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Friday, March 21, 2008

Airplane on a Conveyor Belt

Question:
An airplane is sitting on a conveyor belt. The speed is set to its takeoff speed. Will it take off?


I have to add my two cents to this delightful question. I know little of physics (though I can confidently name all twenty subatomic particles). Grab your Sol Niger, it's science time!

My answer:
No.


It's obvious when you consider the original version of the question from the Medieval Ages:
If ye flag bearer joggeth on the moving ground, Would thoust kingdom's flag fly true with wind?

Obviously, no. If you ran on a treadmill with a flag it wouldn't fly. But you could build speed using a wizard's moving ground and then run off the end to fill your flag with maximum wind.

But let's update this answer into our modern world.

Airplanes fly by running really fast into the wind. A jumbo jet needs to run at about 280km/hour (175mph) to take off. You can help it reach take-off speed using a conveyor belt but it would be stuck on the ground, running on the spot. It still needs the second chemical: running into the wind.

Think of the airplane's feelings. It doesn't give a sh*t how it reaches take off speed. If it could start at 280km/hour it would and take off instantly. But it has to travel the long, sad journey called the runway before it can happily gaze at its own shadow. Aircraft carriers use a slingshot to increase the plane's speed. A giant conveyor belt would be even cooler. But once the plane reached take-off speed you'd need to hit stop on the conveyor built so it could push itself through the wind and take off.

They recently did the airplane/conveyor experiment on Mythbusters (including a wonderful full scale version). It was obvious that the conveyor shortened the runway but, in the end, the airplane needs to move forward so that it could take off.

The science behind it (a more detailed description for scholars):
Since Earth's atmosphere was created by the Mugarath and the wrath of the Seventh Mountain Giant it follows that any attitude taken before the sun smiles upon the shadowedland will be in futility. Listen for the laugh of the Beegoo Root. If the seas ripple clockforth then sip on your nectar. Still on the ground? The wings of Tamforge were built in a day but they must clean the stains of Growth before they can Decay. Hug all the weeds found without eyes. In a pinch, follow the example laid down by four by forty temples before thee. Recall the era of the battle of the secret of the way of the era. And simply do as the Wizard Fozbucket would do: grab your skull staff, hop on (or next to) a dragon, and angrily accuse the sky.

1 comment:

AndyG said...

lol.

nice but WRONG !!!

the plane takes off and here is why:

(no science jargon included)

The forward propulsion has NOTHING to do with the surface the plane is sat on ! You see, a plane uses a propeller or jet engine to achieve forward momentum. This acts in the AIR BEHIND the aircraft for propulsion whilst the wheels simply turn relative to the ground.

If the conveyor belt matched the planes initial inertia then for a brief second whilst the forward momentum was created, the plane would appear stationary relative to the ground. Once the plane started to move forward, the action of the conveyor belt becomes irrelevant as the action of the belt STOPS affecting the aircraft as it moves through the air. Yes the wheels may be turning at silly speeds relative to the rest of the aircraft BUT believe me, the plane WILL move forward simply because the wheels have NO DRIVE EFFECT on the vehicle. They are free-wheeling!

therefore:

conveyor travels 50mph backwards,

plane travels at 50mph forwards,

wheels travel at 100mph,

propeller STILL moves airframe 50mph forwards because the driving force is not affected by the wheels at all.


hence plane leaves !!

/me bows !

i can do science me !!! ;)