Does the plane REALLY take off? It depends.

[Red Squirrel]

 

[Captante]

The real answer is that it depends on the plane. (no fun I know, sorry)

Most winged aircraft have insufficient power to take off without significant lift provided by the wings and that requires air moving over them which isn't normally something a conveyor-belt can do.

 

[TheELF]

Well, if you could produce a treadmill that could respond fast enough and with enough force to counteract the jet engines then you could make the plane take off with magic because that's what you would need to make such a treadmill in the first place.

 

[WelshBloke]

Even with friction the aeroplane is going to take off. The faster the aeroplane goes the more lft, the more lift then the aeroplane weighs less, the aeroplane weighs less the friction is lower. Aeroplane takes off.

 

[WelshBloke]

The real answer is that it depends on the plane. (no fun I know, sorry)

Most winged aircraft have insufficient power to take off without significant lift provided by the wings and that requires air moving over them which isn't normally something a conveyor-belt can do.

Aeroplane is going to go forward, aeroplane don't give a shit about wheels.

 

[Captante]

Aeroplane is going to go forward, aeroplane don't give a shit about wheels.

They DO however care about runways.

Only kind of aircraft that "takes off" without moving quickly forward first is a helicopter or a VTOL. (even something like a "PITTS" biplane has insufficient thrust to fly without it)

 

[Captante]

Mission accomplished!

 

[WelshBloke]

They DO however care about runways.

 

[Captante]

Well, if you could produce a treadmill that could respond fast enough and with enough force to counteract the jet engines then you could make the plane take off with magic because that's what you would need to make such a treadmill in the first place.

Maybe not?

View attachment 79533

So.... the "treadmill" is on pontoons now? (and things will not end well in water with the wheels extended)

Also a seaplane can't even begin to fly without most lift coming from the wings. Pontoons are heavy and cause major drag. (this is partially why larger "seaplanes" use the hull for flotation)

 

[WelshBloke]

Only kind of aircraft that "takes off" without moving quickly forward first is a helicopter or a VTOL. (even something like a "PITTS" biplane has insufficient thrust to fly without it)

Thrust out the back of a jet turbine is not going to be overcome by the friction in the wheel bearings or air friction (and those are the only two forces counteracting the thrust from the engines).

 

[Captante]

Thrust out the back of a jet turbine is not going to be overcome by the friction in the wheel bearings or air friction (and those are the only two forces counteracting the thrust from the engines).

And a jet aircraft REALLY can't take off without moving very quickly forward OR without being in something like a wind tunnel. (otherwise aircraft carriers wouldn't need a giant catapult and/or a launch ramp)

Seriously the practical/technical challenges to make this work are extensive.... AND the "takes off" arguments mostly nonsense based on "comic book" laws of physics. (just like the original thread)

A Harrier takes off. So does a Bell Jet Ranger. (or other helicopter)

An F/A-18 (or a 1950's Piper Cub for that matter) does not "fly" in any even semi-realistic "conveyor-belt/treadmill" scenario.

 

[WelshBloke]

And a jet aircraft REALLY can't take off without moving very quickly forward OR without being in something like a wind tunnel. (otherwise aircraft carriers wouldn't need a giant catapult and/or a ramp)

What's going to stop the aeroplane taking off?
Theres thrust forwards from the engines, where's the equal thrust pushing on the aeroplane?
A little bit of friction in the wheels isn't going to do it. You could put skids on a jet and it would still take off.

 

[Captante]

What's going to stop the aeroplane taking off?
Theres thrust forwards from the engines, where's the equal thrust pushing on the aeroplane?
A little bit of friction in the wheels isn't going to do it. You could put skids on a jet and it would still take off.

A FEW would ... the vast majority would either be completely unable to move or would not be able to attain V1. (they use wheels on most landing gear for a reason)

So should I take this "seriously" and start with the letter "A" then work my way down the list of reasons?




Nah... I'll save time.... in fantasy-land the plane takes off. Otherwise you're walking!

 

[sdifox]

What's going to stop the aeroplane taking off?
Theres thrust forwards from the engines, where's the equal thrust pushing on the aeroplane?
A little bit of friction in the wheels isn't going to do it. You could put skids on a jet and it would still take off.

