|
Post by Funky on Jul 13, 2009 15:30:40 GMT
Now, yes.
|
|
|
Post by edinburghstokie on Jul 13, 2009 15:31:10 GMT
You may have missed my edit. Yes they push the plane forward but only by translating engine thrust into wheel impetus which is a result of friction at the treadmill. The engine thrust is a bit irrelevant. No, No. If the wind is strong enough blowing against a stationary plane (forget the treadmill for the moment) it will take off. No need for any wheel movement. That's why small microlights are tied down when not being used.
|
|
|
Post by jonesinamillion on Jul 13, 2009 15:32:47 GMT
OK, So if you jumped up whilst standing in the carriage of a fast moving train would you go backwards?
|
|
|
Post by edinburghstokie on Jul 13, 2009 15:33:38 GMT
OK, so what you're basically saying is the plane is moving faster than the treadmill? Yes, deffo it'll take off. Like at airports! no, the plane has the exact opposite speed as the treadmill (therefore it actually has some speed and will get lift).
|
|
|
Post by beagriestache on Jul 13, 2009 15:35:07 GMT
No it doesn't! The original statement says the speed of the treadmill and that of the plane are equal and opposite.
No lift I'm afraid, unless the plane goes faster than the treadmill like in your toy car example.
|
|
|
Post by edinburghstokie on Jul 13, 2009 15:37:46 GMT
so if the plane is going forward at 10mph, then the treadmill will go at -10mph. however the wheels will be turning at the equivalent of 20mph
|
|
|
Post by beagriestache on Jul 13, 2009 15:39:29 GMT
I don't get that bit? The speed of the wheels is irrelevant, it's the speed of the plane and that of the treadmill that matter.
But your microlight example is a good one. I said previously it's the air speed relative to the plane that's important to provide lift.
If the plane remains stationary as a result of a clever treadmill, no air speed, no lift.
|
|
|
Post by Deleted on Jul 13, 2009 15:41:45 GMT
Depends which way you were facing.
|
|
|
Post by beagriestache on Jul 13, 2009 15:43:05 GMT
stop it!
|
|
|
Post by edinburghstokie on Jul 13, 2009 15:45:59 GMT
If the plane remains stationary as a result of a clever treadmill, no air speed, no lift. The only way for the plane to remain stationary is if the forces in the forward and backward direction were equal and opposite. You would need a hell of a lot of friction in the wheel bearings to do that.
|
|
|
Post by beagriestache on Jul 13, 2009 15:48:16 GMT
Or a hell of a lot of weight in an aeroplane.
Why do you think 40,000 N doesn't send an aircraft down a runway at 20,000mph?
Come on, you must be close to conceding!
|
|
|
Post by beagriestache on Jul 13, 2009 15:55:29 GMT
This is a cracking example of why a little knowledge in the hands of entertainers can be a dangerous thing. The plane is actually propelling itself along the concrete of the runway beneath the cloth so not really surprising it took off.
|
|
|
Post by edinburghstokie on Jul 13, 2009 15:57:30 GMT
here is the theory for you. the wheels have nothing to do with it.
|
|
|
Post by edinburghstokie on Jul 13, 2009 16:02:33 GMT
The plane is actually propelling itself along the concrete of the runway beneath the cloth so not really surprising it took off. How? the wheels are independent of the engine. What propels the plane forward when airborne?
|
|
|
Post by edinburghstokie on Jul 13, 2009 16:04:41 GMT
The conveyor belt isn't actually counteracting the forward momentum of the plane, it's simply spinning the wheels while the jets push it forward.....
|
|
|
Post by beagriestache on Jul 13, 2009 16:06:49 GMT
The plane is actually propelling itself along the concrete of the runway beneath the cloth so not really surprising it took off. How? the wheels are independent of the engine. What propels the plane forward when airborne? Yes but they're not independent of the plane. How the plane moves forward once in the air is entirely different.
|
|
|
Post by beagriestache on Jul 13, 2009 16:08:15 GMT
The conveyor belt isn't actually counteracting the forward momentum of the plane, it's simply spinning the wheels while the jets push it forward..... That's fine, if the actual forward speed of the entire plane exceeds that of the conveyor belt, it'll take off. If it doesn't, no lift, so it won't.
|
|
|
Post by edinburghstokie on Jul 13, 2009 16:10:47 GMT
Are you saying that the wheels impose a force on the earth (forget about the treadmill for a bit) to push the plane forward?
Then when it takes off the wheels no longer push forward and something else does?
|
|
|
Post by beagriestache on Jul 13, 2009 16:14:53 GMT
No I'm saying that if the plane's forward speed exceeds that of the reverse speed of the conveyor belt, air will pass under the wings and generate lift.
I'm not really interested in exactly how the forward speed exceeds the reverse speed.
If you were right, why bother with runways? Just have short treadmills at convenient locations spinning away beneath free-spinning plane wheels, rev the engines a bit more and off you go upwards in a flash.
|
|
|
Post by edinburghstokie on Jul 13, 2009 16:21:48 GMT
If I am right (which I believe I am), a short treadmill won't allow the plane to take off. It still has to gain enough air speed. The ground speed is irrelevant. The speed of the treadmill is irrelevant, as long as the engine has enough thrust to get over the initial friction between the wheels and floor, it will start moving forward. It therefore has some forward speed and will move forward.
