How do aircraft go off-course even with all their guidance technology? Pilots today have more than enough technology both in the cockpit and in the infrastructure that supports them to know with great precision where they are at any given time. How/why do they still sometimes go off-course?

1) Technology is fallible.

2) Humans are fallible.

Now that aircraft have GPS receivers it is rare for them to be off course by a considerable margin. That said, technology can fail and there are cases where the GPS cannot, or should not, be used.

The crew can also make mistakes, either by incorrectly reading the navigation data or by incorrectly entering flight path details into the navigation system: An aircraft may actually be 'on course' based on what the crew told it to do, but they told it the wrong thing. Depending on how data is entered into the system it's easy to add the wrong waypoint (some have very similar names, there's been a few cases of that happening) or to enter reciprocal bearings or lat/lon points.
On top of that there's simple crew distraction - if they're manually flying then they may be focussing on something else and not notice that are off-course: As happened on the Sukhoi superjet demonstration flight a few years ago.


QF72: How could a disconnected autopilot change the pitch? So I was reading about flight QF72, where the A330 had incorrect sensor data. The aircraft automatically pitched the nose down twice in response to abnormally high incorrect angle of attack data, but it did so AFTER the autopilot was disengaged. (See https://www.atsb.gov.au/media/51218/AO2008070_interim.pdf page 16-17).

How is that possible? Isn't it the autopilot that does that? I am probably getting the wrong idea about what the autopilot does, right?

Also, what would be the idea behind why the pilots attempt to correct the situation by pulling back the sidestick be unsuccessful at first, but suddenly have the desired effect right after he stopped giving that input?

The A330 has a degree of automation that can't be turned off, as part of its 'fly by wire' system.

This is to say that the pilot's controls aren't directly connected to the control surfaces. They are electronic in nature, sending signals to a controller which then decides how much to move the control surfaces.

As part of that, an automatic feature is built in to prevent the aircraft from entering flight attitudes that could be dangerous. This safeguard detects unsafe flying conditions using input from the the Air Data Inertial Reference Unit (ADIRU).

In the QF 72 case, a fault in the #1 ADIRU led it to believe that the aircraft was in a 50 degree nose up attitude, so it automatically forced the nose down. Problem was... the aircraft was flying straight and level, so the result was a very sharp nose down attitude, with negative G's applied to to the cabin (and everyone in it). Anyone not strapped in was slammed into the ceiling, and then into the floor when QF72 recovered from the dive. (only to do it again)

In this case, it wasn't a faulty AOA sensor, but a faulty ADIRU, which appears to have hit an unforeseen combination of inputs... and an unfortunate combination of data and timing that led the Flight Control Primary Computer that actually runs the control surfaces to not figure out that ADIRU 1 was giving it faulty data.

A couple of months later, QF71 encountered the same problem. Fortunately, the pilot was familiar with the QF72 incident, and simply switched the FCPC from the faulty ADIRU 1 to the backup ADIRU 2 that wasn't experiencing a problem. The flight continued without incident.

So the issue wasn't really a faulty AOA sensor, it was faulty code in both the ADIRU and FCPC, which appear to have been triggered by a rare combination of ordinary circumstances.

Note that a frozen angle of attack sensor and consequent incorrect automation responses led to the crash of XL 888, on an acceptance flight when the A320 was due to be returned to Air New Zealand after a lease.


Why can't we use APU bleed air for wing anti ice on the A320? The question says it all. While reading I came across this that we can under no circumstances use APU bleed air for supplying wing anti ice? Any reason?

On multiple PPRUNE threads they incorrectly say:

  The APU bleed is much cooler than the engine bleed system, and would be ineffective for WAI.

But the reason is:

  The APU bleed temperature is unregulated and thus could damage the wing slats if used for anti-ice.

Highlight shows regulation of engine bleed temperature.


Why retract flaps at go-around? As I understand the procedure for go-around it includes retracting the flaps.

Why is this?

The decision to make a go-around must sometimes be made quickly, under stressful conditions, like in bad weather. Retracting flaps introduces one more thing to do under sometimes stressful conditions.

Speed is low during landing and by retracting flaps you give away safety margin for lift. (Speed may also slow further since the nose is raised during go-around.)

Retracting flaps may also affect pitch and thereby make control of the aircraft slightly more difficult in a situation which may already be stressful.

For the same reason that you don't takeoff with full flaps. Because the climb performance sucks.

Flaps do add lift, but also a lot of drag. A low flap setting often provides more lift than drag, assisting climbout, whereas full flap offers a whole lot of drag, which is desirable when you want to be slow for landing.

But a go-around necessitates gaining height quickly, which will not work with landing flap selected. The usual procedure, at least in light aircraft, is to wait until the vertical speed is neutral or positive before retracting flap. This minimises some of the risks you've raised about aircraft control.

It is often said that a go-around is a period of heavy workload, and managing the flaps and airspeed is not easy. That is why the go-around is a fundamental procedure taught right from the very beginning, and practiced and tested regularly.


Can you fly 2000 miles on an engine that costs less than $500k? If so, what type of engine? Ok so Im exploring ways to bring cargo and medical supplies to various rural cities in say Africa without relying on ground infrastructure. Just short and cheap runways spread around the continent. It seems any type of VTOL plane wouldn't have the range. Electric is also out. It also seems like piston planes don't have the range, while turbojets are millions of dollars. What about used turbojets? Whats stopping piston engines from flying longer?

Your best bet would be an airplane/drone that is built from carbon composite and graphlite rod (pull-truded carbon rod with incredible strength - widely used in sailplane spars) powered by a couple of aviation diesels like the Austro Engine E4.

The Specific Fuel Consumption of the E4 is .336 lbs/hp/hr.  Except for similar competing diesels, nothing in any traditional aircraft engine configuration comes close except the old tubro-compound mechanical-monstrosity radials like the R3350 that could get into the high 3s (normal gas piston engines are around .45 lb/hp/hr and turboprops well above that, around .5-.6 lbs/hp/hr).

The E4 is 168 Hp so two would give you 336 HP for take off, and the engine burns 5 US Gal per side at 60% cruise, or 30 lbs per side, so to go 2000 nm, if you can get the thing to cruise at 150kt, you need 130 US Gal capacity plus a VFR reserve, say 140 gal total, or 840 lbs of fuel.

So design an airframe that can haul, say, a thousand pounds of payload with those two engines and 840 lbs of kerosene, and is clean enough to go 150kt, and there you have it.


Do hospitals have radio communications with air ambulances? Do hospitals have a sort of ATC for incoming medical helicopters? What kind of procedures do helis follow when landing at a hospital to make sure they are cleared to land/takeoff, etc?

Kind of...
Hospital heliports are "uncontrolled airports" normally, and don't require a clearance from ATC (unless the hospital itself is within positive control airspace because it's near a regular airport). However, the helipads are private "prior permission required" airports, which means the hospital, as the owner of the pad, needs to give permission to land (same way that a helicopter couldn't just land in your back yard unless you gave permission).
The helicopter will be equipped with an FM 2-way comms radio (examples of frequencies here), that is used to talk with a given hospital's flight coordinator or EMS dispatch to coordinate arrivals and departures for logistics purposes, similar to the radio a police helicopter would use to coordinate with dispatch/911.
So if you were just buzzing around in your own helicopter and thought it would be cool to land at the hospital's helipad because you had the urge for a wonderful hospital cafeteria lunch, you'll get a tongue lashing from somebody. To do it legally, you'd have to have the
required FM radio and get permission.
There will be a normal aircraft comm radio frequency assigned for VFR advisories when coming and going, like here (where you have a VFR advisory frequency on 119.4 mHz).  The pilot will just broadcast intentions on that frequency when arriving and departing, for the benefit of any other helicopters in the area, similar to arriving and departing from any other uncontrolled airport.


What to do if expediting your ascent or descent is impossible/unsafe? As a pilot of a small single engine plane, what do we do if ATC instructs us to expedite our climb/descent and doing so would be impossible or unsafe (i.e. we're already at the maximum safe rate of climb/descent)?

You report unable, and ATC will come up with a different plan.

To provide some context: If I ask you to expedite a vertical manoeuvre, it is probably because you are on crossing tracks with another aircraft, and I want you to pass them either above or below. This could be to meet certain level restrictions, or simply because I want to provide you with continuous climb/descend as a service. At your current rate, you will probably pass them, bot not quite with the 1000 ft vertical separation I need. Because you are so close to fitting into my plan, asking you to expedite is the easiest - it requires the least effort from me, and I won't have to vector you around, giving you a longer than needed flight path.

If you respond with unable, I have other options to choose from, depending on the situation. Typically I would either instruct you to level off or turn. If you are descending through FL160 and I wanted you to go below someone at FL130, I would simply instruct you to level off at FL140, and then descend you further when you are clear, which would only take a few minutes. I could use the phrase "Stop descend FL140, expect further descend in 3 minutes", in which case you could adjust your vertical rate so that you reach FL140 about 3 minutes in the future, resulting in a smooth descend. Alternatively, a turn of 20-30 degrees is often enough to establish lateral separation, which then allows you to descend unrestricted. 3 or 4 minutes later, when you have passed the other traffic, you will be turned back on your track.

The key thing here is communication. As an air traffic controller, when I instruct you to do something, don't think that I don't have backup plans. We are taught to always evaluate situations thoroughly, and come up with 2-3 different solutions to every problem or situation we face. I will start by presenting the easiest solution to you, but if that doesn't work for you, please don't be afraid of informing me - I will then simply choose another solution, and adjust my plan accordingly. And remember, air traffic control is a service. We are here to make your life easier - not the other way around. You can help us doing so by communicating clearly and in due time.


How do ATCs choose between Tower, Approach, and Enroute facilities? Under the FAA system, regarding the allocation to different streams for ATCs, how is this decision made? Do trainees decide early on during training which stream they'd like to work for and participate in respective training? Or do they receive a general/abstract training and are then separated among different streams for further training?

I'd like to become an ATC in the US, but can't seem to find this information anywhere. I'm wondering if tower ATCs get to finish their entire careers in towers? Or do they have to obtain radar licenses at some point and transfer/relocate to radar facilities?

