One example is the Avro 510, which also used an extra float below the tail for stabilization on the water:

Avro 510 (picture source)

Those and especially their bracing struts and wires produced much more drag than sponsons. Later designs sported retractable outriggers which proved to be the least draggy solution.

Dornier 26 with retractable outriggers at mid-span (picture source)

Ground effect grows with a diminishing ratio of both wing chord over height and wing span over height. The first effect is much more pronounced for sponsons in the most drag-intensive phase of take-off from water, namely when the flying boat changes from buoyancy to planing lift, the so-called hump. The second part of ground effect, however, means that the wings also contribute some drag relief; something that works for all flying boat designs. Yes, there is a tiny and unintended advantage from the ground effect of sponsons, but given that water is 800 times more dense than air and slow planing will involve the full width of the fuselage, any aerodynamic help from the sponsons can be neglected.


How is the D8 Double Bubble aircraft by NASA so efficient? How does the 'double bubble' fuselage cross-section of the "Double Bubble D8" aircraft (developed by MIT for NASA) help improve overall efficiency by around 70%?

Image credit: NASA/MIT/Aurora Flight Sciences

The main advantage is its lower flight Mach number of 0.74. This allows it to use minimum sweep, which in turn reduces wing area, structural masses and thrust requirements. Now pick the right definition for efficiency (one that neglects speed), add the engine fuel consumption expected in 20 years, and the concept looks like a winner. If fuel prices go to \$200 or \$300 a barrel, this type of aircraft will lower the cost of flying substantially. The double-bubble fuselage will contribute only a little to the overall savings, though. Most will come from the (hypothetical!) engines and the high aspect ratio wings with little sweep.

Note that the lower flight speed is compensated by the claim of much shorter boarding times, so the double bubble comes out ahead in block times. The only reasoning is that passengers will board more quickly because they can choose between two aisles to get to their seats. Very questionable!

Below is page 105 from this report which shows the fuel consumption improvement of the separate steps from a Boeing 737 reference design to the D8.1 concept. The biggest contribution is from lowering cruise Mach (and increasing cruise lift coefficient, which allows to reduce wing area) and from engine optimization.

As it looks now, the marginal cost of fracking will keep oil prices below $70 for the next years, and airlines will keep ordering planes which look like those they operate today.

Looking through the proposals in the PDF linked in your comment, most of them make me cringe. Since the Seventies we see the same concepts for supersonic travel, and here they are again, only presented in different colors. Some subsonic designs are sound, but again we see hopeless concepts like the boxed wing which is kept alive by a stream of NASA grants, only because it looks so different. I am equally skeptical of those blended wing concepts which pop up with every new generation of aircraft designers.


How is the aircraft stand vertical lux measured? How is the vertical lux measurements taken for aircraft stands? Is it 2 m above the ground with the lux meter facing the light source, or parallel to the centreline?

What is the purpose of the lights on the stand? Is it for the ground services or the aircraft?

In 2m height, from two sides minimum, best if they are perpendicular to the centerline


Why did my IAH-SYD flight avoid Mexican airspace? I'm on UA101 tonight, the very long IAH-SYD nonstop operated by United.  If we look at Flightaware's routing for the flight (verified by the seatback moving map display) it's clear that we departed IAH, flew over El Paso and into southern California, left US airspace just west of Los Angeles, and then proceeded on the "normal" transpacific routing to Sydney.

Source: flightaware.com

What I can't figure out is why we specifically took this routing: it certainly appears that the point was to avoid overflying Mexican airspace, but I can't figure out why. United and lots of other US airlines provide service to Mexico so it's not like the airspace is off limits or anything.  According to gcmap.com the routing we took tonight adds about 300 miles (~40 minutes) to a route that is already VERY long, and the 787-9 that we're on has to be very nearly at MTOW anyway, so adding another 40 minutes of fuel is on the heaviest (i.e. most expensive) marginal part.

The economics of airline travel don't usually allow for things like this - burning a few thousand extra pounds of Jet-A doesn't make for good business.  Now obviously there's some reason for this routing, but I can't figure out what it might be.  I also looked at a few of the other routings for this same flight, and just a couple of days prior the flight did take a more direct routing over Mexico on the way out.

The winds aloft didn't look meaningfully different - Foreflight computed the times as we'd expect, the "longer" one was ~40 minutes more ETE.

Though routing this far north seems to make the flight about 200 miles longer, flight duration doesn't exactly correlate to route length. For a flight this long, wind plays a large role.

Take a look at the image below of the current wind forecast from ADDS, with the two flight paths in blue. You can see if they took the southern route over Mexico they would be flying directly into a pretty strong headwind. But by going further north, they can fly in much lighter wind conditions.


Is it possible to use multiple primary radars to determine an object's location in three-dimensional space? My question is this: if, for example, I have multiple radars across an area, tracking a particular airborne object, can I use the returns from the radars to determine the geographical location of an object in three-dimensional space (its x-y-z coordinates)?

Of course. That is, after all, the whole purpose of radar: to get the position of an object and plot it on a screen. You don't even need multiple radars, one radar is enough.
If you're just talking about primary radar (i.e. bounce a signal off of the skin of the target), then you're going to have some trouble with measuring the altitude. The distances involved mean that a large change in altitude would create a very small change in the beam angle, so altitude measurements are going to come with huge error bars. In fact, civilian radars almost never bother with vertical scanning at all, because such imprecise measurements aren't considered to be worth the extra complexity. Naturally, secondary radar (i.e. transponder interrogation) doesn't have this issue, since the transponder simply tells the radar what its altitude is.


What type of BITE is involved after installing a new display on an aircraft? There are 3 types of BITE (Built-In Test Equipment):

power up
interruptive
continues

which one of these is being used after installation of a new display on an aircraft?

First, let's clarify the terms.
BITE (Built-In Test Equipment) is the hardware and software within a product that performs BIT (Built-In Test).
There are three common forms of BIT:

Power-on BIT (PBIT).  This is run every time the unit powers up. Depending on the unit function, some units have two variations of PBIT; A comprehensive check performed after a cold start, and an abbreviated check performed after a warm start.  Warm starts typically occur in-air after short power interruptions. The abbreviated PBIT is intended to get the unit back online as quickly as possible. PBIT only reports faults.
Continuous BIT (CBIT).  Generally implemented only in critical functions, CBIT provides a continuous (or near continuous, periodic) test. CBIT is a background test and like PBIT, only reports faults.
Initiated  BIT (IBIT).  This BIT is only run when it is initiated by the crew or maintenance personnel. It will typically take the longest time and be the most thorough BIT that can be performed. IBIT will, upon completion, provide a status report.

So to your question; when a new display is installed (or any other unit is replaced) and power is restored the unit will perform a PBIT and potentially begin CBIT (if it exists). After the unit is in normal operation, the technician that replaced it will normally perform an IBIT and verify the unit passed all tests.
It's important to remember that BIT is intended to identify hardware faults. If you are concerned with 'glitches' due to flipped bits (caused by single event upsets) or similar, that is typically addressed using integrity monitoring. This is more common than CBIT and it will only flag 'bad data' as it can't specifically identify what caused a fault. It only identifies that data is suspect as the primary computation and the monitor disagree. A hardware failure will generally result in the integrity monitor providing a continuous fault condition, but it's primary purpose is to identify 'soft' or intermittent faults.


Why does the Eurofighter Typhoon has a long arm canard vs the close coupled canard of Dassault's Rafale or JAS-39 Gripen? Rafale and Gripen are quite similar but the Eurofighter Typhoon has the canards far forward. I've been told that this was due to the shape of the air intake.
Apparently the Typhoon's air intake was designed to work in combination with Thrust Vectoring Control. This feature was never implemented so I believe the canards may be less effective than other aircraft, in terms of performance, (specifically turn/pitch rate).
Am I totally wrong?

The Viggen was the first canard aircraft ever to be built in production quantities. Its close-coupled canard is fixed, with landing flaps being the only movable part. Its purpose is solely to maintain aerodynamic flow over the wing at high angles of attack and thus enhance both manoeuvrability and low-speed handling. Saab were not able to develop movable canard technology in time, nor was it necessary in order to meet the aircraft specification. Nevertheless, getting the darn thing into production after 60 years of failure was a staggering achievement.
The Gripen, Rafale and Typhoon canards are also used to maintain high-alpha airflow. However theirs have an additional function as control canards. Their own angle of incidence can be varied to help control aircraft pitch directly, to contribute to other more subtle manoeuvres, and (at least in the case of the Typhoon) to minimise radar cross-section.
The further forward a control canard is placed, the smaller it need be to provide sufficient control authority, just as a long rear fuselage allows a smaller tailplane. Its only real issue is that it interferes more with pilot visibility, but its smaller relative size minimises that.


What flies better in turbulent wind? I trying to find a way to stay in a jet stream unpowered for a larger question. Is there a glider, kite or plane that flies best when in turbulent weather?

Turbulence is always a nuisance. It will require more control inputs to stay at the desired polar point, which increases drag. Also, small-scale turbulence will cause earlier transition of the boundary layer, which is important for gliders with a laminar airfoil. Powerful turbulence might even overload the airplane's structure.

Jet stream turbulence is low and only becomes noticeable at the boundaries between the fast moving air of the jet stream and calmer air above and below. To stay unpowered in the jet stream is impossible - any unpowered craft will lose altitude due to drag when moving through the air, and even a balloon will be hard to stabilize at the altitude of highest wind speed.

Even a kite is not unpowered - it needs some force acting on the line; either by an airplane flying below or by something holding the end of the line on the ground.

