How can I calculate the "stability state" of air from a given set of data? I would like to know the answer for the above question, it is about how to find whether atmosphere is stable or unstable using DALR (dry adiabatic lapse rate), SALR (saturated adiabatic lapse rate) and ELR (environmental lapse rate). The table also lists RH (relative humidity).

You should calculate the environmental lapse rate (ELR), not use a fixed value. In the table you presented, the ELR is:
$$ \frac{T_{alt_1} - T_{alt_2}}{alt_2-alt_1} \cdot 1000$$
Compare this calculated value to dry and moist (or saturated) adiabatic lapse rates.

If the value falls between them, the air is conditionally unstable.
If the value is larger than the dry adiabatic lapse rate, the air is
absolutely unstable.

For accurate results, you must calculate SALR, as it varies strongly with altitude. Formula is in Wikipedia article.
See Wikipedia: Lapse rate and  Skybrary: Lapse Rate for more in-depth explanation.
Caveat, the aforementioned sites explain absolute unstability differently, I have no recolletion which it actually is, and my study books are buried in the garage...


Would it be possible to build a "rocket" using a series of ducted fans? I'm wondering if it would be possible to build ducted fan "rocket".

My idea is to construct the duct from 18650 batteries, and to have a series of contra rotating fans along its length.

I can 3d print new blades to have a steeper angles as the air-flow/speed increases.

This is the fan I'm looking at.

A 90mm fan will let you make a ring of 16 batteries around the curcumference and it would be 6 batteries tall as it's a 6s motor.

Is this feasable/will it work? what kind of thrust would I get?

Here is a quick render I made:

From the link you provided:

  Specification:

  Rotor Diameter: 90mm
  Fan blades:11 blades
  Weight: about 350g
  Working Voltage:6s(22.2V) lipo battery
  Motor:Brushless Motor 3553 1450kv
  No Load Current: 4.1 A
  Load Current: 83A
  No Load Speed:32190 rpm
  Load Speed:16095 rpm
  Thrust: 3300g
  G/A:45.16

Assuming that 16 * 6/4 = 24 18650 cells would be able to deliver full electrical power for the fan, the issue would be indeed be the local angle of attack of the fan blades.

Thrust at full power is listed at 3.3 kg = 32 N. This would be at standstill/hovering conditions at sea level, since measuring at that level provides the highest thrust level for advertisements. Diameter is 0.09m. Net thrust T =

$$ T = \dot{m} \cdot (V_{out} - V_{in}) = \dot{m} \cdot \Delta V \tag{1}$$

$$ \dot{m} = \rho \cdot A \cdot V \tag{2} $$

Combining (1) and (2) for the hover, with $V_{in}$ = 0:

$$ V = \sqrt{\frac{T}{\rho \cdot A}} = \sqrt{\frac{32}{1.225 \cdot \pi/4\cdot0.09^2}} = ~\text{64 m/s}$$

Impulse thrust considerations usually draw a contracting propeller wake for inducted propellers. Ducted fans work a bit differently and we can take the average velocity behind the fan for further Order Of Magnituding. Below figure is from this research paper, and shows the considerations for ducted fan flow; it contains some methods for more detailed computations.

Rotational speed under load is 16095 rpm = 1,684 rad/s, tip speed = 0.045 * 1,684 = 75.8 m/s. A velocity triangle at the blade tip has as angle $ tan^{-1} (64/75.8) = 40 $ deg. The blade needs to be inclined further than that, usually about 6 deg, so tip blade angle of the standard fan would be 46 deg. Purchasing the actual fan for verifying the above would be a good thing!

For the second fan, this same method can be followed: mass stream will remain the same if the hull is closed, in order for the 2nd fan to deliver the same thrust $\Delta V$ = 64 => ${V_{}out} = 64 + 64 = 128 $ m/s. Tip angle velocity triangle = $ tan^{-1} (128/75.8) = 59.4 $ deg, fan blade angle = 59.4 + 6 = 66 deg, etc.

Note that the above is valid for the hover. As soon as the "rocket" picks up speed, the local angle of attack of the fan blades will reduce and therefore thrust will reduce. So one would have to optimise time of thrust (time of amps delivered) with weight, momentary speed, and expected end speed, then average the blade angles out for the speed function.

Note that opening the hull in between the fans allows for extra air to be drawn in, increasing the mass flow. The paper cited above has results for a setup like that as well - if the increased mass flow relates in lower entry velocity, this might be worth considering.


Should I have one hand on the throttle during engine ignition? I'm training in a Cessna 172 for my private pilot license (PPL).

My flight instructor recommended that I keep my checklist in one hand (so that I can keep looking outside with my peripheral vision) and turn the magneto key with the other.

The other day another instructor told me that the checklist should be on my lap and my right hand should be on the throttle, in case I find the setting too high on starting the engine and I need to decrease power immediately.
He sounded like this was something very obvious and said I'll fail my checkride immediately if I didn't have my hand on the throttle.

To be as safe as possible I could put my checklist down, start the engine with the right hand on the throttle, then pick up the checklist again, but is this really what I should be doing, and if I don't will I really fail my checkride?

Yes hand on throttle when starting, always, except on engines with fuel injection where you have to have it on the mixture because you start on idle cutoff and move it up as the engine catches.  In any case, you shouldn't be reading checklist items during the start; you just learn what to do and do it so you can be in total control.  Back to the checklist after the engine is running and you are satisfied it's running properly on its own and you can divert your attention to other things.  Whoever was telling you to hold the checklist during the start is... well... an idiot.

I don't think you'll fail a checkride, but will probably get marked down a bit for that item.  Most checkride fails are because a series of screw-ups accumulates and drops your overall score, not because of a single item, unless the single item is something critical and screwing it up is dangerous, like taxing onto a runway with an airplane on final or making a really bad judgement call or leaving out a critical item.

When you do your check ride, you will probably be convinced at the end you failed, if you made this little mistake and that little mistake, and will be shocked to hear "you passed".  Because unless you do something that shows the examiner you're dangerous, it's the overall scoring that counts.


How is the bandwidth of an actuator selected for a primary flight control surface? How the bandwidth of an actuator is selected for a primary flight control surface? Is there any standard? Based on what factors this decision is made?

Actuator bandwidth requirements typically flow down from guidance documents like MIL-STD-1797 (Flying Qualities of Piloted Aircraft). Essentially, actuator bandwidth is selected to ensure the flight control system has a sufficient stability margin. For example, see p. 235 of the above referenced document where the bandwidth of the open-loop response from pilot command to control effectors has to fulfill a minimum gain and phase margin.

In particular, this paragraph is relevant:

  A measure of the handling qualities of an aircraft is its stability margin when operated in a closed-loop compensatory tracking task. We refer to the maximum frequency at which such closed-loop tracking can take place without threatening stability as bandwidth ($\omega_{\mathrm{BW}}$). It follows that aircraft capable of operating at a large enough value of bandwidth will have superior performance when regulating against disturbances. A bandwidth criterion is especially useful for highly augmented aircraft in which the response characteristics are non-classical in form (i.e., have large mismatch in equivalent system fits).

In any case, there are other reasons for actuator selection of which bandwidth is a major one. For example, here's the rationale for actuator selection for the A380 flight control system. The selected electrohydrostatic actuators have a higher actuator bandwidth versus the conventional hydraulic actuators fulfilling the stability margin requirements with the potential for improved disturbance rejection.

Higher actuator bandwidth enables the potential for even better handling quality, e.g., gust load alleviation, however that would need to be assessed in relation to actuator lifetime reliability and overall power requirements.


How does the outflow valve work on a cabin pressurization system? When you fill up a cabin with warm air the pressure of the cabin will rise.  An outflow valve controls the desired pressure. But with pressure rising doesn't the temperature rise because you're compressing air into a space? Is this why the outflow valve is there, to regulate the pressure and temperature? Does the outflow value open and close depending on the pressure during phases like climb, cruise, and descent. Or does the outflow valve shut completely once the cabin altitude reaches 8,000ft? But then wouldn't the air get too hot because it keeps getting shoved into the cabin?
Does it use the isothermal rule, if so then what is the work done?

Pressure does not rise because keeping the cabin pressurized begins with releasing air to the outside. The flight starts low, with low cabin altitude, as the plane climbs the cabin altitude rises (lower pressure than it started).

As for the air itself. When it is compressed by the ACM, the temperature does rise, that's why it is cooled before being introduced into the cabin.

See here: Where does the final cooling take place in the air cycle machine of the air conditioning system?

Work is done on the air, then the air does work by passing through a heat exchanger, and then a turbine, which runs the ACM.

There is one plane I know of that maintains sea level pressure up to FL 410. In that case air will still be jettisoned overboard to bring in fresh air, with the same ACM cycle of temperature regulation.


Were civilian aircraft allowed to overfly the Soviet Union? The great-circle route from Western Europe to, say, Japan involves putting in a lot of miles above Russia, for example like this (London Heathrow–Tokyo Narita; map from gcmap.com).

Would routes like that have been possible during the days of the Soviet Union or would civilian planes have had to take a more circuitous route, flying south of the USSR and maybe even avoiding the Warsaw Pact countries, too?

I'm aware that at least some of Soviet airspace was prohibited which, for example, led to the Soviet Air Force shooting down Korean Air Lines flight 007. Presumably, the route shown in the map would be prohibited, since it goes over the Kola Peninsula, where the Northern Fleet is based and Novaya Zemlya, a major nuclear weapons test site.

During the Cold War, Soviet airspace was very restricted to other countries. Flights from the US often had to follow polar routes to Asia and Europe that avoided entering Soviet airspace. The end of the Cold War allowed new routes to be used.

Source

Flights to the USSR were allowed on a limited basis, often in conjunction with service by Aeroflot. Air Canada had the first service (via Copenhagen) from North America in 1966. Some flights were allowed to cross the USSR (JAL started in 1985) but would often stop on Moscow. Otherwise, Anchorage was a typical stop on such a route. International relations may have improved since the Soviet era, but even today not every airline gets permission to overfly Russia.

The strict policies are the reason that flights such as Korean Air Lines flight 007 were shot down when deviating from these routes, and the flight of Mathias Rust to Moscow was a big deal.


