Which modern day prop (piston) engines allow for inverted flight? A buddy of mine is looking to buy an airplane with an old radial engine because he says radial engines can fly inverted in aerobatic flying.  What modern day engines (engines that you can buy today), are capable of flying in inverted flight?

Any “modern day” piston engine can allow for inverted flight if it has the right equipment on it.

The American Champion Citabria with the 7KCAB Inverted Fuel and Oil package along with the American Champion Decathlon are both "Modern Day" aircraft capable of sustained inverted flight.

The major differences between the7GCAA and 7KCAB were in the fuel system and the engine oil system. The engine was replaced with a Lycoming IO-320-E2A of 150 horsepower (110 kW), while a header tank of 1.5 gallons—located beneath the instrument panel—was added to the fuel system. In addition, the carburetor was replaced with a fuel injection system, and a Christen Industries inverted oil system was fitted to the engine. All of these changes were made in order to allow for extended inverted flight, a mode not possible in the earlier models.

disciplesofflight.com/american-champion-decathlon/
You can fly inverted continuously for about two minutes before the fuel in the header tank runs out and the engine falters. Rolling upright will recharge a depleted header tank in about a minute while the faltering becomes a smooth running engine again


What would be the challenges for a pilot taking off into a headwind of just under the clean stall speed? If a strong and fairly steady headwind was coming down the runway at just under the stall speed for a clean configuration/weight, what challenges would a pilot face? Or would it be fairly easy? Is this something that happens often?
Edit: This is the video that made me ask.

"Fairly steady" wind is the only wording that would make it even remotely considerable, with risks of being ground looped or blown over while taxiing.
One scenario may be a light GA plane taking off from a moving aircraft carrier.
Tricycle gear would be a tremendous advantage, as this would help keep the wing at a very low angle of attack to the wind.  This allows the plane to remain on the ground during its takeoff run long enough to establish a safety margin in airspeed before the plane "rotates" to an angle of attack sufficient to generate enough lift to fly.
One must be aware, although this is doable, gusts make it extremely dangerous.  Far better to wait for better weather.
Even with no wind, the safe rotation airspeed will be higher than the clean stall speed.


Where is V15 and how do I find it? My question: Where is V15 and how do I find it?

The question referred to in the practice test:

  Refer to the figure 21, area 2 below: What is the floor of controlled airspace along V15?

The correct answer was 1200 ft AGL.

I want to thank @757toga, and @JScarry for the help on this. I made an 88 on my Drone certification that I took today (10/11/2018)

There is a notation for V15 (low altitude IFR airway) in the southern portion of the top map in your question.

V15 is a Federal Airway, normally used for IFR operations and shown on IFR charts as well as VFR Sectionals. Federal Airways, unless otherwise notated, begin at 1200 AGL. These airways are Class E airspace. If you look in the legend of your Sectional Chart it describes this airspace.


What astronauts and/or pilots had their "own" T-38 for transportation and practice? It appears that the T-38 was used as a means of transportation for certain personnel. Astronauts, and certain pilots? It appears it was also used for training in some cases.
From some articles regarding astronaut training, it seems that some of them had their "own" T-38, that they could more or less use arbitrarily for transportation and training.
I'm curious what pilots and/or astronauts had access to T-38's, and to what degree they had their "own" plane. What were the limitations surrounding their use? Could an astronaut of the Apollo era, take the T-38 for a recreational trip to some other airport?
I'm thinking of articles such as this:

Yes, the jets were used for transportation to training sites.

and this

After the announcement pilots could fly the F-117 during daytime and no longer needed to be associated with the A-7, flying the T-38 supersonic trainer for travel and training instead.

No pilot or astronaut has "their own aircraft". Not in any unit I've ever seen.
Their name might be painted on the side of one, but they fly whatever the maintenance shop gives them for that day and mission.
Transportation? Sure. "Major Snuffy has to go to Houston for some training on the FooBar hardware. Ralph, take him, and go back on Thursday to pick him up."
Of course, this counts towards flight hours, mission and route planning, etc, etc.
"Borrow" a jet"? When I was stationed at Griffiss AFB NY in the late 70's, we sometimes had a pilot go for a weekend cross country. Leave Thursday or Friday afternoon, come back Sunday afternoon. Off to Frostbite Falls, MN Regional airport, to visit Mummy and Daddy for a couple of days. And we were loading golf clubs, skis, whatever, in the underwing travel pod.


What is the Effect of Unsynchronized Propellers? A long time ago, I had the privilege of flying in 4 engine turboprop airplanes in which the props were 'synched'(blades rotating in same speed) which of course is necessary for smooth thrust.

However, one of the exercises we performed(as a military aircraft) was called a "crash and dash"; we dove as steep as we could until we could get as close as we could to the surface, then pull out of the dive and attempt to 'fly below' any surface radar that may be tracking us.

Every time we did this maneuver it threw the props out of 'synch' and cause the airframe to shudder violently. Anything that was literally not 'nailed down' was thrown through the cockpit or cabin.

My question is, what effect does this have on the airframe and does one of the events require an inspection, or shorten the check cycle?

I would agree with the other comments, in that I don't think the extreme buffeting could be caused by out-of-sync props. Maybe if you lost a chunk of a blade and you had out-of-balance props, but that's a bit different. Or if one of the props came WAY out-of-sync. But I know nothing of the Orion aerodynamics or engineering.

My twin experience has been more of the light piston and turboprop variety, but I can tell you that out-of-sync props produce a "whah whah whah" sound that will drive you absolutely bonkers. As soon as I was straight and level, I'd match rpms/prop pitch on my engines (or turn on the prop sync) to get rid of the noise. I never wanted to try it long enough, but apparently acoustic oscillation like that can cause serious fatigue. And I would imagine that long-term exposure can't be good for the airframe.


What was the motivation for revoking the licence to the pilots of Northwest flight 188? This video describes Northwest flight 188, where two pilots overshot their destination by 150 miles, without contacting ATC for an hour. They cited 'cockpit distractions' as the reason and subsequently, both had their licenses permanently revoked.

What exactly was the license removal be for? Overshooting the runway? Not contacting ATC for an hour? And what are the quantitative rules on this, i.e. how long would you have to not contact ATC for or how many miles off course would you have to go to get your license revoked liked these two did (in a commercial setting)?

According to this CNN article the FAA revoked their licences with a letter containing the following reasons (emphasis mine):

The letter said the pilots were "extremely reckless."
"Not only did you not comply with ... [air traffic controller] instructions, you did not even monitor the aircraft's air-ground radios," the letter said. "You were disengaged and impervious to the serious threat to your own safety, as well as the safety of people for whom you are responsible. This is a total dereliction and disregard for your duties."
[...]
The FAA said the revocations cite several violations of regulations, including failure to comply with air traffic control and clearances and operating carelessly and recklessly.

As Adam pointed out in the comments, this would violate FAR 91.13:

§ 91.13 Careless or reckless operation.
(a) Aircraft operations for the purpose of air navigation. No person may operate an aircraft in a careless or reckless manner so as to endanger the life or property of another.
(b) Aircraft operations other than for the purpose of air navigation. No person may operate an aircraft, other than for the purpose of air navigation, on any part of the surface of an airport used by aircraft for air commerce (including areas used by those aircraft for receiving or discharging persons or cargo), in a careless or reckless manner so as to endanger the life or property of another.


Why does the FAA require special authorization to act as PIC in the North American T-28 Trojan? This airplane doesn't have a max gross takeoff weight of more than 12,500 pounds nor does it have a turbine engine.

The FAA requires special authorization to act as PIC in order to fly it.  What is the reason?

As the T-28 is a vintage military surplus aircraft it is normally certificated in the Experimental-Exhibition category. For most aircraft in this category, there is no type rating in the traditional sense. For years, the FAA managed these aircraft and pilot qualifications for them on a case-by-case basis. Approval to fly them was (and for some vintage aircraft still is) granted by a Letter of Authorization (LOA).
About 15-20 years ago, in an effort to reduce the regulatory burden on both the FAA and pilots they moved to a process that more closely aligns with type ratings. It is managed under the Vintage & Experimental Aircraft Program.
The stated coverage of the program is:

This program standardizes pilot certification in the following U.S.
aircraft:

Vintage Type Certificated aircraft which require a type rating
Experimental turbine-powered aircraft
Experimental aircraft with a maximum gross weight in excess of 12,500 pounds, or
Experimental piston powered aircraft with an engine over 800 HP and a Vne (never exceed speed) greater than 250 knots

The T-28 falls under the last bullet as it has more than 800 hp.


What is aeroelastic deformation? Some answers on this site, such as this one, refer to something called aeroelastic deformation.

What is it and how does it affect aircraft construction? Are there any famous lessons learned on this topic as far as aircraft construction goes?

Aeroelasticity is the elastic deformation of a structure caused by aerodynamic forces. An example is the flexing of a wing. The change of the shape of the structure has in turn an effect on the aerodynamics.

Aeroelastic effects can be static, such as the upward deflection of a wing under the influence of lift, or dynamic.

In the static case, the aerodynamic for cause the structure to deform. If the structure is very flexible this can cause a stability problem: the deformation causes an increases of the aerodynamic load, that will in turn increases the deformation until the structure fail.

In dynamic cases there is an interaction between the aerodynamic forces, the inertial forces and the deformation of the structure. Usually the dynamic behaviour is transient and damped.

When the dynamic behaviour is undamped (the aerodynamic forces add more energy than is dissipated in the transforming structure) an increasing vibration will occur. This is called flutter. Flutter is unwanted the because the resulting severe vibrations can cause structural damage.

Here is an example of flutter on a small aeroplane:


What happens when disengaging the electricity generators on a B747? This answer says:

  If let's say, you [...] disengage the electricity generator of every engine (which cannot be re-engaged without mechanical maintenance), [...].

What exactly happens in the aircraft when disengaging the generators and what benefit does it have to be not able to engage them again?
Is it only the B747 that works like that or also other Airliners?