If you want to know what makes turbulence more bearable: Higher wing loading, lower aspect ratio and wing sweep will help. A higher wing loading means higher airspeed, so the relative speed changes from turbulence will become smaller. Both aspect ratio and sweep will reduce the lift curve slope, so changes in angle of attack will result in smaller force changes.


How are spacecraft and aircraft traffic coordinated? From time to time spacecraft cross our atmosphere, either climbing to space or returning from space. While the probability for a collision is tiny, it is certainly not null, especially during reentry, when the trajectory is not vertical and can cover hundreds of kilometers at aircraft altitudes.

Is there any coordination to prevent collisions between spacecraft and aircraft?

A TFR will be issued for the area that the spacecraft is expected to need for safety. Here is an example.

  No pilots may operate an aircraft in the areas covered by this NOTAM (except as described).

No exceptions are described, and the airspace is patrolled (at least for manned launches). As with errant sea vessels, a launch may have to be scrubbed if the safety area is compromised.

The company or agency in charge of the space flight operation would need to contact the FAA to coordinate such a TFR.

For space shuttle landings, Special Use Airspace was established. The shuttle landed in a pretty steep profile, so it only spent a relatively short time in controlled airspace. ATC coordinated directly with NASA while the shuttle was transiting the airspace.


How to calculate TAS and fuel for Diamond DA20-C1? The PoH for the Diamond DA20-C1 is here: http://support.diamond-air.at/fileadmin/uploads/Canada/Tech_Pubs_DA20-C1/AFM/DA202-C1-Rev-28.pdf.
The plane has an MT prop, and the supplement for it is here: https://static1.squarespace.com/static/59b981e8b07869d96fe0c365/t/5e457224a5db6b6a6ce00bc2/1581609513640/DA20+MT+Propeller+Supplement+%283%29.pdf.
I need to calculate fuel consumption and TAS under the following conditions:

8000' pressure altitude (PA)
2600 RPM
-1C OAT

There's two charts in the supplement that I think I need to solve this:

It seems I need to use the first graph to find the density altitude (DA) from the temperature and PA. So for -1C and 8000, the DA appears to be 8000 as well. Looking at the table, this would give me 7.1 GPH and 132 TAS. Is this correct? I'm confused by the "standard temperature" heading in the table.

Your steps are all correct, as is your answer.

I'm confused by the "standard temperature" heading in the table.

Consider this table from your first link:

The column I put in a green box, if it was the only one, then the altitudes would all be density altitudes -- just like the table in the question, with the label "Standard Temperature."


Is an aircraft's maximum landing weight really weight, or is it mass? I'm calculating the lift of a Cessna 172 and I don't understand the numbers given for weight. The maximum landing weight is 2550 pounds which is nearly 1134kg. But does that mean 1134 Newtons (weight) or 1134 kilograms (mass)?

Since weight = mass x gravity, I think the weight of the C172 is in Newtons even though it's written using a unit of mass. Am I correct?

The maximum landing weight given here is actually the mass, not weight.

In general, the various 'weights' given for aircraft are masses, not weights. i.e. they are in kilograms, not Newtons.

This is simply an extension of our everyday usage. As @mins pointed out, if someone asks your weight, you tell your mass (70 kg or whatever), not the weight itself (~686N).


Are there any known instances of airline pilots passing off aerobatics as “turbulence”? Inspired by this Far Side cartoon, which shows the pilots of (presumably) a passenger airliner rolling the plane steeply from side to side, and claiming (to the passengers) that they’re just passing through some turbulence.

Are there any known instances of airline pilots actually doing something like that during revenue flights?  Yes, I am perfectly aware that this would be considered highly unprofessional behaviour, and, as we all know, pilots never behave unprofessionally.

Recent discussion with friends who work or worked for one  major US airline, say they never witnessed such a thing.

One of them points out that on Navy P3 flights, they would do it to newbies. Not often, but sometimes to recalibrate newbies.

With respect to commercial flights, all pointed out that flight attendants are at high risk for injury, and would not tolerate such actions. All it takes is one person getting hurt. A neck injury from an unsecured passenger, or a burn from hot coffee happen often enough on flights with "natural" turbulence.  Creating turbulence could be career ending, and could have civil liability.

The population of pilots I was dining with are all over 45, and tend to be rather risk adverse. One, who has been retired for quite some time (he's in his 80's) says that people joke about it, but in all his experience, he too has never witnessed "pilot induced turbulence."

I have a blow-up of that far-side at my desk, though...


Are ATC radar tracking records and audio recordings considered legally public? In practice, they are simply available online and mostly free.
Alternatively, anyone may purchase an ADS-B receiver to monitor the surrounding air traffic and air-band radio to listen to ATC.

I am wondering if there are regulations, similar to restriction of the use of GPS tracker and phone call recording? Or is it simply assumed that, for public safety, anyone conducting a flight is automatically presumed to volunteer the information of flight path and air conversation to the public?

The FAA is only authorized by congress to regulate FLIGHT, not radio communications.

Radio communications are regulated by the FCC.

Both of these agencies have no power to make laws. They can make only "regulations". In the United States, according to the Constitution, laws can only be made by Congress or the legislatures of the several states.

The position of the FCC is that it is legal for any person to monitor and record any radio transmission that they wish. The only exception to this is listening to private telephone conversations or encrypted military transmissions. The Federal law that prohibits this, explicitly exempts maritime and aeronautical transmissions. This is the language:

  18 USC § 2511 (2)(g.ii.IV) It shall not be unlawful under this chapter
  or chapter 121 of this title for any person to intercept any radio
  communication which is transmitted by any marine or aeronautical
  communications system;

Therefore, by United States federal law it is explicitly allowed and permitted for anyone to monitor and record maritime or aeronautical communications.


Why do non-aerobatic aircraft have a negative G limit? Why do airplane wings have limit load of both positive and negative g's (e.g., the Weedhopper ultralight has a load factor of +5 and -2gs). Why not just have a positive limit load since most airplanes (like the Weedhopper ultralight) don't fly upside down? In particular, why the negative load factors?

You can get negative load factors (g forces) in different ways than just flying upside down:

Change in pitch: When you push on the control column, the pitch will start to decrease. Depending on how fast you do this, the load factor can even become negative from this. Some aircraft do this intentionally to reduce the g force to exactly zero:

(image source: Wikimedia)

By pushing the control column further forwards, you would get negative gs.
Wind gusts: The limiting factor for airliners1 (which rarely do the maneuver described above) is mostly due to wind gusts and up-/downdrafts. This can (for a short amount of time) result in large changes of the load factor, even into negative gs for a strong gust in the vertical direction. When experiencing strong turbulence, the airspeed should be reduced to turbulent air penetration speed (VB), which reduces the impact of the gusts.

  Turbulent Air Penetration

  Severe turbulence should be avoided if at all possible. However, if severe
  turbulence is encountered, use the Severe Turbulence procedure listed in the
  Supplementary Procedures chapter of the FCOM. Turbulent air penetration speeds
  provide high/low speed margins in severe turbulent air.

(Boeing 737 NG FCTM 1.50 General Information)

1 Limits for large aircraft from EASA CS-25:

  (1) The positive limiting load factor
  must not be less than:

  (i) 2.5 g with the EFCS
  functioning in its normal mode and with
  the high-lift devices retracted up to
  VMO/MMO. The positive limiting load
  factor may be gradually reduced down
  to 2.25 g above VMO/MMO.;

  [...]

  (2) The negative limiting load factor
  must be equal to or more negative than:

  (i) -1.0 g with the EFCS
  functioning in its normal mode and with
  the high-lift devices retracted;


How are pilots alerted to the publication of a NOTAM affecting their flight while in-flight? With the length of flights in this day and age, it is possible for an activity to be published in a NOTAM, that NOTAM to be disseminated via the NOTAM system, and the activity to start taking place after a flight whose PIC should have received that NOTAM took off!  Take for instance a by-NOTAM restricted area activation with the minimum 4 hour advance notice, and a 777 whose crew flightplanned through the restricted area based on it being "cold" at the time they briefed their flight, which was oh, another 4 hours before the NOTAM for activating said restricted area was put out.  Keep in mind that the 777 crew took off 2 hours before the restricted area was activated...

How is the flight crew of our hypothetical 777 supposed to find out that the restricted area they were told was cold during their preflight briefing is now hot?  (Of course, this applies to other kinds of NOTAMs as well, some of which can pop up with even less notice; for instance, a mishap-induced runway closure could occur at any time, and a long-haul flight crew would probably rather get that memo before they seek a landing clearance!)

Also, assume this is in US airspace.

In the case of the 777 (or any flight operating on an IFR flight plan) it is ATC's (and the pilot's) responsibility to vector the flight around restricted airspace. In the event of pop-up NOTAM's, ATC will do their best to inform you, especially on an IFR flight plan. The key is you should be talking to somebody, or at least listening in. I have a feeling though that you want a little more...

Flight Information Services (FIS-B) provides weather, text, graphical weather, NOTAMs, ATIS and other information to aircraft in flight over the UAT link. ADS-B (ADS-B Out mandated for all aircraft in controlled airspace by 2020 in the US) will be able to provide similar data to aircraft in flight all the way down to small GA (if they have ADS-B In capabilities, or ADS-B receivers like Stratus).

