Was there a design flaw in the fuel tanks of the MiG-15/17/19/21? Wikipedia article on MiG-15:

  Another major design deficit was that the tank could develop under-pressure if more than half the fuel had been used, which could easily lead to tank implosions, destroying the aircraft.

MiG-17:

  Like its forebear, the MiG-17 inherited the major design deficit which could cause the fuel tanks develop to under-pressure if more than half the fuel had been used, which could easily lead to tank implosions, crushing the main fuselage of the aircraft mid-fight, with almost always fatal results.

MiG-19:

  Initial enthusiasm for the aircraft was dampened by several problems, the most alarming inherited from MiG-15/MiG-17 was the danger of mid-air tank implosions when more than half of the fuel had been used - the leaking fuel of the crushed fuselage fuel tanks located between the engines would then ignite, leading to a fatal explosion;

MiG-21:

  Additionally when more than half the fuel was used up, violent maneuveurs prevented fuel from flowing into the engine, thereby causing it to shutdown midflight.3 and risking tank implosions (a problem inherited from MiG-15/MiG-17 and MiG-19).

None of these entries has a citation.

I would like to know if these aircraft really did have a design flaw in the fuel tanks, and if so, what was it? What was wrong with the tank that made it susceptible to implosions once more than 50% of fuel was gone?

I found a reference to exploding fuel tanks on Mig-21's caused by overheating engines.

 "it had an unfortunate tendency to explode in mid-air. The problem was finally traced to a fuel tank placed under the engines that could cook up when the engines overheated."

  Like its forebear, the MiG-17 inherited the major design deficit which
  could cause the fuel tanks develop to under-pressure if more than half
  the fuel had been used, which could easily lead to tank implosions,
  crushing the main fuselage of the aircraft mid-fight, with almost
  always fatal results.

Tank implosion implies negative tank pressure. Under pressure or negative pressure is caused by improper fuel tank venting.

High pressure pumps sucking fuel out of an improperly vented tank can quickly develop negative pressure which can cause a tank collapse. If the tank was integral to the fuselage it could also cause an airframe failure. A collapsed tank could also leak fuel which could lead to catastrophic failure if the fuel found an ignition source.


How do windshear warning systems work? How do commercial aircraft windshear alert  warning systems work?

Modern commercial airliners have 2 different wind shear protection system:
1) predictive wind shear warning system
2) reactive wind shear warning system.

These systems work independently. PWS (predictive wind shear) works with weather radar. Reactive wind shear works with FAC ( Flight augmentation computer)

Basicly PWS can be switched ON and OFF from the WX-Radar  panel and it has some prerequisite for working :
Ground speed should be above 30 KTS, WX-Radar should be ON, At least one engine working etc. (may differ with different types).

PWS scans 5 NM ahead from 0-2300 ft and 1500 ft below according to phase of the flight. It works like a doppler radar. It scans the movement of air mass in front of you and "predicts" something goes wrong and warns you according to how bad is the situation. Doppler frequency will shift significantly in case of a microburst so PWS will catch this shift and warn pilots with amber or red cautions.

Reactive Wind shear system works with on board computers that takes real time data from all sources. This system will be active generally from 50 ft 1300 ft. (may differ)

Reactive Wind Shear basiclly monitors aircrafts energy level. For Airbus; FAC is responsible for that.
In computing the energy level FACs use different data from different sources: ADIRS - air, ground speed, vertical speed , slope. from other sources - wind gradient, vertical wind etc.

It will be active when the a/c energy level goes below predetermined threshold. It will alter from amber to red if your energy losing trend is faster.

You can read this document from airbus includes many general aviation information for more details :
http://www.airbus.com/fileadmin/media_gallery/files/safety_library_items/AirbusSafetyLib_-FLT_OPS-ADV_WX-SEQ02.pdf

Hope it helps.


How do I fly a direct entry holding pattern when approaching from an awkward angle? If my course lies anywhere within 30 degrees adjacent to the 'direct entry' sector borders, do I fly the holding pattern as depicted below?

To add to Michael Hall's answer, the direct entry is the one where you get straight on to the "racetrack" with minimum maneuvering and that is possible from anywhere within the direct entry sector.  The other two entries involve initial maneuvering "off the racetrack" so to speak.

That entry diagram is a procedural convention, not a hard regulation you must follow exactly.  The whole area is protected airspace, so it's not all that critical that you fly exactly this or exactly that as long as you stay in the protected airspace. You'll get dinged on a check ride for using a bad entry (using a sector's procedure while significantly outside of the boundary of that sector), but ATC would never bust you because you didn't follow the entry protocol perfectly, as long as you didn't leave the protected airspace and you got established properly without too much meandering around.


How does the thickness of a wing affect its aspect ratio? As far as I understand, the aspect ratio equals the wingspan divided by the chord or the square of the wingspan divided by the wing area. Given this formula factoring in only the wingspan, the chord, and the wing area, how does the thickness of a wing increase or decrease a wing's aspect ratio? If possible, please explain in plain English without using too complex mathematical formulas.

Indeed, the aspect ratio is defined as you describe. It is a way to define how slender the wing is for a given wing area, which is the main parameter in determining how to generate enough lift to keep the aircraft aloft. An area is two-dimensional, and a broadly rectangular shape like a wing area is defined by the length and the breadth of it: span and chord.

Aspect ratio describes the proportions of span and chord: a short stubby wing, or a long and slender one? This is one of the main parameters in how much drag the wing creates: a long slender wing minimises one particular form of aerodynamic drag, called induced drag.

 Image source

But a wing is a cantilever beam, subjected to aerodynamic lift. The lift forces bend the wing upwards, and the wing structure must produce internal forces that cancel out the aerodynamic lift. In a hollow cantilever beam like a wing, the skin mainly does that: the upper skin resists compression, and the lower skin resists tension. The further away the upper and lower skin are, the lower the stresses. A structural engineer wants to give as much distance between the plates as possible: he wants the wing to be very thick, in order for it to be light in weight.

But again aerodynamics puts a limit to this: a very thick wing would create too much form drag, so the structures people are given the maximum distance that the aerodynamics can support. Wing thickness affects aspect ratio in defining the maximum AR that can be achieved.

The wing thickness is not part of the induced drag, and does not appear in the definition of the aspect ratio. It is an important defining parameter in wing weight and other forms of drag.


How do class E/G airfields charge for stops without refuel? Do many Class E/G airfields charge for short stops without gas purchase? Sorry for the stupid question...recent PPL here and my training has mostly been T&G rather than full stops to the FBO. Planning a XC to KSHD and wanted to stop in for a bit to check out the facility.

I have found this really varies by airport and even by FBO at a given airport. The only way to know is either to check their website or call in advance and find out. After a quick look I don't see any prices listed on their site.

Often times the price is related to the services they provide by default. If you land and there is a marshaler waiting for you, a golf cart ride from your spot to the FBO building and loads of free local snacks: you're likely to be paying. If you land and the airport manager lives next door but his cell phone number is written on a sign that says "call for assistance", the fuel is self serve, and the gate code is the CTAF frequency: you're likely not paying for parking.

The one thing that's worth noting is if there is a local (usually nominal) landing fee charged by the municipality the airport resides in.

AOPA's airport information site has some fee info on it. For example KLOM has some fairly high fees for a class E un-towered field. While I can confirm from experience that the $5 ramp/parking fee at KDDH is waved for buying fuel.


What is "established" on an RNAV approach? I was looking at the RNAV (GPS) RWY 6 at 12J.  Thinking about my descent profile, I wondered when I could start my descent from my transition altitude if I was told to maintain an altitude until established.

For example, if the controller told me to "maintain 4000 until established," would I start descending after crossing the IAF and tear-dropping into the hold?  Would I start descending on the inbound leg?  Or, would I start descending after leaving the IAF inbound on the approach?

Edit:

This question assumes that a hold-in-lieu-of-procedure turn is required.  The question, really, is if a controller says "maintain 4000 until established," when can you start descending?  Can you descend as soon as you cross the IAF?

NOTE: This answer is specific to the United States as the question uses an example approach procedure from an airport in the United States. Procedures may vary for other nations. Consult the respective Aeronautical Information Publication for specific guidance.

As long as you hear the magic words "cleared  approach," you can begin your descent as soon as you cross the IAF the first time (while beginning your teardrop maneuver) and continue to descend to the minimum altitude while in the circuit, which is at or above 2000 for this particular procedure.

Note that you MUST be on a published segment of the approach before making your descent, otherwise terrain clearance is not assured.

The controller will expect you to proceed from the IF to the FAF after the first circuit is complete (a course reversal maneuver, if executed counts as the first circuit). You must advise the controller if additional circuits are required in order to lose altitude. Also, if the controller clears you for a "straight-in" approach and doing so would result in an excessive descent rate, it is incumbent upon you as the pilot to advise the controller that you are unable.

Reference: FAA JO 7110-615, Approach Clearance


Why doesn't the U.S. Federal Government auction their retired but memorable aircraft? The U.S. Federal Government has scores of old aircraft waiting for dismantling. Why doesn't it auction some of them? Some people might be very much interested in planes such as the B-52, and would be happy if they get it at some considerable price (though, I have no idea what it may be!) to keep them as a memorabilia. Also, this and this suggest that civilians can purchase and fly military aircraft. So why doesn't the federal government give this a shot?

Source

There are a few reasons for this.

First off they may not want the public, or more importantly potentially enemy nations obtaining a large quantity (or any quantity for that matter) of military planes. Even old war birds can still do a lot of damage if equipped by a person with intent on doing damage.

Secondly, the boneyard you have pictured serves a few purposes. For one it houses aircraft that have reached their life time limit. To keep an airplane flying it takes not only money but a supply of parts (or the resources to make your own under certain FAA rules). Out of service planes may be tough if not impossible to keep flying for no other reason than you cant get airworthy parts for them.

