ROFLMAO!
Earth spinning
- Thread starter mollymoo
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ROFLMAO!
You get two san... no wait... you get half a sa.... hang on..... *head explodes*
Imagine a model plane with no propulsion on a treadmill with your finger behind it stopping it rolling off. At your fingertip the forces are the combined rolling resistance of the wheels and the friction in the wheel bearings, this is matched by the reaction force provided by your finger.
With the forces balanced the plane doesn't move. To make the plane move forward you need to overcome the rolling resistance and bearing friction which are relatively small even on a full size aircraft, you've all seen the strongmen pull a jumbo jet along right?
Now a jet engine can generate much much more force than the resistive forces at the wheels. The engines only need to generate enough force to overcome the friction forces at the wheels to keep the aircraft stationary relative to you and me observing. Therefore once the engines are throttled up the amount of friction and resistance at the wheels is negligible compared to engine thrust and the plane must accelerate forwards.
With the forces balanced the plane doesn't move. To make the plane move forward you need to overcome the rolling resistance and bearing friction which are relatively small even on a full size aircraft, you've all seen the strongmen pull a jumbo jet along right?
Now a jet engine can generate much much more force than the resistive forces at the wheels. The engines only need to generate enough force to overcome the friction forces at the wheels to keep the aircraft stationary relative to you and me observing. Therefore once the engines are throttled up the amount of friction and resistance at the wheels is negligible compared to engine thrust and the plane must accelerate forwards.
Soldato
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If the treadmill could keep matching the wheel speed infinately the plane wouldn't take off.
If the treadmill could only get up to a certain amount of speed, even if this is faster than the planes flight speed, then the plane could take off.
If the treadmill could only get up to a certain amount of speed, even if this is faster than the planes flight speed, then the plane could take off.
Soldato
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How about a sandwich on a plate, and it's falling downwards, and you have a breadknife a short distance above the sandwich and you're bringing the knife down to cut the sandwich...
And the motion of the knife somehow affects mavity so the rate of descent of the sandwich always matches that of the knife...
And the motion of the knife somehow affects mavity so the rate of descent of the sandwich always matches that of the knife...
Yes.It.Would.
Wheel speed has no bearing at all on whether a plane could take off. You have planes with skies instead of wheels, or floats (in case of sea planes).
All thrust is from the jet engines attached to the wings, the wheels simply stop it from scraping its belly along the run way.
Soldato
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If the plane was scraping along on its belly at the same speed of the treadmill it still wouldn't take off.
I don't care if it's on wheels, ice skates or a skateboard, if the speed of the plane is equal to that of the treadmill the plane will be static, if it's static it can't take off.
You are totally missing the point. The plane does move forward with enough speed to gain lift and fly. The treadmill simply spins the wheels, it is the jet engine moving the plane forward.
Soldato
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If your moving forward on something that is moving backwards at the same speed as your forward movement you stay still regardless of your source of power or how the force is moving you forward.
I am not sure I can continue.. you'd need to physically see it to understand.
The wheels on a plane free wheel, they are unpowered. If wheels were completely frictionless in construction and someone turned on the treadmill the plane would not move, the wheels would just spin yes?
Now introduce into this the jet engines and the plane would be pushed along (forwards), eventually fast enough to take off. It doesn't matter how fast the treadmill is spinning as the wheels just spin.
You have around 200,000 lb of thrust pushing a 777 forward...for it to stand still you would have to have the same force in the opposite direction.
If you think the plane won't be moving then what, praytell, is this mysterious -200,000 lb force?
If you think the plane won't be moving then what, praytell, is this mysterious -200,000 lb force?
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Soldato
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I understand completely what you are saying, but for the plane to attain a speed where it can take off the wheels need to spin faster than the treadmill / the plane needs to move faster than the treadmill.
It's a completely hypothetical situation but it would be impossible to convert the forward thrust from the jet engine into forward movement WITHOUT the wheels moving faster than the treadmill, as the wheels are the only point of contact.
It's a completely hypothetical situation but it would be impossible to convert the forward thrust from the jet engine into forward movement WITHOUT the wheels moving faster than the treadmill, as the wheels are the only point of contact.
The mysterious force is not mysterious at all. It would come from the treadmill which has just rapidly accelerated to 500,000,000mph going the opposite direction to the plane. The speed of the treadmill emparts a force through the wheels acting backwards onto the plane. The greater the speed of the treadmill the greater this force, the greater the weight of the plane the greater this force.
Soldato
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How would it create the wind resistance / lift without physically moving through the air?
If you stop or even speed up the treadmill the plane will still travel at the speed the jets are making it go. Even if you reversed the treadmill and made it go a million miles an hour all that would happen is the wheels would spin faster, the planes speed would still be determined by the jets.
Because it is moving through the air, it doesn't matter how much you make the treadmill spin the plane will always take off (assuming frictionless wheels of course).