This is how it works on all aircraft with a Constant Speed Drive (CSD) Generator or an Integrated Drive Generator (IDG) - doesn't matter who the airframe maker is.

When you press the disconnect button (the red arrow), the disconnect circuit is completed and the solenoid pulls the pin out of the pinion shaft (the blue arrow) which then engages the worm gear on the drive shaft (the green arrow) and causes that gear to disengage from the drive mechanism. This causes the generator to stop turning.

To reset the mechanism you have to pull the "RESET HANDLE". This drive mechanism is attached to the gearbox on the engine which means that it can only be done on the ground with the engine off


When should I start turning in this circling approach? I've been practicing circling approaches in Homestead General Aviation Airport in Homestead, Florida (X51). I performed the RNAV (GPS) RWY 10 approach with circling minimums.

My questions are:

a) For example if the active runway is Runway 18, then how exactly is the circling procedure performed? Should I start circling after crossing the MAP (XAGUH), or before?

b) And if the active runway would be 36, then the circling procedure would be to enter a downwind, then a base and then a final. Until when should I maintain the Circling MDA?

The FAA instrument flying handbook discusses techniques and the procedures by which circling approaches must be conducted.1

You must remain within the protected area or circling radii, but as soon as you enter this area, you may begin the circling maneuver.  Usually, this means you will begin the maneuver well before the missed approach point.  In particular:

a) "The criteria for determining the pattern to be flown are based on personal flying capabilities and knowledge of the performance characteristics of the aircraft. In each instance, the pilot must consider all factors: airport design, ceiling and visibility, wind direction and velocity, final approach course alignment, distance from the final approach fix to the runway, and ATC instructions."
b) "Fly no lower than the circling minimums until positioned to make a final descent for a landing." (page 10-20 of Ref 1).


Why do model aircraft fly and maneuver so differently from real aircraft? I recently viewed on Youtube many videos of small and giant models of airplanes. In some cases they are small (for example an A330, 1 meter long) and in others they are huge (for example an A380, 5 meters long).

As far as I can see, the smallest ones seem to have electric engines (maybe fake jet engines in which fans act as propellers?) but the bigger ones seem to have internal combustion engines, even if I don't know how they run.

Anyway, the general impression is that even from a great distance it's obvious that they are models and not real aircraft. They are all too quick, too agile, make very short takeoffs, have very low inertia, make quick turns and so on.

Can you tell me why these handling differences exist in models that otherwise tend to simulate with great precision every other detail of the real aircraft (lights, shape, colors, fine details, landing gear, etc.)?

It's partly inherent in the way things scale.

If you double the length of the model, then the wing area (length times width) increases by a factor of 4, but the weight and volume (length times width times height) will increase by a factor of 8 ... so doubling the size means halving the weight-to-lift ratio.

In the most extreme cases, a tiny model will blow away on a puff of wind, and a huge model (bigger than the real plane) can't take off at all.

I suppose you might theoretically try to make small models harder to fly, by adding extra weight.

The above is theoretically true but maybe nonsense in practice: it assumes that structural materials become thinner when the model is scaled, in reality the structure isn't even the same material.

So let's look at it another way:

A full-scale A380 weighs let's say 500 tons, length about 70 metres.
Decrease that to 1 metre model and the surface area has decreased by (70x70=) 5000.
So for the model to have the same weight-to-area as the full-scale plane, it would need to weigh (500 tons / 5000 =) 100 kg.

Your 1 metre model presumably weighs much less than 100 kg, therefore it has much less weight-to-area ratio. QED.

It's also important to consider the Reynolds number, which depends on the air's viscosity and density, and on the size and speed of the model. The Reynolds number affects turbulence, which is very important to a wing's lift (for an example of how even a tiny change has a large effect, see Can a sandpaper-thick layer of ice reduce lift by 30 percent and increase drag up to 40 percent?).

To get the right Reynolds number for a small model you must increase the density (e.g. pressure) of the air, or increase its speed. But given the ordinary speed of aircraft, you couldn't increase (scale up) the air speed because it would become super-sonic, which would change the scenario.

Based on this answer to 'Understanding the Reynolds-number scaling problem', and the comments below it, I think that a 1-metre model of a 70-metre A380 (so a scale of 70:1) might behave like the full-scale model if it were flown under the following conditions:

air density is scaled up, so 70 atmospheres of air pressure
lift and drag are scaled down, so:

weight of the model is 7 tons (instead of 500 tons)
thrust of the model is 4,000 lb (instead of 300,000 lbs), i.e. about 2 tons

air speed is realistic (e.g. 150 knots to take off)

Obviously this would be quite unusual for a model airplane1.

1Air liquifies at 60 atmospheres; and the model would need a specific density of about 100, i.e. 5 times heavier than gold or uranium).


How do planes benefit from flying in formation? Large flock of birds when migrating usually fly in an arrow formation, which helps the birds to save energy while flying the same distance as compared to a situation when the birds are not in a group.

What is the physics behind this?
What is the significance of the specific flying formation?
Can this be applied on airplanes (given the fact that anything analogous to engine exhaust is not present in birds)?

Energy saving

The wing creates lift, which is upward force on the wing. According to principle of action and reaction, there must be a downward force acting on the air. This force creates a downwash behind the wing. As the accelerated air interacts with the still air further away it turns to the sides and back up, creating a slight upwash outside of the wingtips.

Flying in this upwash adds a bit of lift on the next flying thing which in turn means it can fly at slightly lower angle of attack and have less induced drag. This recovers some energy from the wake vortex that would otherwise be dissipated as heat.

Birds

Migratory birds use the typical V formation to take advantage of this, each bird flying aft and to the side of the previous. Since the leader is not getting any advantage, the birds usually take turns in leading the flock.

Aircraft

I have however not heard of this being done with aircraft for energy purposes beyond experiments. Military aircraft usually use similar V formation, but for different reasons. They need to fly in group, because they need to provide mutual defence. And then the V formation is used during cruise to and from target area simply because in it the wingmen see the leader while remaining clear of their downwash and wake turbulence.


How many private jets land at Heathrow airport per day? Heathrow airport is one of the busiest airports in the world, one would assume most traffic there is reserved for commercial airliners because they carry a much larger number of passengers.

How many private jets land at Heathrow airport per day?

On a normal work day
On weekends.

How many private jets land at Heathrow airport per day?

None!

January 2018 movements, source: CAA

Related: Where does an A-lister land when they waft in from paradise? Yes, Luton

To try to explain why this absence of business planes at a large airport, its important to understand that private aviation in Americas and in Europe are not seen the same way.

In Americas private planes are very common, this is not the case in Europe, where you must be lucky to know someone in your neighboring who is a pilot. As a consequence airliners and other planes have separate lives with different fees paid.

For example, I live in Paris: Business planes use Le Bourget aerodrome (the one which hosts the Paris Air Show -- btw nobody here knows what is the Paris Air Show, as everyone calls it Le Salon du Bourget since it exists... --, while airliners use CDG or Orly airports (and now the remote/low cost Beauvais). This is the same in UK.


Is there a relation between the Mode 3/A Code and the ICAO aircraft address? I would like to know is there is any way to match mode 3/a code (which is assigned by ATC to aircraft) and ICAO address of the aircraft. I mean how mode 3/a code is assigned to each aircraft by ATC? Is that unique for that day or certain time period? Is it possible that same address is assigned to more than one aircraft? Is there any relation with aircraft's own 24 bit ICAO address?

There is no relation between the ICAO 24 bit aircraft address and the 12 bit Mode A code. The 24 bit address is unique to the aircraft and stays with the aircraft as long as the aircraft has the same registration. The Mode A code changes from flight to flight and often during flight.

The Mode A code is assigned by ATC based on a local or regional assignment scheme. There are Mode A codes that can be used by many aircraft in one area simultaneously, such as VFR codes (1200, 7000) for flights that are not under air traffic control. For IFR flights, the Mode A code is unique for the control area at that given time. When aircraft move from control area to control area, a code conflict can occur when two aircraft with the same code end up in the same area. In such a case one aircraft will be given a new code.
There are various schemes to prevent code conflicts from happening too frequently. See this answer for more info.

Quite recently (in the last couple of years) IFR flights in Europe can operate under conspicuity code 1000 which is a signal to the flight data processing system to use the Mod S downlinked aircraft ID for identification and flightplan association. This allows many aircraft flying in Mode S surveillance airspace to use code 1000 simultaneously, freeing up Mode A codes and reducing the number of code conflict.


Will you be able to hear a supersonic aircraft flying away from you? I'm wondering if you could be able to hear the sound emitted by an aircraft say traveling at Mach 2 away from you.

I wondered if it might shift the emitted frequencies beyond the audible range. Would you be able to hear it?

Yes, actually you can only hear a supersonic aircraft after it has passed over you and is now flying away from you since it is moving faster than the sound moving towards you. The sound waves will still propagate in all directions and will eventually reach you:

The frequency will be shifted according to the Doppler formula:

$$ f = \frac{c \pm v_r}{c \pm v_s} f_0 $$

Here, $v_r$ is the the speed of the receiver ($v_r = 0$ for you standing still) and $v_s$ is the speed of the sender. It is added when the sender is moving away from you. In your case of $v_s = 2c$ you would get

$$ f = \frac{c}{c + 2 c} f_0 = \frac{1}{3} f_0 $$

The audible range for a typical human is about 20Hz to 20kHz. So you would still be able to hear any $f_0$ greater than about 60Hz after the Doppler shift. The following image shows the frequencies emitted by a Boeing 747 as measured from the ground:

(W.L. Rubin, The Generation and Detection of Sound Emitted by Aircraft Wake Vortices in Ground Effect)

There are a lot of contributions from the aircraft above 60Hz, which should make it clearly audible. Of course an aircraft flying at Mach 2 will be different than a 747, but the general spectrum should not change too much.

