103
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 ...
- 104k
69
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 ...
- 1,023
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 ...
- 10.4k
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 ...
- 2,379
47
votes
Accepted
How do wings generate lift?
To get to the bottom of it, it might help to look at lift at a molecular level:
Every air molecule is in a dynamic equilibrium between inertial, pressure and viscous effects:
Inertial means that the ...
- 217k
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 ...
- 9,199
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.
- 401
45
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 ...
- 96k
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 ...
- 14.3k
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 ...
- 9,199
39
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
...
- 217k
38
votes
Accepted
Would an aircraft with contra-rotating propellers longer than the plane's wingspan be able to fly?
Short answer: This design will probably work, but it will not be very efficient. It can be tweaked into flying, but when you start tweaking, you would continue such that the outcome would look ...
- 217k
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. ...
- 57.8k
36
votes
How do wings generate lift?
Short answer: by exerting a downward force on the air around them.
Long answer: Some outreach people at NASA's Glenn Research Center have written up a very good multi-page explanation, dealing ...
- 12.5k
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 ...
- 16.4k
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 ...
- 12k
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: ...
- 39.2k
29
votes
Accepted
Why did the Solar Impulse flight take so long?
No, it could not fly much faster with the available energy.
Lift is a question of wing area and dynamic pressure. Solar Impulse 2 has 269.5 m² wing area to carry its 2.3 tons of mass. This is a ...
- 217k
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 ...
- 1,286
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.
...
- 4,796
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 ...
- 96k
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 ...
- 15.7k
25
votes
Accepted
What is vortex lift?
The vortex lift is the method by which highly swept wings (like delta wings) produce lift at high angles of attack.
In the case of wings having sharp, highly swept leading edges like delta wings, the ...
- 98.5k
24
votes
Accepted
How much thrust is needed by an aircraft to have vertical takeoff?
First, let's agree on terminology: What you saw in airshows is a vertical flight path. Flying horizontally first, the airplane pitched up until the nose was pointing straight into the sky.
...
- 217k
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
Why is lift larger than thrust?
Thrust is needed to overcome drag, and a good airplane design can create a lot of lift for little drag. In the case of an A-320, the lift-to-drag ratio is 18 in cruise (a little less during take-off), ...
- 217k
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, ...
- 10.4k
22
votes
Principle of aerodynamic lift: are misconceptions also taught in flight schools?
I am a CFI who teaches at a large (+200 students) flight school in the United States. You might be surprised to hear this, but...
We really don't worry about how a wing works that much.
As far as I'm ...
- 22.3k
22
votes
Accepted
Is there a maximum lift to drag ratio?
With current technology the L/D might go up to 70 or 75, and going higher would require an almost impractically large wing span. Gliders need to fly in tight circles to use updrafts, and the larger ...
- 217k
22
votes
What is vortex lift?
What it is
Vortex lift needs two conditions:
High leading edge sweep (ideally 60° and above)
High angle of attack, the more sweep, the smaller the angle when vortex lift becomes effective.
Vortex ...
- 217k
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