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Forums - General Discussion - Plane on a treadmill .. to be on Mythbusters

drkohler on 25 October 2007
z64dan said:
"If a plane is traveling at takeoff speed on a conveyor belt, and the belt is matching that speed in the opposite direction"

this whole concept is a little iffy. Is it traveling at takeoff speed relative to the conveyor belt, or the air?
It simply means that the plane is at the same place at all times, no matter how fast the belt turns. If you stood at the belt, you could enter and leave the plane at any time without moving to the left or right (though I'd not recommend it).

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Sqrl on 25 October 2007
drkohler said:
Sqrl said:
The site is undergoing some big changes right now so there are some new bugs that need to be ironed out. ioi should hopefully have the more annoying stuff fixed by the end of the week.

On Topic: The idea of increasing the speed of the treadmill is an interesting one and will technically work. But the amount of extra speed required to offset the immense amount of thrust this thing will be producing has me cringing at the thought of building such a treadmill. Since only a small fraction of the treadmill's power is actually turning into deceleration for the plane it will take a huge amount of belt speed to counteract the accelerating plane.

I won't hazard an exact guess but it seems like the belt could be required to approach mach speeds to accomplish this task. It really depends on what the actual percentage of treadmill energy is lost in spinning and the percentage that ends up in the frame. It won't be a constant percentage over a range of speeds either, which complicates things. And iirc the faster the wheels are spinning the less energy is actually transferred into spinning and more is lost in heat and in the frame, so that aspect at least is working in our favor.

Let me know if I am missing something.
Agreed. The only solution I see is to actually test the myth is a rotating drum and a fast feed back system to keep the plane (on auto pilot, no real pilot is that suicidal) on top of the wheel. You can pretty much slowly speed up the drum to senseless speeds, but then at some point even the best tyres will probably explode before the take-off speed is reached. The more I think about it, the less likely the experiment becomes a real possibility.

 


There are some advantages to a drum system. It allows us to ensure that the surface the wheels are coming in contact with is extremeley smooth and this allows us to go with solid wheels instead of inflated wheels. As a result there is no chance of an exploding tire.

 

However we still have a problem similar to that of most helicopters. In helicopters they can have issues with extreme stress on the the leading rotors as they swing around to the front of the helicopter. This is caused by the rotor's combined swinging speed and speed of the helicopter approaching mach speeds (aka transonic). The result is large amounts of instability in pressure around the rotors as they swing to the front and even more instability as that pressure is removed (all sudden pressure changes causes instability for a rotor, regardless of increase or decrease).

I think a similar stress problem could appear if the wheels are required to spin that fast, but I feel like there is bound to be a better way around this than what we are looking at.



To Each Man, Responsibility
sieanr on 25 October 2007
drkohler said:
epsilon72 said:

drkohler, normal engines don't create airflow over a plane's wings by themselves. I don't think they're talking about building some strange new plane to do this.

Jetengines, no, but propellers actually do (which isn't the intention of a propeller) but they do as an added bonus. An actual experiment to check the myth will most likely fail anyways with any nornal plane geometry because the engine(s) cannot suck enough air to generate the power required.

 


 Wrong on two counts

1. Props producing airflow over the wing is dependant on the position of the engine. In most cases the lift produced is relativly small - if you wanted anything big you'd need a ducted prop and carefully controlled airflow

2. Jets can also generate lift if placed slight ahead and on top of the wing. In fact, this is far more efficient than any extra lift props would produce and there have been several aircraft built this way.

Either way, claiming that you can take an aircraft off due to enough airflow from the engines alone is bogus. Not least of which is simply not enough airflow over the wings (ever), but also the complete lack of airflow over the "tail" of the aircraft.



Leo-j said: If a dvd for a pc game holds what? Crysis at 3000p or something, why in the world cant a blu-ray disc do the same?

ssj12 said: Player specific decoders are nothing more than specialized GPUs. Gran Turismo is the trust driving simulator of them all. 

"Why do they call it the xbox 360? Because when you see it, you'll turn 360 degrees and walk away" 

drkohler on 26 October 2007
sieanr said:
drkohler said:
epsilon72 said:

drkohler, normal engines don't create airflow over a plane's wings by themselves. I don't think they're talking about building some strange new plane to do this.

Jetengines, no, but propellers actually do (which isn't the intention of a propeller) but they do as an added bonus. An actual experiment to check the myth will most likely fail anyways with any nornal plane geometry because the engine(s) cannot suck enough air to generate the power required.

 


Wrong on two counts

1. Props producing airflow over the wing is dependant on the position of the engine. In most cases the lift produced is relativly small - if you wanted anything big you'd need a ducted prop and carefully controlled airflow

2. Jets can also generate lift if placed slight ahead and on top of the wing. In fact, this is far more efficient than any extra lift props would produce and there have been several aircraft built this way.

Either way, claiming that you can take an aircraft off due to enough airflow from the engines alone is bogus. Not least of which is simply not enough airflow over the wings (ever), but also the complete lack of airflow over the "tail" of the aircraft.

We are not discussing whether you can walk to an airport and see a plane taking off...

Here is a short movie of a conventional propeller plane that 'almost does it'

http://www.alexisparkinn.com/photogallery/Videos/SuperCub18ftTO.mpg

Theoretically it should be possible to build  a much better propeller plane that actually does the trick..