Note: the formula above does not work while the aircraft is moving towards you because the resulting frequency would become negative. This is because sound emitted at a later time reaches you before the sound emitted at an earlier time because the aircraft has moved more towards you than the sound:


How does Mass affect rate of turn? After seeing effect of speed and bank angle on rate of turn, how would one mathematicly calculate the effect of changing mass.  For example, in a 30 degree turn at 100 knots, how would the rate of turn be affected if identical planes, one at 10,000 lbs, one at 9000 lbs were compared.  Granted, the pitch and power settings may be slightly different, generating different amounts of lift.  Would the heavier plane turn faster due to its greater horizontal lift component, or would it's heavier mass keep it more in the same direction?

The second law of motion states that: $F = m * a$

Rate of turn will be determined by the acceleration: $\frac{F}{m} = a$

If your vertical lift is 10,000 lb, in a 30 degree bank, your lateral force is $10,000 * tan(30)$, your acceleration is $\frac{10000 * tan(30)}{10000}$, or $tan(30)$.

If your vertical lift is 9,000 lb, in a 30 degree bank, your lateral force is $9,000 * tan(30)$, your acceleration is $\frac{9000 * tan(30)}{9000}$, or $tan(30)$.

Thus you can see the rate of turn depends on the bank angle, not the mass.


Are DPEs incentivized to fail people on checkrides so they can collect extra money on re-tests? I'm almost ready for my private pilot checkride, and it seems to me there is a perverse incentive for DPEs in passing or failing people.

If a DPE makes additional money on re-checks for students who fail the checkride, then it seems to me that DPEs have have a strong financial incentive to fail people the first time so that they can collect additional fees on the re-test. In fact, it seems that there are no rules in place to stop a DPE from making a student do the checkride 4, 5, or 6 times and collecting additional money from the student every time.

The checkride fee is exorbitant ($900 here in Southern California), but I'm even more concerned that the DPE would be hoping to fail me so they could collect extra money from me on a re-check. It actually makes my blood boil just thinking about it.

I'm not saying that DPEs are bad people, but the incentive structure certainly seems to make it easy for them to exploit eager students, and if economics has taught us anything, it has taught us that people respond to incentives.

I think you are getting worked up about something that isn't a problem.  DPEs are incentivized to develop a professional reputation that upholds appropriate standards, while passing those who meet the standard.  Someone who is motivated by greed to fail students as you suggest would quickly get a bad reputation and people would simply stop scheduling check rides with him/her, so the plan would rapidly backfire.

Think about it, I could easily make the opposite case that I am concerned about safety because a DPE motivated by the desire to get a reputation of passing people the first time to increase his/her business could be tempted to compromise on the standards.  It should all balance out in the end.


Why westward flight takes longer time? • Why fly from east to west takes longer time then flight form west to east and does this apply to both hemisphere?

This is simply due to the jet stream. High altitudes fast air current flowing west to east. Therefore if you are flying against them your ground speed is reduced and it takes more time to go from London to New York than the other way around. Jet stream exist in both hemisphere but they pass through middle latitude in Europe USA and Asia wherase they mostly circle Antarctica in the south. Thus making them less important for aviation.

The jet stream is the main reason why the North Atlantic tracks are updated twice a day to ensure they are aligned at best with the winds to reduce flight time and fuel consumption.


Why is there a pitching moment at aerodynamic center? As far as I know, the pitching moment is an aerodynamic moment and is related to the aerodynamic center.
But I am confused with the following figure, which shows the aerodynamic force applied at the aerodynamic center. So I would think, in this case, that the center of pressure is located at the aerodynamic center which is a quarter chord. If so, why is there a moment ?

https://wright.nasa.gov/airplane/Images/ac.gif

The definition of the aerodynamic center is the following:
"the aerodynamic center is the point along the wing chord where the coefficient of aerodynamic moment is constant with respect to the AOA." It doesn't mean that it is equal to 0.
To make it simple, imagine taking a cambered wing, if you look at the center-line of the profile, it will have a changing AOA along the chord of the profile. Setting the wing at a 0° AOA will result for a positively cambered profile into a negative AOA and a negative lift near the leading edge and a positive AOA and lift near trailing edge. Thus creating an absolute torque pitching down the wing profile. The aerodynamic center is the point where the coefficient related to this torque is not impacted by the AOA.

The point you are referring to is the center of lift ($P$). It's the point where the aerodynamic torque is equal to 0. But this point location is changing with respect to the AOA. You have the following relation:
$$C_{m_F} = C_{m_P}-(x_P-x_F)\cdot C_Z \rightarrow  x_P = x_F - \frac{C_{m_F}}{C_Z}$$
Which means that for a classic wing with positive camber and thus negative torque, the center of lift is located after the aerodynamic center in cruise condition with $C_z > 0$.

It is more practical to always express the aerodynamic load at a given fixed point, the aerodynamic center with the couple (lift, torque) than expressing just the lift at the lift center which is moving with respect to flight conditions.


Does a Boeing 737-800 Have a Ram Air Turbine (RAT)? I am travelling with Thomson on a Boeing 737-800 and wondered if it had a RAT?

No it does not, it does not need one, there is a mechanical connection to the flight controls that can be used if all else fails.

The B737 flight controls are hydraulically powered.
There are three hydraulic systems: System A, System B, and Standby. Only one main system (A or B) is required for hydraulically flying the aircraft, during normal operation they are both operational.
The two main hydraulic systems have an Engine Driven Pump (EDP), which can continue delivering hydraulic pressure when the associated engine is windmilling. All three hydraulic systems are also powered by their own Electric Motor Driven Pump (EMDP).
In case of dual engine failure the APU can power the electrical systems for the EMDPs, still delivering full hydraulic power.
If the fuel has run out and the APU cannot operate, two batteries provide at least 60 minutes of backup power for the electrical systems. The EDMPs can be powered in this stage, however they provide a high load.
If all fuel is gone and the batteries are depleted, the aircraft can be flown by hand, directly overcoming the aeroforces by pulling hard! This is called manual reversion.
In manual reversion, the aileron trim tabs now function as geared tabs, assisting in overcoming the aeroforces. Elevators will have high aeroforces, high friction forces, and freeplay around centre point. Stabiliser trim wheels provide additional pitch control. The rudder has no manual reversion.

The A320 flight control system is pretty similar except for the manual reversion - as a last resort the RAT is deployed for powering the backup hydraulic system. The A320 has no direct mechanical link to the elevators and ailerons, only to the rudder.

Image source


How much fuel does the A380 use for taxiing before takeoff? How much fuel does the A380 use for taxiing before takeoff and after landing? What does it cost at today's pricing?

Fuel burn
To be meaningful it's best to compare it. It is approximately 4 times what an A320 needs. So if both planes are fully booked, then in theory each passenger should pay the same for the taxi fuel -- it would become an issue though when the A380 has a low load factor.

Taxi Fuel is 1 170 lb for an average taxi duration of 12 min.

While for 12 minutes an A320 needs 300 lb.
Cost
As of 20 April 2018, it would cost Emirates -- the largest A380 operator -- about \$360 for a 12 min taxi in Dubai (less than a dollar per passenger).
But Dubai is a busy airport and as such the taxi duration can exceed 12 minutes. For example Emirates 203 from a few days ago had a taxi time of 30 minutes. Operating a large airplane at a busy airport has its costs.

References:

Airbus FCOMs for the A320 and A380
IATA fuel monitor (jet fuel cost varies by region).


How frequent is the use of spoilers during descent? Having flown a number of flights as a passenger recently, I observed that:

Roughly 50% of pilots used spoilers above FL180
Almost everybody used spoilers to pass the 10,000 feet / 250 knots mark
Roughly 25%~33% of pilots used spoilers around 7,000 feet ~ 8,000 feet down to glideslope capture

Are modern airliners so "slippery" that an engine-idle descent is not enough to meet operational requirements? (on the other hand, makes them really good gliders in the event of a total engine failure!)

I was told that companies like to use engine-idle descent as much as possible because it is the most fuel-efficient way to get down; spoilers are only "sometimes" used when ATC clears the descent path unexpectedly, which usually means a short-cut and passengers can expect an earlier arrival. That was in the 90s'.

Has it changed in the last decade? How frequent is the use of spoilers during the descent portion in today's flights?

Very frequent.

Modern airliners are certainly fairly slippery, but it's not so much that they're super-gliders that we can't wrestle down onto the ground.

It's more a function of busy airspace than a property of the aircraft. When you remove power from any aircraft, it's going to descend - the only question is the rate. I promise you that if you found yourself a long way from an airport in a powerless B737, you'd find that descent rate to be faster than you'd like!

The main reason for spoiler use isn't that a modern aircraft glides "too well" - but rather than the airspace is busier so aircraft are expected to respond a little quicker than in the past, which can make it more convenient to descend faster as a pilot. It also means that ATC will often ask pilots to maintain a higher-than-ideal airspeed on the descent: if travelling at 160 knots, you'll descend faster than you would at 180 or 200 knots, for example... but more often these days, you're asked to maintain a higher minimum airspeed for longer. That's often convenient for ATC as it gets you where you're going faster, and it's convenient for you too, because you get to go home faster: but it means you're travelling a lot further in the next minute, making it harder to hit the descent rates required, necessitating the use of spoilers in some circumstances.

Clarification: In this answer I've focused on the later stages of the flight: "Slower = descend faster" is not necessarily a universal constant - aircraft glide best at their "best glide speed" which is a function of drag, weight, and airspeed. This answer assumes that, as for most airliners, best glide speed is in the region of 200-250 knots, and that an airliner is unlikely to descend at/faster than their best glide speed in the approach phases where speeds are typically in the 150-200 knot range.

At lower altitudes when descending under ATC, the above ATC-centric discussion applies. At higher altitudes, it tends to revolve around efficiency and company policy: the longer you can stay at cruising speed/altitude, the more efficient your flight will be: therefore it saves the airline money to descend as late as possible, requiring a higher descent rate. Spoilers, of course, help with that.

