What role do the winglets on the next-generation 737 play? I've flown on a couple of 737's recently and noticed that the wings are quite beautiful and have a distinctive upward sweep at the wingtip, almost like a vertical stabilizer.

What advantages and what disadvantages (if any) does this type of wing provide?  I imagine there is some gain in overall stability.

The wing tips calling as "sharklet" at Airbus A/Cs and "winglet" at Boeing A/Cs. It reduces the tip vortex and helps to prevent from airflow seperation at wing tips. It have positive effects on both fuel consumption and turbulance making. Negative effect of the additional part is increase of the drag coefficent but you can keep it negligible againts the positive effects.


Can a contra-rotating helicopter simply tilt its entire rotor set instead of using a cyclic? I was reading this interesting question and, per answer #1, a normal helicopter cannot do it because gyro effects would probably mean the body of the heli would tilt more than the rotor.

So now I think about contra-rotating helicopters, like the Ka-50. They don't need tail rotors, because the contra-spin cancels out reaction torque (except when they want to yaw, for which they extend little things at the blade tips of one rotor, producing more torque there and therefore opposite yaw).

Anyway, can't a contra-rotator just tilt its whole hub instead of using traditional cyclic (swash plate, scissors link, which in fact are a lot more complex for a contra-rotating helicopter).

Juan de la Cierva, inventor of the autogyro, on the C.30 went to a tilting rotor. Most autogyros tilt the entire rotor for cyclic control. Some autogyros apply engine torque to the main rotor to assist in achieving short takeoffs. Now for this brief time, the autogyro is functioning like a helicopter, and the main rotor is driven by the engine prior to takeoff. There is now a torque from the engine acting on the airframe, that requires more pilot hand force to control the rotor while the engine is driving the rotor. Counter-rotating rotors on a helicopter would neutralize the reaction torque into the airframe. So yes for a very small helicopter, it should be possible to tilt the main rotor for cyclic control, without hydraulic power assist. If one is going to use a swashplate for collective control, it is easier to just control cyclic conventionally.
Here is one example of a helicopter that tilted the rotor for the cyclic:
http://www.aviastar.org/helicopters_eng/bensen_zipster.php


Just how inaccurate are (Las Vegas) VOR radials? I was discussing VOR-based navigation with a pilot, and he mentioned that VOR doesn't provide a very high level of integrity and safety (at least, compared to GPS or DME). He explained that the FAA only guarantees VOR radials listed in approaches and claimed that "one quarter of the radials at Las Vegas are bad".

Are the Las Vegas radials off by just a degree or two or is it worse than that, and how did they get to be so bad? Is it a case of normal variation due to geography and magnetic drift, or is it something more serious like what happened in 2003 to an Airbus A-320-231, G-MEDA on approach to Addis Abeba Airport?

I guess it depends on what you consider to be a "high level of integrity and safety." VOR is a perfectly acceptable means of navigation if you know how to use it. And, I guess, if the transmitter hasn't been flooded.

Let's take a look at the data for the Las Vegas VOR:

Now, that does look like a lot of "unusable" radials, but it's not actually as bad as your friend claims. First of all, you're not "only" guaranteed service on legs of instrument approaches. You're also guaranteed service along Victor airways, and within a standard service volume. Think about it: certainly you can't expect to pick up the Las Vegas VOR in Florida. So where should you expect to be able to use it? The answer is on flight tested legs (approaches and airways) and within its service volume. According to the AIM, a VOR must "conform to flight inspection signal strength and course quality standards throughout the published SSV". The (H) after the VOR name indicates that Las Vegas is a high-altitude VOR. Let's look at its service volume:

Notice first that the service volume only has a radius of 40 NM to begin with at low altitude. Most of those cutout unusable radials reduce this to 35NM instead. So it's not that much of a cut. And above 16,500 feet? It's all usable, and that's where most of its service volume is. So in fact, the vast majority of the Las Vegas VOR's service volume is usable, that is to say, meeting FAA standards of signal strength and course quality.

Where it doesn't, it's usually because of terrain in the vicinity of the transmitter. As a radio signal, the VOR beacon bounces off of nearby hills and mountains.

Now, what does it look like to the pilot using the system if they're in one of those unusable regions and not receiving an adequate signal? VOR receivers are also FAA approved and if they are not receiving a strong enough signal with enough integrity, then they will display a flag. It should not present totally false data without a flag. The problem with your Ethiopian flight seems to be that the VOR transmitter was transmitting the wrong info, which of course the receiver can't know anything about and it did not flag.

That would be a pretty terrible scenario. That is not what is ever going on around Las Vegas. NAVAIDS in the USA are monitored for integrity. The worst that will happen in a receiver in Las Vegas will (hopefully) be a flag that indicates the receiver is not receiving an adequate signal.


Is it possible to fly with throttles staggered? Does the autothrottle realign the throttle lever positions? If the throttle is staggered, does it mean that there is an issue on the engines?

Yes it is possible - as mentioned in a comment, most multi-engine aircraft can (fairly) happily fly with one engine at idle or disabled entirely.

Some autopilots will use some asymmetric thrust for yaw trim, and others will use asymmetric throttle settings to compensate for the engines producing different amounts of thrust. Those sound similar, but aren't quite the same thing.

For example here's a description of that happening on the 777. Neither are ubiquitous and both depend on the aircraft.

http://www.flight.org/the-boeing-777-thrust-asymmetry-compensation-tac

Note that two engines can never be identical, there will always be some level of asymmetric thrust. Traditionally this was countered with rudder trim, but newer aircraft sometimes adjust the throttle instead, as per the above link


Why are non-essential passenger flights still being flown? I'm not asking about essential passenger flights like for "like food, supplies, and flying medical workers.

Oughtn't non-essential passenger flights have been shut down in North America, to curb the spread of COVID19? Have they truly not been grounded because

  The airlines wrote to Congress that they’d lose an additional \$7-$10 billion if there was a mandate airline shutdown.

and airlines are "afraid of losing routes and more money"?

As discussed in this question airplanes carry a lot more than just passengers so shutting down passenger flights can stop the flow of essential supplies as well as people. In some cases charter flights are being used during this crisis but the general movement of people (even essential people) often relies on commercial flights.

Similarly most states are issuing-shelter-in-place and stay-home-orders while it is only the federal government via the FAA that can totally shut down the airspace. Individual states, municipalities and private owners can shut down airports that they control but this may only stop flights in and out of those airports.

Its worth noting that airports in other countries are starting to shut down. It is more than likely flights will be seriously curbed as a result.


Why is the range of transponder digits 0 to 7 rather than 0 to 9? As a controller on IVAO I sometimes assign codes like 0168 and find out later that the code isn’t valid. For me, the range 0-9 seems more logical. Why do we have to use octal numbers and not decimal?

The four-digit transponder code that is entered by a pilot is an octal number rather than a decimal number, and in the octal numbering system, only the digits 0-7 are valid.

As far as why, internally it's actually a 12-bit binary number and octal works really well since can be used as a "shortcut" for entering groups of three binary digits at a time (000 - 111, which is 0-7 in octal).

If it were designed today, with the additional computing power and software complexity available, it would be possible to use a decimal number even if it is stored as binary internally, just so that it is more familiar.  At the time that the system was created though, changing the dials directly set the code in hardware and doing the conversion would have been much more complex / difficult / expensive.

In short, it was convenient for the engineers and manufacturers, and just an oddity for the end users, so they left it that way.


Why is deploying speed brakes not recommended with the flaps extended? I read this in the normal procedures section of the A320 FCOM. Why is it so?

  When the speed brakes are deployed, extending the flaps beyond FLAPS 1 may induce a slight roll movement, and in calm conditions a small lateral control asymmetry may remain until disturbed by a control input or by an atmospheric disturbance.

https://www.eucass.eu/doi/EUCASS2017-318.pdf

Above shows a configuration where the flaps and spoilers are deployed. The blue line shows the vertical velocity of the wing's wake, which is indicative of the lift being generated. Since the effect of the flaps lessens outboard, that causes the downforce shown above near the end of the wing due to the spoilers.

Since spoilers are thin and are allowed to move/flex slightly under aero loads, and since this downforce is far out with a greater moment arm, any slight [asymmetric] disturbance to any outboard spoiler panel will result in a roll, when compared to:

Smaller flaps deflection: since the inboard part of the wing creates less lift (less flaps), the slope (lift to downforce) will be shallower, which lessens the impact of an outboard disturbance.
Speed-brakes are used on their own: there will be a uniform downforce distribution over the wing without the abrupt shift from lift to downforce shown above.

Note that the manual says may and slight. Do not expect a huge roll, just anticipate if it happens, the FBW is not programmed to correct it unless an input is made.

I found the same recommendation in the FCTM of the 747-400 and 737 (all variants). It's flaps 5 and 15 respectively. They don't state the reason, but buffeting was mentioned.

  The use of speedbrakes with flaps extended should be avoided, if possible. With flaps 15 or greater, the speedbrakes should be retracted (737 FCTM).

@kevin also pointed out in the comments that the 777 explicitly states there is no issue with using the S/B in landing configuration, which to me sounds like extra care was taken with the FBW or spoiler design.

Another possible reason is to lessen the load on the actuators of the spoiler panels, with the flaps deployed that's a lot of suction behind them, but that doesn't answer the rolling part.


Does the wing to fuselage fittings of an airplane ever experience shear load? Do wing attach fittings of semi-cantilevered plane (i.e. ultralights) ever get subjected to shear force? For example during roll, does the centrifugal force of the wings load the wing attach fittings with shear?

In general, the answer is yes. The answer depends on the details of the fittings. Note that most realistic loadings are a combination of tension rsp. compression and shear. If - for example - the wing of your ultralight is held together by shear pins (note the name!) which are inserted in vertical (up-down) or horizontal (forward-backward) direction, they will transmit those centrifugal loads as shear from one wing bushing to the other.

The same goes for the transfer of lift forces inside the spar and - again, depending on the details - into the fuselage. The web of the spar is meant to carry the shear loads and those are transferred by ribs to the attachment points. Other designs use a front and rear spar which attach directly to the fuselage.

