What regulations discuss the red/white marked areas on a tarmac at a terminal? This is the terminal at KSTS. Someone mentioned to me that your can't overfly this area. (I fly helicopters direct to the ramp adjacent.) What regulations discuss this? I don't see it in the AIM.

I believe it's a non-standard marking to indicate a Security Identification Display Area (SIDA), where you need a specific badge to have access. The TSA sets the requirements for access. If you zoom in you can see the words "AIRLINE EMPLOYEES ONLY" beside the markings.

I don't think there's any standard marking for SIDAs. There was a proposal in the draft version of AC 150/5340-1K - Standards for Airport Markings (see section 5.15 for all the details):

  The SIDA marking is a rectangular stripe with white legends that are
  centered within a red background. Paint colors are per AC 150/5370-2,
  Item P-620, Runway and Taxiway Painting.

But, it didn't make it into the final version:

  Drops a proposed new surface marking for areas designated by the
  Transportation Security Administration (TSA) and the airport operator
  as a security identification display area (SIDA) (reassigned paragraph
  5.15 to cover markings for aircraft deicing facilities and removed proposed figure C-14). TSA accepted the task to address future
  markings for the airside.

And as ymb1 pointed out in a comment, it's not in the current version of that AC either. Presumably the TSA is still working on it.

If you look at a SIDA at another airport, you can see differences. The SIDA at KLEX (Lexington, KY) is marked by a single red line, for example:


Where can I find accurate information about fuel efficiency of Airbus vs. Boeing planes? I am trying to understand the competitive positions of Airbus and Boeing's large civil aircrafts. I would imagine fuel efficiency would be very important to airline given its large component in the total costs of operating. Where can I get information on the fuel efficiency of the large major planes e.g. A320 vs 737 etc?

Thank you

Fuel consumption is a very important issue, and much besides the airplane or engine manufacturer influences the final result. Both Airbus and Boeing publish only marketing numbers, and require a non-disclosure agreement before they reveal any meaningful figures.

Approximately three quarters of the progress in fuel consumption in the last fifty years has been achieved with better engines, and the airframe and better operational procedures contributed only the remaining quarter. If there is any difference between contemporary Airbus and Boeing planes, it is very small, and any advantage is usually reversed with the next upgrade or new model from either company.

Here is a related question: Atlantic fuel burn estimations. It has links to tools for fuel burn calculations.

For a first approximation, use 55 to 65 g of fuel per Newton-hour or 15 to 18 g per kN of thrust per second with modern jet engines. Please do not use the static thrust at sea level, but the actual thrust at the right flight Mach number and altitude. If you lack this figure: A modern airliner needs thrust equivalent to between 1/18th (5.6%) and 1/12th (8.3%) of its weight. In cruise flight at Mach 0.82 the higher number of 8.3% should be used.

Things which have an influence on fuel consumption:

Flight speed. Usually flying a little slower helps, but normal operations are already quite close to the optimum. See here for a related question.
Flight altitude. Flying as high as thrust allows helps, but is not always possible. See here for a related question.
Operating mass. Lighter aircraft can fly higher and have less drag. Excessive reserve fuel rules cause fuel burn to go up.
Flight path. Usually the direct route is best, but sometimes gains can be made by avoiding a headwind en route.
Proper piloting. Flying with a small amount of sideslip already destroys any advantage winglets might have, and drag goes up quickly with sideslip. This is mostly an issue for propeller airplanes, though.
Maintenance status of the engines. Engines lose a few percent of efficiency over their operating life.
Maintenance status of the airframe. Dirty wings or badly fitting doors produce more drag, and condensed water in the belly adds some additional weight which increases fuel burn. Condensed moisture can accumulate in the fuselage, and airliners in Africa can well have a few tons of condensed water onboard.

This is why in real life the fuel burn varies, so any published figures out of context are hard to verify.


What requirements do A&Ps (AMT) have to work on avionics? Is there any additional requirement for A&Ps to work on avionics or is that even a totally different license?

I just wonder why only a few A&Ps I met, also do avionics.

An A&P may install avionics per an STC or replace a component, but they may not "repair" avionics in the general sense (solder the circuit board). FAR 65.81 specifically prohibits the mechanic from performing “any repair to, or alteration of, instruments.” It takes a FAA Part 145 certified repair station to work on instruments or avionics.  (Remember that autopilots and other “electronic devices for automatically controlling an aircraft in flight”are instruments by definition.) Appendix A to Part 43 defines the calibration and repair of instruments (including autopilots) as an appliance major repair.

Theoretically an A&P could do repairs if he met all requirements for a part 145 repair station but it is highly unlikely it would ever happen.

The repair station or A&P may re-install the part, fill out the maintenance log, and return the aircraft to service. If the A&P re-installs the unit, the reg's say he must have up to date installation manuals, and it specifically requires that “if special equipment or test apparatus is recommended by the manufacturer involved, he must use that equipment or apparatus or its equivalent acceptable to the administrator” to verify system performance (Section 43.13 (a)).

Title 47 of the Code of Federal Regulations, Telecommunication Commission, Part 87—Aviation Services, states that a commercial radio operator license is required to repair and maintain all aircraft stations and aeronautical ground stations (including hand-carried portable units) used to communicate with aircraft.

In the United States, neither the FAA or FCC provide a "Avionics Technician" license or equivalent as the military or other parts of the world do. No certification or license is needed to work for a "repair station".

The FAA is always revising rules and regulations such as promoting ADS-B and   no-longer requiring a STC to promote safety.


How do I find the shear center of an unsymmetrical airfoil? I'm quite a newbie of these systems and I am designing the wing box of a drone. I know where I want my shear centre. However, I have been trying to determine the shear centre of my idealized airfoil. My airfoil is the NACA6412 and it's highly unsymmetrical.
I know this subject have been touched in this forum before and I have read T.H.G Megson a lot, but I think I am missing something.
I have been stuck in this problem for 3 months now and if someone can provide some light on it, it would be great. My goal is to implement this determination in a script or in excel for future situations.

The best way is to assume the airfoil symmetric (since the location of the shear center in the chord is more important) for a preliminary phase; It will help a lot.
Also, don't forget that idealization is a very rough estimate of the stress analysis of a wing structure or fuselage. It helps, however, with initial pre-sizing.


What factors contributed to enable Rickenbacher to be found? In Rickenbacher's autobiography he tells of his flight across the Atlantic in a B-17 after WWII. They ended up running out of gas as I recall, making a water landing in the middle of the ocean. They were stranded for about a month before being rescued.

In the early post-WWII era, how was it that they were able to find him at all? What factors contributed?

Actually it was during WW2 and it was the Pacific:

  One of Rickenbacker's most famous near-death experiences occurred in October 1942 [...] The bomber strayed hundreds of miles off course while on its way to a refueling stop on Canton Island and was forced to ditch in a remote and little-traveled part of the Central Pacific Ocean.

I am not familiar with the episode, and this source is currently not working for me, but from the little information that the wiki reports, I have the impression that the main factor has been pure luck.


How to plot the pressure distribution over an airfoil? I have found only the description of this pattern with experimental graphs.Could anyone please tell me the mathematical formula required to plot the distribution?

I have found only the description of this pattern with experimental graphs.

That's because that is the best way to have detailed and precise data: you either simulate (e.g., with Nastran-Patran or XFoil, as cited by Peter Kämpf in his answer) or build a [scale] model and use a wind tunnel. If you use a scale model, depending on the focus of the experiment, you will have to be careful (while scaling back up) not to damage your data: for this you have adymensional quantities to look after, such as the Reynolds number.

  Could anyone please tell me the mathematical formula required to plot the distribution?

There is not one formula to do that, but rather a method that given the airfoil shape (and the angle of attack) will estimate the pressure distribution. This method was extensively used in the days before computers and FEM tools existed (for what I know SR71 is a notable example where this method has been used in the early phase of the wings design), but, for what I know, nowadays is seldom used.

The method is based on Conformal Mapping, in particular the Joukowsky transform or the Kármán–Trefftz for more detailed and general cases (see Sec. 4.2 of this pdf for a more in-depth explanation). This is a transformation in the complex plane that, from the airfoil profile that you want to analyse, will map it onto a circle.

You want to do this because the ideal flow around a circle is well known:

At this point you have to know that around an airfoil the air will have a certain amount of circulation and that the total flow around it is the sum of the ideal unviscous flow plus the flow induced by the circulation:

 Image from MIT

For this reason, you want to compute the ideal flow around a cilinder that has a rotation speed equivalent to the circulation around your airfoil[*]:

and it turns out that we have some formulas for that (image above taken from this page).

[*]: note that you will have different circulations for different angles of attack.

Now, why did we do all this? Because once we have the flow around the rotating cilinder and
we have the mapping from the airfoil to the cylinder, we "only" have to invert the mapping:

and we immediately have our flow around the airfoil.

And once we have the airflow, finding the pressure distribution is quite straightforward, thanks to Bernoulli (you have the velocity distribution and you can assume that the transit of the air around the wing is fast enough to be adiabatic)


Why are vectors used for sequencing rather than speed control? Why would ATC generally issue vectors instead of simply issuing speed reductions to aircraft? It'd seem more efficient to have aircraft flying less track miles, so is there any reason that speed control is worse than giving vectors to aircraft?

Let's say you have two aircraft that will reach the same point in space at the same time, and your job is to keep them three miles apart.  One way to do it is to calculate how many knots the second aircraft should reduce their speed so that at the time the first aircraft reaches the point, the second aircraft will have fallen three miles in trail.

Unfortunately for you, this means that you have to work a time-speed-distance-wind problem for every single aircraft that you, as a controller, handle.

Alternatively, you pick a point three miles away and tell the second aircraft to fly there.

Air traffic controllers are human, and humans are better at angles than we are at numbers.  The simplest thing for controllers is usually the best thing - they've got lots on their mind already without making them do math too!  This might change in the NEXTGEN air traffic network (where everyone has a GPS position and speed readout right there on the screen) but for now, easy is better than hard.