TL;DR: Some of it stems from the aircraft design being more aerodynamic and therefore better at gliding, but it's more closely related to ATC being busier and therefore keeping aircraft higher/faster for longer, which requires higher descent rates and therefore the use of spoilers, along with the fact it's more efficient to stay high/fast in the cruise for as long as possible then descend later/faster


Is this plasma-thruster experiment actually measuring thrust? This experiment, which is being presented as an initial exploration of the feasibility of using microwave-generated plasmas in a sort of electic jet engine, has been attracting some attention in the general media, for example Ars Technica and Bloomberg News. To put it mildly, I am highly doubtful of the method used to estimate thrust, or even that it is demonstrating any thrust at all, but am I justified in that skepticism?

The experiment involves a vertical quartz-glass tube with an inside diameter of 24 mm. A compressor pumps air into the bottom, and immediately above that, the tube passes through the apparatus to ionize and heat the air, forming a plasma with a temperature up to 1,000 °C. The tube extends upwards beyond that for about another 23 cm, and the upper end is open to the air.

The thrust measuring device is a hollow steel sphere, diameter 75 mm, with a hole in it allowing small steel balls to be dropped into it to change its weight. In use, this sphere is balanced on the end of the quartz tube, and the weight is adjusted until the airflow causes it to wobble (there is a video in the figures section showing this.) The actual measurement of the "jet propulsion force" is the minimum weight of the sphere needed to prevent this wobbling.

On the basis of these measurements, the authors claim to have demonstrated, in this device, a "total propulsion pressure" of up to 24 kN/m², which they say is "comparable to those of a conventional jet engine of an airplane". I am not sure what "total propulsion pressure" is, but my back-of-envelope calculation suggests that they might be thinking of a jet engine's static thrust divided by the nozzle area. Regardless of whether that is so, their figure is simply the weight of the ball divided by the area of the tube, with the corresponding figure for the no-microwave situation subtracted.

Where does one begin to analyze this device? For one thing, at the point where the ball is not yet wobbling, there is presumably no flow (or just a little leakage.) Surely this is a static situation, with little or no relevance to what thrust might be generated? Furthermore, does the weight at which the ball will begin to wobble depend essentially entirely on how much pressure the compressor can reach with its outlet blocked? And pressure given here is only 1/4 atm. -- how much thrust can you hope for, from such a small expansion ratio, even with the best possible nozzle design and a 1,000 °C plasma?

No, it's not measuring thrust.  It might be measuring a proxy for thrust density (force per unit area).  Anybody could use their setup to measure a ducted fan or a turbojet or even a rocket, but nobody does.  They themselves could have calibrated their rattling-ball instrument with a conventional thruster of known, conventionally measured, thrust (a $20 electric ducted fan from a hobby store).  (What's the threshold for rattling, anyways?)

As Jpe61 commented, it would have been much cheaper and simpler to place their thruster on a load cell (a fancy bathroom scale) and observe how downforce increases when the thruster is running.  $100 instead of fancy metalwork.  See, for example, fig. 6 and reference 23 of Prasad et al, "A laser-microfabricated electrohydrodynamic thruster for centimeter-scale aerial robots," https://arxiv.org/pdf/1906.10210.pdf.  See also the fancier inverted-pendulum thrust stand used at Princeton to measure plasma thrusters.


Can diplomats be allowed on the flight deck of a commercial European airline? If a diplomat were to request access to the flight deck with proper identification, would he/she be allowed to visit the cockpit of a commercial airliner during flight?

Generally, airlines are required to have content in their ops manual clearly stating who is entitled to flight deck access from the point the engines are started until shutdown. In some countries, such as the UK, airlines are required to limit access only to essential personnel, and foreign airlines must follow the rule while in UK airspace. I would find it rather disturbing that an airline would allow access to the flight deck during flight ops to someone just because they have a diplomatic passport, given that some countries play it fast and loose with such documentation, and flight crews are not equipped to validate a passport.

SKYbrary is a wiki created by the European Organisation for the Safety of Air Navigation, International Civil Aviation Organization, and the Flight Safety Foundation to create a comprehensive source of aviation safety information freely available online. Its guidance on this subject is crystal clear:

  In the air, procedures vary from airline to airline and from region to region, but the principle that only those with legitimate need must be permitted flight deck access must be paramount. Beyond the pilots at the controls, this will include relief, check and training pilots. Exceptionally, such flight deck occupancy may exceptionally be extended to include other specifically-authorised employees of the operator - pilots, cabin crew and maintenance personnel. Flight Operations Inspectors carrying out observations on behalf of the State Regulatory Body may also be permitted access at the discretion of the aircraft commander subject to valid identification being presented prior to entry approval.


Are well-known IR AAMs 'compatible' with aircraft from other countries? The AA-2 Atoll was a Russian reverse-engineered clone of the AIM-9B Sidewinder.  There are some sources that indicate, with varying degrees of veracity, that it was a good enough clone that the two could be used with the other side's aircraft (i.e. early MiGs launching Sidewinders and Western aircraft of that era launching Atolls).

However, the Russians have developed other short-range AAMs since then (Aphid, Archer), and the US has evolved the Sidewinder quite significantly from its humble roots as well.  In addition, other Western IR AAMs have been developed as well (such as the Israeli Python family).  This, along with the presence of mixed coalitions and even mixed air forces such as Malaysia's in this modern age, has me wondering: whose IR AAMs can be launched from whose planes?

More specifically:

Are current Russian jets (such as Flankers and Fulcrums) backwards compatible to the AA-2's electrical interface? (Bonus points if they can actually launch the AA-2 still.)
How backwards compatible are current Western jets (on external stores stations) to early Sidewinders, electrically speaking? (I know that some early Sidewinders required a cryobottle in the launch rail, we can ignore that for now.)
How forwards compatible are current Sidewinders to early Western jets? (i.e. could you launch an AIM-9M or an AIM-9X in analog mode off of an F-5 or A-4?)
Are other Western AAMs (such as the Israeli Python) compatible with the Sidewinder electrical interface?  (i.e. can a US F-16 hang a pair of Python-4 missiles off its wingtips and have them work "out of the box"?)
Last, and most of all, could you launch a modern Sidewinder (AIM-9L/M/P or AIM-9X in analog mode) from a Russian/Soviet jet (of any era, bonus points if it's one of the modern ones though), or have the interfaces diverged enough over the years to make that impossible?  Do the Malaysians need two stocks of IR-guided AAMs at all times, or could they get by on Sidewinders if they ran out of Archers or vice versa?

The integration of weapons in an aircraft is based on four major issues.

The first issue is the mechanical compatibility: will the airplane break when you transport or fire the missile, because the missile is too heavy and/or is too powerful?
Typically, I don't think you can fire an AMRAAM from a P-51 Mustang....
This is a huge problem, but for the examples you give, the missiles are similar to each other so there is a great chance that both Sukhoi, Mig and McDonnell Douglas fighters have enough mechanical strength to transport and fire the missile. If there is not, you cannot do a lot of things to correct it, unless you change your airplane or your missile.

The second issue is about aerodynamics: will the missile, when fired, hit the airframe? It is likely the air flow around the airframe will create whirls which that might cause the missile to be pushed into the airframe.
This issue is often solved by studying how the missile will behave in the whirls of the aircraft, and by designing it to go away from the aircraft.
Note: you also don't want your air to air missile to go straight down, because it will lose the target. So this question of aerodynamics is always important

The third issue is about sensors: if you fire a missile, you first need to "tell" it what its target is. So you need to have sensors (or external sensors from which the aircraft has info by radio) in your aircraft.
By extension, you need to have the good sensors in your aircraft (the appropriate distance to use the full distance of the missile....). Again, for the modern fighters you mentioned, it will in general be OK. Even more if you're speaking of infrared missiles that don't have that much information before launching.

The fourth issue is electrical and electronic interfaces. In most of the cases, you can plug them in.
But you might have to adapt the current and tension on the electrical interfaces. On that point, you are lucky because the aircraft industry uses conventions of frequency for electrical current in order to have components with the smallest weight. So there is a good chance that Russian as well as Western jets have the same frequency of currents, and can adapt the tension and current.
On the electronic interface, you might have to change the missile launcher on the aircraft to have the correct plugs. I don't know how huge is it to change a missile launcher, but I guess that if it is possible for military people to do it, it takes at least a few hours.

To conclude, there is a high probability that all the missiles you mentioned are compatible with some industrial adaptations provided to the missile and/or the missile launcher, and some programming to do in the aircraft combat system. However, combining these missiles requires that the crew doing it knows in depth both the Western jet technology and the Russian missile technology.... which might be difficult in our political reality!


How are operators of small UAS craft supposed to know about flight restrictions? The FAA is requiring all operators of small unmanned aircraft systems between 0.55 and 55 pounds to register. This is to help ensure that operators of model aircraft and drones act in a responsible manner, etc.

In the Registration and Marking Requirements for Small Unmanned Aircraft document available from the FAA (PDF), there are examples given of drones being flown near wildfires that interrupted firefighting efforts, despite a temporary flight restriction for the area surrounding the fire.

It seems obvious to me that operating an RC aircraft near a wildfire might not be a good idea. However, "temporary flight restrictions" could exist in other cases that aren't quite so obvious. There is no requirement (as far as I know) for sUAS operators to check NOTAMs, aviation charts, etc.

How can an operator be sure they are in compliance in every situation? It seems like it might be very easy to violate some regulation inadvertently.

Information about current and future TFR areas is available from the FAA, even as an easy-to-read map. If someone is planning on flying a manned or unmanned aircraft, that should be on their list of things to check ahead of time.

As far as other airspace restrictions, we have a question detailing the different types of airspace. It would be worthwhile for a UAS operator to learn enough about reading charts to at least know the airspace in the area where they intend to fly.

Another option would be to attend ground school or at least do some amount of self-study. Just as pilots need to know how to operate according to the rules of the airspace system, UAS operators could benefit from the education.


Where is the safest seat in the plane? If I'm going on holiday with my family on an airliner such as one of the ones listed on this page, then where is the safest place to sit?

