can a plane take off from a conveyor moving at the same rate as the plane

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Rex R

Rex R

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the premise is this; airplane is sitting on a conveyor belt. belt is free to move aft at rate equal to the plane's takeoff speed. if the aircraft needs 50 knots for takeoff and the conveyor is moving at 50 knots(to counter the planes forward motion) will the plane a)move backward, b)stand still, or c) take off normally?:)
Rex
 
would it make a difference(on take off) if the runway had a frictionless surface?
 
Only if the runway wasn't level, then you have virtually what most aircraft already have under those conditions anyway. Rolling friction on the wheels is really quite small, assuming the brakes are off ;).

The key with this question is remembering that the engine thrust works directly on the airframe.
 
Rex R said:
the premise is this; airplane is sitting on a conveyor belt. belt is free to move aft at rate equal to the plane's takeoff speed. if the aircraft needs 50 knots for takeoff and the conveyor is moving at 50 knots(to counter the planes forward motion) will the plane a)move backward, b)stand still, or c) take off normally?:)
Rex
Click to expand...
The answer is (b). This is because of the way the question is phrased: "if the aircraft needs 50 knots for takeoff and the conveyor is moving at 50 knots(to counter the planes forward motion)..." The only way that happens is if the aircraft's wheels are motorised to start the aircraft moving up to take-off speed, after which it becomes a glider.

Of course, for a more normal aircraft, things are a little different... ;)
 
engine torque may make a difference in how the aircraft moves :).
 
timbucktoo said:
Wait, isn't that how they roll down the runway?
Click to expand...
They are "motorized" if you consider the engine(s) that are propelling the aircraft forward, but other than flying cars, there is no direct link from the motor to the wheels (nor do they have their own motors or engines to drive them). They are propelled by the thrust of the engine(s). That is why being behind a aircraft that is taxiing is so risky.

 
captbk said:
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.
Click to expand...
The propeller pulls the airplane through the air, creating lift on the wings. The wheels are either spinning across a stationary surface or spinning faster on a moving surface, but either way they're having zero effect on the speed of the plane through the air.
 
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. A real jet would have been FODed out almost instantly under those circumstances (such as by that basket that passes under the front wheel).



Funny observation... The tail number of that plane is K-105... A little changing and I see that as "KIOS" or "chaos". I doubt that was "just a coincidence".
 
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K'Tesh said:
Funny observation... The tail number of that plane is K-105... A little changing and I see that as "KIOS" or "chaos". I doubt that was "just a coincidence".
Click to expand...
Maybe K105 was their favorite radio station?
 
captbk said:
Propellers are not mentioned in the OP. "airplane is sitting on conveyor"
Click to expand...
No matter what kind of airplane it is, propeller, jet engine, or otherwise, the same applies. Planes are pulled down the runway (or conveyor) with whatever pulls them through the air, so the wheels are free to spin at whatever rate they need to.

A moving conveyor or a static runway would be the exact same as far as the airplane is concerned. The engine would move the plane through the air, the air over the wings would create lift, and it would take off just fine.
 
Yeah, but on aircraft carriers, the plane is pulled into the air by the catapult..

So, if the carrier is going backwards at the same speed as the catapult is going forward, would the plane fly off?
 
Probably not. It's all down to the difference between ground speed and airspeed. Even without a catapult, the airspeed of an aircraft sitting on a carrier's deck is the same as the carrier's speed. So simply by launching the aircraft off the bow without any other assistance, it's already giving the aircraft a starting airspeed of a few knots. Then the carrier adds a bit more to that by turning to launch aircraft into the wind, so that the aircraft gets some more airspeed equal to the wind speed in the opposite direction. Finally, a catapult is added into the mix to give the aircraft even more of a boost.

If the carrier is going backwards, or if some idiotic ship designer put the catapult on the wrong end of the flight deck, then the carrier's speed is subtracted from the aircraft's initial airspeed.

Next question: what happens if, instead of an aircraft, you have a train driven by a propellor?
 
dr wogz said:
Yeah, but on aircraft carriers, the plane is pulled into the air by the catapult..

So, if the carrier is going backwards at the same speed as the catapult is going forward, would the plane fly off?
Click to expand...

I don't want to be on an aircraft carrier that is going 165 mph in REVERSE!
 
What if it was the Batmobile?

Or an Estes Blurzz?
 
a carrier w/ a negative airspeed of more than -50 knots...sounds like it is trying to out run a hurricane.
 
I'm not a scientist or academician, but I'll add my 2 cents. Feel free to shoot me down if there are any flaws in my logic. When taxiing on a runway, the pilot is increasing ground speed through engine thrust to the point that the wings and flight control surfaces generate enough upward lift for the plane to take off. If the runway was a giant conveyor belt then if it was moving in a forward direction that would shorten the takeoff distance by incrementally adding to the plane's ground speed. Conversely, if it was moving in a reverse direction to the plane, it would lengthen the takeoff distance (as measured by distance travelled on the BELT). The only way that the plane would stand still is if the conveyor belt could precisely match the ACCELLERATION of the plane in reverse, because a plane taxiing does not move at a constant velocity.
Shoot away while I duck for cover.
EDIT: Think of a person running on a motorized treadmill: no forward air speed, no liftoff.
 
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Think of a person on a treadmill with rocket powered skates, or winged shoes...
 
kuririn said:
I'm not a scientist or academician, but I'll add my 2 cents. Feel free to shoot me down if there are any flaws in my logic. When taxiing on a runway, the pilot is increasing ground speed through engine thrust to the point that the wings and flight control surfaces generate enough upward lift for the plane to take off. If the runway was a giant conveyor belt then if it was moving in a forward direction that would shorten the takeoff distance by incrementally adding to the plane's ground speed. Conversely, if it was moving in a reverse direction to the plane, it would lengthen the takeoff distance (as measured by distance travelled on the BELT). The only way that the plane would stand still is if the conveyor belt could precisely match the ACCELLERATION of the plane in reverse, because a plane taxiing does not move at a constant velocity.
Shoot away while I duck for cover.
EDIT: Think of a person running on a motorized treadmill: no forward air speed, no liftoff.
Click to expand...
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.
 

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