Why are winglets swept back and not front? A winglet is defined by its airfoil shape, profile, sweep angle and height. In case of the sweep angle, why does it always mean that the winglet is swept back. What is the disadvantage of having a front sweep angle

A winglet makes lift like a wing. That's why it's called a wing...let.  It's basically a sail (originally they were called "tip sails") designed to exploit the otherwise wasted circulation of air from bottom to top around the tip, placed so that the local flow curling around the tip strikes it at a positive angle of attack.  It makes lift/thrust and, being a wing, creates a downwash while doing so, which means some of the circulation is being redirected back the other way (an "outwash" in other words).

So the overall effect is the vortex field is weakened, and some its energy is used to make lift and/or thrust.  If the winglet is straight up, its lift component is straight inboard and forward, and is purely thrust and a (wasted) bending moment on the winglet root (which leads to angled winglets).

If it's angled, its lift component is a combination of vertical lift that contributes to holding up the plane, and thrust.   So the dihedral angle is a function of how much the designer wanted the winglet's lift force to be extra lift and how much was to be thrust, the resulting angle being a compromise sweet spot between inboard lift and vertical lift in that particular wing's tip flow pattern (nobody seems to use straight up winglets any more).

The sweep angle is for the same reason the main wing is swept, to reduce high Mach# drag (remember it's not just a fin "blocking" airflow;  it's a wing making lift like the main wing), and also to place the winglet in the optimal location in the circulation for exploiting the energy in the flow.


When can a taxi clearance allow me to cross multiple runways? I was just reading the FAA instrument procedures handbook and saw the paragraph below in Ch 1. I'm puzzled by this, because I routinely get "Cross runways XX right and XX left on Alpha" as part of my taxi clearance. How do I square that with the statement here?

  Instructions to cross a runway are issued one at a
  time. Instructions to cross multiple runways are not
  issued. An aircraft or vehicle must have crossed the
  previous runway before another runway crossing
  is issued. This applies to any runway, including
  inactive or closed runways.

(Top of 1-8.)

The general FAA rule is indeed that ATC cannot issue a clearance to cross multiple runways.

However, waivers are available to airports with parallel runways close enough to make it impractical or even hazardous for aircraft to stop in between them and wait for a second instruction. They are essentially treating such a pair as a single runway for the purposes of this rule.

I'm not aware of any list of airports with such waivers or notification to pilots. However, one could predict whether it is likely by looking at airport diagrams. Consider the example of SFO/KSFO, which has such a waiver on both pairs; even a quick glance reveals why it's needed.

Also, I suspect the main concern behind the general rule is pilots misremembering which runway(s) they were cleared to cross when there is a substantial distance between them. The case of two very close parallels, along with the unusual (and thus memorable) multiple crossing instruction, does not seem to have the same safety concern.


Sensitivity of aircraft stability with respect to the CG location I am working on the design of an aircraft (2 m long, wingspan = 3 m). The platform is longitudinally stable but it is very sensitive to the variation in CG location. For example,
1) CG_location = 100 mm from wing L.E, the static margin is about 15% of MAC.
2) CG_location = 105 mm from wing L.E, the static margin is about 8% of MAC.
3) CG_location = 110 mm from wing L.E, the static margin is about -1% of MAC. (Unstable: Cm vs Alpha curve slope becomes positive)

So, effectively while manufacturing the aircraft or while dropping the payload the CG of my aircraft should not vary more than 1 cm, otherwise it would become completely unstable. Taking into any manufacturing errors, the platform CG might not be exactly as expected and hence having such a small margin creates issues.

How should I deal with this issue? Can I have any suggestions on how do decrease the sensitivity of the longitudinal stability to the CG location? Thanks in advance.

It sounds like it has a horizontal tail, so you basically need to increase the tail volume which will allow you to move forward CG limit forward, allowing you to move the median CG forward and expanding the overall range. So just make the horizontal tail a bit bigger.


Would winglets add fuel efficiency on a Concorde? Would adding winglets to a Concorde have a had a positive impact on its performance and fuel efficiency in retrospect, considering the technology was not widespread or developed at the time these machines were flying and would that at all have reduced/increased its sonic boom?

The answer is no and the airplane in question is intentionally designed this way.

Standard sweptback wings produce the characteristic vortices st the wingtips.  The concentration of these vortices at this point in combination with little lift being produced by the vortices makes a singlet an effective feature to reduce induced drag.  Delta wings on the other hand produce vortices along the entire length of the wing, particularly at low speeds and high angles of attack.  Concorde designers took this into account in order to produce better low speed handling characteristics as well as the olgive delta wing provides a very clean high speed wing.  The wing was one of the most heavily researched and planned features of the jet during development.

The upshot of which is that adding winglets onto a Concorde not only is fairly ineffective way to reduce wingtip vortices and induced drag but impinges upon low speed flight capabilities, requiring greater takeoff and landing rolls and high approach AoA.


Why is the empennage of some aircraft not placed on the centerline? Check the MD80's empennage below.

Can easily tell it's not built on exactly centerline by naked eyes.

Is that because aluminum joint or consider aerodynamics?

I don't think it is manufacturing defects or imprecision.

Some of the small aircraft have the same construction like this.

Couldn't find the similar discussion online though.

The vertical stabilizer is on the centerline.

The line you see is not the centerline, it's the overlap of the aluminum sheets that form the circular fuselage.

(Source)

(Source) Non-aviation example of what I mean by overlap and centerline.

On the other hand, propeller aircraft may employ different methods to counter the left turning tendencies.

  Tail

  The tail group consists of a vertical stabilizer, a horizontal stabilizer, two
  elevators, and a rudder. The vertical stabilizer is mounted on the aft
  fuselage, and the horizontal stabilizer is mounted on the top of the vertical
  stabilizer. The rudder and elevators are mounted on the vertical and
  horizontal stabilizers, respectively.

  The vertical stabilizer is fully cantilevered and sweptback. A scoop for
  cooling the air-conditioning systems is located on the lower leading edge
  section and is heated when the Airfoil Anti-ice is operating.

  – MD-80 Flight Manual

Back to the MD-80 in the photo, from its manual there is no mention of an offset. I searched for multiple terms such as offset, angled, and off center.

Finally, from an official CAD drawing from Boeing's website:


Why the need to use right rudder during stall recovery? Can someone elaborate on why the right rudder is needed during stall recovery for a small single engined training plane like cessna C152 or C172?

Some possible answers are:
A. When recovering from a stall, you need to add power. The increased power induces a torque in the opposite direction.

My problem with this answer is that torque will result in roll and usually ailerons are used to control the roll. Why rudder in this case?

B. This could be to counteract the P-Factor

Since the airplane is pitched down, the ascending blade on the left side will have a higher angle of attack and will produce more thrust, resulting in a yaw to the right. This should need left rudder and not right?

C. This is a variation of A. Since torque induces roll and yaw is a byproduct of roll, you need to apply right rudder. However, in this case we are not using ailerons, so there is no additional drag which will result in a yaw.

Since this question is causing confusion I am adding steps to reproduce the stall and stall recovery and the point at which rudder control is required. See answer from abelenky below which I think is the correct answer.

Step 1: Get to 3000ft, perform clearing turns etc
Step 2: Add Carb heat, Reduce power to 1700RPM, Add flaps and slowly start descending at 55-60KIAS as if you are really planning to land.
Step 3: Idle the power and increase AOA until the plane stalls
Step 4: As the plane stalls, the nose falls, remove back pressure from the yoke and allow the nose to fall

At this point of time you have successfully stalled the plane

Step 5: Remove Carb Heat, Add full power, set flaps to 20 Deg, apply right rudder
Step 6: As the plane recovers and regains airspeed, remove flaps above 60KIAS
Step 7: Gradually return to 3000ft and resume or retry if you want to.

The question is related to Step 5.

You wrote:

When recovering from a stall, you need to add power. The increased power induces a torque in the opposite direction.
My problem with this answer is that torque will result in roll and usually ailerons are used to control the roll. Why rudder in this case?

I think you already know that a stall happens when you no longer have smooth airflow over the wings. Because you don't have effective airflow over the wings, your ailerons are not working. (they may be partially effective, or have no effect at all)
You are right that ailerons are used to control roll during nominal flight; but a stall is not nominal, and the ailerons are no longer effective.
The rudder, as a vertical surface, is not stalled the same way that the wings are.  So while it may not be the ideal way to counter a roll moment, its more reliable than the ailerons.


Why does the Ikarus C42 pitch down when stalled? Apparently, the C42 nose pitches down shortly after stall, like in this video. I know part of the video might be pilot input to recover from the stall, but I've read on various flying forums that this will happen naturally without input anyway. Why is this?

Most aeroplanes are designed with the Centre of Gravity being ahead of Centre of Lift, so when the aeroplane's wing cannot produce sufficient lift anymore -- due to a high Angle of Attack, the nose will drop, therefore, it will decrease the AoA and as the gravity pulls the aeroplane towards earth, the speed will increase which in combination with the lower AoA will hopefully produce enough lift to keep the aeroplane flying again.

In some cases when the CG is not forward of CoL -- e.g. mostly in transport category aeroplanes, the horizontal stabiliser is set/installed on the neutral nose-down Angle of Incidence, which makes the aeroplane fly in a more stable manner and will help the stall recovery by pushing to nose-down.

Generally flying in any type of aeroplane with CG aft of CoL is considered a no-no, for the reasons explained above: 1) Flight instability and 2) possibly unrecoverable from a stall -- which in fact is likely to happen because of the displaced CG will tend to increase the AoA which will decrease the speed, until stall happens.


What does "Request Boxing Vectors" means? I have heard on a request from a pilot: "- Request boxing vectors!"

What's the meaning of this non standard phraseology?

Boxing vectors is not a standard term. I can't tell you exactly what was going through the mind of the pilot (you would have to ask them directly), but based on your description, my interpretation would be that the pilot was requesting delaying vectors to give them time to work checklists. It is pretty common in an emergency situation where the pilots need time to evaluate the situation and plan their actions to request either a holding pattern or vectors around the airport. Boxing vectors could refer to the pilot wanting to be put "in a box" of airspace and left there until they had had time to figure out the gear issue. That would be my guess if a pilot requested boxing vectors on the frequency (although I would ask them for clarification of course).