Human stupidity will stop it dead.

 

[igor_kavinski]

I love AT for these in-depth "scientific" discussions. More schoolchildren should join these forums to learn the basics of what makes our world tick.

 

[WelshBloke]

A FEW would ... the vast majority would either be completely unable to move or would not be able to attain V1. (they use wheels on most landing gear for a reason)

So should I take this "seriously" and start with the letter "A" then work my way down the list of reasons?




Nah... I'll save time.... in fantasy-land the plane takes off. Otherwise you're walking!

Make it simple. A force diagram showing where those forces come from and what they act on.
Your argument is that friction in a wheel bearing is greater than the force of a turbojet engine.

 

[Captante]

My only "argument" is that without adding in some near-physically impossible "conditions" any "taking off" is 100% hypothetical without a practical means of providing lift to the wings.

And I've yet to hear even one for 99% of real aircraft.

 

[WelshBloke]

My only "argument" is that without adding in some near-physically impossible "conditions" any "taking off" is 100% hypothetical without a practical means of providing lift to the wings.

And I've yet to hear even one for 99% of real aircraft.

Pretty much any aeroplane is going to go forward. Prop or jet. The force they put out pushes on the air not the ground. Theres no motive force through the wheels, they just spin freely.

 

[Captante]

Pretty much any aeroplane is going to go forward. Prop or jet. The force they put out pushes on the air not the ground. Theres no motive force through the wheels, they just spin freely.

All it takes to screw a plane taking off (or even reaching V1 sometimes) is a LITTLE too much weight on board or it being improperly loaded/balanced.

With nearly all aircraft, removing the wheels from the landing gear by itself will prevent them getting off the ground in perfect conditions with a smooth, straight runway.

This isn't "my opinion" it's fact.

 

[WelshBloke]

All it takes to screw a plane taking off (or even reaching V1 sometimes) is a LITTLE too much weight on board or it being improperly loaded/balanced.

With nearly all aircraft, removing the wheels from the landing gear by itself will prevent them getting off the ground in perfect conditions with a smooth, straight runway.

This isn't "my opinion" it's fact.

No one's removing the wheels. And I'm not looking at edge cases.
Engines are pushing the aeroplane forward through the connection to the fuselage. The wheels are freely spinning in all take offs, when the aeroplane is on a treadmill they just have to spin faster.

 

[Captante]

The only way you can make the plane take off IS with a very unlikely "edge-case" scenario. Unless on water or snow/ice nearly all winged aircraft will not be able to take off without wheels or some other low-friction mechanism.

Read up on "thrust to weight ratio" and takeoff rolling-resistance. They have major influence on an aircraft's lift/ability to fly.

Sure if I start making $hit up I can come up with a silly physics-defying way the plane takes off (like a 2 mile treadmill or a rocket-powered plane) but IRL OTOH.....

 

[WelshBloke]

The only way you can make the plane take off IS with a very unlikely "edge-case" scenario. Unless on water or snow/ice nearly all winged aircraft will not be able to take off without wheels or some other low-friction mechanism.

What? Wheels provide no thrust at all. They are not involved in any motive force. This is not a car.
No one is saying that there is no landing gear, just that those wheels aren't going to stop the aeroplane regardless of how they are spinning.

 

[WelshBloke]

Look at it this way...
Forward force .....massive thrust of engines pushing against the air.
Backwards force.... Air resistance and?

 

[Captante]

I really am getting the impression you don't understand how flight works.
(YOU started the "serious" part of this conversation)

Except in the case of a rocket-plane or a helicopter/VTOL WINGS provide lift not "massive thrust" and I'm not sure where the "equal resistance" thing was going lol. (even with a helicopter the same "lift" principle applies)

 

[WelshBloke]

I really am getting the impression you don't understand how flight works.
(YOU started the "serious" part of this conversation)

Except in the case of a rocket-plane or a helicopter/VTOL WINGS provide lift not "massive thrust" and I'm not sure where the "equal resistance" thing was going lol.

At no point have I argued that the wings don't provide lift!
Engines push against air, this moves aeroplane forward, forward motion moves air over wing, wing provides lift.
The treadmill isn't going to stop any of that!