Thirdly, some of the planes in these bone yards are scrapped (or kept there) for reserve parts for the planes still in service. Again airworthy parts are not as simple to get as going to your local car parts store. There are many more regulations around them. In this case you can pull parts from an airworthy plane (if you know the cycles its been through) and use them to fix another plane.

Lastly, and this is mainly speculation, maybe the government is hidings its back up planes in plane sight...

On the note about buying old war birds, rules have changed over time and its not as easy to get ahold of government property as in days past. Some military equipment that sees its way to the public hands actually left the US as a sale to another country then that country sold it into public trade as well. For what its worth Trade-a-Plane has a whole section just for war birds.


Optimizing the airplane for best cruising altitude and velocity In the conceptual phase of the design, I am optimizing various entities of an airplane for the best cruising altitude and speed to reduce the cost, which also includes MTOW and fuel weight. Consider a scenario where airplane is undertaking a mission which will burn the entire mission fuel estimated. Now, in-flight it is very much likely that airplane is not able to fly at the best cruising altitude and/or speed. This will result in increase of fuel burn which might not be enough. How to tackle this problem of estimating fuel load for off-design conditions while optimizing the airplane?
One way to address this issue is to rely on the reserve fuel estimated for reserve mission such as loiter time. But, it might happen that airplane has to rely on the reserve fuel and due to increase in fuel burn during cruise, reserve fuel is less for loiter time. I don't think this is a desirable condition. Another way is to optimize the airplane for worst scenario. Now, the question arises what is that worst scenario. Is it flying at the cruise ceiling (cruising altitude and cruise ceiling are different) or something else?
Let me know how to address this problem. Thanks in advance!

Are you designing a new airplane? If I understand the question correctly, For a normally aspirated engine, the engine is most efficient when the throttle is fully open at a particular altitude, where it produces approximately 65% -75% power. Therefore the airframe with respect to wing design, angle of incidence etc should be matched to give the best lift/drag ratio at that altitude. You will have to consult with the engine manufacturer to establish what that altitude is. Your choice of propeller is also going to have to be factored.
Then you calculate the fuel reserves accordingly.
Fuel reserves are calculated according to legal requirements of the country in which the airplane is registered and also in which it is operating. This varies according to the type of aircraft and the operation. For instance the minimum legal reserves are different for a passenger jet on a commercial flight, to a single engine airplane being operated on a VFR flight in the private category. Most countries laws are similar but there might be small variations, and they all have to satisfy ICAO standards if the country is an ICAO member state.


How do the VNAV and LNAV work on the 737NG? So, I'm very confused. Im from a Cessna background, no FMC. So, based on my understanding, you could run the autopilot independent of the FMC right? With Speed mode, HDG SEL mode, and V/S mode, am I right or wrong?

And if you enable VNAV and LNAV, the FMC takes over right? But I heard people say you can change the V/S in VNAV mode. How is that possible? I thought the FMC has full authority, and the flight route you filed in the FMC is final?  And does this mean you can also change the HDG in LNAV mode?

I see some confusion about the Autopilot system here. First let's clear something up:

The B737 has 3 guidance: speed, horizontal and vertical. These are displayed on the top of the PFD from left to right.
Engaging Flight Director displays the guidance but not to follow it, engaging the Autopilot tells the plane to follow the guidance.
Each guidance has several modes. E.g. Possible horizontal guidance modes include "HDG SEL", "HDG HLD", "LNAV" etc. Possible vertical guidance modes include "V/S", "ALT HLD", "VNAV" etc.

LNAV is just one of the horizontal guidance modes. The FMC decides what is LNAV. If LNAV is not engaged, then the FMC does not take part in horizontal navigation.

Your confusion likely arises from armed modes. The B737 allows you to select one active mode, plus one armed mode. For example, consider the LNAV path in FMC is heading North (360 degrees). The plane is to the East of the intended path (right side). By doing the following:

Set the heading window to "340".
Set "HDL SEL" as active mode.
Set "LNAV" as armed mode.

The plane is on a heading to join the LNAV course. When the plane is close*1, the horizontal mode will automatically change from "HDG SEL" to "LNAV".

Similarly, "V/S" can be used to capture VNAV profile when the plane is above or below the intended altitude.

*1: The plane has to be within a certain nautical miles and the intercept angle cannot exceed a certain degree. I will update the exact number when I get reference to the B737 manuals.


Are there any incidents caused by rudder failure in Military jets? Based on this question about the rudder position of the F/A-18 Fighter Jet.

Quote from the user Rhino Driver:

  The logic has its limits though and if the pilot exceeds 14 AoA in a landing mode (flaps half or full), the FCS may accidently depart the jet. This is obviously bad 200 ft above the ground.

  As stated before, there are times when the rudders may suddenly fare themselves which can have devastating effects during the final portion to land. Rudder failures are serious problems and should be treated as such.

Are there any known incidents where the pilot (as example) exceeded 14 AoA in landing mode and the FCS accidently departed the jet?

The FCS has to play a certain role in the incident (like in the example) or like the incident No. 3 from the user aeroalias.

There are certainly a large number of incidents/accidents in military jets involving rudders. I've listed a few cases, not necessarily in takeoff/landing.

A Block 25 F-16C suffered structural failure during flutter tests with the AMRAAM missile. The rudder delaminated and tore off, and the pilot managed to land the aircraft.

Source: f-16.net

B-52 vertical stabilizers were prone to failure during operation at low altitudes. While under testing, a B-52H suffered catastrophic failure of vertical stabilizer. The pilots managed to land the aircraft with help from Boeing test engineers.

"Boeing B-52 with no vertical stabilizer" by United States Air Force - USAF. Licensed under Public Domain via Commons.

However, in other cases, the same failure caused fatal crashes.

A USAF investigation blamed rudder failure for the loss of an F-15 near Hawaii in 2008. The investigation concluded that most probably both rudders in the jet failed due to failure of the aileron-rudder interconnect.
F-14 suffered from rudder hardover incidents, one of which lead to loss of the aircraft. Investigations found the reason was due to mechanical failure of a stop plate attached to the hydraulic actuator.


Why is "LINING UP" used as the proper response to a "conditional" line-up instruction? This is a list of the ICAO's standard phraseologies used for preparation for takeoff. I don't understand why "lining up" is (recommended to be) used as a response to a conditional line-up instruction. It can be very confusing, because it sounds like the pilot is lining up (against the ATC's intention) when he has to wait until the condition is met, like in the situation where the pilot has to wait until the arriving airplane touches down before she can taxi onto the runway to line up. I'm not a native speaker, so it might be just me. Does it sound reasonable to native speakers?

"Lining up" is not a proper response to a conditional lineup instruction;

"(condition) lining up (brief reiteration of condition)" is correct.

To use an actual example:

ATC: "RYR123 behind landing Airbus 320, line up runway 28L behind"

Pilot: "Behind landing Airbus 320, lining up runway 28L behind"

In my opinion, that leaves very little room for confusion.


How will the Rolls Royce UltraFan provide reverse thrust? When perusing the Wikipedia article on the upcoming Rolls Royce UltraFan engine, I noticed that it cited an interesting bit of information from an Aviation Week article:

  As the fan system is designed to vary pitch in all phases of flight, including landing, the nacelle will not include a thrust reverser.

I understand that a turboprop can enter the beta range in order to vary the blade pitch into the negative range in order to supply reverse thrust.

However, my understanding of the UltraFan was that it is to be a geared turbofan design with the fan and the core ducted inside a more-or-less conventional turbofan nacelle (minus the thrust reverser, apparently.)

My question, then, is how does the airflow work through this engine with negative fan blade pitch?

When the blade pitch goes negative, then the fan will be blowing air out the intake rather than sucking it in through the intake, no? Where then is the air coming from which is getting pushed out the front and where is the air coming from that is still needing to go in the normal flow direction through the core? Does the flow direction through the bypass ducts reverse?

The flow direction reverses only through the bypass duct pulling by blades with negative pitch. A portion of it will still be sucked by low pressure compressor making 180° turn into the core. Having to counteract the losses in turn will obviously reduce the performance.
As stated in research paper by the team funded by Rolls-Royce plc: "the core mass flow rate was 57% of that at take-off conditions, for bypass duct flow rates of 74% of total take-off mass flow."

Another design by Pratt & Whitney features reversed position of the whole core requiring two turns of the flow for incoming and outgoing air. So, these turns are not a big problem as we see them traded for other pros.


Why 1st and 2nd class but not fast or slow airplanes? Why do airlines separate passengers into 1st and 2nd class but do not offer fast or slow connections? Isn't the biggest cost the kerosene? And isn't the cost directly proportional to speed?

Concorde was built for speed. But it was costly too. People did not like it much. Reality was that they didn't want to get somewhere faster by paying more. People love to pay for luxury though. That is the reason different travel classes were introduced since late 1970s.

Cost of fuel and speed are NOT directly related. As you may know, Boeing 787 has increased fuel efficiency (claimed to be the most fuel-efficient), and still reaching higher speeds.


How to find total climbing time based on Rate of Climb? I am unsure on how to solve this problem. The only clue i have is to integrate ROC to find time.

A jet aircraft has the capacity to fly at an absolute altitude ceiling of 11000 m,
and a rate of climb (ROC) at sea level of 20.87 m/s. Calculate the time to climb
from sea level to 8000 m. Assume a linear variation of the rate of climb with
altitude during the whole maneuver.

The fastest way is an integration. If you plot the inverted climb speed over altitude like in the plot below, the area under the curve will give you the time to climb. I would suggest you calculate the climb speed at every 1000 m by rule of proportion — at sea level it is 20.87 m/s and at 11.000 m it is 0 m/s. Then you get a plot like the one below. The red circles are the calculated points; the lines between them are straight interpolations.

Since the unit on the Y-axis is seconds per meter and the unit on the X-axis is meters, the area is in seconds. Just calculate the area of each trapezoid between the start and the end altitudes and add them. In the figure below I have crosshatched the trapezoids between 3000 m and 8000 m.