Forces that wing attach fittings must transfer to fuselage? I just saw the naked wing (it didn't have its wing fabric) of a Weedhopper ultralight and wondered the types of forces that the wing lift struts must transfer to the fuselage, apart from the apparent lift force?

Secondly, in a wire braced wing like the Weedhopper, do lift struts carry the lift load on the span between their attach point and the fuselage or do they carry the lift on the span from the attachment point to the wing tip?

For your first question, it depends on the way they are attached, as is often the case in structures. I haven't seen this model up close to know their fitting type, but:

If they are fixed by a joint that allows them to rotate (the easiest and cheapest solution) then they can only carry one kind of load, that being tensile (or compressive) stresses. this would mean they can only transmit force along their own axis.
If they are rigidly jointed (cannot rotate at the joint) then they also carry some torque, although how much is a matter for the structural engineers. My guess is not much as the attachment points already offer a large moment arm.

For your second question, I believe you mean to ask for what part of the overall lift are the lift struts responsible for. That I cannot readily answer without some calculations I don't have time for right now, but it is not as straightforward as you imply. The Wing-Fuselage-Strut structure is hyperstatic (statically indeterminate or over-constrained) so it is a bit too long to napkin-math.


How are leaks in door rubber seals detected? There are few reported incident where the rubber seal on the door was damaged and it took numerous hours to find the cause and then find the location of the damage. I want to know the ways to detect the leaks mostly for the big passenger jets.

I am not sure if this can be detected during maintenance checks or even aircraft is in air.

Testing the doors (and windows) by pressurizing the cabin eats into the aircraft's pressurization cycles. Instead vacuum is used to simulate the in-flight conditions.

A special fabric and a sheet with attachments to hoses are attached to the outside where the door/windows are to be tested. Vacuum is created between the fabric and fuselage, thereby locally simulating an in-flight differential pressure. If the vacuum doesn't hold, it means there is a leak, which can be pinpointed from the inside with sensitive equipment.

Image and reference: Lufthansa Technik AG


Is there a standard text for parachute design? In some technology areas, there are "standard" texts - for GA type aircraft design, I think of Stinton's "Design of the Airplane". For radar, Skolnik's "Radar Handbook".

Is there an equivalent text for parachute / para-airfoil design?

Some useful texts are The Aerodynamics of Parachutes by Cockrell, Ram Air Parachute Design by Lingard, and the Parachute Recovery Systems Design Manual by Knacke.  The Lingard and Cockrell papers both have extensive references that are worth pursuing.  The Knacke manual is, as far as I know, only available in hardcopy.

It seems that the designers of modern sport ram-air parachutes and paragliders are more concerned with protecting trade secrets than they are in publishing research.  The paragliding side of the aisle is a bit more willing to share.  There is an online paraglider design handbook, and there are several open source paraglider CAD software packages available.


How does the propeller position affect the effectiveness of control surfaces? I've found several questions about differences between pusher and puller aircraft, but the effectiveness of control surfaces was not discussed in any of them.

Consider the following three scenarios:

A: Aerodynamic surface in undisturbed flow
B: Aerodynamic surface with a puller propeller
C: Aerodynamic surface with a pusher propeller

In what case is the lift force generated due to the control surface deflection larger? What differences are there between B and C?

A propeller has more effect on a control surface behind it, than on one in front of it. That's because the propeller pulls in air from a large area in front, and ejects it in a relatively narrow stream behind. Since the mass flow rate is the same on both sides, the air in front moves fairly slowly, and the air behind moves faster. Forces on a control surface in an airflow depend on the square of the airspeed, so a control surface in the fast-moving air behind the propeller will deliver larger forces for a given deflection than one put in the slower-moving air in front. Look up Axial Fan Design on Wikipedia, for a cross-sectional view of the airflow through a propeller.


How to find trim condition of a sectional airfoil without knowing the angle of attack? I am using a reflexed airfoil designed for positive pitching moments to achieve a pitching angle matched to the changing of free-stream velocity (Aerodynamically tailored).
I ended up with a pitching moment equation
$$
dM = c*Cm_{a.c} - (C_{l_0}+C_{l_α}*α)*Χ_{a.c}
$$
where $c$ the chord length, $Cm_{a.c}$ the pitching moment coefficient about the aerodynamic center of the airfoil $Cl_0$ the zero lift pitching coefficient, $Cl_a$ the lift coefficient at a certain angle of attack and and $Xa.c$ an offset distance about aerodynamic center.

I want to design a propeller and the data i have is free stream velocity, RPM, and geometry of the blade.
I assume a thin airfoil so the lift coefficient ($(C_{l_0}+C_{l_α}*α)$) is roughly $2π*α$ and $α$ varies with free stream velocity and rotational speed: $α = Δβ - tan^{-1}(V_{inf}/V_r)$ and $Δβ$ the pitch angle.

The idea is to find the ideal angle of attack $α$ that satisfies the pitching moment equilibrium condition $dM = 0$. However, pitching moment coefficient $Cm_{a.c}$ is also unknown.

*Let's say $X_{ac}$ value is given.

So, my question is how this equation can be solved? Can i get any other data from the airfoil's profile that help to find the solution?
Are reflexed airfoils have any characteristics that i should consider in such situation?

If you have access to a model of your airfoil, a moment balance, and a wind tunnel, you may determine $C_{M_{ac}}$ experimentally: the moment the wing experience may be normalized to calculate $C_{M_{ac}}$

Then solving for alpha is trivial. Otherwise a tool like XFLR5 may be useful to find  $C_{M_{ac}}$ for your airfoil.


How does a remote pilot land a fixed-wing UAV? How does a remote pilot land a big fixed wing UAV, whose takeoff weight could be several tons and have to land at a airport with runways? I saw in the TV, these big UAV normally has on-board cameras and its remote pilot work at a station with displays. Is it manual or auto landing? If it is a manual landing, is it similar like manned aircraft pilots to set up the visual contact with the runway and determine the aircraft position in space relative with the runway based on their experience or they have some landing aided system? How they resolve the time delay issue that the image they see thru the onboard camera could be taken seconds ago?

There's a wide range to techniques. In the hobby world, it's much like landing a full-size plane under VFR, you fly a circuit and glide path. Flaps, side-slip, cross-wind, retractable undercarriage, etc can all be used. The difference is that you have to judge the runway centre-line from some distance off to one side, which requires a lot of skill and practice. Also wind-sheer, gusts and unevenness in the runway surface are magnified by the scale. Fortunately the light weight allows models to handle landings that would wreak the full-size.

At the other end of the spectrum, large UAVs can land autonomously, similar to an airliner auto-land, using all the electronic aids of a modern runway.

In the middle are small UAVs, operated away from a runway. Small, slow UAVs can just circle a GPS position with the motor off, gliding until they reach the ground. Faster UAVs fly into nets or a vertical arrestor wire - again autonomously.

For completeness, I should mention that there is a specific branch of model competition for landing on a simulated carrier deck, with an arrestor wire.


Apart from the C-130, are there other airlifter aircraft that are able to perform LAPES drops? The C-130 is well known for her ability to perform a LAPES (Low Altitude Parachute Extraction) drop to deliver vehicles to an airhead.

I'm wondering if other larger military airlift aircraft that are also able to perform this maneuver, in particular the C-17, or (unlikely) the C-5?

Just the C-130. The C-17 was intended to have that capability, but it was decided against.
That's according to a 1995 report to congressional committees (gao.gov; PDF):

C-17's Intended Role Has Changed
(...) the C-17's unique 60,000 pound low-altitude parachute extraction system (LAPES) capability is not needed, and the aircraft cannot meet original airdrop requirements.
Unique C-17 LAPES Capability No Longer Required
LAPES is a means of extracting equipment while an airlifter flies at low levels. At present, the C-130 is the only aircraft capable of LAPES operations, and it is limited to extracting 42,000 pounds of equipment. In 1981, the Army identified an "urgent need" to develop a LAPES capability up to 60,000 pounds. According to Army officials, this capability was needed to extract armored artillery pieces, ammunition, and towing vehicles from the same LAPES platform, which would minimize dispersion over the drop zone. The C-17 was intended to provide this unique capability. In March 1994, the Army acknowledged that " LAPES has been an expensive, unused, untrained capability and is potentially of limited battlefield use." The Army stated that the current C-130 42,000-pound LAPES capability "appears to more than adequately address foreseeable Army requirements." The Army intends neither to maintain the material systems and rigging required for the 60,000-pound LAPES platform nor to conduct C-17 LAPES training. Thus, the C-17 will not be used for this mission. However, AMC officials noted that testing of a 42,000-pound C-17 LAPES capability is currently underway.

While the report is from 1995, it is the only official mention of the matter that I've been able to find. That's probably why you haven't found videos for it either. The C-17 does parachute down equipment though from higher-than-LAPES altitudes.


Can a 737NG still fly when every single electric run device/system is dead? So, as my title suggest, I wonder if the 737NG can still fly without any of it's electric run systems, which means anything that runs on electricity is dead.

TLDR: Yes, the 737 can still fly, the gear can be lowered and one can brake after landing.

A complete failure of every single electrical system is extremely unlikely. The QRH (Quick Reference Handbook) does not even mention this case. Usually, at least the battery remains and can power all emergency systems for at least 30 minutes (60 min, if 2 batteries are installed). See also What happens with the avionics if in midair there is loss of power or fuel flow interrupted?.

Even in the unlikely case of a complete electrical failure, the aircraft is still flyable. As long as hydraulic pressure is still available, the flight controls would function normally. But even without any hydraulic pressure the aircraft can be controlled via manual reversion. This means the mechanical link of the flight controls to the hydraulic actuators at the control surfaces can transmit the forces to the control surfaces (similar to what happens when hydraulic power steering fails in your car). The forces required will be substantially higher than usual, but the aircraft is flyable. Also manual pitch trim via the trim wheel in the cockpit is still possible.