So the crew of your hypothetical 777 will be notified multiple ways:

ATC will notify them about the need to vector around restricted airspace.
ATC will notify them about the closure of an entire destination airport as filed
NOTAMs will pop up on the FIS-B display in the cockpit
The ATIS or automated information broadcast will be updated to include NOTAM'd airport or runways
Crew will see the FIS-B display when they check destination airport weather/closures enroute
At the very least, ATC will notify the flight on approach ("Airport is currently closed, please continue to the filed alternate" or something like that)

Now, on the flip side let's say that you are a J-3 Cub with no radio humming around to your local uncontrolled field. The field was just closed due to a water buffalo migration and NOTAM'd out of service until the beasts can be removed from the property. You are on a 5 mile final and all the water buffalo are hiding in the woods next to the runway...

If you land you've violated the NOTAM and airport closure. This may warrant a call to your FSDO but you will probably be able to explain that the NOTAM wasn't active or identified prior to departure and they'll let you off (and the next thing you should do is go buy a handheld radio). At the very least you should make a report in the Aviation Safety Reporting System (ASRS) in case somebody raises concerns.

Either way if possible the FAA recommends a 4 hour minimum notification time for closures that can be planned. Why 4 hours? Most GA aircraft have about a 4 hour endurance and most domestic flights are less than 4 hours long. Obviously not everything can be planned, but ATC will work with aircraft in flight to disseminate the information as required.


How can I calculate the speed gain from using multiple STC modifications together? Looking at a parts manufacturer website, they list various STC'd modifications for Mooneys with estimated (cruise?) speed gains for each.

However, I've heard that those gains are not additive. For instance, if you applied three mods with 5mph gain each, the total gain would be less than 15mph.

Is there a way to calculate what the gain should actually be if you applied several at once, assuming the gains listed are accurate when applied in isolation?

Most appear to be aerodynamic improvements (i.e. reducing drag) but a few are engine improvements (i.e. increasing thrust). I'd prefer an answer that addresses both sides in an integrated way, if possible.

Not practically speaking no.  With sufficient engineering data you could perform calculations to come up with a model for what the additive effects would be of the various modifications.

The problem with the aerodynamics to horsepower relationship is that almost all of the basic calculations have exponents.  So a mod that gives you 5 knots over a given 'stock' airspeed will not give you close to the same number at a different higher base airspeed.  So with three 5kt estimated improvements you end up with maybe 5 knots for first mod, 3kt for 2nd, and perhaps 1tk for the 3rd.  Add to that the complexity of really subtle interactions in aerodynamics could mean that one mod may make the other 2 yield no differences in cruise.

Take for example a TBM850 which cruises 300mph on maybe 800hp vs a Cessna 210 at under 200 mph on 300hp vs a piper cub going 100mph on 75hp.

Not apples to apples, but to give a sense of the scale these effects have.


How do friendly stealth planes locate each other? Stealth planes can't be seen (very well) on radar. So one stealth plane should be unable to locate another stealth plane on its radar and vice versa.

So how would one stealth plane locate another, friendly, stealth plane?

The accounts that have been published of F-117 missions indicate that they generally flew single-ship, rather than formation missions, and it seems probable that B-2 aircraft do likewise.  So in a sense, the important question for those aircraft isn't "how do I know where (another stealth aircraft operating nearby) IS," but "how do I ensure that we don't collide with each other," and that's a much easier question.

There are several ways to "deconflict" multiple aircraft operating in relatively close proximity that don't involve seeing or painting each other on radar.  One aircraft operates at one altitude, another operates at a different altitude is one method, while timing over a point (you get to waypoint ABC no later than 19:00:00, and I'll be there no sooner than 19:00:30) is another, and physical separation (you stay west of this longitude line, I stay east) is another.  In practice, all of these can be combined to ensure that "your" mission is deconflicted from "my" mission.

Of note, it isn't only stealth aircraft that will use tactics like this.  Helicopters operating blacked out at night don't have air-to-air radar, and even with NVG's, the ability to see each other isn't reliable enough to plan on "see and avoid" and the "big sky theory" to preclude a mid-air, so they'll use some fairly detailed deconfliction plans incorporating separation in space and time.

More recent stealth aircraft such as the F-22 and F-35 are reported to have datalink capabilities so that they can "see" each other without radar, by means of an encrypted, stealthy broadcast of each aircraft's position and track.  This would allow multiple aircraft to fly in formation (not close formation, but perhaps 1000' or more apart), and to work with other aircraft equipped with the same datalink, so even though the bad guys would only be able to see the non-stealth aircraft on radar, the friendlies could all see each other.


What are the differences between fuel types (comparing with vehicles)? I find it funny that at gas stations, generally you can purchase "regular" gasoline (in various octane levels) or diesel. At airports, generally you can purchase 100LL avgas or Jet-A.

Can you compare diesel to Jet-A, and "regular" gasoline to avgas? If so, what are the differences? Why are there only two classes of fuel - are there others that I don't know about?

Broadly speaking, there are three families of motor fuel that you're probably interested in: Diesels, Kerosenes, and Gasolines.
The difference between the families mainly has to do with the molecular weight (and thus boiling point / vapor pressure) of the fuel components - in order above from heaviest to lightest. The differences within each family are related to refining, blending, and additives, as well as process controls imposed on the fuel.

The Diesel Family

In the diesel family we have things like Highway Diesel and the various grades of home heating oil.

For transportation purposes these fuels are used in compression-ignition engines ("diesel engines"), where a high temperature and pressure will cause the fuel to ignite and burn, producing power.
For other purposes (like heating) we basically light the stuff on fire and are happy it burns.

The Kerosene Family

The Kerosene family are close cousins of the Diesels, including K-1 and K-2 Kerosene (obviously) and Jet-A.

Jet-A is a high-purity kerosene based fuel manufactured under a specific ASTM standard (D1655), with specific physical properties, and is used in jet turbine engines.  Fuel not meeting the Jet-A specification is generally recycled in the production chain for other purposes (for example it may be used in blending kerosene for heating, or blended into highway diesel).

Jet-A is suited for turbine engines, but can also be burned in other compression-ignition piston engines like diesel can (there are a wide variety of aerodiesel engines available from several manufacturers).

Other grades of Kerosene are used for motor fuels, cooking fuel ("camp stove fuel" is typically kerosene) heating, lighting, etc. depending on their refining and purity.

The Gasoline Family

In the gasoline family we have Avgas, Autogas, and "Gasohol", all designed for use in spark-ignition engines.

Aviation Gasoline (Avgas)

Avgas actually comes in several grades, all manufactured to an ASTM standard (D910), with specific physical properties and specific permitted and required additives (such as Tetra-Ethyl Lead - TEL).

The grade (octane rating) of aviation gasoline is identified by colored dyes added to the blend.
The colors used in the US are:

Green: AvGas 100 (100/130 Octane)
Blue: AvGas 100LL (100/130 Octane)
(This was formulated as a replacement for AvGas 100, with half the lead - hence 100LL - Low Lead)
Red: AvGas 80 (80/87 Octane)

Generally 100LL is the most widely available aviation fuel because it works in the widest range of engines.

Autogas (automotive gasoline)

Automotive gasoline comes in multiple octane grades, but generally it's all varying blends of "regular" (87 octane) and "premium" (93 octane or higher).
Automotive gasoline is manufactured under a different ASTM standard from Aviation gasoline (there are several applicable standards, D4814 is commonly used), which permits different additives including ethanol (usually up to 10%).

"Gasohol"

Gasohol is a slang term for automotive gasoline with any amount of ethanol blended into it, but these days it's often used to refer to blends like E85 (85% Ethanol, 15% gasoline stock).
Flex-fuel car engines and a few other specialty engines are designed to burn this fuel.

So what's the difference?

Why don't we burn highway diesel or heating kerosene in a 747?
In a word, purity. The additional controls imposed on Jet-A fuel by the associated standard produce a product with well-known properties. When you fuel a plane with Jet-A you can be confident that fuel won't freeze in the tanks at altitude (at least not unless you cold-soak it below -40 degrees). You also know the fuel will be "clean" and won't gunk up fuel filters or leave deposits inside the combustion core of the engine that can cause problems later.

On the other hand we don't burn Jet-A in a Mack Truck because it would be prohibitively expensive: Highway diesel doesn't have to meet the same strict tolerances as jet fuel, and theres no reason to burn a more tightly specified (and thus more expensive) fuel when a less expensive one is readily available.

The difference between Aviation Gasoline and Automotive Gasoline is a bit more subtle: the core blend stocks are extremely similar, but the additive packages are very different.

The biggest concern for aviation users is usually the ethanol commonly blended into automotive gasoline: Rubber components in aircraft fuel systems were not designed to handle alcohols, and can be damaged/degraded by ethanol.

For cars the concern is the lead found in aviation gasoline. Any "modern" car (with a catalytic converter and oxygen sensors in the exhaust system) can't burn leaded fuel as the lead byproducts in the exhaust will foul both the catalyst matrix and the oxygen sensors (though a 1950s Plymouth Belvedere would have no trouble burning the stuff).

Work on an unleaded aviation fuel is ongoing - theoretically the fuel that comes out of that process could be equally suitable as a road fuel and an aviation fuel, however the chances of it making its way to your corner gas station are relatively slim, except possibly as a blend stock from batches that don't meet the final specification for a 100-octane unleaded aviation fuel, but are suitable for recycling into automotive gasoline blends.


Is the quickest way to reverse direction by turning horizontally or vertically? Assume my aircraft is flying with Mach 2 and I want to quickly change my direction of travel 180°.

