How does traffic handoff between ZMA and Cuba work? Cuba and the US have long had "frosty" relations.
With some limited easing of restrictions, there are now direct flights between Miami, FL (controlled by ZMA) and Havana, Cuba.

Does Cuba have an ARTCC?  Do they coordinate with ZMA for passing off flights?Has this been an ongoing system even before the recent easing of sanctions, or is it relatively new?

After some searching, I found a paper from Wikileaks from November 19th, 2009, that reads in part:

  (SBU) SUMMARY:  Miami and Havana air traffic controllers
  signed a letter of agreement (LOA) on November 12 updating
  procedures for the coordination of flights between Cuban and
  U.S. controlled airspace.  Both sides stressed the excellent
  working relationship between the Miami Air Route Traffic
  Control Center (ARTCC) and the Havana Area Control Center
  (ACC).  The U.S. delegation agreed to review information to
  be provided by the Cuban delegation regarding flights
  operating under the rules of "due regard" that could pose a
  safety risk.  Both sides also agreed to discuss switching
  from verbal to electronic flight data sharing, on the margins
  of a regional aviation meeting in Miami in May 2010. END
  SUMMARY

Apparently handoff procedures have been a regular occurrence for a long time, and are cooperated on extensively.


What do aviation agencies do to make waypoints sequences more easy to remember to prevent navigation mistakes? Inspired by this question.
What examples are there of waypoints strung together on airways or approaches which are funny or tell a story in order to help controllers and pilots reduce navigation mistakes?  I'm not looking for individual waypoint names, but connected waypoints.  For example:

WONZA JOLLY SWAGGY CAMBS BYLLA BONGS UNDER ACOOL EBARR TREES arriving from the West into Perth.
WEEEE WLLLL NEVVR FORGT SEP11 on the Freedom airway to Washington International.

Australia

Brisbane / Melbourne FIRs boundary
PUDYA SWEED LIPPS ALIDL CLOZA TOUDA PHONE
(Put your sweet lips a little closer to the phone, Jim Reeves)
Brisbane RWY19 STARs
LEAKY BOATS SINNK and
DRAIN PLUGG SINNK.
BLAKA MOOVI by the South.
Gold Coast (YBCG) SID 14/32
LUVLY MEETA MAIDS
(Lovely meter maids)

USA

Frederick, Maryland (KFDK) RNAV (GPS) RWY 5
PHILB DEFND GEEAY
(Phil Boyer, AOPA president, defends GA)
Kansas City, Missouri (KMCI) ILS/LOC RWY 1R
SPICY BARBQ TERKY SMOKE RIBBS HOTBI
Lebanon, New Hampshire (KLEB) ILS/LOC RWY 18
HAMMM HAANK BURGR FRYYS
Nashville, Tennessee (KBNA) ILS/LOC RWY 2C
LRETA JCKSN GRRTH
(Loretta Lynn, Alan Jackson and Garth Brooks)
Orlando, Florida COSTR THREE ARRIVAL
From LA BELLE Tacan: DOWNN MOANS BIGGR
From BOXKR ANDRO SETME
(I'm quite sure I missed some other)
Palm Beach, Florida (KPBI) Ivanka One Departure
The various departure paths include
UFIRD DONLD TRMMP IVNKA
(The FAA scrapped this procedure and some of the associated waypoint names in 2015.)
CRYER UTLEY FINNS PYRUT AHABB
(Captain Ahab is a fictional character in Herman Melville's Moby-Dick; Jimmy Buffett song: A Pirate Looks at Forty; Jimmy Buffett song: Fins; Michael Utley: musician; Jon Cryer(?): actor)
Portsmouth, New Hampshire (KPSM) RNAV (GPS) RWY 16
ITAWT ITAWA PUDYE TTATT - IDEED
(I thought I saw a pussy cat - I did!)
Salt Lake City, Utah (KSLC) RNAV (GPS) RWY 34L
HOAMR MARRJ BAURT LIEZA
(Simpsons characters)

Community wiki.


How much lift do planes produce before rotation? In the takeoff roll, I'm pretty sure planes produce some lift before rotation, but how much? Is it insignificant compared to post-rotation, or is it large compared to the post-rotation lift?

Check out this plot (taken from wikipedia), of the lift coefficient against angle of attack. During takeoff roll, lift will be increasing due to the speed increasing, however not enough (in general) for the plane to achieve takeoff without rotation.

Once rotation starts, the lift increases dramatically, for (a very rough) example, consider a plane on takeoff roll, then rotating to 15 degrees angle of attack. By looking at the lift/AoA plot, we can see that the lift coefficient increases from roughly 0.55 to 1.7, giving roughly 3 times as much lift as before rotation.


Why Do They Continue To Abbreviate Weather Products? Can We As A Community Change This? Why are area forecasts, METARs, and TAFs written in an abbreviated manner? I understand that in the beginning, each digit or symbol costs money. However, that is no longer the situation. Why not make an area forecast as clear as possible? Aviators kill themselves because they do not understand the weather. Is there a reason the FAA continues to do this? Can the community of aviators change this?

The language of aviation is terse, compressed and intended to leave minimum room for interpretation or misapprehension.

It makes heavy use of formulas, themselves intended to to be unambiguous, but which are not always obviously and immediately meaningful to those who are unfamiliar with the language.

This is the norm for potentially critical communication in all fields that I'm aware of - the military, medicine and throughout the transportation industry.

The users of this language are trained in it; being familiar with it is an essential part of their competence.

Language, interfaces, procedures and tools in aviation don't need to be user-friendly, they need to be utterly precise, be usable in difficult circumstances, and on every occasion they're used have exactly the same outcome.

It's possible that an aviator has failed to understand a weather forecast and died as a result, but a weather reports that allowed themselves the liberty of free expression would kill a lot more than that.


Why is the phrase “infinite energy” used by this (alleged) ATSB investigator? In the Air Crash Investigation episode, “Titanic In The Sky”, a Quantas Airbus A380 suffers an uncontained engine failure which partially cripples the plane. In the investigation part of the episode, an “ATSB Investigator” says that:

  […] the fragments [from the rupture of the fanblade] are released with an infinite energy, which means that there's nothing that can stop the engine pieces¹.

Did he forget to add virtually, or is the ATSB just not very accurate when they talk about these incidents on TV? Or is this terminology actually used in aviation contexts?

If you accelerate an engine blade to have infinite energy, hydraulic failures would be the least of your worries².

It should be noted that I cannot find unlimited or infinite in the preliminary ATSB report.

You are correct in that this is not a quote of the report -- the final report does not use that phraseology either.  What the investigator means is that the energy is effectively infinite, as it is impossible to stop something with that much kinetic energy within the mass budget of an airplane engine cowling.


Why isn't a human required to confirm visually that flight controls are moving? On this A380 flight  after pushback and engine start and before taxi, Capt Juergen Raps and   and Sr FO Harald Tschira  rely solely on their FID to check flight controls. On a regular flight without the Pilotseye.tv camera crew, they obviously can't see if flight controls respond.

Why isn't a human third-party (ground crew) required to confirm the flight controls' movements? This is obviously shrewder, and adds another safety measure to forestall the possibility that the FID shows a  flight control to move when it doesn't.

Same linked video @ 7:03

    [A] safety measure to forestall the possibility that the [display] shows a flight control to move when it doesn't.

The display (above) doesn't mimic the input, it shows the positions of the sensors independent of the input signal. Since the position change that is being checked is confirmed to be related to direct input, the data is valid.

In other words, an unexpected result with/without input would be an issue with a sensor and/or surface.

In lieu of digital displays, planes like the earlier 747 variants and Concorde had analog instruments that also read sensors. And with the hydraulics operating on a plane like the 737, the fact that the controls are able to move the full range unjammed, indicates that the control surfaces are responding and are also unjammed.

It gets trickier with a plane like the MD-80 where the controls move tabs instead of surfaces (a tab is a control surface on a control surface). It has resulted in an overrun in 2017. No human [visual] inspection could have detected it as the tab would have still moved as expected, but not the stuck surface, also as expected – tabs need airflow to move the surface.


Does a type rating give a person the privileges of an instrument rating in any category or class of aircraft which he/she is certificated in? Suppose someone obtains a PPL-ASEL, then obtains a type rating in an aircraft requiring that rating e.g. jet, etc.  This type rating functions as an instrument rating, allowing the pilot to fly the new aircraft under IFR.  But does said type rating then grant the pilot the privelages to operate ANY appropriately equipped airplane single engine land under IFR as well?

61.63(d)(1) requires that if you don't have an ATP that you hold an instrument rating to obtain a type rating. The type rating itself does not grant instrument privileges.

(d) Additional aircraft type rating. Except as provided under paragraph (d)(6) of this section, a person who applies for an aircraft type rating or an aircraft type rating to be completed concurrently with an aircraft category or class rating—
(1) Must hold or concurrently obtain an appropriate instrument rating, except as provided in paragraph (e) of this section.

Paragraph (e) exempts aircraft incapable of instrument maneuvers and instrument flight from this requirement.
This does mean that you can do the instrument checkride concurrent with the type rating. If your hypothetical PP-ASEL gets typed in a citation, he will end up with a PP-ASEL with instrument airplane rating and the citation type.


How is ATFM handled in the USA? In my answer to this question, I describe how calculated takeoff times (CTOT) are used as a tool in European air traffic flow management to prevent overload and maximize capacity. I expect the ATFM system used in the USA to be quite similar, but I'm sure there are technical differences. I am hoping someone can provide a similar answer, detailing ATFM procedures in the USA.

original question:

Air traffic flow management (ATFM) is a service established with the objective of contributing to a safe, orderly and expeditious flow of air traffic by ensuring that ATC capacity is utilized to the maximum extent possible and that the traffic volume is compatible with the capacities declared by the appropriate ATS authority.

In Europe, air traffic flow and capacity management (ATFCM - notice the additional C) is handled by EUROCONTROL.