The initial assignment has been made when you're hired, and you'll be sent to either Enroute or Terminal training. The split there occurs as they're hiring to fill a class, or just sending out names to facilities to pick from, or some other factor that they keep changing. The terminal option I believe they'll say class x will get to choose between the following facilities in order of how well they did in class.  (How facilities get assigned is changed a lot, and I'm not positive how they're currently assigned).

If you go to a tower or a Tower/Tracon(up/down facility), then you'll go to the academy for the tower initial class. If you get assigned to a TRACON, you'll go to a tracon dedicated class. Enroute goes to an Enroute class. Each has their own lengths. If you're at an Tower/TRACON combined facility, you'll go through the Tower course in Oklahoma, and then go to your facility and get trained in the tower, once done there, you'll then be sent to Oklahoma again for the Radar course, and return to your facility for training in the TRACON.

A career in the US ATC system is generally what you make it. Enroute people generally stay at their centers, they don't move facilities as much, mainly as they're at the upper level facilities and at the top of the pay levels. People in the terminal environment move a lot more. In the past to move to the highest level towers, they often wanted to see a radar certification, or some other way to differentiate candidates. But things have changed recently, and I'm not sure how they're picking candidates fully now. Also you can changed tracks, from Terminal to Enroute or vice versa, but it's generally a less common move.


What factors made my flight land at runway 02 in El Prat? Aircraft normally land at Barcelona's El Prat airport using either of the 25 runways, along a flight path hugging the coast, with a flip to the 07 orientation generally associated with bad weather.

Earlier today, though, my flight landed on a cross runway, 02, which I never knew existed, with a flight path at a rather steeper angle to the coast; there is some light cloud cover but nothing to write home about. What factors drive the change to this mode of operation? I'm interested both in the general criteria and in the specific conditions tonight.

And, more generally, what are the standard resources (or types of resources) that one should use to find out this type of information?

Because 02 is the default runway for landing during nighttime (23 local time to 07 local time).

Night time configuration between 2300 and 0700 LT:
Preferential: North configuration intersecting runways
Arrivals: 02
Departures: 07R

(AIP Spain AD-2 LEBL - 8)
Airports usually have preferential runway configurations that will be used unless certain conditions (such as weather) require something else. These are usually created to avoid excessive noise to adjacent residential areas and to maximise traffic throughput.


Where do LAX commercial cargo planes land/take off? At the Los Angeles airport, do commercial freight planes such as a 777F, 737F etc. take off near the Lufthansa / FedEx / DHL cargo areas from the 25L /25R runways towards the ocean ?

Do they land in the same direction but farther down the runway?

Large airports like LAX see hundreds of planes departing or arriving every day. They manage traffic flow in the entire area (class Bravo airspace) to optimize their traffic. Cargo aircraft will be treated just like any other aircraft. Which runways are in use for departures and which ones for arrivals, depends on the current winds and preferred configurations of the airport. Due to the high traffic, the airport will not deviate from this configuration to accommodate a single cargo aircraft, which would then be closer to its cargo area. Cargo aircraft will then taxi to their respective cargo areas just like passenger aircraft taxi to their gate on the ground.


Are there any calculations involved for designing pulse jets? Are there any requirements for calculations to determine things like exhaust length, combustion chamber size, etc? Also, does the end of the combustion chamber need to be a semi-sphere, or can it be flat?

YES

There are calculations involved in the design of a pulse jet. (title question)

YES

There are requirements for calculations... (first body question)

NO

The end of the combustion chamber does not need to be a hemi-sphere. (second body question)


What prevents jet engine designs with larger bypass ratios? In commercial aviation, it seems jet engines grow and bypass ratio increase with newer engines. Here is some examples:

1963: bypass ratio: 0.96 (P&W JT8D)
1970: bypass ratio: 5.0 (P&W JT9D)
1984: bypass ratio: 5.3 (P&W PW4000)
1984: bypass ratio: 6.0 (P&W PW2000)
2004: bypass ratio: 8.5 (Rolls-Royce Trent900)
2007: bypass ratio: 10.8 (Rolls-Royce Trent1000)
2015: bypass ratio: 12.0 (P&W PW1124G)

The bypass ratio has been multiplied by nearly 2 in 30 years (1970 -> 2015).
I understand the need of really high bypass ratio to decrease fuel consumption while increasing thrust. To have big bypass ratio, the high pressure part of the engine must be small compare to the overall size of the engine.

What prevent jet engine designer to design smaller high pressure part or bigger jet engines to increase the bypass ratio?
Is there someone that has made prediction about the increasing bypass ratio in the next decades and written it in a serious article?

For ungeared two-spool designs, bypass ratios cannot be increased further. Since the fan is coupled to the low-speed turbine, increasing it would overload the turbine. Only if the engine is run at a higher core temperature can the power provided by the low-speed turbine be increased. This would require either better materials (which are not available) or lower times between overhauls (which are costly).

Note that the engines of the Rolls-Royce Trent family have the biggest bypass ratios. Rolls-Royce went with three-spool designs which allow for a finer adjustment of the speed of the different engine components.

When a reduction gearbox is placed between fan and turbine, even a two-spool design can support a larger fan, and this solution will be used in the next generation of P&W engines. Smaller engines like the ALF 502 which is used in the BAe 146 rsp. Avro RJ, used this already years ago to fit a fan to a single-spool engine. For bigger engines, transmitting the enormous power in a compact gearbox was too challenging until now. Just the heat generated by the gearbox of a 200 kN thrust class engine running at 98% efficiency would be almost 400 kW - this needs to be shed somehow!

Another problem remains, however. Bigger fans need bigger nacelles, and their drag increases with the square of the fan diameter increase. Increasing the bypass ratio of a high-bypass engine even further yields diminishing returns, which tend to be compensated by the increased nacelle drag once the bypass ratio grows beyond 12 to 15. To make bigger bypass ratios economical, active laminarisation on the nacelle will be needed.


How does flying below the freezing level in a thunderstorm help avoid the most critical icing? AC 00-6A (Aviation Weather) Chapter 11 states:

Do's and Don'ts of Thunderstorm Flying

To avoid the most critical icing, establish
a penetration altitude below the freezing
level or above the level of -15 C.

I'm trying to understand how flying above an altitude where -15 degrees Celsius occurs would help me avoid icing. I'm also trying to understand how flying below the freezing level would help me avoid icing. What is the explanation?

The icing occurs due to the presence of supercooled liquid droplets. From FAA AC on Icing:

  The condition most favorable for very hazardous icing is the presence of many large, supercooled water drops.... Thus, heaviest icing usually will be found at or slightly above the freezing level where temperature is never more than a few degrees below freezing.

For ice to form on the aircraft, the following conditions are required:

The presence of liquid water i.e. rain or cloud droplets.
The temperature at aircraft structure should be at or below freezing point.

Now, as the altitude increases, temperature decreases. Using this, the best way to avoid these conditions would be to either:

Fly above the altitude where the temperature is below -15 degrees, where supercooled water drops are not present (they would've frozen already), or
Fly below the altitude where the temperature is above freezing point, where the water droplets, if present are not supercooled.


Is there a difference between "aerobatic" and "acrobatic" flight? I hear and read both the terms "aerobatic" and "acrobatic" used to describe the more extreme maneuvers such as spins, rolls, loops and more. My questions is about the terms themselves. It seems that they are interchangeable, but is one actually more correct to use than the other? Why do we have these two very similar words in the aviation vernacular that seem to mean the same thing?

Acrobatic is being incorrectly used, although it is slightly more complicated than that.

"Aerobatic" refers specifically to flight, and "acrobatic" refers specifically to feats of the human body, so referring to an aircraft as performing acrobatics is wrong.

That said, the word "aerobatic" is derived from "aero-acrobatics" and sounds nearly identical, so it's an understandable and relatively common error.


Can I log any PIC time if my medical certificate is out of date and I haven't flown in 20 years? I haven't flown in 20 years. My medical certificate is not up to date. Can I log a fam flight with a local instructor?

To answer your question, specific to the US, you may log your fam flight with a CFI as dual received, and also as PIC for the time you are the sole manipulator of the controls (which will likely be the entire flight).

You don't need a medical to log PIC, but you will likely need one to act as PIC, depending upon what you are flying.

But for training, you clearly can log time as PIC when you are the sole manipulator of the controls, in a class and category for which you are rated.

Have fun!


What is the correct way to get established on the outbound track on this approach? If you have been cleared to LCA (from the direction shown by the red arrow) then outbound on the procedure, what is correct way to get established on the outbound track?
Ideally, I'm looking for an ICAO/PANS-OPS reference or similar (not US).
Many thanks!
---- Edited for clarity ----
So, to avoid a situation like this:

What is the correct action to take?
Is it to request the arrival pattern hold to better align yourself:

Or manoeuvring space to the south to better align yourself:

Or something else?

I do not have a specific ICAO reference. By my interpretation of the chart, you can approach the airport at any assigned altitude above 2300 feet MSL from your specified East direction. Just as long as your aircraft stays between the 71° radial clockwise to the 215° radial of the VOR. But, you would have to be above 4900 MSL to intercept any part of the instrument approach. Once you are established on the approach, you can drop down to the appropriate designated at-or-above altitude marked on the approach. If you are joining the approach at the LCA VOR, you would enter the hold, either climbing or descending until you reach an altitude where you can safely descend down to 1500 feet MSL during the teardrop course reversal. Remember, you have to remain at or above 4000 feet MSL until passing the VOR when leaving the hold. This will be your Minimum Holding Altitude as well as your Minimum Crossing Altitude at the LCA VOR.
If you have already been cleared for the procedure at LCA, you would just have to make your radio call once you reach the VOR for the hold, and again at the VOR when you leave the hold (if one is necessary to gain/lose altitude).


How to identify transmit labels for a particular equipment in ARINC429? As i can see, each equipment has a set of labels which the equipment may supposed to be received. Say if i am Equipment 03Ch (Tire pressure monitoring system), i will be configured to receive below labels
LABEL 060 -> Tire pressure (Left Outer)
LABEL 061 -> Tire pressure (Left Inner)
LABEL 062 -> Tire pressure (Right Inner)
LABEL 063 -> Tire pressure (Right Outer)
LABEL 064 -> Tire pressure (Nose)
But how may i know, what are the labels should i send ?