In an emergency situation, the pilots don't really care where they are going (as long as they stay relatively close to the airport) so it makes sense to let it be up to ATC to decide. ATC then has the opportunity to move the flight to a quiet piece of airspace where they are not in the way for other traffic and let them run the checklists. It's a way for the pilots to reduce mental workload, as all they have to do it punch in a new heading every few minutes, instead of calculating and setting up an holding pattern in the navigation computer.


What does feathering mean and how does it work technically? Before I ask "What does Feathering mean when it comes to Jet/Propeller Engines" I have to say what I think I know:

Feathering jet/prop engines mean achieving a sufficient turbine rotation speed at which, the general functionalities such as VFG drives (elec), pumps, etc. could start operation.

I would very much appreciate an explanation with any anomalies.

Feathering is only possible with variable pitch propellers and means that the blades are turned such that their mid-to-outer section is aligned with airflow and they create minimal air resistance. This is done when the engine is shut down and the propeller should create minimal drag. This means also that all accessories on this engine will not be powered anymore.

Due to the normal twist of a propeller blade, some sections are still not completely aligned with airflow and produce more normal force and drag than they would if all sections could be aligned with airflow at the same time, but in total those forces will cancel out, and the propeller stops windmilling.

This picture of a C-130 engine with feathered prop should help to illustrate the concept.

On pure jets no equivalent setting is possible (we have to wait for variable-pitch fans to add this in the future).


Do ballonets control the buoyancy of a Zeppelin NT? Ballonets are bags of air inside the lifting body of the airship.

I have read about Zeppelin NT, a semi rigid helium filled airship. It uses ballonets to maintain constant over-pressure inside the aerostat. I can't see how this airship would use ballonets to ascend/descend. However it has swiveling engines and actually takes off heavier than air.

I have read that ballonets were also used to control altitude of an airship. However I can't see how it could work since air is neutrally buoyant in air. Maybe in older airships the air in the ballonets was slightly pressurized to make them heavier. Maybe on the landing hydrogen was released and ballonets were filled with air to maintain constant pressure.

The NT, being semi rigid, does not work like a balloon where buoyancy of the airship is controlled by adding or releasing helium. The quantity of helium carried is set at the beginning of the flight, and is set so that the aircraft is heavier than air. Vertical motion is then controlled by engine power. Buoyancy control is not the ballonet's purpose.

Ballonets are used to maintain constant pressure in the hull, as this is required for structural integrity. Whatever additional volume is required beyond that consumed by the helium carried is filled by air pumped into the ballonets. This air may also be released to control pressure as the craft ascends, and pumped back in as the craft descends. The hull is not designed to be pressurized beyond 5mbar.

Zeppelin GMBH technology

  Envelope - Non-flammable Helium, contained in a high strength, multi-layered laminate, provides the necessary lift. The envelope pressure is maintained at only 5mbar above atmospheric. Air chambers, the so-called “Ballonets” help to keep a constant interior pressure at all flight altitudes, and maintain a rigid hull.


Why are commercial airplanes painted at all? While there was debate over why airplanes  are painted white and a question about how much a new paint job costed, what hasn't been asked is why airplanes are painted at all.

I remember one airline company sent out a press release in the 1980s or 1990s that keeping its planes unpainted (i.e, a nice silver) saved several hundred gallons of paint as well as considerable cost savings because the plane was also lighter and used less fuel.

If there are considerable positives to keeping planes unpainted, why do airline companies bother painting them?

This is prompted by a recent flight I had on an US Air airplane that had just been repainted in the American Airlines livery. The captain joked that the paint was still so new that we shouldn't try touching it. Both companies are famous for always being in severe debt -- so saving every penny should have meant going for the 'naked' look.

Related: A quora question on how much money would be saved if airlines stopped painting their liveries and a Boeing white paper on painted vs unpainted

I remembered hearing that paint actually reduces the drag of the plane. Searching a bit I found this Boeing document  describing it.

So the painting reduces the fuel costs, instead of increasing them. Another interesting thing is, that planes are regularly repainted to keep the drag low. Of course there is the billboard effect too.

From the report:

  In response to numerous questions raised by
  Boeing customers regarding the efficacy of
  surface coatings to reduce drag, Boeing has
  investigated some possible airflow physics
  explanations. Possible explanations postulated by Boeing aerodynamicists include:

  Increased regions of laminar flow due to reduced surface roughness.
  Reduction in surface roughness resulting in lower skin friction drag, when flow is turbulent.
  Reduction in dirt and/or insect adhesion resulting in reduced roughness and hence reduced skin friction drag.


How does an aircraft report crew programming of the FMS to the ground? I am reading in the news that the MH370 flight changed its course by "Computer entry" and that it was programmed into the computer at least 12 minutes before the last voice contact with the plane.

How can they know that the change in the computer was done 12 minutes before (while the plane was still flying as on the original course)? And how do they know it was done in the computer, rather than the pilot steering manually?

The aircraft's Flight Management System (FMS) can be loaded with software that periodically sends position reports and flight tracking data to ground stations via ACARS.  If the particular software in use sends the full flight plan or at least the next few fixes periodically with estimated times, this would expose any changes in the flight plan to the dispatch office.

The incident flight in question had its ACARS turned off at some point and the "12 minute" figure is probably derived from the time between the last ACARS message being received and the radar observed turn off course initiated.   They would not be able to know exactly when the buttons on the FMS were pressed, but they could narrow the time down to a range when information changed between two automated reports sent via ACARS.

Relevant chronology:

01:07 final ACARS transmission
01:19 final voice communication

Interval: 12 minutes.


How does a commercial flight pilot handle turbulence? In general, passengers dislike turbulence. Avoiding all turbulence sometimes is not viable, as it would make the flight too long, too expensive (fuel consumed), or simply not having alternatives.

How does the pilot deal with turbulence? Does he or she keep the same altitude? The same speed (relative to the wind)? Increase power?  AoA?

Most of the time the turbulence we experience is termed "chop", which is akin to what you experience on a boat on the lake -- bumps but no real altitude deviations.  With altitude deviations we'll call it "turbulence".  Within these broad categories we'll qualify them with "light", "moderate", "severe" and "extreme" in reports to ATC and other aircraft.  These reports do suffer from a fair bit of subjectivity with respect to aircraft type (wing stiffness) and pilot experience.

If it is light chop, I'll generally just ride it out and turn the seatbelt signs on.

The first thing I'll do if encountering moderate chop or turbulence is to query ATC and get ride reports from aircraft ahead of us and at different altitudes than us.  From this information I'll make a determination to ride it out or to request a climb/descent.  If the turbulence was particularly bad, slowing down was an option, but I only came across that need a few times.  Our ability to descend would often be limited by route length and fuel and major lateral deviations also depended on contingency fuel, so in some cases we had no choice but to stay in the chop.  If the turbulent areas were well forecast or had lots of PIREPS, our dispatchers would sometimes route us differently.

As for power adjustments, if we weren't slowing down due to aircraft limitations I would just adjust power so that maximum airspeed deviations stayed below Mmo.


What are the pros and cons of vacuum and pressure gyros? Inspired by this question, I would like to know what the pro's and con's of the mostly used vacuum-gyro and the less used high-pressure-gyro is.

Side-question: Are there any other ways to make the Artificial Horizon work?

Inspired by this question, I would like to know what the pro's and
  con's of the mostly used vacuum-gyro and the less used
  high-pressure-gyro is.

It is largely related to the instruments in your aircraft but in reality its all about air pressure and the systems are really doing the same thing in the end of the day.

Lets look at the evolution a bit, early aircraft that lacked an electrical system generally used a small external venturi to generate low pressure suction for the early gyro instruments. Note the venturi tube in front of the door about half way up the body on this early Cessna 170.

(source)

Since it was easy to generate low pressure this way early instruments were built as suction based. As planes got faster and external (drag educing) things were removed these systems went internal. Since the instruments were already suction based it was logical to make engine (or electrical) suction pumps to drive them.

When pumps moved into the engine compartment they came with some issues. Wet suction pumps have an oil issue that can seep into the system and cause issues with the instruments. That was solved with the advent of the dry pneumatic pump however that was a bit more susceptible to debris clogging but could provide both positive and negative pressure.

This paper outlines both systems as well as their pros and cons in depth and answers the question quite well. However the end result is that both systems provide the same outcome and in the view of the instruments there is no real difference.

  Gyro Instruments Within the case of the gyro instrument the air flows
  through the air seals of the gimbalsʼ bearings and across the rotor,
  spinning the rotor on its axes. The exhausting airflow from the rotor
  housing applies precession forces to maintain a reference to earth in
  the attitude gyro and the attitude of the aircraft in the directional
  gyro. The mechanics of the gyro instrument remain the same, whether it
  is driven by the airflow in a pressure or vacuum system. The air- flow
  through the instrument is a result of the differential pressure
  between the instrumentʼs air inlet and the air outlet ports. In a
  vacuum system the pressure at the air outlet port is lowered below
  atmospheric pressure. The differential pressure between the atmosphere
  and the pump now forces air to flow through the instrument. In a
  pressure system the pressure at the air inlet port is raised above
  atmospheric pressure and the airflow is in the same direction.

So what are some pros and cons,

In a vacuum system the filter is upstream and air is pulled through it and it does a good job of keeping the air clean.

  ...filtering the air entering the instrument. This filter will remove
  most contaminates from the air, but moisture is not one of them.
  Periodic replacement of this filter will ensure clean airflow through
  the instruments.

While in pressure based systems the air filter is generally mounted in line but has a similar effect

  In a pressure system there is an inline filter in the line between the
  outlet port of the pump and the inlet port of the gyro instrument.
  This restricts, but does not completely stop, the flow of all
  contaminates to the instrument.

However pressure systems have a moisture problem since the compression of air creates moisture, this may add moisture while a suction system will only draw ambient moisture.

  Unfortunately when air is compressed, moisture is created. Although
  the pressure is extremely low (approximately 2.5 to
  4.5 PSI), this system is no exception. Moisture is the No. 1 contaminate, contaminating the gyro bearings in a pressure system.

The paper also outlines that both systems are susceptible to downtime due to pump inspections and system maintenance. Which is a con of both systems.