Inverted climb speed over altitude plot. Caution — this is a generic plot I did for this purpose earlier, so it uses different numbers. I crosshatched the area between 3000 m and 8000 m, because I made the plot for calculating the climb time from 3000 m to 8000 m.


How do fighter jets measure how high they are? I know most of the commercial planes use altimeter to find how high they are. I was just curious in finding out what fighter jets use to to find their height and what are the other technologies that could be used other than pitot tubes to find speed of an aircraft or fighter jet.

2. What material are used to make pitot tubes in aeroplane?

Fighter jets have the same system as commercial aircraft: An altimeter based upon external air pressure. this measures their altitude relative to pre-defined atmospheric conditions. Many will also include a secondary system that relies on GPS (or local equivalent) signals to produce a height above the reference geoid rather than an atmospheric datum.

Regarding your second question - you should only post one question per topic. An answer is difficult as the construction varies significantly between manufacturers. Many pitots are made of steel variants, however.


Why is air mixed with bypass air on the A/C of an aircraft? Air is taken from the compressors, then it is cooled by the air that comes from the ram air inlet. After that, it is compressed and cooled again by an expansion turbine. When finally air is condensed, it mixes with bypass bleed air. What is bypass bleed air?

In short

Bypass bleed air is a fraction of the bleed air coming from the core compressor. It's named like this because it doesn't cross the air cycle machine of the packs as does the regular bleed air.

On the following picture this bypass bleed air is identified as trim air. Its purpose is to be mixed with cooler bleed air from the packs to modulate the temperature in the different zones.

Mixing is done by the mixing and distribution unit (see more below).

Use of trim air on the Airbus A320 family. (Source: A319/A320/A321 ECS Familiarization and Training Manual)

Boeing has open a new approach for air conditioning and pressurization using ram air rather than bleed air. The first aircraft with this approach is the B787, this requires dedicated compressors.

Details

The air conditioning and pressurization systems on large airliners are quite similar. Here is the overall picture:

Air conditioning and a part of the pressurization are obtained using the environmental control system (ECS)
Bleed air, the high pressure air taken from the engine cores and APU, is very hot.
Ram air, the cool low pressure air taken from the aircraft belly, is used to cool the bleed air in heat exchangers. This ram air, which gets warmer in the process, is rejected in the atmosphere without entering the cabin. A fan is used to create the ram air flow when the aircraft is on the ground.
Air conditioning packs are mainly air cycle machines (refreshers) that receive pre-cooled bleed air and deliver air at ambient temperature. There are usually 2 or 3 packs for redundancy.Some bleed air bypasses the ACM and can be used later by the mixing unit.
Air from the packs goes to the mixing and distribution unit which role is to mix air from packs with air already in the cabin, and deliver the result to different zones of the aircraft. The unit can vary temperature according to zones by mixing packs output air and bypass bleed air. The unit also mixes air from the ground supply when at the gate and engines and APU are not running.
Air in the cabin is recirculated by two or more fans which return it to the mixing unit.
As air is pumped into the aircraft by the mixing unit, air also exits the aircraft through one or several outflow valve(s). The exact quantity of air leaving the aircraft is controlled so that the pressure inside the aircraft is at the required value.This value is usually expressed as cabin altitude, that is the altitude we would find this pressure in the standard atmosphere. Pressure is about 1013 hPa at sea level and then decreases continuously when altitude increases.However the cabin altitude doesn't climb as high as the aircraft because there would be an insufficient oxygen pressure in the cabin. The cabin altitude is kept proportional to the aircraft altitude, but usually the minimum of pressure is a value equivalent to 6,000 to 6,500 ft.
All those elements are driven by controllers that can be monitored and programmed by the crew.

Let's look at the ECS for the Airbus A320.

1. Location of elements

(When not specified, the source of the images is the A319/A320/A321 ECS Familiarization and Training Manual)

2. Packs

A view of a pack with the triangular ram air inlet (the ram air outlet has been removed):

The pack includes:

Two air-to-air heat exchangers: main (MHX) and primary (PHX). Ram air is used as the heat receiver fluid for both.
A centrifugal compressor (COMP) and a turbine (TURB). They compose the air cycle machine (ACM) which cools and reduces pressure of bleed air.
A reheater (RH), a condenser (COND) and a water extractor (WE) to dry bleed air.

3. Air cycle machine

4. Pack operation

A pack works this way:

Hot high pressure bleed air is directed to the PHX which cools it a bit so that it can be processed more efficiently by the ACM.
Cooled air is sent to the compressor. Increasing the pressure allows for more heat to be extracted in the next step. Air gets very hot again.
Compressed hot air is sent to the MHX which remove as much heat as possible, possibly below the ram air temperature, which is great while on the ground.
Cool air, which contains water vapor, goes to a reheater and a condenser to create liquid water, water is collected by the water separator. This water is reinjected into the ram air to cool it before it is used in the exchangers.
Cool air finally rotates the turbine which extracts energy from it to drive the compressor and a ram air fan. The energy loss produces a cool low pressure air which can be used in the cabin and cockpit.

The exact temperature and moisture of air delivered by the pack are obtained by mixing air from the ACM turbine, cooler air from the PHX and warmest bypass bleed air taken upstream the MHX.

Water extraction is controlled by adjusting the temperature, in the same way, of the airflow going through the condenser.

Bypass bleed air is also delivered by the pack to the mixing unit for zone temperature trimming.

5. Water extractor

Collected water is reinjected into ram air flow.

6. Air temperature and pressure at each step

FCV: Flow control valve (bleed air input)


What's this aircraft in the background? I took this photo from the Wikipedia entry on afterburners. What's the circled aircraft in the background behind the Phantom?

The aircraft (I presume you mean what’s visible behind the green F-4 Phantom in the right of the photograph) appears to be a rare surviving prototype of a Dornier Do31 VTOL transport aircraft.


Why does the U.S. keep thousands of retired aircraft in storage? A view of Davis-Monthan AFB shows thousands of retired aircraft sitting in the desert.

They go through great lengths to preserve them, even sealing them with an opaque white, hi-tech vinyl plastic compound called "spraylat."

Such an enormous stash of aircraft makes me wonder what they're being kept for. I'm sure there are a few uses for some of them but certainly not all of them. There can't be a big demand for spare parts from obsolete planes. It seems like they would want to scrap them.

Are they being kept in case there is some sort of all-out war and they need cobble together a bunch of F-4's and C-141's to support the air force? Would that even be feasible?

Does it somehow cost more to scrap them than the materials are worth?

Why are they keeping so many retired planes?

Photos retrieved from airplaneboneyards.com

Some aircraft sold or loaned to outside military forces are built in batches. These aircraft stay in service for a longer period of time than those in the advancing military power, making spares very difficult to obtain and replacement aircraft for those lost in action are going to be impossable to get. I remember on 19 Squadron in RAFG Wildenrath (1979/82), the F4 Phantom was very demanding on which panels and parts would swop between aircraft. The Phantom also went through many states of evolution and when our Govenment decided it was cheaper to buy more F4 aircraft, they had to consider the spares, fitment and training that would be needed to keep our units similar. The Phantoms that were purchased I believe came from the boneyard.
Of course, the 'all out war' theroy also holds true, if a planet size war was to break out, and you recall all your old pilots.... easier to shove them in aircraft they flew 30-40 years ago than train them in the newer stuff.... going to get very messy up there and replacing pilots/ planes will be a priority, numbers can sometimes win wars. Life expectancy of our frontline pilots were 2/3 sorties at best, Ground crew in fixed bases were 2 days at most..... I miss the old days.


How do larger aircraft compensate for reduced visibility from the cockpit, e.g. less visibility of the rear of the aircraft? In smaller planes, pilots has apparently great visibility in front, on the sides and a good portion of the rear of the plane. But as the plane's size is increased, the visibility is also reduced. One obvious factor is height of the cockpit from ground, but it appears (from pictures) that pilots of bigger Boeing/Airbus planes have too many blind spots. However, I did notice that some bigger planes have a camera behind the nose gear to ease in taxiing etc.

So the question is that how do pilots compensate for this lesser visibility? Do they always need external help (e.g. ground crew)? Is there some sophisticated technology helping them? I am sure they cannot just raise or lower a wing or some other maneuver to check nearby traffic.

Appearances can be deceiving. The view "behind" a Piper Cherokee looks something like the image below: no rear window so you can't see what's behind you, but that really doesn't matter since there's no way to go "backward" in this aircraft using the flight controls.

Visibility aside, ground handling is often a a complex production, particularly for larger aircraft or when you have a lot of aircraft in proximity to each other or obstacles.

Moving small aircraft around typically requires at least 3 people. When you're moving forward you will have the person operating the tug and two "wing walkers" who stand a few feet off the wingtips and walk along to make sure the wings aren't going to hit anything. When pushing an aircraft back in a tightly packed hangar there's sometimes a fourth person walking ahead of the tail to make sure you don't back the plane into something.
Since there's not usually much for the pilot to do inside the plane at this point, they usually serve as one of the walkers.

Larger aircraft observe similar procedures, but for push-backs or power-backs it's known that the area behind the aircraft is clear (this is usually coordinated over the radio), and as long as the tug driver or pilot keeps the nosewheel on the appropriate pavement markings there will be wingtip clearance.

Line personnel are also often stationed to guide aircraft to and from parking in close quarters where positioning is critical (e.g. when pulling an airliner up to a gate, or parking a small aircraft on a busy ramp).

The other half of the picture is taxiing under your own power and control.

When taxiing, it's generally assumed that the pilot knows their aircraft's dimensions and will avoid hitting things. This usually works out well, but that is not always the case.

Airport taxiways are marked so an aircraft with a specific maximum wingspan will be clear of any obstacles while taxiing along the centerline, and as you're generally only going forward that's where visibility is most important (you can assume if the area your wingtip was going to hit was clear 15 seconds ago when you last saw it and nothing was heading into that area it's still clear now, and you're relying on the pilot of the aircraft behind you to be paying attention and not taxi into your tail).