As Gerry mentioned in their comment, the equipment ID label (377) indicates to the receiver how to decode the labels being received on that ARINC 429 channel.
The transmitting equipment (Tire Pressure Monitoring System) would send label 377 with the value 03C at it's appropriate rate (usually every 1000 ms) and then labels 060 through 064 at their appropriate rate.
The receiving equipment gets the Equipment ID from label 377 it received and then knows to decode labels 060-064 according to the TPMS definitions.


Why was this Twin-Otter Take-Off unsuccessful? Watching this video I was asking myself, what was the error or cause of this unsuccessful take-off?

Comments under the video say clearly:

According to Transportation Safety Board (Canada) report # AO7W0128,

Take-off weight did not meet performance capabilities of the Aircraft.
Calculations to clear 50ft obstacle were not performed.
Southeast end of runway, not clearly marked.
Take-off was attempted in an up slope direction with a slight tailwind which increased the necessary distance to clear a 50ft obstacle.
Center of gravity (CG) calculations were off and found to be too far forward.


What is an obstacle identification surface and why would a pilot intentionally penetrate it during an ILS approach? What is an obstacle identification surface?

Why would a pilot intentionally penetrate it during an ILS approach?

Obstacle Identification Surfaces apply to departures and the portion of an non-precision IAP beyond the Visual Descent Point. If you are in the clouds, you should never penetrate the OIS on departure.
On arrival, the VDP assures obstacle clearance with a normal approach to landing. ILS only approaches do not have a VDP depicted so there is no OIS to penetrate. (The glide slope takes you right to the touchdown zone.) ILS/LOC (and Localizer only) approaches do have a VDP for the non-precision version of the approach. You could penetrate the OIC on a localizer approach and if that happens, visibility minimums are increased as explained in the last paragraph from the AIM below.
AC 150-5300-13-c12 Airport Design has a good visualization of the departure OIC.
(As an aside, it has lots of charts and graphs showing how departures and approaches are designed.)

AIM 5−2−8. Instrument Departure Procedures (DP) − Obstacle Departure Procedures (ODP) and Standard Instrument Departures (SID)

…if an obstacle penetrates what is called the 40:1 obstacle
identification surface, then the procedure designer chooses whether
to:

Establish a steeper than normal climb gradient; or

Establish a steeper than normal climb gradient with an alternative that increases takeoff minima to allow the pilot to visually remain
clear of the obstacle( s); or

Design and publish a specific departure route; or

A combination or all of the above.

The 40:1 obstacle identification surface (OIS) begins at the departure end of runway (DER) and slopes upward at 152 FPNM until
reaching the minimum IFR altitude or entering the en route structure.
This assessment area is limited to 25 NM from the airport in
nonmountainous areas and 46 NM in designated mountainous areas. Beyond
this distance, the pilot is responsible for obstacle clearance if not
operating on a published route, if below (having not reached) the MEA
or MOCA of a published route, or an ATC assigned altitude. See FIG
5−2−1. (Ref 14 CFR 91.177 for further information on en route
altitudes.)

5−4−5. Instrument Approach Procedure (IAP) Charts

h. The Visual Descent Point (VDP), identified by the symbol (V), is a
defined point on the final approach course of a nonprecision
straight−in approach procedure from which a stabilized visual descent
from the MDA to the runway touchdown point may be commenced. The pilot
should not descend below the MDA prior to reaching the VDP.
i. A visual segment obstruction evaluation is accomplished during
procedure design on all IAPs. Obstacles (both lighted and unlighted)
are allowed to penetrate the visual segment obstacle identification
surfaces. Identified obstacle penetrations may cause restrictions to
instrument approach operations which may include an increased approach
visibility requirement, not publishing a VDP, and/or prohibiting night
instrument operations to the runway. There is no implicit obstacle
protection from the MDA/DA to the touchdown point. Accordingly, it is
the responsibility of the pilot to visually acquire and avoid
obstacles below the MDA/DA during transition to landing.

Edit: This AIM is consistent with what the Instrument Procedures Handbook says about non-precision approaches but not consistent with what the handbook says about the potential for obstacles on ILS approaches.
p 7-9

...if an ILS is configured with approach lights or a nonprecision
approach is configured with either MALSR, SSALR,or ALSF-1 lighting
configurations and the procedure has a published visibility of 3/4 SM
or greater, a penetration of the final approach OIS may exist. Also,
pilots will be unable to determine whether there are penetrations of
the final approach OIS if a nonprecision procedure does not have
approach lights, or is configured with ODALS,MALS, or SSALS/SALS
lighting since the minimum published visibility will be 3/4SM or
greater.
As a rule of thumb, approaches with published
visibilities of 3/4SM or more should be regarded as having final
approach OIS penetrations and care must be taken to avoid any
obstacles in the visual segment. Approaches with published
visibilities of 1/2 SM or less are free of OIS penetrations...


Do the engines still spool up when reverse thrust is selected, but the reversers are not deployed? The recent question When a large commercial jet touches down, is it committed to stopping? referenced the crash of Red Wings Airlines Flight 9268, which overran the end of the runway at nearly full touchdown speed due to failure of the reversers to deploy. According to the Wiki article, due to a crosswind, the aircraft touched down on only one of its main gear. Even once the nose gear was on the ground, the right main gear strut had still not compressed. The pilots selected full reverse thrust when the nose gear touched down. Since the right gear strut had not been compressed, the reversers were not deployed, however, the engines still spooled up, resulting in forward thrust.

I understand the reasoning behind not deploying the reversers when one or both of the main gear struts isn't compressed. However, it seems to me that preventing deployment of the thrust reversers should also prevent spooling up the engines for exactly the reasons that the Red Wings flight crashed. Applying full forward thrust when the pilots have selected full reverse thrust seems like a very bad idea to me.

I'm wondering whether this behavior is typical of modern transport-category jets. That is, would, for example, a Boeing or Airbus aircraft prevent the reversers from deploying, but still spool up the engines (as the Tu-204 did in this accident) or would they also prevent engine spool up when reverse thrust is selected while thrust reverser deployment is locked out?

Am I missing a reason why still spooling up the engines would be desired when reverser deployment is locked out?

Although not exactly the same thing you're asking you might be able to surmise an answer about Airbus from what happened in the crash of TAM flight 3054.

It was an A320 landing in Sao Paulo with a known inop T/R on the right engine. The pilots retarded the left thrust lever to idle to engage spoilers and then into reverse to engage left T/R but left the right lever in CLIMB. The autothrust turned off and due to the lever positions the left engine went into reverse thrust while the right engine went into full forward thrust causing them to veer off and overrun the runway and crash.

According to Airbus this had been a problem before so they changed the procedure for single T/R. It was previously to bring both to idle then only the working one to reverse. This was apparently confusing the pilots causing accidents so they changed it. The correct procedure is now to bring BOTH levers to idle then at touchdown, BOTH to reverse. Obviously if this is the procedure the A320 will not normally spool up the engine that did not have reverse thrust. The only reason it did was because the pilot left the right lever in the climb detent.

I'm not sure if this is true if the T/R's were PREVENTED from deploying due to the wheels not touching down but I would figure it would.

The way the A320 thrust levers work is that you release a catch then pull the levers aftward past the idle detent. (Not a pilot so correct me if I'm wrong here) Other a/c have a separate set of levers, for reverse thrust, sometimes hinged to the main thrust levers.

According to this illustration I found at this site the DC10 did have such a system to prevent the thrust to be increased until the reversers were deployed.

According to a BEA investigation report the B747 has a similar system:

  The thrust reverser mechanism is commanded by one lever located on each thrust lever. In the ground position and when the thrust levers are at idle, it is possible to pull the thrust reverser levers back to the "interlock" position which corresponds to reverse. This unlocks the reversers and initiates their deployment. There is blocking in the interlock position when the reversers are in motion or incompletely extended. The use of full reverse thrust is possible when the "in transit" lights are off and the "unlock" lights are on (see appendix 2) to indicate that the reversers are deployed and locked. (BEA site)


Can the bleed air for deicing the wings of the aircraft be switched on and off for jumbos? Considering the large surface areas of the wings of the Boeing 747 and Airbus A380, can the bleed air for deicing the wings be switched on and off as needed and if so, is that automatic and where are the sensors to control this (on which parts and why).

Yes. Automatic operation exists as well (may not be installed/chosen by the operator).

Nitpicking: this bleed air is for anti-ice, not de-ice (but even manufactures get it wrong in the manuals sometimes, see below).

Saving this bleed air when not needed saves fuel and engine wear, and allows higher more efficient cruise altitudes.

Speaking of the A380, due to its thick wing, it does not need much anti-icing.

(Source: A380 FCOM)


Can you fly an airliner without an ATPL? The "captain in the right-hand seat" discussion got me thinking. As of 2013, you need an ATPL to operate any plane operating under Part 121 (as part of an "airline"). Both Captain and FO need this level of license, and new Captains require at least 1000 hours as FO.

However, all you'd need to fly the same model of plane for hire in any other situation is a CPL and the applicable type rating for the aircraft. Prior to 2013 that was all you needed to be hired as an FO on an airliner and get yoke time towards your ATPL and the left-hand seat.

The question is, are there still opportunities for a civilian CPL holder to fly large turbofan-powered airframes for a living on his way to an ATPL? My first thought was freight, but cargo planes for FedEx or UPS operate under Part 121, same as American Airlines. The only thing that really leaves is charter flights, which operate under Part 135 and thus may not require the same stricter regs as a pilot on a scheduled service. But, I don't know how many charter operations are using anything bigger than a narrow-body.

You don't have to be an ATP to fly an airliner. In fact, you can fly an airliner as a private pilot. John Travolta is the best example I can think of... He has a house right by a private airport and flies his own personal Boeing 707 (with Qantas livery) and another jet aircraft (Gulfstream I think). With any large aircraft like this over 12500 lbs or with turbojet engine(s), a pilot does need a type specific rating to fly such an aircraft as well as needing to be "current" in that type, but may do so as long as current at any certificate "level" of private pilot or above. However, to fly an airliner as a scheduled air carrier pilot, then yes, an ATP is required as this type of flight would not fall under part 91 or part 135 of the FARs, but instead part 121 which requires that all pilots have ATP certificates.