  Side-question: Are there any other ways to make the Artificial Horizon
  work?

Yes, electricity

(source)


Why do aircraft fly over land rather than over the Adriatic Sea? When flying from central Europe to Greece or Egypt, I've noticed the plane often follows down the eastern coastline of the Adriatic Sea, instead of flying in the middle on a path I imagine would put less noise on the ground. Why is this the case? Closeness of emergency landing airports?

Most air routes in Europe are unchanged since the days before GPS, when they were defined by radials from VOR and NDB radio beacons. As these have a limited range, they could easily be used to define routes across the Adriatic, but less so down its several-hundred-mile length. Routes would therefore normally be defined over land where the plane can route from beacon to beacon, rather than over the sea where (unless you are flying towards or away from a coastline) you cannot fly with as much navigational precision as when following a radial to/from a beacon.


Negative number in ARINC-429 I'm a little bit confused by representation of negative number in ARINC-429.
Let's consider the following example:

Significant bits is equal to 7 (it does not count sign bit),

Resolution is equal to 1,

DATA section has to represent -1 value.
Initially I thought that DATA section is represented as follows:
1 1 1 | 1 1 1 1 | 1 0 0 0 | 0 0 0 0 | 0 0 0 0

But I'm confused by sensor documentation. There sign bit is not in DATA section and I started to think that maybe bits 29-11 should look like that:
1 0 0 | 0 0 0 0 | 1 0 0 0 | 0 0 0 0 | 0 0 0 0

Which way of thinking is correct?

BNR labels that can be negative are represented in 2's complement form
2.3.1.1 Numeric Data

The Mark 33 DITS should accommodate numeric data
encoded in two digital languages, (i) BNR expressed in
twos complement fractional notation and (ii) BCD per the
numerical subset of ISO Alphabet Number 5

If your label is indicating 7 significant bits and an LSB of 1, your range must be +/-128. Bit 29 is the sign bit, and the data bits work down from there.

-1 = 1 1 1 | 1 1 1 1 | 1 0 0 0 | 0 0 0 0 | 0 0 0 0


How long after takeoff for a Boeing 747-400 to reach cruise speed? Assume it is fully loaded (pasengers and cargo) and optimal conditions, almost no wind, etc etc...

How long after takeoff does the plane reaches cruise speed?

If he goes in a straight like on the axis of the airport strip (i.e. makes no turns), how far will have it traveled when it reaches cruise speed?

I did a search on FlightAware for 747-400 aircraft in flight, and sorted by the estimated time enroute. A Qantas flight from KLAX to YSSY came up. I'm assuming that for a 6500 Nm flight, at 13.5 hours, the aircraft is fairly heavy at takeoff.

The flight data shows a departure at 03:28:33, reaching an initial cruise level of FL300 at 03:52:59, after a continuous climb. It was at cruise speed at this point, which gives a time of 25 minutes after takeoff. Comparing the coordinates of these two reporting points gives a distance of about 180 Nm, which from the track is pretty straight.

If you just want to know when it reached a speed around that of cruise, this was about 10 minutes and 80 Nm earlier in the climb, when it reached a ground speed of about 480 knots.


Why is the A330neo more efficient than the A350 on shorter routes? For A330neo Wikipedia page, is written:

  A330neo enables profitability on shorter ranges where the longer-range A350 and Boeing 787 aren't optimized.

For what reasons it is true?

A330 and A350 have almost the same size, weight and passenger capacity (the undeveloped A350-800 should be also more similar), and also engines are very similar, the same family Trent 7000 vs Trent XWB.

I thought that with almost similar planes, the bigger difference for calculating range could be only the fuel capacity (surely bigger for A350), but efficiency (in terms of lower weight due to advanced materials, lower fuel burnt due to new engines technologies) could be an "always true" concept.

So, why for shorter routes A330neo is more efficient than A350? Could not be enough to have an 350 with lower fuel capacity (in case shorter length) and maybe reduced engine power (the opposite of higher power in A350-1000) thanks to reduced weight?

I found this similar question, but I think that mine is more focused to general concepts because I'm asking also "what makes an aircraft more optimized for longer/shorter routes.

A330-900neo    A350-900
Seating       287–440        325 / 173 (ULR)
MTOW          251 t          280 t
OEW           137 t          137 t
Unit cost     US$296.4 M     US$317.4 M
Thrust/eng    324 kN         375 kN

The A330 having fewer seats means a bigger chance of high utilization on any given flight (or having high-density small seats for shorter durations / dense routes). Shorter flights are typically more frequent on a weekly basis, so the flying customers get more spread out in a low-demand season.

With more frequent airport usage, the lighter MTOW means lower fees (typically it's a function of MTOW). Having the ability to carry some 30 tonnes more, pay for it, but not utilize it (carrying fuel), is not good.

They have similar Operating Empty Weights (OEW), which typically means a similar unit cost (~\$2K/kg), but due to the generational gap of the airframe (development cost), getting a discount on the A330neo will be easier (9% bigger discount for the -900neo as of 2014).

Turbine engines give the best fuel economy when they are running near their design power. Having extra power that an airline won't use to carry lots of fuel for an ultra long-haul flight will mean not running at the best power setting. A smaller A350 could have a derated R-R XWB, but a tailored Trent 7000 (6 inches smaller fan diameter) will provide better economy outside the ultra long-haul segment.

The A330 maintenance is also mature, with enough supply, demand, and expertise, this translates to cheaper maintenance cost, especially if the customer already has A330ceo's – flying relatively short hops rackes up airframe/engine cycles more quickly.

In short, it does indeed depend on the route. Some carriers benefited from the full potential of the 787 performance, others didn't, but each carrier is sold the right projections. See: Did any Boeing 787 operator achieve the 20% fuel efficiency improvement over the 767?

Case in point, Emirates has recently (Feb 2019) decided to purchase 40 A330-900s and 30 A350-900s. (airbus.com)


Converting lat long & altitude into a line of sight target? I want to design a long-range ADS-B receiver with a directional antenna (like a Yagi), but in order to maximize its range, I'll need to orient the antenna towards a target (plane) based on existing data from external sources like FR24. I can easily find latitude longitude and altitude data for planes, but how do I convert these values into polar and azimuth angles that I can orient my antenna towards? Essentially, I need to calculate the line of sight my antenna needs to point at in order to make contact with the plane with the antenna's main radiation lobe. Does anyone know I could go about doing this?

Here's javascript source code with a detailed explanation, too long to paste into a standalone answer, but by the time this goes offline certainly a dozen more will appear if they haven't already.
https://github.com/cosinekitty/geocalc/blob/master/compass.html

Online calculator for the same:
https://doncross.net/geocalc/compass.html


Are tower simulators used in civil ATC training? Pilots use cockpit simulators, what about training  of air traffic controllers working in control towers?

Control tower of Québec / Jean Lesage airport (CYQB). Source.

How do they train? Are there full visual simulators with runways, taxiways, radio traffic, etc?

The question is valid for a country with large aerodromes.

Absolutely (and not just civil ATC training - military as well). A large part of modern ATC training is simulator training. This is true for all types of ATC - area control, approach and aerodrome (tower).

For area and approach, the simulator is fairly simple, since the essential bit is a radar screen and a screen with flight information. For tower, there is the visual aspect as well, which makes tower simulators quite large and complex. Some tower sims are relatively simple - 4 big TV-screens with a 3D model of the airport, and a couple of computer screens with radar and other equipment. There are also full size, 360 degree sims, where the "windows" are created by an array of projectors or large screens. After working traffic in one of those for a few minutes, you start to forget that you're not in a real tower.

During simulator training, students can run scenarios in the simulator that are either based on generic airports or real airports. The traffic levels and situations can be tailored to match the expected learning curve of ATC students. This makes simulator training a great tool for both initial and recurrent training of air traffic controllers. Much like pilots, after getting our license, we have to go back to the sim once a year to practise unusual situations, emergencies and so on.

For every controller position in the simulator, there are 2-3 connected "blip driver" positions, from where the aircraft movements are controlled. The controller in the simulator will talk to the blip drivers via "radio", and the blip drivers will respond as pilots and provide the necessary input to make the planes move around accordingly.


How do you calculate the range of a VHF transmitter that is on-board an aircraft? I'm trying to calculate the range of a VHF transmitter on an aircraft output power 50W, frequency 130MHz, and reciever sensitivity of -100dBm.

The calculations I have made give me ridiculously high numbers in the regions of thousands of Kilometres. The formula I used for this is as follows:

Is there perhaps a different formula that I am not aware of?

VHF radio transmissions are primarily limited by line of sight. The formula for this is d = 1.23 * (√h1 + √h2) where h1 and h2 are the altitude s in feet, and d is the max range in miles.


Class B and C Airpsace Ring Data in Text Class B and Class C airspace has multiple rings where each ring can be a custom polygon shape.

I want to extract following data into text:

the shape of these polygon rings in lat/long (ideally a geoJson object)
distance between the rings and
high / low limit for each ring

Is this data available for free or purchase?

For the US, the FAA National Flight Data Center (NFDC) is the place. There is this set of files: Class B,C,D,E Airspace Shape Files, which is free and contains borders of airspaces in the GIS shapefile format.


In an airliner, does the Captain or the First Officer fly the airplane? If there is such a thing as a 'normal' flight (in a commercial airliner), who flies the plane? Is it usually the Captain, the First Officer, or whomever needs the hours?

At the commercial airline level, there is very little difference between a captain and a first officer, other than the amount of time that they have been at the company (seniority).

Typically, each of the two pilots takes turns flying the airplane.  For instance, if today's trip is from Miami to Charlotte to Chicago to Atlanta to Miami, the captain may fly from Miami to Charlotte, the first officer from Charlotte to Chicago, the captain from Chicago to Atlanta, and the first officer from Atlanta back to Miami.

The duties in the cockpit are divided between the Pilot Flying (PF) and the Pilot Not Flying (PNF)/Pilot Monitoring (PM).  These duty positions are independent of the captain/first officer designation.  The PF is responsible for physically flying the airplane (usually only during takeoff and landing) and for controlling the autopilot.  If the autopilot acts up, the PF immediately takes over.