The picture shows the front spar attachment of the B-17 (source). Granted, this is not exactly an ultralight, but the same principles apply. At positions C, D and E it uses shear pins to transfer the lift loads into the fuselage bulkhead.


In a turbofan what holds the spinning axis? When the turbofan is spinning inside the housing, what holds the axis? All I know is that the axis holds the fan blades.

Stationary frames
The supporting structures of a turbofan are two stationary frames with their characteristic struts, located at the ends of the engine core: One is behind the OGV stator of the fan module, the other at the aft end of the turbine module:

CFM56 with the two frames visible (source)
Stationary frames to spinning shafts
In the case of an engine with two spools, the frames support the longest shaft (N1, low pressure), which in turn supports the coaxial N2 shaft (high pressure).

Shafts are centered within frames by bearings (drawn in magenta in the next picture).
Shaft to rotors
Disks of rotors on a spool are bolted together to form a continuous structure fixed to the related shaft. The structure is used as the inner wall for the related air duct:

Frames, shafts, bearings. Adapted from CFM56-7B Familiarization Manual
A view of the N1 shaft and the two frames, before adding the bearings and their oil sumps. The fan shaft (darker / trumpet-shaped) is fixed to the N1 shaft using grooves and can be considered part of the N1 shaft:

LP shaft, fan frame and turbine frame of a CFM56-7B
The bearings and the oil sumps are added to center the N1 shaft (blue tubes are used to pressurize air-oil seals of the fan sump). The clevises used to hang the engine under the pylon strut are (barely) visible on the top of the rear frame (see this question for details):

LP shaft, fan frame, turbine frame, bearings and sumps of a CFM56-7B
Another CG view which additional elements:

The fan disk bolted on the N1 shaft (actually fan shaft).

The fan cone and spinner bolted on the fan disk.

The two extremities of the N2 shaft coaxial to the N1 shaft.

Shafts of the CFM56-7B
The HP/N2 shaft (shown in red above) is centered on the LP/N1 shaft by bearings. All rotors of the HP spool form a single structure bolted to the HP shaft (shown in light blue below):

HP rotors of CFM56-7B. Adapted from CFM56-7B Familiarization Manual
Frames to core stators
Similarly, outer shrouds of stators and intermediate rings of a spool are bolted together to form continuous structures.
Four stationary structures are built:

The LP compressor (booster) stators assembly is fixed to the mid-box of the fan frame (on the fan side).
The HP compressor stators assembly is fixed to the mid-box of the fan frame (on the other side).
The combustion chamber is fixed to the HP compressor assembly.
The turbine stators assembly is fixed to the combustion chamber on one end and to the rear frame on the other end.

Overall CG view with some components highlighted:

CFM56-7B cutaway. Original CG model by vhfine3d, at DeviantArt
From frames to wing strut
The engine is supported by a pylon, which is supported by the wing. There are only two mount points connected to the pylon, located on the fan and rear frames. Thrust is usually transferred to the wing using the forward mount point.
If it is not practical to transmit the thrust from the forward mount, e.g. because space is lacking to build a strong mount, then thrust links are used to transfer thrust to the aft mount which transmits it to the pylon:

Sources: left, right
Other components
There are a few other components to support.

The air inlet is fixed on the fan case.

The fan case (which role is to create a duct for the fan and contain any broken fan blade piece) is fixed on the fan frame.

The nacelle, that is the fan cowls and the thrust reversers ducts, including the reversers, is fixed directly to the pylon. The nacelle is not really part of the engine.

The exhaust nozzle and cone are fixed to the turbine frame.

To sum up
Engine component are kept together using two frames.

Rotors are fixed to shafts, which are maintained within the frames by bearings.
Stationary components (fan case, stators, combustion chamber, etc) are bolted together and fixed the directly to the frames.


Are there security checks on private flights in your own plane? On commercial flights there are some "typical" security checks - metal detectors, luggage X-rays, etc. - are there similar security checks if you're flying in your own private plane?

Are there different or additional security checks when flying into other countries (such as a trip from Canada to the United States)?

No, at least not at the Class C and D airports I have been to. There is just a locked gate with an attendant who makes sure you are either flight crew or are boarding a flight. This is to prevent the possibility of a random person walking around on the ramp.

The PIC of the aircraft, of course, may question you ("your hunting rifle is unloaded, right?") or may search your bags or body cavities or whatever he wants to do before he will let you get on. It depends on the situation. For a charter flight normally they will just verbally talk to you to make sure you aren't unknowingly bringing anything dangerous aboard.

When you fly into a country from a different country, everybody has to go through customs. So, what happens is that you all wait around in the lobby of the GA terminal while some dude from the airport examines your customs forms and goes through your luggage. Sometimes they will search the whole plane too if they want to be dicks. In smaller airports, like in a Caribbean island, you will be routed through the same customs lines that commercial passengers use.


What causes Gusty winds? ( Meteorlogy) I was wondering why winds can become gusty. I know that gusty winds tend to be related with frontal passage. Thanks : )

Since you mention 'frontal passage' it is assumed that the term "air mass" is understood and also the reasons for the movement of air masses. The movement of an air mass relative to the earth's surface is what we, standing on the surface, physically feel and experience as wind.
There are things that affect the smooth flow of the air mass, such as terrain, pressure gradients, other air masses, man made obstacles etc. and these can occur at different scales. By this we mean at the continental/oceanic scale, down to the scale of human made buildings or small but significant natural outcroppings.
Localised and somewhat unpredictable short term disturbances to the smooth flow of the air mass are what we perceive as 'gusts'. Visualize it in a similar manner to the way flowing water is churned by an obstacle in its flow path and the factors that cause the churning. Try listing these factors for yourself, both for water, and for the atmospheric air.


Did the F-8 have a stall speed of 1.6x its landing speed? Wikipedia says that the F-8 was to have

  a landing speed of no more than 100 mph (160 km/h)

This web page says that the F-8 did have

  Stalling speed 157 mph.

The two don't explicitly discuss exactly the same thing, but I do note that e.g. the quoted cruise speed of 570 mph agrees on both. Unfortunately, neither page seems to specify the actual landing speed of the final aircraft.

From an aerodynamics perspective, this doesn't really make sense to me: it seems awfully difficult, to not say outright impossible, to have a stall speed that is significantly higher than the landing speed. Intuitively, the two should be just about the same, or the landing speed should be higher than the stall speed.

Did the F-8 actually have a stall speed of around 1.6 times its landing speed as suggested?
Is that even possible?
What were the stall and landing speeds of the F-8?

The stall speed your source is referring to may be the speed for a clean stall which means with the flaps are in flight position (= 0°).

Flaps on powered planes usually increase lift as well as drag. This means basically that you can fly slower and stall happens at a lower speed.

Here are the speeds from the F-8D flight manual (big pdf):

From the chart, in landing configuration with 19,000 lbs gross weight, the stall speed is ~113 knots.

  does ground effect come in to play for landing scenarios? – Owen

Ground effect reduces the touch down speed by reducing the stall speed below the value mentioned in the manuals.

The strength of the ground effect depends on the construction of the plane. Low wing planes have stronger ground effect then high wing planes.
This means that the difference of landing speed and touch down speed is grater for a Low wing plane. On the other  hand the ground effect increases the flare phase of the landing for a   Low wing plane.


Why don't airliners use in-air refueling systems? Right now if an airliner wants to fly a really long distance (eg., a Boeing 787 flying from Seattle to Tokyo), it has to load itself down with lots and lots of fuel, which in turn weighs thousands and thousands of pounds.  This, of course, makes the flight of the aircraft less efficient than it could be1.  Thus, if the craft could theoretically carry half as much fuel, that should increase the fuel efficiency of the craft, right?2

Mid-way refueling seems like it would be a Good Idea™ at that point.  Of course, landing would add a heck of a lot of time to the flight, so it seems the better option would be mid-air refueling.  It would allow for the aircraft to be more efficient, without the need for stopping on a long journey.

Boeing and Airbus both make a few airplanes | that can do | mid-air refueling, in fact one of them is a highly modified 747-200 (properly called a VC-25) used as Air Force One:

(source: wordpress.com)

I assume that, because Airbus and Boeing's engineers and sales managers are really quite smart, they have a really good reason that they don't fit/sell this feature on any civilian transportation aircraft.  But I'm not sure what that reason is.

Does anyone know why airlines do not use aircraft that are capable of mid-air refueling?

1 If I'm not mistaken, increased weight means an increased AoA to maintain level flight, which in turn increases induced drag from the wing.  Less fuel would mean less induced drag or, if mid-air refueling were common practice, a wing that was designed to be more efficient because it was required to handle less weight.

2 I don't know by how much, if it's not that much, well, that might explain why nobody does this.

Fuel Quantity Unlike smaller fighter jets, you would need to offload a substantial quantity of fuel. For a B777, you're looking in the range of 60 tonnes of fuel for half a tank. The boom of a KC-135 (faster than a basket) can do around 3 tonnes a minute. The math comes to then 20 minutes of aerial refuelling. The KC-46 can do perhaps 180 tonnes, so you might squeeze out three refuelling operations from one flight.

Risk This is considerably more dangerous than the very conservative safety margins aircraft normally operate within. You would have one aircraft filled to the brim with fuel, and another aircraft with 300+ passengers. A quick search on YouTube is enough to propose this entire thing is very dangerous.

Furthermore, you need to consider that the aircraft needs safety margin to divert should refuelling not work, which cuts into the benefits you can expect.

Many intercontinental routes will be flown at night, making the manoeuvre more difficult.

Refuelling Area Looking at the route you proposed, the closest airfield would probably be in Alaska, at least 500km away. Guess another relevant area would be Iceland/Greenland. Even if you did reroute, you'd get away from the jetstreams that aircraft over the Pacific use lying considerably further south, reducing efficiency. The same scenario applies for eastbound Atlantic flights.