Each air navigation service provider (ANSP) is responsible for declaring the capacity of their ATC sectors in terms of a maximum number of movements that can be safely handled in given time intervals.

All IFR flightplans in Europe are processed centrally by the Integrated Initial Flight Plan Processing System (IFPS). If, based on the flightplans, it is calculated that capacity within a sector will be exceeded, flights might be rerouted or level capped, or they receive ground delay (a slot time).

This system works very well, and ensures an efficient and safe flow of air traffic within Europe. However, flights originating outside of Europe cannot be processed in the same way. For example, flights departing outside of Europe will not receive any slot times, which makes the system inflexible, since these flights still have to be taken into consideration, but cannot be adjusted the same way other flights can.

This has made me wonder, why is it not possible to simply link the European system with similar systems around the world, to create a global ATFM network? Specifically, I am interested in how ATFM works in the USA. I would like to identify the main differences between the European system and the system in the USA, with the goal of understanding what prevents these systems from working together.

The problem with working together on a global scale or even trans-Atlantic is the long time and distance between. Flow control at least in the U.S. (and I'm sure elsewhere) is more short-term (1-2 hours out), mainly based around airport acceptance rates (AAR) which can change hourly or even more frequently for example because of runway configuration changes, or weather or visibility changes. There is also short-term projected sector saturation issues, and short-term sudden localized things like weather buildups that can come and go.

That means for trans-oceanic flights you can't effectively implement departure metering (the main tool in the U.S. for flow control) or ground stops because you can't predict 5-10 hours in advance the traffic level and acceptance rate at the destination airport. It's much more effective to wait until they're back in radar coverage and closer time-wise to the destination when flow control calculations will be more accurate, and controllers can achieve miles-in-trail spacing requirements with quick radar vectoring. Over the ocean, outside of radar coverage, significantly adjusting in-trail spacing is more difficult because you really only have speed adjustments which are limited because of the narrow aircraft envelopes at high altitudes.

For situations where there will need to be long-term flow control (such as, the only other runway is suddenly closed and will be indefinitely), we already do have a manual process to implement flow restrictions trans-oceanic, by each facility passing restrictions to adjacent facilities, on and on up the chain.  For example, Shanwick can tell Gander we need 10 minutes all aircraft all tracks landing EGLL, Gander tells Boston 12 minutes in trail, Boston coordinates with U.S. command center, etc to ensure Boston doesn't get overwhelmed with EGLL-bound aircraft. Those kinds of things happen very rarely though, so it's probably not worth connecting our different automation/flow control systems together and instead just keep handling it manually on a case by case basis.

(Source: I'm a former FAA controller and worked in flow control/Traffic Management Unit for several years).


What is the relationship between temperature, dew point and the formation of clouds? What can you infer from the temperature / dew point values in this METAR?

  EGJG 121630Z 09012KT 9999 SCT006 15/14 Q1015

I understand the temperature is 15 degrees and the dew point is 14, and I found this:

  The temperature / dew point spread is low, so the risk of cloud
  forming is high especially if the temperature falls.

Why is the risk of clouds forming high, especially if the temperature is falling?

The dew point is the temperature at which condensation (a cloud) forms.

If the dew point is the same as the temperature on the ground, then there will be fog.

The temperature usually decreases as the altitude increases. This is called the lapse rate. In general, the closer the dew point is to the ground temperature, the lower the cloud ceiling will be.


What are the FAA sport-pilot self-certification standards? Consider a hypothetical pilot who knows they have a medical condition which the FAA considers disqualifying (under the standard medical qualification standards). Is that pilot permitted to operate under sport-pilot privileges if they do not believe their condition interferes with their ability to safely perform their sport piloting duties? Must that pilot consult with a private physician? If so, must the physician offer some sort of approval?

The FAA has a similar question on the FAQ, but doesn't seem to answer it fully. They "suggest" consultation with a physician. Does that suggestion indicate a pilot who does not do so is in violation of a FAR?

edit: This question is concerning operation of a powered airplane.

Unless the pilot has had their certificate revoked or suspended by the FAA for their medical condition or has failed an application for a medical certificate1, they would probably be fine after seeing a physician. FAR 61.23(c)(2) states that sport pilots using a driver's license to satisfy medical requirements must:

  (ii) Have been found eligible for the issuance of at least a third-class airman medical certificate at the time of his or her most recent application (if the person has applied for a medical certificate);

  (iii) Not have had his or her most recently issued medical certificate (if the person has held a medical certificate) suspended or revoked or most recent Authorization for a Special Issuance of a Medical Certificate withdrawn; and

  (iv) Not know or have reason to know of any medical condition that would make that person unable to operate a light-sport aircraft in a safe manner.

If the holder has a valid US driver's license, it would (presumably) be taken upon the certificate holder to have "reason to know" by virtue of having a checkup with a physician to check that this condition does not affect their ability to fly safely, especially if the person involved was in any sort of doubt as to their medical condition.

However, if they have had a checkup with a physician that finds no particular issues, and that condition does not affect the validity of their driver's license, they should be fine.

1: By section (ii), the pilot must still have a medical test and pass for at least a Class 3 medical certificate, if the FAA has revoked or found unsatisfactory their previous medical under a Class 1 or Class 2 certificate.


Why hasn't Boeing updated the 747 with technology from the 787? Why hasn't Boeing updated the 747 with technology/designs from the 787 Dreamliner? Surely this would be a very successful aircraft as it could have the best of both designs.

Has Boeing explained why? Are there any reasons this couldn't or shouldn't be done?

They did, in the 747-8:

Wikipedia:

  Similar in nature to the 747X, the stretched 747 Advanced used technology from the Boeing 787 Dreamliner to modernize the design and its systems. On November 14, 2005, Boeing announced that it was launching the 747 Advanced as the "Boeing 747-8"

(Emphasis mine)

The 747-8 includes technology in the cockpit, cabin, wings, and engines borrowed or learned from the 787 and 777 aircraft programs. Obviously you can't just pull the wings off of a 787 and stick them on a 747, but the wings were redesigned with aerodynamic information learned in the 777/787 program.


How many tanks does an A350 have? How many tanks are there on an A350? Where are they located? Is it a common configuration among large aircraft?

The two configurations of A350 have different capacity.

A350-900: 138,000 liters / 36,456 US gallons
A350-1000: 156,000 liters / 41,212 US gallons

The tanks are shown in this picture:

Source


Could flight control be achieved by rotating a wing entirely? In a typical airplane, one of the main flight control mechanisms are the ailerons/flaperons, which allows one to tweak the lift/drag profile of both wings independently.

I was wondering about the feasibility of achieving similar flight control by means of rotating an entire wing around its lengthwise axis. As I understand it, such tweaking of the aoa would have very similar flight control characteristics as regular ailerons.

Obviously this is a somewhat awkward design mechanically; the point where the wing meets the fuselage is one of the most heavily stressed parts of the airplane, so to add a pivot there takes some consideration. But I am thinking here in the context of an RC plane; where i think just nesting two carbon tubes at the center of lift will work fine.

Some potential advantages are that while the static loads on the articulated part will be high, the forces required to actuate the mechanism could be lower or approach zero, assuming the center of lift can be held reasonably constant. Also, ailerons are aerodynamically awkward and draggy when not in neutral position; moreso than an airfoil tilted tilted from its optimal L/D. Mostly I am just curious though, what something like this would look like in practice.

I cant seem to find anything on google about a design like this, but surely someone must have tried this before? If not, there must be good theoretical reasons I am missing why we should expect this to be a disaster. Is there a search term anyone is aware of that would lead me to similar designs?

Yes, it has been tried before and is regularly used on many horizontal and even some vertical tails.

However, in subsonic flight an elevator will offer better efficiency. Only in supersonic designs is the full-flying tail the clearly preferred option.

To move the whole wing needs very strong hinges and actuators, but there were some which did even this:

Mignet HM 14 Pou du Ciel (picture source). It was light and flew slowly enough that moving the whole wing was not an issue.

The Vought F-8 "Crusader" and XF8U-3 "Corsair III" could jack their wings seven degrees up in order to improve fuselage attitude and pilot visibility during take-off and landing (picture source).

Even all-moving outer wings have been tried for roll control, albeit in only very few aircraft. Three I know of (and all of them were built once only) are:

Granger Archaeopteryx,
Short SB.1 glider, and
Short SB.4 Sherpa, the rotated wingtip of which is shown below (picture source).


How does the FOVE system work with the Airbus FMS? The Flight Operations Versatile Environment (FOVE) is a separate software system used with Airbus aircraft by dispatchers to determine performance data to enter into the FMS. There seems to be little info on the interwebs about it.

Since the FMS takes the parameters and makes its own calculations, I'm not sure why a separate system is needed. A U.K. CAA bulletin says:

  "As [FOVE] gives more accurate performance figures it is generally used on occasions where takeoff performance is more limiting."

In what way does it produce more accurate figures than the aircraft's own FMS? Is FOVE created by Airbus or a third party? If it's third party, has Airbus approved it?

How does FOVE work with the FMS? Do they just override the FMS calculations, or does it give them alternate data to enter into the FMS to create the required parameters?

(Source)

Whether the FMS is capable or not of calculating the V-speeds, it should be checked and may be overridden. It is because the airplane database wouldn't know if there's a temporary crane that will affect the climb limit weight, or if 400 ft of the runway are unusable due to maintenance, for example. In other words, 10,000' corrected-length runways are not always the same.

As to FOVE, it is an Airbus tool made by Airbus. The Airbus LPC (Less Paper in the Cockpit) is a laptop* used by the pilots. Essentially an EFB (electronic flight bag). This laptop serves two functions. One, is having the manuals in electronic format, two, is the FOVE—which handles all the performance related calculations.

* Depending on the company, the laptop can be a tablet, or an integrated EFB. I can't speak for the integrated, but the laptop/tablet do not communicate with the FMS, and changes are done manually.

It is more accurate than manual calculation, because manual calculations rely on approved graphs. Interpreting graphs inherently reduces accuracy. See below for a 737-800 example:

(Click to view)

And that's for one flap setting and one condition.