Is it legal to takeoff in a crosswind that exceeds the design limit of my aircraft? Suppose the max crosswind rated for my C-182 is 15kts, but the wind is directly across and gusting to 20kts.  Is it legal for me to go? I've heard plenty hangar flying stories of many an operation that exceeds the design specifications of certain planes that end successfully.

The 15kt crosswind for the 182 is not a design limit at all. If it were a design limit, it would be specifically stated in the POH. To be honest, I think there's no such thing as a design limit for crosswind. It all comes down to how much rudder authority there's left at a specific crosswind strength. And even that depends on many factors like approach speed, flap settings, weight, CG, etc.

This is what the POH for the C182T says:

  Demonstrated Crosswind Velocity is the velocity of the crosswind
  component for which adequate control of the airplane during takeoff
  and landing was actually demonstrated during certification tests. The
  value shown is not considered to be limiting.

and:

  The maximum allowable crosswind velocity is dependent upon pilot
  capability as well as airplane limitations. Operation in direct
  crosswinds of 15 knots has been demonstrated

So it is perfectly legal to land and takeoff with a stronger crosswind component. It's up to the pilot to determine if it's safe to do so or not. It all depends what the pilot's capabilities are.


Can an airline schedule two same-number flights to leave the same airport on the same day? I've read: Why have different flights with the same flight number?
and I guess I understand this can make sense. But - is it allowed for a domestic US airline to schedule two flights with the same number, on the same day, with intersecting routes? Specifically, which have legs scheduled to fly out from the same airport on the same day?
This would be potentially quite confusing for passengers, even if the departure times are spaced many hours apart.
Motivation: I'm seeing what seem to be records of this occurring a few times in a USDT flight data table. Concrete example (edit: this is a significant example, but the question is about the general case) - some US airways flight legs from 2006:

uniquecarrier
flightdate
flightnum
origin
dest
crsdeptime
crsarrtime
tailnum
deptime
arrtime
cancelled

US
2006-01-25
634
LAS
PHL
645
1416
N632AU
642
1407
false

US
2006-01-25
634
LAS
PIT
2257
607
N808AW
2252
556
false

US
2006-01-26
634
LAS
PHL
645
1416
N621AU
650
1428
false

US
2006-01-26
634
LAS
PIT
2257
607
N833AW
2303
603
false

US
2006-01-27
634
LAS
PHL
645
1416
N633AU
643
1404
false

US
2006-01-27
634
LAS
PIT
2257
607
N832AW
2249
545
false

US
2006-01-28
634
LAS
PHL
645
1416
N629AU
645
1404
false

US
2006-01-28
634
LAS
PIT
2257
607
N806AW
2256
544
false

US
2006-01-29
634
LAS
PHL
645
1416
N602AU
640
1409
false

US
2006-01-29
634
LAS
PIT
2257
607
N827AW
2256
602
false

US
2006-01-30
634
LAS
PHL
645
1416
N632AU
641
1422
false

US
2006-01-30
634
LAS
PIT
2257
607
N801AW
2250
536
false

US
2006-01-31
634
LAS
PHL
645
1416
null
null
null
true

US
2006-02-01
634
LAS
PHL
645
1416
N628AU
652
1420
false

US
2006-02-01
634
LAS
PIT
2257
607
N810AW
2300
549
false

Short Answer:
Flight 634 LAS-PHL at 0645 was most likely "US Air 634" on those dates, while flight 634 LAS-PIT at 2257 was most likely "America West 634" on those dates.  Even if both were to have flown with the ATC callsign "Cactus 634," that wouldn't be a problem for ATC since they were separated in time by several hours. (No more an issue than N12345 flying KABC to KABC more than once in a day.) But most likely, they flew with separate callsigns too, as explained below.
Why is this the likely answer?
The LAS-PHL flights in the OP were flown by aircraft whose registrations end in "AU" such as N628AU for example. The airfleets website shows that this aircraft was a US Air (later, US Airways) jet until it was re-registered in December 2006 (the dates on that site are DD-MM-YYYY format). Generalizing from that example, these jets were legacy (pre-merger) US Airways jets.
The LAS-PIT flights in the OP were flown by aircraft with registrations ending in "AW" such as N810AW. Airfleets shows that this was an America West jet until it became a US Airways jet in October 2006.  Again generalizing from this example, the "AW" jets were "American West" aircraft at the time of the OP's data.
So at the time, the one flight was being flown by jets in US Airway livery, and the other by jets in America West livery.  And to the passengers, they almost certainly were sold under the respective brands, so one could buy a ticket for "US Air flight 634" from LAS to PHL in the morning, or a ticket on "America West flight 634" from LAS to PIT in the evening. You'd have to use two separate websites to do so, but there would be no confusion.
Okay, so the remaining question:
Why do they both have the "US" (presumably meaning US Air) uniquecarrier ID in the table?
As described in this paper from Embry Riddle Aeronautical University,

America West Airlines acquired the bankrupt US Airways on September 27, 2005
to form the US Airways Group.

The two airlines became fully one in 2007, when a single operating certificate covered them both.  During the interim,

Both of the merged airlines retained their names and continued operating until September 25, 2007, when America West's FAA certificate was merged into US Airways.
(source)

This interim period is when the flights shown in the OP occurred.  At this point, the airlines were in the process of merging their operations, although their website weren't merged until May 2006.  Thus, in the January/February timeframe posted, the tickets for each would be sold separately.
The wikipedia article notes that the callsigns remained separate until 2008, as "US Air" and "Cactus"; after October 2008, the entire operation used "Cactus".
While it's hard to retrace each step along the way from two separate carriers to one unified carrier, it's clear that various steps are involved, so it seems probable that whatever data source gives the uniquecarrier identifier in the table, either switched over separate identifiers before the dates of these flights, or else it was retroactively changed over to make them all "US" even though at the time some would have been "AW".
In the general case...
So, is it possible, to have two flights with the same number at the same airport at the same day? Yes, although the data shown above probably doesn't indicate that LAS saw a "US Air 634" twice a day during the timeframe shown.  But as long as the first flight and the second don't overlap in time, there is no ATC constraint that prohibits is.  (Military aircraft do this all the time... Cool06 can fly from KDLF to KDLF on a training mission multiple times during the day -- Laughlin AFB in this case.) It's possible, but sufficiently unwise because of the potential to create confusion, that it probably happens for an airline somewhere between very rarely, and never.
As a matter of avoiding confusion, an airline would probably work to avoid scheduling their flight 123 more than once in a day:

"I'm here for my flight 123."
"Sorry, but YOUR flight 123 isn't for another 10 hours; this is the other flight 123 today."

But, if flight 123 is scheduled to depart at 2300 and one day it runs over an hour late, the next calendar day will have two "Flight 123" operations, and nothing will break.
All that to say, what the data in the OP most probably shows, is an artifact of how US Air operated during the transition from two airlines into one, and may not really be particularly indicative of anything more widespread, nor generalizable, than that.


What is the name and purpose of this part on the flap at the DA40? There is a part on DA40's and also DA42's flap. I cannot find the technical document and I couldn't decide what is the purpose of that part. Is it a mass balance part or what? You may see the part at picture. (Note: First picture is not showing the part I meant to ask. The picture was wrong but I keep the picture not to make comments meaningless about it. Correct part is marked at second picture.)

Edit:

Sorry everybody, I drew wrong part before by mistake. The part marked at first picture is the aileron control rod. All previous answers and comments are correct for aileron. I add a new picture for the correct part and I found out it functions as a mass balance horn. We see housings from pictures but the related part is inside the housing.
Edit time: 11th Nov, 2016 10:30 UTC

It is an actuator fairing. It covers the flap actuator so to minimize the drag created by it.

An actuator directly exposed to the airflow would create more drag, increasing fuel consumption and reducing the flight range.


Do aerodynamic forces and moments change aircraft pitch and yaw in the same way? Several questions on the Aviation SE site have dealt with the question: can the rudder alone turn the aircraft:

This one, which was marked a duplicate of
this one, which was itself marked as a duplicate of
this question, with a skilful and detailed answer.

So we know in triplicate that the rudder alone can turn an aircraft. Not very comfortably due to the side forces, wrong way lean, different airspeeds on inside & outside wing etc, that is why the normal way to turn is to bank.
However, the following has been posted in the comments (partial quotes only due to length):

Yaw does not cause aircraft turn. It only causes yaw. Yaw is not turn.
Lift, pointed in a direction other than perpendicular to the horizon, is what creates turn. Nothing else.
With no other yaw force on the aircraft, if you have right rudder, that does create a leftwards force, but it also creates a right yaw (sideslip) which itself creates a rightwards force that opposes the leftwards force from the rudder.
It works in exactly the same way as it does in pitch. The elevator pulls the tail down and, because it's behind the CG, creates a nose up pitching moment (torque). Lift on the wings lifts the aircraft up, and because it's also (generally) behind the CG it produces a Nose down pitching moment. Because the moment arm of the elevator is so much longer the torques balance, but the Up force from wings is much larger than the down force from the elevator and the aircraft is able to fly. The force from the rudder, and the force from the sideslip angle of the fuselage act in the same way.
The nose of the aircraft does not "turn" away from the "direction the pilot ... " it only "yaws" away, and it only yaws away until the sideslip angle reaches the point where equilibrium occurs.

The gist of all this is that the aircraft would behave in yaw in the same way as in pitch: rudder deflection only causes an angle of sideslip, not a continuous turn in heading. That would conflict with the earlier questions posted above.
So the question is: does yaw really behave exactly like pitch? Does deflecting the rudder only cause a greater angle of sideslip but no flight path change?

Of course will yaw also change direction if we define this as a change in the flight path. But it does so much less efficiently than banking.

Yaw creates a side force on the fuselage and fins which accelerates the aircraft sideways. This does change the resulting flight path, but the amount of side force is small due to the low aspect ratio of the fuselage. The lift-to-drag ratio of the fuselage is poor, so another change to the aircraft's vector is a deceleration if the increased drag is not compensated by more thrust.

Banking also creates a side force (when seen in the geocentric reference system), but now the wing is responsible for that force. Its lift-to-drag ratio is much better than that of the fuselage, therefore, the amount of side force is much higher and less drag is created. By first banking and then pulling more than 1g, the pilot changes the flight path much more effectively while maintaining altitude.