Expensive You would need to get another aircraft (~$200m for a KC-46) with special equipment and crew training. The receiving aircraft crew would also  need special training. The airframe modifications would be complicated and require certification. Furthermore, you would need to get everybody to agree on some common standard.

Logistics Planning is difficult. Each aircraft would have to be rerouted to intercept the tanker at a certain time and place. You want to refuel them perfectly one after an other, which is almost certainly not possible. There's just not the volume of aircraft movements feasible for this, especially for the ultra-long flights where it may have the greatest benefit.

Other Landing Benefits
Include changing crews and possibly offloading passengers.

Applicability
The number of flights where this can be practically implemented and used is very limited and for all intents and purposes, you can just land the plane itself and refuel it. Even for the route you propose, it's around 7,500 km which is not a lot for a B777.


Would a takeoff be aborted if 'rotate' is not called out? As captain of a Boeing 747 on a take-off roll I am expecting my co-pilot to call out V1, Rotate, but he does not call out rotate. Do I abort the take-off?

That could end up being a really bad idea if you've accelerated past your V1 speed -- your abort would then put you off the end of the runway, and the consequences from that range from bad to catastrophic.

A much better idea would be to look at the markers on your airspeed indicator, and if you're at/above rotation speed, go ahead and rotate.  Then sort out what's up with your copilot.

The worst case is, he's incapacitated, unconscious, experiencing a stroke or heart attack or something similar, and you'll probably end up returning to land as quickly as possible.  While the idea of staying on the ground to get him EMS help sooner might seem to be appealing, he'll probably NOT get better attention if your aircraft just ran off the runway, through the airport fence, and into whatever terrain/water/civilization lies beyond, because you didn't start your abort until several seconds after you should have been flying.  Better to come back and land with ONE sick person on the airplane, rather than crash, making your copilot now one of potentially MANY injured/scared/incapacitated people on a damaged jet -- and he with the very least ability of any of them to evacuate himself!

Or, maybe he got distracted and he's fine, and after he overcomes his embarrassment for missing the important callouts, the rest of the flight will go fine.

So, no, if the copilot doesn't call "V1, Rotate" I would NOT recommend aborting the takeoff.  If you see him slumped over when he should be making an "80 knots" or "airspeed alive" call, that might be a different decision; at that sort of speed you're in no danger of running off the runway & you could probably taxi back to the gate promptly.  But if he's missed his calls at significantly higher speeds, aborting is a bad plan.


Is it normal ops to dispatch an airplane after a stick shaker was on throughout the previous flight (Lion Air 610)? I've been studying Figures 5 and 7 of the Lion Air interim report and cannot understand why the airplane was dispatched on the "Loss-of-control" flight when the Left stick-shaker was on throughout the entire previous flight (Figure 7). Can this occur in normal operations everywhere?
I have no experience with ground operations (just 35 years with design of flight control equipment), so I'm asking the airline folks here. (I understand that often multiple causes lead to a crash, so I'm looking for understanding, not blame.)

Well, if the shaker was running abnormally like that, the crew would have done a QRH procedure, if any, for that condition, and reported the snag at the next stop, and something would have been done by maintenance to release the plane.  Like a part was changed, or the problem went away and couldn't be duplicated after a test was done on the ground, whatever was required to get a maintenance release.  It would have to have been released as serviceable, one way or another.


Can I do a dual VOR check on the ground? I know that the regs are ambiguous on the subject, but does anyone have a good argument as to why or why not you can do a dual VOR check on the ground if the VOR signal is good?

For my particular situation, I'm at KRDM which is about six miles from the DSD vortac. There is a clear line of sight to the station, but the airport is a couple hundred feet lower than the VOR.
Seems to me that a dual ground check would be fine since no flags are visible and the station can be identified, but I'm not sure.

Be careful performing a dual VOR check on the ground, especially if you are located near other aircraft or buildings that may interfere with the signal.  I have performed a VOR check on the ground at a few airports around the Southwest, and I have found that you can get erroneous readings, on the ground, compared to performing the dual check in the air. I would say its more accurate in the air.
As for how to log it. DATE, PLACE, ERROR, and SIGNATURE. Place, meaning the VOR station identifier. 91.171(d)


How is a plane with only ailerons and jet (no props) controlled? I saw this video and was wondering how he is controlling the plane:

It looks like he only has ailerons. It does look like he is shifting his body weight. Is that the answer? If so, that's pretty surprising! But I guess it's like a hang glider?
Does anyone know how you should shift your body to increase/decrease pitch, and increase/decrease yaw?

The ailerons in most flying wings can also move together up and down, then working as an elevator. This is called an "elevon", combining both words as the device is combining both functions. Since flying wings mostly use reflex airfoils, loads on the rear part of the wing tend to be small and the force to keep elevons at their right deflection is small, too. In case of the SB-13, they are pre-loaded by a small, adjustable spring but otherwise free-floating.
In this case, however, it could be that they only work as ailerons.
When used for pitch control, elevons must move up and down together on both sides. This means they will be freely floating and must be held in position by some force. It would be easier to cross-link them so they only can move against each other, and then they only work as ailerons.
The airplane, called OpenSky M-02, is the brainchild of Tokyo University of the Art professor Kazuhiko Hachiya and has been built by Aircraft Olympos of Japan. OpenSky M-01 was a lighter, unpowered version.
As Louise Hose writes on Kitplanes:

Hachiya designed the project and is the only pilot to fly the resulting “Open Sky M-02J”. He started with a hand-launched, scale model to test the airfoil characteristics. Once he was satisfied with the basic design, he partnered with aeronautical engineer Tota Ueno of Olympos Company in Tokyo to scale up to a glider capable of carrying one person…Hachiya himself. The glider, first flown in 2006, was launched from the ground by teams of people pulling a bungee cord. Once satisfied with its flight characteristic, Hachiya and Ueno worked to find the “right” engine to add as the powerplant. Between 2010 and 2013, they were doing high-speed taxi tests and working through issues…particularly powerplant and regulatory issues. They ultimately decided to use the NIKE jet engine made by AMT Netherlands which produces 176 pounds force. The jet was designed and mostly used in target drones.

At least the model couldn't be steered by weight shifting, and looking at the harness of the pilot, his capacity for weight shifting is rather limited. My impression is that weight shifting is primarily used for ground control. If you watch the YouTube movie, it becomes apparent that he is barely capable of controlling the direction on the ground, and has to lean to the left on take-off to prevent it to escape the runway. Also, his movements are more sideways than back-and-forth. The control surfaces hardly move, but show linkages on the bottom side, so they are moveable. If you look closely, you can see pulleys on the left and right of the pillow Hachiya-san is lying on, and as @quietflyer says, they should control the elevons, but he adds his weight to help controlling both pitch and roll.
Louise Hose of Kitplanes again:

To date, Hachiya has made about 150 “jump” flights and 70 circling flights. He has flown it up to nearly 500’ agl but believes it can fly much higher. (Airspace restrictions in Japan have prevented him from trying to fly higher.)


Guidelines for using a constant speed/adjustable pitch propeller I have been trained in a single engine fixed pitch prop ( C152). I'm trying to move to Piper Arrow II which has an adjustable pitch propeller. I understand how constant speed propellers work. I'm trying to understand how to use this new feature in cruise flight.

My understanding is that in the highest RPM configuration, the propeller will provide the highest thrust. This implies that the lower RPM will result in lower thrust ( true? ). If the objective is to get to the destination in the shortest possible time ( the most common objective ) why would anyone want to mess with the pitch of the propeller?

I understand that using a lower RPM may have other advantages like lower engine temperature, lower noise and possibly longer engine life. I'm hoping there is an answer like: ( you can reduce the pitch but maintain cruise speed ..) :) OR for a significant reduction in noise level you will sacrifice 5kts in speed.

This answer doesn't answer my question.

why would anyone want to mess with the pitch of the propeller ?

A propeller runs at its highest efficiency when used at a particular combination of forward speed and RPM. By changing pitch, you change this combination, so the best efficiency can be shifted over a range of airspeeds.

For the physical background please consult this answer.

  This implies that the lower RPM will result in lower thrust ( true? )

Yes, lower than maximum thrust. If you need less than maximum thrust, a lower RPM is sensible to reduce engine wear. Reduce RPM only if the remaining prop speed can still absorb the power; in other words, make sure the RPM is high enough to allow the engine to run at the speed needed for the desired power. But do not control thrust with RPM - this is what the throttle is for.

A piston engine outputs a constant amount of power, regardless of airspeed. This power output grows about linearly with engine RPM. You control this power with the throttle (and measure the power indirectly with the manifold pressure) and use the prop pitch to allow the engine to run fast enough to create the desired power at all. If you run the prop faster by reducing pitch, it will operate at a blade lift coefficient which is lower than that of optimum blade L/D, so you lose efficiency. Also, the engine will run faster and be in the partial-load operational range where it also runs less efficiently. Run the prop slower by increasing pitch and you will slow down the engine so it cannot produce the desired power. Also, now the propeller will run at a higher lift coefficient, efficiency will drop and part of the prop blade might even stall if you increase pitch too much.

As to what is a significant reduction in noise: This is subjective and I advise you to find out for yourself.


How is the marine perimeter of a coastal airport secured? Nice Côte d’Azur Airport is bounded on three sides by the sea, which is infested with oligarchs screaming around in powerboats and industrialists on huge yachts, all in close proximity (meanwhile the airport is full of their private jets).

A lot of this and other incessant marine activity takes place within swimming distance of the edge of the airport itself. The airport looks remarkably vulnerable to someone who could in effect simply swim up to the edge of the runway.

How is the security of this apparently porous perimeter, and that at other airports in similar positions, maintained?

Often time there will be a fence installed as is the case at Maho Beach where people line up at the fence to get up and close to takeoff. The fence appears to have what looks like barbed wire on top.

If there is not enough clearance markers in the water may denote an area for boats to stay out of. Such is the case in St Barts. Aside from creating something a prop can snag these provide little security.

Assuming its a controlled airfield there is a good chance the controller in the tower can physically see the coast (with binoculars). If you floated up in any boat of size there is a good change you would simply be seen.