Even if converted to table format, still there will be gaps between any two values, whereas a computer can produce those 'in-between' values, which may provide a takeoff performance advantage.

(Source)

See here for FOVE training manual that has lots of screenshots, etc.


What happens when the eigenvalues of the longitudinal A matrix in dynamic stability analysis, are NOT two sets of complex conjugate pairs? The complex conjugate pairs of eigenvalues of the longitudinal A matrix characterize phugoid and short period dynamic responses, this information is well established.
My question is - what happens when the eigenvalues consist of 2 real roots and 1 complex conjugate pair?  Can this happen (assuming no error on input, or does it only happen with an error?) and if it does what does this say about the dynamics of the system?  Examining the eigenvectors I'm wondering how to interpret two eigenvectors that consist of all real values?

Thanks!

what happens when the eigenvalues consist of 2 real roots and 1 complex conjugate pair?

This means that the one complex conjugate root is still an oscillation but the other has split into two aperiodic movements. One of them should be a positive and the other a negative real value. While the negative root signifies a damped, aperiodic movement, the positive root shows that the airplane has one instable, divergent mode.

Can this happen?

Yes, for example when the center of gravity is moved aft of the neutral point, the phygoid will split into two real roots. The positive one describes the divergent behavior when static stability has been lost.
Backgound:
The equations of motion describe how acceleration, speed and pitch rate of the airplane react to small changes of the control parameters (elevator angle and throttle setting). They are second order differential equations and can be solved similar to systems of quadratic equations where the coefficients form the elements of a square matrix. The eigenvalues of the matrix describe frequency and damping of the movement which is caused by changes to the control parameters while the eigenvectors describe how acceleration, speed and pitch rate are affected in detail.
Note that this only concerns longitudinal movement (forward-back, up-down and pitch). The equations can be expanded to cover roll, yaw and left-right movement as well, but the question only concerns the simpler longitudinal part.


Are you required to fly a full hold when doing a course reversal? When doing a hold in leu of a procedure turn are you required to do a full hold for the course reversal or just the entry to the Fix and then proceeding in bound for the final approach course?

When performing a HILPT, typically the aircraft will pass the hold point outbound and perform the correct entry.  When you are inbound, you will continue with the approach once crossing the hold point again.
The aircraft will only pass the hold point twice unless a request is made to ATC for further hold to get ready to fly the approach.


Is there a Risk of Tail Tipping during Push-back of a passenger aircraft? I remember that there were countless incidents occurred in which the aircraft sits on the tail as the aircraft was heavily loaded at the back of the cargo and/or cabin compartments or the cargo compartments were offloaded incorrect order. I know that these incidents are more commonly happen in cargo aircrafts.

Is there a risk that the aircraft will sit on the tail during the pushback process as a result of the tri-cycle design of the aircraft?

Is there any tail tipping incident reported during pushback/towing operation?

Which types of aircraft (narrow/wide body) can this risk be higher?

During pushback the (usually quite substantial) weight of the tug pulls the nose down, and additionally when it's pushing backward the line of force is below the CG and acting rearward, so that would also tend to counteract any tipover tendency.

As Jan mentions in comments, the tipover situations tend to happen during loading when the CG is moving around. I suppose if the tug were first attached and then the aircraft were grossly misloaded, it's conceivable that it could tip over backward as the tug detaches and removes it's weight, but I've never heard of that happening.


Did Wolfgang Langewiesche ever change his mind about rudder pedals? I get the feeling that if aviation was a religion and had a holy book, that book would be Stick and Rudder.  Mostly because it's often spoken of with great authority by people who have never read it.

Well, I'm reading it right now.  And let me tell you, Wolfgang has got some opinions.  Here's one of them, from Chapter 11.

  The important thing to understand about the rudder pedals is that they are unnecessary; like your wisdom teeth, they serve no very good purpose but can cause much trouble.  The airplane needs no rudder pedals.  It should have no rudder pedals.  In all probability it will have no rudder pedals 10 years hence.

I have to give him credit: he put his money where his mouth was.

However, the fact that it's now 2014 and rudder pedals are still very much in vogue makes me wonder:  Did Wolfgang Langewiesche ever change his mind about rudder pedals, or did he go to his grave defiant to the end?

NO

There is no written record that I have found in researching this question that Langweische ever 'recanted' his beliefs. I cannot source or cite this negative however. I don't actually like this question, since only an answer that he did recant can be sourceable. Any cites showing him supporting his own written beliefs could be disputed by saying "but what about later in life?" This means that a negative answer can only be opinion.

It's not like he left in his LW&T the statement that everything he had written previously was a lie.


Why does each part of span not produce equivalent downwash? I know that it is associated with Prandtl lifting-line theory and that ideal elliptical wing actually meets the condition of my question. Unfortunately I am not good at fluid dynamics and I would like a relatively simple explanation why downwash (and lift) differs along wingspan (of non-elliptical wings). I would like to understand at least the basics and satisfy my curiosity :)

Why should non-elliptical wings not produce constant downwash over span? They do at one angle of attack, given a proper twist distribution so that the circulation distribution over span is elliptical.

However, once the angle of attack is different from that of the elliptical distribution, the change in local circulation varies in proportion to local chord. If the chord distribution is not elliptical, the new circulation distribution due to that angle of attack change is also not elliptical, and so is the change in local downwash angle.

Sometimes it is desirable to not produce an elliptical circulation distribution rsp. have an elliptical planform. If the objective is to minimise drag, it helps to reduce weight and pure lift/drag optimization is too narrow. What should count is the best ratio of lift minus wing weight relative to drag. R. T. Jones wrote a NACA Technical Note back in 1950 in which he looked at this problem analytically. Wing weight goes up when much lift is created near the tips, because this lift will cause a disproportional root bending moment, and the wing spar, which has to carry this bending moment, is a significant part of the wing structure. Therefore, reducing lift at the tips and adding more lift at the root will create a lighter wing for a modest drag increase, resulting in an overall optimum with an almost triangular lift distribution. When compared to an elliptical wing planform, the total wing span of such an optimized wing is bigger for the same overall drag, but this wing will weigh less.

Another example is wing stall. An elliptical wing without washout will have a constant lift coefficient over span, and Reynolds number effects ensure that the wing will stall at the tips first. An unsymmetrical stall will result in an accelerated roll departure: The stalled side of the wing loses lift, drops and sees an increase in angle of attack which worsens the stall condition. This effect gives an elliptical wing poor handling characteristics and is the reason why many GA aircraft have rectangular or trapezoidal planforms of little taper.


Are there any reference values for Cl and Cd of a NACA 0012 airfoil to verify CFD simulations? I am having trouble finding the established results of inviscid flow CL and Cd variation over NACA 0012 airfoil, for the transonic region. I need the data to verify the results I am getting through my CFD simulations. I have recently started learning CFD and the actual results would be really useful to me as they would clarify whether I am in the right direction or not.

Please suggest any site, research paper or book.

Four sets of measured data can be seen in this plot, the difference caused by different Reynolds numbers during measurement. The figure is from Helicopter Performance, Stability and Control by Raymond Prouty. The book is still for sale and is a treasure cove of knowledge on all things sub-sonic. From page 426 onwards it has a section on representing airfoil data with equations, using NACA 0012 as example.

This graph is from Theory Of Wing Sections by Abbott & Von Doenhoff. Contains a chapter of compressibility effects.

$C_L$ and $C_M$ are more extensively represented in the reference books than $C_D$, which is more generally lumped into considerations of Mach divergence number. The same two books will help you further.

The NACA technical report server can be of help as well, a starting point there would be NACA TR 832.


Which aircraft had the shortest operational life? I read in Wikipedia that the operational life of Consolidated B-32 was limited to just a handful of months (January to August 1945).

Please note that B-32 wasn’t an experimental model, but an aircraft which was industrially produced in relatively large scale, was issued to some operative wings and was engaged in some actual combat events, showing even several appreciated features.

Was it the most short-lived aircraft type, all that considered?

I mean, is there another military aircraft type, assigned for combat mission to operative units, which was discontinued earlier than the B-32 (only seven months after the beginning of service)?

Japanese Ki-100 made its combat debut on the night of 9 March 1945. The last loss of a Ki-100 occurred on 14 August 1945, a day before the surrender of Japan. Hence the  interceptor has been in the service for 158 days, or 5 months 5 days, with 396 units produced.

Looks like nothing bad can be said about this interceptor. It has been recently developed, without major flaws, and, as such, was obviously superior to the older models. It was between the first interceptors to feature the factory-installed armor and self-sealing fuel tanks, and some think it was the best interceptor used by the Army during entire war. But, with the end of the war, it was no longer required.


What market share does Jet A-1 have in the commercial airline market? I know that Jet A-1 is the most widely used fuel in the commercial airline market, but what is its market share in percentage?

Are there any big users of Jet A rather than Jet A-1? And if so, why?

Chevron writes

Jet A is used in the United States while most of the rest of the world uses Jet A-1. The important difference between the two fuels is that Jet A-1 has a lower maximum freezing point than Jet A (Jet A: –40°C, Jet A-1: –47°C). The lower freezing point makes Jet A-1 more suitable for long international flights, especially on polar routes during the winter.
However, the lower freezing point comes at a price. Other variables being constant, a refinery can produce a few percent more Jet A than Jet A-1 because the higher freezing point allows the incorporation of more higher boiling
components, which in turn, permits the use of a broader distillation cut. The choice of Jet A for use in the United States is driven by concerns about fuel price and availability. Many years of experience have shown that Jet A is suitable for use in the United States.

Notably, the US is also the single largest market for aviation fuel worldwide, so it has the volume to support a separate type. There's consumption numbers in the same document.
The disadvantage with Jet A is with long-haul flights that experience cold air, the 7 degrees can make a difference, forcing the flight to descend to warmer levels to heat the fuel, increasing consumption.
One thing that can be done is a sample of the loaded fuel is taken and the actual freeze point determined, and that number used in flight. Usually for Jet-A this lies somewhere in between the two specs.