Some things to consider:

A complete electrical failure would include a failure of both EECs (Electronic Engine Control) and therefore both engines would be dead. You would have to sail the aircraft down. As Ralph J pointed out in the comments, the engines could still windmill and might still provide some hydraulic pressure via the engine driven pumps, but far from normal pressure.
Normal flaps extension is powered by hydraulic system B. The FCOM says that the flap lever

  selects position of flap control valve, directing hydraulic pressure for flap
  drive unit
  position of the LE devices is determined by selecting TE flap position

so this might still work with hydraulic pressure. But note that there are electronic components like the flaps/slats electronics unit (FSEU) involved, which would no longer function without electrical power. I am not entirely sure if that would already prevent normal flap operation. See also the flaps and slats control diagram below.

Flaps can also be extended without hydraulic pressure using the alternate flap extension mechanism, but this is electrically powered, so alternate flap extension would be impossible in this case.
Normal gear extension is powered by hydraulic system A. If the pressure is still sufficient to release the up-locks, the gear can then fall down assisted by gravity and the airflow:

  When the LANDING GEAR lever is moved to DN, hydraulic system A pressure
  is used to release the uplocks. The landing gear extends by hydraulic pressure,
  gravity and air loads.

Otherwise, manual gear extension is always possible via three mechanically connected cables in the cockpit using a gravity drop of the gear. It is however not guaranteed that the gear will lock in place.

  If hydraulic system A pressure is lost, the manual extension system provides
  another means of landing gear extension. Manual gear releases on the flight deck
  are used to release uplocks that allow the gear to free–fall to the down and locked
  position. The forces that pull the gear down are gravity and air loads.

Without hydraulic pressure, both normal and alternate braking is unavailable. The brake accumulator will however still have sufficient pressure in it for braking after landing.
Older 737 NGs still have mechanical standby instruments (artificial horizon, airspeed indicator, altimeter). These could still function. Modern NGs have replaced this with an electric standby instrument. Without any instruments, it will be extremely difficult to control the aircraft.
All radios and the transponder would be inoperative, so no airport would even know that you are coming to land there.

Without any hydraulic pressure, the following components are inoperative:

  All flight spoilers inop

  Roll rate will be reduced and speedbrakes will not
  be available in flight.

  Trailing edge flaps normal hydraulic system inop

  The trailing edge flaps can be operated with the
  alternate electrical system. Alternate flap
  extension time to flaps 15 is approximately 2
  minutes.

  Leading edge flaps and slats normal hydraulic system inop

  The leading edge flaps and slats can be extended
  with standby hydraulic pressure. Once extended,
  they can not be retracted.

  Main landing gear normal hydraulic system inop

  Manual gear extension is needed.

  Autobrake inop

  Ground spoilers inop

  Landing distance will be increased.

  Normal and alternate brakes inop

  Inboard and outboard brakes have accumulator
  pressure only. On landing, apply steady brake
  pressure without modulating the brakes.

  Nose wheel steering inop

  Do not attempt to taxi the airplane after stopping.

(Boeing 737 NG QRH 13.12 Manual Reversion)

(Boeing 737 NG FCOM 9.20.24 - Flight Controls - System Description)


How does an aircraft turn while taxiing? I know that an aircraft uses its own power (thrust) while taxiing to move forward. But how does it turn?

Do the front wheels pivot?
Do you simply apply more power to the left engine if you're trying to make a right turn?

If you do apply power to turn, how much power? Wouldn't it tip over the plane? And how do you do it on a single-engine or prop aircraft?

Primarily steering is accomplished in two main ways:

Steerable nosewheels - Usually limited to tricycle undercarriage, and usually controlled using the same left/right pedals as control the rudder in flight
Using the rudder itself - Often associated with the traditional undercarriage (tail draggers to some). In this case the rudder works on the ground in much the same way as it does in the air - ie, deflecting the rudder pushes the tail in the opposite direction, thus causing the nose to pivot in the required direction.

In addition, steering can be augmented in two ways

Differential braking - often the left and right main undercarriage have their own deferentially controlled brakes. These are usually controlled by "hats" on the top of each rudder pedal. By applying greater braking pressure to, for example, the left wheel will cause the aircraft to pivot more around that wheel causing a left-turning tendency.
Differential thrust - in a similar vane to above, greater thrust applied to the left engine will cause a  right turning tendency.


I wonder if it's possible to make a "compressed air" turbine engine I wonder if it's possible to make an efficient turbine engine that uses only hot compressed air to move but only that, meaning there is no ignition involved. To put it simple can we use compressors like turbo or superchargers to make a small turbine engine that will be able to move (not lift) 100+ kilos at high speed, well lets say around 40km/h (25 m/h)? I've studied it a bit and to actually know i need to make it but before that i thought to ask people that know certainly more than i do. Also if you can think of a way to do it i'd love to hear it cause iv'e thought of something but it might not work (i guess that's the fun of it tho doing tests and rebuilding and stuff). Ok, in addition to all that let's say that power for this comes from batteries and it's meant to work for short periods of time.

Well, ships have been using turbine engines powered by super-heated water since the late 19th century.  But you still have to have an energy source to heat the steam.  And it's no good for a "jet" engine since the whole point is thrust by accelerating air through the engine, where the turbine and compressor are there just to keep the cycle going.  It would only work for a turbo-prop or turbo-shaft where the turbine's job is to produce torque for doing the work.

Theoretically, you could have a turboprop powered with a steam turbine, or some other heated gas, but you still have to have an energy source.  Maybe some kind of weird and wonderful battery powered water heater, or a tiny nuclear reactor?  Then you also need a huge supply of water or other fluid or gas to heat up.

It is possible however to have a closed system that recycles the water used for the steam.  You then have pretty much a small nuclear power plant or nuclear sub.  It's theoretically possible though, to have a nuclear powered turboprop that could fly for months.  If it works for subs and aircraft carriers, why not, if you could make the whole thing light enough.

Actually, none of that stuff is really new.  There were nuclear powered aircraft concepts in the 50s, that weren't really practical.

The thing about turbine engines powered by kerosene is that it's still the most efficient way to convert potential energy to kinetic energy in a light weight and trouble free package.  50 years from now?   Who knows.


Can a TCAS be alerted when the intruder aircraft has a transponder in stand-by mode? Can a TCAS give a TAs (traffic advisories) if the intruder aircraft has a transponder in stand-by mode?

No. If the intruder's transponder is in standby it will not respond to interrogations and will be invisible to the TCAS. TCAS can't act on targets it can't interrogate.


Is it true that a soda can or a bag of chips will pop in a plane at high altitude? I've heard some conspiracy theorists claim that if you were to bring a soda can or a bad of chips onto an airplane, they would pop?

Is this true? If so, why?

Not likely.  Consider how food products normally make it to you.

Any competent US maker of soda or chips will design their product to be shipped

on Interstate 70 or 80, via Sherman Summit (8650') or the Eisenhower Tunnel (11,158')
or more likely by rail, via again Sherman Summit (8015') or Moffat Tunnel (9239').*
Aircraft are pressurized to a pressure altitude of 8000' typically, so Sherman Summit (rail).

If a food manufacturer were to botch their packaging, they wouldn't have your problem of a soda can bursting, they'd have an entire container load of sodas or chips burst and ruined for sale.  That is simply unacceptable, so manufacturers have a big incentive to get this right.

Other markets will have similar issues - the EU has the Alps, and China and India have the Himalaya. It does not apply to regional sellers in flatland areas, so a regional/indie Florida chipmaker, all bets are off.

It does, however, apply to soda manufacturers, whose cans must endure extreme temperature (e.g. solar loads in a car) also in high places.

* Tennessee Pass (10221') doesn't count, it is weedgrown, rusty and cut in several places, being held for future capacity needs.


After hernia surgery, what do I need to do to be cleared to exercise the privileges of my PPL? After hernia surgery, what do I need to do to be cleared to exercise the privileges of my PPL?

I recently had hernia surgery in the past few weeks and just had my follow-up appointment with my surgeon yesterday. A week or so ago, I called the FAA Medical Hotline to self-report on my condition and was told that I was grounded until I received a doctor's notice clearing me for normal activity.

The research I've done shows that I need to submit a doctor's letter and an operative report to the FAA to be considered medically eligible again.  My doctor's notice from my recent appointment says that I am cleared to return to normal activity on 1/31/20. Is this sufficient for the FAA to clear my grounded status?

What makes you think you need to inform the FAA of your status? I know of no rule that requires notifying the FAA until you go for your next medical. The FAA has a list of disqualifying medical conditions, and hernias aren’t among them. They do recommend that you not fly for 5-times the maximal hour dose interval after taking certain medications, but presumably you are off the pain meds by now.

If your doctor clears you for normal activity (including driving) then you would have no reason to know of any medical condition that would make you unable to meed the requirements of the medical certificate.

  14 CFR §61.53   Prohibition on operations during medical deficiency.

  (a) Operations that require a medical certificate. Except as provided
  for in paragraph (b) of this section, no person who holds a medical
  certificate issued under part 67 of this chapter may act as pilot in
  command, or in any other capacity as a required pilot flight
  crewmember, while that person:

  (1) Knows or has reason to know of any medical condition that would
  make the person unable to meet the requirements for the medical
  certificate necessary for the pilot operation; or

  (2) Is taking medication or receiving other treatment for a medical
  condition that results in the person being unable to meet the
  requirements for the medical certificate necessary for the pilot
  operation.


Why is the maximum speed of current fighter aircraft lower than those from the 1960's and 1970's? While reading about the characteristics of the newest fighter aircraft, I observed that their maximum speed is lower than of the aircraft in the same roles half a century ago.

For example, the iconic F-14 and Mig-25 have a higher maximum speed than their modern equivalents.

After the Cold War ended, the major air forces are only engaged in ground support and bombing against low-tech opponents who use asymmetrical warfare, and no modern scenario would see the top fighter aircraft directly engaging each other any time soon. However, for any fighter aircraft in the interceptor role, I would expect speed should be an important characteristic. Also, military aircraft are designed and introduced over a long time period, and are expected to be used for many decades.

Why did maximum speed become less important? Wouldn't it be easier to design even faster fighters now than with the technology available 50 years ago?