If you are talking about the departure end of the runway, it can also be difficult to just walk up to the back of a spooled up jet.


How do turbofans and piston-engines compare in terms of maintenance costs? I want to compare piston engines and turbofans on a maintenance basis. Let's say both engines are capable of 100 kN of thrust. Let's say both engines fly for 10,000 hours.

Over that time, what kind of maintenance can we expect from those engines. In particular:

How many times will the engine need major servicing?
How many man-hours does that servicing require?
About how much does it cost to do that servicing?

Major servicing for a piston engine would be something more than an oil change. For a turbofan it would be an overhaul.

Come to think of it, I don't know exactly what kind of servicing goes on for a piston engine other than an oil change. Is it like an overhaul where you dissasemble it and make sure everything fits together properly?

In case you're wondering, I'm envisioning these engines in a commercial cargo role. So no excessive dirtiness or hard throttling.

Your question has some areas that depend on circumstances, models, etc. but to answer in general:

Piston engines are generally fully overhauled every 1200 to 2000 hours or so. Time to overhaul one varies with the engine model, and where the overhaul is done, as it can be done at the factory, at a repair shop, or by a qualified A&P/IA (a field overhaul). A piston engine overhaul can cost as much as $25,000 or more.
Turbofan engines will likely not require major service during those 10,000 hours. Most turbofan engines are inspected regularly and continue to operate on condition unless manufacturer recommended time periods are reached or exceeded. Time to overhaul varies greatly by engine model. Costs vary greatly as well, but in the case of turbofans you're talking in the hundreds of thousands of dollars.


How is the zero-lift drag coefficient calculated? The drag coefficient is usually given as a funtion of the lift coefficient and the zero-lift drag coefficient ($c_{D0}$):

$c_D=c_{D0}+k\cdot c_L^2$

How can I calculate/estimate $c_{D0}$?

You can look it up in reference books. For wings, the NASA report server is your friend. For complete aircraft, there is some data available in books about pre-design of aircraft. The one I have is Synthesis of Subsonic Airplane Design by E. Torenbeek, and gives the following numbers for $C_{D_0}$

0.014 - 0.020 for high subsonic jet aircraft
0.018 - 0.024 for large turboprops
0.022 - 0.028 for twin engine piston aircraft
0.020 - 0.030 for small single engine aircraft, retractable gear
0.025 - 0.040 for small single engine aircraft, fixed gear
0.06 for agricultural aircraft without spray system
0.070 - 0.080 for agricultural aircraft with spray system

Appendix F of the same book gives a method for more detailed estimation in the pre-design phase, when no wind tunnel data is available, based on data of the components that make up an aeroplane.


What materials are suitable for making a mini gas turbine engine? What materials are suitable for a mini/model gas turbine engine, specifically the fan, compressor, combustion chamber and turbine?

Materials are one thing. You also need tools and machinery to build one: the turbine and compressor in a mini jet engine rotate at ~100,000 rpm so they're subject to significant stress. They have to be balanced perfectly.

If you want to build one yourself, look into using a turbocharger from a car engine as the core. That gives a decent base for the high-temperature parts of the engine. Others have built DIY jet engines from turbochargers.


Why would engine fire cause loss of control? I was wondering why engine fire would cause of loss of control or crash. There is loss of power and even drag. But could some expert please expand on the troubles of a engine fire?

In general, an engine fire in a modern jet airliner should not cause a loss of control.

Even though engine fires are rare, pilots are highly trained in dealing with them. Once detected, pilots are able to cutoff the supply of fuel and hydraulic fluid to the engine, and then discharge fire extinguishing agents. Even if the fire was not extinguishable, it would most likely not damage the wing structure or controls since the heat and flames would be directly away from critical systems by the forward movement of the aircraft.

An "uncontained" catastrophic engine failure where parts of the engine penetrate the aircraft wing and fuselage could possibly cause major damage to critical systems. There have been some incidents of uncontained failures that resulted in a loss of control and fatalities.

Here is a list of Notable uncontained engine failure accidents

Three of these accidents resulted in a loss of control and fatalities. The most notable was United Airlines Flight 232 where the failure of the rear General Electric CF6-6 engine caused the loss of all hydraulics forcing the pilots to attempt a landing using differential thrust and resulted in 111 fatalities.


What is the structure of the crew documentation used in flight for a commercial aircraft? Common documentation easily found online (using A320 family as an example):

Flight crew operating manual (FCOM, multiple volumes)
Flight crew training manual (FCTM)
Standard operating procedures (SOP)
Quick reference handbook (QRH)

(Source)

What are they used for? What are the other major documents necessary to fly? Do they differ with manufacturers or airlines? Are they available on paper or display?

The documents legally required on-board differ by jurisdiction. I can only speak to the case here in the US which falls under the FAA. If the flight is between two jurisdictions there may be local regulations to comply with at your destination as well. For example if leaving the US all onboard must have their passports as well as any pertinent custom forms.

  What are they used for?

Generally these documents are all used for reference. Here in the US its generally forbidden to read personal material in the cockpit however the pilots are free to read documentation relating to the aircraft and operations. They may chose to use time in flight to read up on things.

These documents also include emergency procedures that the crew may need to use in the event of a failure.

  What are the other major documents necessary to fly?

Aside from what the plane needs the crew must also have current medical certificates and pilots license on their persons.

If we take a look at FAR 121.135

  (a) Except as provided in paragraph (c) of this section, no
  certificate holder may operate an aircraft unless that aircraft—

    (1)
    Is registered as a civil aircraft of the United States and carries an
    appropriate current airworthiness certificate issued under this
    chapter; and

    (2) Is in an airworthy condition and meets the applicable
    airworthiness requirements of this chapter, including those relating
    to identification and equipment.

  (b) A certificate holder may use an
  approved weight and balance control system based on average, assumed,
  or estimated weight to comply with applicable airworthiness
  requirements and operating limitations.

  (c) A certificate holder may
  operate in common carriage, and for the carriage of mail, a civil
  aircraft which is leased or chartered to it without crew and is
  registered in a country which is a party to the Convention on
  International Civil Aviation if—

    (1) The aircraft carries an
    appropriate airworthiness certificate issued by the country of
    registration and meets the registration and identification
    requirements of that country;
    (2) The aircraft is of a type design
    which is approved under a U.S. type certificate and complies with all
    of the requirements of this chapter (14 CFR Chapter 1) that would be
    applicable to that aircraft were it registered in the United States,
    including the requirements which must be met for issuance of a U.S.
    standard airworthiness certificate (including type design conformity,
    condition for safe operation, and the noise, fuel venting, and engine
    emission requirements of this chapter), except that a U.S.
    registration certificate and a U.S. standard airworthiness certificate
    will not be issued for the aircraft;
    (3) The aircraft is operated by
    U.S.-certificated airmen employed by the certificate holder; and (4)
    The certificate holder files a copy of the aircraft lease or charter
    agreement with the FAA Aircraft Registry, Department of
    Transportation, 6400 South MacArthur Boulevard, Oklahoma City, OK
    (Mailing address: P.O. Box 25504, Oklahoma City, OK 73125).

  Do they differ with manufacturers or airlines?

Airlines may publish excess documentation and checklists that meet or exceed the manufacture specifications this some airlines may have slightly varying procedures. Aircraft makers must publish documentation for the aircraft that includes its operational limitations you can find a good chunk of the regulations in the FAR's here. Specifically,

  §23.1581   General.

  (a) Furnishing information. An Airplane Flight Manual must be
  furnished with each airplane, and it must contain the following:

  (1) Information required by §§23.1583 through 23.1589.

  (2) Other information that is necessary for safe operation because of
  design, operating, or handling characteristics.

  (3) Further information necessary to comply with the relevant
  operating rules.

  (b) Approved information. (1) Except as provided in paragraph (b)(2)
  of this section, each part of the Airplane Flight Manual containing
  information prescribed in §§23.1583 through 23.1589 must be approved,
  segregated, identified and clearly distinguished from each unapproved
  part of that Airplane Flight Manual.

  (2) The requirements of paragraph (b)(1) of this section do not apply
  to reciprocating engine-powered airplanes of 6,000 pounds or less
  maximum weight, if the following is met:

  (i) Each part of the Airplane Flight Manual containing information
  prescribed in §23.1583 must be limited to such information, and must
  be approved, identified, and clearly distinguished from each other
  part of the Airplane Flight Manual.

  (ii) The information prescribed in §§23.1585 through 23.1589 must be
  determined in accordance with the applicable requirements of this part
  and presented in its entirety in a manner acceptable to the
  Administrator.

  (3) Each page of the Airplane Flight Manual containing information
  prescribed in this section must be of a type that is not easily
  erased, disfigured, or misplaced, and is capable of being inserted in
  a manual provided by the applicant, or in a folder, or in any other
  permanent binder.

  (c) The units used in the Airplane Flight Manual must be the same as
  those marked on the appropriate instruments and placards.

  (d) All Airplane Flight Manual operational airspeeds, unless otherwise
  specified, must be presented as indicated airspeeds.

  (e) Provision must be made for stowing the Airplane Flight Manual in a
  suitable fixed container which is readily accessible to the pilot.

  (f) Revisions and amendments. Each Airplane Flight Manual (AFM) must
  contain a means for recording the incorporation of revisions and
  amendments.

  Are they available on paper or display?

Depends on the carrier, a great deal of movement to iPads and the such has seen the digitization of many things.


What is the main reason of air-cooled radials producing much less HP/L compared to liquid cooled Vs? Is it because of the inherent limitations of cooling the cylinder walls, only 2 valves per cylinder, relative ease of scaling up instead of dialing up the boost, or some other reason?

I read somewhere once, maybe I can find it again, but it is because of the inherent limitations of cooling the cylinder walls. Air cooling is not as controllable, because the temperature of the air varies with altitude and season. Hence, the temperature of the cylinders in an air cooled engine are not as tightly controlled as a liquid cooled engine. So, the cylinders need to be able to operate over a greater temperature range. Since metal expands with temperature, that means the gap between the cylinders and the bore is typically greater in an air cooled engine than a liquid cooled one. So, this greater gap, even with piston rings means some of the cylinder head pressure after combustion escapes rather than act on the piston. Makes sense to me...