The answers to this question seem to imply that the seats at the rear of the plane would be safer:
Why are flight recorders generally located in the tail?
but of course I can think of quite a few things which might make it different for passengers versus the flight recorder.

I realise that flying is statistically a lot safer than driving, so I don't need to be told not to worry about safety - I'm not worrying, I'm just interested in the difference in safety between different seats in the airliner. Because if I get a choice of seats then (ceteris paribus) I can't see any reason not to choose the safer ones.

I'm guessing it might be affected by things like proximity to the exits, and so might be different in different models of airliner. If that's the case then can you tell me what factors affect the safety of each seat? E.g. is it more important to be close to an exit or to be further back in the plane? What should I look for?

Is it different on long-haul versus short-haul? Or are there other differences in the type of flight (and therefore the more typical type of accident) which change the 'safest place to sit'?

A few articles I've found on the topic:
 - Popular Mechanics, 2007 (statistical review: back is safest)
 - Discovery / Channel 4, 2013 (one-off crash experiment: back is safest)
 - BBC, 2014 (expert opinion: no safest place)
 - CAA, 2006 (statistical review of evacuations: exit rows and adjoining rows are safest)

Before I start, remember that we're talking about statistics of location in the aircraft, within statistics of survival of an accident (95%), which is itself dependent on a statistic of particular type of accident (approx 85% have no fatalities at all), within something which is already a very unlikely event (an aviation accident).

So let us for a moment assume that you're in a semi-survivable accident, ie where there are a mixture of fatalities and survivors - this is already a very unlikely scenario... in the vast majority of accidents either everybody dies (rare), or nobody does (most common).

To give you the straight out answer to your question, in such an accident, the rear of the plane is safest - more passengers have survived plane crashes in those seats than any other. This is due to most accidents being nose-first, so if it's going to be partially survivable your ideal location is near the back: the front of the aircraft essentially acting like a crumple zone. Thus, if an accident is survivable, you are more likely to survive in the back of the aircraft.

Of course, every accident is different - if your aircraft runs off the runway and spins, the back can impact first. Similarly if your aircraft stalls and pitches up. Alternately you could slew sideways into another aircraft in a taxiway etc etc... but in most cases, the impact is more likely to be nose-first, thus the rear is the safest place.

Also statistically, being near to a door but not next to a window gives the "optimum" chance of survival - more people survive in such locations. This is due to ease of evacuation (being near the aisle and the exit), and without being whacked in the head by a crumpling fuselage.

So if you're going on purely "increasing your chances", a non-window seat near the rear door is the best possible place to be in an accident... other than on the ground, having missed your plane.

The thing to remember, though, is that (referring to modern aviation)

Accident rates work out as roughly 1-per-1 million flights
Around 85-87% of aviation accidents involve no fatalities (so fatal accidents are around 15-per-100 million flights)
Even if you're in a crash where someone dies, Aviation accidents with fatalities have a fatality rate of somewhere between 5% and 25% (which is to say, even if we only look at accidents where one or more people do die, 75-95% of people in those accidents survive).

So that gives you a 1/4th to 1/20th of a chance of a 3/20th of a chance of a 1 in a million chance of becoming a statistic in my next post on this subject. So that would take you somewhere between 20 and 100 million flights before you die.

You have a 1-in-100-million chance of being in a fatal accident, and even then you a 75-95% chance of surviving it anyway.

So in short, if it's going to get you it will, if it's not it won't. By the time you've survived enough accidents for it to be anything more then sheer atrocious luck that you die at all, you'd already have developed a healthy fear of flying and have gathered enough air miles to take a taxi....


How do aerobatic aircraft land? The aerobatic aircraft I've seen don't have any flaps or air-brakes, besides they're taildraggers so I guess they usually have to do stall landing or three point landing but I don't understand how the pilot controls the approach speed or just how they slow down.

The same as any other powered aircraft would - controlling their descent with a combination of pitch and power.

Most small GA type aircraft don't have air brakes, spoilers etc anyway, so that's fairly immaterial.

I'd imagine almost any civil aircraft can be landed quite safely without flaps - it certainly forms part of the standard training syllabus for the PPL and you'd likely be expected to demonstrate a flapless landing on your skills test. The only difference is a slightly faster approach and more nose high attitude.


Advice for a future pilot? I've always wanted to be a pilot from the age of 3. I've always dreamed about flying high in the sky above the clouds and getting that amazing experience that you can't get any other way.

I'm now turning 16 and am realising it is coming close for me to start my goal of becoming a pilot.

I would appreciate if anyone could give me some advice on what to do to become a pilot.

What qualifications you need?
Where you train?
Wages?
What are the health requirements?
Etc

This is for a pilot in the UK who is hoping to work in Dubai for Emirates.

Thanks.

What you could do right now is train to be a glider pilot. You probably already have the right age. It is a wonderful experience, and it will be a good basis for a power license.


Is there a maximum possible size for an airplane? Is there any theoretical or practical limit to the maximum number of passengers - and therefore size - one can build an airplane for?

It is no accident that the biggest birds are flightless. The ability to fly goes down with increasing size, so there is also an upper limit for aircraft. The main reason is that as size increases, masses go up with the cube of the size increase while the load-carrying structures like wing spar cross sections only grow with the square of the size increase. This power law is the simplest of the scaling laws.

Since the loads on an aircraft's wing depend not only on its size, but also on many more parameters (angle of attack, speed, aspect ratio …), there is no clear boundary, and advances in materials help to shift the size limit up. If one would try to build the biggest airplane in the world, the wingspan could easily be double of what todays biggest airplanes measure, but the utility of this airplane would be very limited.

Using this airplane for passenger travel would add more restrictions like the number of emergency exits and the maximum distance to the nearest exit, but this could be overcome by using several smaller fuselages. A double-hull airplane would also spread out the payload weight, so the wing would experience a reduced root bending moment. Going from this (source):

to this (source):

would immediately raise the size limit substantially. However, it would require new, wider runways to take off from. And adding more fuselages to the same wing will run into flutter problems soon.

The next indication could be designs which have been studied and deemed feasible but were eventually not built for economical reasons. Here the biggest are ground effect vehicles: Flying slowly in dense air pushes the size limit up. The Boeing Pelican was planned with 152 m wingspan, and Beriev proposed one with 2500 t take-off mass and 125.5 m wing span.

I would guess that a wingspan of 200 m is still feasible, and when spreading the weight even 500 m should be realistic, but totally unpractical. Taking a lesson from history, this would be a multi-hulled flying boat which flies in ground effect, similar to the (mono-hulled) biggest aircraft record holders in the 1920s.


What is the "A/B AUTO EXT" button for in a Falcon 7X? What is the "A/B AUTO EXT" button in the overhead panel of the Dassault Falcon 7X? I see it's in the Flight Control section but I don't know what is its purpose.

(sorry for low quality image)

It's the arming switch for Air Brake Auto Extend on landing.  The airplane has speed brakes (often called Flight Spoilers) the pilot can operate manually for glide path control.  This mode extends them automatically as lift dumpers after touchdown.


Where can I find information on the DC-9's turn radius in flight? Does anyone know where I can find information on a DC-9-30's turn radius at various altitudes and airspeeds?  I've tried Googling it, but all I've found is information about its turn radius while taxiing.

No different from any other jet.  Use this turn radius calculator http://www.csgnetwork.com/aircraftturninfocalc.html


For subsonic aircraft, would adopting a higher wing loading decrease drag? First, let's assume that problems with approach/TO speeds can be fixed by high-lift devices.
Here we read that the wings create more drag than the fuselage. So, an improvement seems obvious; shrink the wings.
However, for a given weight, altitude, and airspeed, such a wing would need to fly at higher angle of attack, creating more induced drag. How does this compare against reduced parasitic drag?
If one wants to reduce induced drag, than one must fly at lower altitude. This means more parasitic drag - again. But does the former outweigh the latter?
Induced drag can be reduced further by the weight reduction from a smaller wing. How does this compare to the above?

Generally, you are right. Reducing wing area is reducing overall drag. Within limits.
Induced drag depends on speed and span loading. If the reduced wetted surface allows you to fly faster, reduced drag will be lower, leaving more of the power budget to overcome viscous drag. However, if wing span is reduced, induced drag will be higher at the same speed, so it is better to reduce chord than to reduce span. This can be witnessed by the recent development in airliners where the reduced fuel flow of engines has allowed to build smaller wings with higher aspect ratios. A similar but older example is the Davis wing which combined extreme root airfoil thickness and an aspect ratio of 11 to minimize overall drag and keep wing weight reasonable. Other aircraft designed for long range even sported an aspect ratio of 14.5!

If one wants to reduce induced drag, than one must fly at lower altitude.

Don't focus on induced drag reduction alone! Please remember that the lowest overall drag is at the polar point where induced and zero-lift drag are equal. Move away from this point and overall drag for lifting the same weight increases.
Turbine engines profit from colder air. Flying higher means higher true air speed for the same dynamic pressure. Therefore, wing area should be sufficient to allow operation close to the tropopause. Going higher than that does not improve things, but staying well below the tropopause means to forego an obvious advantage. Only airplanes designed for low level missions will have a wing loading well above the 600 kg/m² which is typical for airliners. That's the limit mentioned above.


When is an aircraft cleared to land? In Is there a minimum separation between a landing aircraft and another crossing its runway? it was explained that once an aircraft has clearance to land, that runway is reserved for the exclusive use of that aircraft.

At busy airports you can usually see a long line of four or more airliners descending a glideslope towards a runway.

Image by nustyR AirTeamImages (found via LondonReconnections)

Looking at FlightRadar24, the time between aircraft appears to be of the order of about 85 seconds according to my stopwatch.

It seems as if, by the time the previous aircraft has turned off the runway, the following aircraft has a very short time to obtain clearance or decide to go around.

At what point is each aircraft given clearance to land by ATC?