What happens to US military demo teams following unexpected pilot turnover? Following up on recent events involving the Blue Angels and the Thunderbirds, what is the typical procedure for these teams following a unexpected turnover of a pilot (in this case, a fatal or other serious crash)?

Do these teams have a "B" team in training to pull talent from, or possibly have a larger pilots roster that will rotate in and out throughout the season to pull from?  Maybe even have multiple teams that trade off show duties and training during the season?

(I assume that the Thunderbirds will just paint up a new plane and give the pilot a good pep talk).

I can't answer for the Blue Angels or the Thunderbirds, but I can for the UK equivalent, the Red Arrows.

The Red Arrows have no spare pilots (or 'B team'). The nine pilots on the team fly every display in their 3 year tour. The explanation is that a spare pilot would not fly frequently enough to be current and safe. They do however have the capability to do an 8-plane display (rather than the usual 9) which they can use if a pilot is temporarily incapacitated. They also have a spare plane, something I know also applies to the Thunderbirds.

In the event of any kind of serious accident, it is likely that displays would be suspended for at least a while, in order to investigate and also out of respect. If all pilots are available when displays resume everything would be normal, using the spare plane if required. If a pilot was out for a short time they might fly the 8-plane display. The Arrows fly standard planes with minimal modifications, so presumably a new one could be readied fairly quickly.

In 2010 when Flt Lt. Ling was injured too badly to continue with display flying he was replaced by a pilot who had already flown with the team in a previous season.


What is the weight of the batteries on the e-Fan? Airbus' own (early) page with technical data about the e-Fan provides some information about the batteries.

It can, for instance, be calculated that they hold approx. 19kWh of energy if you accept a somewhat simplistic calculation by multiplying number of cells (120) with capacity (40A ) and voltage (4V).

What I can't find is information about the weight of these batteries. Is this information available somewhere or can it be reasonably estimated?

The weight of the battery is mentioned here:

  Power is provided by 127 kg. of 250-volt lithium-ion polymer batteries
  from Kokam in South Korea built into the wing.

A slightly different weight is specified here:

  ... E-Fan has two lithium-polymer battery packs weighing 65 kg each.

I could not find which Kokam battery is being used on the e-fan, but this page has specifications for all of their batteries.


What's the difference between True vs Magnetic headings? What is the difference between a true and a magnetic heading?

Why are/were magnetic headings used in aviation?

The "heading" refers to the direction an aircraft is pointing. For a Magnetic Heading, this is in relation to Magnetic North. For a True Heading, this is in relation to True North.

True North is directly over the earth's axis.

Magnetic North is somewhere over Canada, moving towards Russia.

To get the Magnetic Heading, you just read it off the magnetic compass.

To get the True Heading, you need to first read the magnetic compass, then either add an Easterly, or subtract a Westerly, magnetic variation; based upon the isogonic lines on your sectional (the purple dashed lines labeled 5°W, 3°E, etc).

Example 1: Magnetic Heading 177 w/ 3 degrees East Magnetic deviation = true course 180.

Example 2: Magnetic Heading 177 w/ 3 degrees West Magnetic deviation = true course 174.

Because of this, in the past, magnetic headings were used because a simple compass could be used. Finding reliable true headings was difficult until the era of things like the gyrocompass (patented in 1906 (Germany) and 1908 (USA)) and more recently, GPS.


How can drag induced by the landing gear be reduced? What are some of the methods used to reduce the drag caused by the landing gear for aircraft with non-retractable landing gear?

The Pilot's Manual: Ground School has a nice diagram that explains it pretty well. It's all about streamlining. Airplane designers add landing gear fairings (I've heard them call "wheel pants") over top of the wheels and also on the landing gear strut. Beyond this, there isn't much else to do. The fairings could be made out of single pieces of material to limit the parasite drag introduced by rivets, etc.

There can be different variations on the fairing, but it pretty much comes down to fairings to reduce the drag:

NACA (precursor to NASA) details more in REPORT No. 518 THE DRAG OF AIRPLANE WHEELS, WHEEL FAIRINGS AND LANDING GEARS II-NONRETRACTABLE AND PARTLY RETRACTABLE LANDING GEARS

They also looked at wheel shape, but it primarily comes down to creating some sort of streamlined fairing to reduce the amount of eddying.


Are magnetic compass acceleration errors due to the southern side of the compass being weighted? When I was in college, I had an instructor who taught me that the acceleration errors in a magnetic compass were due to a counter-weight installed on the south-facing side of the compass that was intended to counter-balance the magnetic dip on the northern side.

It makes sense that this would reduce or prevent north/south-facing turning errors, and would also create acceleration errors while facing east or west.

For example, flying east the weight would be on the right, south-facing side, of the compass, which is the side labeled as 'N'.  Now imagine a straight line acceleration...

The heavier, right side, would move rearward in relation to the aircraft due to its inertial lag, bringing the, weighted, southern side of the compass (which reads north) closer to the compass window causing the viewed indication be a number closer to north, making the "accelerate north" error, true.

The thing is, I have never seen this explanation on paper, just that it is "magnetic dip" error.  Is it true, and can you find a source that says so, or was my professor wrong?

Some compasses are counterweighted to decrease magnetic dip. Older and/or cheaper compasses for land navigation are this way. Many to most are not weighted, especially in aviation compasses. Weighted compasses would require different compasses for the North and South hemispheres. Instead, aviation wet compasses are built with the low friction mounting point above the CG and magnetic bar. This causes the CG to move to the South polarity end of the compass assembly when the magnetic bar dips downward to the North Pole and to the North polarity end when dipping towards the South Pole. I like this article that explains this phenomenon.

Several decades ago, my unit had the opportunity to train with the Australian 3rd Para Regiment in Australia. Many of us had been using personally owned GI lensatic compasses because the tritium markers worked better than the newer, issued lensatic compasses. We were warned that the older models may not be accurate down under due to them being Northern Hemisphere compasses instead of the universal ones. I did not understand the reasoning for this until many years later.


What is the difference between slice, segment and leg? I have heard of the terms slice, segment and leg. Since I am a newbie in travel industry, I would like to know and understand the basic differences between the three.

Could someone please explain the three, using some kind of example?

I'm pretty sure those terms are not used consistently across all organisations in the air travel industry.

They are not defined in an IATA glossary I looked at but I did find this:

  Definition of Flight Segment

  The International Air Transport Association (IATA), the international trade body for airlines around the world, defines a flight segment as the operation of a flight with a single flight designator between the point where passengers first board an aircraft and the passengers' final destination. A flight designator includes an airline code, which has two letters or a number and a letter in combination, and a flight number of up to four digits. A flight segment can include any number of stops where passengers board and deplane the same aircraft operated by a single airline.

  Comparison of Flights and Legs

  A flight is defined by the IATA as the operation of one or more flight legs with the same flight designator. Unlike a flight segment, a flight may involve one or more aircraft. The IATA defines a leg as the operation of an aircraft from one scheduled departure station to its next scheduled arrival station. A flight segment can include one or more legs operated by a single aircraft with the same flight designator.

From eHow


What is the primary means of IFR navigation for private pilots? I have been doing a lot of reading into IFR navigation, and have been looking at the various instruments and systems that are used.  I am going to exclude GPS here, as I have been focussing on some of the more 'old-school' methods.

My question is, if a private pilot decided to fly their GA aircraft from A to B, lets say a distance of 500nm, what IFR systems would they use to navigate?

My first answer myself would be VOR, but the range seems to be a limiting factor.  For example, high altitude VORs have a maximum range of roughly 130nm (http://flighttraining.aopa.org/magazine/2000/December/200012_Features_The_ABCs_Of_VORs.html).  If we were flying between two major cities, this wouldn't be an issue, as I would expect plenty of stations to track to on the way, but what if I was flying between two airports where the VOR stations were positioned 300nm apart?  Is this sort of IFR navigation only possible with GPS?

Thanks in advance.

There are numerous options, and it depends highly on your route. But there are generally enough VORs scattered across the country such that you should be in range of a couple of them pretty much everywhere. As mentioned in another answer, there are NDBs, but in the continental US, generally, the ones not on an approach are getting fewer, as the FAA has followed a path of not repair them once they break. Other parts of the world, still use them and there are also NDB based airways(AIM has examples for how they can be charted on US charts).

If you had to plan a  flight from a field that doesn't have a navigational fix, and you don't have GPS, you'd start by looking for airways near where you are. Once you find some that go in the general direction you want to go, you start figuring out intersections near that or how you plan to intercept the airway. Then you end up most likely planning a zig-zag course following airways towards your destination.


Any ideas on what caused my engine failure? On my second solo flight I came back to do a few landings, and after the first landing I applied full power for takeoff to which the engine responded by just shutting off on me. Not sure if my mixture was too lean, if I applied power too quickly (which I read can temporarily lean mixture too much to keep the engine running), or something else. My CFI wasn't sure what caused this either.
After an embarrassing talk with ATC I was able to get it started up again just fine, and the plane has ran well ever since, so I'm 99% sure I caused the incident. Just not sure exactly what.
I fly a 1976 Cessna 150M. Airport elevation is 5500 above sea level (hence why I leaned my mixture in the first place, as it's advised in the POH). Weather that day was around 0C but very arid.

The most likely cause of your engine cutout is what's known as a rich cut caused by coarse application of full throttle. Most carburetors have an accelerator pump which jets extra fuel when the throttle is pushed in quickly, this is to make sure the engine has enough fuel and prevent what's known as a lean cut. However, at high density altitude your mixture needs to be leaner than at sea level, so it can in some circumstances do the opposite and give your engine too much fuel to burn.
It's also possible your mixture was too lean, so advancing the throttle caused it to die on you. There's no way to know for certain.
In the future advance the throttle smoothly, it doesn't have to be super slow, just don't jam it in. 2-3 seconds from idle to full is about right (same goes the other way too). If it starts going gluk gluk gluk on you enrich the mixture a couple of turns and see if that resolves it. Don't forget on a touch and go you have the option to abort, don't be afraid to use it if there's issues. Remember that takeoffs are optional, landings are mandatory.
And remember that carb heat! Icing can happen in any conditions.