Does angular momentum contributes in lifting a helicopter? I want to know whether it is possible to make a helicopter with blades that rotate counter-clockwise (CCW) seen from below. I have difficulty understanding the angular momentum in this situation.
As we may see in the picture below, the rotor rotates clockwise (CW) seen from the pilot seat look up. So far, the rotations I have seen. To extend this question: is it possible for a single engine airplane to have propeller rotating counter-clockwise (CCW) seen from the rear, looking in the direction of the nose (as so far, what I found is that every single engine airplane is rotating CW). As we know from physics, the angular momentum of a CW helicopter will be pointing up, and the angular momentum of a single engine with CW rotation is pointing forward. To be clearer: Is there any impact (i.e. power efficiency, etc) if a helicopter's blades rotate CCW (seen from below), or if a single engine plane's propellers rotate CCW? Of course their torques will be different, but it is not the case in my question as long as it is not affecting the performance (i.e. reduce the power efficiency, etc).

Picture source: Picture 1, Picture 2;

Well helicopters are designed with both types of rotor systems.  American built helicopters have main rotors which rotate counter clockwise whereas European built helos have clockwise turning rotor systems.  Near as I know there is no particular advantage to one over the other, though you do have to reverse anti torque pedal corrections for collective inputs on a CW turning rotor system vs a CCW system, transverse flow effects are reversed and LTE events are more likely from right vs left crosswinds.
Just to be clear, torque is VISUALIZED as a vector perpendicular to the plane of rotation; it is not a force.  If the latter were true, you could propel craft to the moon and beyond using just a gyroscope.


Which are the largest planes to have operated on an aircraft carrier? In 1963, the C-130 was tested by the US Navy for air carrier operations. Have there been any other comparable or larger aircraft that have landed and taken off from the deck of an aircraft carrier?

By large, I am referring to two parameters: wingspan and weight.

U-2s also landed and took off from aircraft carriers.


What direction should a traffic pattern be at an uncontrolled or non-towered airport? What is the standard direction for a traffic pattern at an uncontrolled or non-towered airport?

When aviation literature mentions "the standard traffic pattern", it's usually a left-hand counterclockwise pattern; regardless of wind direction, the runway will always be to your left side and you make left turns to follow the pattern through crosswind, downwind and base legs. This is the default pattern direction when there are no overriding signals.

However, this is only the default, and airports are free to change the procedure as needed to comply with local terrain or development. An airfield near a neighborhood to its east, for instance, may require that traffic circle around the west side of the airport; therefore this airfield's 17/35 runway will require a left-hand pattern when using runway 35, but a right-hand pattern when using runway 17.

When an airfield establishes a non-default traffic pattern, they must provide this information to pilots in a readily-visible manner. The standard recommended (though not required) set of runway and pattern indicators is known as the segmented circle, so called because its most visible identifying feature from a distance is a 75-foot circle of dashed lines:

In the center of the circle as pictured is the runway direction indicator aka the tetrahedron; this will indicate which strip of asphalt to use and which direction to take off and land on it (the narrow end points in the direction that planes should take off and land).
Off to one side is the windsock, which is the only piece of equipment that is required at any airfield; it indicates approximate wind speed and direction. FAA guidelines for the sock say it should reliably turn to the wind direction at 3 knots, begin to inflate at 5 knots and be fully extended at 15. The windsock can replace the tetrahedron in the center of the circle; in that configuration you would simply approach the airfield using the runway closest to the direction in which the tip of the windsock is pointing (if winds are calm and/or the airfield has multiple runways, the tetrahedron is preferable).
On the ground just outside the segmented circle are L shapes; these are the pattern indicators, and point in the direction of the base leg when approaching the runway from that end (so if you're following the pattern, the end of the L should be pointing at you before your turn to final).

So, the circle in the above picture tells aviators several critical things without any human (or computer) having to relay the information vocally:

The approach direction is from the upper right to the lower left of this picture.
The wind is roughly in line with the runway, so no crosswind landing procedure is required.
Winds are very strong (the windsock is fully extended which indicates wind speeds in excess of 15 knots) so ground speed will be much lower than IAS at takeoff and landing.
Most relevant to your question, airfield traffic should be on a right-hand pattern at this time; if the winds and thus the runway in use were opposite, traffic would use a left-hand approach.


Does Daylight Saving Time affect the flight time? Say an example flight FRA-LHR, was scheduled say 9am every day. Now will that flight be then moved to 10am once the change to DST happens or will it remain at 9am?

I would expect the flight times schedule to remain the same i.e. the daily morning FRA to LHR flight will be always departing at 9am (independent of summer/winter time changes). My knowledge in this area is limited so I wanted to know what the experts on this site say.

My question is more directed at the flight schedules i.e. the daily flight scheduled at 9am for example - does it undergo schedule change and is moved to 8am/10am or is this time fixed (underlying assumption being: in general a flight is scheduled for a certain time to meet a demand, so moving the local time is not necessarily feasible).

It will affect scheduled flight times the same way it will affect your favorite TV show's air time.

i.e. it won't*

It will affect apparent flight duration if the departure and arrival airports switch to DST on different days of the year, but actual time in the air will remain the same.

* The caveat for that is if you happen to be in an area that A) does not switch to DST and B) your favorite TV show happens to be broadcast from an area that does switch to DST. (This situation happened every year in Indiana for many years until IN joined the 19th** century and switched to DST in the summer.)

** Yes I know that DST was a 20th century invention, it's just that Indiana is a bit behind the times...


What is the length of the escape rope in the cockpit? specifically A330-300 (If possible) I understand you could measure from height of the cockpit window, but is there any official dimensions stated anywhere such as FCOM or FCTM documents?

For the A320, this can be found in the CCOM (Cabin Crew Operation Manual)...

So the A320 is a 5.5 meter (17.04 foot) knotted rope stored above the side cockpit windows. There are 2 ropes in the cockpit (one on each side).

I can't find the CCOM for the A330 but it should be a similar size.


How many planes did the Soviet Union lose to Stinger missiles during Afghanistan War? I have read Wikipedia articles about the war in Afghanistan, and it is often said that the Stinger had a great impact on the air mobility of the Soviet military.

Beside the role of interdiction (A2AD) of the helicopters to go to the mountains and deliver assault and special troops, did the American-built missile destroy or damage a lot of airplanes and helicopters?

What sort of technologies and tactics did the Soviet Union deploy to avoid being shot down?

This quotes an estimate of 269 aircraft, but I think its hard to find the exact number:

Kuperman, Alan J. “The Stinger Missile and U.S. Intervention in Afghanistan.” Political Science Quarterly, vol. 114, no. 2, 1999, pp. 219–263.


Why is the wing bending so much in this video? On a recent vlog, YouTuber CGP Grey mentioned how much the wing of the plane he was on bent. I understand that wings are designed to bend a little,  but what actually causes so much deformation?

Here it's a video of it:

Why does this happen?

Because that wing is a cantilevered beam which is now supporting over half the weight of the jet on it.  This causes the wing to flex, much like a leaf spring, when loaded.  While fascinating to watch this is benign and designed to do this.  In addition, this wing flexure helps to absorb bumps, air turbulence, dampen flutter, maneuvering loadings, etc. much like the coil springs in your car's suspension do.  Don't be alarmed to see this.  Those wing structures have been tested to far worse loads and conditions that you will ever see on a revenue carrying flight before failure occurs.  A 747's wingtips can flex by as much as 12ft up/down during flight.  Newer composite wings are capable of much greater flexure.

This was video shot of Boeing's destructive testing on the 777 wing.  Note the wingtip flexes by as much as 20ft upward at a loading over 150% that of its design load limits before structural failure occurred.


Why does using carburetor heat increase fuel consumption? As written above, why does using carburetor heat increase fuel consumption? Because I found such information in a few SOPs for piston airplanes and I do not understand why does it happen

I can think of two reasons:

The efficiency of heat machines depends on the difference between lowest and highest temperature in the cycle, relative to the highest temperature, as formulated first by Sadi Carnot. Simply put, the efficiency cannot be larger than $$\eta_{max}≤\frac{T_{max}-T_{min}}{T_{max}}$$
where all temperatures are expressed relative to absolute zero. If the entry temperature $T_{min}$ is raised by carburetor heat, the value of $\eta$ will drop. For the nitpickers: Piston engines are best described by the Otto cycle which uses an isochoric addition of heat and is a bit more messy to describe than the ideal Carnot cycle. If you want to include Diesel engines, use the Trinkler or Seiliger cycle.
With the higher entry temperature, all temperatures in the cycle are higher and you need to lean less in order not to exceed the desired cylinder head and exhaust gas temperatures. More fuel is needed for cooling, so the richer mixture will drive up fuel consumption.


AWACS - what do these antennas do? In a press release for a new Boeing "wingman" (BATS) drone being built in Australia, a closeup of this Australian AWACS flying in formation was provided. What would be some of the specific uses for the antenna farm located all over the fuselage?

The image below labels each of the antennas. To summarize based on your groupings:

A: Multi-Role Electronically Scanned Array (MESA) made by Northrup Grumman. It has a similar role to the large rotating dome on the E-3 in tracking airborne targets. Instead of being rotated mechanically, it can be electronically scanned.

B: Communications/Navigation, GPS, ELT (emergency locator transmitter)

C: Missile warning, infrared countermeasure

D: Electronic surveillance

E: Communications

F: Communications

G: Communications/Navigation

H: Missile warning, electronic surveillance

Source


Is this photo of an aircraft in a flood genuine? I stumbled upon this picture somewhere on the internet:

I don't believe an aircraft would be able to take off like that; I also don't expect a normal landing be allowed if this were on a runway. I suppose, in case of emergency, it could possibly land into such water. Generally, I think that either this picture is fake or the aircraft was parked at a stand before the area was flooded.