So for a horizontal turn flight I found the formula: angular velocity = g* sqrt(n²-1) / v
For a looping flight I found the formula: angular velocity = g* (n-1) / v

So for the same load factor n my aircraft should do a faster turn with maneuver number 1. Since my angular velocity is higher.
Are my considerations right?
Also, according to both formulas above the ability to do a quick turn around is (let us neglect velocity) only affected by load factor. So my LIFT FORCE (no matter where it acts on my aircraft) is the limiting factor, nothing else. Is that correct? (And lift force is limited for many other reasons...)
Because I had the considerations: if I let the lift force act far away from the center of gravity, I will get a big lever arm and this way a big moment which should create a higher angular velocity. So lift should not be responsible for a quick turn but the lever arm?

The formulae appear correct, as far as they go. But there are some problems with the underlying assumption of the question; specifically, that you can achieve either condition in a steady-state fashion.
Firstly, and most importantly, you can see looking at both formulae, the most significant thing you can do to improve your turn rate (angular velocity) is to slow down. This also has a significant effect on the turn radius as well. Since the scenarios where one cares about maximum performance turn rate often also involve a need to avoid an obstacle (cumulonimbus, cumulogranite, etc.), minimizing the turn radius can be just as important as maximizing turn rate, and both can be accomplished by drastically reducing speed.
Conveniently, one of the things that makes it difficult to compare the two scenarios is the fact that the moment you begin the turn, the increased load factor will cause an increase in drag, which will help reduce the speed. The speed reduction (which may be aided by judicious reduction of power) can dramatically improve turn performance, but this reduction will depend on exactly how that turn is made. It may even involve an increase in speed, if attempting the looping turn by performing a split-S.
Importantly, you are trying to compare apples-to-apples by keeping the load factor identical in both scenarios, but I don't find that a plausible assumption. It's not too hard to maintain a constant load factor during a level turn, but a looping turn is likely going to involve either increasing-then-decreasing, or decreasing-then-increasing load factor, making the assumption of load factor being the same in both scenarios unreasonable. And in either case, the speed will be changing by a large amount, eliminating the possibility of using those formulae in an apples-to-apples manner.
Finally, there is the issue that many planes cannot be safely looped, and even among those that can, you may not be able to initiate a loop (Immelmann or split-S) from cruise speed. You have set the assumption that you are cruising at Mach 2, which seems to be an attempt to address this concern. But it raises new ones: even an airplane capable of traveling at Mach 2, may only be able to fly that speed when at altitude, and at an angle-of-attack close to its critical angle of attack, making an Immelmann loop impractical, if not impossible. Similarly, it does not seem likely that one could safely accomplish a split-S that is initiated at Mach 2. The altitude loss incurred could easily exceed the altitude the airplane is starting the turn at, and even if not, the increased airspeed from Mach 2, as well as the G load required at the bottom of the loop, could easily exceed the airplane's structural limits (or the pilot's!).
The conclusion of your question is particularly confusing:

my LIFT FORCE (no matter where it acts on my aircraft) is the limiting factor, nothing else. Is that correct?

and

lift should not be responsible for a quick turn but the lever arm?

Indeed, during a level turn, with a large enough bank angle, one can improve turn performance at the expense of added drag and reduced speed by pulling on the elevator, i.e. adding nose-up elevator input.
But I'm not sure that's what you're asking. It sounds like maybe you're wondering about using lift to modify the attitude of the airplane. If so, that's not how it works. While it's true (for a conventional airplane configuration) that whether in level flight or not, the pitch of the airplane, controlled by the elevator input, changes around the center of gravity, it's important to keep in mind that the center of gravity in unaccelerated flight is directly below the center of lift, since the elevator has effectively added weight, shifting the CG rearward.
I.e. there's no "lever arm" related to any distance between center of gravity and center of lift.
But more to the point, changing the attitude of the airplane isn't the same as changing the flight direction of the airplane. Taking this to its extreme, you can imagine an airplane that could somehow yaw 180 degrees instantaneously. Such an airplane would not effect a 180 degree turn instantaneously; instead, it would just wind up flying the same direction it had already been going, just backwards.
The bottom line: the formulae you're using do not appear to be amenable to an apples-to-apples comparison, so the academic line of reason doesn't seem resolvable. And in the practical sense, if you're going Mach 2 and actually need a maximum performance turn, one of the first things you need to do is slow down. It is most likely safest and most practical to accomplish this in a level turn, or possibly some combination of bank and climb (e.g. like a chandelle). Either way, it's likely the main limiting factor will be the maximum load factor that the airplane and pilot are capable of sustaining.
I don't think it's possible, given only and based solely on the formulae and conditions stated in your post, to determine whether it's always true that a level turn or either type of looping turn is going to produce the maximum rate of turn, first and foremost because you're never going to keep the velocity term in the formulae constant, but for other reasons as well.


What were the "flap pump" and "gear pump" on the F-4E Phantom II? When I choose the F-4 in X-Plane 8 there are "buttons" labeled "flap pump" and "gear pump", whose tooltips say something like:

  Manually operating and closing flaps/pumps in a failure

So

How did pilots operate these hand pumps? Video is appreciated.
How much "pumping" was needed to open and close the landing gear?
How much "pumping" was needed to move flaps a single unit?
Did you need to be powerful in order to operate these hand pumps?
How did these pumps work?

There is no "Flap Pump" or "Gear pump". There is a hydraulic system on the F4 though. All those systems need hydraulic power. They run on hydraulics.


What causes the phase to change in a VOR? I get the light house analogy, and how the VOR essentially works, although I'm wondering what actually causes this phase shift? As it hits magnetic north the variable and reference signal are in phase, as it continues it begins to go out of phase. What's causing it to go out of phase? Is it using constant frequency modulation, where both are being constantly modulated, and at a certain point they both hit the same frequency for a second?

The latest decades VOR are Doppler VOR (DVOR) where the bearing signal is produced by a 14 m diameter circular array of fixed Alford loops antennas. An additional central antenna radiates the reference signal.

Thales Doppler VOR 432, source
DVOR is an improvement of the conventional VOR (CVOR) where the bearing signal is encoded by frequency modulation, more reliable than amplitude modulation used in the CVOR. FM is not produced in the station itself, it is a Doppler artifact created by the apparent displacement of the bearing signal source relatively to the receiver.
DVOR principle
The so-called dual sideband DVOR uses one pair of diametrically opposed antennas from the array at a time, switching to the next pair counter-clockwise at the angular speed of 30 revolutions per second (30 Hz, 1,800 rpm).

One antenna radiates an unmodulated signal at $\small f - 9.96$ kHz ($\small f$ being the frequency of the VOR)

The opposite one radiates at $\small f + 9.96$ kHz.

The receiver sees the two constant frequency sources moving along the circle, one approaching, one moving away. Because they move relatively to the receiver, their frequency is altered by a Doppler shift proportional to the relative velocity.

Doppler shift on the DVOR sidebands antennas
For the receiver, the observed signal frequency is increased for the approaching antenna and decreased for the retreating antenna. By chance for engineers, the Doppler shift applies in opposite quantity on the antennas, and the frequency remains mirrored relatively to the carrier frequency $\small f$ whatever the shift.
At the same time the central antenna radiates a carrier at frequency $\small f$, modulated in AM by the reference signal. This AM signal is not subject to the Doppler shift, as the signal source is fixed.
For the receiver the signal from the central antenna and the two signals from the rotating antennas appear as the three components of single HF signal of frequency $\small f$, modulated in amplitude at 30 Hz (by the reference) and a subcarrier at 9.96 kHz, itself modulated in frequency at 30 Hz (by the variable signal). This signal is therefore entirely compatible with one from a CVOR.
The Doppler shift depends only on the receiver relative bearing
While the timing of the reference is imposed by the VOR, the timing of the subcarrier modulation depends entirely on the aircraft position. E.g. the Doppler shift is null when the axis of the antenna pair is aligned with the aircraft direction, and both antennas move only from left to right from a receiver standpoint:

Doppler shift is null when the receiver is aligned with both antennas</sup
Similarly, and when the distance of the receiver is large compared to the array diameter, the maximum shift is observed when the antenna pair is perpendicular to the previous position (in practical the parallax error can be ignored).
Therefore the delay between the reference and the variable signal is representative of the bearing. Periodic signal phases are actually angles between 0 and 360°, so the bearing is determined at any time by subtracting the current phase of the FM variable signal from the current phase of the AM reference using a phase detector.

Phase of a sine signal
Note the receiver works only by comparison of the phases, their actual values is irrelevant, only the difference is meaningful. If that were not the case, the DVOR wouldn't be compatible with a CVOR receiver.
The CVOR also relies on the phase difference. It works by forming a rotating directional cardioid pattern by space modulation. The result of this modulation faces north when the variable signal which electronically steers the pattern has the value 135°. So the reference was aligned on this value and given the value of 135° for north (in the DVOR north is associated with the reference value 0°).
The diameter of the array gives the variable signal phase its correct value
The tangential velocity when moving along the perimeter of a circle is $\small v = \pi d \times rpm$. Applied to our array: $\small v = \pi \times 14 \times 30 \approx 1,320$. The relative tangential velocity of the sideband antennas is between -1,320 m/s and +1,320 m/s. The value of the Doppler shift for a given velocity is: $\small s = v \cdot f / c$. Applied to a frequency of 110 MHz, the Doppler shift is $\small 1.32e3 \times 1.1e8 / 3e11 = 484$, that is between about -484 Hz and +484 Hz. The exact diameter of the array is actually a bit less, in order to obtain the FM swing of the conventional VOR (480 Hz). This way the DVOR signal can be received by a CVOR receiver (there is no specific DVOR receiver).
As explained earlier, this shift is not encoded by the VOR into the variable signal but added by the Doppler effect in space. However the receiver sees the result and interprets it has if it had been generated by the VOR.
When the never modulated FM subcarrier is nevertheless processed by the receiver demodulator, it produces a 30 Hz sine which phase varies according to the Doppler shift which produced it, therefore depending on the correct diameter of the array.
VOR frequency spectrum
The receiver sees:

A signal at frequency $\small f$, AM modulated by the 30 Hz reference

A signal at $\small f - 9.96$ kHz, FM modulated by a 30 Hz sine (1,800 rpm).