Refuelling an airbus to maximum The airbus A350 aircraft when being refuelled seems to drop when the wings are filled.How  much is the drop from empty to full.Thankyou

That’s going to depend on a lot of things including how well serviced the struts are, what the existing payload on the aircraft is and whether the aircraft is parked on any sort of grade.

I don’t work the A350, but I work other heavy aircraft and I’ve had them “settle” quite a bit when putting on a full fuel load.


From which aircraft does this vintage altimeter come from? I bought this vintage U.S. Navy Kollsman altimeter at a market in Bangkok, Thailand.

Unfortunately, I don't have any info other than what you see in the photos.

It's a Kollsman altimter and the model or serial number is KO-67ICLU-035 Type/6433 MB-I

There is another serial number(?) on the scale which reads MS28044LI, and below ALT it reads 50,000FT.

Here's another clue: This sticker says the altimeter was serviced in the PNCLA (Pensacola) 89771 NAVAL AIR REWORK FACILITY in the 3rd fiscal quarter of 1981.

Another sticker says it was tested at the Naval Air Rework Facility Pensacola (NARF) and found to be free of radioactivity, also in 1981.

Finally, S/N-71 is embossed on the backside of the altimeter.

So what type of aircraft could this instrument have been part of?

What you have is a Kollsman C-12 altimeter manufactured by the Square D Company in Elmhurst, New York. The 50,000 FT marking below the Military Standard number means that the altimeter is accurate up to 50,000 feet of altitude but this number might far exceed the capabilities of a particular aircraft as it was universally used on many different types. The free of radioactivity sticker means that this instrument does not have the radium dials found on earlier models (common on WW-2 instruments) or, was later retro-fitted with a non radium face. Since you purchased this instrument in Thailand I am suggesting it came from a T-28 Trojan. The Royal Thai Air Force operated 120 T-28s from 1962 to 1988. The United States Navy ceased T-28 operations in 1984 but by then many of their T-28Bs  had been modified into "Ds" as counter insurgency aircraft and shipped abroad. Since the Thai Air Force recieved all their aircraft from America, there is a excellent possibility that your instrument came to Thailand either in a ex Navy T-28 or as a spare in a support maintenance package.


Is implementation of CPDLC mandated by EASA? Is CPDLC (Controller–pilot data link communications) mandatory by EASA? I have not heard any update that Airlines are using CPDLC. While talking to some of the pilots I heard that they have been instructed to switch the System due to satellite cost. What is the real scenario?

according to eurocontrol, http://www.eurocontrol.int/services/link-2000-programme:

  The LINK 2000+ Programme started in 2001 and is now in the full scale
  implementation phase governed by the DLS IR which requires:

  • All newly delivered aircraft operating above FL285 to be equipped as
  of 2011,

  • Core European ANSPs to be operational by 7 February  2013,

  • The rest of European ANSPs to be operational by 5 February 2015,

  • All existing aircraft operating above FL295 to be retroffited by 5
  Feb 2015 (unless exempt).

What aircraft are exempt? See page 4 of this pdf: http://ec.europa.eu/transport/modes/air/single_european_sky/doc/implementing_rules/2014_01_22_2nd_exemption_under_29_2009.pdf


What is the relation between sweep angle and lift-to-drag ratio? What is the relation between sweep angle and lift-to-drag ratio?
Ans does depend on wing planform?
For subsonic speeds.

This is my take on this.
We assume that an infinite-span swept wing is under compressible flow, and that the flow acts on it as in Figure 1 below:

With that, we can now utilize the equation of motion to find the relation between the sweep angle and the coefficient of lift, which in turn, will make the relation with the ratio L/D
From the equation of motion, we have:
$$(1-M^2_{\infty}\cos^2\Lambda)\frac{\partial^2 \phi}{\partial x^2} + \frac{\partial^2 \phi}{\partial y^2}$$
Now, only the perpendicular component acts we have that:
$$(u'_c)_n = \frac{\partial \phi}{\partial x} = \frac{1}{\sqrt{1-M^2_{\infty}\cos^2\Lambda}} \frac{\partial \Phi}{\partial x} = \frac{(u'_i)_n}{\sqrt{1-M^2_{\infty}\cos^2\Lambda}}$$
$$C_{p_c} = -2\frac{\cos\Lambda(u'_c)_n}{U_\infty} = -2\frac{\cos\Lambda(u'_i)_n}{U_\infty\sqrt{1-M^2_{\infty}\cos^2\Lambda}}$$
Now, since:
$$C_L = \frac{1}{c}\oint C_p dx$$
We have that:
$$C_L = \frac{C_{Li} }{\sqrt{1-M^2_{\infty}\cos^2\Lambda}}$$
The above equation shows that the lift coefficient is sweep angle dependent, therefore, the ratio L/D is also sweep angle dependent.
This is a very complex side of aerodynamics and understanding it completely requires some study. I recommend studying Chapter 11 from "Fundamentals of Aerodynamics" by J. Anderson (a classic) and Chapter 8 from "Aerodynamics for Engineering Students" by E.L. Hughton.


Why would an airplane pilot choose to intentionally use more runway than required for a takeoff? An assumed temperature takeoff intentionally requires a pilot to use more runway than would be normally required.  Why would someone want to do that instead of getting off the runway in the minimum distance possible?

Imagine you're doing a takeoff at a high density altitude. You need more runway to get up to speed because your engine is producing less power and you need to move faster to move the same amount of air over your wings as you would at a lower DA.

Aircraft can pretend the DA is higher by using a higher than normal temperature when calculating takeoff information. In jets with automated engine controllers, this setting -in a round about way- allows you to set the engines to produce only the minimum thrust required to get off the ground safely. Since that results in less thrust, there is less wear on the engine and that adds up significantly over time.

Your trade-off for this decreased wear is that you need more runway, which is usually readily available. If you suddenly need full power you just move the throttle to the Take-Off/Go-Around (TOGA) or emergency power setting (or push a TOGA button on the throttle), which overrides the temperature preset.


Is there a type of instrument/display that guides pilots along a certain path? What do you call an instrument that can help a pilot fly along a predetermined flight path (e.g. path thru GPS coordinates), showing them when they stray a little so they can correct? Not a control system, but just a visual feedback display. I want to say I've seen something like it before, that had two panels each with a plane symbol and "reticle", but I would like to know what it is that I'm describing. Thanks

What you are describing is a Course Deviation Indicator or CDI.

These are fairly standard across most aircraft however they may also be combined with a heading indicator resulting in an Horizontal Situation Indicator. There are also variants that have an aircraft symbol such as you describe.

Depending on how your aircraft is setup these units can be referenced off a radio beacon such as a VOR an ILS system for approaches or a programed GPS route.

This video covers some basic operation if you are curious.

A lot of GPS units with moving maps are generally able to display the info you describe as well.

There are even various apps that allow you to display such info on your tablet or smart phone


What should a pilot do if he does not know where he is and has no form of communication? I know this is an almost impossible situation, but... Imagine that a pilot is kidnapped and placed inside a Cessna plane. At a certain point the kidnapper jumps out of the plane, destroying the radio and taking all the aeronautical charts with him.

My question is: what should the pilot do, since he does not know where he is (he does not even know which country), there are no signs of civilization where he's flying, and he has no aeronautical charts?

The first thing you should do during a lost com's situation is fly the plane (that is really the first thing you should always do).

The second thing you should do is use visual reference points to figure out where you may be and get some situational awareness. Even in a foreign land a pilot may be able to identify known land marks like city skylines or prominent geological features. Even something like a coast line can be identifying. If the pilot becomes concerned about fuel (which any good pilot will at some point) then they should be on the look out for an airfield or a nice area to put the aircraft down.

The third order of business is to squawk 7600 on your transponder. This will alert any ATC facilities pinging you on radar, that you are unable to transmit and/or hear them.

This falls in line with the FAA's general advice of "Aviate, Navigate, Communicate".

Just a bit of an applicable side note: In the US under the FAA, and in other jurisdictions there are lots of areas that full under "uncontrolled" airspace where no radio or charts are required to be onboard anyway and many pilots are proficient flying in such a situation. Id even go so far as to say that a solid chunk of Piper Cubs are still flown this way.


What is this abandoned airport between Montague and Rothbury, Michigan? It appears to have had two intersecting paved runways, each very roughly 2000 feet long (give or take); the one that runs closer to north-south is still legibly numbered as runway 17/35, but the other runway is in much worse condition (suggesting that it was closed some time before runway 17/35), and its pavement is too broken up for me to make out the numbering.  Runway 17/35 has considerably larger turnaround areas at both ends than the other runway does.  There is a cleared strip extending for approximately 400 feet past the southern end of runway 17/35.

West of the intersection of the two runways, there appears to be a dilapidated apron, with taxiways connecting it to both runways; immediately north of the apron, there is what could be the remnants of a collapsed hangar, or could be something else entirely (there is another area of junk just to the southwest of the apron).

Google Maps link to location of the former airport here.

Google Maps screenshot showing the mystery ex-airport:

The airport is Ottiger Airport (2MI6) which is closed indefinitely. I cannot find any information on when it was closed or for what reason. The last update date that I can find for the charts is August of 2006, which is probably when the airport was closed.

Apparently there is one person who is trying to revive the airport for private use according to this post on Facebook.


Why do the engines of the PAK FA (Sukhoi T-50) seem not to be not aligned parallel to each other? The nozzles of the Sukhoi T-50 seem to be aligned not perfectly parallel. However, it is not very pronounced.

What may be the reasons for aligning the nozzles engines not perfectly parallel.

Edit: in my original post I asked about the nozzles, however, as it was pointed out, this plane used 3D thrust vectoring, so the nozzle arrangement might be this way by chance. However, also the engines seem to be aligned not perfectly parallel. The question has been edited accordingly.