Unfortunately, as the picture was so small, it's virtually impossible to see any details, and thus difficult to analyse for "fakeness". Could this picture possibly be real?

Yes, the photo is a "Fake".

The photo was taken by Gary Watt of Aberdeen Scotland and then photo-shopped using the  "Flood Filter".

PPRUNE explanation

  Hi all
  Amazing how this image gets around after posting it to someone some months back.
  Yes, it's a fake. It's my photograph taken at ABZ and the 'Flood Filter' done in Photoshop.
  Great tool and can produce some fantastic effects.
  For all the doubters, the engines ARE running as it was taxiing to 34 for departure.
  I can still confirm it\'s fake and if anyone else thinks different, ye need yer heids examined
  Cheers
  Gary Watt


How do pilots decide what their cruising altitude will be? When filing a flight-plan for a long-haul high-altitude IFR flight, how do pilots select a specific cruising altitude? Typically in the range of 25,000 - 35,000 ft.

As has been stated, ATC will assign you an altitude, taking into account your requested altitude, traffic conditions, and of course the FAR.

Peter's formulas will apply from a design standpoint. The aircraft designer will use something like that to calculate typical values, which will be included in the aircraft's operating handbook.

The table below is listed by pressure altitude and gross weight. At each combination there will be performance values such as:

Average N1 (for a turbine)
Max TAT for thrust rating
IAS Knots
Mach number
ISA fuel flow LB/HR/ENG
ISA TAS Knots

The flight distance will determine the approximate gross weight, which corresponds to an altitude and cruise speed that provide the best efficiency. Here is an example from a virtual 737 handbook, with the values I listed. The optimum performance is in blue. Higher gross weights have been removed for clarity.

Airlines may have their own performance tables, choosing a custom balance of efficiency and speed. Dispatchers for the airline will take the flight information and decide on a cruising altitude for filing the flight plan, which the pilot will then receive. As you can see, as the aircraft burns fuel and gets lighter, it will be more efficient at higher altitudes. This is the step climb that Peter mentioned, where the aircraft will climb to higher altitudes as the flight progresses when they are cleared by ATC.

Modern planning systems can take into account weather factors such as winds aloft and turbulence to pick the most efficient route.


Can military officers change occupation to become pilots? From what I have read, the paths to become a fixed-wing pilot in the Air Force, Navy, and Marines, are to go to a military academy, enroll in ROTC in college, or go to an officer training school after earning a bachelors degree. In any case, a person will know if they are going to become a pilot before they become a part of the military.

For someone who is willing to become an officer in the military but is not offered a pilot slot when they join, is it possible for them to change their occupation before their contract has ended?

In the USAF, it has, historically, been common for rated Navigators to be selected for pilot training, and possible, though less common, for young officers in other career tracks as well.

That said, this process is

competitive (so certainly not guaranteed for a particular individual), and
dependent on the "needs of the service", so what is going on "now" may be entirely different from what was going on "then".

Also, the demand for UAV operators may have changed this dynamic considerably; it may be a far different process to become a "drone pilot" from a non-rated field, than to become a "real pilot."  Talking with active duty officers (not recruiters) who are up to date on this landscape is indispensable for getting the most current picture.


Is ADS-B UAT required below 18,000 ft for ADS-B ES equipped aircraft? If an aircraft is flying in the USA with 1090 MHz Extended Squitter (ES) and it is below 18,000 feet, does it then need to also have 978 MHZ Universal Access Transceiver (UAT) so that aircraft flying below 18,000 equipped with 978 MHz (UAT) can detect it?

No. ADS-B ES equipped aircraft do not have to have UAT to allow ADS-B UAT equipped aircraft to 'see' them. Below FL180, they are tracked by ATC radar and their track is translated and re-transmitted to UAT equipped aircraft via TIS-B service. More information, as well as coverage maps are available at the NextGen ADS-B site.


Is this a Convair C-240? This aircraft is at Dodson International in Rantoul, KS. I've boiled it down to Convair. Looks most similar to a C-240. And does anyone recognize the livery?

It has USAF painted in the top of the right wing, as can be seen from satellite at 38.541248,-95.103554

N43941 (USAF 53-7801) Convair C-131B.

Link to history.

It saw better days:


Why on weather surface charts high pressure is blue and low pressure is red? Is there any relation with the temperature of the air or is it just a standard procedure?

Red/blue for pressure is in no relation to surface temperature. Storms develop where the pressure is very low. Red being associated with danger is a good color choice for low pressure.

  Storms are created when a center of low pressure develops with a system of high pressure surrounding it.

Low pressure is also associated with decreased aircraft performance, both lift and engine power. See below and find the strongest storm system.

(Source)

Blue for cold and red for hot is used for coloring the weather fronts:

(Source) 1. cold front 2. warm front 3. stationary front.


Is there a way to code Minimum Enroute Altitude using ARINC 424 file format? I am studying ARINC 424 file format, and I have noticed that there is not any reserved space for coding Minimum Enroute Altitude (MEA), as far as Instrument Flight Procedures are concerned.

I find this value to be really important for properly specifying the characteristics of a procedure. It seems strange that in ARINC 424 specification, MEA is omitted. I have also checked FAA's Coded Instrument Flight Procedures file (CIFP), which are based on ARINC 424, and MEAs are nowhere to be found.

Perhaps I am missing something? Could someone point me in the right direction?

As the name suggests, MEA is coded for enroute segments lik ethe airways (ARINC permits this).  In so far as Instrument Approaches are concerned, the templates takes into account vertical clearances in Primary and secondary areas and then arrives at safe heights at each segment. Geometry of primary and secondary areas and the clearance therein depends on types of approach. For example, in ILS approach, half full scale deviation is considered safe. Also, it stems from this, obstacle clearance at different segments of the approach would be differen, so, specifying a minimum altitude may not be applicable. Secondly, in emergency, Minimum Sector altitude (MSA) centered 25 nm around airport/nav aid provides requisite obstacle clearance..


How should I decide whether to pursue an EASA ATPL or an FAA ATPL? What are the advantages/ disadvantages of FAA vs EASA ATPL's, and does this translate into the real world with airlines preferring one training standard over the other?
As a trainee pilot, it's pretty confusing looking at the array of courses offered around the world, with huge number of flight schools all advertising ATPL courses under different jurisdictions.

Any insight, experience would be very helpful.

Both the EASA and FAA ATPL programs are good, I know people who have both and their view is that neither has an intrinsic benefit over the other. The EASA one has more theory in it which most of the ATPLs I know think is worthless, however if you know how to study it's really not that bad.

The question of which is best for you is who you want to fly for and where their airplanes are registered, as it's the country of registration which defines which ATPL you need, not the location the airplane is in. An FAA ATPL will let you fly US registered (N Register) airplanes anywhere in the world, and an EASA one will let you fly an EASA member's airplane, so most of Europe anywhere in the world. If you want to fly for a US airline you need an FAA one, if you want to fly for a european airline you need an EASA one.


What happens during a carrier take off? Watching videos of jets taking off from a carrier, it appears the pilot is holding a hand grip as the jet is catapulted along the deck; then there is 'jerk' type motion as the jet leaves the deck with the pilot then taking control.  Could you please describe what happens during the take off.  It looks like a really rough ride for the pilot.

A carrier aircraft launcher is called a "catapult", for good reason! It's job is to get an aircraft up to flying speed very quickly, which of course results in a very high acceleration for the plane and pilot. Sometimes as high as 4G.
On modern American aircraft carriers, the catapult is about 300 feet (90 metres) long, and can get a large plane up to flying speed, 140 knots, in about 2 seconds. By comparison, taking off on a conventional runway a plane might need 2 kilometres to get up to this speed.
As you can imagine this puts a lot of stress on the planes, carrier aircraft are built much more rugged than an aircraft that would only fly off normal runways.
Each catapult-launched aircraft has different procedures for launch. In the case of the F/A-18, the pilot keeps his hands off the control column during the actual launch, grabbing it as soon as the plane leaves the edge of the deck. This is not the case for other carrier aircraft, such as the C-2 Greyhound, nor is it the case when taking off the same aircraft from a runway.
I found this in the F/A-18E/F flight manual (PDF here):

Immediately after the end of the catapult stroke, the aircraft will rotate to capture the
12° reference AOA (hands-off). To avoid PIO with the FCS, do not restrain the stick during catapult
launch or make stick inputs immediately after catapult launch. The pilot should attempt to remain
out of the loop but should closely monitor the catapult sequence.

AOA = Angle of Attack, PIO = Pilot-induced oscillations, FCS = Flight Control System.
Which roughly translates as "The F-18 will fly itself and find the optimal climb angle without pilot input during the launch."  This is not the case though for other aircraft.


What do the Thunderbirds pilots do when they can't fly? I went to an airshow recently, and the Thunderbirds performed. However, by the time they finished the startup and flight check ceremonies, bad weather had rolled in. However, they did still taxi into position at the end of the runway to wait for the bad weather to blow over. About 45 minutes to an hour later, they decided visibility was to bad to fly, and they taxied back to the ramp.

My question is if there is a solitaire game built into the Thunderbird flight software or something to keep them from dying of boredom, or if they just stoically stare at the end of the runway.

I would imagine they do the same thing all pilots do when they go to the airport expecting a nice day and wind up grounded by weather: Sit around at the airport with the other pilots and complain about the lousy weather. (In this case, since they're all sitting in position waiting for the weather to clear up any griping was probably done over the radio.)

There are of course other things they can do, being a fairly well-known demonstration team and an important component of the public relations arm of the US Air Force, for example signing autographs and talking to spectators at the airport.


Does an airfoil in supersonic flow have zero circulation? In incompressible flow, the Kutta-Joukowski theorem can be used to relate the lift (per unit span) to the circulation around an airfoil. However, if we look at an airfoil or the flat plate (see below) in supersonic flow with shocks, how can we show that there is circulation? And, if there is circulation, then how do we calculate it?

Maybe I'm missing something obvious to you, but why do you think there's zero circulation?