Can the FAA CPL 2-hour cross country flight requirement include stops? One of the requirements for an FAA commercial certificate is:

§61.129: (3) 20 hours of training on the areas of operation listed in §61.127(b)(1) of this part that includes at least—
...
(iii) One 2-hour cross country flight in a single engine airplane in daytime conditions that consists of a total straight-line distance of more than 100 nautical miles from the original point of departure;

Since it just says 100 nautical miles from the original point of departure, would a flight that was 268 NM and 2h 29m, but included a stop halfway count for this requirement?
Also, does the "20 hours of training" mean that the 2-hour/100 NM flight needs to be with an instructor?

Affirmative.  That flight will have to be part of the dual training time required for the airman certificate.

And, yes, you can do a stopover during the flight; the experience requirement does not prohibit it.


What is propeller / engine sync and how does it work? In some models of multi-engine airplanes there is a switch labelled something similar to "prop sync" or "engine sync".

My questions are:

What is engine synchronization?
How is it achieved?
Why is it important to use?
What happens if you don't use it?

I don't know how it is achieved, but here is the reason:

If you have two sources of the same noise, with nearly the same frequency, the sum of both noises will be a noise of slowly increasing and decreasing volume. It's called beat and can become very annoying.

The math says

$$\sin(2\pi f_1t)+\sin(2\pi f_2t)=2\cdot\sin\left(2\pi \frac{f_1+f_2}{2}t\right)\cdot\cos\left(2\pi \frac{f_1-f_2}{2}t\right)$$

To demonstrate this, there you see two sinus-tones of almost same frequency, and what happens if you mix them:

The blue curve is of frequency $(f_1-f_2)/2$.

As example, one machine running at 3000rpm and one at 3030rpm results in a noise which increases for one seconds before it decreases within one second again.

As said, I don't know how it is done, but synchronization must be done very precisely to avoid this beat.

Edit:

Here is what happens if the two noises do not have the same volume. One of the curves has three times the amplitude of the other. The envelope is not a pure sin function, but the blue function fits it quite well.


Why is the shape of the cargo compartment similar in large aircraft? Why are the lower deck areas shaped like that, does that save some space? I find it common across lot of big aircraft.

Pic of a 777:

The answer lies in the existence of something called a Unit Load Device (ULD) -- basically a cargo pod for aircraft that's the equivalent of the shipping pallet.
ULDs allow oddly-shaped cargo (bags, assorted-size boxes, etc.) to be loaded efficiently in a standard volume and easily secured for flight (using hold-down lugs in the floor).

The shape of the cargo deck is designed to pack in as many ULDs as possible:

and as you can see from the cross-section the sloping sides on the bottom are a concession to the circular cross-section of the fuselage/pressure vessel.

Some other advantages of ULDs as they pertain to airline operations and baggage loading are described over on this question.


Do I need Customs clearance to fly an N-registered aircraft from Italy to Switzerland? I need to fly from Italy to Switzerland in my aircraft with N markings.
I've been told I need a clearance from a customs office within an airport prior to crossing the border. Is this true?

It's true. You need to take off from a authorised Airport with customs in Italy and land at an airport with customs in Switzerland as your first stop.

Here is all information you need including a list of airports with customs.
https://www.ezv.admin.ch/ezv/en/home/information-private/waren-anmelden/einfuhr-in-die-schweiz/warenanmeldung/grenzueberschreitende-fluege.html


Limits on piston-engine power for a given airframe? I'm looking for an authorative textual source (and indeed any guidance would be useful) on the relationship bewteen a given airframe and the maximum power that it can realistically harness/cope with from a piston powerplant.

For example; if looking at something like a warbird, is there a theoretical way to work out the engine power beyond which the basic airframe design would be unable to cope with the excess torque/force/weight or is it more of an art than a science?

Thank you!

It really depends on how long you want to fly for. Big engines generally require a lot of fuel so dropping a huge power plant on a small airframe may burn through all the fuel you can practically carry fairly fast. But if we assume that you don't want to fly all that long then we run up against the next issue.

You can always try to bolt a merlin engine to a C-150 airframe if you are willing to get creative with your bracket fabrication and perhaps beef up the nose wheel. The issue you will run up against here is at least in part a CG issue. A 1600LB engine on the front of an 800 LB airframe is bound to get interesting. But lets say you move the wings around, and put some ballast in the aft areas to even it out a bit and get a workable CG. You now have nearly 1600 HP up front to have fun with. So what happens?

If you can get this beast to fly you will eventually hit aerodynamic issues depending on the airframe, like Mach Tuck and ultimately at some point you are just going to rip the airframe apart.

So you need to balance structural integrity, aerodynamic stability, CG, the ability to carry enough fuel to actually do something practical and the limits of actually building an aircraft mechanically. There are also practical limits on scaling piston engines in general.


How do flying wings respond to crosswinds? Is the vertical tail the primary reason for causing landings to be skewed in a crosswind? Please explain the effect of the fuselage, the tail, or other components.

If the vertical stabilizer is the primary reason for crosswind landings, do flying wings with no vertical tails (say, the B-2) experience this issue?

Short answer: The reason for crabbing (skewed flight, as you call it) during an approach in crosswind is to keep the wings level while maintaining sideslip-free flight. Flying wings are not fundamentally different, because they, too, have stability characteristics similar to those of conventional aircraft.

Airplanes want to be flown without sideslip. Flying in a sideslip (where a component of the airspeed comes from one side) incurs lots of complications:

Some of the lift is also pointing sideways, so the airplane drifts sideways.
Weathervane stability will make the aircraft yaw into the wind. This comes mainly from the vertical tail, but is only one of many components to make the aircraft controllable.
The dihedral effect will cause a rolling moment, lifting the windward wing.
Wing sweep will increase this rolling moment and add more yawing moment.
Since the vertical tail sits upward of the line of symmetry in most airplanes, this also adds to the rolling moment.

Most of these effects are desired, because they make the aircraft easier to fly, but during approach they make it harder to line it up with the runway. If the fuselage is held parallel to the runway, the windward wing needs to be lowered, so some of the lift points sideways into the wind, compensating the side force caused by sideslipping. This is achieved by keeping the ailerons deflected to work against the aforementioned effects, and the rudder needs to keep the airplane from turning into the wind. This is no problem as long as the airplane is high enough. On touchdown, however, such an attitude cannot be maintained, or the aircraft will hit the ground with a part of the wing or an engine nacelle first.

Only by pointing the fuselage into the wind can the course of the airplane be aligned with the runway in a sideslip-free way. This is called crabbing, because when seen from the ground the aircraft's speed has a lateral component, a little like a crab wich is also known for its sideways movement. Now the wings are level, so the touchdown will happen with the wheels first. Unfortunately, now the wheels' rotation direction is not aligned with the runway, and to reduce wear, pilots kick the rudder just before touching the ground to re-orient the aircraft parallel to the runway.

The Lockheed C-5 and the B-52 can rotate their gear struts, which enables both aircraft to touch down in crabbed flight. All other types produce more tire smoke and jerk the aircraft sideways if they touch down this way.


What is the aviation term for what the navy calls "fire control system"? The weapons systems, including computers etc, in a naval ship can be referred to as the Fire Control System. I'm not sure if FCS would be considered an appropriate acronym for fire control; I'm using to hearing FCS as Flight Control System.

Is there a specific aviation term equivalent to Fire Control System? If so, what acronym does it use (if any)?

It is still called the (Airborne) Fire Control System; found about it here from a Google search.

Well, the acronym for (Airborne) Fire Control System is FCS (As well as Flight Control System) according to a military acronym website


What does the indication "ATC" in some Take-Off Minimums mean? While studying FAA's Standard Instrument Departure Procedures, I came across the La Guardia Five Departure SID. Take, for example, the Take-Off Minimums for runway 13L:

  Rwy 13 (Coney Climb): 400-2 or Standard with minimum climb of 280' per NM to 500. ATC climb of 900' per NM to 1500.

How should I interpret this "ATC" indication? What difference does it have from the previous minimum climb gradient requirement ("climb of 280' per NM to 500") which omits this particular indication?

I believe I have found the answer to my own question, while examining the records of a meeting held by FAA concerning this subject ( source ). It clearly states:

  [ AERONAUTICAL CHARTING FORUM Instrument Procedures
  GroupMeeting 17- 02 –October 24, 2017 ]
  When ATC crossing altitude restrictions require a climb gradient on a SID, it is proposed to establish a single climb gradient that would allow compliance with all ATC restrictions. These climb gradients would be
  identified on the chart as ATC climb gradients. Rich explained how the aircrew should treat each climb gradient differently. An obstacle climb gradient should be treated as a plane that the aircraft cannot ever penetrate from above, that is, the aircraft must always remain above the climb gradient’s surface. Conversely, an ATC climb gradient only represents the average gradient needed to meet the crossing restriction at the fix where it’s established. In this case, the aircraft’s altitude between the point where the climb starts and the point where the altitude restriction is established is not that important, provided the crossing is made at the fix at (or above) the minimum charted altitude. The purpose of the ATC climb gradient is to inform the pilot of the necessary performance needed to comply with the altitude restriction. The working group suggested that a SID should be limited to one obstacle climb gradient, and if necessary, one ATC climb gradient. Further, an ATC climb gradient and the associated crossing restrictions should be eligible for cancellation by ATC when not needed or when aircraft performance is limited.


How can I decode Lycoming engine number? How can I decode Lycoming engine number suffices?
What does D3G mean in o-320-D3G or D2A in o-320-D2A?
Is there any chart or tabel for decode suffixes?

I got the following information for this website:

Also if you scroll down here you can see the model numbers that you talk about in your question.

The last character seems to be an indication of the variant of the engine as shown in the document.  The D indicates Dual Magnetos and the 2 or 3 seems to indicate some type of counterweight application.


How is fuel dumped in aircraft? I have heard incidents in which commercial aircraft are required to dump fuel in event of an emergency to avoid landing over maximum landing weight. What systems do aircraft have in place to dump fuel? How is a fuel dump initiated from the cockpit?

Commercial aircraft have fuel dump nozzles located under the wings for dumping fuel. Fuel is gravity jettisoned from the tanks located in the wings and the fuselage. Large commercial aircraft such as the 747 can dump upto 6000 lbs of fuel per minute with all fuel jettison pumps open.

Interestingly, the fuel dump nozzles are in different places on different aircraft:

On the 747, the nozzles seem to be located near the wingtips:

Whereas on the A380, the nozzles seem to be much closer to the fuselage:

It is triggered by activating the FUEL JETTISON switches in the cockpit on the overhead panel. Below is a picture of the same in an Airbus A380-800. Both the ARM and ACTIVE switches must be pressed to start a fuel dump.