Image source Wikimedia

Edit 2: Here is another picture
Image source, Wikipedia again

The Sukhoi T-50 operates Thrust vectoring nozzle control at low speeds. The nozzles are a part of the Fly By Wire system and will deflect as per the control input given by the pilot. The nozzles move in coordination with other flight controls and it is not necessary for them to be parallel in all conditions of flight. However on the ground they will appear to be parallel.


How does NOAA's P3 Orion safely navigate hurricanes? I've been watching NOAA's P3 Orion fly though Hurricane Matthew a bit on Flight Radar 24.  Looks a bit like this for the curious:

source

It's the only plane actually in Hurricane Matthew.

What I'm curious about is how they get through there safely?  I know they have done it with prior hurricanes, and I assume they have some sort of weather radar on board (being a NOAA aircraft and all), but I also assume there is much more to why that P3 is able to make it through a Hurricane without breaking apart.

Anyone have some insights into what makes this possible?  I'm especially curious about what they do to avoid the worst pockets of the storm (assuming they do).

And for anyone curious about how it looks like when that plane hits the middle of the storm, here you go:

source

Clearly there's not that much weather to avoid in the eye of the hurricane, but getting through those walls has got be pretty difficult considering all the wind shear.

The National Oceanic and Atmospheric Administration uses three aircraft for carrying out hurricane research- a Gulfstream IV SP and two Lockheed Martin WP-3D Orions, while the USAF 53rd WRS 'Hurricane Hunters' uses the WC-130J for this purpose. Of these only the latter ones are used for penetration purposes.
The Gulfstream is used to fly around and over the hurricane (the 45,000' ceiling helps). From noaa page:

The NOAA G-IV jet usually does NOT penetrate the hurricane eye, but is assigned to fly synoptic scale patterns AROUND the storm, deploying dropsondes along the way, in order to profile the environmental flow that is moving the hurricane.

The other two aircraft- the Orion and Super Hercules are not modified structure-wise (except for extra fuel tanks) for carrying out these missions. From the hurricane Hunters site:

These aircraft are not reinforced in any way in fact the only differences between a WC-130J and a C-130J is the addition of two external fuel tanks ..., a radiometer pod on the left wing and the two addition crew pallets in the cargo bay

The aircraft does have onboard weather radars, one of which is used exclusively for flight safety, with the others used for research:

Each WP-3D aircraft has three radars: nose, lower fuselage and tail. The nose radar (a solid-state C-band radar with a 5° circular beam) is used strictly for flight safety and is not recorded for research purposes.

The aircraft are also fitted with INE and GPS and also satellite communications for transmitting and receiving real time updates. During the flight, the flight crew are in constant communication with the flight director, and make adjustments according to the requirements:

During the most dynamic portion of the flight, Price is in constant communication with the Flight Director, who provides real-time flight guidance based on the radar picture.

As far as flying through storm is concerned, looks like they simply punch through it to get to the center- in the end, the aircraft could handle it. From USAF site:

... airplanes are built to go very fast through the air, and they don't care if the wind is 5 knots (nautical miles per hour) or 150 knots! .... Although there are usually some bumps on the way through, they are nothing that the airplane can't handle..

The NOAA officials say pretty much the same thing in this reddit AMA:

The WP-3D is built like a tough old pickup truck. It can handle a lot of abuse in the storm environment and come back and fly the next day.

Incidentally, according to noaa the aircraft crew are more concerned about the turbulence rather than the actual winds in the eye wall:

... hurricane's rainbands and the eyewall, which can get a bit turbulent. The eyewall is a donut-like ring of thunderstorms that surround the calm eye. The winds within the eyeall can reach as much as 200 mph [325 km/hr] at the flight level, but you can't feel these aboard the plane.
... the turbulent updrafts and downdrafts that one hits. Those flying in the plane definitely feel these wind currents. These vertical winds may reach up to 50 mph either up or down, but are actually much weaker in general than what one would encounter flying through a continental supercell thunderstorm.

Looks like they simply fly through it anyway. Basically, they 'crab' into the hurricane so that they reach the eye of the storm. From the Reddit AMA:

Depending on how strong the winds are you have to point the nose of the aircraft so that your track will lead you into the eye. The difference between heading and track is known as your drift angle. Sometimes you can have as much as 20-25 degrees of drift angle. We sometimes call this “crabbing” into the storm, where we are pointing the aircraft to the left or right to flight straight.

The image below shows the path taken by one of the aircraft during flight into Hurricane Hugo.

Zoomed-in radar image of Hugo's eye, taken during NOAA 42's flight. The flight path of NOAA 42 is shown as the white line (note the loops made within the blue area, the eye of the hurricane). The eyewall (red and pink areas on the radar image) contained violently strong winds. Image credit: wunderground.com; Image from hurricanscience.org


Does ARINC 825 (Aviation CAN bus) follow the same protocol as automotive CAN buses? From what I can gather it is derived from the automotive industry standard CAN (Controller Area Network) bus, but I was wondering if they share the same protocols. If you took an automotive bus reader and hooked it up to a ARINC 825 system would it read the same?

Yes, the underlying CAN protocol is the same.  The 825 standard specifies some CAN IDs/priority scheme for standard purposes, similar to the ARINC429 label standard.  It also specifies certain CAN bit timing configuration, such as 1 sample per bit at 75% of the bit time, and re-synchronization jump width at 1 time quanta.  These are all settings in the CAN standard.

This datasheet provides some hints, but unfortunately being an ARINC standard there isn't much public information about the label and data structures.

Holt HI-3110 ARINC 825 compatible transceiver

If you connect a CANBus tool that supports extended ID's you should be able to see the CAN data.  The bus is comparable at a CANbus and electrical level.


How do I pick the right ATC channel to listen to my flight? I'm trying to listen to my flight's ATC communications (flying United out of SFO). What is the difference between ramp, ground, and departure channels? Ground and departure have multiple frequencies, so I'm wondering which ones I should listen to for my flight?

As you would have noticed, it's not published which frequencies your flight will use. So it requires dedicating some time on your part (to some, it's time well spent).
The terms

Ramp control: For the big airports, those frequencies are typically not staffed by FAA controllers, but airport/airline employees handling a section of the airport ground where the planes park and push back.$^1$ Also see: How do terms apron, ramp, tarmac, taxiway, parking area, gate, hardstand relate to each other?

Ground: For the big airports, there may be more than one, say one for the northern part of the airport, and one for the southern. Figuring out which runways are used when (time of day; winds) will make it a bit easier. Ground handles ground movement, anything that is not ramp or runways.

Tower: Same as ground, there may be more than one, and this one is for runways (taking off and landing).

Departure: This varies wildly, even for a single airport, it will change depending on the winds, time of day, and traffic load. It may even be combined with arrival/approach. This is the airspace around the airport outside the tower's jurisdiction, which connects to the en-route/center controllers.

Figuring it out

Find out from which gate/terminal you'll board.

Start listening to all channels days ahead and try to find your flight. You can search for archives of recordings too (there is no need to free up your schedule).

Take notes of the other flights as well, and where they park. Some flight tracking websites show the planes that are parked on the ground (playback/archive functions exist on some as well).

Use the 4-letter ICAO airport code, in this case KSFO, to search for free parking charts. Plenty of flight simulation groups release custom made versions of those charts, but of course they are of no value for real flying. Note: FAA charts are public domain, but as far as I know the ones with the parking stands are not published.

Get the rest of the charts, and combined with the above, start learning how the airport operates.

Easy way 1
If your flight will receive its flight clearance by voice radio (computerized/data clearances are taking over) on the delivery frequency, just listen closely and start switching frequencies to match those given to the pilots (e.g., United xxxx, contact tower on xxx.xxx). If not, once you catch your flight on a frequency, start frequency-hopping with them.
Easy way 2
If United still offers "Channel 9", just cheat: How was I able to just plug in my headphones and listen to ATC and pilot chatter?

$^1$ https://www.nap.edu/read/24668/chapter/15


What are the types of class E airspace? I don't quite understand the various categories of Class E airspace.

Check out this publication from the FAA

  Class E airspace extends
  upward from either the surface or a designated altitude to the overlying or adjacent controlled airspace. When designated
  as a surface area, the airspace is configured to contain all
  instrument procedures. Also in this class are federal airways,
  airspace beginning at either 700 or 1,200 feet above ground
  level (AGL) used to transition to and from the terminal or
  en route environment, and en route domestic and offshore
  airspace areas designated below 18,000 feet MSL. Unless
  designated at a lower altitude, Class E airspace begins at
  14,500 MSL over the United States, including that airspace
  overlying the waters within 12 NM of the coast of the 48
  contiguous states and Alaska, up to but not including 18,000
  feet MSL, and the airspace above FL 600.

This image may help to visualize it

(source)

In more general terms its the airspace that covers most of the US below 18,000ft. Its the area where a lot of the General Aviation traffic lives (although some of it is making its way into the flight levels these days)

Side note: Depending on how you look at it class E airspace is bound to an upper limit of either 400,000 feet (76mi) which is what NASA considers re-entry altitude or what The Fédération Aéronautique Internationale defines as space starting at 62 miles so either one of those can be used as an upper bound for Class E (although officially the FAA does not define an upper bound). Re-entry point is where air drag comes into play so you would be hard pressed to get a plane over that altitude. Practically speaking the jet altitude record is held by the SR-71 Blackbird at 85,069ft and the Concorde pulls in at 60,039 ft for commercial flight.


Is it possible to survive a free fall from an airliner at cruise altitude? If an airliner were to breakup in flight, and a passenger were ejected from the cabin, would it be possible to survive the fall?

Assume that the aircraft broke up at a cruise altitude 30,000-35,000 feet. If it improved the odds, suppose the person were wearing a heavy winter jacket and a backpack with additional clothing in a plastic bag.