A signal at $\small f + 9.96$ kHz, FM modulated by a 30 Hz sine but with the opposite shift.

It just decides those three signals are components of a single one from a single antenna: The first signal is the carrier, and the two other are sidebands.
It composites the whole thing this way:

This is a carrier of frequency $\small f$, modulated in AM by a 30 Hz signal (reference),

This carrier is also AM modulated by a subcarrier at 9.96 kHz.

The subcarrier is itself FM modulated by a 30 Hz signal (variable) with a modulation swing of 480 Hz.

VOR signal spectrum


How much does it cost to ground a B737 max aircraft for an airline? What are the cost items for which an operator with such an aircraft in the fleet incurs per aircraft because of the grounding of the Boeing 737 max aircrafts and how much is the average cost incurred?

Is there any possibility of claiming the losses by the airline companies from the Boeing company?

Well we can look at another grounding case to see what it costs.

Boeing grounded the 787 Dreamliner. This grounding lasted about 90 days (at least as of the estimated costs by ANA, I think the actual grounding lasted about 116 days).

Japanese carrier ANA had the largest 787 fleet at the time with 17 of the 51 in operation estimated it's costs at $15 million.

Doing some simple math, \$15,000,000 for 17 aircraft works out to be about \$882,352 per aircraft for the 90 day grounding. This is about $9,800 per day/aircraft.

They also estimated that this resulted in ¥1.4 billion in lost revenue. This is \$12.7m USD (in today's dollars). That gives a lost revenue of about $3320 per seat, per day (averaging 250 seats per aircraft).

Now taking into account that there are 393 737 MAX aircraft as of the grounding, with an average seating of around 190 passengers, this could cost airlines significantly. Just in terms of costs, extrapolating the 787 numbers and assuming they are grounded for 6 months, looking at about half a billion dollars (*assuming the costs for grounding the 737 are 75% of the 787 in terms of storage and maintenance) for the entire industry.

In terms of lost passenger revenue, we can assume the numbers are about on par with the 787 since it is a more heavily utilized aircraft (shorter routes, more flights/day). Using the same 787 numbers we would be looking at about $44.6 billion dollars, again, industry wide (and yes, this number seems extremely high to me, but working from what ANA claims).

Can they claim this cost for Boeing? Maybe. They may be able to recover the costs of storing and maintaining the aircraft during the grounding. It is unlikely that they would be able to recover the lost revenue (and it would put Boeing out of business to do so). We'll have to see when this all washes out what the airlines do with Boeing. Most likely they will negotiate deals with Boeing for preferential pricing on future aircraft or some other kind of cost-offsetting deal.


Where is the F-4 Phantom II's flap lever? I'm trying to fly this fighter for the first time in X-Plane 11 but I can't seem to find the flap lever in the cockpit. Where is it on the real plane?

(flickr.com)

On a real F-4 it's the flap-shaped switch on the left console aft and left of the thrust levers. Also here is the cockpit items poster (see item no. 5 on the left).


Can anyone explain why and how flames shot out of an F/A-18 as it crashed? Can anyone explain why and how flames have shot out of the left engine of this F/A-18, whose left engine was apparently not generating power, the picture is here. And the source website where I got the infomation from is here.
The accident happened in Lethbridge, Canada in the July of 2010. Below is a comment posted on the forum in response to the post of the crash on ED forums:

  It was a fuel control problem (sticky piston) on the right engine, isn't #1 the left? The open nozzle of the left engine indicates that it's either a) at idle or b) at full power/burner which it was in this case as the pilot was executing a high alpha pass at the time.

The comment about the left engine not hasving power is here:

  The left engine has the nozzle fully open, showing that #1 engine was developing no power.

Fuel has to reach the engine to make it work, so there is a path (pipes) available for the fuel to get from the tanks into the engines.

Looking (*) at the video linked by Pierre Chevallier it looks like some fuel got pressed out of the tanks, into the engine(s) and out the engine nozzle, and in the process it got ignited.

I cannot say why the fuel got only in one engine, I can guess that the valves on the fuel lines were in different positions.

(*) I suggest using the option to visualize at x0.25 speed, starting at the 0:30 mark


What are maximum G forces humans can survive? I read that very high g forces could kill a pilot, brain pushing into the skull.

Is there a way of decreasing or surviving these forces and how would it work if you ignore aircraft capabilities.

If not what is the maximum survivable g force with current technology.

I read that very high g forces could kill a pilot, brain pushing into
  the skull.

High G-Forces cause blood flow to the brain to be impeded due to blood pooling low in the body under high acceleration. This causes the pilot to black out eventually.

  Is there a way of decreasing or surviving these forces and how would
  it work if you ignore aircraft capabilities.

Yes, most if not all modern fighter pilots wear G-Suits. The basic principal of operation is to constrict blood flow to the lower body to prevent pooling in a high G maneuver to increase blood flow to the brain. The g-suit typically buys the pilot about 1G of increased tolerance. The average human tolerance is between 3G and 5G. Aside from possibly some aerobatic planes I dont know of any civilian or commercial aircraft equipped with G-Suits. Generally speaking good heart health can help mitigate the effects in sustained G situations. This why it is so vital that fighter pilots be in top physical shape as fighter planes are capable of very high G maneuvers.

You can decrease the overall G-Force experienced by altering your maneuver (i.e. not undergoing as much acceleration). However in a combat situation some high G maneuvers may be warranted and thus the suits are used. In civilian flying all deliberate maneuvers are well within human limits.

  If not what is the maximum survivable g force with current
  technology.

This depends on the exposure time to the G-Force, see this question/answer.


Do pilots use electronic checklists? I read that pilots often use printed checklists.

Is this a legal requirement, or are there also electronic versions available?

Yes they do, and according to the FAA they're better than paper ones. All sorts of aircraft can have electronic checklists, from large airliners to small Cessnas: modern avionics like the G1000 support checklists and the older but very common GNS430 does too.

In the US at least there's no legal requirement to use checklists in any form - electronic or paper - with some caveats:

They're considered a fundamental best practice in aviation, so if you don't use them then someone could argue that you're acting carelessly or recklessly
Incorrect - especially missing or incomplete - checklist use has been linked to many accidents (see this question too) so clearly it's in your own best interests to use them properly
If you're flying for an airline then your OpSpec probably requires use of checklists, in which case they're mandatory

As for mobile devices, there are already many EFB applications and standalone apps that support checklists. In some cases the app provides a template for a specific aircraft type, in others you have to enter it all yourself. There may be some copyright considerations, but third-party checklists are very widely available so obviously it isn't a huge issue.

Finally, it's worth noting that many pilots - especially those who own their own aircraft - customize checklists for their own needs.


Would an airliner fly more efficiently on a fatter wing at a low altitude? Flying at 1000 ft, would giving an airliner wing more girth but not length, allow the plane to fly more efficiently than it normally would at that height?
Yes, airliners fly best around 35,000 ft, but if it was restricted to fly at 1000 ft., what would be the best shape wing for it?

Silly comments aside, "fat" wings, ones with greater camber, were all the rage 100 years ago when designers found they could eliminate draggy external bracing by building cantilever wings.  Hugo Junkers was one of these pioneers.
Wind tunnel testing also showed increased camber not only increased lifting efficiency, but also, combined with large, rounded leading edges, produced very benign stalling characteristics.  One result of this research, the Fokker D.VII., so terrified opposing pilots that it was specifically banned after the end of the "Great War".
Heavily cambered wing design such as the Davis wing lived on until aircraft began pushing the limits of the "sound barrier".  Aircraft fly higher to get more speed with the same amount of drag, and this works great until the wing approaches its critical Mach number.  Above this, drag greatly increases, ending the reign of the "fat wing".
Modern "super critical" wings, literally "surf" the slower bottom airflow, leaving the top of the wing as flat as possible.  This is what airliners use at 35,000 feet.
But at 1000 feet, where airspeed is limited to 250 knots, the "fat wing" makes a comeback by deploying slats and some flap.  For a given wing area and Angle of Attack, the "thin wing" is only more efficient when Critical Mach Number is approached.
This is why many airliners have a never exceed speed for lower altitudes, and a Mach limit for higher altitudes.


Is there a list of directs and preferred routes within USA airspace? In Europe it is possible to find a list of directs which are contained in the Appendix 4 of the Route Availability Document from the Eurocontrol website.

My goal is to find the analogous information for the US airspace. I tried to look in the FAA website but without success.
Can you please tell me a way to achieve my goal?

In the US, the National Flight Data Center (NFDC) publishes a database of preferred routes.  You can query it or download the entire database.

Here is the result of entering only BWI to PHX:

A practical resource for planning a real flight is to review the routes of previous flights.  I browse the origin and destinations, or nearby airports to my flight and select a similar aircraft to which I am flying. On FlightAware, the route is shown in the lower right.  Here's an example:


What is that CFM56 with a toothed exhaust on an A321? I stumbled upon a wikimedia picture and I saw something that I have not seen before: a CFM56 with a toothed engine exhaust. Can someone explain to me what engine variant that is?

