Mythbusters punk'd whole internet

[Fenixgoon]

Originally posted by: spidey07
And in order for it to move forward the wheels have to go faster than the treadmill.

This is NOT allowed. If it is then the treadmill is not matching the speed of the wheels.

the treadmill can go *however fast it wants* and the plane will STILL move forward. the tires of the plane will spin freely in whatever direction the treadmill goes.

 

[GuitarDaddy]

Every time this topic comes up I lose a little more faith in humanity

 

[dainthomas]

Originally posted by: GuitarDaddy
Every time this topic comes up I lose a little more faith in humanity

Unbelievable that it's 2007 and people still don't know how airplanes fly. Orville and Wilbur are spinning in their graves.

 

[spidey07]

Originally posted by: dainthomas

Originally posted by: GuitarDaddy
Every time this topic comes up I lose a little more faith in humanity

Unbelievable that it's 2007 and people still don't know how airplanes fly. Orville and Wilbur are spinning in their graves.

What's sad is that people don't even understand the very definition of velocity.

 

[RapidSnail]

Originally posted by: RapidSnail
Simple solution:

If the speed of the treadmill matches the speed of the wheels, the plane can not take off.

If the speed of the treadmill matches the speed of the plane, the plan can take off.

Originally posted by: spidey07
And in order for it to move forward the wheels have to go faster than the treadmill.

This is NOT allowed. If it is then the treadmill is not matching the speed of the wheels.

You're using the first scenario, aren't you?

 

[spidey07]

Of course. I thought it's very clear the plane can't take off.

 

[RapidSnail]

Originally posted by: spidey07
Of course. I thought it's very clear the plane can't take off.

Except everyone's talking about the second scenario...

 

[LTC8K6]

The speed of the wheels is the same as the speed of the plane, unless you mean the RPM of the wheels, and then the question makes no sense.

The forward speed of the wheels is the same as the forward speed of the plane, since they are bolted together.

 

[SnipeMasterJ13]

Originally posted by: LTC8K6
The speed of the wheels is the same as the speed of the plane, unless you mean the RPM of the wheels, and then the question makes no sense.

The forward speed of the wheels is the same as the forward speed of the plane, since they are bolted together.

LOL

Here is an example I like to use to help explain how the ground doesn't matter - for all realistic purposes.

Lets take a top fuel dragster and our jet. We are going to bring them to a drag strip and race them. The track is perfectly prepped. The drag car and plane fire up their engines and take off down the track. No problems.

Now, we will bring the drag car and jet to a new drag strip that is made out of perfectly flat ice. Fire up the engines and go full throttle. The drag car will sit and spin, while the jet takes off without a problem at all. You could even lock the brakes so that the wheels on the jet do not spin, and it will still take off. The ground doesn't matter (in all realistic scenarios).

So your wheel speed =! plane speed in this case.

The plane takes off (unless a tire blows out or bearing locks up causing the plane to crash and explode. Granted, if the bearings lock up while on ice, it still takes off. That is enough for now...)

 

[LTC8K6]

"So your wheel speed =! plane speed in this case. "

Yes it does. Unless the wheels leave the plane, they are always moving at the same speed as the plane.

 

[Leros]

Originally posted by: LTC8K6
"So your wheel speed =! plane speed in this case. "

Yes it does. Unless the wheels leave the plane, they are always moving at the same speed as the plane.

a) The plane doesn't take off:
The plane is moving at 0mph. The wheels are moving at the same speed as the treadmill.
plane: 0 mph
wheels: same speed as treadmill


b) The plane does take off. The plane is moving forward at X mph. The treadmill is moving backwards at Y mph. The wheels are moving at X+Y mph.
plane: plane speed
wheels: plane speed + treadmill speed

The speeds apply to the edge of the wheel. If we're talking the center of the wheel, then thats a different story.

 

[RapidSnail]

Originally posted by: LTC8K6
"So your wheel speed =! plane speed in this case. "

Yes it does. Unless the wheels leave the plane, they are always moving at the same speed as the plane.

That's about as irrelevant as saying the cockpit moves at the same speed as the airplane. Obviously the wheels move at the speed of the plane as they are attached to the plane just as any another part of the plane is attached. Rotational speed was supposed to have been inferred by the reader.

 

[JRich]

Let me reiterate, the plane takes off.

/thread

 

[SnipeMasterJ13]

I was referencing the rotational speed of the wheels. In the ice example, the wheels do not need to spin at all. So the RPM of the wheel has no effect on the jet taking off.

Now, if you were to say there was a strong wind going in the direction of the jet matching its speed, then it wouldn't take off.

 

[SnipeMasterJ13]

Originally posted by: RapidSnail

Originally posted by: LTC8K6
"So your wheel speed =! plane speed in this case. "

Yes it does. Unless the wheels leave the plane, they are always moving at the same speed as the plane.

That's about as irrelevant as saying the cockpit moves at the same speed as the airplane. Obviously the wheels move at the speed of the plane as they are attached to the plane just as any another part of the plane is attached. Rotational speed was supposed to have been inferred by the reader.

Thank you sir.

 

[Leros]

The plane will take off. My god. It just hit me. I've been arguing for the other side this whole time. Time to spread the word.