Is is possible the person could survive the fall? Are there steps the person could take that might increase the chances of survival?

Chances are you would not survive but lets explore this a bit more in depth for the sake of education.

This article from popular mechanics explores the very issue. There is some research that has gone into the topic of hitting the ground but the research is rarely about cases from the height you are asking about (~30,000ft). Some relevant info

First off at that altitude you really can't breathe that effectively so hypoxia will be your first concern followed closely by extreme cold.

Hitting water:

  Studies of bridge-jump survivors indicate that a feet-first,
  knife-like entry (aka "the pencil") best optimizes your odds of
  resurfacing.

Hitting the ground:

  The question of how to achieve ground contact remains, regrettably,
  given your predicament, a subject of debate. A 1942 study in the
  journal War Medicine noted "distribution and compensation of pressure
  play large parts in the defeat of injury." Recommendation: wide-body
  impact. But a 1963 report by the Federal Aviation Agency argued that
  shifting into the classic sky diver's landing stance—feet together,
  heels up, flexed knees and hips—best increases survivability.

Your best bet for surviving the airplane break up is if you are stuck in a situation similar to that of Vesna Vulović who did survive the situation you describe. Unfortunately there is some debate as to what actually happened so take the info at face value.

  “Speed has never killed anyone. Suddenly becoming stationary, that's
  what gets you.”  ― Jeremy Clarkson


Is the war pilot obligated to fly the same plane daily or must he change the plane according to every required mission? Can the pilot change his plane, or can he fly in any plane, obediently, to the same plane as the one trained on it?

Of which type of pilot are you asking:

Student
Military
Private (hobbyist)
Corporate
Airline

I will be using the term licensed to loosely mean certificated, current, and proficient with the proper endorsements and documentations.

The short answer is no. They are not obliged/obligated to fly the same aircraft. The pilot can choose to fly in any aircraft they want. They will more than likely choose an aircraft that fits their mission.

The long answer depends on the mission. This might determine if the pilot gets the opportunity to fly at all. Or, what “mission” (job, employer, flight school, opportunity) they choose to seek. But, all aircraft fly a differently from each other. In the same make and model, the differences may be slight. In the same category and class, the differences may be very challenging. In different categories, classes, and types, the differences may be too great to overcome without specific training.

Students:
Most instructors will want their students to stick to one type of aircraft for their initial training (first 35-80 hours). That does not mean it will be the exact same aircraft. Large schools may have several identical aircraft of the same make, model, and avionics (when possible). The students will be expected to fly whichever aircraft is available at the time of the lesson. Although, the instructor can endorse the student to fly solo in any aircraft the instructor feels the student can handle on their own. This is essential in developing habits, muscle memory, and structure.

After initial training, the student (then private pilot) is then only limited to flying the same category and class of aircraft in which he/she was trained. Although he student can seek training in another category and/or class. I flew both single engine land airplanes, and helicopters.

Private (hobbyist):
A private pilot can fly any aircraft for which they are properly licensed. The license will only stipulate category and class of aircraft for which a type rating is not required, type rating, and other flight category ratings. Type ratings are usually required for large and/or turbine aircraft. Some other ratings are based on flight categories (VFR vs IFR). There are some restrictions based on medical requirements. And, some flight categories will require specific endorsements (tailwheel, high altitude, high performance, complex, aerobatic, etc.) They can also fly in aircraft for which they are not properly licensed if a properly licensed Pilot-in-Command is also flying at the controls.

There is a class of hobbyist pilots who are very limited in the type of aircraft that they fly. These pilots need endorsements for any aircraft outside of their specific category, class, or type of aircraft.

As a practical matter, a hobbyist pilot may fly several aircraft based on availability. There are flying clubs and aircraft rental companies that give pilots access to aircraft as they wish. Provided the pilot has the proper license and is able to perform adequately on a flight evaluation. I regularly fly several different Piper Cherokee varieties, Cessna 150/2, 172 and 182 varieties, SportCruisers, Robinson R-22s, etc. Availability and cost both play a factor.

Corporate & Airline:
Generally, these types of pilots will hold type ratings in specific makes and models of aircraft. Since it is a pretty large expense to maintain currency of these type ratings, which ones they will be able to exercise might be limited. Which specific aircraft they fly within their license requirements will be up to the needs of their employer at that time. They may fly different aircraft day by day, or even flight by flight on the same day.

These pilots can still exercise the privileges of their private pilot certificate and many do. In which case, they are free to fly any aircraft for which they are licensed. Their employer may limit them to only fly on a for-hire basis for the employer, solely. That does not limit them from flying as a hobbyist.

Military:
The military is going to determine which aircraft the pilot flies. It is the military after all. What the pilot flies is going to be based on the needs of the military. The pilot can make requests. But, being in the military means that the pilot has volunteered (in the U.S.) to do what they tell him/her to do.

Generally, that is going to be mission and budget based. The military will train the pilot for a specific type of aircraft, for a specific type of mission. If the pilot or aircraft does not suit the mission, they use a different pilot. If the military chooses to use the original pilot, they send them back to training for that specific aircraft, for that specific mission.

Both the trained pilot and the aircraft they are flying are very valuable assets. They are expensive tools that the military will handle with care (sort of). Mistakes cost lives and money.

What this means from a practical sense is that a pilot will not flip-flop between types of aircraft. There would have to be a very compelling reason to do so (like change of duty station or aircraft inventory). For the most part, the pilot will be assigned a specific individual aircraft unless the mission dictates otherwise. After all, it is their weapon. They must be proficient with it.

Think of it this way. You are not obliged/obligated to drive a certain car. You drive the car that fits your needs and budget. But then again, you are not obliged/obligated to work for an employer who may require you to drive a certain company vehicle.


Why do airlines retire the flight number after a crash? Perhaps it seems obvious, but I couldn't find a plausible reason why they do so other than that it evokes negative emotions among passengers and crew. Could there be other reasons to do so?

For example, flight number MH370 was retired as a "mark of respect" for the passengers and crew.

And out of interest, is there any case where an airline company reused a retired number for any reason or in certain circumstances?

consider if you Google a flight number you can see the flight status, imagine if the number was from a past crash, you might for a moment think the one you're looking up had crashed


How do mixed-bag-of-hardware military coalitions handle communications, IFF, et. al. interoperability? Back in the Cold War era, there were Western-allied air forces on one side using NATO-standard communications and IFF equipment, and Warsaw Pact-allied air forces on the other side using Soviet-standard communications and IFF equipment, and they never met except as adversaries in battle.  Both sides exported equipment aggressively, but only to countries they considered friendly enough.

Now, the Cold War is basically over.  The major players (US, Europe, Russia) continue to make sales in the export market for their equipment, while more independent-minded folk in minor powers are not restricting themselves to a single source, leading to cases like the Royal Malaysian Air Force where Flankers and Hornets share the same flightline.  However, in that case, the RMAF has the power to order or retrofit everything with the same comms radios and IFF gear, and probably has done just that so they can all talk to each other and figure out who's who securely.

However, the fall of the Cold War has also meant that fighting has centered around coalitions to neutralize specific belligerent "hotspots" (the First Gulf War being a prime example of this).  This means that in some areas of the world, it is quite plausible that you have an air force with MiGs and an air force with F-16s on the same side of the fight, trying to work together against a common foe.

This raises a question though: how do you get everyone on the same side of the fight on the same page regarding communications and IFF gear?  Did the Russians reverse-engineer and adopt the NATO COMSEC and IFF standards, relying on key control to keep the streams from mixing?  Or would there be much furious last-second swapping of radios and IFF boxes in such a coalition situation to allow the MiG pilots and their F-16 pilot friends to talk to each other securely and to know where each other is?  Would the communication situation fall on ground relays to straighten out?

You do multinational exercises

This is a good question that was in part answered for some NATO and neighboring countries under a program called the "Partnership for Peace."  That's one of many methods various nations have used to exercise and practice interoperability, which includes figuring out the communications play.  SEATO was another regional interoperability vehicle, as is OAS.

The first exercises I got involved with (mid-to-late 90's) were Non Combatant Evacuation Operations and Peace Keeping exercises with former Warsaw Pact countries.  It was very much a crawl, walk, jog, trot, run, sprint development model.  It doesn't happen overnight, but exercises, practice, training, and extensive military-to-military contacts go a long way toward identifying what is and what isn't interoperable.

As to "swapping IFF boxes" that's rather pointless.  You can develop procedural control for (Return to Force)RTF procedures, and you  have to accept that in a lot of cases you can't use encrypted comms.  What you do as a group is develop a comm plan that uses generically common radio equipment (do we all have VHF? Yes? No?).  Each operation will have its own wrinkles and details.

You build on previous multilateral operations like UN Peacekeeping

Since the UN stood up in 1945, over a hundred nations have some experience in contributing forces and equipment to UN Peace Keeping operations, and to other UN combined operations (like the UN Operations in Bosnia before 1995, or the peace keeping in the Sinai forever).  With this experience, nations have built up some "lessons learned" as a base for working with each other.

There is no easy button; you have to do formal planning

You don't just show up with your five helicopters, say "We are here!" and get to work right away.  Your air force staff will be in contact with the other countries' air force staffs and a communications plan will be established.  A general layout for forces will be agreed, such as "who goes where?" and it takes detailed effort to establish that.  A whole host of other details get ironed out like how to get the fuel to the airfield. (See problems in Rwanda, 1994, for a prime example of the nightmare that can be).

Military Planning, both long term and short term, is an art in and of itself. (It's painful -- been-there-done-that-got-the-t-shirt -- but it must be done).


Can a delta wing fighter engage an arrestor net without its main landing gear? A delta wing fighter aircraft with underwing drop tanks while landing loses its main landing gear, but the nose wheel is extended. Is it an option for the pilot to engage the barrier net of type EP-15 or MENA-30 at the end of the runway, or will the pilot eject?

Which is the safest and why?