Do large aircraft have carbon monoxide detectors? Do big aircraft (e.g. Boeing 737 or Airbus 320) have carbon monoxide (CO) detectors installed in them? I don't know if the pressurized cabin means they aren't needed, but I do remember there are CO detectors in small planes and there are some reported accidents due to inhaling CO from engines.

Haven't seen any. Cabin heating is done quite differently on jet aircraft than on pistons. Bleed air is taken from the engine before the combustion chamber, so engine exhaust can't end up in the cabin, even if there was a greater fault in the A/C packs.


What criteria make an airport suitable for a technical stop for a large airliner? Assume you have a large airliner such as a 747, and you're taking off from a place, such as Ovda, where you can't load enough fuel to make it to your destination without stopping somewhere along the way.  From all the airports along the route to your destination, what criteria are used to determine what a suitable "somewhere" to stop at for fuel is, assuming that runway size and fuel availability have already been filtered for?

Some factors might be:

Price of fuel at the various airports?
Landing fees?
Are any of the airports so busy that you might have to hold waiting for landing clearance? (You don't want to plan a fuel stop at LHR).
Can you expect long taxis in some places? (All other things being equal, a single runway with a ramp next to it is better news than something like Schiphol or O'Hare).
If you're carrying passengers, are some of the airports in countries with significantly more cumbersome immigration rules applying to technical stops than others? Some may want airport transit visas from passengers of certain nationalities even if they don't disembark.
Political considerations such as the ones mentioned by Terry in the comment.
And, of course, the total expected fuel burn for the two legs, which will depend on your refueling points. Your operations department will make concrete calculations for a number of likely stops, and weather has an influence on top of geography. If you have several possible airports that all happen to be right on the shortest path between your origin and destination, the math will tend to favor a refueling stop roughly in the middle -- this will minimize the total cost-of-lifting-enough-fuel-for-the-rest-of-the-leg.

Finally, if you're planning a recurring scheduled flight, will any of the options provide a business opportunity to take on some extra passengers on days where the demand from the actual origin is low?


Is this calculation for the 'free' climbing speed when flying in a headwind with a gradient correct? From energy considerations, it can be found that a plane flying straight and level, if it enters a headwind with a positive gradient, will climb, extracting energy from the wind gradient.

The extra energy involved will be

$E_{EXTRA}  = mg(h_f – h) = \frac{1}{2} m (vfg^2– vg^2) $

where $m$ is the mass of the plane, $h$ the initial altitude, $h_f$ the final altitude after the climb, $vfg$ the speed of the plane (when starting the climb) in relation to the mass of air present at the altitude where the climb will end, and $vg$ the TAS of the plane when starting the climb.

Now, the question is what the extra power of that airplane will be when climbing under those conditions. It’s clear that there is an extra power, since energy is being taken from the wind gradient at a given rate…

As that rate is related to the magnitude of the gradient, we may say that, for a given wind gradient $ß$, the extra power $P_{EXTRA}$ will be:

$P_{EXTRA} = E_{EXTRA} · ß$

$P_{EXTRA} = \frac{1}{2} m (vfg^2 – vg^2) ß$

Knowing the power, we can now find also the extra vertical speed w of the plane of mass m due only to the gradient:

$w = \frac{1}{2} m (vfg^2 – vg^2) ß/mg   =  (vfg^2 – vg^2) ß/2g$

In order to 'test' the formula, we may think that the difference between the wind speeds at the top and the bottom of a 'block of wind' is $12 m/s$, that we fly with a TAS of $vg = 60 m/s$ and that $vfg = 72 m/s$. We set the gradient at $10 m/s/100m = 0.1 s^{-1}$. Thus, the height of the ‘wind block’ will be 120 m.

Then,

$w = (722 - 602) · 0.1/2 · 9.8  = 8.08 m/s = 1591 feet/min$

Not implausible, I think…

I propose to look at it in a different way. Let's assume a constant airspeed climb.

We have two scenarios: one where there is no headwind gradient, and one with a headwind gradient. We can calculate the achieved climb speed in both scenarios and then compare them to see what the effect of the wind is. By selecting a constant airspeed, the drag is constant in both scenarios so they can be easily compared.

In both scenarios the aircraft will have the same constant thrust, such that the thrust exceeds the drag. The excess thrust is equal to 5% of the weight.

For the purpose this answer, I do not look at calibrated airspeed but only at true airspeed. Basically I neglect effects of changing density with altitude.

Also, the angle of climb (flight path angle $\gamma$) is sufficiently small to be in the linear domain (such that $\cos\gamma \approx1$ and  $\sin\gamma \approx \gamma$)

Scenario 1: climbing in a constant wind field

In the first scenario the aircraft is climbing in a constant wind field. This can be no wind at all, or a constant headwind or a constant tailwind.

For the aircraft to perform a constant airspeed climb in this constant wind field, all forces acting on the aircraft (thrust, drag, lift, weight) need to be in equilibrium.

Thrust = green
Drag = red
Lift = blue
Weight = black

$\frac{dV}{dt} = \frac{T - D - W sin \gamma}{m} = g\left( \frac{T - D}{W}  - \sin \gamma\right) = 0 $

With a thrust excess ($T-D$) of 5% of the weight, the aircraft need to climb at a flight path angle of 0.05 radians which is approximately 2.86 degrees.

$\frac{T - D}{W} = \sin \gamma = 0.05$

The vertical speed $w$ is then equal to:

$w = V\cdot\sin\gamma $

So in the first scenario the aircraft will achieve a climb speed that is equal to 5% of the true airspeed. Taking 60 m/s from your calculation for the airspeed, the aircraft will climb at 3 m/s = 591 ft/min.

Scenario 2: climbing in a wind gradient

In our second scenario, the same aircraft climbs with the same velocity and same thrust setting, but now it encounters a headwind gradient of 10 m/s per 100 meter of climb. This equates to a wind gradient of 0.1/s:

$\tau = \frac{10 \textrm{ m/s} }{100 \textrm {m}} = 0.1 \frac{1}{\textrm{s}}$.

A climb of 3 m/s would result in an effective wind increase of $\tau \cdot w$ = 0.3 m/s2 which is effectively an increase of true airspeed. Therefore, this isn't a constant speed climb anymore.

To make sure the climb is performed at a constant air speed, the aircraft needs to climb faster.

$\frac{dV}{dt} = \frac{T - D - W sin \gamma}{m} = g\left( \frac{T - D}{W}  - \sin \gamma\right) + \tau V \sin \gamma = 0 $

$\sin \gamma =  \frac{g}{g-\tau V}\cdot\frac{T-D}{W}= \frac{9.81}{9.81-0.1\cdot 60}\cdot0.05 = 0.129$

$w=V\sin\gamma =$ 7.72  m/s = 1521  ft/min

In the wind gradient the climb speed of 1521 ft/min is considerably higher than the 591 ft/min achieved in a constant wind field with the same power setting. The difference is a factor of 2.57 which can be attributed to the wind.


Why are true headings followed above 73N in the northern hemisphere, whereas in the southern hemisphere the change is made at 60S? The question is in regards to the asymmetry of the changeover latitudes and NOT about why it needs to be changed.

Earth's magnetic field is not symmetric north to south.  In particular,  the magnetic declination can get significantly larger at a given southern latitude than it does at the corresponding northern latitude.  This can be seen by looking at a world declination map:

Curves of a given declination reach much lower southern latitudes than they do northern latitudes.  For example, the highlighted curve is 40° west of north declination;  its southernmost point in the northern hemisphere is at about 75°N, but its northernmost point in the southern hemisphere is at 35°S (!).  Another way this manifests is that the South Magnetic Pole is at a significantly lower latitude than the North Magnetic Pole (~65°S vs. ~85°N).
As to why the Earth's magnetic field is so asymmetric, that's a question for Earth Science.SE.  My understanding is that you may not get a good answer over there either;  the behavior of Earth's magnetic field is complex and not fully understood.


How does Reynolds Number affect skin friction drag? I'm an aerospace engineering student, and I'm worried about efficiency as it relates to high and low Reynolds numbers. I don't understand which is more helpful for a aircraft.

On a website I read this:

  If the Reynolds Number is large, the viscosity effect is small. For the for us practical values the inertia or density forces dominate, and the parasite drag increases with the square of the velocity. However, although the viscosity is unimportant, it may still affect the very thin boundary layer, leading to the creation of turbulent flow.
  Thus the importance of the Reynolds Number is that it tells us the type of flow we can expect. It tells you whether you can hope for having laminar flow over the wing and other parts of your airplane. A low Reynolds Number gives laminar flow while a high Reynolds Number gives turbulent flow. For both a laminar and a turbulent boundary layer increasing Reynolds Number gives lower skin friction drag. However, because of the higher energy loss in the boundary layer, a turbulent layer always has higher skin friction drag.

In this, there is something like this: For both a laminar and a turbulent boundary layer, increasing Reynolds Number gives lower skin friction drag. I didn't understand the meaning of that statement.

Is there a rule like "Higher Reynolds number, higher drag force"?

And what exactly do parasite drag and boundary layer do?
And what do their vastness or rarity contribute to?

Simply: how big should a Reynolds number be for an aircraft to be efficient?

First of all, friction is bad for efficiency. It slows moving things down and needs a constant energy supply to be overcome. The more friction, the more energy has to be supplied, and this energy is lost as heat.

Aerodynamic friction is caused by viscosity. The Reynolds number tells you how big viscosity is in relation to inertial forces. A bigger Reynolds number signifies lower viscosity. This means a higher Reynolds number almost always results in lower friction. If you look at the plot below, the downward trend can be easily spotted.

Friction drag coefficient of a flat plate over Reynolds number (picture source). Note the double logarithmic axes.

  Is there something like " higher Reynolds number, higher drag force " stuff ?

Yes, sometimes. Please look at the transition curve: Here a flow which is initially fully laminar slowly changes with increasing Reynolds number into one with a laminar start and a transition to turbulent flow somewhere downstream. This adds a section of turbulent boundary layer where at a lower Reynolds number the flow would had been laminar. You will notice that for the same Reynolds number, a fully laminar flow (lower line) is much less draggy than a fully turbulent one (upper line). Therefore, replacing some of the laminar flow with a turbulent one will result in more drag.

