will it take off?

[MrJimi]

After reading all these replies?
I would suggest all of you to get a real Pilots license and read your book very good
and go from there
This whole thing has been misrepresented to all of us big time
Jim

 

[Botabill]

Why in the world did you bring this beaten dead horse back to life? Let it go.

 

[RonMar]

Re: Mythbusters/airplane/treadmill

The big argument was the use of the words:

matches it exactly in the opposite direction

Which they did on the show. It probably even exceeded the aircraft's speed in the beginning as the truck probably accelerated faster than the plane did. It will simply have no effect on anything other than the wheel RPM. The only possible effect would be from wheel drag and that is inconsequential in a properly operating bearing, particularly when you are talking about hundreds of pounds of prop thrust. The thrust from the prop will overcome the drag in the wheel bearings and away the plane goes...

Here is another similar anaolgy for you. An airboat can go upstream in a river just as fast as it can go downstream(virtually no difference in speed once the hull is on a plane). It can do this because it's thrust is developed in the air over the river and has very little to do with the river itself A conventional boat will have a difference in speed upstream to downstream because it's thrust is developed in the moving fluid of the river. Now give the airboat or an airplane a 30KT headwind and you will see a difference in upwind and downwind GROUNDSPEED performance.

 

[ray66v]

Re: Mythbusters/airplane/treadmill

Heres another way for people to think of this that might help:
Because the wheels of a plane are free spinning, and not propelling it. no matter how fast the conveyor turns them it will have no effect on the plane taking off.
When the plane is set for take off it is not propelled backward by the treadmill, Because the wheels spinning freely simply match the speed of the conveyor, that is the only effect that the conveyor has on the airplane {if the wheels are turning}. The conveyor makes the wheels turn period. the wheels free spinning cancels out any and all forces from the treadmill. Then, because the plane is propelled by the prop, when the take off power is set, the take off roll begins as it would on a fixed runway. The plane does not care if the wheels are spinning already when the take off power is set. The wheels simply turn faster and the plane takes off.
The free spinning wheels do not have the ability to stop or limit the forward thrust from the prop no matter how fast they go or how you test it.
Does that help anyone who is still on the other side of this?

 

[MossRoad]

Why in the world did you bring this beaten dead horse back to life? Let it go.

Never!

 

[SPYDERLK]

Re: Mythbusters/airplane/treadmill

Heres another way for people to think of this that might help:
Because the wheels of a plane are free spinning, and not propelling it. no matter how fast the conveyor turns them it will have no effect on the plane taking off.
When the plane is set for take off it is not propelled backward by the treadmill, Because the wheels spinning freely simply match the speed of the conveyor, that is the only effect that the conveyor has on the airplane {if the wheels are turning}. The conveyor makes the wheels turn period. the wheels free spinning cancels out any and all forces from the treadmill. Then, because the plane is propelled by the prop, when the take off power is set, the take off roll begins as it would on a fixed runway. The plane does not care if the wheels are spinning already when the take off power is set. The wheels simply turn faster and the plane takes off.
The free spinning wheels do not have the ability to stop or limit the forward thrust from the prop no matter how fast they go or how you test it.
Does that help anyone who is still on the other side of this?

No. Those of us looking at the way that spinning the wheels can cancel thrust are not concerned with the speed of the wheels. It is the force the conveyor would exert to cause high rotational acceleration of the wheelmass that can cancel thrust. This is explained repeatedly in the previous thread. Its sad that MBs ignored that possibility.
larry

 

[ray66v]

Re: Mythbusters/airplane/treadmill

Ok, If I see your point correctly, are you looking at the gyroscopic effect that the wheels could eventually develop if enough speed is applied???
Because rotational acceleration as I know understand it, I'm having trouble applying to this example.

 

[MossRoad]

Re: Mythbusters/airplane/treadmill

This is explained repeatedly in the previous thread.
larry

Larry pretty much sums it up. Let's continue the discussion there, please, as this has the potential to go another few hundred posts.

 

[tallyho8]

Re: Mythbusters/airplane/treadmill

No. Those of us looking at the way that spinning the wheels can cancel thrust are not concerned with the speed of the wheels. It is the force the conveyor would exert to cause high rotational acceleration of the wheelmass that can cancel thrust. This is explained repeatedly in the previous thread. Its sad that MBs ignored that possibility.
larry

Let me get this straight in non-technical terms. If you are saying that my skyrocket that I put wings and wheels on, and put on top of a modified very high speed belt sander, won't take off, then I have one very angry neighbor who will say that you are wrong.

 

[RonMar]

Re: Mythbusters/airplane/treadmill

With the thrust forces involved, both that of the prop moving the plane forward and the belt pulling backward, the ammount of energy needed to accelerate the wheels to a VERY high RPM is inconsequential. It just dosn't take that much force to spin up a lightweight aircraft wheel with good bearings.

Put the rear end of your car up on jackstands. Start the engine and stomp on the gas and see how long it takes to get to redline. Now remove the wheels and repeat the experiment. Even with large heavy steel or alloy auto wheels, the difference in engine acceleration with and without the inertial load of the wheels is pretty small...