In August 2009, a Saab Gripen pilot forgot to extend the landing gear, and walked away from the landing unharmed. And this was without any preparation of any kind.

There is no reason to eject from a perfectly good airplane just because you can't extend the landing gear. Belly landings are a pretty "routine emergency" (if that term makes sense).

The metal scraping across the runway will probably generate as much if not more friction than the tires would, so the risk of a runway overshoot is rather negligible, and there is no need to use any arresting gear at the end of the runway.

What could make sense, though, is to use arresting gear at the beginning of the runway, if the aircraft is equipped with an arresting hook and the runway is equipped with arresting wires.

It might make sense to drop the drop tanks if they are full.

The delta wing does not play a role here, this applies more or less to all kinds of wing planforms.


What happens when an airplane gets struck by lightning? I know that they certify airplanes for lightning strikes (at least some of them anyway), but does it cause any damage to the airplane or to the electronics?  Are there any required inspections if an airplanes is struck by lightning?

The vast majority of aircraft require an inspection, from small Cessna singles to Boeing airliners. Usually, they require at the very least:

A visual inspection of the aircraft for damage, particularly the nose, tail section and wingtips. Most of the time, the damage is easily visible as "burn" marks or erosion of parts of the skin.
A check of the communication/navigation systems, both visually and functional testing
A check of all avionics, including GPS systems
Propeller should be removed and inspected by an A/P for damage
Engine should be inspected by a procedure similar to the following:

Remove the engine from the aircraft and disassemble it.
Inspect the engine for arcing and heat damage to the crankshaft,
main bearings, counterweights, camshaft lobes, bearings, gear teeth
and any other parts applicable to your engine. Any magnetic parts
should be degaussed following the specific procedure in your manual.
Measure each other part to make sure it is within tolerances for your engine.
Reassemble, then install the engine.

(depends on company) Send in an lightning strike report to your manufacturer
Confirmation of compass being within 10 degrees of another (stricter for transport low visibility operations) after completion of repair/inspection works

Sources:

Cessna 172R Maintenance Manual
Aero Magazine -- Lightning Strikes: Protection, Inspection, and Repair (Boeing, Q4 2012)
Continental Maintenance and Overhaul Manual: M-18


What is the physical meaning of circulation found in Kutta condition? The Kutta–Joukowski theorem is applicable for 2D lift calculation as soon as the Kutta condition is verified. When this is the case, there is a circulation $\small \Gamma$ around the airfoil. My question is related to this circulation:

What is the physical meaning of the circulation $\small \Gamma$, often represented like this (example 1, example 2, example 3):

(Own work)

I'm interested in a simple explanation of the circulation (is air moving around the airfoil? for dummies) and how does this circulation relate to a view of the airflow in a wind tunnel, where there is no apparent air flowing clockwise around the airfoil:

Source: Youtube

The rest of this post is a presentation of the circulation theory which motivates my question, and as I understand it, but is not part of the question.

The Kutta condition is linked to stagnation points, the points where air tubes separate to flow on a given side of the airfoil, and where they join again behind the airfoil. The Kutta condition stipulates the latter point coincides with the airfoil trailing edge:

  Wikipedia: A body with a sharp trailing edge which is moving through a fluid will
  create about itself a circulation of sufficient strength to hold the
  rear stagnation point at the trailing edge.

(Own work)

According to theory, when the airfoil moves through air, the circulation moves the rear stagnation point to the trailing edge, and then maintains it at this position. When at this position, the circulation is finite and can be used to compute lift with Kutta–Joukowski theorem:

  Wikipedia: The theorem relates the lift generated by an airfoil
  to the speed of the airfoil through the fluid, the density of the
  fluid and the circulation around the airfoil. [...] The lift per unit
  span $L^{\prime}$ of the airfoil is given by:

  $$L^{\prime} = −\rho_{\infty} V_{\infty} \Gamma$$

  where $\small \rho_{\infty}$ and $\small V_{\infty}$ are the fluid
  density and the fluid velocity far upstream of the airfoil, and and
  $\small \Gamma$ is the circulation defined as the line integral

  $$\Gamma = \oint _{C}V \cdot d \mathbf {s}$$

  around a closed contour $C$ enclosing the airfoil and followed in the
  positive (anti-clockwise) direction.

Circulation of a fluid around an object by itself will produce no lift. The classic example of this is the spinning cylinder with no other airflow. Viscosity will cause the fluid near a cylinder rotating clockwise to circulate in a clockwise direction around the cylinder. If a left to right horizontal flow is introduced there will be a vector sum of the two flows. This results in the stagnation points near 8 o'clock and 4 o'clock (as opposed to the cylinder with no rotation in the left to right flow having the stagnation points at 9 and 3 o'clock.) The net result of this is the Magnus effect where lift is generated in the 12 o'clock direction.

In your first diagram (typical inviscid flow) there is no circulation. The shape of the airfoil in viscid flow causes the trailing stagnation point to move to the trailing edge (second image -- the Kutta condition). This has the same effect on the airflow as the spinning of the cylinder, in that it creates a clockwise circulation about the airfoil.

The line integral describes, for an arbitrary closed contour around the object, the dot product of the fluid flow velocity vector with the vector path moving around the contour. The simplest contour to analyze is created by following flow streamlines above and below the airfoil and connecting them before and after the airfoil with lines perpendicular to the streamlines.

Since the dot product of perpendicular vectors is 0, the integral along perpendicular portions of the contour are 0. The dot product of parallel vectors  is just the multiplication of the scalar values, and since the direction of the contour is reversed between the upper and lower streamline the effect is adding one and subtracting the other. Due to differences in lengths and the different flow speeds (Bernoulli...) along the contour, the integral is non-zero. This number represents the net effective circulation about the airfoil (total flow minus the horizontal flow.)

The interesting thing is that if you extend the contour behind the airfoil far enough to enclose the wake of the airfoil from the beginning of movement, the circulation will be zero as the circulation of total wake is the vector opposite of the circulation about the airfoil.


Why don't we see diverging nozzles or diffusers? When it comes to fully subsonic propulsion, all outlets are converging nozzles (I did say fully subsonic so no converging diverging). From what I understand, they are flow regulating devices (changing the exit diameter allows to control the mass flow through the propulsion system, be it a turbofan or ducted electric fan).

Why don't we ever use diverging outlets, i.e. diffusers? Is it due to the back pressure? Wouldn't such a shape increase the pressure recovery, i.e. more thrust.

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

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


What is this "Supersonic French" aircraft? To celebrate Bastille Day, Ubisoft released the below (2D) in-game charm for their game, Tom Clancy's Rainbow Six Siege.

Despite frantic searching on Wikipedia, I cannot for the life of me figure out what aircraft the charm is based on, or if indeed a real-world equivalent exists at all. At first it looked like a Rafale, but the vertical stabilizer does not seem to fit any that I could find an image of.
It's not a question of life and death, but I would very much be interested in what aircraft is actually portrayed here.

I believe this is the Alpha Jet

Source of pictures: Wikipedia
It is famously used by the Patrouille de France (the French military acrobatic demonstration unit). They are most famous for overflying the Champs-Élysées during the July 14 celebration, drawing a French flag in the sky.


Best way of learning the aviation alphabet? I want to learn the aviation alphabet, and when searching the Internet on how to, I see a plethora of approaches, so I thought of asking here!

If it's primarily opinion based, let me know.

Presuming you're referring to the ICAO Alphabet* , (alpha, bravo, charlie, delta, echo, etc.) the easiest way (in my experience, from learning it as a disambiguator for phone work) is repetition, same way you learned the alphabet as a child, or the same way you'd memorize a poem.  Get a written list of the letter names, read them through several times a day, and over time, start reciting without reading.
Do this several times a day for a week, you'll be close if not there.  A second week and you should start to think in phonetic alphabet.  A third week and you'll wonder why everyone doesn't think in phonetic alphabet.
*corrected from comments, originally International Phonetic Alphabet, which is a whole different thing.


What is the minimum separation between two A380's while taxing in-line? If you are tailing another A380 on the taxiway, how much separation do you need from your nose to the A380 that you are tailing?

For a Turbojet @ or < slow taxi power, the min distance behind is 30m

Thanks


What software generated this VFR flight plan? I recently came across this screenshot of a VFR flight plan.  Does anyone know what software was used to generate it?

This flight plan was generated with Skyvector
Click here for the specific flight plan from your example
Then click "Nav Log" for the log itself.


Do pilots of airliners and jumbos do a walk around preflight check for every flight? Do pilots of airliners and jumbos do a walk around preflight check for every flight?  How do pilots of large airliners and jumbos do sumping.  If its not a requirement because of aircraft design, why not implement the same design attributes to smaller and ALL other aircraft?

NO, not all airline pilots do a walk-around for every flight.

At my airline, maintenance personnel do a "Pre-Departure Check" (PDC) before each flight from all main bases on all wide body aircraft. (A330, B767, B777, and B787)

The PDC includes:

1) a walk around

2) a check of critical systems

3) a signature in the Journey logbook

As a result pilots very rarely do a walk around on the wide body aircraft.

If we happen to land somewhere without company maintenance, then a walk around would be done by the pilots. If it were an ETOPS flight, we would also have to make an entry in the Journey Log Book stating that the APU oil level was checked by noting the EICAS APU Oil Quantity reading.

In addition to the maintainance walk around, the ramp crew also does a quick walk around inspection just prior to push back.


Why can US deny airspace to commercial flights? On September 25, 2011 i flew from Mexico City (MMMX) to Frankfurt, Germany (EDDF).

It was a comfortable night flight in a Boeing 747 until we started to fly over the Gulf of Mexico in holding pattern.

After some time, the passengers started to ask what was happening and the cabin crew told, that everything was fine.

After more time the flight crew told, that the United States airspace was denied to our flight and that the crew was doing everything possible to arrive to Frankfurt on time, including the request of permission to Lufthansa central for changing the route adding a refueling stop somewhere.

