# Tag Info

103

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 explosion in a pipe. On missile like AMRAAM, Sidewinder, or Sparrow, the vanes are wings and the missile is a rocket powered aircraft that can climb, descend and ...

68

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 equal weight, otherwise the aircraft would be accelerating. That is, it's rate of climb would be changing. But it's more usual to define lift this way: Here, lift ...

55

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 the other one, perpendicular to that 'drag' is termed 'lift'.

54

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 effective wings are. It is the ratio of the lift to the total drag. The engine only needs to overcome the drag. With L/D equal to unity you would need the same ...

47

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 mass of the particle wants to travel on as before and needs force to be convinced otherwise. Pressure means that air particles oscillate all the time and bounce ...

47

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 jewel cases and Post-Its to prevent any air leakage under the scale's sensor plate. Others can easily replicate these results. Per FlanMan's comment, without the ...

46

Yes, otherwise airplanes would be unable to go upwards into the sky.

45

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 minutes, where the pilot states (please note there is no official transcript of the podcast and I typed this as I listened to it, please see the official podcast for ...

43

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 airplane in the direction of the lift, according to Newton's Second law. $$\mathbf F=m~\mathbf a$$ Please note, the entities in bold face are vector quantities....

40

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 wing is fast enough, let's say more than the airplane's stall speed, then the wing must generate enough lift to support the airplane, causing it to take off. It's ...

38

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 differently. Now let's look at your questions one by one: How feasible is it to use a propellor larger than the wingspan? Is there any law of physics that ...

38

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. Depending on rotor head design this is done in different ways: By a flapping hinge at the hub, allowing vertical rotation. By a teetering hinge on two-blade designs, ...

36

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 individually with each contributing effect, as well as some discussion of why explanations you might have heard at school don't work. Since the navigation there is a ...

36

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 First of all, lift is only one part of the aerodynamic forces. It is the component normal to the direction of airflow. Since the aircraft will distort the local ...

32

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 to add an ultimate load test, so here is the 777 tested to failure. Sorry for the early 1990s video quality. Boeing 777 wing fail at 154% design load

32

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 lift force (upwards force) while requiring relatively little thrust (forwards force). How well they do this is expressed by their lift-to-drag ratio (L/D ratio). ...

30

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: you're flying 80 knots and the headwind is 20 knots. Over a time of 3 minutes, the headwind gradually reduces from 20 knots to 10 knots. Since the change is ...

29

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 of time than when you accelerate a large air mass. This is because the force is proportional to the change in momentum of the air mass, whereas the power is ...

29

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. Consider a simple paper airplane. It flies for a long time with no engine at all, until the drag on it causes it to slow down and if loses lift and descends to the ...

28

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 wing loading of just 8.53 kg/m²; much less than even gliders have (they start at around 30 kg/m²). This allows it to fly very slowly; if we assume it ...

27

@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 a plane down while you pull the wing up. If you are building a home build in your garage its far simpler to put some sand bags on it and let gravity do the ...

26

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 does this is what we measure as lift. In the case where the airflow over the top of the wing separates from it, the parcels of air flowing by do not get ...

25

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 leading-edge separation vortex phenomenon occurs at subsonic speeds. However, the separation does not destroy the lift as in the case of low sweep wings; ...

24

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. Surprisingly, no thrust is needed to perform this maneuver. Even gliders can do it. What happens is that kinetic energy is converted to potential energy, the rate of ...

24

Yes. Bernoulli end effectors are used in industrial applications to pick up items without physical contact using this principle. Example:

23

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), so to lift those 78 tons needs only 4.33 tons of thrust. All it needs is the right amount of forward speed, and the engines only need to maintain this speed. ...

23

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, the vertical velocity would not be constant, since any non-zero balance of the vertical forces would result in an acceleration...

22

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 the wingspan becomes, the bigger the speed difference between inner and outer wing will be. Also, landing such a wide wing without dropping a wingtip will be very ...

22

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 lift is caused by flow separation at the leading edge. While this indicates a severe stall on unswept wings, the separated flow along a highly swept edge will ...

22

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 constant lift force, regardless of pressure or altitude, when at equal pressure and temperature with the surrounding air. Therefore, a change in altitude will not ...

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