Now I need to explain why increasing the Reynolds number leads to more turbulent flow. For this, I turn to this answer:

Inside the laminar boundary layer, small disturbances become less and less damped the higher the local Reynolds number becomes, and at a Reynolds number of around 400,000 in unaccelerated flow some frequencies become unstable (see Tollmien-Schlichting waves) and will eventually create so much cross movement that the boundary layer becomes turbulent. Now parcels of air which flow at high speed in the outer part of the boundary layer will move close to the wall and kick the slow parcels there ahead, greatly reducing the deceleration of the flow close to the wall, at the price of slowing down and expanding the whole boundary layer.

Simply put: A laminar boundary layer cannot be sustained indefinitely but will change to a turbulent one if the Reynolds number is high enough. This will swap some of the previously laminar portion of the boundary layer to a turbulent one, increasing drag.

While all of the above is only strictly true for flow over a flat plate without a pressure gradient, real flow will complicate things again: Now turbulent flow is not all bad; the example of the dimpled golf ball shows that a turbulent boundary layer in flow with a pressure gradient can also lead to lower drag, given the right circumstances.


Are fighter jets vulnerable to .50 caliber gunfire? As I've seen in the movies, could a .50 caliber round shoot down a fighter jet?

By .50 caliber, I believe you are referring to the .50 BMG cartridge.  The answer is yes, you could shoot down a jet fighter using such a round and plenty of jet fighters, such as MiG-15s, have been felled using that round during the Korean War.

In some respects the .50 BMG is a superior round to modern cannon rounds for shooting down jet fighters.  It's a small, fast round with good range, muzzle energy and penetration capability and can be fired at high rates, saturating sections of the sky with rounds, particularly useful for high off-angle snapshots in ACM.

In regards to penetration power, even a .22LR round could punch through the skin of a modern fighter.  The structure has to be kept light for weight and performance reasons.  Armor on fighters is almost unheard of, save for some plating on flight crew seats.  One exception to this is ground attack aircraft such as the A-10 or SU-25 which do have armor around the cockpit to protect the pilot at low levels.  The rest of the aircraft does not have armor and relies more on structural integrity and redundancy to protect the aircraft from ground fire.


Why are westbound transatlantic routes located hundreds of km away from eastbound routes? Are jet streams a net benefit in time and fuel savings? provides (basic) explanations about jet streams in the Pacific. However I'm looking for an answer focused on North Atlantic area, explaining the track system and the tracks location. In addition BA 185 route seems to be composed of two arcs, did they change their mind in flight because of the wind? or is this related to ETOPS or alternate airport at Santa Maria?

Looking at flights between NY and London (click to see route):

BA 185 (EGLL - KEWR)
United 941 (EGLL - KEWR)
United 16 (KEWR - EGLL)

The FlightAware anticipated routes are quite similar in both directions, but the actual routes for past flights are really remote from each other:

The two westbound routes are either 800 km north or 1,000 km south of the eastbound route (the dotted line shows the shortest path).

Why are the two westbound routes different and so remote from each other? Why this difference of about 1,800 km?
Why BA 185 route seems to be composed of two arcs?
Did the pilots changed their mind in flight because of the jet streams? Is it related to ETOPS constraints, or alternate airport at Santa Maria? or something else?

The reason this is done is due to the winds aloft. The Jet Stream is a powerful current of air that blows in a west to east direction. Airplanes crossing the Atlantic from west to east take advantage of the jet stream to get there faster and save fuel, so a course is chosen to stay in the stream as much as possible. Airplanes going from east to west will be slowed by the jet stream, using more fuel and taking longer to get across, so a course is chosen to avoid the strongest winds.

The difference can be very significant, I've been on flights from NYC to London which take 6h 30m, and ones from London to NYC that take almost 9 hours.


How does SOFIA cope with open hull? On the SOFIA aircraft, the aircraft is designed to fly at very high altitudes (higher than what can be achieved by regular 747), with a cargo door open.

https://upload.wikimedia.org/wikipedia/commons/8/8a/SOFIA_ED10-0182-01_full.jpg

I know that oxygen mask are a standard feature for most airliners but:

How is the aircraft designed to handle this situation ?
What about redundancy ?
If there is supplemental oxygen, is it really without adverse effects ?

pic credits wikimedia

From the picture I can see a bulk head forward of the telescope area. This modified 747SP might have a re-positioned bulk head then. Anything forward of the telescope would be pressurized.

This source confirms, bulk head was moved from the aft to be ahead of the telescope.


Why do helicopters have windows near the pedals? What is the purpose of the clear windows in some helicopters in the floor of the nose, right where the pilot's feet and pedals are?
For example, here's a Huey with windows clearly visible:

Airbus helicopter example:

These fall into a category known as vertical reference windows. They can be used for many purposes, but essentially, they allow us to gain a better spatial picture of the orientation of our aircraft, the skids, and anything that might be slung beneath the aircraft. As someone who has landed many helicopters on trailers, it is extremely helpful to be able to see through the floor when precisely placing the skids. Holding a pinnacle approach and hover is much easier to execute as well. Further, when you have something on a line, it makes it easier to keep it in view, especially when it is closer to the aircraft.


Why do pilots say "clear of the active" at non-towered airports? At the non-towered airport I fly at, pilots when clear of the runway always say "X Traffic, Skyhawk N123 clear of the active." Why not say the runway number? At a one-runway airport, I understand that this could be redundant, but wouldn't it be better to get in the habit of saying the runway number so that--should there be more than one runway--it wouldn't be an issue?

Honestly? It's probably because they heard someone else do it, and thought it sounded cool (or otherwise just got it stuck in their head).

You're 100% right - saying the runway name is, if slightly longer, certainly a bit more informative. It's the kind of thing that can help arriving pilots know which runway is in use, keeping later radio clutter ("Um, uhh, Jeffco Traffic, um, say runway in use?") to a minimum for pilots already on frequency. Even a 'one runway airport' still has two runways (09/27, for example), and it's nice to know which one you should set up for when winds are light.

The preferred terminology is more like "Jeffco Traffic, 3AC, clear 29".


What is the maximum pitch for the Boeing 787 Dreamliner? I recently watched a video of the Boeing 787 training before Farnborough.  This aircraft climbed very fast; does someone know the maximum pitch of this aircraft?

30 degrees.

Boeing aircraft, including the 787, have a Pitch Limit Indicator (PLI) in the flight display that tells the pilot how far the wing's angle of attack (AOA) is from stall.

  the PLI also is limited to 30 deg of pitch attitude, regardless of AOA.

But it depends on aircraft configuration

  During takeoff climb, there is no single target AOA to fly that will guarantee certified takeoff performance. Takeoff-climb AOA will vary with such factors as airplane gross weight, thrust, altitude, flap setting, and CG. Takeoff-climb speeds (hence, AOA) are limited by stall speed, tail clearance, and minimum control speeds. The higher speed and greater thrust of an all-engine takeoff reduce the AOA significantly relative to an engine-out takeoff at the engine-out climb speed (V2 ).

From Boeing Aero No.12

At Farnborough 2014, pilots Neville and Bryan were pulling stunts that would get airline pilots fired. Most airlines limit pitch to 20 degrees (or in a few cases 25) from what I've read.

  They kicked off the demonstration with a spectacularly steep takeoff, pitching the plane up just shy of 30 degrees.

I'd guess they flew just inside what Boeing consider unsafe for those conditions.

  Boeing won’t reveal ... just how steeply it can take off

From Wired - "terrifying" (my emphasis).

I think we can be reasonably confident that no production 787 will ever, after take-off, initially climb at greater than 30 degrees.

Flight envelopes

The way I understand it, asking about the "maximum" of anything for an aircraft is less useful than understanding the flight envelope. This is because the maximum depends very greatly on the exact situation of the aircraft including things like altitude, weight, speed etc.

Actual flight data from the six Boeing 787 test aircraft.


Why can't ramjet diffusers be stacked to achieve a good overall pressure ratio? The problem with ramjets is that they only gain efficiency similiar to turbojets at speeds above mach 2. However, ramjets can operate at speeds of a few hundred km/h. Why therefore cant ramjet diffusers be stacked, analogously to compressor stages in a turbojets to achive a high compression ratio and efficiency at low speeds?

A diffuser is simply an expanding piece of pipe that converts kinetic energy (i.e. velocity) to pressure energy (i.e. pressure) according to Bernoulli's principle (which is just a formulation of the law of conservation of energy for fluid flow).

The air enters the diffuser with the velocity corresponding to the speed of the aircraft, and must still retain some speed through the combustion chamber. So only the speed above that can be converted to pressure. Few hundred km/s is already more than the speed in the combustion chamber, so there is some pressure gain, and the engine starts to work at all, but only above M2 the pressure gain becomes comparable to what a trubo-compressor can provide.

Also diffuser is simply an expanding piece of pipe and stacking two expanding pieces of pipe behind each other is still just an expanding piece of pipe. And two expanding pieces of pipe with a narrowing piece in between is no better than one of them, because the pressure only depends on the initial and final cross-section and not on the shape in between.


Why do only some aircraft require tail anti-icing? Why do some aircraft require anti-icing on the tail while others (Dassault Falcon Jets, Boeing 737, 747, etc.) don't?

Some airplanes don't need the horizontal stabilizer to have anti-ice because it was shown during flight testing that there were no adverse effects from having ice on the tail.

This is mainly because the horizontal stabilizer/elevator has been designed so that even with a degradation of lift due to the ice, it still produces a sufficient tail down force to maintain control, even when approaching the stall speed.

The airplanes that do have anti-ice usually either have smaller horizontal stabilizers or (on some older designs) couldn't get the FAA to sign off on a design without it.  Some designs are also more prone to collecting ice (based mainly on the radius of the leading edge) so must demonstrate sufficient handling qualities with even more ice, which may not be possible.


What is the maximum Mach number for a titanium aircraft? What is the maximum achievable Mach number for a titanium aircraft assuming speed is limited by structural heating?  The answer would be even better if there is a list of different materials and maximum Mach numbers.