Speed was life in air combat until the jet age. The pilots who became Air Force generals in the Fifties had learned their trade in the Thirties when speed was the most-desired quality in a fighter. Naturally, the ability to be faster than any adversary was very important to them. When the requirements for new fighter aircraft were written in the Fifties, those generals made sure that a higher top speed was part of the specification.

When those supersonic-capable aircraft were used in real conflicts, something very surprising and unforeseen happened: They did hardly ever fly supersonic. When the Air Force in the late Sixties accumulated the flight data from several years of Vietnam war air combat, they found that all aircraft had accumulated just minutes at Mach 1.4 and only seconds at Mach 1.6 out of more than 100,000 combat sorties¹. Never was even Mach 1.8 flown in aircraft which had been optimized for Mach 2.4 (F-104, F-105, F-106A, F-4D/E and F-111).

To cite from this study why speed stayed mostly subsonic:

  The first of these reasons lies in the shape of the turn rate vs Mach number relationship for an aircraft. […] In combat, each pilot has the tendency to to fly his aircraft so as to maximize his turn rate. He thus gains angular position on the enemy which, in turn, may permit a missile launch or a gun firing. […] It can be seen that the pilot's urge to maximize his turn rate will unfailingly drive his Mach number to about 0.7. Thus, if the pilot is going to join in combat, […] his speed will inevitably drop to subsonic speeds. […]
  Note also, that even if the turn rate is held constant while increasing the speed, […] the turn radius and load factor increase, bringing with it increasing problems of keeping the enemy in sight.

The second reason given in the study is the dramatically smaller combat radius (the maximum distance the airplane can travel from its base, accomplish an objective and return) once the aircraft starts to fly at supersonic speeds. Even for flying into the combat arena supersonic speed was rarely advantageous. Northrop studied a multitude of intercept cases and found that speeds above Mach 1.1 were almost never helpful because they curtailed the combat radius severely.

Now you need to know that the top speed is an important driver in airframe design. Flying at Mach 2+ requires heavy and complex intakes, a heat-resistant structure, high wing sweep and heavy, low-bypass engines. This all degrades the combat qualities at high subsonic speed, which was where those aircraft were used the most. Building into them the capacity for Mach 2+ made them worse for what they were actually used for.

From the late Sixties on this lesson was incorporated into the newer designs like the F-16. Stealth again decreased the importance of supersonic capability, and the maximum sustained speed of the F-22 was actually reduced from Mach 1.8 to Mach 1.6 to reduce the heat load on the composite wing leading edge.

¹ Source: Northrop F-5 case study in aircraft design, AIAA Professional Study Series


How do combat jets know when to launch flares to counter IR missiles? From my related question, it seems fighter jets do not usually track missiles by radar. Instead, they have a system that warns of radar lock.

So what about infrared missiles (heat-seeking missiles)? Flares are a countermeasure to these, so how does the jet know when one is incoming?

I would be pretty surprised if such a system didn't exist. I want to know more about that system and when it was first implemented.

Actually most aircraft don't actively know when a missile is being fired at them. I have worked on helicopters and fighters that deploy counter measures.

The first is an IR jammer which we call a disco ball. It is made up of mirrors at different angles that resemble a disco ball. It radiates an IR signal at different angles to confuse the missiles.

The flares or chaff are fired periodically in known hot spots. This creates heat signatures similar to the engines and confuses the missiles.

There are active systems but they don't work well. I have seen a helicopter in testing suspended from a wire with countermeasures turned on. A missile was fired and the countermeasures didn't even get deployed. This is why they usually keep firing the flares or chaff in known hot spots.

Hope that helps.


What is that wire connecting What is that wire connecting the tail fin to the fuselage in beechcraft 1900 and so many other airplanes

It’s a high-frequency antenna, used mostly on flights traveling across seas and oceans, where there tends to be areas without VHF and UHF coverage. This was the case on older aircraft, most newer ones have a smaller hidden one on the tail-fin.


What is the upper altitude limit for propeller driven aircraft? Is it possible to fly 100 kilometers with a propeller driven aircraft? and if not what is the limit of a propeller driven aircraft?

The altitude 100 km is also known as the Kármán line. It is also called the 'edge of space'. No aircraft can fly higher than this line. Because of the sparseness of the atmosphere they would have to go so fast in order to generate lift that they would reach orbital velocity. Therefore they would be spacecrafts, and not aircrafts.
As you can see it's a theoretical limit, in practice aircraft fly a lot lower than this.

So in effect, no it's not possible for a propeller driven aircraft to fly above 100 kilometers altitude, but this is also true for any other kind of propulsion.

About your other question, I believe it's already answered quite nicely here: How high can propeller airplanes fly?


For FAA currency purposes, must flight time be in an N-registered aircraft? I currently hold a Commercial Pilot Certificate issued February,2018. My Flight Review has to be done no later than February 2020.

I have convalidated my FAA License to Colombia. The 90 day currency for carrying passengers applies to both FAA and Colombia.

If I fly Colombian airplanes, does that flight time apply to the 90 day requirement in the U.S.?

In other words, can FAA certificate currency be demonstrated in non-N-registered airplanes?

14 CFR 61.57(a)(ii) details "category, class, and type" but does not mention registration of the aircraft.


What would happen to a flying aeroplane if there's suddenly a brick-size hailstorm? What would happen to a flying aeroplane if suddenly there is hail in the sky?

For example, ice the size of a brick.

There was a case where an easyJet Boeing flew through a hailstorm; the accident report is here, with a PDF download available, which lists some of the damage (which includes a cracked windscreen and damaged leading edges on wings and other surfaces).

There are photos showing the damage incurred, including the one below. Search for "easyJet hailstorm damage" to find more.


How do pilots respond to wind shear? I am aware that wind shear is the geostrophic wind between two pressure levels and am also aware of the catastrophic effect microbursts can have.

If informed, can the crew avoid wind shear? And if not, how do they deal with it?

When an aircraft experiences changing winds as it climbs or descends, this is technically "windshear" and it can have consequences (changes in airspeed and turbulence), but the much more dangerous phenomena is the microburst, and discussions of windshear avoidance and recovery are mostly concerned with that.
There are some good tools available for avoidance: major airports typically have Doppler radars that are designed specifically to detect microbursts and significant windshear events, and tower controllers broadcast those warnings.  Airliners and other aircraft with modern radar systems have similar capabilities, looking ahead into their flightpath for the next few miles.
Without those capabilities, windshear detection was essentially accomplished by comparing groundspeed (from an INS or GPS) with indicated airspeed, and noting any changes in that relationship.  So if your GS was 120 and your IAS was 100 (the difference due to combined effects of the wind plus the delta between True and Indicated Airspeed), then suddenly you had 130 knots GS and 95 knots IAS, you've suddenly picked up some tailwind, and if that trend continues, the loss in indicated airspeed could become catastrophic, and so an escape is necessary.
On a more basic level, some cues are typically published that may indicate windshear on approach:

± 15 knots indicated airspeed

± 500 fpm vertical speed

± 5 degrees pitch attitude

1 dot displacement from the glideslope

unusual thrust lever position for a significant period of time
(Source)

When you receive a warning from Tower or your onboard systems, aircraft that haven't started taking off (or are very early in the takeoff roll) stay on the ground, and aircraft on approach will discontinue the approach (go around).  Since the effects of a microburst are much more pronounced close to the ground, the difference between encountering the microburst at 3000' AGL instead of 500' AGL may be the difference between a bumpy ride instead of a truly dangerous event.  Also, if the microburst can be localized, either from radar or visually by observing virga or a storm cell, then turning away from it is often appropriate.
What is also practiced (in the simulator!) is what is referred to as a windshear escape maneuver, which is the aircraft manufacturer's (and possibly, operator's) best guidance for your best chance of surviving a windshear encounter.  This would typically involve steps like advancing the power to the maximum available, retracting speedbrakes (if extended) to reduce drag, rolling wings level, and climbing as quickly as possible.  At least in Boeing aircraft, it is not advised to change the flap configuration because doing so would increase your stall speed, and it's also not advised to retract the landing gear, because even though this would reduce the drag, it would also make any contact with the ground far more damaging.  Each aircraft has its own procedure, but that's a general case.
A couple of links:

Excellent discussion from Airbus of windshear & dealing with it
FAA Discussion of Microbursts


Why don't airlines provide smoke hoods? In
Fire-involved Accidents and Incidents Reviewed
, Rudolf Kapustin stated in 1993 that

  Nearly all aircraft accident fatalities that are not the result of
  crash/impact injuries are the result of post-crash fires and the
  inability to exit aircraft quickly, which in most cases is attributed
  to incapacitation from toxic smoke, fumes or injuries.

This makes me wonder why airlines don't provide smoke hoods for their passengers in case of a fire, the same way they provide life vests in case of a water landing. If flights crossing a body of water must have life vests available for all passengers in case of a water landing, why not make an equivalent law for smoke hoods in case of a cabin fire?

Protective breathing equipment, or smoke hoods are protective head coverings that prevent wearers from breathing the smoke, particulates and toxic gases generated in a fire. There are two main types of hoods: those that have a source of breathable air and those that just filter the particles out of the air.

The smoke hood for aircraft passengers wouldn't need to be a firefighting grade smoke hood, just enough to get everyone out of the plane before they get asphyxiated.

Today, the recommendation in case of a cabin fire is to stay near the ground where the air is more breathable. If passengers could be equipped with smoke hoods, they could walk out instead, which would likely make an evacuation faster.

Granted, the smoke hoods would be used on rare occasions, they have a cost, take up space, weigh something, and you have to explain to the passengers what to do with one in case an accident happens. So it is unlikely that an airline would spontaneously decide to equip all seats with an emergency smoke hood.

But life vests have all of those disadvantages as well. It seems to me that these hoods would not be any heavier or any more expensive than the life vests, and might be used on more occasions than the life vests. I've seen smoke hoods the size of a soda can, so finding a place to fit one on each seat can't be so hard.

So why aren't plane equipped with emergency smoke hoods for passengers?