So the answer is yes, yaw behaves the same way as pitch. Only the wing and elevator are replaced by the fuselage and fins, with all changes to the magnitude of the forces this causes. The only difference is that pitch is needed to adjust lift, and changing the pitch attitude will change the speed of the aircraft or the load factor. Flying in a sideslip with no adjustment for the side force by a corresponding bank angle will continuously accelerate the aircraft sideways and will result in a uncoordinated turn. Now the sideways load factor (which is zero in coordinated flight) will be nonzero while in the longitudinal motion the normal size of the load factor is one (and be different from one when pitch is changed).

EDIT:

@TomMcW has contributed a practical example in the comments. Consider a crosswind landing with a glider or motor glider where crabbing is your only option to fly a straight approach over ground. Right before touchdown you should then step on the rudder to align the aircraft with the runway so the tires can touch down without moving sideways. Now consider that you stepped on the rudder too early and the aircraft floats along the runway with a sideslip angle. You will drift leewards, right? That is exactly the change in flight path I am talking about.

In crabbed flight the aircraft flies without sideslip. The fuselage with its forward center of pressure position destabilises the aircraft in yaw and the vertical tail adds the required stability. Both create no side force in crabbed flight. Now you want to align the fuselage with the runway and step on the rudder: The tail swings the aircraft around into a sideslip until the fuselage points into the desired direction. Now opposite rudder must be applied briefly to stop the yawing motion and then returned to a position between neutral and the initial deflection in order to trim the new sideslip. Note that this works exactly in the same way as the elevator when a new angle of attack is trimmed!

In the sideslip condition both the fuselage and the vertical tail will create a side force in the same direction. The side force of the fuselage is higher because its center of pressure is closer to the center of gravity than that of the tail, and in order to reach an equilibrium, both must point to the same side. This combined side force accelerates the aircraft sideways such that a speed component is added which reduces the sideslip condition. Since the aircraft is trimmed for a specific sideslip, the changing balance of moments with a change in sideslip will yaw the aircraft further so that the trimmed sideslip angle is restored.

Why is that? Remember that the rudder is deflected. This creates a camber in the vertical tail which moves its zero-sideforce angle of sideslip away from the sideslip angle of zero to a negative angle (for example, right rudder deflection will shift the zero-sideforce sideslip angle on the tail to a left sideslip value). Any change in sideslip will, therefore, bring a relatively larger change in side force at the tail which changes the balance of yawing moments such that the old sideslip is restored. Note again how similar this is to static longitudinal stability.

This means that the aircraft must maintain a slow yawing motion in order to keep the sideslip constant. The side force causes a reduction in sideslip and the yawing motion is a result of the sideslip-maintaining tendency of the vertical tail.

And, no, yaw is not a moment. Please let's all use an agreed version of English.


What is this aircraft from ca. 1925 (crash included)? I recently found the following family pictures from ca. 1925 and have been trying to identify the aircraft in them:

A second picture of the same aircraft was taken shortly after the first one:

Both of the occupants supposedly walked away unharmed - my guess is that confident look in the first image didn't linger.

Judging by the inscription on the top of the second image they were taken in Lausanne, Switzerland.

Bonus Question: Does the registration number of 85 mean anything in particular? For example, is this the 85th aircraft registered in Switzerland? Or the 85th aircraft of this type made by the manufacturer?

Looking at the holes in the engine cowling, landing gear, struts and wires configuration and general geometry, it may very likely be a 1918 Halberstadt C.V

(source)

(source)

Horizontal stabilizer and elevator shape, handles on the upper wing, "square grid" on the upper wing, also tells it is a Halberstadt CV

This document explains how swiss military aircrafts/airships are numbered.

Aircrafts numbered 64 and 703 were supposed to be DFW C.V But the one in the pictures you provided is definitely a closer match to Halberstadt C.V, anyway there were also DFW C.V built by Halberstadt company. Most surprising is the fact that number 85 is missing.


Will 1090 Mhz band become too congested in the future? 1090 Mhz is currently used for SSR Mode A/C replies and Mode S communication(ELS-EHS replies and ADS-B broadcasts) by civilian aircraft and some of military IFF modes.

With the infamous 2020 ADS-B Mandate about ADS-B usage in certain airspaces(Mandate) , it is expected that this frequency will be very crowded in future.

There are certain methods/precautions to prevent congestion like randomized broadcast timing(between 0.4 s and 0.6 s for Airborne Position for example). F.R.U.I.T. and garble problems are also not new to this frequency.

Are there any discussions in the aviation circles about precautions in anticipation to congested 1090 Mhz band for certain airspaces?

There are some areas where the 1090 MHz frequency is already very busy. The area around Frankfurt am Main in Germany and the Los Angeles Basin airspace is the USA are the most congested in the world.

The direct of impact of ADS-B is an increase in the frequency use of 1090 MHz. At the same time it allows a reduction of number of Mode-S radars, it enables the development of a more effective TCAS with reduced interrogation rates (known as ACAS X), and it reduces the number of interrogations needed by WAM systems. On the long term the impact of ADS-B will likely be positive.
But with the increase in number of flights the 1090 MHz congestion will remain a concern.

There are many discussions in the ATC surveillance circles about the topic and the 1090 MHz frequency (and 1030 MHz as well) is are frequently monitored. There are ground based monitors and periodically there are measurement flights to identify areas of high frequency load. Adding new radars to already congested areas is made very difficult by spectrum protection regulations, instead cross-border surveillance data sharing is encouraged. Some countries monitor 1090 MHz transmissions around the clock and the are plans to have a permanent monitoring service of 1030 MHz and 1090 MHz across Europe that will analyse spectrum usages trends and identify rogue transmission.


Are there passenger flights with stops in the middle? Train and bus lines usually have a number of stops along the way where some passengers can get on and off, while the rest stay onboard and continue to their destinatiom. For sufficiently long routes, drivers may be swapped out in the middle of the line, and the bus can be refueled, while passengers stay inside and continue their journey after the stop. But on all the (non-direct) flights I have taken, everyone must get off on the first stop, and get onto a different plane with a different crew to get to their final destination. Why? Are there any commercial flights with at least one stop in the middle, where some but not all passengers get on and off, while everyone else stays on the plane? If yes, why are they so unusual? If no, why do they not exist?

These "direct" flights are actually not unusual, at least in the US. I was surprised by this discovery based on the routes I personally tend to fly, but fortunately we have the Bureau of Transportation Statistics to provide objective information. Using the July 2019 data for all major carriers, I identified direct flights by counting multiples of the same flight number on the same day with the same aircraft, as opposed to single-segment "nonstop" flights. Here's what I found:

Some interesting notes:

Over a third of all flights are direct.
The practice is not limited to low-cost carriers. In fact, the two largest traditional carriers (American and Delta) operate around half of their flights direct and together operate almost two-thirds of all direct flights.
Nevertheless, Southwest uses more direct flights for its size than any other airline, nearly rounding out the other third.
On the other hand, JetBlue, which is commonly considered a low-cost carrier, barely operates any direct flights. Other low-cost carriers use anything from zero (Allegiant) to about a quarter (Spirit, Frontier) direct flights.
The other traditional carriers use direct flights sparingly. Hawaiian flies only nonstop routes, which makes sense.

I may have missed a few direct segments that departed past 12am on the day after the previous segment, but I don't think there's enough of those to substantially alter the results. In any case it would just increase the number of direct legs.
It'd be interesting to run some more analyses to see historical/annual trends in the practice, but that would require someone with more patience and/or computing power than I have. These data sets are huge and can only be downloaded month by month. I chose July 2019 because that was about the peak of commercial passenger aviation.
There's also some fun aviation memorabilia associated with these "direct" flights:
(source)
On airlines with no assigned seats, plastic cards like this used to be provided so that even the passengers continuing on could deplane if time permitted. Somewhere I have a couple old ones from Alaska Airlines. Nowadays I believe the airsickness bag doubles for this purpose in some cases. I suppose if you really didn't want someone to take your seat, you could leave a full one behind.
Note: A previous version of this answer had a much lower count of direct flights. Turns out Excel just wasn't done calculating yet.


why some airplanes have their exhaust gases vectored above the wing? I was looking at images of the SkyCourier shown below

and i have noticed the asymmetrical exhaust pipes in both engines (one pointing up and one is straight), doing my research on the internet, i found that it is used to take advantage of the Coanda effect and the flaps so that the gas moves from the top side of the wing and then gets deflected downward for a high lift effect in takeoff...

Yet i believe you can get the same effect if the gases were vectored under the wing and made hit the flaps, so why would they vector the gases above the wing, and why the second exhaust is not deflected upward ?

Assuming that both props are rotating clockwise as seen from the rear, the orientation of the exhaust pipes makes sense if the goal is to ensure that the exhaust gasses are kept clear of the wing.
The rotating propwash will tend to carry the exhaust from the right-side pipe (in rear view) of each engine well below the wing.  If the left-side exhaust pipes were similarly positioned, their exhaust would be carried up by the propwash to impinge directly on the wing.  The position we see in the photo helps ensure that the propwash carries the exhaust from the left-side exhaust pipe of each engine well above the wing.
A comment from another ASE member (John K) has stated that exhaust impinging directly on the wing can lead to galvanic corrosion due to carbon deposits.


Companies that currently manufacture aircraft with center stick controls? I was wondering if any general aviation manufacturers currently produce center stick control aircraft.  (Not including LSA, Sailplanes, Helicopters). I'm asking about four+ place aircraft other than the diamond da40.

Some of the lancair airplanes have it but those are kit built so Im not sure if you can count them as true production planes.

Vans aircraft
Most Variants of the Piper Cub like planes that are still made
Extra Aircraft
Pipistril Aircraft
Czech Sport (formally Piper Sport)

Its worth noting that Cessna did recently have a run trying to make the "Sky Catcher" which was quickly discontinued but center stick none the less.

A lot of light sport airplane and aerobatic planes tend to have center sticks.


Is navigation around thunderheads done at the pilot's discretion? It's my understanding that if a pilot is flying over an ocean or otherwise uncontrolled airspace and they encounter a cumulonimbus, they navigate around it at their discretion.

