Will It Take off?

[Developereo]

Is helicopter really an ideal example fitting this scene?

As the forces acting downwards, so helicopter won't need runway to gain effective momentum for takeoff.

The crucial factor is a sufficient flow of air over the airfoils to generate lift. The helicopter achieves this by rotating the airfoils themselves. In the case of a prop-plane, the propeller's main purpose is to move the plane forward so that there is motion relative to the ambient air. However, there is also a fair amount of air that is shoveled back by the prop itself which will provide some lift.

The question becomes more interesting if you have a jet engine whose exhaust goes nowhere near the airfoils.

 

[Mysterious]

No definitely not.....many members have already explained taht it will need air pressure difference to
take off.....regarding helis, they got their rotor which is used to create pressure diffrence, so that they could take off directly......

 

[Mysterious]

OK guys, here's the answer....

Cars and planes don't work the same way. A car's wheels are its means of propulsion--they push the road backwards (relatively speaking), and the car moves forward. In contrast, a plane's wheels aren't motorized; their purpose is to reduce friction during takeoff (and add it, by braking, when landing). What gets a plane moving are its propellers or jet turbines, which shove the air backward and thereby impel the plane forward. What the wheels, conveyor belt, etc, are up to is largely irrelevant.

Once the pilot fires up the engines, the plane moves forward at pretty much the usual speed relative to the ground--and more importantly the air--regardless of how fast the conveyor belt is moving backward. This generates lift on the wings, and the plane takes off. All the conveyor belt does is, make the plane's wheels spin madly.


Yep! The plane will take off!!

Cheers!

The case of the plane and conveyor belt

i don't think sooo... the engines are used to provide the forward thrust which ultimately increses the flow of air on wings....without moving forward there will not be any velocity with respect to ground which is requried to create a pressure differnce around wings

 

[SQ8]

This is a relative question..
The person who has proven it has made a crucial mistake in thinking that air pushed back from a prop equals air hitting the wings.
For a proper explanation to this.. its better to think of it in airliner terms..two jet engines.. sucking air in push the aircraft on the belt. The belt itself acting as a surface as a layer of air on it.
that air WILL move.. And following Bernoulli effect.. enough lift will develop that it will push the aircraft into the air.
The Model airplane example is incorrect as many of these aircraft have engines powerful enough to move air across the wings from dead stop in a static indoor environment... and have T/W ratio's much greater than 1:1.

 

[Developereo]

All the examples, including the Mythbuster's example, that show the plane taking off are not being true to the spirit of the myth. I believe the core question is whether the plane will take off if it is at rest wrt to its surroundings. The surroundings includes the block of air around it.

Things like propellors and jet engines create a flow in that volume of air, so it's hard to test the myth properly. If you could hook up a car engine to power the wheels and turn off the prop, the plane would not take off even if you "moved" at the take-off speed.

 

[OrionHunter]

Yes.

There is no doubt that the plane, of any sort, will take off. But the problem is that, it is not feasible. If it could be done, runways would be no longer used for take-offs.

You would still require a runway. Because as I mentioned earlier, the speed of the conveyor belt in the opposite direction is of no consequence. The engines produce the thrust that moves the plane forward RELATIVE TO THE SURROUNDING AIR and NOT relative to the conveyor belt, unlike a car that has motive power in its wheels. An aircraft DOES NOT USE ITS WHEELS FOR MOTIVE POWER. An aircraft uses its engines to thrust itself forward. Wheels only have brakes to stop an aircraft on the runway together with reverse engine thrust in bigger planes.

In other words, an aircraft would need the same amount of runway to take off whether it is on a conveyor belt or not!

Cheers!

 

[truthseer]

A big plane won't fly since no movement relative to air shall take place

 

[jagjitnatt]

It won't.

There has to be a difference in the speed of conveyer belt and aircraft take off speed to take off.

 

[tvsram1992]

It would fly. The reason is very simple. The plane does not need to move in relation to ground in order to get air born or remain in air. It just needs to be moving forward in relation to the air surrounding it. As the prop is providing that air, which is going around the wings, the plane will take off, with or without running on tarmac. The other scenario is like if there is a wind blowing against an aircraft on the ground and the wind speed matches the take off speed of the plane. Such a plane would become airborn too. In fact some planes have been destroyed this way in storms. All you need is the air move over the wings in fast enough velocity and the plane will get airborn.

Absolutely wrong evaluation . The air need to move in opposite direction which happens in wind tunnels . But here only the surface is moving . It may move air to some extent but not complete air . Toy planes can lift because the small fraction of air could moved by surface could be enough to create lift .