Aircraft On A Conveyor Belt

yeah cheers guys lol I worked it out just as I was falling alseep last night 🙂

DP – Thanks for explaining it 🙂 I dont appreciate being told to put my brain in gear, all ive done is completely overthink the experiment.

I reckon you think too much:D If you were serious about trying something out I am of the opinion that it is far better to overthink the problem rather than underthink it. All you’ve done is think more than you had to but that is the way to take as many variables as possible out of the problem.

If you take a helicopter. Tie the skies to a piece of plywood the same diameter as the rotor blades, will the helicopter be able to take off?

BTW this was done on Mythbusters too but they used toy helicopters 🙂

well with an aircraft carrier the situation is different.

Relative to the aircraft carrier – V = 0 for the aircraft

however “V” relative to the air around the aircraft etc will depend on how much wind there is and how fast the aircraft carrier is travelling – this would then be deducted from speed of rotate :nod:

With any experiment we have to make some assumptions, or have a control… I read this with the assumption that any forward movement by the aircraft on its wheels is equalled by the reverse movement of the treadmill on which the aircraft is standing. I also assume zero wind. Final assumption is that we’re looking for the aircraft to fly through conventional means… By that I mean we’re looking for the wing to produce the lift, not the engine.

The engine is simply a means of propelling the aircraft through the air so that the wing can generate lift.

The wheels are simply a mechanism to allow the aircraft the travel along the ground in order that air can flow over the wings, thus producing a change is pressure, and thus producing lift. If any forward movement of the aircraft is equally countered by opposite movement of the ground (the treadmill), then how does the aircraft get the necessary airflow over the wing to produce the lift?

None of the answers I’ve read actually answer that question? Lift is produced by airflow over the wing. The aircraft doesn’t move the air because it’s forward movement is equalled by a reverse movement of the ground. Therefore the aircraft cant fly. The only way I can see the aircraft flying is if the airflow produced by the prop pulling air over the wing were sufficient to create that change in pressure, but in most cases that would not happen.

Another scenario… If my aircraft gets airborne at 35Kts, and I travel down the runway with a 35Kt tail wind, will the aircraft fly?… NO. because there isn’t the necessary fly of air over the wing.

Assuming that you guys are rings, then what part of my logic breaks down?

Firstly I agreed with the above then post#20 by Nashio cleared all out..thnx.
However on an aircraft carrier which is specially designed taking into account the airflow requirements for lift-off of naval planes. Even a stationary aircraft will produce a lift; enough for take-off that is debatable.

Thanks Nashio,

Now I get it. The theory being that even with the engine off and the belt moving, the aircraft will remain stationary and the wheels will simply turn. Engine on and it will move forward. I think reality is that the aircraft would travel backwards along the conveyor belt, but at least I get the theory.

Mmm – Time for a beer!

Not trying to confuse you but the original question was if the a/c moved forward, the runway moved at the same speed in the opposite direction. Therefore, the ‘belt’ can’t move until the aircraft moves. Doesn’t make any difference really. Enjoy your beer.:D

It has elsewhere…

Yes, in General Discussion…..read the thread if you dare!!! :diablo:

http://forum.keypublishing.co.uk/showthread.php?t=75778&page=2

(Start at post #40.)

Its a very difficult question to get your head around I find – When I first read it I was exactly of the same opinion ad VX it took a LOT of arguing and debate until I realised how I was wrong lol

Yes, with the lumps off, the A/c would move back along the conveyor belt, there would be some movement of the wheels so it wouldn’t go back at quite the same speed. Do it yourself with a bit of paper and a heavy Dinky toy.
As soon as some thrust is added, the A/c will move forward until it reaches the counter of the belt speed then it will “Actually” go forward until V1 and skywards.
The wheels are nothing to do with the equation. For those who still believe the A/c won’t move, then ask thesen why A/c are heavily tethered for an engine test.

Thanks Nashio,

Now I get it. The theory being that even with the engine off and the belt moving, the aircraft will remain stationary and the wheels will simply turn. Engine on and it will move forward. I think reality is that the aircraft would travel backwards along the conveyor belt, but at least I get the theory.

Mmm – Time for a beer!

:diablo: Trustworthy? Meeeeeeeeee? 😀

Moggy old chap, if you look at the date when I posted this and my reply to VX above you’ll find I realised I was wrong last week 🙂

Apologies – didn’t read the whole thread. After all, you chaps are trustworthy 🙂

Moggy

It took me a LONG time to get it right in my head

If the wheels were driven and moving at 150mph in the opposite direction then it would stay still.

However the wheels are castors, so if you were to move the conveyor belt backwards, the aircraft would move, yes but not at exactly 150mph? the wheels would spin etc.

The thrust from the engine, is not a direct force acting against the conveyor belt – it will still pull the aircraft through the air regardless of the speed at which the belt rotates/speed at which the wheels spin.

In short, the bearings might give out/tyres pop – she will fly 🙂

With any experiment we have to make some assumptions, or have a control… I read this with the assumption that any forward movement by the aircraft on its wheels is equalled by the reverse movement of the treadmill on which the aircraft is standing. I also assume zero wind. Final assumption is that we’re looking for the aircraft to fly through conventional means… By that I mean we’re looking for the wing to produce the lift, not the engine.

The engine is simply a means of propelling the aircraft through the air so that the wing can generate lift.