How does this happen in controlled airspace though? What instructions do ATC and a PIC typically exchange if a PIC wants to request navigation around a thunderhead?

If you are in controlled airspace its very possible ATC will direct you around weather, you can find out more about that in this question.

However what ATC can see on their scope varies from place to place and weather moves quickly. As such pilots can, and often do request deviation for weather. Lets say you are flying along dodging some clouds here and there, popping in and out, and all of a sudden you pop out with a cell forming in front of you. You may request something like:

  N123AB requesting left turn 20 degrees for weather

  N123AB left 20 approved for weather avoidance

It may also not be a bad idea to file a PIREP to help others out.

Ultimately as pilot in command you can deviate from any rule to ensure a safe flight. If you were about to fly straight through a storm and ATC was not allowing a deviation or not issuing one a case could be made for deviating any way. You can read more about that here.


What is a jet (unit) shown in Windows 10 calculator? From Windows 10's calculator:

What is a "jet" (physical unit)?

And why does it equal 480 knots or 888,88 km/h, if a jetliner's cruising speed is around 950 km/s? Or why does it equal 0.73 M, if a regular jetliner's cruising speed is 0.85 M?

It is not a unit. It is just Microsoft trying to be funny. Or to convey an idea of the magnitude.

Thanks @Jackie for pointing out that around March 2019, Microsoft has released this calculator as open source under MIT license. It is available in this Github repository. The source code sheds light on the definition of these pseudo units:

Description in ./src/Calculator/Resources/en-GB/Resources.resw:

<data name="UnitName_JumboJet" xml:space="preserve">
   <value>jumbo jets</value>
   <comment>A jumbo jet (eg. Boeing 747), used as a
            comparison measurement unit for length.
            (...)
    </comment>
 </data>
...
<data name="UnitName_Jet" xml:space="preserve">
   <value>jets</value>
   <comment>A jet plane, used as a
            comparison measurement unit for speed.
            (...)
    </comment>
 </data>

Conversion coefficients in ./src/CalcViewModel/DataLoaders/UnitConverterDataLoader.cpp

/*categoryId, UnitId, factor*/
static const vector<UnitData> unitDataList = {
        ...
        { ViewMode::Speed, UnitConverterUnits::Speed_Turtle, 8.94 },
        { ViewMode::Speed, UnitConverterUnits::Speed_Horse, 2011.5 },
        { ViewMode::Speed, UnitConverterUnits::Speed_Jet, 24585 },
        ...
        { ViewMode::Length, UnitConverterUnits::Length_Paperclip, 0.035052 },
        { ViewMode::Length, UnitConverterUnits::Length_Hand, 0.18669 },
        { ViewMode::Length, UnitConverterUnits::Length_JumboJet, 76 },
        ...
};

Apparently these definitions assume length in meter, and speed in cm/s. Thus, in Redmond the typical cruising speed of a typical jet is 478 knots. We also learn that Clippy is 3.5 cm tall.

888.88 km/h are very, very lucky speed digits for Chinese people. Any aircraft manufacturer or airline would benefit from promoting this cruising speed...


What is the purpose of the extremely high cabin altitudes in military aircraft? The Lockheed SR-71 and the (old) Lockheed U-2 were engineered to maintain cabin altitudes in excess of 25000 feet AMSL at an altitude of more than 70000 feet AMSL.

However, in both airplanes, pilots are required to wear space suits which maintain the safe pressurisation and oxygen content anyway. If the space suit develops a pressurisation leak, I think it's unlikely that the very high cabin altitude in these airplanes would buy the pilots any more time to descent to a safe altitude safely as the time of useful consciousness at 25000 feet AMSL is the order of a few minutes. Furthermore, it seems strange that aerospace engineers would install a pressurisation system on the Lockheed U2, an airplane already struggling to be as light as possible.

So why is this pressurisation maintained at such a high altitude in the airplanes?

Even the unmanned RQ-4 Global Hawk has a pressurized compartment. The low air density at altitude would not be sufficient to cool the electronics, so a pressurized electronics compartment had to be added.

I am not sure, but I expect the same reason required pressurization in the U-2 and the SR-71. The electronics were, besides the pilots, also an occupant of their pressurized cockpits.

At the pressure of 25.000 ft a human will not stay conscious, but will be able to survive. When the pressure drops below that of 30.000 ft, the breathing reflex will stop. If the pilot initiates a descent when his pressure suit starts to leak, he has a good chance of waking up at lower altitude before the aircraft hits the ground if the cabin can prevent the air pressure from falling to that of ambient air.


Does the SyberJet SJ30 really exist? It is amazing to think about a single-pilot jet with that much range. They have a site, they have some 2 minute videos talking about the aircraft... but there is no video of the thing flying or any review of its interior, no one talking about their experience of owning one...

Does SyberJet SJ30 really exist or is just a project that never made it off the drawing board?

It certainly seems to exist, at least in the sense that at least one has been built and registered. The Wikipedia article "SyberJet SJ30" contains a picture of one.

The registration number on the aircraft pictured is N7SJ, and the FAA's website says that that aircraft is indeed an SJ30.


How might one fly from KRYN to SDRS in a de Hallivand DHC-6 Twin Otter? First of all, this is not a flight I'm attempting myself; it's for a writing project. I myself have absolutely no knowledge at all of flight. The plane would depart from Ryan Airfield, Arizona (ICAO: KRYN) and land at Resende Airfield (SDRS). As the de Havilland DHC-6 has a range of only 886.7 miles, I assume a great deal of refueling is required. I have no knowledge of flight, so the logistics of a flight this length, (about 5,900 miles), in a light aircraft, are completely alien to me. Importantly, the passengers on the flight (4) do not have passports, but must still be able to enter the country. I’m guessing this means they’d land at a small airport/airfield. Assume the pilot has connections that allow his passengers to bypass any security at the small/private airport. The most important information would be: how long it would take, where/when they’d need to stop on the way, and where could the final destination be.

Your help is greatly, greatly appreciated! :)

Also, assume the situation is urgent and the pilot is a risk taker. He wants to get his passengers there quickly as possible.

I would recommend that you go to https://skyvector.com/ and create a flight plan.  It isn't too difficult, just click on "Flight Plan" in the top left corner and you should be able to figure out the rest.

You obviously have some familiarity with ICAO airport identifiers, simply look for airports along the way that will keep you under a 886.7 NM leg length, and enter them one by one to build your route.  I would use a cruising speed of around 150KIAS based on a quick Google search of Twin Otter performance.  The website will calculate the times for each leg based on this airspeed.

As far as researching suitable airfields that can provide fuel and other services, that will take quite a bit of additional work.  I don't have a handy reference for you, but you could start by searching for World or Latin American Airport Directories.  I wouldn't expect anyone here to do all that work for you and post it as an answer.  If you have any detailed questions as you go don't be afraid to ask.

Regarding your questions about avoiding immigration authorities, that's up to your fertile imagination to come up with fictional scenarios.  There is no aviation specific way to answer this, and most people would be hesitant to recommend methods to circumvent the law.


What is the physical experience of passengers in the cabin during an Emergency Descent? I am not a pilot so please forgive any misuse of aviation terminology; I'm merely a person who is working hard to overcome a sudden and intense fear of flying.

While working through a course to overcome this issue, the topic of emergency descents came up. I learned the purpose of these and the actions the captain / copilot must take, but the experience of the passengers was not discussed.

If a commercial jet is at 40,000 feet and experiences rapid depressurization, and the captain decides to make an emergency descent to 10,000 feet, what does this feel like for the passengers? Is it like being on a rollercoaster with a 30,000-foot drop instead of the typical 100-foot? In other words, do passengers experience freefall / weightlessness?

Do unbuckled passengers go flying all over the cabin? Is all unfastened material thrown across the cabin? What happens to crew who cannot make it to a seat fast enough? How common are these rapid descents in commercial flying?

I imagine this is probably the most terrifying experience a person can have, if it's anything like plummeting like a meteor.

No nothing like that.  If there was what is usually called "explosive" decompression, like a window blowing out, there will be a loud BANG, maybe a short howling sound as air rushes out, possibly fog will form in the cabin, and you will feel the air pressure in your head trying to get out until it equalizes.  It might make your ear drums hurt until it does.
The air will be chilled by the temperature drop caused by the pressure drop.

The big surprise is you can't feel the "thin" air when you breathe (you'd have to be exerting yourself - just sitting still, you can't tell).  The masks drop and at that altitude you have maybe 15 seconds to get one on before you pass out.

At any rate, explosive decompressions are pretty rare and emer descents are usually triggered by more gradual situations, like a slow loss of cabin pressure, or a windshield that suddenly cracks (although with several laminations and it normally won't fail totally - still, it'll scare the flight deck crew pretty good).

As far as the plane goes, you'll notice the thrust going to idle, the airplane decelerating temporarily, and you may feel the sensation of the nose pitching down to maintain speed, maybe a slight cresting-a-hill-in-a-car reduction in G sensation momentarily, but that's about it.  Nobody floating around the cabin.

When the capt gives the command for emergency descent, whatever the reason, (after they get their masks on and establish communication with each other) the procedure is to pull the thrust to idle right away, spin the altitude select knob for the autopilot to a lower altitude, and set the autopilot to "speed" mode, which tells the autopilot to pitch the nose to maintain airspeed (if the pilot were to shove the nose over manually, it could result in going zero or negative G and making people float around, but the procedure is usually done using the autopilot, which does the pitch over gradually, so that shouldn't happen).

The autopilot will start to pitch the nose over to keep the speed up since the thrust was taken away, so there will be the initial deceleration from pulling power, then a very gradual acceleration in the descent. If the plane has "flight spoilers", the kind that can be extended in flight, they will also be set fully out, so there'll be the rumble from that, and possibly the capt may drop the landing gear to increase the descent rate, depending on the speed and the airplane.

As it starts to pitch over the pilot will dial the speed to maxmimum operating speed if he/she is confident there is no major structural damage.  If unsure, you are supposed to stay at the speed you were at when whatever happened happened.  The most unpleasant part will probably be the noise level in the cabin if there was a rupture of some kind.  Even if there is nothing blown out, when descending at maximum speed the overall noise level is pretty high, a lot louder than cruise.