This is an issue on airline passenger safety that has been debated since a very long time, and there are various arguments for and against the use of smoke hoods.

A classic example which showed the requirement for smoke hoods was the British Airtours Flight 28M, which had an engine failure during its take off roll at Manchester International Airport in August 1985. The ensuing fire and black smoke made the evacuation very difficult, and as a result 48 people died from smoke inhalation. Perhaps, the presence of smoke hoods could have saved many more lives. But at the same time, the subsequent investigation revealed there were other factors which contributed to the tragedy, such as the restricted access to exits and standard operating procedures which did not take into account the wind direction before turning.

From what I have read and researched, smoke hoods might involve unnecessary time wasted in wearing them. After all, airline crews are trained to evacuate a passenger aircraft within 90 seconds with half the emergency exits blocked. This time is considered sufficient to escape toxic smoke related fatalities. Secondly, the passengers might require some detail as in how to use them. Surely, space, weight and cost issues are secondary and can easily be overcome, but these are other issues which prevent their use.

In case of a fire upon crash landing, the immediate action is to evacuate and go as far away as possible from the aircraft. Since the passenger will not be staying in the smoke, it does not seem logical to provide smoke hoods. A water landing on the other hand might require passengers to float on the water surface for some time till emergency services arrive. This necessitates the need for a life jacket, otherwise lives can be lost due to drowning.


Which cruise altitude is prefered in engine-out operations of Boeing airplanes? On Engine Out Operation in Boeing Airplanes, which altitude is preferable, the OPT Altitude, the MAX Altitude or the RECOM Altitude of the ENG OUT CRZ Page?

You'd typically drift down to your max single-engine altitude, which means essentially that max continuous power on the operating engine is sufficient for level flight at that altitude.  Higher than that, you have a slow descent going in order for the thrust you have to maintain the recommended driftdown airspeed.

In general, there wouldn't be any advantage to descending lower than this until you need to do so for approach and landing, so you'd probably remain at that max altitude.  As you burn off fuel, your max engine-out altitude would slowly increase so (hypothetically) you could actually step-climb up a little bit if you were going to be at that new Single Engine cruise altitude long enough, but in practice you'd need to lose the engine a LONG way from landing before the idea of step-climbing up to a higher SE cruise altitude would make practical sense.

The "Max" altitude is only reachable with the thrust of 2 engines, and the "OPT" altitude is probably well above what your max SE altitude is anyway -- it's optimum for cruising with both engines operating, after all.  Granted, a sufficiently high Cost Index and/or strange winds can pull the Optimum altitude down, but in 99% of the cases, Optimum is going to be well above Max Single Engine altitude.


Why Clyde P. / Boeing B-52H Stratofortress flight from 1962 took the longer route? Third on list of longest non-stop, non-commercial powered aircraft's flights is January 10–11, 1962 flight on Boeing B-52H Stratofortress made by major Clyde P. Evely and crew. Can anyone provide any details about this flight?

Wikipedia says, that it was a flight from Japan (Okinawa) to Spain, via Tokyo, Seattle, Fort Worth, Washington and Azores. I'm especially interested in knowing, why that way? Most (all) of today commercial flights are flying Europe to Japan / Far East the opposite way, that is through Asia.

Is there any source of information, why did that flight took the longer route? Was that specially made to break the world record or was there any other circumstances to take such decision?

The B-52 Stratofortress is a military jet, and specifically a US military jet, which if flown over USSR was very much in risk of being harmed. Thus, it was an intelligent decision to follow a longer route, rather than being a victim of ongoing cold war, following the longer route could have also helped the crew in achieving the longest flight record. Secondly, the B-52 did not have a very good history even before 1962, thus taking precautions was a necessity for the crew, and they did this by choosing to fly over more helpful nations.  Also, aviation was not developed very much in Asia back in 1962 with very few strips of a large distance, to be used in case of emergency.

For more information, you may refer this and this!


How can I estimate pressure altitude? How do I find pressure altitude?

Find pressure altitude using rule of thumb for 1498 feet when the altimeter setting is 27.83" Hg.

I did (29.92-27.83)*1000+1498=3588

Did I do this correctly?

You are 1498ft above the place where the pressure is 27.83InHg. So how high are you above the place where the pressure is 29.92InHg?

27.83 is 2.09InHg higher than 29.92, ie roughly 2090ft higher. So you are 1498 + 2090 above the place where the pressure is 29.92InHg, ie your Pressure Altitude is ~3588ft.


How far from a taxiway, can a walking or biking trail be built? How far from a small single runway airport's taxiway, can something like a walking or biking trail be built?

ICAO recommends somewhere between 16.25 and 57.50 metres from the centreline, depending on the type of aircraft that use the taxiway (code letter A-F).
From ICAO Annex 14:

3.9.8    Recommendation.— The separation distance between the centre line of a taxiway and the centre line of a runway, the centre line of a parallel taxiway or an object should not be less than the appropriate dimension specified in Table 3-1, except that it may be permissible to operate with lower separation distances at an existing aerodrome if an aeronautical study indicates that such lower separation distances would not adversely affect the safety or significantly affect the regularity of operations of aeroplanes.

...

3.11.1    A taxiway, other than an aircraft stand taxilane, shall be included in a strip.
3.11.2    Recommendation.— A taxiway strip should extend symmetrically on each side of the centre line of the taxiway throughout the length of the taxiway to at least the distance from the centre line given in Table 3-1, column 11.


Is it feasible to circumnavigate the Earth in a sailplane? Would it be feasible and survivable to circumnavigate the Earth in a glider or sailplane without propulsion and without landing until the circumnavigation is completed, when you'd return to the same location you were disattached from the carrier plane or winch? What would the major obstacles be and how could one handle it? Did anyone ever attempt such endeavor?
Edit: The two-seated Perlan II sailplane once reached an altitude of more than 70,000 ft (21 km) so perhaps let's discuss more over that single plane, whether the Perlan II, assuming it reaches 70,000 ft, could cross huge areas of sea for instance. If the two pilots manage their time so that one of them navigates while the other sleeps, isn't it likely you could circumnavigate the Earth in the Perlan  II?

No. Both night and oceans would be major obstacles.
Night time can be survived by parking the glider in ridge lift but it requires a steady wind during the night. This is possible and has been demonstrated decades ago, but is only possible with the right weather conditions. To have those lined up between thermal-powered daytime flying is rather unlikely.
Oceans are too homogenous to create thermals. You will notice that when crossing a large body of water in a glider: Over water the air is calm while over land it is easy to find thermals. Why else would albatrosses resort to dynamic soaring if the much less stressful thermalling would be possible? Dynamic soaring works much less well for human-sized gliders because of the limited height of the wind shear layer above the ocean's surface. Besides, it is beyond normal human capability to fly intermittently at 3g over many hours without sleep.
If you start high enough, a large lake can be crossed since the lack of thermals means you also will not hit downdrafts and your glide ratio will be easy to predict. But no thermal will carry you high enough to hop between Pacific islands or from Scotland to Iceland, which is a nearly 1000 km overwater trip.
For a true circumnavigation you would need to touch the southern hemisphere and there are too many long stretches of water to plan any feasible course. Only flying across Siberia and on to Alaska, Canada and Greenland does not make it a circumnavigation. Also, I very much doubt you will find thermals over large bodies of ice and snow, too.


Why changes the lift during turning with sidewinds? Why is there relative wind in the wind-frame? I started doing some simulations with XPlane and could observe a very interesting effect when doing turns in the presence of constant wind:

All simulations are done with the XPlane Cessna 172 (?) with the motor turned off in gliding. (I want to simulate an emergency approach)

I control my plane to have a constant glide path angle and a constant roll angle. No coordinated turn. When I do so without wind, I get perfect circles with a true airspeed (TAS) that is decreasing with decreasing elevation. My glide angle controller has not too much work to keep the gliding angle perfectly constant.

However, if I turn on some constant wind, I can observe,

firstly: my circles change to trochoids over ground
secondly: my glide angle controller needs to counteract depending on the relative heading to the wind. When I am in a sidewind situation where the wind attacks the outer (higher) wing, the true airspeed is decreasing and when after a half circle the wind attacks the inner, lowered wing, the true airspeed needs to be increased to hold the gliding angle. In the quarters of turning with straight headwind or tailwind, the true airspeed is equal. So this results in a sine-like true airspeed profile with respect to the actual turning heading.

So in principle, I can imagine, that wind attacking the higher wing increases lift as it raises the whole plane from below and when it attacks on the lowered wing, it pushes the whole plane down from above.

What I don't really understand is why I experience this relative sidewind at all? My plane flies trochoids over ground instead of circles, as the wind blows the whole wind frame away. But shouldn't be the windframe kind of windless with regards to the plane?

My naive idea was, that the whole plane with its own wind frame is moved constantly by the wind, and calculating true airspeed within this wind frame is the same as in the no-wind condition. (see e. g. https://aviation.stackexchange.com/a/26332/30632)

Where do I over-simplify?

Wind cannot 'attack' your wing, because there is no wind relative to your aircraft, only relative to the ground.  You are flying in still air; the still air in which you are flying is moving over the ground.

Your path over the ground is affected by the wind, so your first bullet point is correct.  'Wind' (in the weather sense) is the parcel of air in which you are flying, moving relative to the ground.

In your second bullet point, if your speed is varying, it must be due to a change in the controls, resulting in a pitch attitude change, or a change in power setting.  I'm not sure what you mean by "glide angle controller" but that would usually be the pilot.  Your speed cannot vary as a result of the wind, as there is no wind relative to the aircraft.  Only by referencing an external frame of reference (looking at the ground, looking at GPS) can you tell that there is any wind.

So if you are experiencing any sidewind (or any other wind), it is caused by whatever is controlling the aircraft (pilot or something in the program) referencing something other than the air.  This experience cannot be caused by a constant wind.


Would fuel quantity indications be affected by extended flight at nonzero bank angles? If flying with a 20kt crosswind requiring yaw input as well as roll input to maintain course, would the fuel indicators show different loads depending on the roll angle of the aircraft (in this case, an MH-53e)

Clarification: With a left bank angle of 15-20 degrees would it appear that the right side fuel cells were using fuel faster with a quantitative fuel quantity system?

