104
votes
Accepted
How do conventional missiles fly?
Air-to-Air guided missiles are little airplanes. If there are only fins at the tail, it's a ballistic rocket, basically a fin stabilized artillery shell accelerated by a rocket motor instead of an ...
- 126k
72
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 ...
- 1,053
55
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 ...
- 2,546
55
votes
Is lift in fact a kind of drag?
An 'aerodynamic force' (just one force...) appears when a body is immersed in a fluid stream. By convention, two components are chosen, one of them parallel to the stream direction, called 'drag', and ...
- 11k
47
votes
Accepted
Can lift occur if air is flowing over an object, but not under it?
Yes. This jar of paint weighs 34.8 g, but only 32.6 g to 33.4 g when a fan blows at it. The reduction of weight persisted when I repeated the experiment with a hodgepodge of baffles made from CD ...
- 10.6k
46
votes
Accepted
Was the Space Shuttle aerodynamically neutral while piggybacking, or did the combination act like a giant biplane?
This podcast with one of the pilots answers just about every question on the shuttle carrier you could have and it's worth a full listen. But to cover the flight dynamics, I would skip to 50:33 ...
- 101k
46
votes
Can a wing generate lift in excess of its aircraft's weight?
Yes, otherwise airplanes would be unable to go upwards into the sky.
- 501
43
votes
Accepted
Can a wing generate lift in excess of its aircraft's weight?
Yes, a wing can (given sufficient forward speed and angle of attack) generate lift greater than the weight of the aircraft. As with any "unbalanced" force, this will result in an acceleration of the ...
- 17k
40
votes
Accepted
How complete is our understanding of lift?
Short answer: Yes, our understanding of lift is complete, but solving the equations for some practical cases needs more resources than what is technically sensible.
Lift is a matter of definition
...
- 230k
40
votes
Could propeller wash provide sufficient lift to take off - even in theory?
Yes. The wing doesn't care what is causing air to flow past it. Headwind, propwash, 747 wake, gopher sneezes.
If the airplane is restrained from forward motion, and the propwash over most of the ...
- 10.6k
38
votes
Accepted
Why do helicopters not roll over when flying forwards?
Juan de la Cierva's first autogiro did roll over, twice, and he then applied the principle of blade flapping, a stroke of genius. Flapping is created by allowing the blade to move up and down. ...
- 61.3k
32
votes
Why are wings load tested upside down?
A wing can be tested in any orientation as long as the load is applied correctly. The classic wing test photo is the 787 in a fixture showing its extremely flexible wings.
I thought it might be fun ...
- 19k
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 ...
- 12.9k
30
votes
Accepted
Does a sudden drop of the velocity of the headwind affect the airspeed by lowering it?
Your airspeed does not remain constant because of inertia: it takes more time for the airplane to adapt to the new relative wind, compared to the time it takes for the wind to change.
Example One: ...
- 39.7k
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
27
votes
Why are wings load tested upside down?
@PilotHead is correct, but to elaborate a bit on why traditionally weight was put on the bottom is largely because its just easier. If you are Boeing you can afford to build a rig large enough to hold ...
- 101k
26
votes
Accepted
Why does a stall decrease lift, rather than increasing it?
For a parcel of air to generate a lift force as it flows over the wing requires the wing to tip that air parcel's momentum vector downwards slightly; the reaction force that the wing experiences as it ...
- 20.8k
24
votes
Can lift occur if air is flowing over an object, but not under it?
Yes.
Bernoulli end effectors are used in industrial applications to pick up items without physical contact using this principle.
Example:
- 341
23
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, ...
- 11k
23
votes
Why a kite flying at 1000 feet in "figure-of-eight loops" serves to "multiply the pulling effect of the airflow" on the ship to which it is attached?
The giant kites mentioned aren't the quadrilateral kites kids fly. They are airfoil shaped parachutes with open noses that generate lift as they move through the air. Ram air pressure inflates them ...
- 19k
22
votes
Accepted
How exactly can an airship lose lift?
The reason is a temperature difference between the lift gas and the surrounding air, and probably water uptake by the hull when descending through clouds.
A given mass of hydrogen will create a ...
- 230k
22
votes
How do conventional missiles fly?
The missile's wings are very large for it's mass, and produce a great deal more lift than the wings of the aircraft firing the missile.
One thing to note from the OP's linked video is that the F-35 ...
- 6,317
21
votes
Do any aircraft out there use negative lift?
A lot of aircraft generate negative lift- not in the wings, but in the tail plane. This is used for stability. Consider a trimmed aircraft as shown below:
Image from grc.nasa.gov
On most aircraft, ...
- 100k
20
votes
How do conventional missiles fly?
In the video you posted, the missile appears to continue falling even after the motor ignites -- you can see the missile start to overtake the aircraft even as it continues to drop:
By the last ...
- 681
20
votes
Accepted
Why does NASA say $v^2$ is velocity squared rather than speed squared?
The proper technical term for the quantity is velocity, and it is a vector quantity. Speed is a colloquial name. If physicists use it, they only use it for the magnitude of velocity, but most of the ...
- 56.2k
18
votes
How complete is our understanding of lift?
From this paper:
The principle of
equal transit times holds only for a wing with zero lift. [!!]
[...]
The air passes over the wing and is bent down. Newton’s
first law says that them [sic] must be ...
- 793
18
votes
Can a wing generate lift in excess of its aircraft's weight?
Furthermore to @Zeiss' answer, whenever an aircraft is steady-state banked, the lift will be greater than its weight. However, its speed will be constant; instead, the acceleration is centripetal and ...
- 11k
17
votes
How is lift produced when the aircraft is going down steeply?
The angle of attack is the angle between the chord of the wing and the incoming airflow.
Let's look at the case where the nose is 30 degrees down as you mention in your answer. The wing chord is ...
- 82.9k
16
votes
Does lift equal weight in a climb?
Short answer: No.
Long answer: When the flight path is not horizontal, lift will not be vertical but perpendicular to the direction of motion (in still air). Thrust will also have a vertical ...
- 230k
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