They'll be heading for 10000 ft and it'll only take a couple of minutes, so it'll be over pretty fast.

Thing to keep in mind about those plastic cabin windows (the structural outer panel, not the one next to you with the tiny vent holes at the bottom). If it's 8" x 10", there is over 600 lbs pushing on it with the cabin pumped up to 8 psi.  Sounds dicey.   But the acrylic plastic is very thick and the window actually has roughly the same strength as the (much thinner) adjacent sheet metal, so it's actually subjected to a fraction of the stress it's able to take.


Is it possible to take a liquid/gas inside aircraft cabin to contaminate the air? As per the security rules, i think upto 100ml of liquid ( medicines, perfumes etc) can be taken on-board by a passenger but is it possible that, that 100ml can be converted to fumes/gas and contaminate the air inside the aircraft?

Any such incident has ever been reported?

To answer your first question: it depends what you mean by "contaminate". The air in an aircraft cabin is constantly being renewed every two or three minutes (source (Airbus) - Boeing aircraft are similar), and the airflow pattern is such that the air only flows "across" the cabin, not along it. In other words, any contaminant you introduce will only reach the passengers seated in the same row as you (and perhaps the rows directly behind and in front of you), and will only stay there for a few minutes before the air exchange carries it overboard.

About 50% of the air which leaves the cabin is recycled back into the cabin, but it passes through filters first, which will stop any particles but will let gases through. Statistically, the concentration of whatever was introduced will drop to nearly zero after two passes through the ventilation system (due to dilution with fresh outside air).

My understanding is that the "100ml" rule is more designed to stop passengers from building liquid explosives aboard an aircraft (source (TSA)) than to stop them introducing harmful contaminants into the air.

I don't know of any incidents where an airborne substance was used maliciously in an airplane cabin, but you would get a similar effect through an on-board fire. The aircraft's ventilation system is designed to clear the cabin and flight deck of smoke within a short period of time (often by disabling the air recirculation system and increasing the fresh air flow into the aircraft).


How is tire rubber removed from the runway? Every time an aircraft touches down, the tires are spun up rapidly. As a result, some rubber is left at the touchdown zone.

(image source)

As time goes on, more rubber is accumulated at the touchdown zone. How is this rubber removed from the runway surface?

(wikimedia.org) High pressure water removal.

  Runway rubber removal [requires] high pressure water, abrasives, chemicals and/or other mechanical means.

ICAO Annex 14 notes:

  The surface of a paved runway shall be maintained in a condition so as to provide good friction characteristics and low rolling resistance. Snow, slush, ice, standing water, mud, dust, sand, oil, rubber deposits and other contaminants shall be removed as rapidly and completely as possible to minimize accumulation.

And ICAO Doc 9137 Part 2 Chapter 8 talks about the different methods. Of the methods not mentioned on Wikipedia is hot air blasting. The document notes that high pressure water is only suitable for light deposits. For the chemical they note:

  Chemicals having a base of cresylic acid (a derivative of creosote) and a blend of benzene, with a synthetic detergent for a wetting agent, are used for removal of rubber on concrete runways. For removal of rubber on asphalt runways, alkaline chemicals are applied.

High pressure water and hot air are considered mechanical methods.

(airport-technology.com) Friction tester.

A friction tester is used to determine if a runway needs rubber removal, note the 5th wheel above. A fixed load is applied to that wheel, and any slipping is noted by sensors as the car drives up and down the runway.

Related: Do landing strips suffer from landing wheel tire tracks?


Can state or local laws regulate where aircraft can take off and land? Say you have as private strip, but your neighbors get tired of hearing your plane. Can the local authorities pass, and enforce a law saying you can't take off and land there? Or do FAA rules override local authority as to where you can and can't land?

As any licensed pilot knows, the FAA and the US military are the "de-facto" regulators of 99.9% of what goes on in the air over the US (see: https://aviation.uslegal.com/government-regulation-and-control/state-aviation-regulations/ ).  Still, state and local governments are not entirely powerless here.  The general theory being more or less that, in cases where there is no obvious conflict with the FAA, or the US military, then local jurisdictions may still have some small level of control over certain very limited "air-spaces" (see: http://caselaw.findlaw.com/us-6th-circuit/1140229.html ).  Suggestion: 99.9% of the time, the FAA wins, but hey, don't let that slow you down!  (Still, in view of the findings of the second case I just listed above, if I were you, I might try keeping peace with my neighbors over trying to save just a few steps on the way home.)


Why does NASA have F/A-18s? I always remember playing FSX as a kid and using the NASA F/A-18, and never thought much about it.  And then I saw the picture of the Space Shuttle on top of the 747 being escorted by these planes.

Why does NASA have these fighter jets?
What are they usually used for?  Military?  Science?  Advertising NASA?

NASA uses them for pilot training and as chase planes for research aircraft.

  The two-seat F/A-18 support aircraft are normally used for photo or video chase. They are configured to transmit live video pictures from the air back to Dryden so engineers can visually monitor the mission as it is being flown. This feature greatly enhances flight safety.

There's an article from Armstrong Research Center with some more information, but that pretty much sums it up.

NASA also currently operates (and has operated) many other military aircraft types, either as chase planes or as subjects of research projects. Some examples off the top of my head include F-15s, F-16s, and of course their ubiquitous B-52s.

You say "obviously they are battle ready", but they are not – NASA aircraft are unarmed, and the ones in the photo certainly are carrying no missiles. They may have been fighters in a previous life, but the weaponry has been stripped. "Escort" doesn't mean "fighter escort" in this case!


What is the climb-out angle of a twinjet upon one engine failure scenario? Take a typical 737-800 or A320 at MTOW how much difference in take off angle does a 1 engine out failure scenario make, compared with a normal 6-8 degree take off angle with full engines.

The 737 and A320 are certified under Part 25, and they meet the certification requirement in 14 CFR § 25.121. With the gear retracted and one engine out:

... The steady gradient of climb may not be less than 2.4 percent for two-engine airplanes ...

Aircraft Flight Manuals (AFMs) don't typically include the all-engines gradients of climb as noted in AC 120-91A:

... It is recognized that many AFMs generally contain only the OEI performance for loss of an engine at V$_1$ on takeoff ... [emphasis added]

The OEI (One-Engine Inoperative) scenario is what matters more for obstacle clearance.
MTOW alone isn't useful
The performance tables are typically set up for ease of use. Instead of gradients, they list the maximum weights that would guarantee the regulatory gradient for the different pressure altitudes and temperatures, which are known as climb limit weights.
Consider a 737-800 at MTOW at a hot-and-high airport, it is not given that it can attain the 2.4% with an engine out. The TOW needs to respect the climb limit.
And a 737-800 at MTOW at sea level and cold temperature may exceed the 2.4% with an engine out. In this case, that 737 is not climb limited.

As an example, here's the climb limit graph for a 737-800 with flaps 5, note how when it's hotter and/or higher, the climb limit weight is reduced.

Source: 737-800 FPPM; click to view


Why is there still an Air Berlin branded plane operating as of Sep 5th, 2018? Yesterday, I flew from TXL and was quite surprised to see this during taxi:

It very much looks like people boarding an Air Berlin flight, an airline that supposedly does not exist any more. Local time was 12:20pm.
What happened here? Did some subsidiary survive the bankruptcy? Did someone buy the brand rights? Did they just not find the time to rebrand all the sold planes (in almost a year)?

Edit:

Since requested in comments: I do have another shot further to the right. Zooming in seems to reveal that the registration number is D-ABKM (or D-ABKW?)

Paintshops have been very busy in the past year.
So getting a slot to repaint an airplane is not that easy.
In addition, apart from the fact that the livery is not the one of the owner, the plane is perfectly fine.
And while applying a new paint scheme the airplane is not earning money.

What airlines do is, repainting the planes when a longer technical check is due anyways.


What are the EU-equivalent terms of the FAA ATC tower, TRACON, and center in radio calls? Does ATC in the EU have equivalents to the US FAA tower, TRACON, and center facilities? What are they called?

Area control centre   CONTROL

Approach control    APPROACH

Approach control radar arrivals ARRIVAL

Approach control radar departures   DEPARTURE

Aerodrome control   TOWER

Surface movement control     GROUND

Radar (in general)  RADAR

Precision approach radar   PRECISION

Direction- finding station HOMER

Flight information service INFORMATION

Clearance delivery DELIVERY

Apron service APRON

Company dispatch DISPATCH

Aeronautical station RADIO

Aerodrome Flight Information Service AFIS

Heliport Information Service HIS


How do typical ground marshaling signals differ for helicopters? There are common hand signals used by ground crew for fixed wing aircraft like 'taxi forward', 'spin up engine #1', 'turn right', or 'stop', for example:

At most airports, general helicopter traffic doesn't need to be marshaled, but I'm sure that pilots must be required to at least know some standard signals, in case of some communication issue that would require the use of hand signals.

Do these signals differ for helicopters, and how so? Do helicopter pilots have a different set of signals they must know?

All of the signals used for marshaling fixed wing aircraft apply to rotary wing aircraft as well.

There are additional signals though related to hover maneuvers such as move left or right, hover left or right, forwards, etc.
and land (or rather cleared to land), take off into the hover, etc.

Marshaling large helicopters can be very difficult, especially in dust and snow conditions.

Source: ex. 7 Sqn Chinooks


Does the landing distance required for a wet runway needs to be within a certain range of the landing distance available? Conform the regulations the landing distance required (LDR) for propeller engine aircraft needs to be within 70% of the landing distance available (LDA). The LDR for a wet runway needs to be multiplied by 1,15 (115% LDR). I was wondering whether this 'wet LDR' also needs to be within the 70% of the LDA to meet the regulations, or does it only need to be within the total LDA?
And does the same count for contaminated runways?

Short Answer = Yes.

Long Answer = landing within 70% of the LDA rule is a HARD limitation. The runway's length does not change with the weather, so the 70% cannot be changed. But, of course, your A/C landing distance does change with weather. Thus, your 115% landing distance required must still be within the 70% LDA.

in practical application, not every landing you do will use 70% of the LDA, or even close to it (It's only a limitation, right?). In many cases, There's still lots of room for your 115% LDR to land safely within the 70% LDA.

Hope this helps!