Usually, the clearance is given when the runway is clear of traffic or, at least in Europe, when two conditions are met:

Reduced Runway Separations is in use and the criteria for issuing the landing clearance are met.
The previous traffic will have left the runway when the following aircraft crosses the threshold. (Non-withheld landing clearance)

  321.5 Landing clearance need not be withheld until prescribed separation exists
  if there is reasonable assurance that the appropriate separation will exist
  when the aircraft crosses the runway threshold. However, do not clear an
  aircraft to land before a preceding landing aircraft has crossed the runway
  threshold.

Aircraft can also be made aware to expect a late landing clearance.

Clearing multiple aircraft to land in a sequence on the localizer is not used in countries operating under ICAO rules. This is more of an FAA procedure, as described in the other answers.


What are the limitations in adoptions of GTF (Geared Turbofan) technology? The only recent engine using GTF technology is the PW1000G, however some old designs like ALF502 or TFE731 use this technology. I understand the basic concept of the benefit obtained by the engine introducing this technology (basically giving another parameter to optimize RPMs at low pressure turbine and fan) and that benefit is compensated by the increase in weight.

What is blocking this technology to be further included in modern turbofans? Is it only a business case for P&W architecture?

What made it possible in PW1000G that blocked PW8000?

The factors that are relevant here are:

Increasing the bypass ratio is very desirable in order to improve the efficiency of the engine, and for the same amount of thrust, this means increasing the fan diameter.
In order to keep the fan mostly subsonic, the fan rotational speed has to decrease with increasing fan diameters. Supersonic fan blade tips are possible and in use, but you lose efficiency and increase noise, so it's desirable to limit this to the outermost area.
For the same efficiency, a low-speed turbine requires more stages and therefore more weight compared to a high-speed turbine. Compare the PW1100G's 3-stage LPT (geared) with LEAP-1A's 7-stage LPT (not geared).
The only way to decouple the rotational speed of the LPT from the rotational speed of the fan is by using a gearbox.

In the long run, this is therefore a question of whether the gearbox is heavier than a slower-turning LPT and whether a possible increase in maintenance costs due to the gearbox is acceptable for the given gain in efficiency or reduction in engine weight. With further increases in engine bypass ratios, the gearbox becomes increasingly attractive.

In the short run, this is also a question of whether a company wants to risk developing a completely new component, with potential problems before and after entry into service. Additionally, with a given amount of money and manpower to develop a new engine, management will ask: Where are the engineering hours going to make a bigger difference, in improved fan, compressor, turbine and combution chamber designs/materials/... or in a gearbox design.

So while, for example, Rolls-Royce does not manufacture a geared turbofan right now, their "UltraFan" research engine project does include a gearbox. I think it's safe to say that it is only a matter of time until most commercial turbofans will include a gearbox.


Are there any "captains-only" airports in the U.S.? Some airports in the world only allow captains to take off or land the aircraft, due to airport design or environmental conditions (obstacles, high winds).

Examples include:

Funchal (Madeira, Portugal)
Heraklion (Greece)
Paro Paro (Bhutan)

Are there any airports in the United States that are "captain-only", either for take-off or landing or both? Why so?

As already mentioned in the comments, I don't think there is such a thing as "captains-only" airports. The airline/operator might impose special requirements on crew, such as a certain amount of experience and/or being a captain. It might also require the crew to be additionally trained for that specific airport (this can for instance be conducted during the Operators Proficiency Check).

To add to that, I could be captian on one flight, and be first-officer on the next. Makes no sense to not allow me to conduct the approach/departure, just because my rank is not captain on that specific flight.

In Europe, I know of some airports in the Alps (and Cannes on the French coast, just to name one) that require a yearly theoretical test to be made by pilots operating on the airport. This is due to some very specific rules at those airports.


Why does the DC-8-70 have the same MTOW as the DC-8-60, despite its more powerful engines? The DC-8-70 is a more-or-less straight reengine of the DC-8-601, replacing the obsolete JT3D-3B low-bypass turbofans of the DC-8-60 with the CFM56-2C1 high-bypass turbofan.  According to Wikipedia, the maximum takeoff weight of the DC-8-70 was unchanged from that of the DC-8-60 (which resulted in the DC-8-70, with the heavier CFM56, having a slightly lower payload capacity than the DC-8-60):

  The DC-8-71, DC-8-72 and DC-8-73 were straightforward conversions of the -61, -62 and -63 primarily involving replacement of the JT3D engines with more fuel-efficient 22,000 lb (98.5 kN) CFM56-2 high-bypass turbofans with new nacelles and pylons built by Grumman Aerospace and fairing of the air intakes below the nose. The DC-8-71 achieved the same end but required more modification because the -61 did not have the improved wings and relocated engines of the -62 and -63. Maximum takeoff weights remained the same, but there was a slight reduction in payload because of the heavier engines. All three models were certified in 1982 and a total of 110 60-Series DC-8s were converted by the time the program ended in 1988. DC-8-70 conversions were overseen by Cammacorp with CFMI, McDonnell Douglas, and Grumman Aerospace as partners. Cammacorp was disbanded after the last aircraft was converted.[10]

Emphasis mine.

But maximum takeoff weight is determined by engine power,2 and the CFM56-2C1 has nearly a quarter again as much thrust (98 kN; 22 klbf) as the JT3D-3B (80 kN; 18 klbf), which should result in a proportionate increase in MTOW for the CFM56-2C1-equipped DC-8-70.

So why does the DC-8-70 have exactly the same MTOW as the DC-8-60, despite its significantly-increased engine power?

1: The DC-8-72 and -73 are literally just reengined DC-8-62s and -63s; the DC-8-61 required some additional modifications to make it into the DC-8-71.

2: It's the maximum weight at which the aircraft is physically capable of attaining liftoff speed on an infinitely-long frictionless runway at zero density altitude with one [for twinjets] or two engines [for more-than-twinjets] inoperative; beyond this weight, the aircraft has insufficient one-or-two-engines-out thrust to push it fast enough to generate enough lift to lift off.

But maximum takeoff weight is determined by engine power

not by engine power alone. The airframe also has to be strong enough for the intended takeoff weight. There is a structural strength margin, but this margin is mandated by the certification authority so you can't use it. The design won't have much more than the required margin because that would make the aircraft heavier than necessary and less competitive.

At a minimum, you'd have to get the aircraft certified at the new MTOW, which requires expensive testing. Worst case, you have to modify the design of parts like the wing box/spars, landing gear, and fuselage structure.

By 1988 the writing was on the wall for narrowbody 4-engined aircraft, with ETOPS-180 coming into force.

  It's the maximum weight at which the aircraft is physically capable of attaining liftoff speed on an infinitely-long frictionless runway at zero density altitude with one [for twinjets] or two engines [for more-than-twinjets] inoperative;

No. That would make the definition of MTOW useless in the real world. Compare to the FAA definition:

  The Federal Aviation Administration has defined Maximum Takeoff Weight (MTOW). The MTOW of an aircraft is the maximum weight at which the pilot of the aircraft is allowed to attempt to take off, due to structural or other limits.

The MTOW you see in manufacturer specifications is a figure established in the certification process. This will be below the physical maximum weight the aircraft can handle, to make sure there's a margin of safety.

In many circumstances (airfield runway length, altitude, temperature)

  an aircraft may not be permitted to take off at its MTOW... The maximum weight at which a takeoff may be attempted, taking into account the above factors, is called the maximum permissible takeoff weight, maximum allowed takeoff weight or regulated takeoff weight.


How do radio communications work en-route for intercontinental flights over the oceans? What is the altitude one must reach in order to communicate with the ground?
Is it possible to talk to ground via radio flying over the oceans?
How to know the exact position of an aircraft over the oceans?

As Ron mentions in the comments aircraft flying transatlantic routes (or really any long route for that matter) may use HF radios operating in the 3-30MHz range to communicate over long distances. HF radio waves have the ability to "skip" off the ionosphere if directed properly and thus propagate over the horizon and beyond line of site.

You can find some various frequency info here.

Honeywell also offers at least one satellite based solution.

You can also find a lot of good info here under the "communication" tab.

As for knowing the exact position of the an aircraft, this answers covers most navigation methods out there.

This thread quotes FL300 (30,000 Ft.) as the minimum altitude for continuous coverage across the Atlantic as does ymb1's answer here (route dependent).


Is this opinion on personal computer flight simulators too strict or is it actually true? A couple of days ago I had a discussion with a commercial pilot and his opinion on personal computer flight simulators were a bit surprising to me.

He said that flight simulators, even with expensive payware aircraft are about as close to the real plane as Call of Duty to real warfare.

He said that most of the time the systems and the switches appear to look similar but key factors when operating those systems are missing, mainly because the manufacturer keeps those details more or less undisclosed. The developers don't even know what to simulate and it makes every single flight simulator just a simple game that bares a slight resemblance to reality but that's about it.

This surprised me to say the least, because I thought the well known, premium payware planes simulate the instruments and the systems very well and all the details regarding those systems are available in manuals that we can easily find online.

But I didn't really know that pilot well so I just accepted his answer, I didn't want to seem rude and try to debate him, but I'm very curious if he told the truth or he just tried to exaggerate. I'm especially skeptic about his comment on the undisclosed nature of flight systems.

It isn't true, not as an indictment of the simulator software community as a whole anyway. It may be that your pilot friend doesn't have experience with modern simulators, let's take X-Plane for example...

X-Plane has a "professional use" version, which is simply the regular X-Plane with a commercial license and a few extra features. The underlying software is still the same. X-Plane "for professional use" can be FAA certified as a training device.

This means that the aircraft behaves exactly as would be found in the real world. In fact, X-Plane is sometimes used to verify flight models before more expensive methods are used, and they are relatively accurate. NASA has even written research tools to utilize X-Plane. X-Plane's Garmin G-1000 is incredibly realistic, and X-Plane "for professional use" can drive G-1000 simulator devices.

You can buy other "professional level" simulators for home use like the Redbird Jay which runs the same FAA approved software as the certified simulators. The same is true with Elite Simulator.