Thank you sir. That is a better way of saying it.

I don't know what fuel quantity indicating system is installed on the MH-53, but most aircraft use a capacitive indicating system. Basically, there are multiple probes spaced throughout the fuel tank(s). During a turn or bank, the fuel will accumulate to one side of the tank, which increases the capacitance on the respective probes on that side of the tank. Meanwhile, the capacitance decreases on the probes that aren't covered as much. Total capacitance of all the probes is then summed and processed. Basically, no matter how the aircraft is oriented, in a properly operating system, there should be no detectable change in fuel quantity.


Possibility commuting using GA aircraft between rural towns? Last week I went to visit my friend out in California City and noticed they do have an airport over there, so here is my idea.
Would it be practical to fly GA aircraft between California City and Los Angeles on a commuting basis, multiple times every week if not daily? Or generally commuting using aircraft in the rural area?
I know some areas in Alaska people doing exactly just this, but is this doable everywhere?

As for the latter part of your question, is it doable everywhere, the answer would be a resounding no.

Unless you are a proficient IFR pilot, the climate would be one of the limiting factors in many places. For example where I live in, we have four seasons, of which the fall, with mostly IMC weather, lasts for about 6 months, leaving the other half of the year somewhat doable for a proficient VFR pilot. Now, I'm not kidding, it really is like that here: a couple of years ago it was cloudy (low level overcast) for three months in a row. Most of the cloudy days then were of the sort that would have made commuting under VFR very risky to say the least.

Another hurdle might be the cost. Again, as an example, where I live flying a private plane is ridiculously expensive. Even more so, if you want to hold an IFR -licence, which would be an absolute necessity if you wanted to commute by private plane here.

And one thing is scheduling. Unless you live and work very near an airport, you must consider transit times between your home, departure airport, destination airport and your workplace, and the other way around. Add half an our of flight preparation twice per day, and any time savings you might have thought of will quicky dissapear.

Generally I'd say it depends heavily on local conditions, but commuting by a private plane is (unfortunately) not a viable option everywhere. And I do not think it's a financially viable option anywhere...


Do pilots ever suffer PTSD after emergency landings? I have watched a few documentaries about plane crashes where the whole crew and passengers survived. Of course the passengers are usually all scared, but what about pilots?

Do they ever suffer from Post Traumatic Stress Disorder (PTSD)? Are they ever too scared to fly again after such landings?

Yes, for a while: Capt. Al Haynes, after saving 184 lives on United Flight 232.

I was lucky enough to have dinner with Al Haynes a few years ago, and he told me that he had a very difficult time overcoming the guilt of the disaster. The talks he gives have been a way of coping.  (As a side note, he also donates all the money he receives from the talks to the survivors of the crash).
Capt. Haynes has said the same thing in various interviews:
The Seattle Times:

Haynes said it took many sessions with a psychiatrist to overcome his
survivor’s guilt. He resumed flying three months after the accident;
mandatory retirement at 60 followed two years later. [link]

NY Mag:

It was very hard to get past the guilt of surviving. My job had been
to get people from point A to point B safely, and I didn’t do it. I
felt that I had killed them. I had a lot of psychiatric help at the
hospital and afterward. Finally, one psychiatrist said, “You’re not
going to find an answer. You just have to accept that it happened.” [link]

AvWeb:

Haynes said, at the time, that he remained troubled by the accident
and constantly wondered if there was something he could have done,
some overlooked decision that would have saved all aboard. [link]

Before his death, Denny Fitch said something similar:

"To find out 112 people didn't make it, that just about destroyed me,"
Fitch once said. "I would have given my life for any of them. It was a
really tough time." [link]


How does the Pratt & Whitney F119 achieve its features? The Wikipedia article on the Pratt & Whitney F119 that powers the F-22 says the following:

  The high pressure and low pressure turbines are single stage and counter-rotating, thus shortening the engine and saving weight.
  Turbine: Counter-rotating 1-stage high-pressure, 1-stage low-pressure turbines
  Type: Twin-spool, axial flow augmented turbofan

We also find:

  Thrust augmentation is using additional fuel in a turbofan's cold bypass air only, instead of the combined cold and hot gas flows as in a conventional afterburning engine.— Afterburner

What's the benefit of lighting the bypass air compared to relighting the exhaust? Wouldn't the cooling benefits of the bypass air be lost?
Does that mean that the F-22's "supercruising" could be "augmented"?
How does by counter-rotating the two-spools, the engine becomes shorter and lighter?
How are the turbines counter-rotated?

While the answers are probably buried deep in the Integrated High Performance Turbine Engine Technology program, hopefully some educated guesses can entertain my curiosity.

My only guess for 4. is the use of aggressively curved and converging stators, which would otherwise stall a normal none counter-rotating LP turbine. Or perhaps the lack of a stator in the turbine section, since it's a single LP stage, which would also answer 3.

The afterburner is aft of the gas core of the engine in the jet pipe and bypass air from the fan would have already been mixed with the exhaust gases from the core prior to passing through the afterburner flame holders.
Supercruise is by definition supersonic cruise flight without the use of afterburning, so augmentation would not be in use here
Counter rotation of the spools reduces net torque from the spools upon the structure of the engine requiring less metal and therefore lightens it.  The length of the engine is reduced by making use of a single stage, high efficiency turbine rotor per spool as opposed to multiple turbine stages per spool, which would make the hot section of the engine longer.


Why were "pattern a" and "pattern b" removed from the Instrument Flying Handbook? If you search around on the Internet, have an older copy of the Instrument Flying Handbook, or talk to a seasoned CFII, you may run across the concept of "pattern a" and "pattern b." These were exercises which involved tracking courses, flying procedure turns, hold entries and sometimes constant speed climbs and descents. They seem like valuable maneuvers for honing instrument flying skills.

At some point in the last several years they seem to have been removed from the Instrument Flying Handbook. I don't actually own an out-of-date copy of the handbook to verify this, but if they were removed I'm wondering if anyone knows why. Does the FAA frown upon the use of these maneuvers in training?

Beyond the question itself, I'd love to find a current publication that teaches pattern a and pattern b for reference.

I can't say for sure, but I would assume that the pattern-based drills were removed because of the new emphasis on scenario-based ("real world") training the FAA has been moving toward: While Pattern A and Pattern B are useful for honing your skills (and I'll even admit they're kind of fun to fly) they're not something you'll fly in the "real world" - you are unlikely to string together that particular set of elements in that particular order on any kind of regular basis.

That doesn't mean the Pattern A / Pattern B maneuvers are not useful tools or that the FAA "frowns on" them - they really don't care how you acquire the skills necessary to pass your checkride and if flying Pattern A / Pattern B helps then by all means fly your heart out! Just know that when you take your checkride you will not be asked to "Fly Pattern B" - it's not an element of the practical test.

A copy of the maneuver diagrams for Pattern A and Pattern B can be found in Gleim's Additional Instrument Flight Maneuvers handout, which also has some valuable notes on how the maneuvers should be performed.

Personally I prefer the diagrams from Privilege Aero because I find them a little easier to read (Patterns A & B are listed as Patterns D & E respectively, except the Gleim version of Pattern B includes a descent & go-around at the end of the hold).

I've reproduced the Pattern E diagram below in case any of the links above break.


Is a failed ditching of an aircraft also Controlled Flight Into Terrain (CFIT)? Does CFIT apply in case of a plane (not an seaplane) failing a "landing" emergency in the open sea?

Boeing defines it in the following way:

  Controlled flight into terrain (CFIT) describes an accident in which a
  flight crew unintentionally flies an airplane into the ground, a
  mountain, water or an obstacle.

Since it's not unintentional, it's better described as forced landing or in your case, ditching.


How can the lift force be changed without changing velocity? I am facing a problem for calculating the 4 forces affecting the aircraft balance.
Suppose the following inputs:
Aircraft velocity is 222 m/s.
Aircraft mass is 23500 kg.
Aircraft weight is 227360 kg.m/s2
At zero angle of attack the lift coefficient is 0.2
By Calculating the lift force from one wing 172899 N.
for the two wings lift force *2 = 345799.125 N

The problem is:
Now I want the aircraft to go to balance state to move with constant velocity.
So all the four forces should equals to zero thus the lift force should equlas the weight force.
How Can I decrease the lift force?

Assuming:
I still need the aircraft to move with constant velocity 222 m/s.
The lift is affected by angle of attack which is zero.
The air density is constant.

how can I the aircraft balanced with velocity 222 m/s?
Can I decrease the lift force without affecting the velocity?

The problem is:
  Now I want the aircraft to go to balance state to move with constant velocity.
  So all the four forces should equals to zero thus the lift force should equlas the weight force.
  How Can I decrease the lift force?

This can be done by simultaneously reducing AoA (which in-turn reduce CL) by introducing little down elevator and reducing the engine power accordingly to maintain the airspeed.


How often does an airline pilot use the rudder pedals during flight? How often does an airline pilot use the rudder pedals during flight? Is it only during takeoff and landing?

I am interested to know the rudder pedal usage time in minutes per average short range flight (A320, Domestic flights, ~1-2 hr flight duration). When on autopilot, the rudder control will be automatic. There are even automatic rudder trim features for most of the commercial aircraft.

Transport category aircraft have a yaw damper that will maintain coordinated flight when the aircraft is in the air unless the flying pilot overrides it with the rudder. It operates even if the autopilot is not in use. The usual procedure is that you take your feet off the rudder pedals as soon as you have lifted off and don't put them back on the rudder pedals until on short final.

The pilot will possibly use the rudder shortly before or going into the landing flare to slip into a crosswind and/or to align the aircraft with the runway if they were flying a crabbed final. However, with most if not all transport category there's nothing wrong with touching down in a crab correctly being flown to correct for a crosswind if desired.

So whether a short range light or a long haul flight, the amount of time in the air that the pilot needs their feet on the rudder pedals is minimal and is in seconds, at most a minute or so.

