Steve,
Thank you for the correct and concise summary!!! albeit many repays back...
Thank you for the interesting riddle.
Steve,
Thank you for the correct and concise summary!!! albeit many repays back...
For the plane to be moving forward its wheel speed needs to be greater than the belt's speed. If they are exactly equal the plane isn't moving, assuming the treadmill itself is stationary.
This might not be the right formula.
The wheels will always be spinning at the same speed as the conveyor belt.
If the conveyor belt is moving at 100 mph and the wheels of the plane aren't turning, wouldn't the airplane have to also be moving at 100 mph? If 100 mph is fast enough for the plane to take off, won't it take off?
(Hint, the speed of the wheels and the speed of the conveyor belt are irrelevant. It's only plane's speed relative to the air that matters.)
--Roger
Turning things around ... if the conveyor belt is moving at 100 mph and the wheels of the plane aren't turning, wouldn't the airplane have to also be moving at 100 mph? If 100 mph is fast enough for the plane to take off, won't it take off?
Now, stop the conveyor belt. The wheels start spinning. But, the airplane is still going 100 mph. It can still take off.
Now, instantly start the conveyor belt moving in the other direction at 100 mph. Now the wheels are spinning really fast, but the airplane is still going 100 mph. It can still take off.
(Hint, the speed of the wheels and the speed of the conveyor belt are irrelevant. It's only plane's speed relative to the air that matters.)
--Roger
So so you said the belt would be moving back at 100mph. But that (since the plane is moving forward at 100mph) would make it accelerate to 200 mph, driving the wheels to 300mph, and so on so forth. Eventually, the belt is going so fast that it impairs the plane's ability to take off, whether from the shock waves or turbulence or melting the wheels off.
So so you said the belt would be moving back at 100mph. But that (since the plane is moving forward at 100mph) would make it accelerate to 200 mph, driving the wheels to 300mph, and so on so forth. Eventually, the belt is going so fast that it impairs the plane's ability to take off, whether from the shock waves or turbulence or melting the wheels off.
This smells wrong.
Forward motion of the planes and wheel-hubs is equal. If the plane is going 100, so are the wheels. If the plane is going 200, so are the wheels.
I'm getting the impression Incon's either still confusing rotation with translation, or is just arguing for argument's sake.
That wheel's going to be ROTATING twice as fast as it would on ground. But that will not have any effect on the plane's forward motion behind making the engines work a little harder.
Does a plane's wheel turn before it lands?
The belt is dependent on the speed of the wheel. Because the wheel is on the conveyer, the wheel is, in turn, rotated by the belt.
If the plane brakes, it will stop. The brakes are required to be able to hold the aircraft idle while the engines are throttled all the way up. (Reference)
That's true, it will be stopped relative to the surface of the conveyor belt. But if the conveyor is driven by some other force or even allowed to move, the plane would still be moving relative to the ground.
Steve Shannon
Accoording to the question, the conveyer matches the speed of the wheel. No other force is allowed in the scenario, because otherwise, the conveyer would not match the speed of the wheel anymore.
No. They spin up when they make the screeching noise at touchdown. Pondering why they don't spin them up is probably due to the differences between landing air speed and ground speed. Most of the tyres are designed to be minimum weight to conserve fuel and still be able to do their job. Centripetal force tries to tear the tyre apart as it spins, and there is not much safety margin due to keeping the mass down. I could envision that the variability in the rotational rate (if they used something like vanes to spin them up) could take them up into the danger zone for shredding the tread. If they were to drive them with motors it would be even more additional mass to carry, and also a problem if it seized up.
So, looks like the KISS principle prevails...
Interesting. Do you know which ones?There are some wheel that are at speed when the plane lands.
So that means the conveyor bearings are allowed to freewheel, right? If the non-turning tire is moved forward by the thrust of the engine(s) the surface of the conveyor will move to keep up.
Steve Shannon
No , the 747 is stationary. What color was the belt?Let's simplify things a bit.
We we have a stock Boeing 747, no modifications.
It is on a magical runway sized conveyer belt that matches exactly the speed of the wheels on said 747 in the opposite direction. Magic. No exceptions or anything like that.
Can the Boeing 747 take off from the magical conveyer belt?
No , the 747 is stationary. What color was the belt?
I have been entertained a great deal by the answers on the BMABA (Balsa Model Aircraft Builders Association) Facebook page.
View attachment 311812
This question looks like that it is their version of the "what does CATO mean" on rocket forums.
https://www.facebook.com/groups/1510169962560076/
Greg
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