When were flares first used as IR countermeasures, and by whom? I've been trying to find the history of flares (as countermeasures to heat-seeking missiles), but have not had much luck. Closest thing has been this wiki article which has but a single sentence in its history section saying "First deployed during the Vietnam War", with an explicit "citation needed" tag.

Another article is also surprisingly void of history details, and doesn't even have a history section.

Who first conceived of flares as IR countermeasures? When and where were they first used on a large scale?

The only hint I have is that the AIM-4 Falcon was the first IR-seeking AA missile to enter service, doing so in 1956. So presumably flares would not have shown up until that year or later.

The document Genesis of Infrared Decoy Flares- The early years from 1950 into the 1970s by Naval Surface Warfare Center has a lot of details about the work done on decoy flares in the initial stages, at least in the US.

According to the report, the first use of IR flares was not as a decoy, but as a tracking device for drones. The T-131 flare was used in this capacity. From the report:

  NOTS, China Lake was involved with infrared target augmentation since 1954. ... The T-131 tracking flare developed at NOTS was the first infrared source for drone use. Six to sixteen of these are needed on the F6F-5K drone to provide a suitable signature.

The first IR flare developed as a countermeasure is the NOTS Model 704, which was developed around 1959. However, the studies on decoys for IR started in the mid fifties, though the concept of using flares came later (the initial concepts were towed decoys). From the report:

  The Hayes Corporation, Birmingham, Alabama initiated infrared countermeasures and radiation suppression studies in 1955. ... There was a need about 1957 to create a decoy device that would simulate the signature of a turbojet engine. Instead of the pyrotechnic decoy flare approach,
  ... proposed an inflatable envelope that absorbs the energy from a self-contained pyrotechnic and re-radiates this energy at a lower temperature approximating that of the heated surfaces of the turbojet engine.

Initial flares (RR-77, probably) were fitted in the B-47 and B-52 bombers, which were deployed through the AN/ALE-14 dispenser around 1960. Though the report has indications that the flares were used in the Vietnam war, there is no data on the exact time and location of the use of flares in combat. However, we can be sure that the IR flares were used in combat in Vietnam. The report says,

  In 1967, Dr. Edwards of Air Development Test Center at Eglin Air Force Base, requested Picatinny Arsenal to improve the ALA-17 flare. The Air Force wanted a quick fix to the poor rise time of the ALA-17 flare. They also required that a single ALA-17 flare would have decoy capability to protect B-52 bombers in Southeast Asia against seekers operating in the 2μm to 3μm and 3μm to 5μm bandpass.

indicating feedback from combat operations. Though I'm sure that the Soviets too were developing IR flares at the same time, not much detail is available about their effort.


Why do airlines over-estimate/over-calculate flight times? A specific example I'm referring to is Cathay Pacific's CX138 flight between Sydney and Hong Kong. This flight is scheduled to be 9 hours & 40 minutes long (departing SYD at 22:20 local time and arriving HKG at 05:00 local time) but in reality from Flightradar24 data, as well as having been on the flight, it seems that this flight consistently arrives around 03:45 to 04:00 average, which is a very early arrival. So why is the scheduled flight time so over-stated ? (Ironically, other CX flights between SYD & HKG at other times of the day have shorter scheduled flight times)

Mainly, to improve their image. Though I'm not sure about this specific flight (or airline, for that matter), it appears that over estimating flight time is usual.
For airlines it is better to overestimate the flight times and then claim that they are punctual, rather than correctly say the required time and then be late due to some unforeseen reasons. For example, if an airline says that a flight takes 80 minutes (while in reality, 60 minutes suffices) and then completes it in 70 minutes, the perception will be that the flight is early. After all, nobody is going to check the exact time required for flight.
In general, the airlines would add some extra time to cater for things like tarmac congestion, holding time, connecting flight etc. However, it appears that the airlines are increasingly padding their 'block times' (which includes estimated flight time, taxi time at both ends, and time for short delays) in order to appear punctual.
This report by USAToday points out that (in US) more flights were arriving early than late (in 2012) and it appears that the trend remains the same. The report points out:

The average flight from Boston's Logan airport to New York's LaGuardia took one hour in 1995. In 2012, it took 75 minutes.
Yet the Logan-to-LaGuardia early-arrival rate soared to 38% last year from just 2% in 1995 as Delta and US Airways added nearly 20 minutes to the schedule.

This makes the passengers think that the flights are on time, though they are actually late (when compared to earlier timing). For example, U.S. Department of Transportation considers a flight as 'on time' if it arrives at its destination within 15 minutes of the scheduled arrival time and without being diverted or canceled and can penalize chronically delayed flights i.e. if they are more than 30 minutes late 50% of the time.
There are other issues here- it takes time to buildup data in specific routes and airlines are cautious in the meantime, airports are getting more and more congested making the total flight time to increase etc., but even taking these into account, it is better for airlines to overestimate than underestimate.


Why do some airlines not use containers for luggage? Many planes allow the use of ULD containers to store hold luggage: such luggage is placed into the containers, then the containers are stored in the hold of the plane.

There are many advantages to this, as explained here: Why is luggage required to be loaded in containers?

However, some airlines do not use ULD containers even when that is possible. I have in mind Easyjet on their A320-family planes, which don't use containers, at least on some flights, even though the planes definitely can handle them.

What could be the possible reasons for this? Given the high emphasis on saving every single penny they can, I suppose they have tried both approaches and come to the conclusion that not using ULDs is actually somehow cheaper than using them, which seems counter-intuitive:

it should take longer to load and unload luggage one by one than just move containers in
more manipulations increases the risk of damage to the luggage

Possible reasons I can guess at (but not verify) are:

loading the containers is actually not so much faster, with containers possibly getting stuck or some similar problem?
loading containers requires more equipment, and turns out to be more expensive for this reason
it depends on the amount of luggage being carried?

Does anyone have any insights on this?

In addition to the reasons given by @aeroalias, cargo containers also waste space.

From the A320/321 Operator's Manual:

The A320 can hold up to 7 containers. The A319/320/321 do not use the standard LD3 containers. They use the slightly smaller AKH container.

Each of these has a volume of 3.7 m3, so seven of them totals 25.9 m3. When bulk loaded the A320 has 37.28 m3 of cargo space. That's almost 44% more room.


Do airlines in Middle East use higher cost indexes? Cost index equals time cost divivded by fuel cost. Given that, do the airlines in Middle East generally use higher cost indexes because fuel costs are much cheaper?

Not all of the Middle East countries are oil rich. And recent developments highlight that there's a shift away from an oil-based economy. Most recently Saudi Arabia introduced taxes for the first time, with a 83-127% hike in petrol prices. And Dubai introducing VAT also for the first time.

An in-depth analysis of Emirates' financials as of Jan 2017 can be found here, in an article titled, 'Is Emirates in trouble?'.

  Jet fuel is still the highest operational cost item but has declined sharply since 2014/15.

They also had issues with yield and load factors. It's a business like any business, if you can't fill the seats, you're not making money.

Here are the latest fuel prices from IATA as of 2 Feb 2018:

A metric-ton is \$17.7 cheaper than the most expensive region. So for a long-haul that needs say 100 tonnes of fuel, that's a saving of \$1,770. But, don't forget that when a Gulf carrier flies to anywhere outside the region, they'll fill up their tanks there, likewise for say a European carrier filling up in the Middle East.

It may be more beneficial to a regional low-cost carrier though. But since short flights are not as affected, any little saving will help towards a profit. Also note a high cost index is not just about cheap fuel, but also expensive maintenance. It is used when the flight-hours need cutting down as the plane ages. A low cost-index could also be used to delay the arrival to let a storm subside (even with cheap fuel on board). It's complicated.

Taking Emirates for example, when they fly westbound with the cheaper fuel, they could use a higher cost index to offset the headwind, and on the return, a low cost index to offset the more expensive fuel they picked up, but since now they are in tailwind, the time penalty won't be big.

As for the exact cost indexes, that information is not public, and with the aforementioned developments and putting the fuel costs in perspective, I hope that helps.


Are we changing the angle of attack by changing the pitch of an aircraft? For example:

if I pitch the airplane up, but also increase power and am able to maintain the same speed, then no, the AoA hasn’t changed, although it may have varied in the transition between one situation and the other. And yes, I’ll probably be climbing, although there are exceptions, becuase…
if I pitch up, slow down, and maintain the same altitude, then undoubtedly the AoA has increased. Flying slower reduces the amount of lift generated. An increased AoA gets that back so I can maintain the altitude.

Can someone explain these situations why exactly are they producing different results in AoA?

Can someone explain these what is going on in terms of forces?

Please explain in reference with these forces ( in the pic )

First of all, note that the diagram linked in the question is erroneous.  The equations may be right, but the forces are drawn in the wrong proportion-- lift is erroneously shown as greater than weight, when it should be less than weight.  Also thrust appears to be about equal to drag, when it should be distinctly greater than drag.  Only when lift is less than weight and thrust is greater than drag can we build a closed vector triangle-- meaning that net force is zero-- from weight, lift, and (thrust minus drag ).  For more, see this answer to a related question Does lift equal weight in a climb? .  (If you want to see a similar diagram from an outside source, see the one included in this answer to a related question Is excess lift or excess power needed for a climb? )

Just as NASA also messes up the proportions in this diagram for gliding flight--  https://www.grc.nasa.gov/www/k-12/airplane/glidvec.html -- again, lift is shown as being greater than weight, when it should be less than weight, so we can build a closed vector triangle from weight, lift, and drag.  For more, see this answer to a related question What produces Thrust along the line of flight in a glider?

Now as to your questions-- to a first approximation we can think of our pitch control inputs-- the position we are placing the control stick or yoke in, in the fore-and-aft direction-- as most directly governing angle-of-attack, not pitch attitude in space.  Pitch attitude in space is influenced by the climb angle which is influenced by power setting.  Now, there are all kinds of inter-relationships that complicate things-- for example on a high-wing plane with flaps down, adding power may produce a strong downwash over the tail that tends to lead to an increase in angle-of-attack.  But to a first approximation we can think of our pitch control inputs as governing angle-of-attack.  There is a slight delay between a change in pitch control input and a change in angle-of-attack, due to the aircraft's rotational inertia in the pitch axis.

