Think sea plane. No wheels at all!Think of a person on a treadmill with rocket powered skates, or winged shoes...
Think sea plane. No wheels at all!Think of a person on a treadmill with rocket powered skates, or winged shoes...
Shoot away while I duck for cover.
As the planes picks up speed to takeoff velocity, don't the wheels turn faster?No, you are still assuming that the speed of the wheels has an impact on the speed of the vehicle. The wheels are only there to keep the plane from dragging on the ground.
I agree that the lift force is caused by air travelling over the air foil (wings). But if the forward motion of the plane is matched by the rearward motion of the conveyor belt, isn't the air speed 0?Unless the brakes are on, the only connection between the plane and the surface of the treadmill is rolling friction and bearing friction. Those are minor and may be ignored. In other words the speed of the treadmill has nothing whatsoever to do with the airspeed of the plane. The treadmill has almost no effect on the air that travels over the wings. Air traveling over the wings (more accurately the wings traveling through the air) is the only thing that causes the airplane to lift.
I agree that the lift force is caused by air travelling over the air foil (wings). But if the forward motion of the plane is matched by the rearward motion of the conveyor belt, isn't the air speed 0?
I agree that the lift force is caused by air travelling over the air foil (wings). But if the forward motion of the plane is matched by the rearward motion of the conveyor belt, isn't the air speed 0?
Not at all. Any extra rolling friction from the rearward motion of the conveyor is negligible compared to the forward thrust of the engine
In rocket terms, it'd be like saying "If an infinitely long launch rod/rail were moving downwards at the exact opposite speed of the rocket, would the rocket move at all?" Yes it would, the buttons would melt, but it would indeed move
OK, let me see if I've got this straight: once the rolling resistance is overcome, the forward acceleration of the plane will happen regardless of what is happening to the ground. Is that right?
I'm perplexed why this is even a question worthy of discussion. Once you know that airplane wheels are not used for locomotion, and that forward thrust comes only from the props or jets or whatever, that's the end of it. Where's the mystery here?
Put skids on the plane. Now what happens?
Put skids on the plane. Now what happens?
beings how no mention of the planes engine being used, pretty much what i thought here.Airspeed equals lift. If its just sitting on a spinning treadmill and just the wheels are turning, there is no forward speed and so no lift for the wings.
It's easy to make the wrong assumption that the conveyor is moving at the same rate as the wheels always and not just a constant 50 knots.I'm perplexed why this is even a question worthy of discussion. Once you know that airplane wheels are not used for locomotion, and that forward thrust comes only from the props or jets or whatever, that's the end of it. Where's the mystery here?
Boeing C-17 Globemaster is one I know of that can drive on its wheels. It can do a three-point turn on the runway when needed. Impressive. I am sure there are others, but not many. Carrying the extra mass of drive motors is detrimental to fuel economy every time they fly. That is not tolerable on commercial aircraft currently.The only "aircraft" I can think of (outside of a flying car) with direct drive to the wheels is the "F-16" from "The Jewel Of The Nile", but that was a prop, and not a real aircraft.
Imagine it's a toy plane on a treadmill in a gym. You're sitting on the floor next to it, holding the plane in your hand with the wheels on the treadmill.As the planes picks up speed to takeoff velocity, don't the wheels turn faster?
Think sea plane. No wheels at all!
Boeing C-17 Globemaster is one I know of that can drive on its wheels. It can do a three-point turn on the runway when needed. Impressive. I am sure there are others, but not many. Carrying the extra mass of drive motors is detrimental to fuel economy every time they fly. That is not tolerable on commercial aircraft currently.
Now, the sea/float plane concept was a good one. If you are on a float plane on a river, should you take off upstream or upwind?
You may be right with that, but I don't remember the jet engines changing pitch when I saw the maneuver. I don't have definitive knowledge.My recollection from flight test videos is that it’s ability to turn on the runway is from thrust reversers, not from anything in the landing gear.
Whatever gets you into the air quickest. Depends on river and wind conditions on the day. I am guessing they have tables or a calculation for that for each aircraft and load configuration. Maybe they just take off from lakes .Now, the sea/float plane concept was a good one. If you are on a float plane on a river, should you take off upstream or upwind?
It travels the same speed and direction as the treadmill surface. If the treadmill is going fast enough it could even lift off, but if the plane isn’t creating its own propulsion it will begin losing airspeed as soon as it leaves the treadmill.
My point was that the plane is now "stuck" to the treadmill and will move with it. I should have added that I meant for the treadmill to be moving backwards relative to the plane.
Let's imagine the plane sitting on a runway on really sturdy skis. I would think most people can see how the plane will move forward if it can generate enough power to overcome the static friction between the skis and the runway. It may make a helluva racket and throw sparks everywhere, but it could takeoff if it had enough power.
So now put the plane on a treadmill that is locked down and won't move. The plane took off from a runway so it should take off from a stationary treadmill. Right? Now move the treadmill backwards at 1 foot per second. It is a little more difficult, but again the plane should still take off if it can generate enough power. At what speed of the treadmill can't the plane take off? That would be when the treadmill is moving backwards at a speed that prevents the plane from generating enough forward thrust to attain lift off.
Now swap out wheels for the skis. What has changed? I have removed a tremendous amount of friction, but nothing else. Think about it.
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