An exception, of course, is if there is an engine failure, in which case the pilot will use the rudder to counteract the adverse yaw from the asymmetrical thrust.


Where can I find good data on volume of air traffic? I want to have a look at air traffic fatalities data, and have found good information on number of accidents, like this on AviationSafety.

For comparison I want some (world-wide) data on passenger air traffic volume, like number of flights (journeys) per year, or passenger-km per year. So far I couldn't find it. Some good reference?

For $799 you can buy IATA's World Air Transport Statistics (WATS)

IATA publish a few summary data values in various reports

Scheduled Passenger - Kilometres Flown
Scheduled Passengers Carried
IATA Annual Review 2013
IATA Annual Review 2014
IATA Statistics

Note that I think this is data is only collected from IATA members and much of the data is for western-built jets (figures for other manufacturers are much worse, according to comments in IATA reports)

Passenger Km
Total (International + Domestic)

Rank  Airline                   Millions
1     United Airlines           286,802
2     Delta Air Lines           277,560
3     Emirates                  209,377
4     American Airlines         206,551
5     China Southern Airlines   147,841
6     Southwest Airlines        145,124
7     Lufthansa                 144,236
8     Air France                136,405
9     British Airways           130,129
10    Qantas Airways            110,203


Why are safety demonstrations done while taxiing? In airliners, safety demonstrations are performed when the aircraft is leaving the gate. I understand it cannot be done latter as an aircraft incident including an evacuation may occur at take off roll. But I think it could be done earlier (e.g. in waiting area before boarding). This way, if any passenger has any question (e.g. this one), this passenger has plenty of time to ask flight attendants before takeoff. This time may also be used to explain why safety demonstration include all those items (life vest inflated outside the airplane is not the only item that could raise questions). Moreover it could be a good use of waiting time before boarding.

EDIT: As highlighted by one answer, some airliners use video to do this demonstration. In this case, the generic items (i.e. not aircraft specific) of the video could be played on screen in waiting area in addition to the actual briefing.

Many passengers don't reach the gate until seconds before the gate closes for a variety of reasons. They won't get the pre-boarding briefing.

Taxiing is the only time before takeoff where the crew knows for sure that all passengers that will be on the plane are there.


How do I locate a list of restrictions that would prevent a pilot from flying in the US? I have a privacy preserving technology that could conceivably help prevent the Germanwings crash of 2014.  The idea would be there is a long list of issues that would prohibit a pilot from flying encoded on a ID card that anonymizes a pilot's information:

I'm guessing that a list might look like this:

Overwork (no sleep)
Simulator experience, test results
Medical issues (temporary)
Drug tests
Psychological issues

A list of medical providers would link the results together, anonymously, and during the pre-flight check, the ID card would be scanned and rather than a specific issue being highlighted, (depression), the pilot would be asked to rest for a while.  No system would know why the rejection occurred, except for the pilot himself.

This might for a balance of privacy, safety, and accountability without compromising need to know.

That being said, I would appreciate any official, or carrier specific list of reasons a pilot would be rejected from flying.  The closest I've gotten to learning about this is MSFT Flight Simulator and a few hours in a Cessna

Supplemental information would be helpful as well (your thoughts about this solution)

Scope

Per the comments below this question, the scope is limited to US

The list is exactly one item long:
Any condition which would impair your ability to conduct the flight safely, and in accordance with FAA Regulations.

Any more specific list will miss things and be riddled with loopholes - at some point we have to trust that pilots are sane and responsible individuals, just like we do when we let people get in a car.

From a medical perspective the general medical certification information page at faa.gov is a good starting point, and the FAA's guidance for Aviation Medical Examiners has lots of details.

There are also some disqualifying conditions which are explicitly listed in the regulations, and a list of (some of the) medications which will prevent the FAA from issuing a medical certificate.

The things I noted above will prevent you from getting a medical certificate.  Once you HAVE that certificate the "I'M SAFE" checklist or something equivalent expands upon that and tries to help pilots determine whether they're fit to fly right at this moment. There are various ways of interpreting the acronym, but a common one is:

I for Illness
Do I have an illness or any symptoms of an illness?

M for Medication
Have I been taking prescription or over-the-counter drugs?
If so, do they have a negative affect on my ability to perform this flight?
Are any of them disallowed by the FAA?

S for Stress
Am I under psychological pressure from the job or personal issues?

A for Alcohol
Have I been drinking within eight hours? Within 24 hours?

F for Fatigue
Am I tired and not adequately rested?

E for Eating
Am I adequately nourished, or at least "not hungry"?


How does flight duration affect the hourly fuel consumption in heavy aircraft? A 15 hour flight across the Pacific obviously requires more fuel than a 7.5-hour transatlantic flight.  How significant is the hourly fuel consumption increase due to the additional fuel carried at the beginning of the longer flight? Another way of asking the question would be: How much more more fuel do you need to carry (in a typical heavy plane such as the B747-400) for a flight that is twice as long?

General Answer

The heavier the airplane, the more fuel it will burn in a given amount of time.  Therefore, if you takeoff with enough fuel to fly further, you will be burning more fuel in each corresponding hour than if you took off at a lighter weight to fly a shorter distance.

Example

I don't have performance information for the 747, but I can give you an example for a G-IV corporate jet.  Instead of comparing a short trip to a longer trip, I planned the same trip with different amounts of fuel in order to make the airplane heavier.  I planned the flight for the following conditions:

Flight Conditions

Fly from Los Angeles to Detroit, using the same route and average Boeing winds for July
Climb to and maintain the optimum altitude, with step climbs where appropriate

Trip 1: Climb initially to FL450 and stay there for the entire flight (the optimum altitude for this weight)
Trip 2: Climb initially to FL410 and then climb to FL450 2:32 into the flight (the optimum altitude the weight initially followed by a climb once the optimum altitude has changed)

Fuel:

Trip 1: Takeoff with enough to land with a 1:30 reserve - 59,000 lb. takeoff weight
Trip 2: Takeoff with max fuel, landing with a 5:39 reserve - 73,000 lb. takeoff weight
Taxi fuel is not included in the first hour burns, but climb fuel is.

Results

          Trip 1      Trip 2
Hour     Fuel Burn    Fuel Burn     Diff
 1        4,212         4,844      +13.7 %
 2        2,536         3,088      +21.8 %
 3        2,411         3,123      +29.5 %
 4        2,163         2,103      -2.8 %
 Total    11,722        13,558     +15.7 %

Summary

As you can see, the fuel burn is significantly higher in the first 3 hours due to the additional fuel that we were carrying (and therefore the higher weight of the aircraft).  Hour 4 is almost the same because of the idle power descent used in the planning software.


What are the empty weight and maximum takeoff weight of the Moller Skycar? I know what are empty weight and MTOW, which are data I need for my school project. But the website for Moller Skycar only shows the gross weight and net payload: https://www.moller.com/moller_skycar400.html.
But in the wiki for the same vehicle, it shows that the empty weight is the gross weight and the MTOW is the gross weight + net payload: https://en.wikipedia.org/wiki/Moller_M400_Skycar.
Could you guys please help me figure out what is the correct value for the Moller Skycar 400?

First of all, Wikipedia does not regard itself as a reliable source, and nor should you. It is only as reliable as the last editor, and since it is the encyclopedia that "anyone can edit" (and frequently does, me included :-) ), that is not saying much. In fact the last editor to touch those stats has messed it up and the stats given do not match the sources cited.
An aircraft's gross weight is the weight of the plane and everything on board. Typically the maximum gross weight is also the maximum takeoff weight (MTOW), although a few planes can take on extra fuel when airborne so that their gross weight then exceeds the MTOW.
As stated in another answer, the M400 is just a recurrent daydream and all figures are estimates provided by the daydreamer. But, with that in mind, the daydreamer's own numbers are clearly the definitive daydream. In other words, go with the website.


Why do tailplanes provide down force, if not for longitudinal static stability? We can see that most conventional aircraft have their horizontal tail surfaces arranged to provide a down force. This question asks if that is required for static longitudinal stability, and the answer is: not necessarily.

But if static stability is not the reason, what is? Or is it just a meme indeed?

Because the safe situation is: a gravitational moment nose down, trimmed with an aerodynamic moment nose up. In all flight conditions. The critical situation is not cruise, but the conditions at low speed.

At TO and landing the Angle of Attack is high: a nose up attitude, commanded by a downward tail force. Velocity is low, so the large force is achieved by a large upward deflection of the elevator and/or a negative stabiliser incidence. The AoA range is from around zero in cruise, to 15-20 deg nose up: the required elevator range is from zero deflection to large up deflection (plus superimposed manoeuvre requirements down & up). The average required force is downwards.
You don't ever want the horizontal control surface to stall, but particularly not at low airspeeds = during take-off and landing, the most critical phases of the flight. Placing the tail at a lower average incidence angle than the main wing means that there is Angle of Attack margin: when the main wing approaches stall AoA, the tail surface has some AoA left before stalling. This implies that in cruise, if the wing has zero pitch angle, the horizontal tail has negative pitch angle.

But despite the lower incidence, the horizontal tail could stall or partly stall, for instance in a sideslip where a large portion of the horizontal tail is in the wake of the aft fuselage. If it does, we want the aircraft to have a nose down moment, not a nose up moment. If the wing is not stalled yet, the lift force is now not in n.p.$_{fixed}$ anymore, but in a.c.$_W$ And that implies that in the above situation, the nose moves up and the main wing will stall as well. Only when the c.g. is in front of the a.c.$_W$ and the tail force is downwards, will there always be a nose down moment in a stalled tail situation.
And in line with 2. and 3.: it must be certain that there is a stabilising moment in all flight circumstances, at all airspeeds, all angles of attack, all angles of sideslip. That is hard to guarantee when the main wing is optimised for cleanest aerodynamic flow and the stabiliser is in the wake of the main wing: efficiency of the main wing will be higher in all circumstances. By choosing an equilibrium state where the horizontal tail produces a downforce, and therefore less lift with increasing AoA, this problem is solved and the guarantee can be issued, without any additional analysis required. Very good in the olden days of aviation, before CFD.