Take the simplest case of an infinitely thin 2D flat plate in linearized supersonic flow. The solution in the perturbed velocity potential ($\hat{\phi}$) is:

$$\hat{\phi}=
    \begin{cases}
    0 & x\pm\beta z<0 \\
    \frac{1}{\beta}\alpha(x-\beta z) & 0\le x-\beta z\le c, & z>0 \text{ (upper surface)}\\
    -\frac{1}{\beta}\alpha(x+\beta z) & 0\le x+\beta z\le c, & z<0 \text{ (lower surface)}\\
    \pm\frac{1}{\beta}(\alpha c) & x\pm\beta z>0
    \end{cases}
$$

where $c$ is the chord length of the flat plate, $x$ and $z$ are the horizontal and vertical coordinates, $\alpha$ is the angle of attack and $\beta=\sqrt{M_\infty^2-1}$ is the supersonic Prandtl-Glauert factor.

The velocity field ($\vec{V}$) can  be obtained as:

$$\vec{V} = \begin{bmatrix}V_\infty \\ 0\end{bmatrix}+V_\infty\nabla{\hat{\phi}} =
\begin{bmatrix}V_\infty\pm\frac{1}{\beta}\alpha V_\infty \\ -\alpha V_\infty\end{bmatrix}$$

where $V_\infty$ is the free-stream airspeed. The first equation is plus for upper surface and minus for lower surface.

Take an infinitely thin closed path ($C$) that wrap around the upper and lower surfaces, and calculate the circulation ($\Gamma$):

$$\Gamma = \oint_C\vec{V} \cdot \hat{n} ds=\frac{2\alpha c V_\infty}{\beta}$$

This is obviously non-zero. In fact, this can be readily seen by the potential jump in the wake.

And when we calculate the lift coefficient ($C_l$) of this flat airfoil using the Kutta-Joukowski Theorem ($L'=\rho_\infty V_\infty \Gamma$), we retrieve the classic supersonic lift relation:

$$C_l=\frac{L'}{1/2\rho_\infty V_\infty^2 c}=\frac{4\alpha}{\beta}$$


What is breaking away/peeling off in military lingo? About breaking away or peeling off:

Is this synonymous of a wing over?
Is this a signal to your wing mates that you are leaving formation deliberately to engage the enemy?
Does that mean you would subsequently roll on your back to scan for possible enemy aircraft below, complete the roll, and proceed toward the enemy?

I believe these are slang terms for element separation, where a leader and wingman break formation from each other either in order to reform in a new formation for tactical purposes e.g. Spread formation etc. fly a tactical maneuver to defeat a threat like a champagne or in order to land flying an overhead approach.  Wingovers are aerobatic maneuvers, very similar to Lazy Eights, intended to teach student pilots the art of flying the airplane with constantly varying stick and rudder inputs and are not involved with element separation.


How do the cockpit controls of a tiltrotor aircraft work? I'm having trouble trying to imagine the primary flight controls in the cockpit of a tiltrotor aircraft - how would one design it?

In an airplane, turning the wheel to the left would always deflect the ailerons (even when the plane is stationary!), while in a helicopter moving the stick to the left would always tilt the rotor disc. However in a tiltrotor neither is true - not to mention, we need to control the aircraft when it is transitioning between hover and cruising state!

So, just exactly how does one pilot a tiltrotor aircraft?

This video explains it nicely starting at about 1:20 in.

Also see here.

This is a pretty interesting article on flying it as well. It really seems to depend on mode but its summarized here nicely,

  Climbing into the front seats of the Osprey definitely does not
  produce the most graceful entrance: it requires some contorting around
  the armrest, center console and overhead panel. The cockpit is
  dominated by four night-vision-goggle-compatible, six-inch-square
  multi-function displays that allow access to flight, navigation and
  system information. Mechanical flight controls consist of a center
  control stick, thrust control lever (TCL) and rudder pedals. The
  control stick functions as cyclic control while in conversion and
  helicopter modes, but steadily fades into a traditional airplane
  control stick as the nacelles transition to airplane mode.

  The TCL
  moves fore and aft just like an airplane throttle, unlike a helicopter
  collective. It does operate as a collective control, however, and
  becomes a traditional throttle during the transition. While this may
  seem counter-intuitive to helicopter pilots, it actually makes a lot
  of sense, because regardless of the mode of flight, youre always doing
  the same thing: controlling the thrust vector. Forward on the TCL in
  helicopter mode is the same as raising the collective in a helicopter,
  and vice versa. The first couple of hours for helicopter pilots
  transitioning to the Osprey highlight a bit of collective dyslexia,
  but very quickly it never becomes a further problem. A spring-loaded,
  knurled rotary knob on the TCL that lies in contact with the pilots
  left thumb controls the nacelles. Roll the thumbwheel aft and the
  nacelles rotate to the vertical, roll it forward and the nacelles
  continue to the downstops. The controls follow the hands on throttle
  and stick, or HOTAS, concept, and have all the controls necessary on
  them to control multiple systems on the airplane.


Do twin engine airplanes have increased roll stability? Do twin engine airplanes with counter rotating props have increased roll stability?
Imagine a gust of wind hitting the airplane from the front right quarter.
The gust hitting the front of the plane first would yaw the plane to the left, before the rear vertical stabilizer can counter the yaw, the airplane will then roll to the left as the right wing sees more lift.
With a twin engined aircraft, the left engine would counter that yaw.
If less yaw, would that mean less roll, and therefore more roll stability?
Is this correct thinking?
If not, what can be done to increase roll stability besides using a maximum dihedral of about 6 deg and the addition of ventral fins, and wing sweep?

You're imagining the wind coming from the right, pushing the nose to the left. That doesn't happen. In fact, this is much more likely to push the nose to the right, because the vertical stabilizer, being a large panel that's far from the center of mass, creates a larger torque. This phenomenon is called "weathervaning", and is a huge concern for tailwheel planes and seaplanes particularly.
But, to get to the actual question: You are correct in thinking that, if a plane is yawing to the left, the outside wing is going to generate more lift, causing it to roll left. But, no, having multiple engines on an airplane will not stabilize it in either roll or yaw. For all the thrust from the left engine is doing to counter the yaw, the right engine's thrust is balancing it out, so a twin engine will not be any more stable than a single engine, all else being equal.


How to calculate airfoil geometry with the maximum lift to drag ratio for a given Reynolds number? How does one determine the optimal cross sectional geometry to maximize Cl/Cd?

The optimum airfoil is a cambered line of zero thickness. If operated at just the correct angle of attack, it will produce the highest L/D possible. It's cross section is trivial: It has none. However, it will not allow to build a clean wing since it has no space for a spar. It would need to be kept in shape by lots of wire bracing, and then the overall L/D of the resulting aircraft would be horrible.

Next, if the angle of attack is only slightly different from the optimum value, the sharp leading edge will cause early separation on one side, causing the L/D figure to plummet. This airfoil will not be practical for any purpose other than establishing a theoretical optimum figure.

Real airfoils need a blunt nose and some thickness. There are plenty enough airfoils to choose from already. All of them were designed not just for one single design point, but as an overall compromise to cover a wider range of parameters in real-world operation.


Why are "canard" not used on commercial aircraft? As of today and as far as I know, there is no commercial aircraft with canard, while they are used on several military aircrafts (like Rafale, Typhoon).

Plus, during take off the empennage pushing the rear of the aircraft down to pitch up add pressure on wheels, and this was for example one big design flaw on the Concorde:

  Because of the way Concorde's delta-wing generated lift, the undercarriage had to be unusually strong. [...] Combined with the high airspeed at rotation (199 knots indicated airspeed), this increased the stresses on the main undercarriage in a way that was initially unexpected during the development and required a major redesign..

I feel like addind a mobile canard in front of the plane would help to rise the nose up to take off.

Why are "canards" not used on commercial aircraft?

Edit about possible duplicate: I do not feel it is a duplicate of this question because "my" plane would be a three-surface aircraft with a canard, a main wing (not delta but classic) and conventional tail-plane. The canard would be mobile and add pitch control.

Well the Tu-144 was one example of an airliner which made use of canards.  The design configuration has been proposed before for large transports such as Boeing's ill-fated Sonic Cruiser.

And I suppose if you consider other, smaller aircraft, like the Paiggio P.180 Avanti for use in Part 121 and Part 135 operations, the that configuration is used often.

Probably the biggest reason is there hasn't been a pressing need to do so or the costs to abandon all of the engineering knowledge base in favor of a brand new design does not outweigh its potential benefits.


Is breaking a FAR an issue when flying outside of FAA jurisdiction? When flying outside the US it is advisable to follow the FAA rules when they are stricter than ICAO, and when it does not violate the local flight governing body's rules.

Can you still be fined or get into trouble or does the FAA only have jurisdiction in USA airspace?

The FAA only has Jurisdiction over US airspace and you must follow the rules of the airspace you are flying in/through. If you are talking about N registered airplanes they must follow FAA rules for airworthiness etc. even if they are kept outside the country.

Here is in interesting question on breaking laws on a plane in general (sort of applicable here)

Side Note: Although the FAA does not have jurisdiction outside US airspace if there is an accident involving a US built aircraft (mainly Boeings at this point) the NTSB will send a representative to compile their own report (and aid in the investigation). I know this happens for commercial accidents I am unaware if they send representatives for US build GA plane accidents outside the country.

Side Note 2: US pilots licenses are valid elsewhere in the world and allow you to fly elsewhere in the world certain actions elsewhere in the world (if caught/reported) may lead to the revocation of your US issued license. There is some info on that here


How are fan and compressor discs balanced? @curious-cat brought up an interesting question on another thread. How are the fan discs, compressor spools and turbines balanced on a jet engine. As they wear they surely get out of balance. Do they add weights as is done on your car tires?

And what method do they use to determine where the balance point is?
I'm imagining a giant version of this

This article covers the issue (and is a pretty interesting read) but does not really explain how they do it. It just says

  After machine balancing, the part can then be manipulated (mass added
  or removed) and retested on the machine until satisfactory balance
  tolerance is achieved.

In answer to this question,

  And what method do they use to determine where the balance point is?