If the plane were standing still in comparison to the ground/air, it would not have any speed, and the treadmill would not be moving anyway.
|
|
|
Post by shiny nosehair on Jul 13, 2009 16:22:59 GMT
How? the wheels are independent of the engine. What propels the plane forward when airborne? Yes but they're not independent of the plane. How the plane moves forward once in the air is entirely different. I can assure you how the plane moves forward whether in the air or on the ground is exactly the same, engine thrust, there is no drive to the wheels
|
|
|
Post by edinburghstokie on Jul 13, 2009 16:24:30 GMT
If the plane were going 10 mph forward and the treadmill 10 mph backward to an observer off the plane and treadmill, it would seem to someone on the treadmill that the plane is travelling at 20 mph (or vice versa). It is all about points of reference.
|
|
|
Post by edinburghstokie on Jul 13, 2009 16:26:27 GMT
Right, I really have to do some work. I'll leave you and any others who wish to join in to muse it over a bit.
Go back to this example, and it should make sense.
Consider this, take a toy car and tie a string to the front. Place it on a treadmill and pull it forward. pulling on the string represents the propulsion from the propeller, the wheels will spin as fast as they have to, but the toy car will move forward because there is a force pulling it in that direction. that is why the plane will take off. Now take a toy car with a motor and put it on the treadmill with the speed of the car and the treadmill equal, it will not move because the speed is powered by the force supplied to the wheels.
|
|
|
Post by beagriestache on Jul 13, 2009 16:27:18 GMT
If I am right (which I believe I am), a short treadmill won't allow the plane to take off. It still has to gain enough air speed. The ground speed is irrelevant. The speed of the treadmill is irrelevant, as long as the engine has enough thrust to get over the initial friction between the wheels and floor, it will start moving forward. It therefore has some forward speed and will move forward. If the plane were standing still in comparison to the ground/air, it would not have any speed, and the treadmill would not be moving anyway. I agree, there is no air speed, therefore no lift. It only gains air speed by moving forward through the air or by having air move towards it over its wings eg your microlight example. Once the plane moves forward it takes off. A stationary plane relative to the air beneath its wings will remain grounded.
|
|
|
Post by beagriestache on Jul 13, 2009 16:45:05 GMT
Right, I really have to do some work. I'll leave you and any others who wish to join in to muse it over a bit. Go back to this example, and it should make sense. Consider this, take a toy car and tie a string to the front. Place it on a treadmill and pull it forward. pulling on the string represents the propulsion from the propeller, the wheels will spin as fast as they have to, but the toy car will move forward because there is a force pulling it in that direction. that is why the plane will take off. Now take a toy car with a motor and put it on the treadmill with the speed of the car and the treadmill equal, it will not move because the speed is powered by the force supplied to the wheels. This example does make sense but proves my point if anything. The car (plane) moves forwards because its propulsive forces are stronger than those of the treadmill. It doesn't matter how it is propelled forwards (string, engine, whatever, that's a red herring) the point is it goes forwards because one force is greater than the other. In this way the plane has forward motion, air moves beneath its wings and up it goes. I agree with the second part. No forward motion, no air movement beneath the wings no uplift.
|
|
|
Post by edinburghstokie on Jul 13, 2009 16:48:46 GMT
The car (plane) moves forwards because its propulsive forces are stronger than those of the treadmill. It doesn't matter how it is propelled forwards (string, engine, whatever, that's a red herring) the point is it goes forwards because one force is greater than the other. In this way the plane has forward motion, air moves beneath its wings and up it goes. Sorry, I can't resist posting... Exactly. However if the treadmill was set at -10 mph and the car was pulled along (from something not connected to the treadmill) at 10 mph (all from a fixed point of reference off the treadmill) would the car be moving?
|
|
|
Post by beagriestache on Jul 13, 2009 16:54:47 GMT
The car (plane) moves forwards because its propulsive forces are stronger than those of the treadmill. It doesn't matter how it is propelled forwards (string, engine, whatever, that's a red herring) the point is it goes forwards because one force is greater than the other. In this way the plane has forward motion, air moves beneath its wings and up it goes. Sorry, I can't resist posting... Exactly. However if the treadmill was set at -10 mph and the car was pulled along (from something not connected to the treadmill) at 10 mph (all from a fixed point of reference off the treadmill) would the car be moving? Me neither! I've no idea, I just know that unless air moves under a plane's wing it'll go nowhere. So, you either a) push it forward or b) push air towards it. Your original post said the treadmill moved at exactly the same speed as the plane, therefore no movement relative to the air. No lift.
|
|
|
Post by edinburghstokie on Jul 13, 2009 17:06:42 GMT
"Your original post said the treadmill moved at exactly the same speed as the plane, therefore no movement relative to the air. No lift."
what about this then? Two cars touching each other rear to rear. They both drive off in opposite directions at 10 mph. They both move. They move away from each other at 20 mph.
The same is the case for the treadmill. If the plane moves forwards, then the treadmill moves backwards. I never said the plane can't have movement relative to the air.
|
|
|
Post by beagriestache on Jul 13, 2009 17:20:40 GMT
That's easy then. Movement relative to the air = take-off. (Sorry for delay, was just helping my daughter with her Shrek game )
|
|
|
Post by iilforddave on Jul 13, 2009 18:14:05 GMT
I know this has been on the internet for a while, but haven't seen it on the oatie, and thought it would make a change to the conspiracy theories and how wank britain is.A plane is standing on a runway that is made of a large conveyor belt. The plane fires up its engines, but as it moves forward, the conveyor belt senses the speed of the plane's forward motion and instantaneously moves at exactly the same speed in the opposite direction. Can the plane take off? Discuss. I say yes. I've not read the rest of the thread, but the answer is an unequivical NO. Lift is created by the difference in air pressure between the upper and lower surfaces of the wing passing through the air. if its on a treadmill, it will be stationary in relation to the air, some air may be moved by the treadmill, but not enough to create any lift
|
|