112
votes
Accepted
Why does it feel like a plane accelerates just before touching down?
The aircraft flares just before touching down. It descends with a constant velocity, and just before touching down pulls the nose up to reduce the descent. This results in a higher angle of attack, ...
- 62.3k
73
votes
Accepted
Does lift equal weight in a climb?
It depends on exactly how you define "lift" and "weight". You might say intuitively that lift is all the forces acting on the aircraft in the upward direction, like this:
In this case, lift must ...
- 1,063
58
votes
Accepted
Do airplanes need brakes in the air?
What you saw is called a speed brake, which is one of the functions of the spoilers. From the Boeing 737 NG FCOMv2 (9.20.5 Flight Controls - System Description):
Flight Spoilers
Four flight ...
- 57.6k
56
votes
Accepted
Does a carbon fiber fuselage suffer wear from pressurization/depressurization?
Yes, it does.
CFRP's fatigue manifests through multiple mechanisms. It usually begins with matrix cracks, causing a loss of bonding, and grows through delamination, i.e. loss of adhesion between the ...
- 28.2k
54
votes
Accepted
Are wings any more efficient at creating lift, versus orienting the engine's thrust downwards?
Interesting question. Purely empirically, it is the lift-to-drag ratio you are looking for. If you take this value as given for any particular aircraft, you have a direct answer for how much more ...
- 2,766
42
votes
Can someone explain the damage distribution on this aircraft that flew through a hailstorm?
Although the exterior of a jet airliner may just look like uniform aluminum with windows, the construction is actually much different than the outward appearance suggests.
The front of modern jet ...
- 2,767
38
votes
Can passenger airliners hover completely motionless in the air?
In theory they can stop moving relative to someone standing on the ground. In practice this does not occur.
Aircraft fly through the air and, yes, below a certain airspeed, an aircraft will stall. ...
- 102k
38
votes
Accepted
Why does each fan blade have a different mass and frequency?
Because manufacturing processes are not perfect, and the minute differences between parts as-designed and as-produced are amplified by the high rotational speeds and large diameters of modern jet ...
- 8,611
38
votes
Accepted
Can a plane bank without turning?
Yes it can. The steady-heading sideslip (SHSS) maneuver is used in flight testing to demonstrate static lateral/directional stability (similar maneuvers exist as sideslip approach in crosswind, or ...
- 11.1k
37
votes
Why do planes fly at a high angle of attack when flying slow?
Lift is (among other things) a function of the airspeed and the angle of attack of the wing. Hence, if you reduce your speed, you have to compensate the associated lift loss by increasing the angle of ...
- 11.1k
37
votes
Accepted
Has there ever been a case where elephants are carried by aircraft?
Pakistan to Cambodia. DHL.
https://www.stattimes.com/news/dhl-safely-relocates-the-worlds-loneliest-elephant-air-cargo/?infinitescroll=1
the first adult elephant to board an airplane in Pakistan
...
- 9,650
36
votes
People in a rollercoaster or falling elevator feel the rapid descent, so why don't pilots in the cockpit?
You only feel the acceleration downward. In roller-coaster this sensation is maximized for maximum thrill. A stall isn't instant: some parts of the wing can be stalled while the rest still provides ...
- 27.5k
34
votes
Is a "stalled" aircraft free-falling?
If the cables break on an elevator (and the safety brakes fail), you won't be in true freefall. You'll still have friction from wind resistance, from the guide rollers on the rails, etc. The same is ...
- 12.8k
33
votes
Flying upside down without feeling it
This sounds like a barrel roll.
This is a corkscrew-like flight path in which the airplane rotates around an axis between its longitudinal and pitch axes by flying along a path which lies on the ...
- 236k
32
votes
How can lift be less than thrust that is less than weight?
Your misunderstanding lies in your thought that lift is smaller than thrust, while in fact, lift is much larger than thrust.
The lift is provided by the wings. Their purpose is exactly to create a ...