To give an answer, I first need to get answers to a few more questions:

First question: Which titanium alloy would you consider? The choice of alloy will impact the answer much more than the base metal of the selected alloy. Since strength at elevated temperature is the figure of merit here, consider the spread of values:

Strength of various Ti alloys over temperature (picture source)

Second question: Which cooling is available? Is the aircraft propelled by liquid hydrogen which has a massive heat capacity per kilogram of mass and needs to be heated before it is injected into the combustion chamber. Or do you run it on kerosene, which allows to dump much less heat into it? The answer will tell you how much cooler the structure can be than the air flowing around it is.

Third question: What wing loading is possible? This is driven by the range and payload requirements of the aircraft, and your question doesn't give any details on this. A higher wing loading will translate into a higher heat flow since the air density needs to be higher, so the cooling can be less effective.

Fourth question: Do you insist on an attached shock which produces much higher peak temperatures in parts of the structure, but less thermal load overall, or is a separated shock possible which increases drag and thermal load, but reduces peak loads considerably?

Depending on the answers to those questions, the possible flight Mach number can be anywhere between Mach 2 and Mach 5. If you allow for specialty materials for highest thermal loads and make only the inner structure from titanium, the Mach number can reach into double digits.


Which airports have ILS Cat IIIC? Are there any airports with ILS working CATIIIC?

What do the charts for this procedure look like? Is there a missed approach procedure?

This is not implemented anywhere in the world.

Wikipedia:

  As of 2012 this category is not yet in operation anywhere in the world
  as it requires guidance to taxi in zero visibility as well. Category
  IIIc is not mentioned in EU-OPS.

Airliners:

  As far as I know NO airport in the world currently offers catIIIc as
  it has the most ridiculous minima both in the horizontal and vertical
  plane ...


How to communicate a circling approach over CTAF? The FAA ATC job order says:

  Circling approach instructions may only be
  given for aircraft landing at airports with operational
  control towers.

But I could not find a phraseology example that can describe the circling approach below (which I drew based on this image).

So for non-towered airports, is there a standardized phraseology used to describe the non-standard circling loops to other pilots in the area? Be it good weather or not.

According to this site, there are hundreds of ways to fly a circling approach. Any jurisdiction is fine by me, it's just a curious question.

"Overflying the field at [whatever] MSL to enter the left downwind for runway 18"
is what I would call at a nontowered field.  It's also the phraseology that tower controllers have used when I've done that particular approach at a towered field.


Can a steady flow have stagnation points? I am confused by this idea. If a flow is steady, its streamlines are unchanging. Taking the typical example of an airfoil, there is (at least) one streamline which will hit the leading edge of the airfoil and stagnate. Stagnation point is defined as:

  a point in a flow field where the local velocity of the fluid is zero.

Now my question is, if the velocity here is zero, and fluid particles that pass through the streamline which results in a stagnation point have nonzero velocity upstream, where do these fluid particles go? Since they are on the streamline, they have to reach the stagnation point? Does this not defy the conservation of mass law?

Further, an online Fluid Mechanics course I have been following has in one lecture shown streamlines going away from the stagnation point. If the velocity at this point is precisely zero (and is unchanging since the flow is steady), then how can the fluid particles go in other directions?

I must be missing something, do enlighten me.

The idea of a stagnation point is an idealization. This point is infinitesimally small, and air particles flowing along a streamline which leads into it will slow down on their way. The closer they come to the stagnation point, the slower they flow, and in the end they never arrive at the stagnation point.

In reality, air molecules have a finite size, so they flow either above or below the stagnation point streamline. Even if one particle manages to arrive at the stagnation point and stays in place (which is not possible in theory), a small angle of attack change will wash it away in the next moment.

One streamline goes away from the rear stagnation point which is located in the trailing edge. This point is doubly idealized, because it requires inviscid flow to have a rear stagnation point. Again, molecules flowing along the wall of the airfoil will be slowed down by the stagnation point pressure the closer they are to the trailing edge. Since they arrive either above or below the rear stagnation point, they will accelerate once they have passed the point of highest pressure and move on above or below the streamline emanating from the rear stagnation point.

The concept of a stagnation point is really helpful for understanding flow phenomena, however. There is really a line (in 3D it is a plane) which separates air that will flow over the wing from that which will flow below it. This line changes with angle of attack, and the simple stall warning vane is based on this principle. Once the line ends below the vane, air will press it upwards, closing an electrical contact which activates a buzzer in the cockpit.

Stall warning vane (small metal thingy sticking out from the wing)


Are large jet turbofans so easy to spin? In this question, in the accepted answer, there is a comment by alephzero that says one can actually rotate a large turbofan's blades with one finger! Is that true, can someone elaborate? As an example, does this apply to my google search for strongest turbofan GE9X too?

Yes, large turbofans can be turned by hand without too much force. On smaller aircraft this is regularly done as part of the preflight walkaround. You can see an example in this YouTube video of an A320 walkaround:

Admittedly, the pilot turns the engine with four fingers here, but you can see that not much force is required. Turning it with a single finger would easily be possible.
On a larger aircraft like a Boeing 777 you cannot reach the fan when standing on the ground in front of the engine. Spinning the fan by hand is therefore not usually done during the preflight.
This video shows a GE engineer turning the fan blades of a GE90 (the predecessor of the GE9X) engine by hand:

Again, it is not one finger, but he is not using much force to turn it, so it should be possible with one finger.


How can I correctly decode CPR positions from ADS-B frames? I am decoding Compact Position Reporting (CPR) positions from ADS-B frames (the airborne position and surface position frames).

Most of my results give realistic longitude/latitude values, but some return things like 0,781518968485169 177,220642089844; or 1,76377118644068    -0,664306640625; or 2,12129237288136 -2,838134765625.

I have a feeling like I must be missing some kind of validation or some kind of frame type identification. Where can I find more information about the decoding process?

We were decoding Airborne Position frames having TypeCode 0, 9-18 and 20-22.
Apparently, frames with TypeCode 20-22 and possibly 0 have to be decode a different way.

(For now I think that I get enough information out of TypeCode 9-18 frames so I'll just skip the other ones.)


When was the concept of V1 introduced? When was V1 speed first introduced? Was it the result of a particular accident or series of accidents?

There were a series of RWY overruns during the days of the first group of jet airliners (early to mid 50's), possibly 3 within a 12 month period. Mainly early rotation resulting in the airplane stalling during the takeoff roll at full thrust. Such accidents caused review of the take off maneuver and birth of the RTOW (Regulatory Take Off Weight) calculations.
A description of 2 cases, 26th Oct 1952 and 3rd Mar 1953


What is rotor damping and how does it affect helicopter stability? What do we mean by rotor damping (in terms of helicopters)?
How is it affected by air density?
How does helicopter stability depend on rotor damping?

I will try to answer these questions in terms of structural dynamics.
Please correct me if I say dumb things on other parts of my answer.
You ask about damping. Damping must be considered when dealing with structural dynamics, or vibratory phenomena. In a helicopter rotor, multiple phenomena can lead to vibrations. For instance :

Differences in blade properties (mass mostly, but also stiffness)
Rotor imbalance due to machining uncertainties
Bearings
Engine, which may produce torque oscillations of some sort
Gearbox, which may also produce oscillations (look for gear mesh vibrations)
Helicopter operations (if you have quick flight trajectory modifications, this may lead to increased or reduced lift needs, which induce torque oscillations in the drive line)

So long story short, multiple phenomena can excite the rotor.
As any structure, a helicopter has natural vibration patterns called natural modeshapes, associated with natural frequencies.
However, if you excite a component enough on its natural frequency, this may result in a fatigue failure, hence the utmost importance of damping.
As far as I know, the most visible technology used to increase damping on a helicopter rotor are the blade root dampers. Multiple technologies exist, however they seem to damp the same phenomenon : blade edgewise motions or so-called lead-lag motions or hunting motions.
If you want to have a deeper understanding of these issues, have a look at this article for instance. This page may be helpful as well.
The first paper addresses semi-active dampers to control the blade edgewise bending motions in order to reduce the constraints on the hub. Basically, if the blade was mechanically fixed to the hub, large constraints could occur due to vibration loads, leading to for instance fatigue failure. In the configuration presented in the paper and reproduced here,

the liaison between the hub and the blade is a cylindrical liaison, allowing in-plane rotational motion. The (stiffness-)damper system is then used to absorb the kinetic energy of the blade in order to limit the loads on the hub, which allows to reduce its overall weight.
The second paper provides some more general concepts on the technologies involved in helicopter rotors. In particular this here

is a good schematic of a full articulated rotor.
Other rotor technologies exist : semi-rigid or rigid rotors but they use a different strategy for vibration reduction and blade-hub liaison.


Is there a standard that defines all Special Service Requests? I'm wondering if there's an international standard set of SSR codes. I see some references to IATA standardizing these, however, I can't find a reference to where IATA would publish these codes.

... however, I can't find a reference to where IATA would publish these codes.

You can find it here.

Before committing to the purchase of the document, check the free Table of Contents to make sure it has what you want.


What did the "gear warning horn" on the North American P-51 sound like? I'm working on a sound project for a P51 simulation and I'm having real trouble trying to find a reference on how the P51 gear warning horn sounded like. What mechanisms were used in the '40s to make these kind of sounds?

Interesting question.  Unfortunately, I couldn't locate the part in the P-51D/K parts catalog, but, if an E-bay seller is to be believed, it had an E-2 Faraday horn, which appears to be an electrically actuated alarm.  Faraday is (was) the name of an alarm manufacturer most commonly known for their fire alarms.  Based on a history paraphrased from cteksys.net (emphasis is mine), this seems to be plausible:

Faraday, was founded in 1875 and is now one of the leading
manufacturers of Notification Appliances, Fire Alarm Control Panels,
and Clock Systems in the United States.  (Statement in 2002) ...
... In the 1940s Documents have been located with the name Schwarze-Faraday at 130 Church Street Adrian Michigan showing the
company pressing into signaling equipment for industrial applications
including factories , ships, and airplanes.

It's not the original, but a circa-1960s Sperti-Faraday horn (the company name from 1937-1965) sounds like this:


Why do you have to keep your seat belt fastened after landing? What's the point of the usual "please keep your seat belt fastened until the aircraft stops completely (at the gate)" in large passenger aircrafts? Since the plane is on the ground, it is not moving very quick. Even if it stopped abruptly, the seat belt won't prevent me from banging my head against the seat in front of me since it's a two-point seat belt.