 

[NatePo717]

How about we look at it like this.

If you have thrust you have drag as Thrust ~ Drag in normal flight and >= Drag during take off. In order to have drag air has to be moving around the object which implies that the plane is moving relative to the air since we have drag (assuming we have free spinning wheels). As long as the plane can generate enough thrust the plane will take off. Move the ground any way you want.

Source for concept reference: Mechanics and Thermodynamics of Propulsion SE by Philip Hill and Carl Peterson.

 

[RapidSnail]

Originally posted by: Leros
The plane will take off. My god. I just hit me. I've been arguing for the other side this whole time. Time to spread the word.

Be careful hitting yourself, violence is never the solution.

 

[Darwin333]

Originally posted by: SnipeMasterJ13
I was referencing the rotational speed of the wheels. In the ice example, the wheels do not need to spin at all. So the RPM of the wheel has no effect on the jet taking off.

Now, if you were to say there was a strong wind going in the direction of the jet matching its speed, then it wouldn't take off.

On the flip side, if the wind was blowing fast enough in the other direction the jet could take off without even starting its engines and without the wheels moving an inch. Granted it wouldn't stay airborne for long but it would still achieve the lift necessary to leave the ground.

 

[Leros]

Originally posted by: RapidSnail

Originally posted by: Leros
The plane will take off. My god. I just hit me. I've been arguing for the other side this whole time. Time to spread the word.

Be careful hitting yourself, violence is never the solution.

I swear somebody is messing with my posts. In another thread, I said put shits on my bed instead of sheets. Or I have too much on my mind and should be studying instead of posting on ATOT.

 

[LTC8K6]

Even if I surrender that point about the wheels it changes nothing. As long as the wheels can rotate freely, the plane can take off.

The question is meant to be simple, but has gotten twisted along the way.

Can an airplane take off on a treadmill or not?

The speed of the treadmill has no effect on the airplane's takeoff. It only varies the rotational speed of the plane's wheels.

The treadmill has absolutely no way to impart enough force to the airframe to counter the engine's thrust.

I see no way for the treadmill to counter engine thrust.

 

[Auric]

Originally posted by: gorcorps

Originally posted by: Auric
A float-plane cannot take off against a river if it cannot overcome the flow of water. That's what the theoretical treadmill is like, n'est ce pas? The planes need to overcome the moving surface acting against them -they aren't suspended above already with the surface just sliding past. Rather, they are "physically" connected to it by gravity and that is only overcome with 'nuff ground speed to achieve lift. If the surface negates said speed they cannot overcome gravity. Ergo, they cannot take off.

A float plane is being impeded by the water stopping the plane from going in the direction it wants. A plane on wheels is not the same because the wheels keep all friction forces contained in themselves and don't effect the body of the plane like water does. I agree that a float plane can't take off against a strong enough current, BUT that's not the same as wheels on a treadmill. If the wheels were locked and you had to overcome that friction then yes it would be the same, but because the wheels are free it's not.

Theoretically, why can't the acceleration of the surface prevent breaking the friction so the wheels remain stationary?

 

[RapidSnail]

Originally posted by: LTC8K6
Even if I surrender that point about the wheels it changes nothing. As long as the wheels can rotate freely, the plane can take off.

The question is meant to be simple, but has gotten twisted along the way.

Can an airplane take off on a treadmill or not?

The speed of the treadmill has no effect on the airplane's takeoff. It only varies the rotational speed of the plane's wheels.

The treadmill has absolutely no way to impart enough force to the airframe to counter the engine's thrust.

I see no way for the treadmill to counter engine thrust.

Nobody was debating that the plane doesn't take off. They were saying that your wheel interpretation was incorrect.

 

[Auric]

Originally posted by: LTC8K6
Even if I surrender that point about the wheels it changes nothing. As long as the wheels can rotate freely, the plane can take off.

The question is meant to be simple, but has gotten twisted along the way.

Can an airplane take off on a treadmill or not?

The speed of the treadmill has no effect on the airplane's takeoff. It only varies the rotational speed of the plane's wheels.

The treadmill has absolutely no way to impart enough force to the airframe to counter the engine's thrust.

I see no way for the treadmill to counter engine thrust.

Indeed, in simple reality the plane will take off. But theoretically, can it be prevented?

 

[LTC8K6]

A 737 coming in to land has lost it's brakes and it's reverse thrusters are out of service.

The airport activates it's giant runway conveyor safety system so the 737 can land safely without brakes.

This conveyor runs opposite the direction of the landing aircraft to stop it.

Airplanes land on it, and because it's running backwards at the matched rotational speed of the aircraft's tires at landing, the aircraft can be stopped safely by the conveyor.

The conveyor is linked to the aircraft's speed sensors and the conveyor gradually slows to a stop, halting the aircraft.

Except that it won't work. Since the aircraft wheels are free to spin, the conveyor will have only a tiny effect on the aircraft's speed, and won't stop it at all.

It will be just as if the conveyor was not there.

The only difference will be the tires rotating much faster than normal.

The plane will roll just as far as as it would have on a normal runway, adjusted slightly for the small extra friction of the higher wheel rotation speeds.

If the pilot decided to go around after touchdown, he'd hit the throttles and away she'd go, just like there was no conveyor.