Source Author: Konstantin Nikiforov CC-BY-SA-3.0

The “toothed” exhaust are called Chevrons and they reduce noise. They are an option on CFM56 equipped A321 aircraft.

Wikipedia CFM International CFM56

”GE and Snecma also tested the effectiveness of chevrons on reducing jet noise. After examining configurations in the wind tunnel, CFMI chose to flight-test chevrons built into the core exhaust nozzle. The chevrons reduced jet noise by 1.3 perceived loudness decibels during takeoff conditions, and are now offered as an option with the CFM56 for the Airbus A321”


VORTAC symbol over KMOT airport - is the small dot the center? I am looking at KMOT and I see a little dot over the airport symbol, is that the center of the VORTAC?

The dot in the center of the star means that there is a rotating beacon available on the airport from sunset to sunrise.

See the FAA Aeronautical Chart Users Guide Page 8.

The actual center of the VORTAC is the small dot between the runways:

Which you can find the description of in the chart users guide on page 8 as well:


Are landings easier during the day or at night? When is it easier for a pilot to perform a "good" touchdown: during daytime or nighttime?

Considering typical flights for 737s to holiday destinations so mostly small airports with a single runway.

In the above, "good" is defined as a firm landing with both rear wheels simultaneously on the ground.

During the night the runway is brightly lit and all the guiding lights are clearly visible, but the actual tarmac is more difficult to spot. During the day there is flare from the sun and the lights are less visible but on the other hand the tarmac is clearly visible.

I'm going to answer this in somewhat of a more general sense but first let's clear up a few things.

  During the night the runway is brightly lit and all the guiding lights
  are clearly visible, but the actual tarmac is more difficult to spot.

This is not always the case. Maybe at large international airports the runway is quite well lit with lots of extra lights, but there are plenty of airports in the US that are poorly lit (granted not all of them service commercial traffic); it's worth noting that not all runways are well lit. Runway lighting varies quite a bit as well.

  During the day there is flare from the sun

Only if the sun is right in front of you, there are lots of runway directions and you may often land with the sun behind you.

  ...and the lights are less visible but on the other hand the tarmac is clearly visible.

The lights are not visible at all, they are off, but yes the tarmac is easy to see during the day.

A "good" landing by a proficient pilot should not be greatly affected by day or night conditions. What will affect a landing is the prevailing wind and weather conditions. Generally speaking wind (and thermal activity) dies down at night so the air is far more calm. In my experience night landings are smoother because of this. During a hot summer day, even in super clear weather, with the wind whipping and the clouds kicking thermals around you are bound to have a "fun" approach.
(from the FAA's handbook on night operations)

  Night approaches and landings do have some advantages over daytime
  approaches, as the air is generally smoother and the disruptive
  effects of turbulence and excessive crosswinds are often absent

More recently LED light technology has allowed some extremely bright landing lights to be installed on even the smallest of aircraft, this has greatly increased pilot visibility on short final at night.


Calculate parasite drag coefficient from drag polar The drag polar of an electric-powered unmanned aircraft is

$$ C_D = 0.038 + 0.0458 C_L^2 $$

What is the parasite drag coefficient?

Well, $C_D = C_{D,0} + k_1 C_L^2 + k_2 C_L$ according to Brandt et al's "Introduction to Aeronautics: A Design Perspective," so the parasite drag coefficient is $C_{D,0}$ or 0.038.

(Also, $k_1 = 0.0458$ and $k_2 = 0$.)


Would jet fuel for an F-16 or F-35 be producible during WW2? I understand that different types of engines use different types of fuel, and as the description of the [jet] tag says, turboprops and jet engines use different types of fuel.

So if – like in the works of fiction The Final Countdown and 1632 – modern aircraft did find themselves in 1940, which aircraft would you readily be able to find fuel for? And which would you have to (re)develop the fuel for?

Let's take the following aircraft as examples:

AH-64 Apache gunship
Airbus EC 135 P2e
AgustaWestland AW101
Boeing 747 (whatever variant is most prolific today)
Lockheed C-130 Hercules
General Dynamics F-16 Fighting Falcon
Lockheed Martin F-35 Lightning II
Bombardier Dash 8

My assumption is that even the turboprops will not be able to use the aviation fuel available.

Which aircraft could have been fuelled "locally" first? And will any fly with 1940 aviation fuel, maybe with an additive?

Jet fuel is mostly kerosene, with some aromatic hydrocarbons mixed in for stability, temperature range and the like. You could probably run military jets on pure kerosene if they were magically transported back to WWII, but you wouldn't have to as it would have been possible to make reasonable jet fuel. The Jet-A standard was made in the 50s, and there were no major differences in the fractions available from WWII.

Before it was an engine fuel kerosene was primarily used for heating and lighting, and it was widely used across the world for that purpose in WWII. It still is in some places around the world where electricity isn't available. The aromatics in jet fuel aren't anything special, so it would have been entirely possible to make a jet fuel.

You could go farther back than WWII and still run a jet on raw kerosene as the modern process to distill it from petroleum was invented in the 1850s.


Why does the stick force per-g test require it to be harder for pilots to pull back on the yoke instead of easier? What happens when it’s easier to pull back banked at such steep angles, wouldn’t it be a good thing that a pilot can maintain his altitude easier than harde?

No because if stick force per G is too low, when maneuvering it becomes too easy to pull a lot of G and that's bad. It's like having power brakes in your car that don't build up more resistance in the pedal the harder you brake; it becomes difficult to regulate braking effort and too easy to lock the brakes (assuming no ABS).   Like with brakes, it's desirable to have the stick force build smoothly  with G force, because this provides good tactile feed back that helps you regulate how hard to pull.

If the force gradient is too shallow, too little effort is required to pull G and if above maneuvering speed it becomes too easy to pull the wings off by yanking on the stick too hard, and if below maneuvering speed, too easy to enter an accelerated stall while maneuvering.

It's an interesting point you brought up because there is a very popular 2-place cabin homebuilt airplane called the Wittman Tailwind, that's been around since the 50s. A very speedy, efficient airplane, designed by a famous air racer.  It has a very shallow stick force gradient, which builds to only about 5 lbs at limit load (I'm recalling from an article from the 80s).  This means if you are above maneuvering speed, it only takes a 6 or 7 pound pull on the stick to possibly pull the wings off, or at minimum bend something.  Wittman designed in the shallow force gradient on purpose because he was a pylon racer and really liked very light controls including pitch, more or less for similar reasons as you described.

However the Tailwind is not for the ham-fisted.  A pilot that is used to the airplane and had a light touch would be fine with it and would enjoy the very low stick forces, but for someone not adapted to it, it's dangerous.  Most airplanes have stick forces that build to 20-40 pounds or more, but you are never pulling that force in anything but aerobatic maneuvers.  Most normal maneuvering requires a 5 or 10 pound pull, and you're only holding it for a short time.

Transport airplanes with hydraulic controls get their stick force gradients by artificial feel devices that mimic the feedback forces that you would feel from airloads if the controls were manual, with loads that increase with speed and G.  I dimly recall that on the CRJ airliners the feel force for pitch was limited to 50 lbs and I believe most transport airplanes are similar.


Why don't aircraft use gimbaled engines instead of flaps? Why do aircraft use flaps rather than vectoring the engine or angling the engine?

Elon Musk said he would gimbal the engine like a rocket with the aim of reducing total weight of the aircraft and thus increasing its range.

  Aircraft have all these unnecessary things like tails and rudders and elevators - not needed. Just gimbal.. anyway.. gimbal the electric fan. For some weird reason gimbaling motors is normal in rockets and not in aircraft. Why not.— Elon Musk (YouTube)

Historically, flaps and control surfaces were moved manually: The pilot would move a stick, a control column or pedals, and pulleys or pushrods would transfer this force to the control surfaces. To do this with engines was physically impossible.

With the introduction of hydraulics, large enough forces for tilting engines were available for the first time. Some aircraft used them, but this application did not find widespread use because the possible lift increase was smaller than what could be achieved with flaps. The same goes for controlling the aircraft: Directed thrust control forces are much smaller than what was possible already with control surfaces. Also, the responsiveness of tilting a heavy engine is much worse that that of a light control surface. Consequently, moveable engines were mostly used for short take-off and landing (STOL) applications. The Do-29 was one of several experimental aircraft which could pivot the propellers to take off at lower speed. Note that in case of the Do-29 the engines stayed in place; only the propellers and their driveshafts would move. Other designs would tilt their wing and with it the wing-mounted engines. In all those cases this was only done to enable short take-off runs, not to control the aircraft.

Do-29 in the Dornier museum (picture source)

Other applications were for special cases like flying boats:

The Dornier Do-26 could tilt the rear engines up for operation on water to reduce the impact of spray on the propellers (picture source). Note that this was not for control, but for lifting the props out of the spray area.

Control surfaces are better suited for creating control moments:

Control surfaces sit at the ends of the aircraft, so they have a much better leverage. Engines were placed close to the center to minimize the control problems caused by a loss of a single engine.
Control surfaces modify the lift force, whereas engines modify thrust, which is in the order of magnitude of drag and, consequently, an order of magnitude smaller than lift.

However, this is only true as long as aerodynamics works in a linear fashion. Which is not the case with separated flow and stalled flight surfaces. To overcome this limitation, the exhaust stream of jet engines is deflected by pivoting the nozzle (or paddles, as done on the X-31). This is much easier to do than to move the whole engine. Also, since the engine stays aligned with the airframe, the intake will continue to work and the frontal area of the airplane does not increase; both important considerations which stand against pivoting the whole engine.