- 13.7k
30
votes
People in a rollercoaster or falling elevator feel the rapid descent, so why don't pilots in the cockpit?
You only feel the plunging sensation during the initial downward acceleration. Once stabilized at a constant rate of descent, things feel normal again. The other thing is, the amount of vertical ...
- 134k
29
votes
Are wings any more efficient at creating lift, versus orienting the engine's thrust downwards?
With regard to energy expenditure and power,
for a given amount of force that is to be produced by accelerating
an air mass,
more power is required when you accelerate a small air mass
in each period ...
- 1,306
29
votes
Are wings any more efficient at creating lift, versus orienting the engine's thrust downwards?
In a traditional aircraft the majority of the power from the engine is used to keep the aircraft moving forward at a certain speed. Very little of that power is actually needed to create lift.
...
- 4,876
28
votes
Accepted
What's the use of so much torque on propellers?
Even small 1 hp electrical motors can achieve that RPM
Yes, but can it sustain that RPM when something tries to stop it, that is the question. 1 hp combustion engines can get to 2700 rpm as well, but ...
- 62.3k
27
votes
Accepted
Plane that always flies into the wind?
The short answer is no.
All the glider feels is its flight relative to the air. What the ground is doing beneath it is not relevant, the wind could be blowing a hundred kilometers an hour and the ...
- 7,092
26
votes
Accepted
Why does an airliner have a shallow descent when heavier, opposite to gliders with ballast?
If you can forgive my limited Paint skills:
It's the variable/constant speed that makes the difference.
Weight changes endurance (time to ground) and not range (distance to ground) if speed is ...
- 7,980
26
votes
Accepted
Why is thrust inverse to speed in piston engines?
Your question already contains the answer. As you say
kinetic energy is proportional to velocity squared, so it is easier to accelerate air from 0 to 100 m/s than from 100 to 200 m/s.
The same is ...
- 236k
25
votes
Do airline pilots use this high-speed, high-drag technique for losing altitude?
Airline pilots certainly do use gear/flaps/spoilers to descend more quickly if needed. However, SOP typically requires an approach to be stable upon reaching a certain altitude on the approach. This ...
- 73.5k
25
votes
What does it mean when an aircraft is statically stable but dynamically unstable?
Static stability means that a deviation from a trimmed state produces forces which return the system to this trimmed state.
If these forces produce an overshoot which increases over time, such that ...
- 236k
24
votes
Accepted
Can a barrel roll really be executed at a constant 1G?
You are absolutely right, a load factor of greater than 1 is impossible to avoid in a proper barrel roll. The barrel part of its name comes from the spiral path the aircraft needs to perform in order ...
- 236k
24
votes
Can passenger airliners hover completely motionless in the air?
Unequivocally: no. Big airliners (or passenger planes of any size for that matter) do not hover in air.
From a moving car, train or such it is possible to have an illusion that an airplane hovers ...
- 30k
23
votes
Accepted
How possible is a successful landing just with 1 wing?
This would be possible with other fighter jets that are of similar design to the F-15, i.e. have a low aspect ratio, much of their lift produced close to the centerline, and a lot of control authority....
- 28.2k
22
votes
Does lift equal weight in a climb?
In an aircraft that is climbing at a constant vertical velocity, the total of the upward-directed vertical forces is the same as the total of the downward-directed vertical forces.
Were it not so, ...
- 11.1k
22
votes
Why do planes fly at a high angle of attack when flying slow?
In order to maintain level flight, an airplane must generate lift equivalent to its weight. The lift generated by a wing diminishes rapidly as the airspeed decreases. To compensate, the angle of ...
- 2,688
21
votes
What would happen if a plane lost half of its weight instantly?
In steady flight, the lift $L$ generated by the wings equals the loaded weight so that there is no vertical acceleration. Thus, the lift just before the bomb is dropped is
$$
L = m_1g = 245\,250 \;\...
- 543
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