Is trimming aircraft to relieve pilot of applying force on control stick/Pedal still applicable? I know that historically pilots used to trim an aircraft to relieve continuous application of force during climb/cruise/descent, and at that trim tabs existed on control surfaces (elevator, ailerons, etc) which could be used to hold the position of the control surface without the pilot applying any force. But now, we don't usually have trim tabs, and with fly-by-wire systems forces have been reduced on the pilot.

Does trimming do anything other than reduce pilot workload? Also:

Do modern aircraft still follow this concept of trim to reduce pilot's continuous force on the flight controls?
Apart from pilot workload and fuel efficiency (I know that trimming an aircraft can produce drag), what other benefits does trim offer?
Without trim tabs, how is trimming accomplished?

Almost all airplanes have trim (I'm fairly certain that the Wright Flyer didn't, so I can't say all airplanes do), but a lot of newer designs don't use trim tabs because they are less aerodynamically efficient than alternative designs.

For instance, the Falcon 50 & 900 that I fly doesn't have a single trim tab on it.  Normally the flight controls are moved by hydraulics and a small electrical actuator is used to adjust the position of the aileron and rudder for trim purposes.  Pitch trim is accomplished by moving the front of the entire horizontal stabilizer in order to adjust the angle and amount of lift produced by the tail.  This is done so that the elevator can be neutralized and not create the additional drag caused by being in the airflow.

On FBW airplanes, they may or may not have manual trim that is used (under normal circumstances) by the pilot.   Trimming is still taking place on FBW airplanes without manual trim, but it is simply automated.

Boeing typically designs their FBW airplanes so that they behave like a "normal" airplane, and require the pilot to trim in order to relieve the control forces.  This is all completely artificial though, programmed simply to give feedback to the pilot.

Airbus on the other hand doesn't give any feedback to the pilot through the side stick so there are no control forces to relieve.   When you release the side stick, it centers and the aircraft maintains its current pitch and bank angle.  In this case, the autopilot automatically trims the airplane for the current conditions, and the pilot doesn't need to worry about it.


Where to find comprehensive description of Special Use Airspaces (SUAs)? Can you suggest me some document or website where I can learn about Special Use Airspaces?

My goal is to understand the following topics:

SUA definition
Types of SUAs
SUA pubblication
SUA creation and activation
Documents in which SUA geometry and time information are stored.

If you know some website, pdf or book where I can learn about SUA I would be very glad. Feel free to add to the answer also your suggestions and knowledge about what you know relative to SUAs (especially about where geometry and time infos are stored).

Note: I know wikipedia or eurocontrol have some definitions but they are too concise for me. I would like to get something quite detailed and complete.

The definition of Special Use Airspace according to Wikipedia are:

  Is an area designated for operations of a nature such that limitations may be imposed on aircraft not participating in those operations. Often these operations are of a military nature.

Types of SUA's

  restricted airspace, prohibited airspace, military operations areas (MOA) and temporary flight restriction.

Two relevant PDF documents:
https://www.faa.gov/documentLibrary/media/Order/7400.8SBasic.pdf

https://www.faasafety.gov/files/events/GL/GL05/2007/GL0515004/CH_3_Sec_4.pdf

Wikipedia link: https://en.wikipedia.org/wiki/Special_use_airspace


How complete is our understanding of lift? I'm currently studying for my PPL and one of the accepted textbooks contains the following disclaimer at the end of the Principles of Flight section on lift:

  It is important to note that the forgoing explanation of lift, and its reliance on Bernoulli's theorem, is very much the 'classical' theory of lift production and the one on which the exam questions are usually based. There are differences of opinion amongst scientists on the subject....[snip]

The same book previously also describes the venturi theory which NASA discredits.

Additionally, one of my previous CFI's told me that during a previous successful job interview he had been asked to explain lift and had merely responded with "Which theory would you like me to cover?"

On the contrary - we must have an excellent understand of some components because of the way we're able to design and build such stable (and unstable when we want) aircraft. Plus, I see some absolutely incredible mathematics described on this website which seek to accurately answer complex questions.

So, my question isn't how is lift generated -it's how complete is our understanding? Which bits are still in dispute, and which bits are fully accepted?

Short answer: Yes, our understanding of lift is complete, but solving the equations for some practical cases needs more resources than what is technically sensible.

Lift is a matter of definition

First of all, lift is only one part of the aerodynamic forces. It is the component normal to the direction of airflow. Since the aircraft will distort the local flow around itself, this direction is taken ideally at an infinite distance where the air is undisturbed.

The other component is, of course, drag. It is defined as the part of the aerodynamic forces parallel to the direction of airflow.

The aerodynamic forces are the sum of all local pressures, which act orthogonally on the local surface of the airplane, and the shear forces, which act parallel to the local surface.

When aerodynamics was researched first, electric fields were new and exciting, and the same equations which help to calculate electromagnetic forces could be used to calculate aerodynamic forces. Therefore, abstract concepts like sources or sinks were used to explain aerodynamics. This made it not easier to understand, and many authors tried to find simpler explanations. Unfortunately, they were mostly too simple and not correct, but the next generation of authors would mostly copy what had been written before, so the wrong concepts were still bandied about.

To get to the bottom of it, it might help to look at lift at a molecular level:

Every air molecule is in a dynamic equilibrium between inertial, pressure and viscous effects:

Inertial means that the mass of the particle wants to travel on as before and needs force to be convinced otherwise.
Pressure means that air particles oscillate all the time and bounce into other air particles. The more bouncing, the more force they exert on their surroundings.
Viscosity means that air molecules, because of this oscillation, tend to assume the speed and direction of their neighbors.

All three contributions are well understood, and with the Navier-Stokes equations they can be completely mathematically expressed. What is still improving is our ability to solve these equations, and in turbulent flow the characteristic length required to capture all effects is so small that it is practically impossible to solve those equations fully with finite time and resources.

Flow over the upper side of the wing

Now to the airflow: When a wing approaches at subsonic speed, the low pressure area over its upper surface will suck in air ahead of it. See it this way: Above and downstream of a packet of air we have less bouncing of molecules (= less pressure), and now the undiminished bouncing of the air below and upstream of that packet will push its air molecules upwards and towards that wing. The packet of air will rise and accelerate towards the wing and be sucked into that low pressure area. Due to the acceleration, the packet will be stretched lengthwise and its pressure drops in sync with it picking up speed. Spreading happens in flow direction - the packet is distorted and stretched lengthwise, but contracts in the direction orthogonally to the flow. Once there, it will "see" that the wing below it curves away from its path of travel, and if that path would remain unchanged, a vacuum between the wing and our packet of air would form. Reluctantly (because it has mass and, therefore, inertia), the packet will change course and follow the wing's contour. This requires even lower pressure, to make the molecules overcome their inertia and change direction. This fast-flowing, low-pressure air will in turn suck in new air ahead and below of it, will go on to decelerate and regain its old pressure over the rear half of the wing, and will flow off with its new flow direction.

Note that lift can only happen if the upper contour of the wing will slope downwards and away from the initial path of the air flowing around the wing's leading edge. This could either be camber or angle of attack - both will have the same effect. Since camber allows for a gradual change of the contour, it is more efficient than angle of attack.

Flow over the lower side of the wing

A packet of air which ends up below the wing will experience less uplift and acceleration, and in the convex part of highly cambered airfoils it will experience a compression. It also has to change its flow path, because the cambered and/or inclined wing will push the air below it downwards, creating more pressure and more bouncing from above for our packet below the wing. When both packets arrive at the trailing edge, they will have picked up some downward speed.

Behind the wing, both packets will continue along their downward path for a while due to inertia and push other air below them down and sideways. Above them, this air, having been pushed sideways before, will now fill the space above our two packets. Macroscopically, this looks like two big vortices. But the air in these vortices cannot act on the wing anymore, so it will not affect drag or lift. See here for more on that effect, including pretty pictures.

Lift can be explained in several, equivalent ways

Following the picture of a pressure field outlined above, lift is the difference of pressure between upper and lower surface of the wing. The molecules will bounce against the wing skin more at the lower side than at the upper side, and the difference is lift.

Or you look at the macroscopic picture: A certain mass of air has been accelerated downwards by the wing, and this required a force to act on that air. This force is what keeps the aircraft up in the air: Lift.

If you look at the wing as a black box and only pay attention to the impulse of the inflowing and outflowing air, the wing will change the impulse by adding a downward component. The reaction force of this impulse change is lift.

Either way, you will arrive at the same result. By the way: Most of the directional change happens in the forward part of the airfoil, not at the trailing edge!

Supersonic flow

When the aircraft moves faster than pressure changes propagate through air, the changes in pressure are no longer smooth, but sudden. The aircraft will push the air molecules aside, producing a compression shock. Behind the shock front pressure, temperature and density are higher than ahead of it, and the increase is proportional to the local change in flow direction. The incremental pressure change $\delta p$ due to the aircraft hitting air with an incremental angle of $\delta\vartheta$, expressed in terms of the undisturbed flow with the index $\infty$, is proportional to the change in the streamlines:
$$\delta p = -\frac{\rho_{\infty}\cdot v^2_{\infty}}{\sqrt{Ma^2_{\infty} - 1}}\cdot\delta\vartheta$$

Gas pressure on a molecular level is the number and severity of particle collisions. The air molecules experience more collisions on the downstream side of the shock, since air pressure is higher there. The average  direction of the additional collisions is indeed orthogonal to the shock, because it is the boundary between blissfully unaware molecules at ambient pressure ahead of the shock and their bruised brethren downstream which have just crossed that boundary. Once a molecule has passed the shock, the collisions are coming again equally from all sides and its speed does not change any more.