Vectoring nozzles on the Sukhoi 35 (picture source)

Generally, aircraft are controlled by changing moments which in turn rotate the aircraft such that the desired flightpath change is effected by the changed aerodynamic forces. There have been attempts at direct force control, however: One Dassault-Dornier Alpha Jet was fitted with moveable wing pylons which could be rotated around a vertical axis. When moved, this would create a side force which enabled the pilot to directly shift the aircraft's flight path sideways. With moment control, you first need to roll the aircraft in order to tilt the lift vector sideways and then roll back shortly before the desired sideways change is complete. This is much harder to get right with moment control than with direct force control, especially for small corrections.


Is there a good resource for ACARS messages? Is there a good place to find out all the types of data that ACARS can send and receive? I've seen high level descriptions, but I'm looking for the data that actually gets fed from or to the Flight Management System.

Unfortunately the term ACARS is one of the most misunderstood and misused terms in aviation. ACARS - Aircraft Communications Addressing and Reporting System - was created as an end-to-end datalink between aircraft and the airline dispatchers. It provided basic text data using the ARINC Specification 618-8. (Unfortunately not free.)

As datalink functionality has grown, ACARS has been modified and patched and added to to support these new functions. What is defined in A618 is now classified in the datalink world as AOC - Airline Operational Communications. AOC messages can be found in ARINC 633-3.

The issue with that is that it is communicating with the dispatcher not ATC. That falls under the title ATS - Air Traffic Services. Early versions of this will be found in ARINC 623-3. That has mostly been replaced by newer applications defined in ARINC 622-5 which supports bit-oriented protocol (over the older character based protocols.)

In the last 20 years or so, there has been a plan to provide ATS globally. The European industry which wasn't tied as closely to the ARINC systems as the US took a more more clean sheet approach referred to as ATN - Aircraft Telecommunications Network which isn't interoperable with the ARINC standards. So the industry now supports a mix of infrastructure. As it has moved towards global capability, the standards are migrating into the ICAO ecosystem.

So the best reference available to find answers to almost any aviation datalink related question is the Global Operational Data Link Document (GOLD) published by ICAO.


When are the engine bleed air, APU and packs turned on in the B737? When do I have to turn on the engine bleed air and APU? In videos I have seen that they are always on, and sometimes they turn them off after take-off. I also have the same question about the packs.

The general answer is, the engine bleeds stay on almost all the time.

The times they're turned off:

For a bleeds-off takeoff to get more power from the engines.
During deicing on the ground, so that deicing fluid doesn't get in the bleed air system.
When you are using the APU bleed air, the #1 engine bleed switch needs to be off IF that engine is running above idle power. If you're using APU bleed air & the isolation valve is open, the #2 engine bleed switch also needs to be off (if that engine is running above idle power).

The reason for the last requirement is because the engines, running above idle, put out greater bleed air pressure than the APU does, and you want to avoid the situation where the failure of a check-valve could put high pressure bleed air into the APU -- back-pressuring the APU, which could cause serious damage.

That scenario plays out if you're using the APU to run the cabin air conditioning (typically, on a hot day with lots of passengers), since it puts out a greater volume of bleed air than the engines do when they're operating at or near idle (i.e. typical taxi power settings). In that case, you close the engine bleeds, open the APU bleed and the isolation valve, and let the APU run both packs.

That scenario also plays out when starting an engine while taxiing; the switchology is reasonably intuitive but a little lengthy to describe.

There is no need when starting the engines initially to close the engine bleeds, since the normal procedure is to close the APU bleed & turn it off before taxiing the aircraft.

For a bleeds-off takeoff, the configuration is, engine bleeds off, APU bleed on, packs on, isolation valve closed. After takeoff, the steps are, #2 bleed on, pause, APU bleed off, pause, #1 bleed on, then isolation valve to Auto.

There is a procedure for a bleeds-off landing (to get more engine power for a go-around), and there are some QRH instances when you might turn a bleed switch off, but all of that is fairly rare.

If the OP is using a flight sim, the simple general answer, always leave the engine bleed switches on, will work fine.  Turn off the APU bleed after start. If you get the Master Caution for "Dual Bleed", you forgot to turn off the APU bleed, do so.

Edit, pack switches: off for engine start, on otherwise (except as directed by the QRH).


How can I estimate wind speed and direction in VFR? I am new here, I started to do VFR navigation (no G1000) so I try to deal with the wind.
I notice that I have some problems to find the wind speed and direction during flight. I am going to try to explain better: I am looking for some easy method to find the values (for example no CRP5 or too long trigonometry formula), something that can give me a fast idea from where the wind is blowing and the speed so I can anticipate the correction.

I used to do this when I was flying in the bush on floats, where there is very little time for planning and you are in a flying environment where you are living by your wits (which is what made it such great fun).
The only thing that really works to any (limited) degree, just by observation in the moment, is to look for bodies of water and observe the telltale signs of the surface winds.  Wave or wavelet size, streamer markings, lee side shoreline wind shadows. Or better, smoke columns from fires.
The wind typically veers (rotates clockwise) with altitude, so if you see a lake or someone burning something that suggests the wind is blowing on it from the west, with signs that suggest it's blowing at, say, 10kts, you can expect it to be more northwesterly the higher you go, and faster.  So if you guess the wind is 10kts and 270 at the surface, you can expect it to be maybe 300-ish and 20-30 kts at, say, 4000 ft.
Those are just signs that can help you make a better wild guess.  In the absence of any ground signs, the only other thing you can do is hold a constant heading for a couple of minutes on a timed run between two points, and note the difference between heading and track, and difference between ground speed and TAS.  Ground speed same as TAS, wind is at 90 degrees to your course (or velocity is zero), less than TAS it's forward, more it's behind. Ground speed less than TAS and significant crab angle to the left, the wind is quartering left/front.  Lots of crab and minor GS penalty, closer to 90 deg off your left, less crab and more GS penalty, closer to straight ahead.
With a bit of practice you should be able to make an educated guess on direction within maybe +/- 30 degrees and velocity +/- 15 kts.  With everybody using moving maps these days, these are skills that are becoming long lost.


What is the requirement for fire fighting equipment on board a passenger flight? What is the legal requirement regarding fire fighting equipment on a passenger flight, e.g. fire extinguishers and fire hoods? I imagine that the number is proportional to the airplane's max capacity.

I'd prefer ICAO since it applies internationally, but if there is none, a FAA reference would be a good as well.

You have this tagged  both FAA and ICAO but for the FAA thats governed under

  § 121.309 Emergency equipment.

  (c)Hand fire extinguishers for crew, passenger, cargo, and galley
  compartments. Hand fire extinguishers of an approved type must be
  provided for use in crew, passenger, cargo, and galley compartments in
  accordance with the following:

  (1) The type and quantity of extinguishing agent must be suitable for
  the kinds of fires likely to occur in the compartment where the
  extinguisher is intended to be used and, for passenger compartments,
  must be designed to minimize the hazard of toxic gas concentrations.

  (2)Cargo compartments. At least one hand fire extinguisher must be
  conveniently located for use in each class E cargo compartment that is
  accessible to crewmembers during flight.

  (3)Galley compartments. At least one hand fire extinguisher must be
  conveniently located for use in each galley located in a compartment
  other than a passenger, cargo, or crew compartment.

  (4)Flightcrew compartment. At least one hand fire extinguisher must be
  conveniently located on the flight deck for use by the flightcrew.

  (5)Passenger compartments. Hand fire extinguishers for use in
  passenger compartments must be conveniently located and, when two or
  more are required, uniformly distributed throughout each compartment.
  Hand fire extinguishers shall be provided in passenger compartments as
  follows:

  (i) For airplanes having passenger se ats accommodating more than 6
  but fewer than 31 passengers, at least one.

  (ii) For airplanes having passenger se ats accommodating more than 30
  but fewer than 61 passengers, at least two.

  (iii) For airplanes having passenger se ats accommodating more than 60
  passengers, there must be at least the following number of hand fire
  extinguishers:

  Minimum Number of Hand Fire Extinguishers Passenger seating
  accommodations:

  61 through 200:   3

  201 through 300:  4

  301 through 400:  5

  401 through 500:  6

  501 through 600:  7

  601 or more:  8

  (6) Notwithstanding
  the requirement for uniform distribution of hand fire extinguishers as
  prescribed in paragraph (c)(5) of this section, for those cases where
  a galley is located in a passenger compartment, at least one hand fire
  extinguisher must be conveniently located and easily accessible for
  use in the galley.

  (7) At least two of the required hand fire extinguisher installed in
  passenger-carrying airplanes must contain Halon 1211
  (bromochlorofluoromethane) or equivalent as the extinguishing agent.
  At least one hand fire extinguisher in the passenger compartment must
  contain Halon 1211 or equivalent.

You may also find some pertinent info here.


Why is there really only one basic design for passenger airplanes? So when I look around on the airport, I don't really see many differently shaped airplanes.

They all look pretty much the same, only subtle differences.

  Image: Aircraft Recognition

Why is this design so common? Why don't we have more extravagant designs?

Or am I not looking closely enough to appreciate the differences?

It seems like there could be so much potential for a variety of designs, offering more space and comfort for passengers for example... Or is it too risky to try something new?