If I tell you that I've increased my aircraft's pitch attitude by 10 degrees but I don't tell you what I did with the elevator control to make that happen, nor do I tell you whether I've added power or not, then you have no way to guess whether I've kept the angle-of-attack constant and started climbing due to added power, or I've managed power as needed to keep altitude constant while transitioning to a higher angle-of-attack and lower airspeed, or any number of other possibilities-- I might even have put the stick or yoke forward to decrease the angle-of-attack and still added enough power that the aircraft transitioned into a climbing flight path resulting an in increase in pitch attitude.  For example when a jet fighter aircraft is climbing vertically on raw thrust alone, the control stick is probably forward of the position where it would be during horizontal flight at the same airspeed.  Certainly the angle-of-attack is lower in the vertical climb, than in horizontal flight at the same airspeed!

From the standpoint of what is really going on physically with the aircraft, most flight training curricula vastly over-emphasize the idea that the pilot is directly controlling the aircraft's pitch attitude.  What he's really doing is controlling angle-of-attack and power setting.  Yet the former way of looking at things works well enough in actual practice (e.g. flying an ILS glide slope by referring to an attitude indicator rather than an angle-of-attack meter as the primary guide to pitch control) and is simpler to think about.

A key point is that our flight operations are usually conducted on the "front side of the power curve", where for a given power setting, an increase in angle-of-attack usually results in an increased climb rate and an increased climb angle.  Therefore moving yoke or stick aft results in an increased angle-of-attack AND an increased climb angle (or a decreased glide angle) AND an increased pitch attitude. On the "back side of the power curve", like just above stall speed, an increase in angle-of-attack will generally lead to a decreased climb angle or increased sink angle, and the aircraft will end up in a more nose-down pitch attitude, so the idea that we're somehow directly controlling pitch attitude with the control yoke or stick no longer works very well.

Your question indicates a desire to better understand some of the physical relationships at play.  Lift is proportional to (lift coefficient * airspeed squared).  Lift coefficient is determined by angle-of-attack, with higher angles-of-attack creating higher lift coefficients.  As shown in the vector diagrams attached to the two links given at the start of this answer, for shallow to moderate climb or dive angles, lift is NEARLY equal to weight.  Actually, lift is a little less than weight unless the flight path is exactly horizontal, but for shallow to moderate climb or dive angles, the difference is small.  Since weight is staying constant, we can conclude that for shallow to moderate climb or dive angles-- with no other accelerations going on (airspeed is staying constant or changing only slowly, and the flight path isn't curving up or down, and the wings aren't banked so the flight path isn't curving to describe a turn), lift is also staying nearly constant.  This means that for shallow to moderate climb or dive angles, airspeed ends up being a pretty good guide to angle-of-attack-- to keep lift nearly constant, if the airspeed is low, the lift coefficient and angle-of-attack must be high.  So the airspeed indicator is in essence an angle-of-attack gauge.  At very steep climb angles where lift is quite a bit less than weight, things get more complicated-- if the aircraft is climbing straight up, lift must be zero, so lift coefficient must be zero, and angle-of-attack must be nearly zero (actually it must be slightly negative, unless the airfoil is completely symmetrical), no matter what the airspeed indicator reads.

In actual practice in general aviation, commercial aviation, etc, a shallow to moderately steep climb is NORMALLY carried out a higher angle-of-attack and lift coefficient--and therefore a lower airspeed-- than we'd use for high-speed cruising flight.  It's more efficient this way, and it also gives us the most climb performance out of a given, limited amount of thrust available.  Why?  Because a high lift coefficient also correlates with a high ratio of (lift coefficient to drag coefficient), which means a high ratio of lift to drag.  For shallow to moderate climb angles, the higher the L/D ratio we can achieve, the steeper we can climb for a given amount of thrust.  This is explored in more detail in the first link given in this answer. To look at climb rate rather than climb angle, we'd have to look at a chart of (power-available minus power-required) at various airspeeds or various angles-of-attack, but we'd come to a similar conclusion-- our best climb performance will be achieved at an angle-of=attack well above what we'll be using in high-speed cruising flight.

The diagram in the original question doesn't touch in any way on the relationship between airspeed, angle-of-attack, lift coefficient, magnitude of lift vector, and L/D ratio, so it doesn't help us to understand why a shallow to moderately steep climb is normally carried out at a higher angle-of-attack than we'd use for high-speed cruising flight.

Your question included the statement "if I pitch the airplane up, but also increase power and am able to maintain the same speed, then no, the AoA hasn’t changed, although it may have varied in the transition between one situation and the other."  For shallow to moderate climb angles, your statement is true for all practical purposes, but it is not EXACTLY true.  If we want to be very precise about it, we could note that since lift is slightly reduced in the climb, if airspeed stayed constant than angle-of-attack must have been slightly reduced, and if angle-of-attack stayed exactly then airspeed must have been slightly reduced.  This same idea came up in these two related answers to related questions, though in these cases the lift vector was reduced because the aircraft was in a descent rather than a climb -- 'Gravitational' power vs. engine power and  Descending on a given glide slope (e.g. ILS) at a given airspeed-- is the size of the lift vector different in headwind versus tailwind?


What is required to 'upgrade' software from DAL C to DAL A? What are the things to be noted or considered if a software which was initially treated as DAL C and later wanted to be considered as DAL A?

The main difference in effort is in the amount of verification required.

Design Assurance Level (DAL) C only requires statement coverage whereas DAL A requires MC/DC coverage.

Some of the DO-178C objectives have to be meet with independence where they didn't need to be previously, and some life cycle data goes from CC2 to CC1.

I would suggest looking at the objective tables A1-A10 in DO-178C


Can a Rutan Quickie be made into a legal Part 103 Ultralight? I was was thinking about buying a 80s rutan quickie q-1, it has a 18 hp motor. I want to get a ultralight but I like this one because it is fast. Can I get a motor that would be within the requirements? I don't know how I would be able to make this an ultralight. Iwas wondering if a Rutan 277 engine would work well in it and if this would be in the requirements

I doubt the Quickie would fly well enough at very slow speeds to meet the rest of the Part 103 requirements -- specifically, the limit on maximum level flight speed.  Limiting fuel capacity is easy, and the 18 HP original engine worked well enough on the Q1 -- but it was a lot faster than 55 kt (close to double, as I recall).  From comments (thanks, Gerry) I understand the Q1 has a stall speed of 42 kt -- fairly reasonable for a light aircraft, but well above Part 103 maximum of 24 kt.

You might be able to slow down enough by installing a flatter-pitch propeller, but that would have other effects (overspeeding the engine, for instance) that would need to be addressed, and then you'd be trying to fly with almost no speed range -- 42 to 55 kts isn't, IMO, a safe performance envelope (and yes, the Q1 would still go faster than 55 kt in a dive, but the level flight and climb performance are where the safety issues lie in this case).


What is this four-engine propeller airplane? I came across this print at a bargain store a couple weeks ago. At first I thought it might be a variant of a Lockheed L-188 Electra; then I noticed that it has at least 6 engines, as the print extends around the edge of the canvas and you can see a couple of propeller tips there. I haven't had any luck finding a 6- or 8-engine aircraft that matches it.

Edit: after looking at it a little closer, I think the edge might be a printing effect, an imprecise mirroring around the edge line (for example, some of the splotches look very similar to those in the front). So maybe it is only four engines?

I believe it's an Ilyushin Il-18. Pic from here:


Can I get an EASA class 1 medical if I am red/green color blind? When I got the Class 2 certificate(one week ago), AME told me that I am red/green color blind and the certificate is valid by day only. Is it possible for me to pursue an aviation career and pass the Class 1 certificate?
I failed almost all red/green Ishihara plates. I heard something about a test called CAD, and if I pass this test I can continue but im not sure.

For an applicant failing the Ishihara test, the next step is a medical assessor. If they're deemed "colour safe" (defined below), they can get Class 1 medical.
In your case, presumably, you were not deemed colour safe since you're daytime-only Class 2, if that's indeed the case, then unfortunately Class 1 will not be possible according to the EASA regulations below:

MED.B.075 Colour vision
(a) Applicants shall be assessed as unfit, where they cannot
demonstrate their ability to readily perceive the colours that are
necessary for the safe exercise of the privileges of the licence.
(b) Examination and assessment

Applicants shall be subjected to the Ishihara test for the initial issue of a medical certificate. Applicants who pass that test may be
assessed as fit.

For a class 1 medical certificate:

Applicants who do not pass the Ishihara test shall be referred to the medical assessor of the licensing authority and shall undergo
further colour perception testing to establish whether they are colour
safe.

Applicants shall be normal trichromats or shall be colour safe.

Applicants who fail further colour perception testing shall be assessed as unfit.

For a class 2 medical certificate:

Applicants who do not pass the Ishihara test shall undergo further colour perception testing to establish whether they are colour safe.

Applicants who do not have satisfactory perception of colours shall be limited to exercising the privileges of the applicable licence in
daytime only.

— Commission Regulation (EU) No 1178/2011

"Colour safe" from the same source means:

... the ability of an applicant to readily distinguish the colours used in air navigation and to correctly identify aviation coloured lights.


Can single engine aircraft fly in class A airspace? A friend surprised me the other day by saying that single engined aircraft are not allowed to fly in class A airspace.

I understand that the aircraft is under IFR in class A, with ATC clearance, (flight plan) and must meet PBN specifications, however I can’t find any documentation in my textbooks, EASA or ICAO stating that single engined aircraft are not allowed to fly in class A.

If anyone could resolve this issue it would be much appreciated.

Single-Engine aircraft can fly in Class A airspace. Pressurization or oxygen masks are required above 18,000 feet (no cannulas).