If the surface curves away from the local flow direction, the air produces an expansion fan which re-sets the old pressure and density values when the air flows again in its original direction.

Pure supersonic lift is only a matter of the angle of incidence, and any local curvature of the wing will not change overall lift (but increase drag). Now the total aerodynamic force is normal to the wing, and drag will become proportional to the angle of incidence. In hypersonic flow you will get good results with the venerable impact theory first formulated by Isaac Newton.

Separated flow

This happens when the air molecules are no longer able to follow the contour of the aircraft. Instead, you get a chaotic, oscillating flow pattern which is very hard to compute exactly. This is really the only part of aerodynamics which cannot be predicted precisely, even though the effects are well understood. Separated flow will produce lift, too, but less than attached flow. In delta wings, this separation is produced on purpose to create what is called vortex lift.


Does an A320 revert to Direct Law if both engines flame out? In the case of a  flame-out in both engines on the two-engine A320, does the aircraft revert to Direct law or does it maintain Normal Law?

An example is US Airways 1549 (the landing on the Hudson).

The airplane will no longer be in normal law mode if both engines fail and no other electrical generator is online.

The airplane needs a primary source of electrical power in order to remain in normal law (among other things of course). If both engines lose power, then the generators on those engines also lose power. The only other primary electrical source is the APU generator. In addition to the batteries, the RAT (ram air turbine) is also available to supply electric power (along with hydraulic power) in an emergency situation. In this mode, the flight controls reconfigure to alternate law until a generator is brought back online.

From the US Airways 1549 report, page 88:

  ...the captain started the APU, which improved the outcome of the ditching by ensuring that a primary source of electrical power was available to the airplane and that the airplane remained in normal law and maintained the flight envelope protections


Who has authority to close a runway/airport? In the recent runway excursion at LGA, visibility was bad, and an airport ops vehicle called the tower to inform them of the excursion and that runway 13 was closed, and then that the airport was closed.

The tower is in charge during normal operations. Who has the authority to close a runway/airport? Is this codified somewhere?

This also applies on a smaller scale, as I've heard of such things as chunks of taxiway pavement going missing.

Generally two groups have authority to close a runway (or airport) for an incident/emergency, and if either says it's closed, it's closed:

The airport owner/operator/management.
It's their facility, so if they say it's closed, it's closed.
Specifically it's the persons authorized to issue NOTAMs for the airport who can close a runway (by issuing the NOTAM saying it's closed), but the chain of command for making this decision may vary from airport to airport.
Runways may also be closed by airport administration without issuing a NOTAM (this happens frequently at Brookhaven airport (KHWV) - "Closed Runway" X's will be put out on the crosswind runway when the banner tow operators are set up for pick-up/release on that runway). Often there's a blanket NOTAM about "banner tow ops" or similar that sort-of covers this situation (basically "Expect strange things to be happening because the banner tow people are doing...whatever it is they do".)
The control tower (if one exists).
Whether or not they have the administrative authority to "close" a runway, they certainly have the practical authority to do so by denying anyone clearance to take off/land from it or to enter it, and by issuing NOTAMs indicating that a runway is closed/unusable for some reason.

At an airport like LaGuardia where you have both an FAA Control Tower and a robust airport operations/management group (The Port Authority of New York & New Jersey) a Memorandum of Understanding (MOU) or similar agreement is likely in place to ensure that everyone knows who is authorized to do what when, but in cases like this where an aircraft has a runway excursion the course of action is pretty obvious and nobody is going to want aircraft to be moving around on the ground until the situation is under control and safety can be assured.


Why is it necessary for pilots to have trim controls on fly-by-wire aircraft? On Airbus family airliners why is it necessary for the pilots to have the facility to trim when there is no aerodynamic feedback through the flight controls?

Airbus FBW aircraft have an Autotrim system, so the trim wheel is only there as a backup. In normal law, the trim system is invisible to the pilot. The sidestick pitch inputs control load factor, unlike in a yoke aircraft where it controls elevator deflection. This means that that the farther you move the stick forward and back the faster it pitches, but at center it is a zero load factor, so it stays at its current pitch angle.

As an example of the difference, if you want to pitch up 10° in a yoke aircraft you pull back on the yoke until it reaches 10° and hold it there. If you let the pressure off it will return to 0° unless you retrim for 10°. Whereas in Airbus normal law, to pitch to 10° you pull on the sidestick until it reaches 10° then let go. The FBW system automatically maintains the new pitch angle. If you don’t do anything else the FBW system will automatically trim the stabilizer to the new pitch angle. There is no feedback as to elevator deflection because it’s not directly controlling the elevator.

Pilot misunderstanding of the Autotrim function was a factor in the crash of XL Airways flight 888T. When the AoA vanes froze, the computer switched to Alternate 2 law, which does not have the Autotrim function. Due to the AoA fault, the autopilot had trimmed the aircraft full nose up. When the AP disconnected and control law degraded it remained there and notified the pilot that he needed to trim manually. The PF did not realize this, so never moved the trim wheel. With the stabilizer in full nose up trim he didn’t have enough elevator authority to prevent a stall and crashed into the ocean.


What do professional pilots keep track of in their pilot log books? Professional pilot logbooks (either paper or electronic) always seem to be more elaborate than those used by private pilots.

I am curious as to what a professional pilot finds important to track in their logbooks besides just total flight time in aircraft type.

The experience required is simply flying hours on the type or configuration, and flying hours, for pilot logging purposes, is time from engine start to engine shutdown.  If you're flying an airplane with a Hobbs, which usually starts/stops using oil pressure, you can just use the Hobbs value.  If no Hobbs, record the engine start/stop time yourself and use that, or if you forgot to, just use the tachometer hours reading (which is closer to air time, or time airborne) and add a 10th.


Why do emergency exits over the wings have "step up and through motion" rather than having floor level exits? My questions stems from the following paragraph from Wikipedia:

  Additionally, during aircraft evacuations, it has been found that the
  majority of overwing window exit designs of Boeing 737 (NG) Next
  Generation Line along with the Airbus A320, hamper evacuation in
  comparison with traditional floor level exits due to the inherent
  "step up and through motion" required of passengers as they exit the
  aircraft, unlike the designs of older generation wide body aircraft
  such as the McDonnell Douglas DC-10 and Lockheed L1011 which are all
  floor level.

One more question I had, wouldn't it be better to have the same emergency exit procedures with respect to opening the exit door etc. on all type of commercial aircrafts?

(Image source)

The reason is the fillets (wing root fairings). They're curved as shown above.

You could have a plane without those fillets, but then there are two downsides:

Considerable increase in fuel consumption, and thus reduced range
Potential extra strengthening required for the fuselage/wing connections, as a direct floor-to-wing-top exit might change how the load transfers are distributed, resulting in increased aircraft weight.


What might have been the reasons for this low flight altitude? I was flying from Heathrow to Miami last wednesday (AA 39) and for the first ⅔ of the flight we were flying at 28.000 feet, only afterwards did it go up to 33.000 feet. So far I was under the impression that for reasons of fuel efficiency, airliners would try to fly as high as possible, and looking at the same flight on different days, it seems like they do in fact usually fly higher. So what could have been the reason for such a low altitude? Was it just weight due to being fully loaded, or are there other reasons as well?

Looking at the route your plane took, this low altitude flight was likely to avoid the polar jetstream. This is a band of wind that blows west to east in roughly the area the first half of your flight was flying through. It exists mostly between 30,000 and 39,000 feet altitude, and can range from about 60mph to over 200mph. I suspect that the low altitude was to keep the plane below this jetstream, avoiding the headwind and fuel and time costs that flying through it would create. To answer the other part of your question, as I mentioned in the comments, weight shouldn't have been an issue because the plane you were in (a 777-300ER), has more than enough engine power to maintain a higher altitude, even fully weighted.


Are there any aircraft where the wings are swept forward of the cockpit? Are there any aircraft where the wings are swept forward to form a C shape ahead of the cockpit? Something like this:

  --  --
 //    \\
 || /\ ||
 || || ||
 \\_||_//
  \____/

I want to do a research on that kind of aircraft and there are many science fiction examples, but I wonder if there are any real-world ones? If so, what is that wing configuration called?

The closest thing from the real world that comes close to the ones you found on deviantart are "Canard Aircraft"

If you read about this concept you will find that it is complicated to implement it succesful.
Then most of the art employ a forward swept wing, this has some complications as well. I would suggest you read some more about the NASA X-29

As far as I know a combination of the two has never been demonstrated in real life and only exist in fiction, therefore there is no general name for as far as my knowledge goes.


Why are emergency water landings the majority of the pre-flight safety briefing if they're so rare? According to an article published in the New York Daily News a few months after the "Miracle on the Hudson", when US Airways flight 1549 safely landed (watered?) on the Hudson River to the survival of all 155 souls on board, this incident was only the second ever emergency water landing that did not result in significant injuries and casualties in commercial aviation history.

And yet, the safety briefing at the beginning of every commercial flight adhering to aviation regulations spends more time discussing water landings than nearly any other topic, focussing on how to use life jackets, where to find them, where to inflate and where not to inflate them, how to use the emergency rafts, and so on.

Further, a very large amount of weight on commercial aircraft is devoted to equipment chiefly or entirely present to aid in water landings, with most commercial aircraft today having four or six emergency life rafts, hundreds of life jackets, and even the design of the aircraft itself adhering to minimum float time requirements.

With water landings so rarely attempted and even more rarely successful, why is there so much emphasis put on the current, ineffective methods? In other words, if water landings with current methods and technology generally don't work, why hasn't this changed?

The entry doors to an aircraft that is required to have life rafts are equipped with "slide rafts," which are dual purpose (land/water) so there is not any material difference in the weight. Some aircraft will also have perhaps one (maybe two) rafts in the cabin overhead (depending on the need for extra life raft capacity not covered in the entry door slide/raft).