We threw 18 tons of fuel over the Gulf of Mexico and returned to Mexico City airport.

Mexican federal police entered to the cabin and peacefully took some passengers out.

The airplane was quickly refueled and because the long runway was under a routine maintenance, we had to wait a lot inside the plane.

People got crazy, some passengers were worried about losing connections with other airlines. On the second attempt the airspace was granted and landed in Frankfurt with around 4 hours delay.

Why can US deny airspace to commercial flights?

Every country regulates its airspace. You will find the ones for the US airspace on the FAA website.

https://www.faa.gov/air_traffic/publications/us_restrictions/airspace/

What went wrong is speculation, but most probably had to do with Advance Passenger Information System (APIS). When filing a flightplan the passenger list is transmitted and the request for overflight was obviously denied.


In the gyroscopic precession left turning tendency, why does a pitch down cause a forward force at the top of the propeller? I'm a student pilot, and all the textbooks and online resources I'm reading show a pitch down as a forward force acting on the top of the propeller (causing the resulting forward force on the right side of the prop, thus a left yaw). Where does this force come from? Isn't a pitch down a downward force on the prop hub, since the rotation is occurring about the airplane's center of gravity (behind the prop)?

The prop is a big gyro.  It's the gyroscopic precession force created at the propeller when it's subjected to an input changing its axis of rotation, where, as with any gyro, the inertial resistance to the change in axis acts at 90 degrees rotationally to the input.

The airplane pitches down, rotating the axis (extending forward) of the propeller down, acting through the hub.  Being a gyro that is being forced to change its axis vertically, it results in precession feedback acting through the hub at 90 degrees (as if there was a thrusting force at 3 o'clock), yawing the airplane to the left.

It doesn't matter where the prop's axis is in relation to the rotational axis of the airplane in pitch, just that its axis changes as the airplane pitches.

The best way to experience it is to take off in a tail dragger with a large prop, like a Cessna 180, and force the tail up early in the takeoff run before the rudder is having any effect.  The swing to the left from propeller precession is pretty strong.


What is the working principle of tip jets? Tip jet refers to the jet nozzles at the tip of some helicopter rotor blades, to spin the rotor. What is their working principle?

Tip jets spin the rotor by blowing out compressed air. It's the same principle as a jet engine or a jet-ski impeller, just that the exhaust is pushed out through the rotors. Some designs even had jet engines on the rotor tips! The primary advantage of the design are that there is no torque created, so no need for anti-torque rotors or thrusters, the tip jets also increase the rotor's moment arm and mass, making autorotation safer in some cases, although the drag from the tip jets often slowed the rotors down in many cases. Some say it is easier to learn to fly and safer to fly a tip jet design as there's no torque.

There are very few systems which use tip rotors, the main disadvantages would seem to be a lack of efficiency and drag from the tip jets. The rotor design is complex as high-pressure air must be carried through them, causing many design and materials challenges. Also, lack of a tail rotor means there's no way to pivot in hover unless unless you put some sort of tail thruster on.


Third Class medical license, what changed, if anything? Supposedly, in 2016, Congress passed a new law making it easier to fly without the usual medical examination requirements. However, in looking at one of the rather obtuse "FAQs" on this new law, I don't really see what has changed. You still have to have had a medical exam, so new pilots apparently get no benefit whatsoever, they still have to be examined by a doctor. Not only that pilots still have to pass a medical exam at least every 4 years as far as I could tell. So, after years and years of lobbying for a medical-free third class, is the end result that now pilots only have to have an exam every 4 years instead of every 2? Here is an excerpt for the proposed law as I originally saw it:

Fly with drivers license. Did this not happen?

Short answer: politics killed the "driver's license medical" idea for private pilots, but there are still reasons why BasicMed has significant advantages for some pilots.

The literal answer to your question is "nothing": the third-class medical hasn't changed at all. What you're referring to is an additional option called BasicMed, which you can hold instead of (for some operations) or even in addition to a third-class medical.

I won't get into the details of BasicMed itself (the regulations are in 14 CFR 68), but AOPA has a lot of great information about it. Instead, I'll focus on your "why is this any better than a third-class medical?" question, which seems to be quite a common one right now.

In summary, if you're under 40 and healthy then BasicMed may not seem very interesting. But if you're over 40 and especially if you currently have a Special Issuance then BasicMed could be a much easier and cheaper way to fly.

As you said, as a new pilot you still have to pass a third-class medical once so let's assume that you've done that successfully. It's certainly true that some people aren't happy with that requirement because they were hoping for a "driver's license medical" where a private pilot could fly without any medical certificate, as sport pilots can do. That idea didn't survive the political process, however. If you want to fly without any medical you still have gliders, ultralights or LSAs.

But when it comes time to renew, here are some reasons that you might consider BasicMed (most of this information comes from the AOPA FAQs):

If you're over 40, you need to renew a third-class medical every two years, but you only need to see a doctor every 4 years under BasicMed
Special Issuances still exist under BasicMed but for a more limited number of conditions than for a regular medical. Practically, that means you may be able to avoid expensive tests that the FAA requires for a third-class. This is a huge benefit for some pilots because it can save a lot of time and money (health insurance typically doesn't cover 'unnecessary' tests).
Any state-licensed physician can sign off on BasicMed, but only an AME can sign off an FAA medical. That means in theory it should be easier and cheaper to find a doctor for BasicMed. In practice people's experiences have been mixed on this, but BasicMed is still very new and it's not surprising that some doctors may not be comfortable with it.
Because the BasicMed medical questionnaire is effectively a general physical exam, some people have successfully combined it with an annual checkup paid for by their health insurance

There may be other reasons, but those are some common ones I've read about. If you're a member, the AOPA forums have a lot of discussions about individual experiences.


What is this aircraft parked in Oceanside Municipal Airport? I was on my way to the beach at Oceanside on October 2020. On 4:32, I saw multiple Cessna or Beechcraft aircraft, as well as a Velocity V-Twin, on the runway of the Oceanside Municipal Airport.
When I was looking at the further spots, I noticed an odd-looking, single-engined twin tail aircraft parked on the runway. As seen in this photo, the red arrow indicates the strange aircraft.

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


What happens in a turbine high-temp combustion? I'm designing an aircraft, and I notice that in high bypass turbofan engines, the fuel is used at relatively low temperatures. So I'm wondering, what happens if the fuel is burned at high temperatures? Does something happen to the metal?

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


What knowledge is needed to build a small aircraft? It is my dream to make a basic flyable small scale aircraft (the size of a model aircraft). What is the basic knowledge needed to be able get started in the first place?

In particular, I would like to be able to design and build aircraft that can actually fly, while understanding why it all works. I imagine that there is a need to study fluid mechanics, the structures of aircraft, and certain mechanical and electrical systems.

It would be really helpful if you can enlighten me, and help jump start the learning process. In particular, suggestions about learning resources would be appreciated.

P.S. I have at least first-year university physics and I am always learning more.

One way is trial and error. That is how the early pioneers learned it, and building a few models is a good way to learn the basic stuff, too. That would be

Aerodynamics (what forces keep the aircraft in the air)
Flight mechanics (how to control it and make it fly straight by itself)
Structural design (how to make it light and stiff)
Systems (what equipment is needed to operate it)

My next recommendation might sound boring, but reading the federal regulations for light aircraft will cover all those aspects and more. In many cases you will wonder what that particular regulation tries to accomplish: This is your chance to learn! Post a question here and don't give up until you have fully understood why that particular regulation has been added. Yes, this will take a while, but building an aircraft all by yourself is no mean feat.

Last, join the local chapter of the Experimental Aircraft Association or whatever organisation supports experimental aircraft builders in your country.


Did the NSDAP help to fund Lufthansa? During WWII, a number of German companies received financial backing and slave labourers from the government at the time. Companies such as Hugo Boss, Volkswagen and Lufthansa.

A thread on Airliners.net from 1999 mentions a documentary showing Lufthansa planes flying with the Swastika on their tail. I found this image online:

What is the story behind Lufthansa's involvement with the National Socialist Party? Did they indeed receive large monetary backing from the then-government?

NSDAP was the elected ruling party in Germany from 1933 to 1945 (only the first part of it elected though); thus Lufthansa was given government money, not "Nazi"-money. During this time, they made the Swastika the flag of Germany. American Airlines sport the American flag all over their tail, and I'm sure they (at some point) have received government money as well. If you replace every occurrence of "Nazis" in your question (including title) with "government", you'll notice it becomes slightly less provocative, and the parallels to other airlines and other countries become readily apparent.

When the war started, I would assume the military requisitioned all the assets they needed including airplanes and services from Lufthansa. I'm not much of an historian though, so I can't give you any details, but I'm sure they're out there to find. I realize this doesn't really answer your question (Lufthansa's involvement with the German government), the point I'm trying to make is that it's very hard to answer, as with any airline and any government.


What are the advantages and disadvantages of ruddervators? Can someone clearly explain the advantages and disadvantages of ruddervators? I cannot find the answer anywhere else.

More induced drag

A disadvantage (especially critical during landing) is that there is more induced drag to make certain movements.
The image below helps to understand this:

Source

To yaw, you have to use both ruddervators (contrary to just a single rudder movement for a normal tail). This is done in order to compensate the unwanted vertical component. This leads to increased induced drag, which is a big problem during take-off.

Less interference drag

The number of intersections goes down. In the case of a conventional tail you have three intersections (fuselage - left elevator, fuselage - rudder, fuselage - right elevator), whereas for a V-tail you only have two (fuselage - left ruddervator, fuselage - right ruddervator). This reduces the interference drag.


Are lessons available for FlightSim X? I have Flight Simulator 2008, and there were some really good lessons for student pilots.

Are there flight lessons in FlightSim X, either part of the software, or available from external sites?

The FSX Learning Center shows some, but it seems you can't use them.

FSX has lessons. See the Learning centre.
You have to scroll through the text, and then you can fly some lessons.