The device is pretty similar to that of a tire balance, here is a video of one in use and here is an interesting sales brochure for one.


Why didn't the A330neo and A320neo share the cockpit of the A350? Recently Airbus presented its lastest projects A330neo and A320neo.

I'm sincerely surprised about the cockpit, in that it is essentially the same of the original A330, while I was expecting that renovation would affect not only the engines, installations, and lights but also the cockpit instrumentation taking inspiration from the new bigger screens of the A350.

I know that in this way the training for pilots is much easier, but at the same time I think that if a new cockpit is developed for a new plane (taking into consideration that "Type Rating" is anyway considered the same), it should be because of more safety, readability, and situational awareness.

In the past Boeing completely updated its cockpit inside the B747-400 and B737NG models from the original mechanical/analog gauges to the new glass cockpit. In those cases, surely the necessary training was very hard for pilots so, why not now for minor updates?

The short answer is that it's what the market wanted.  There is  always a lot of discussions between the airlines and manufacturer's before Airbus or Boeing commits to building a new aircraft.  In this case both Boeing and Airbus came to the same decision -- the airlines were being driven by one single factor to replace their A320 or B737 fleets, they just wanted to reduce fuel expenses.  That's why the Airbus is the 'neo' new engine option.

The airlines made it clear that any new aircraft purchases would be based on operational savings and that's primarily driven by fuel burn and the resulting costs.  The solution to that is a new engine.  Putting in a new flight deck is a huge expense for the manufacturers which would drive costs up and the airlines won't pay extra for something that doesn't save them money.

There's no cost benefit to a new flight deck, especially when (as others noted) you have a huge investment in an existing fleet.  In fact, all it's likely to do is add costs.  With a new flight deck you'll have a huge increase in maintenance and spares costs due to the need for stocking more parts with new part numbers (just adding a part number to a logistics system costs significant money.)  You'll also need new crew training simulators due to the different displays and controls, whereas the neo option can be handled with software upgrades.  And if it drives a need for new type ratings, that would mean more training costs and making sure you have the crews with the right rating at the right time.

In my experience in 20 years dealing with this market, airlines only spend money for two reasons:

It will increase their profit margins
The FAA (or other regulatory agency) mandates that they have it.

Aside from that, you should consider Airbus' side.  They're trying to sell airplanes and they have to compete with Boeing.  Since the avionics architecture is quite different between the A320/A330 and the A350, moving to it would add huge costs and a couple years delay in entry into service.  They also have to deal with the fact that airlines don't want to see a big price increase.  Prices for the A320neo and B737MAX are not significantly higher than the current/older versions.  If the competition can offer a 7 to 9% reduction in fuel burn for approximately current prices, spending an extra 2 or 3 years to match that with a new flight deck means a lot of lost sales in the interim.  And you probably won't make enough margin to recoup the new flight deck costs.


Which airliners have carried the most passengers? I'm fairly sure that the Boeing 737 series will be in first place, with the Airbus A320 family coming second and perhaps the 727 third.

However, perhaps there are some estimates of actual figures that would provide more information.

See also Which individual aircraft has carried the most passengers in its lifetime? for a related question about passengers carried by an aircraft series.

As you note the 737 and A320 have a huge leg up on most other aircraft simply by production numbers. The 737 is the unquestionably the most produced large passenger jet aircraft in history when compared to the A320 it has 20 years of extra flights under its belt which is a lot of time to move a lot of people. Its a bit dated but Boeing provides a bit of data on this and estimates:

  • The 737 family has carried more than 16.8 billion passengers; that
  is equivalent to every single man, woman and child flying at least
  twice. (2013 world population was
  7.1 billion).*

  *As of December, 31, 2013

Airbus provides a similar stat estimating:

  15,6+ billion passengers carried since Entry Into Service

  As of November 2018

So it seems that the 737 is clearly in the lead over the A320 as 5 years ago they had already carried an estimated Billion more passengers than the A320 has as of last month.

These are the only two large commercial jet aircraft that even appear on the most produced aircraft list linked above. Other sources quote the 747 as carrying 3.5 Billion passengers, the 727 comes in around 2.2 Billion in its lifetime and the 757 is somewhere in the 1.3 Billion passenger range which is similar to the A330's 1.3 Billion (as of 2013) none of which even approach double digits so the 737 is clearly the leader from the estimates I can find.


I need to clean my aircraft's windows - what do I use? I need to clean my aircraft's windows what do I use?

Note: I hope this is not a "subjective" question, as I don't want to put a potential harmful substance on my aircraft's windows and as a new aircraft owner, I would think this would be a logical question.

I assume that your aircraft has acrylic windows. This is a very soft material which is easily scratched and cracks under stress. For cleaning, use these steps:

Rinse with lots of water to remove dust.
Wipe with a wet, soft sponge. Don't press on the sponge and move it in the direction of airflow. Moving the sponge sideways will increase the risk of sideways scratches which are caused by the movement of dirt particles over the acrylic surface. Those sideways scratches will impair vision when flying into the direction of a low sun.
Dry the surface with a chamois leather, again moving in flow direction.

Superficial scratches can be removed by polishing the surface with an acrylic or metal polish. Be careful with sandpaper because this could take off more material than necessary, resulting in optical distortions when looking through the polished area at an angle.

Never use alcohol or other organic solvents!


Why was the Junkers Ju 87 not upgraded with a jet engine? Given that the Stuka dive bomber was famous during ww2 for its dive bombing attack but as we all know it was easily shot down by enemy fighters because of its slow speed especially during the later war years when the Germans lost air- superiority.

A simple solution would be to replace the piston engine in the Stuka with a jet engine instead and the problem would be solved.

Why didn't the Germans thought of this solution?

First, the Ju-87 was not easily shot down. It had manoeuvrability superior  to all fighters due to its lower wing loading and Junkers flaps, and it could take a lot of damage. With the rear-facing observer the Ju-87 pilot was in a much better position to evade all maneuvers of a pursuer. Only when faced with large numbers of enemy fighters could a Ju-87 not escape.

Battle damage on a Ju-87 (picture source)

But to put a jet engine into an airplane with a fixed landing gear will not make it faster than the much sleeker piston-powered designs to its days. Instead, the idea was to develop a new design with a retractable gear and a prone pilot position. This was the Henschel Hs-132, pictured below (source)


Can cameras and LCD screens replace cabin windows? Windows in aircraft create a weakness to the structure, that is why they are very small. I'm not asking about installing them in the cockpit, which would create safety pitfalls, but could the windows in the rest of the fuselage be replaced by cameras and LCD screens that provide real time images of the outside world that even passengers sitting in the middle of wide bodied aircraft can enjoy?  This could even include a sky camera for night travel.

Note that the windows are a safety feature: You need to see outside in case of emergency, e.g. to know which side of the plane is surrounded by flames, or how deep in the water you are. This is actually the reason why the inner lighting matches the outside conditions for take-off and landing and the window shades have to be open. Even worse, the potential rescuers need to see inside to know the conditions in the plane (flames, smoke, attackers, debris etc.), so you would need to have some system that reliably works both ways.

I don't see how your hypothetical plane would get certified with even more emergency features relying on electricity and on something that's basically an entertainment system.


What are the SOPs following an overweight landing? Modern commercial aircraft are certified to be able to land at any weight providing that the runway is long enough.  The "overweight landing" QRH procedures for the 734 and A320 are correspondingly quite short, referencing mainly the approach reference and target speeds and adjusting for wet/contaminated surfaces.

This video (which by the way, deserves repeated watching - there is just so much to look at, e.g. the vortexes high above the wings and from the flap outboard trailing edges) unfortunately is clipped from shortly after the emergency response crews arrive until the aircraft vacates under its own power.

This made me curious as to how the decision to taxi clear is made.  Are there QRH/SOPs for this, either the operator or the airport?

My guess is that the fire fighters will check the bogies for any sign of fire and, coupled with the crew checking EICAS and the wheel and tyre temperatures and pressures, make a joint agreement that it is safe to vacate.

Following vacating, would the QRH/SOP be to stop when clear and allow extra time for cooling (which could be a long time) or taxi to the stand?

Wouldn't taxiing to the stand increase the risk of a fire starting even if there was none after it had stopped on the runway?

And that video, oh, watch it again.

The answer very much depends on the operator and type of aircraft (or rather its manufacturer).

First of all, overweight landing would normally be performed for the following scenarios:

Medical emergency on board that requires prompt medical attention
Any fire/smoke that cannot be extinguished/ventilated
QRH dictating "Land at the nearest suitable airport"
Any situation where safety might become further degraded by prolonged flight

It's hard to list all the situations here, and most of the time the Captain will have to make a decision whether to do an overweight landing or not.

Having made the decision to perform an overweight landing, the crew needs to take into consideration the following items:

Runway length available - landing at significantly higher weight than MLW increases landing distance substantially
Missed approach climb gradient - this might be a problem at airports with high terrain nearby
Reduced landing flap - normal landing flap speeds at higher than MLW might be too close to Vfe (maximum speed for the selected flap setting)
Required brake cooling - if heavy braking is required to stop within the required landing distance available, then it's best to vacate the runway and have fire services check the brakes and tires. Fuse plugs might have melted and tires might have deflated. Subject to all clear from the fire services, aircraft might taxi to the stand, have the chocks set and wait there with brake released for a while.
Overweight autoland is normally not recommended, as the autopilots are not certified for this.

After an overweight landing, an inspection is required by engineers to make sure there are is no structural damage on the aircraft, particularly its landing gear and the skin. According to my knowledge, the overweight landing inspection is just a bit more thorough walkaround by the engineer, provided the overweight landing wasn't a hard landing. If it was a hard and and overweight landing combined, the aircraft is likely grounded for a while, as more detailed inspection is required.

All Part 25 (FAR 25, CS 25) aircraft are certified to be able to land with sink rate of 600 ft/min (10 ft/s) at MLW and 360 ft/min (6ft/s) at MTOW, so unless you do a particularly poor landing when overweight, there should be no structural damage, even when landing straight away after a takeoff at MTOW.