The wheels are simply a mechanism to allow the aircraft the travel along the ground in order that air can flow over the wings, thus producing a change is pressure, and thus producing lift. If any forward movement of the aircraft is equally countered by opposite movement of the ground (the treadmill), then how does the aircraft get the necessary airflow over the wing to produce the lift?

None of the answers I’ve read actually answer that question? Lift is produced by airflow over the wing. The aircraft doesn’t move the air because it’s forward movement is equalled by a reverse movement of the ground. Therefore the aircraft cant fly. The only way I can see the aircraft flying is if the airflow produced by the prop pulling air over the wing were sufficient to create that change in pressure, but in most cases that would not happen.

Another scenario… If my aircraft gets airborne at 35Kts, and I travel down the runway with a 35Kt tail wind, will the aircraft fly?… NO. because there isn’t the necessary fly of air over the wing.

Assuming that you guys are right, then what part of my logic breaks down?

It has elsewhere, but not here

You are wrong. It can take off unless it is a very odd aircraft that uses powered wheels to reach flying speed.

Moggy

Moggy old chap, if you look at the date when I posted this and my reply to VX above you’ll find I realised I was wrong last week 🙂

This is a good one to drop into a drunken conversation then go and chat up the women while all the blokes shout at each other. I agree with the consensus by the way, the u/c just keeps the thing off the tarmac.

Another one is “does a jet engine suck the aircraft along or blow it along?” I spent days in an argument about this with someone who claimed to be an expert in fluid dynamics. I gave up in the end – okay air is sucked in but the expanding gases from combustion provide the thrust surely?

If am being thick please forgive me 🙂

Guys – im sure this has been done to death

It has elsewhere, but not here

Someone please tell me im right in saying the following

You are wrong. It can take off unless it is a very odd aircraft that uses powered wheels to reach flying speed.

Moggy

I must confess, I dont get it? Maybe because it’s 1am, and I should be sleeping, but lift is caused by airflow over the wings…. Its nothing to do with the engine. The engine simply provides forward movement through the air to allow the air to pass over the wing.
Correct, and that produces lift.
If you assume that there is no wind, then what causes the airflow over the wing? Wind has nothing to do with it. Only the forward motion of the wing through the air is necessary.The ‘treadmill’ cancels out any forward movement, the aircrafts position relative to the runway remains the same and thus there is no increase in airflow.Only if the wheel brakes are on.

If you liken it to a person running on a treadmill. If you run on the open road you’ll feel air passing over your face…. You can run at any speed on a treadmill, but you will never feel any movement of air passing you. Forget treadmills, that’s a totally different set of circumstances.

How does the aircraft take off? Unless someone else know another way to take off without air passing over the surface of the wing, then I dont see how it’s possible.

Look at it this way. Forget the wheels and put the aircraft on skis, on the most slippery ice ever formed so that there is no friction between the skis and the ice. The slightest touch and the aircraft moves. OK, start the engine and the a/c moves forward (No wind situation) Does it matter if the ice moves in the opposite direction, can the ice drag the a/c backwards? Remember, no friction equals no connection of any sort. The engine is still pulling against the air and the a/c is still moving forward. It doesn’t matter how fast the two surfaces are passing each other (ski and ice) the a/c keeps accelerating until it takes off.

Now, imagine the ice is covered with a layer of small ball bearings then look very closely at the interface of ski and ice with the bb’s in between. As the a/c moves over them, they’ll rotate, very fast, without affecting the a/c nor the ice, right?
The faster the a/c goes, the faster the ice goes in the opposite direction, the faster the balls rotate when the a/c skis reaches and passes over them. That is exactly what the wheels do in the standard description, they rotate at twice the speed of the normal rotational speed for any given airspeed. They are just another very slippery interface between the a/c and the runway. They cannot slow anything down unless the brakes are applied and friction is added into the scenario. The a/c keeps moving forward at an every increasing speed, the runway matches that speed in the opposite direction and the wheels spin like ****. THE PLANE TAKES OFF.:diablo::diablo:

yeah cheers guys lol I worked it out just as I was falling alseep last night 🙂

DP – Thanks for explaining it 🙂 I dont appreciate being told to put my brain in gear, all ive done is completely overthink the experiment.

No offense intended mate, just our way of saying ‘clear your mind’, which you eventually did. Good onya.

I had this going over and over and over in my mind, for hours the other night 🙁

The U/C Wheels are not driven. they’re castors – as a result the loss in forward momentun will be minimal and be dependant on the friction of the aircraft against the belt 🙂

The forward motion of the aircraft unlike that of a car doesnt have to act against the full opposite force of the conveyor.

So the wheels will spin REALLY fast but the aircraft will move forward eventually etc

With me? lol

I must confess, I dont get it? Maybe because it’s 1am, and I should be sleeping, but lift is caused by airflow over the wings…. Its nothing to do with the engine. The engine simply provides forward movement through the air to allow the air to pass over the wing.

If you assume that there is no wind, then what causes the airflow over the wing? The ‘treadmill’ cancels out any forward movement, the aircrafts position relative to the runway remains the same and thus there is no increase in airflow.

If you liken it to a person running on a treadmill. If you run on the open road you’ll feel air passing over your face…. You can run at any speed on a treadmill, but you will never feel any movement of air passing you.

How does the aircraft take off? Unless someone else know another way to take off without air passing over the surface of the wing, then I dont see how it’s possible.