Heicopter Question

Rabidlamb

Say a plane needs to accelerate to 80kph to take off.
If it's sitting on a massive treadmill going 80kph in the opposite direction could the plane take off ?.

alphaLaura

Say a plane needs to accelerate to 80kph to take off.
If it's sitting on a massive treadmill going 80kph in the opposite direction could the plane take off ?.

No - the speed that the ground is moving beneath an aircraft is irrelevant. What matters is how fast the air is moving over the wings. The treadmill doesn't move that air.

prinz

Rabidlamb wrote: »

Say a plane needs to accelerate to 80kph to take off.
If it's sitting on a massive treadmill going 80kph in the opposite direction could the plane take off ?.

Wasn't this on an episode of Mythbusters last week on the Discovery Channel?

RoryMurphyJnr

First question OP would be how to spell helicopter correctly

ronnieryan

That treadmill question was on mythbusters

Capt'n Midnight

Manic Moran wrote: »

At the equator, the earth's surface is spinning at about 1,000mph. No helicopter can have an indicated forward airspeed of that magnitude, so, no.

NTM

But we aren't at the equator

A helimacopter at the poles could easily take off from from the Greenwich meridian and land 180 degrees away. You might point out that a helimacopter can't carry 12 hours of fuel, but we could use in flight refueling, but we don't even need that since the helimacopter would already be 12 time zones away when it landed.

Capt'n Midnight

Rabidlamb wrote: »

Say a plane needs to accelerate to 80kph to take off.
If it's sitting on a massive treadmill going 80kph in the opposite direction could the plane take off ?.

Yes if the threadmill was long enough

but if it was held stationary on the threadmill then wind direction would be a factor , some planes can take off vertically into a headwind as Manic Moran pointed out it's all to do with indicated forward airspeed of that magnitude.

Donny5

Capt'n Midnight wrote: »

But we aren't at the equator

A helimacopter at the poles could easily take off from from the Greenwich meridian and land 180 degrees away. You might point out that a helimacopter can't carry 12 hours of fuel, but we could use in flight refueling, but we don't even need that since the helimacopter would already be 12 time zones away when it landed.

If a helicopter took off near or at either pole and hovered, it would stay exactly above that point on the Earth's surface until it landed, unless an outside force acted upon it.

Doc

The world rotates at approximately 1040 mph so if you jumped in the air for one second you end up 0.28 miles down the road. Thats how I get to work every day. I have to get the bus home though as it only works one way.

newmug

Deleted User wrote: »

Wrong. For a body to orbit the earth it has to be travelling extremley fast, such that the centripetal force caused by its circular path around the earth exactly counters the force of gravity at its orbital altitude. This is why the space shuttle must move at 17,000+ miles per hour to attain even low earth orbit. If it were not moving this fast it would just fall back to earth. It is not possible to just "hang" above the earth (and before someone mentions geostationary orbit at 36,000 km altitude, that doesn't count).

Jaysus complicate things for the OP even more why dont ya:rolleyes:

Rabidlamb wrote: »

Say a plane needs to accelerate to 80kph to take off.
If it's sitting on a massive treadmill going 80kph in the opposite direction could the plane take off ?.

If its propellor driven, yes. Its all about the speed of the air passing over and under the wings.

Pherekydes

newmug wrote: »

If its propellor driven, yes. Its all about the speed of the air passing over and under the wings.

A jet engine and an engine-driven propellor do the same thing: they take air in the front and push it out the back a lot faster. For every action you get an equal and opposite reaction, so the engine is pushed forward. Anything that's attached to the engine, like an airframe, moves forward with it, hence you get wind flow over aerofoil surfaces and, consequently, lift.

Aircraft engines push against the air. It's irrelevant what the A/C is sitting on.

newmug

Pherekydes wrote: »

A jet engine and an engine-driven propellor do the same thing: they take air in the front and push it out the back a lot faster. For every action you get an equal and opposite reaction, so the engine is pushed forward. Anything that's attached to the engine, like an airframe, moves forward with it, hence you get wind flow over aerofoil surfaces and, consequently, lift.

Aircraft engines push against the air. It's irrelevant what the A/C is sitting on.

Not quite. What you have described is how a jet engine affects an aeroplane. If you had a prop driven airoplane sitting on a threadmill, the aeroplane wouldnt move until enough windflow was generated by the props, to cause lift. Then it would just take off. Whereas the jet driven aeroplane would act as you have described above, pushing against the air, and bringing everything attached to it along with it, causing lift. There is a difference. It has been tested.

FreudianSlippers

newmug wrote: »

Not quite. What you have described is how a jet engine affects an aeroplane. If you had a prop driven airoplane sitting on a threadmill, the aeroplane wouldnt move until enough windflow was generated by the props, to cause lift. Then it would just take off. Whereas the jet driven aeroplane would act as you have described above, pushing against the air, and bringing everything attached to it along with it, causing lift. There is a difference. It has been tested.

Well that would also depend on whether the prop was a tractor or pusher.

The propeller creates thrust. Then the thrust must balance drag.
Secondly, thrust must exceed the drag and cause acceleration.

As the air or gas meets the wing, it is pushed downwards giving the object lift.

OldGoat

/Throws in the words 'jet','impeller' and 'hovercraft' just to muddy the waters.

Donny5

newmug wrote: »

Not quite. What you have described is how a jet engine affects an aeroplane. If you had a prop driven airoplane sitting on a threadmill, the aeroplane wouldnt move until enough windflow was generated by the props, to cause lift. Then it would just take off. Whereas the jet driven aeroplane would act as you have described above, pushing against the air, and bringing everything attached to it along with it, causing lift. There is a difference. It has been tested.

Everything in this post is wrong. Propellers generate thrust by pushing air to the rear with angled panels spun at high speed. Jets work by compressing air and fuel before burning it, where the exhaust gases expand. Both result in gases going backwards and the plane going forwards.

On a treadmill, the plane's unpowered wheels would simply spin as fast as the combined speeds of the treadmill belt and the plane. The plane's engine would push it forward until it reached takeoff speeds or ran out of treadmill.

The propeller plane and jet plane would act in largely the same way. Your idea that the propeller could generate enough airflow under the wings to lift the plane without also pushing the aircraft forward is an aberration of Newton's Third Law.

Basq

I don't know what's worse..

The absurdity of the question or the fact it's the basis of an "ongoing argument".

I mean, for f*cks sake!