The only reason I can think of is if two aircraft collided with each other, which could potentially generate enough force for the seat belt to be useful. Though, I could argue that when a plane is taxiing to the gate, it has to abide to a certain speed limit, which would render any kind of collision not serious enough to be prevented by two-point seat belts.

Ground operations are just as dangerous as air operations. Strictly speaking the deadliest aviation incident actually happened on the ground (not saying seatbelt played a role or not however severe accidents do happen on the ground). The comments cover things well, (keeping people seated, keeping people from accessing over head compartments etc.) Planes are not safe simply because they are on the ground, they are only safe from flight related incidents and once on the ground they are susceptible to ground related incidents. By some estimates 27,000 ground incidents happen a year. The fact remains there are plenty of things to hit on the ground and plenty that can go wrong in taxi. These accidents are classified by ICAO under (RAMP) and (GCOL) codes (and potentially others). Boeing has a breakdown of accidents by flight category (taxi and ground ops make up about 10%).

Furthermore here in the US under the FAA FAR 91.107 as well as FAR 121.311 in the commercial case(basically the same wording) requires it

  ...(3) Except as provided in this paragraph, each person on board a
  U.S.-registered civil aircraft (except a free balloon that
  incorporates a basket or gondola or an airship type certificated
  before November 2, 1987) must occupy an approved seat or berth with a
  safety belt and, if installed, shoulder harness, properly secured
  about him or her during movement on the surface, takeoff, and landing.
  For seaplane and float equipped rotorcraft operations during movement
  on the surface, the person pushing off the seaplane or rotorcraft from
  the dock and the person mooring the seaplane or rotorcraft at the dock
  are excepted from the preceding seating and safety belt requirements....


Could you use radial blowers to propel a model aircraft? I was inspired by stealth planes like the Boeing Phantom Ray:

I'd like to make a model aircraft that's as thin as possible, and has integral engines that are not visible from the outside. I have been wondering how this might be possible.

One way might be to place a radial blower in the centre of the fuselage. Radial blowers suck in air through their rotary axis, and blow it out the sides.

Usually, they are housed so that air is constrained to come out in one direction. However, you can always give the air two exit ports.

I wonder if something like this might make a good engine for a plane? The air intake would be at the top of the plane, and the exhausts would be at the back.

Questions:

Would a single large engine have a power:weight benefit over two smaller engines?
Would the intake actually provide additional lift by reducing the pressure above the plane?
Might be intake be starved of air if the plane is acting as a lifting body?

Interesting question, and I can only answer in general terms because much depends on speculation.

Short answer:

use one central exhaust
one big blower is better than two small ones
one short flow channel is better than two long ones
suction on top might be beneficial for high lift

Radial-flow compressors are very light and achieve high pressure gains per stage. However, the simple plastic thing in your illustration will not have good efficiency. Generally, cambered blades are better than straight blades, and the thinner they are the better. Thick blades block more of the flow path. The drawback is their high diameter, and by placing the blower on its side, you get around this obstacle in an elegant way.

The idea of using two exhausts complicates things; if you use a single one, you can avoid problems due to unsymmetrical thrust. Given that the compressor runs in one of two directions, asymmetries will be very hard to avoid. By placing vanes into the exhaust you can actually give the model plane some degree of sideways thrust vectoring. Also, two flow channels will have more surface area per cross section than a single channel. Your losses will be higher if you use two like in the illustration because they are longer than necessary.

The same goes for the blower: A single, larger one will always be more efficient. The gap size in a small blower is probably relatively bigger than that of a larger blower, and gaps are real efficiency killers.

Another efficiency killer is flow separation in the ducts. Make sure that cross section changes are gradual and avoid bending the flow as much as possible. It will probably help if you install cambered guide vanes at the entry of the exhaust to convince the rotational flow to change direction and leave the round compressor chamber.

Suction on top is also interesting. There have been many ideas about boundary layer suction to increase maximum lift, and your turbine inlet will certainly help to remove some of the boundary layer where it will separate first. Normally, turbine intakes are placed where the normal flow field already shows some pressure increase due to ram effects, but at the speed of a model airplane this will not be a factor. I expect the best intake in your case is a hole on top of the aircraft with nicely rounded edges. Those rounded edges should already produce some lift, and the whole configuration will probably achieve a higher stall angle of attack when the engine runs at full power than at idle power.

I can only speculate how much power will be converted to thrust, but I bet placing an ordinary propeller at the usual place will be more efficient. But the configuration you propose has its own merits.


What is the temperature range of engine mounts connected to the pylon? I want to know what is the temperature of the engine mounts in modern turbofan engines for example, Rolls Royce Trent 900. Also, what are the temperature considerations you need to make while designing a pylon?

This is an order of magnitude educated guess:
Based on this picture from Wikipedia:

You can see that the aft mount is attached to the turbine rear frame.  As such, it'll get relatively toasty.  I'd say maybe 900 - 1000 F.
The forward mount is attached to the fan frame just above the compressor case.  As such, it will be much cooler.  Maybe 200 - 300 F.
Again, that's just an educated guess.  I'm not aware of any publicly available data.
Edit:
in response to the comment, no it's not the big red box at the front. That's approximately where the forward mount would be in a typical Boeing style engine, but Airbus does it a little differently.  In the below, I found an image of a model of the pylon (from here), and showed where the pylon meets up with the engine.  The left most line points to the aft mount, the middle line to the forward mount, and the forward line meets up with the inlet (not a mount, just to show you how it lines up).  The top orange bar in the engine picture, and the lower white bar in the pylon picture are ground support equipment.  Would be removed when the engine is attached to the pylon.


Why do the engines seem to power down and then back up after take-off? What is the phenomenon on a commercial airliner (say, a 737-800) where shortly after takeoff and before we reach 10,000 feet the engines feel like they slow down dramatically or even power off momentarily, then spin back up?

This happens fairly frequently when I'm flying and, although I'm used to it, it still takes me by surprise every time!

There are several kinds of power reduction which could happen after takeoff:

Cutback (noise reduction when the airplane is very low, after takeoff)
Climb thrust

Both are set on the CDU (Control Display Unit, the screen and keyboard of the FMC, Flight Management Computer).

Since you describe a temporary and dramatical power decrease, this should be the cutback. When you hear the power increase again, it must be that the setting goes from cutback to climb thrust.

In the B737-800

The cutback option on the CDU

This is the CDU (Control Display Unit), where you set up the cutback. It is in the second page of TAKEOFF REF. Here is the screen before turning cutback ON.

ACCEL HT : This is the height (above ground level) at which we will let the plane accelerate (we will lower the pitch a little bit and gradually retract flaps).
EO ACCEL HT: Same as above, but applies when one engine is not running (Engine Out Accelaration Height). This setting will be used in case of engine failure after takeoff.
REDUCTION: This is the height at which the thrust setting will go from TOGA to CLIMB. We need maximal thrust during takeoff, because it's a critical phase and it's safer. But at the same time, keeping this setting too long decreases the engines lifetime because of the high temperature. It also burns more fuel, it's noisier and less environment-friendly. That's the reason why the airplane won't climb with maximum thrust.

But this question is about cutback. Here is CDU again after turning cutback ON.

CUTBACK N1: This will be the target N1 setting when the REDUCTION height will be reached. The Auto-throttle together with the EEC will arrange for maintaining this lower shaft speed (here you can see it's 84,6%). This will be a lot less noisy but will still provide enough power to climb!
EO ACCEL HT: Same as above
REDUCTION: At this height, cutback will happen and CUTBACK N1 will be the engines target N1 speed.
RESTORE: This is the height at which cutback is no longer needed, and climb thrust N1 setting will be the new N1 target for the engines (92.3% in this example).

Takeoff with cutback

This is the takeoff roll. IAS indicator is not active yet (below 45KIAS). Ground Speed is currently 35kt.
N1 and TO/GA are displayed on the FMA (Flight Mode Annunciator) at the top of the PFD (Primary Flight Display). On the right, you can see on the ED (Engine Display) that the green marker is indicating TO thrust (because of TO/GA mode).

Few seconds after the rotation. You can see at the bottom of the PFD the radio altimeter indicating 300ft AGL. We haven't reached the REDUCTION height, so the cutback is not active yet. The ED still indicates TO thrust and the green markers are just below 100% N1.

Few seconds after reaching REDUCTION height. N1 is active on the FMA. Radio altimeter indicates 960ft AGL, this is above our REDUCTION height, so the cutback should be active and our engines should be a little quieter. A look at the ED and we can see that the green target N1 marker is now indicating 82.6% N1. Our engines are still rotating faster than that (98% N1), and the EEC is currently decreasing the fuel flow arriving to the combustion chambers.

We are now reaching 2500ft AGL. This is below the RESTORE height of 3000ft, so the cutback is still active, as shown by the ED. The green target N1 marker is indicating 83.0% N1 and the current N1 for both engines is also 83.0% N1. In 500ft, the N1 target speed should increase again to climb thrust settings.

We've just reached the RESTORE height (above 3000ft AGL), and we can see the green markers show 92.3%. We are back to the climb thrust settings and our plane is loud again! The flaps are still down, and the pink speed marker on the PFD just moved to the top. We are going to retract the flaps and slats, and accelerate to 250KIAS. It seems that RESTORE height is also the ACCELERATION height when cutback mode has been turned on. [I'm not sure, could a B737 pilot confirm this?]

The flaps are up, our speed is now 250KIAS.

Further readings

http://www.boeing.com/commercial/aeromagazine/aero_21/quietclimb_story.html
http://www.flaps2approach.com/journal/2013/6/29/avoiding-confusion-using-the-following-acceleration-height-t.html


Where could I find the FOD examples of C17? I want to find some FOD examples of huge planes in reason of ground vortex,where should I  go to search?

You can search the National Traffic Safety Board here

https://www.ntsb.gov/_layouts/ntsb.aviation/index.aspx

as a starting point.

Under Aircraft:Category, select Airplane.

Under Model, Select C17.

Scroll down and select  Submit Query.

There are couple of hits on C17s on the first page of results, I didn't look at  further pages.

Try this stack exchange link also on the same occurrence, but not just limited to C17s.

How does this vortex form inside a jet engine?


Please identify this twin-engine airliner Could someone please identify this aircraft for me.