I imagine, if controlled water landings were more frequent, design and technology might be modified in some way to make successful evacuations more efficient if that were necessary.  But, as you point out, controlled water landings are relatively rare, so likely the cost/benefit of creating an entirely different fuselage/wings/evac system would not be justified.

Of course, the fairly recent successful controlled water landing and evacuation into the Hudson is ample justification for having personal flotation devices (life vests, etc.) and associated emergency equipment designed primarily for water survival. Also, the design of that aircraft apparently provided for adequate flotation and evacuation as can be seen from the photographs.

The safety briefing before each flight by the Flight Attendants is relatively short and maybe 60 seconds are dedicated to explaining the operation of emergency equipment specific to water landings.


Are same-era military aircraft cockpits designed to be familiar to transitioning pilots? The wonderful SR-71 ha what looks to me an intimidating cockpit:

However, lots of planes of that era have ostensibly-similar cockpits to the layman, take this F-5 for instance:

I choose the F-5 as it was flying around the time the SR-71 was introduced, and thus potential SR-71 pilots may have been familiar with it. Would the cockpit designers have taken this into consideration? In general, are next-generation airplane cockpits designed to be familiar to pilots of current-generation aircraft?

Elements that may or may not be taken into consideration:

Placement and relative placement or grouping of instruments
Size and relative size of instruments
Lighting, colours
Calibration
Materials selection

Unless there is regulation enforcing certain aspects (e.g. as in the automotive sector), it is practicability would be the most probable cause leading to similar-ish cockpit designs.

Another reason would be convention, e.g. prior to the introduction of the side-stick, the center-stick was the way to do it.

Also, ergonomics is a very strong driver. During the landing approach, you wouldn't want to take your eyes far away from the windscreen to check altitude, speed and rate of sinking. Thus, these instruments are found in similar locations in most airplanes.


TCAS II - bottom omni-directional antenna I know that the TCAS II system has a lower antenna which can be either omnidirectional or directional.
How does the functionality of the system change? If the antenna is omni then I think / assume that it cannot know the bearing of an intruding aircraft and therefore can not provide data to position it on a display. Is it only used for transmitting interrogation and/or receiving other data?

Thanks,

Ori

The directionality of a TCAS antenna is ONLY used for positioning the bogey on the TCAS display, it is NOT used for determining time-to-contact. So you're still going to get TAs and RAs from the Omni antenna even if the upper antenna is blanked, but you won't get the display of that traffic.


What engine are these fan blades from? I bought these from a metal scrapper and paid about $30.00 total figuring they're worth more than that in cool factor. Problem is they aren't nearly as cool if I can't figure out what engine (and hopefully aircraft) they come from. All I know is the compressor blade is titanium and the turbine blade has a high nickel content. So here I am hoping someone has an idea.

Also what might cause the wear patterns at the tip of the turbine blade? I appears like it may be cracked and then repaired. I cant imagine they would repair damage that extensive.

I cant find any pitting on the edges of either blade, leading me to believe neither blade was ever used, is my thinking correct?

Turbine blade

source album

Markings:
Suction side

1475M85  (Possible 1475M35)
BF P01 C (could potentially be a G at the end)

Pressure side

FDW157B9

TE

1435P02
59669 (hard to see, could be something else)
G12P

Compressor blade

source album

Markings
Foot:

B778503 FC
MOJR

Turbine Blade
The turbine blade (part number 1475M35P01) is from the High Pressure Turbine (HPT) a CFM56-3 according to this ATSB report on performance testing of the engine. The report contains several images of blades which look similar to your photos.

Compressor blade
A search on locatory.com for the part number (B778503) lists the description as C-3 suggesting it could be a Stage 3 compressor blade. This would fit with the high aspect ratio of your blade.


What is some of this extra "stuff" on jet engines? At the risk of sounding too broad, I want to better understand the complications of jet engines. This time, I'm asking about extra "stuff", which unfortunately I have no better name for since I don't know what it is.

I'm familiar with the basic cycle of jets. Compressor stages draw in air and pressurize it, combustion heats and expands the air, and turbine stages extract some torque from the jet to drive the engine.

It all seems so simple. However, then I see pictures like these:

It's a modern turbofan. What is all that extra stuff? Can it really all be fuel and air lines? I'm especially scratching my head because the basic design has only a handful of moving parts (the stages/blades) all driven by the turbine and its shaft, so I can't imagine those are mostly hydraulic or electric lines either.

I found a simpler example here (Tumansky RD-10):

It is a turbojet and much older.

Of course the basic concept of a turbine engine is relatively simple, but the devil is in the details. To make an engine efficient, reliable, powerful, and safe, a lot more components are needed.

Fuel. Obviously an engine needs fuel to operate. The fuel is burned in combustors located around the circumference of the engine. This requires separate fuel lines to each of the combustors around this section of the engine. The fuel must be connected to the main fuel supply, and to the throttle/engine controls to meter the fuel flow.

Oil. All the rotating machinery inside of a turbine means that oil is needed to keep everything moving smoothly. There is an oil tank, and tubes to move it to where it is needed.

Main bleed air. Bleed air is taken from certain sections of the engine. This serves the air conditioning and anti-ice system and can be used to start other engines. This bleed air is taken from multiple places around the circumference, and from multiple stages provide the required pressures at different engine speeds.

Other bleed air. The basic design of a turbine engine has air entering the front and leaving the back. However, in a real engine, a lot more movement of air is going on. Engines have to operate in a huge range of conditions. Sometimes air needs to be bled from a certain section to manage the pressures and maintain stable operation. Sections of the turbine are also cooled by bleed air. It takes more tubing to move all this air around.

Sensors. Modern engines measure a lot of information to remain stable and efficient. This includes temperatures and pressures at multiple places all along the engine, as well as fire detectors and the speeds of the different rotors. These are all hooked back to the engine controls.

Generator. This is connected to one of the engine spools, and provides power to the aircraft, including all of the electronics on the engine itself.

Starter. Usually separate from the generator, also connected to an engine spool. This uses bleed air to turn the rotors in order to start the engine.

Control. Usually on the outside of the fan case (at the front of the engine, left side of the RR image in the question), modern engines run with a lot of electronics, referred to as Engine Electronic Control (EEC) or Full Authority Digital Engine Control (FADEC). All of the items above require wiring for control and feedback. Each tube will need different valves, connected back to the electronics, to control the operation. Liquids will need pumps and filters. There are also additional movable components inside the engine that can be adjusted by the engine control system.


Which aircraft had such a luxurious-looking navigator's station? I'm reading the BBC's How Fiji changed the way we travel; The little Pacific island nation was the first to incorporate GPS into its aviation system – and in doing so forever changed the way we get from Point A to distant Point B. and saw this photo of a spacious navigator's station with a large, elegantly designed desk, bay windows, and a small set of instruments.

What aircraft and timeframe was this? Does the photo portray a commercial flight?

bonus points: Were flare guns routinely stored out in the open like that at the time?

  Until the late 20th Century, flight crews often included a flight navigator whose job it was to keep the plane on course (Credit: Museum of Flight Foundation/Getty Images)

It's a Boeing 314 flying boat. From the late 30s (look at the two rectangular windows behind the cockpit).

The last dedicated navigators on long range flights had started to disappear by the late 60s in the airline business.


Why did the RAF buy the F-35B model and not the A model If the only issue is the in-flight refueling system (probe/drogue), wouldn't it make more sense to buy the A model and modify the tankers. The refueling issue doesn't compare to the performance penalty (range/internal weapons) of the B model.

The most probable reason is because of commonality, to reduce costs and support logistics. But, it also increases operational flexibility. The UK MOD want to operate them off the Queen Elizabeth carriers, and they do not have a catapult launch, but a ski jump. Only the B version can get airborne with this setup. So, the RAF had to go with the B version also. As mentioned in this article, having all aircraft as B versions means it is easier to always have the amount needed to fill operational squadrons for the carriers. If you split the buy between A and B versions, A versions cannot fill the place of B versions down for maintenance. Note however, the decision wasn’t “plain sailing” (without debate), as mentioned by J Southwell’s answer.


What safety differences exist between carrying laptops in checked versus carry-on baggage? Recent rumors say that the laptop ban might be extended to flights originating in Europe heading for the USA. This made me think, if laptops are not safe for carriage in the cabin how can they be safe for carriage in the belly of the aircraft? Say that a notebook is short wired such that if it turns on it ignites the battery. Storing the laptop in your carry on luggage would result in a cabin fire which can be put out by the cabin crew. But if this same laptop is in a checked-in bag there is no cabin crew near it. How is this risk mitigated? Or what are the procedures in case of a belly fire?

Furthermore if a laptop is carried inside a carry-on bag it can be switched-on at the security checkpoint to verify that it is a working laptop.

It's not about genuine laptops being safer as checked baggage. They're not, they're safer as carry-on baggage, where eventual fires can be identified, isolated and dealt with. That's why we have rules to make passengers carry-on lithium batteries more instead of checking them in. example

The reasoning explaining the ban is that an attacker might use the shell of a laptop to carry something on board. Turning on the laptop doesn't really prove much about it being genuine. You can take a Raspberry Pi that's size of a matchstick box, pair it with 2 AA batteries to create fake internals and  connect them to the original display. That'll make a gutted-out laptop appear to run for few minutes, enough to fool any quick inspection. Leaving rest of space and mass budget to hide something sizeable, like a bomb or a weapon.

That's why you can't circumvent the ban by removing the battery and taking a charger instead. It refers to "large electronic devices", not necessary ones with a battery.


What is the fastest single-engine civil turboprop aircraft with cabin seating? I was having a discussion with some friends about general aviation aircraft with cabin-class seating. We were discussing cruise speeds and there were some "shop talk opinions" flying around about what the fastest single-engine turboprop in general aviation is. I'm curious to know who holds the title.

In civil GA aircraft, TBM 900 is the fastest one with a top cruise speed of 330 knots (at 28000 ft).

Source: flightclub.jalopnik.com

However, if one considers all single engined turboprop aircraft, the fastest is the Pilatus PC-21, with a top speed of 370 knots.