Note that all above considerations are not really a huge concern in cruise: can the horizontal tailplane ever encounter a vertical wind gust with a velocity that can stall it? The velocity triangle says no, this is not likely to occur in 10$^9$ flying hours. A large aircraft can apply Relaxed Static Stability in cruise: pump fuel to the tail tanks and reduce average down force plus associated trim drag to a minimum, because AoA at cruise is very low. Or trim such that the stabiliser has an upforce, like in the drawing where there is static stability. But at start and landing, the trim tanks must be empty!

The additional burden for certifying this situation is a more elaborate analysis considering gusts at cruise altitude and the influence on static stability: are there any vertical gusts at a higher frequency than 10$^{-9}$ flying hour that can destroy the static stability? Such an analysis was impossible in the starting days of aviation, it is possible now of course.


How does the reverse thrust work while landing? During the landing reverse thrust of an aircraft engine is seen that the compressor fan rotates in opposite direction to counter the aircraft's forward motion if I'm right So, my question here is "does the engine stops its rotation(clockwise) and than starts to rotate it in opposite direction(anti-clockwise) So, as to perform the reverse thrust operation?

In a nutshell my question is does the engine stops midair to perform the reverse thrust operation!

During the landing reverse thrust of an aircraft engine is seen that the compressor fan rotates in opposite direction

This is wrong

Reverse thrust does not reverse the rotation of the fan/compressor/turbine.

Reverse thrust "simply" redirect the airflow coming out of the turbine in the reverse direction (well, almost, as we'll see in a moment) w.r.t. the usual one.

In the image you posted, the thrust reversers are deployed, and you can see them circled here:

The airflow is the coming out not from the back of the engine, but from the sides, slightly directed forward. The thrust (i.e. the force that the airflow is imposing on the aircraft) is directed backwards, while normally is directed forwards, it is then reversed.

This is nicely illustrated in this image (source)

NOTE: there are different typologies of thrust reversers, this is only one of them, but none of them require spinning the engine in the opposite direction.


How can I calculate CLmax for a wing with multiple airfoils? How should I do the math to find the CLmax of a wing that has more than one airfoil, each with a different CLmax?

I am trying to make a model with a portion of the wing tip with a airfoil that has a low Cm, but it has a low CLmax too. So...how can I calculate my CLmax?

The result depends on the wing twist and its taper ratio. You will never get the full 2D lift with a 3D planform, and how much you get depends on the details of your wing. The first step would be to apply Hans Multhopp's methods for calculating the lift distribution of wings (Subsonic Lifting Line Theory), and a search on Github shows a variety of codes to try. Factor in the different airfoils with local twist according to their zero-lift angle of attack.

Lifting line theory does not deal with flow separation and stall, so you need to interpret the results. Ideally, your airfoils will reach their stall angle of attack with a straight lift curve slope, and this stall angle of attack is reached at the same time over the whole span. This should maximise the lift from that wing. Adjust taper and twist until you reach this result (and subtract the twist from the differences in the airfoil's zero-lift angle to arrive at your geometric twist distribution).

However, if you also care about handling, leave some margin at the outer wing in order to have stall start first at the root. Also, you might want to add the effects of aeroelastic deformation in order to avoid unpleasant surprises.


What is the range of pressures a space shuttle can withstand? Pressures, as on the external surface of the space shuttle. I want to design my own functioning space shuttle (on an extremely fundamental level with consideration of only the external structure, nowhere close to the real thing) and would like to run a wind tunnel test on it, and I wanted to know what pressures a space shuttle can withstand in order to design my own spacecraft to match and potentially exceed those values.
I appreciate any help that anybody can give me, even if it happens to be some advice, constructive criticism, or the answer to my question.

The Shuttle Crew Operations Manual has basic information which might answer your question. Starting on page 799 (section 4.3) you'll find Airspeed Limitations.
During ascent the dynamic pressure limit is 819 psf. The limit is based on thermal protection constraints, rather than other structural concerns.
During entry, the dynamic pressure limit varies by velocity. The limit is based on stability (controllability) constraints.

During a Return to Launch Site (RTLS) abort, the allowed limits were a bit higher:

Page 1002 has a graph showing typical Ascent dynamic pressure:


Why is there a time range for holdover times charts? 2016-2017 FAA Holdover Time Guide

The FAA publishes holdover times for each winter season and gives a time frame for how long each type of fluid should protect the aircraft from further contamination.

Why is there a time range for these numbers?  Are there different procedures to follow if your takeoff will be before, in between or after the specified time?

The document answers your question - Look under the table, in the section titled "Cautions:" --

   The time of protection will be shortened in heavy weather conditions. Heavy precipitation rates or high moisture content, high wind velocity, or jet blast may reduce holdover time below the lowest time stated in the range. Holdover time may be reduced when aircraft skin temperature is lower than outside air temperature.

Thus each category has a range of holdover times - longer for the most moderate conditions (barely enough snow to show up in the METAR), and shorter as conditions become more adverse.
For example if we split the difference in the "Rain on Cold Soaked Wing" category, Light Rain (-RA) would have a  holdover time around 5 minutes, Regular Rain (RA) would probably be around 3 minutes, and Heavy Rain (+RA) would wash the fluid off in 2 minutes or less.


Why do jets with 3-D thrust vectoring never hover nose up, but instead move slowly forward? I've seen several impressive videos of fighter aircraft moving incredibly slowly by essentially hovering on the engines, balancing using thrust vectoring. For example:

This Su-10

This Su-37

Large RC jet aircraft often take this maneuver one step further, by coming to a complete stop in the air before accelerating away. Do airshow pilots choose not to attempt to come to a stop because it's too dangerous, or is there some hardware difference between RC jets and military jets that limits their ability to hover in place?

There are limitations in the ability to articulate the thrust vectoring that would limit the ability to hover in space and requires some small amount of forward speed to keep the Sukhoi in a controllable state.  It looks like the RC jet has a vector nozzle that can operate in all directions so that it can be hovered in place like a helicopter, although I imagine the skill level on the part of the operator is pretty high.

My favourite airshow performance of all time was a guy, Wayne Handley, with a monoplane aerobatic machine, the Turbo Raven, with a PT-6 engine, which had a thrust to weight ratio of well over 1:1.  The elevator and rudder surfaces allowed him to control attitude while hanging on the prop, and the ailerons provided anti-torque control.  At Osh in 1998 or 99 I remember him hovering in front of the crowd, moving around in a square box pattern, like outlining a picture frame in the sky, then accelerating straight up until he was a speck.  He stopped doing the act after a crash, from the prop not wanting to come out of ground beta during a descent maneuver, about a year later.  Never seen anything like it since.


If there was an engine malfunction, could we breathe contaminated air? If the engine on airliners has for example, an oil leak, can the oil or other substances contaminate the air on the passenger cabin? How would this situation be avoided?

Yes, an malfunction in a jet engine can cause contaminated air to reach the passenger cabin. It is a rare occurrence, but it does happen.

One of the most famous cases was British Midland Flight 92 on Jan 8th 1989 in Kegworth England.

Kegworth air disaster

"After taking off from Heathrow at 7:52 p.m., Flight BD 092 was climbing through 28,300 feet to reach its cruising altitude of 35,000 feet when a blade detached from the fan of the port (left) CFM International CFM56 engine. While the pilots did not know the source of the problem, a pounding noise was suddenly heard, accompanied by severe vibrations. In addition, smoke poured into the cabin through the ventilation system and a burning smell entered the plane".

In addition to contamination from engine failures, there is a much more public debate over contamination due to perceived weaknesses in the design of the aircraft cabin air systems. These weaknesses have not been positively identified but many believe it is due to faulty engine seals and/or air conditioning packs. There are numerous reports of pilots, flight attendants, and passengers feeling ill from "toxic air" on aircraft.

The name "Aerotoxic Syndrome" is also used to describe the problem of bad air in aircraft. More information here: Aerotoxic syndrome

Here is a website dedicated to Toxic Cabin Air. Toxic Cabin Air


Can an engine on a Boeing 737 fly just using compressed air instead of jet fuel? I was just curious because the air is very compressed in the engine and some things do run on compressed air. And what if the engine was powered all by electricity?

Where would you get the compressed air from? Jet engines "contain" compressed air because the engine itself compresses it using the energy from burning fuel. Asking if you could power the engine by that compressed air is like asking if you could power a car engine by the rotation of the gearbox: it's confusing cause and effect.


Who decides the regular procedure followed by the pilots before takeoff? Pilots need to go through a checklist before they take off. Are these procedures decided by the airlines and (or) the manufacturer, or by the Civil Aviation Regulatory Authority of the respective country?

The manufacturer will publish a checklist.  Some airlines will choose to use the manufacturer's checklist verbatim, while others will adapt it to their specific operation based on things like safety reporting data from their fleet.  The end result will need to be approved by the regulating authority (in the US, the FAA -- specifically the Certificate Management Office or CMO for that airline) before it's used by crews.

An example of how an airline might modify the checklist would be to adapt it in light of new Human Factors research.  Telling crews to "run this checklist" during some large interval of time (say, between leaving the gate and reaching the runway, or between leaving cruise altitude and starting the approach) can lead to a missed checklist, and research recommends "anchoring" the checklist to some cue that's unlikely to be missed.  So, "run THIS checklist before you release brakes and start to taxi, and THIS checklist when you have about 2000' left to taxi before reaching the end of the runway, and THESE 3 items as you take the runway for departure" gives crews anchor points that they'll observe anyway and leave them less likely to look back and wonder "did we read the Before Takeoff checklist?"

The manufacturer might have made it all one long 15-item checklist that they have crews read "whenever," but the airline could separate out the items that are best accomplished before starting to taxi (knowing that the more items you put here, the longer the delay before the aircraft starts moving), the items that can be accomplished while taxiing (probably not stuff that requires a lot of 'heads down' time like reviewing the FMC routing), and the items that should be delayed until immediately before departure (strobes lights, landing lights, radar etc).