jwstewar
Elite Member
Someone said to bring this thread back up and say I told you so.
So, I told you it would fly.
So, I told you it would fly.
will it take off?
- Thread starter schmism
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patrick_g
Elite Member
So, is any of this renewed interest due to last night's airing of a "Myth Busters" episode where the airplane vs the conveyor was tried in models and real A/C with a pilot?
I guess their conveyor was not as magic as the one we worked with previously in this thread, huh?
I was surprised that the pilot actually thought he would not take off... but he did.
It is easy to see the difference between the myth guys approach and the MAGIC CONVEYOR we had to contend with. It is an apples to oranges comparison and as interesting and fun as the myth guys episode may have been it DID NOT have the attributes with which we struggled and its results are not valid as regards the discussion here. It was trivial to predict the outcome considering their conveyor did not have the requisite acceleration to take advantage of the inertia in the wheels of the plane and so forth.
Pat
I guess their conveyor was not as magic as the one we worked with previously in this thread, huh?
I was surprised that the pilot actually thought he would not take off... but he did.
It is easy to see the difference between the myth guys approach and the MAGIC CONVEYOR we had to contend with. It is an apples to oranges comparison and as interesting and fun as the myth guys episode may have been it DID NOT have the attributes with which we struggled and its results are not valid as regards the discussion here. It was trivial to predict the outcome considering their conveyor did not have the requisite acceleration to take advantage of the inertia in the wheels of the plane and so forth.
Pat
Dmace
Elite Member
I am going to quote myself from page one on Nov 8, 2006 just to say "Told you so".
It is simple physics and it amazes me that so many people don't get it.
THE WHEELS DO NOT PROPEL THE AIRCRAFT, IT DOES NOT MATTER HOW FAST THEY ARE SPINNING ON A CONVEYOR BELT. OBVIOUSLY IF IT WAS A CAR, THE CAR WOULD NEVER MOVE.
Here is a new one for you guys:
Dmace said:
It is simple physics and it amazes me that so many people don't get it.
THE WHEELS DO NOT PROPEL THE AIRCRAFT, IT DOES NOT MATTER HOW FAST THEY ARE SPINNING ON A CONVEYOR BELT. OBVIOUSLY IF IT WAS A CAR, THE CAR WOULD NEVER MOVE.
Here is a new one for you guys:
tallyho8
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Dmace said:Here is a new one for you guys:
OH MY GOSH! This one ought to be good for another 750 replies!
MossRoad
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Re: Mythbusters/airplane/treadmill
For anyone that missed the EXACT wording of the problem as originally posted on TBN, here it is:
a plane is standing on a movable runway( something like a conveyor).as the plane moves the conveyor moves but in the opposite direction.the conveyor has a system that tracks the speed of the plane and matches it exactly in the opposite direction.
the question is
will the plane take off or not?
For anyone that missed the EXACT wording of the problem as originally posted on TBN, here it is:
a plane is standing on a movable runway( something like a conveyor).as the plane moves the conveyor moves but in the opposite direction.the conveyor has a system that tracks the speed of the plane and matches it exactly in the opposite direction.
the question is
will the plane take off or not?
MossRoad
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Re: Mythbusters/airplane/treadmill
The big argument was the use of the words:
matches it exactly in the opposite direction
The big argument was the use of the words:
matches it exactly in the opposite direction
RedRocker
Veteran Member
Dmace said:I am going to quote myself from page one on Nov 8, 2006 just to say "Told you so".
It is simple physics and it amazes me that so many people don't get it.
THE WHEELS DO NOT PROPEL THE AIRCRAFT, IT DOES NOT MATTER HOW FAST THEY ARE SPINNING ON A CONVEYOR BELT. OBVIOUSLY IF IT WAS A CAR, THE CAR WOULD NEVER MOVE.
Here is a new one for you guys:
Yes, and play great tunes!
Egon
Epic Contributor
Must have something to do with the moustache!
Hercule would not approve!
Hercule would not approve!
Egon
Epic Contributor
I'm confused again. Why are the airplane tire's rotating with this magical conveyor belt???
MrJimi
Elite Member, Rest in Peace
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
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
RonMar
Elite Member
Re: Mythbusters/airplane/treadmill
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.
MossRoad said:
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.
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?
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
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Botabill said:
Never!
SPYDERLK
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Re: Mythbusters/airplane/treadmill
larry
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.ray66v said:
larry
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.
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
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Re: Mythbusters/airplane/treadmill
Larry pretty much sums it up. Let's continue the discussion there, please, as this has the potential to go another few hundred posts.
SPYDERLK said:
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
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Re: Mythbusters/airplane/treadmill
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.
SPYDERLK said:
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
Elite Member
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...
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...
