Plane + Conveyor

Seen it on a lot of other websites, but no pilot would ever be seriously confused by this "riddle" - the propeller pulls the aircraft thru the air, and the aircraft is not powered thru the wheels like a car. Result should be obvious for all but the uninitiated.

 

The thrust rom the propeller would simply pull the aircraft forward irrespective of the wheel speed. It would be like a plane on skis, wheel speed is irrelevant other than as a producer of drag from contact with the surface, and if the conveyor is matching the speed of the wheel there would be very little, so the thrust produced by the propeller would pull the aircraft forward right off the conveyor just like it does when you pull the chocks - no mystery.

 

This whole thing is stupid. Poorly written question or not, the airplane is GOING to take off, if takeoff power is applied. The rest is just noise. Notice the original question says the airplane moves in one direction and the runway moves in the other direction. Absolutely NOTHING will happen unless and until there is motion. Until there is SOME motion by the airplane, there is NO motion on the belt.

So lets keep this real and end this now. LOL

 

Under what set of circumstances can this possibly happen? (Hint: It can't.)

Which makes any other interpretation of the scenario pointless and irrelevant. There is no set of circumstances where the airplane will not move.

Huh? Not sure I follow. There is a correct set of assumptions and an incorrect set.

 

That's a complete non sequitor. It's a meaningless statement - move forward relative to what? What if the aircraft is a helicopter? a VTOL?

Resorting to "miracle" inventions ?????????????

 

As I said (more or less) in the Fchat thread; .....................regardless of any factors mentioned, the plane will not fly until air passes around the wings with enough velocity to create lift. PERIOD! CASE CLOSED.

I can't believe that thread went to 1400 and I'm REALLY glad I didn't read all of it.

 

Yes that is true. But if the prop is turning at takeoff thrust, there will eventually be airflow over the wings. REGARDLESS of what the belt does.

 

I was talking real world. There is no way the airplane WON'T move. Irregardless of how the scenario is worded. If you want to take the scenario at face value, you also must accept that the scenario is flawed, can't happen and shouldn't even be debated.

 

Propwash doesn't create lift. Forward movement relative to the fixed wing tractor aircraft at a speed ( V) fast enough to produce the pressure differential and downwash is necessary for the wing to react. If we are talking about a Lockheed Electra there will be enough propwash to generate some reaction but it wouldn't get the airplane airborne.
What the hell is the airplane doing on a conveyor anyway?
Switches

 

Trying to waste our time - enough already!

 

LMAO. Best response yet!

 

Everyone take note here, the conveyor matches the speed of the plane (means the plane is moving) and matches the speed, only in the opposite direction.

IOW, if the plane were moving forward at 100 knots, the conveyor would be retreating at 100 knots the opposite direction. Wheel ground speed would be 200 knots. The tires or wheels may not like spinning that fast, and on some large aircraft that take off at 150 knots, 300 knots on the wheels might blow the tires, but I see nothing to stop the plane from moving. Its sitting on wheels that roll, and roll they will.

Another thing even many high time pilots forget, is that as the plane gains speed, even though its not at flying speed, its becoming lighter. Probably a crude way to calculate it, but at half stall speed, the plane probably has gained 1/4 its weight in lift. So even if the wheels were to fail from overspeed on the conveyor, once a certain speed has been reached, there probably wouldnt be enough drag to stop the plane from gaining airspeed and becoming airbourne.

Another issue to consider is ground effect, which with the ground (conveyor belt) moving by that rapidly under the aircraft, could no doubt effect ground effect induced lift, possibly allowing the plane to become airbourne at an airspeed much lower than it would normally.

 

Its the new launching system NASA invented, only the aircraft is on it backwards.

Thats the new question. If the plane were parked on a conveyor with the brakes on, engines not running, and the conveyor accelerated forward with the plane facing the direction of travel, would the plane fly?

There was a clip I found on youtube of a small float plane taking off from a trailer towed behind a car. Its pretty cool to watch.

 

Reminds me of an incident that happened here in Seattle some years back. North of the city there was a short grass strip on the shore of a lake. The strip, at right angles to the shore. The lake was too short for some airplanes. One genius who owned a float equipped Cessna 180 figured that he wanted to take his plane to a bigger lake so he removed the wheels and installed floats and somehow hoisted it on top of a truck with a flat bed that he had built on it.
With the C-180 on top and running full bore, his buddy in the truck running full bore down the runway, they attained launch speed and the pilot attempted a liftoff. In their cleverly designed blocks and wedges to hold the airplane on the the pad they achieved total success. So total that when they reached the end of the strip the airplane was still on top of the truck and both of them roared into the water. The design had not allowed for the airplane to rotate so that it could lift off. The floats worked fine, however, in the inverted position with the airplane under water.

 

Good grief!

If you walk under a plane in the opposite direction is the plane moving?
Of course not!

So why would a conveyor be any different.
(Ummm.... That was a statement, NOT a question)

Ok then, ... lift the plane off the ground, spin the wheels as fast as you are walking

DUH! .....No difference! Plane still isn't moving and as Rob said ....
Well, ya all know what Rob said...

Same as doing a run up with the wheel brakes locked.

Why this is so astounding to some, is beyond me!

Charlie

 

No, it just means conveyor matches the speed of the stationary, but spinning wheels

Try using vectors to plot conveyor speed with wheel speed.

+1 -1 = 0

+100 -100= 0 it makes no difference what speed you use.

You will find they cancel each other. So, it all equals zero

Everything that follows is false, because the plane isn't moving! (sigh)

 

So what, then, exactly is the point? We all know the propeller pulls the airplane through the air, not the wheels. So it really does not matter what the conveyor belt is doing, nor does it ultimately matter what the wheels are doing. Regardless of how the scenario is worded, the airplane WILL take off because there is nothing the conveyor belt can do to the airplane that will stop it.

 

Yes! That is correct!

My point , Greg, was that the conveyor, / spinning wheels have no effect on the planes movement.
Therefore, all assumptions that it does, creates a false conclusion.

Charlie

 

I know that....

I was commenting on Artvonnes first line:

Which in itself, isn't true.

If the speed of the plane were zero, so would be, the conveyor speed. Plane is not moving, even though the speeds of both, are the same (matched)


C.