The arplane on a conveyor belt conundrum

Originally posted by launchpad

Originally posted by sooks

Basically what you have to think of is the forces acting onto hte plane. the 4 major forces are thrust say to the right.... drag to the left........ normal force up and gravity down. so to accelerate the force of thrust must overcome the force of drag. the drag forces are wind resistance (which is the same as on a normal runway.) bearing reisistance (which is so minute can basically be ignored) and rolling resistance of the wheel on asphalt. the equation for that is the coefficient of rolling friction.... which is something like ,001 * Weight. the equation hsa nothing to do wiht speed. so basiclaly the wheels mean nothing but to provide a platform of less resistance then if say the wheels were cement blocks. so thrust overcomes the friction and it accelerates to takeoff in probably a little longer distance than a normal runway with the wheels travelling twice as fast as they would normally.

Actually, SOOKs the drag of the wheels turning DOES increase with speed.

yes, static friction has a higher coefficient thant dynamic(sliding) friction. (your coefficient of ROLLING friction is not just something you pull off a chart- it is put together from hundreds of varibles in itself: tire material; air pressure; weight of object; WIDTH of tire, material of roadway, number of tires, etc, etc.

However, you are using a basic first year physics equation which does not include all the little things like HEAT generated and parts swell and FLUID friction due to the grease on the bearings, eventual cavitation of the liquified grease, etc, etc. sure it is negliable - to a point. But every basic equation given in the text books is there to get a general point across and later on you find it has tons of little things that go with it- like IF's and at some point they become the deciding factor. (pick up a 'simple' book on bearing design if you do not believe me!)

i guess along those lines: if this experiment goes on long enough - At some point the darn wheels temp will increase sooooo much it/they will pop and that plane if it does not have enough air speed you will have a very spectacular crash as it toubles down the conveyor and then possibly reverses direction. hope it is remote control!

Anyone put this one up to the Myth Busters yet?

Yes,... i agree with that... However, they say that on a normal runway, the CRF is between .001 and .007. the coefficient of friction has to increase a huge amount to be greater than the thrust coefficient... it would have to increase to somewhere in the lines of like .3 or .4 thats an enormous difference.... basically it doesnt have near enough of an effect upon it to prevent takeoff