For most transport aircraft, aerodynamic efficiency is the key parameter as it allows lower fuel consumption. The layouts you see most often are the most efficient known:

For jets low swept wings with engines mounted under and ahead of the wings and conventional tail is most efficient known layout. Tail-mounted engines used to be common on smaller jets, but as that puts lot of bulk far aft, they are worse with respect to Whitcomb area rule, worse for weight and balance, and wing-mounted engines also help damp flutter. So new regiojets are switching to engines under wing too.
Propeller aircraft fly slower, so they have straight wings. Low mounted wings are slightly more efficient, but then the plane has to have long gear to maintain sufficient ground clearance for the propellers, so high wings are more common. T-tail is then simply used to put the elevator above the most turbulent wake of wing and engines.

The only deviations from these three basic layouts are on special-purpose plane that have other more important concern. The most notable is military cargo planes are generally high-wing so they can sit low on the ground for easy loading and unloading using built-in ramp. Their marked anhedral is to avoid overstabilizing the aircraft in roll as both high wing and wing sweep increase roll stability. Earlier regiojet designs used tail-mounted engines for the same reason; to sit lower on the ground so they can be easily loaded via built-in airstairs and these are not too heavy and bulky.


How do you choose a feature to line up on when approaching to land? I've been taught that when I'm on final approach to land, I should pick a feature or landmark that's some distance along the extended centre-line, so that when I'm close enough to the ground that I can't properly see the runway edges any more, I can still look forwards and check my heading against this landmark. This is necessary on aircraft without flaps where the nose (the engine cowling) restricts the pilot's view of the runway in the approach.

The view along the runway changes completely from circuit height to runway level, and it's not obvious which features will be visible from less than 100 ft height. At my home aerodrome, it's easy to learn which feature to line up on, because I've seen them all before many times. When I'm landing at a new aerodrome, how can I select a feature to line up and be reasonably confident that it's still visually obvious all the way through the landing?

Probably the best thing to do is to start looking for your reference as you start to lose the runway under your nose. Hopefully at that point you'll be low enough to identify something that will stand out from the crowd all the way down to the ground. You may also favor choosing something closer in from the horizon at 2000AGL, to ensure you don't lose it behind the horizon as you descend. For me, flying out of Addison, it's pretty easy; the runway faces downtown Addison about 3 miles south-southeast (a row of corporate headquarters buildings along the Dallas North Tollway) which is far enough out to line up on but close enough and tall enough you'll see it right up until you pass the numbers. Flying into a more rural strip, you might have more trouble identifying a good reference that you can keep in sight as you descend.

Some potential issues with this general strategy:

Your reference point will lie well beyond the runway by design. Don't fixate on it; that will cause you to subconsciously stay higher than your intended glide path as you fly toward your reference, potentially overshooting the runway.
Your reference is a single point. That point and your aircraft make a line, which you want to be colinear with the runway. But, your aircraft is a moving point, so it's not necessarily true that you'll be in line with the runway even if your nose is on the reference point. Instead of one reference point, I'd pick two (even if they're not perfectly in line) and focus on keeping both reference points steady relative to each other.
If you can't see the runway, you may not be able to see surrounding visual aids like the glide slope indicators, which are just as important as staying lined up. Addison's PAPI lights are off to the right when approaching runway 15, which is stupid as my instructor can see them perfectly while I'm blind unless I nose down every few seconds to keep track (not an option without flaps).

While I wouldn't rely on it completely in VMC, if you have a VOR receiver aboard and the runway has an instrument approach, you can tune into the ILS frequency and use the "cross" alongside visual references to manage your approach during the time the runway is hidden from view. The ILS system is pretty well-standardized, while the visual references at each airport are not, so if you become accustomed to an ILS-augmented visual landing, the basic procedure can be applied to any airport.

The reasons I wouldn't rely totally on it include:

You're not instrument-rated (unless you are) so flying with your head in the gauges can easily kill you. Glance at it to ensure you're where you think you are, but rely on your visual references whenever you can.
You're not flying a pure instrument approach under IFR, so you still have to "see and avoid" even if you have tower staff spacing traffic around you (unless you ask for a "pop-up" instrument approach, effectively switching from VFR to IFR).
ILS availability/accuracy is not guaranteed in daytime VMC because the ILS critical areas are not required to be protected during these times. If you tell the tower what you're doing, they can advise ground traffic to use the ILS holds, but there may already be traffic in an ILS critical area and if so there's little the tower can do.
ILS may contradict visual indicators to varying degrees, because the ILS glideslope is projected from a different point along the runway than the PAPI/VASI array. You therefore shouldn't expect the ILS cross to be perfectly centered along the same path that gives you two white PAPI lights.
Radio-based ILS isn't available at every airstrip. In such cases you simply must fly a purely visual approach, and having relied on ILS to give you the proper glide slope instead of developing your sight picture will prove to be a crutch in such situations.


What are static discharges for on an airliner? I have never noticed these on any boeing planes before, so why are these on airbus a320 series and not on the boeing 737 and also what are they for?

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


Are all US airline aircraft certified into known ice? Are all  US airline aircraft certified for flying into known icing (FIKI) conditions?

I assume all the large (100+ PAX) aircraft come FIKI certified from the design stage?

What's the largest passenger aircraft that would be non-FIKI certified?

Title 14 CFR part 121.321 regulates scheduled airline operations in icing conditions.  It requires airframe ice protection systems in order to operate in "conditions conductive to airframe icing", which they define as:

visible moisture at or below a static air temperature of 5 °C or a total air temperature of 10 °C, unless the approved Airplane Flight Manual provides another definition.

This essentially means that any airline that can operate in IMC is going to be subject to this requirement unless they have very niche operations at low altitudes in warm lattitudes where they can stay below the 10 C level when in IMC.
Aircraft operated by airlines that operate in IMC at temperatures colder than 10 C must either have an ice detection system or a means of detecting the first formation of ice on the airframe and then activate ice protection systems or they must, in the absence of detection, always operate their ice protection when operation in conditions conductive to airframe icing.
For smaller on-demand operations operating under part 135, 14 CFR 135.227 regulates flight into icing conditions.  This regulation requires that any airplance flying into forecast icing (IFR only) or known icing conditions (VFR or IFR) has functioning de-ice or anti-ice protection.  This means a 135 operation ferrying passengers from Miami into the Bahamas probably doesn't have to worry about this, but a IFR 135 operation anywhere it gets cold probably does.
For non-121 and non-135 operations in airplanes with 20 passenger seats or more, the applicable regulation is 14 CFR 125.221 and reads exactly like the part 135 regulation.
Summary
Combined, parts 121, 125 and 135 regulate the majority of commercial operations.   The requirements of part 121 realistically mean that any airplane suitable for scheduled airline operations is equipped with ice protection.  Part 135 can utilize a broader range of aircraft and while ice protection is not required it is quite limiting for the operation if it is not present (no flight into known or forecast icing conditions under IFR).
This means that all airline aircraft (part 121) are certified for FIKI but not all passenger airplanes (operated under part 125 or 135) are certified for FIKI (and cannot operate in those conditions if not equipped).
Regs

§121.321   Operations in icing.
(a) When operating in conditions conducive to airframe icing, compliance must be shown with paragraph (a)(1), or (2), or (3) of this section.
(1) The airplane must be equipped with a certificated primary airframe ice detection system.
(i) The airframe ice protection system must be activated automatically, or manually by the flightcrew, when the primary ice detection system indicates activation is necessary.
...
(2) Visual cues of the first sign of ice formation anywhere on the airplane and a certificated advisory airframe ice detection system must be provided.
(i) The airframe ice protection system must be activated when any of the visual cues are observed or when the advisory airframe ice detection system indicates activation is necessary, whichever occurs first.
...
(3) If the airplane is not equipped to comply with the provisions of paragraph (a)(1) or (2) of this section, then the following apply:
(i) When operating in conditions conducive to airframe icing, the airframe ice protection system must be activated prior to, and operated during, the following phases of flight:
...
(ii) During any other phase of flight, the airframe ice protection system must be activated and operated at the first sign of ice formation anywhere on the airplane, unless the Airplane Flight Manual specifies that the airframe ice protection system should not be used or provides other operational instructions.

§135.227   Icing conditions: Operating limitations.
(c) No pilot may fly under IFR into known or forecast light or moderate icing conditions or under VFR into known light or moderate icing conditions, unless—
(1) The aircraft has functioning deicing or anti-icing equipment protecting each rotor blade, propeller, windshield, wing, stabilizing or control surface, and each airspeed, altimeter, rate of climb, or flight attitude instrument system;
(2) The airplane has ice protection provisions that meet section 34 of appendix A of this part; or
(3) The airplane meets transport category airplane type certification provisions, including the requirements for certification for flight in icing conditions.


Per the AIM, Helicopter pilots may fly non-copter approaches at half the published visibility. Where is that in the FAR? In AIM 10-1-2 Helicopter Instrument Approaches, paragraph a1 says the visibility reduction rule comes from 14 CFR Section 97.3. From what I can see, that section is just definitions. What is the AIM referencing?

I'm not sure what source you're looking at for the FARs but the reduction is indeed there in 14 CFR 97.3:

Copter procedures means helicopter procedures, with applicable minimums as prescribed in §97.35. Helicopters may also use other
procedures prescribed in subpart C of this part and may use the
Category A minimum descent altitude (MDA), or decision altitude or
decision height (DA/DH). For other than “copter-only” approaches, the
required visibility minimum for Category I approaches may be reduced
to one-half the published visibility minimum for Category A aircraft,
but in no case may it be reduced to less than one-quarter mile
prevailing visibility, or, if reported, 1,200 feet RVR. Reduction of
visibility minima on Category II instrument approach procedures is
prohibited.