"Pilatus pc-21 hb-hzc lands arp" by Adrian Pingstone (Arpingstone) - Own work. Licensed under Public Domain via Commons.


Why does the low voltage warning light not illuminate when the alt switch is on, but the engine is off? As part of the pre-flight inspection, one of the checks is to verify that the low voltage light is illuminated when switching just the battery on. This makes sense; there's a low voltage and the battery is being discharged because we're running everything off the battery, and the alternator is not providing any power.

However, as part of the startup - just before ignition - we switch both the battery and alternator switches on. At this point, the low voltage light is not illuminated, despite the alternator not providing power as the engine is not running. This doesn't make sense to me - though we've turned the ACU on, the alternator is not providing power. This seems like something that should trigger the warning light.

I've examined the C152 POH and it shows a basic electrical layout. I'm not sure as to the copyright of the handbook, so I won't post it here. It is available online for those interested, figure 7.7. Unfortunately, this did not help explain the behaviour I'm seeing.

I've reproduced this on two different 152s. Why does the warning light not detect the fact that the alternator is providing no power, or am I completely misunderstanding the function of this light?

If the ALT switch is not closed, but the BATT switch is closed, battery power is allowed to flow through the ALT FIELD breaker, through the Over Voltage warning light, and grounds through the Over Voltage Sensor.  If both the BATT and ALT switches are closed, current flows through both the ALT switch and maintains battery voltage at both terminals of the Over voltage warning light which prevents it from illuminating.  This design feature allows the Over voltage warning light to illuminate when either the alternator is not connected to the main electrical bus or the alternator is malfunctioning.


Are the instrument panels in the cockpit spill / waterproof? There are multiple switches and buttons in the cockpit, with different shapes and layouts. Are they spill proof?

What if the pilot spills water or coffee on them, will they still function?

No they are not, at least not fully. There have been instances of equipment failure caused by coffee spills, resulting in the need to abort the flight.
This example shows a flight that needed to divert because a coffee spill disabled the communication equipment.
This Boeing 707 had to make an emergency landing after the crew inadvertently spilled water on the autopilot panel causing the stabilizer trim wheel started to rotate. Control was lost as the plane pitched up and down. Three people died in the accident.
This Boeing 737 report had smoke in the cockpit because the previous flight crew spilled coffee and sugar over the avionics.
This Boeing 720 suffered control problems (resulting in Dutch roll) after a coffee spill cause a short circuit in the yaw damper.
This Airbus A330 diverted for an emergency landing after liquid was spilled onto electronic devices in the cockpit causing the smoke.

Source: Transport Accident Investigation Commission of New Zealand


What are the advantages and disadvantages of level flight with a nose-down attitude? This is a questions about fixed-wing aircraft in general -- commercial planes and smaller. I have seen on a video that planes are capable of flying in a holding pattern with an nose-down attitude "for greater passenger comfort".

So, what are the advantages and disadvantages of level flight (not descent) with a nose down attitude?

And for what reasons do pilots fly like this?

Generally, a slight nose-up attitude gives the best performance. This allows the fuselage to create some lift without producing too much drag, thus filling the drop in the spanwise lift distribution created by the interruption of the wing by the fuselage. However, in passenger aircraft this will make the job of attendants much harder because their trolleys need to be pushed uphill and will roll away when not secured.

Therefore, a neutral attitude is preferred in cruise. When the aircraft slows down, it needs to increase its angle of attack, so the nose-up attitude results. When flaps are deflected, the zero-lift angle of attack is reduced, so a smaller angle of attack will again be possible. The precise attitude is a side effect of speed, air density and flap settings, and is not deliberately controlled when flying a holding pattern. By this time the flight attendants have returned to their jump seats, anyway.

Note that some aircraft will fly a nose-down attitude by design. The Boeing B-52 has powerful flaps which are designed to allow it to lift off without rotating, and when the aircraft accelerates during the initial climb after take-off or flies its approach, the fuselage will have a nose-down attitude. See the picture below of the B-2, the B-1B and the B-52 all flying at the same speed, each with its own fuselage attitude.

B-2, B-1B and B-52 flying at the same speed (picture source).


What is the scratching sound produced by aircraft on the ground (taxi-in/taxi-out)? Since I have flown in aicraft as a kid, there was a sound audible when the aircraft is on ground (before taking off or after landing) which is similar to the sound a DJ does when he scratches the disks.

Sorry for the wird example, but I do not know how to explain it better. It is like the scratching of a disk and the sound starts at a higher pitch and it ends at a lower pitch. I am really interested in finding out what it is and why it happens, since I have never been able to find out how it is produced.

There is a variety of sounds an aircraft can produce, some even depending on the type of aircraft you are sitting in. Without any further data or reference, the most likely events that you can hear during pushback, taxi or vacating the runway are:

Cargo Doors being shut and locked
Flaps being extended to take-off position
Flaps being raised after landing

There are many more things that you can hear from the cabin, so without further information, it will be difficult to pin-point.

Another option, if it was predominantly on Airbus aircraft, is the Power Tranfer Unit, which is described to sound like a barking dog or like a drill.

See also this question and the answers:
What is this sound from Airbus aircraft before take off?


Why is alcoholic gasoline such a showstopper for aviation? One of the main reasons the common avgas grades are still full of 3-plumba-3,3-diethylpentane is the incompatibility of many aircraft fuel systems with the oxygenates (primarily ethanol, with some ETBE) used as octane boosters in mogas, as mentioned (for instance) here:

  [...]  87UL/E0 (similar fuels are called 82UL or 85UL) -- This is a tightly specified form of motor gasoline (mogas) -- without any ethanol or oxygenates in it, as many aircraft fuel systems aren't compatible with ethanol -- that is used in low-compression aviation piston engines mounted in airframes certified or STCed for operation on motor gasoline.  [...]

Bolding in original; emphatic italics added.

But the automotive industry had the exact same problem, and, yet, adapted easily to the advent of alcoholic unleaded gasoline (namely, by replacing incompatible fuel lines and seals and whatnot with ones not dissolved by ethanol).  So why are oxygenates so much more of a stumbling block for aircraft fuel systems and engines?

The modifications required are just not economically viable.

The main issue is vapor lock, because ethanol has a lower vapor pressure (i.e. more likely to vaporize) than gasoline.  Worse, mogas ethanol levels are varied to achieve ideal vapor pressure for different temperatures.  This is fine for cars that go through a tank of gas every week or two, over a relatively small temperature range, but a serious problem for planes where the gas may sit for months and then experience a wide temperature range at different altitudes in a single flight.

Vapor pressure matters because engine-driven fuel pumps, which are the norm on planes, pull fuel through the fuel lines.  Especially when combined with low wing tanks, ethanol may vaporize in the lines and block any further fuel flow, which is a far more serious problem for a plane than for a car.  Pure gasoline has a high enough vapor pressure that doesn't happen.  When ethanol was first added to mogas, carmakers solved this by moving the fuel pumps to the tank so the fuel is instead pushed through the fuel lines and therefore won't vaporize regardless of its vapor pressure, and given normal fleet turnover, that was the norm within a few years.  Some planes do have tank boost pumps like cars, but they are usually not intended to be run full-time; ethanol would require tank boost pumps that can run full time, which means either replacing the existing ones or adding new ones.

Ethanol is also more corrosive than gasoline.  Using ethanol regularly may mean replacing fuel pumps (both engine and, if applicable, tank), fuel lines, seals, injectors or carbs, etc.  To make such modifications, you'll need an STC for each.  Developing an STC is expensive and the market is quite limited, so the companies selling them need to charge a lot to recover their costs--on top of the high cost of the parts themselves, which have the same issues.  Also, while many engines were retroactively rated for mogas (even with ethanol in some cases), you still need an expensive STC to change the old placards that require avgas.

Also, while not directly related to ethanol, mogas doesn't contain lead.  Older airplane engines still require a tank of leaded avgas occasionally to lubricate valve seats and guides.  That can usually be fixed by replacing certain parts with newer ones made from newer materials, but that's not cheap either and usually best delayed until the next overhaul.  Until then, you can't run mogas full-time, regardless of the ethanol content.

Once you add up all these costs, retrofitting most GA aircraft for ethanol could easily end up being more than the planes are worth.


How do pilots align the HUD with their eyeballs? In fighter jets, how do pilots align the HUD with their eyeballs?

The other way around - you set up the pilot for eye-to-HUD alignment. When you are in the right position then you can see all the data-fields on the HUD - if you can't see them, you move your seat.


Why is A320's CG optimum position at 25% MAC? I have read a320's optimum CG position is 25% MAC. But, the aerodynamic center is also at 25% of chord.
So since CG and aerodynamic center at the same position, there would be no moment arm of lift, so what will be the use of tail plane?
Also, as fuel burns,
the CG shifts rearward,
in that case aerodynamic center will be in front of center of gravity.
wouldn't that mean center of gravity is behind the center of pressure?
I have read center of gravity is ahead of center of pressure in airliners, so wouldn't this be a violation.
Please explain my two questions.,

I do not know much about the specifics of the A320 design, but I will try to come up with some general answers to your questions.

  So since CG and aerodynamic center at the same position, there would be no moment arm of lift, so what will be the use of tail plane?

Even if it was the case in the A320 that the CG and AC coincide (I do not know), it does not mean that there is no moment from lifting forces. The aerodynamic center is not the point of zero moment, it is the point of constant moment within reasonable angles of attack. Hence there will be a moment from the lifting force. Assuming CG and AC coincide, the moment generated by lift will not change the total moment on the aircraft. Therefore a stabilizer is still required.

  Also, as fuel burns, the CG shifts rearward, in that case aerodynamic
  center will be in front of center of gravity. wouldn't that mean
  center of gravity is behind the center of pressure?

Not necessarily. The center of pressure is usually for most angles of attack behind the aerodynamic center. Therefore, under the assumption that the CG and AC coincide, the CG can move aft of the AC and still be in front of the center of pressure.