Sequel to SOAP: Plane on a treadmill... will it fly?

[gloryaccordy]

Yaw the mechanical engineer says no

Premise:

U put a plane on a treadmill and turn on the jets, then crank up the throttle

Jets push plane forward

Plane starts to move

Treadmill matches rolling speed of tires

Tires reach rolling speed of takeoff

Plane takes off...

Why Yaw says it won't work: Plane needs lift

Lift requires relative airspeed

There is no airspeed for a plane on a treadmill staying still

Plane does not leave ground.

What do you think? There's a heated argument at H-T about this between the creationists and the evolutionists

[lokuputha]

lol.

[cp[mike]]

weird question.

this is my take:

the plane will move forward at X mph.

the treadmill will move backward to match at X mph.

the planes wheels will spin at X*2 mph but that doesnt keep the plane from moving, as the treadmill is only spinning the wheels, not moving the jet backwards. itll still take off like normal, because as far as the jet & air is concerned, everything is normal. the only difference is that theres something causing the wheels to spin twice as fast as normal.

[ChIoVnIdCa]

The treadmill is not even a factor. The plane will move under the power of the jets regardless if the treadmill is there. The treadmill would just double the speed of the wheels.

[ChIoVnIdCa]

weird question.

this is my take:

the plane will move forward at X mph.

the treadmill will move backward to match at X mph.

the planes wheels will spin at X*2 mph but that doesnt keep the plane from moving, as the treadmill is only spinning the wheels, not moving the jet backwards. itll still take off like normal, because as far as the jet & air is concerned, everything is normal. the only difference is that theres something causing the wheels to spin twice as fast as normal.

lol you already got it before me

[deevergote]

How long is the treadmill?

As stated above, the wheels do not move the plane, the jets do. So the plane will move as if it were on unmoving ground. The wheels will just spin faster. As long as the wheels don't fail, or slow the plane down considerably, it will still reach takeoff speed. The plane WILL move.

HOWEVER... if the treadmill isn't long enough for the plane to reach takeoff speed... it will crash.



So, the determining factor is the length of the treadmill. The direction of the treadmill only affects the plane negatively if it slows it down.

[gloryaccordy]

*EDIT* The plane will take off!!! I'm an idiot

The wheels have nothing to do with the forward thrust, it's all in the jets. The treadmill physically could not hold back the plane. Man I'm a dumbass...

[deevergote]

The treadmill could hold back the plane if the wheels couldn't spin fast enough. If they fail, or slow the plane down, then it would either crash or take longer to get up to speed.

As I said, the amount of runway the plane has is the ultimate factor.

[blizzard335]

wheres Scott when we need him LOL!!

i still dont get it. u need lift to make an airplane airborne.

how does the treadmill affect this? is the plane rolling on a treadmill? is the treadmill attached to the plane?

[gloryaccordy]

The treadmill could hold back the plane if the wheels couldn't spin fast enough. If they fail, or slow the plane down, then it would either crash or take longer to get up to speed.

As I said, the amount of runway the plane has is the ultimate factor.

We're stuck in car terms thinking of wheels on a dyno... the wheels on a plane are not drive wheels...

If you strapped a rocket to a car on a dyno... it would leave the dyno unless u strapped it down. It's the same principle...

I can't believe I argued against it flying...

[deevergote]

Agreed. But the drag created by the wheels, especially if they reach their mechanical rotational limit, could slow the plane down. If the wheels are spinning twice the speed that the airplane is flying, they may give out. It's hypothetical and situational, but still a factor. If the wheels create friction, they will slow the plane down. If the takeoff space is limited, the plane will not fly.

The proposed situation leaves too much to be imagined in order to be totally true or false.

Based on the concept of the treadmill vs the jets... it will fly. I'm just bringing in other possible factors (c'mon Yaw... you're the engineer here! You should know that unless every factor is taken into consideration, you can't assume anything based on two known factors!)

[blizzard335]

we have to do a large scale experiment to verify this!!

[gloryaccordy]

we have to do a large scale experiment to verify this!!

Mythbusters is doing something in mid-December... I think they're filming it now

Deev I don't think the friction in the wheels will be enough to overcome DA POUWAAH of the jets... unless a plane has to go at full throttle to take off. Even then it wouldn't hold the plane back, just take longer.

I don't know where they are going to get this huge treadmill though....

[The G-Man]

NO NOT THIS AGAIN! Last year there was a very heated discussion on this here.

/thread once Scott chimes in.

[cjv998]

Okay, posted a reply, then thought about it and realized it wasn't right, so here's my new opinion: I agree with cpmike...the speed the wheels are spinning at doesn't affect the jets, provided the bearings are relatively low friction.