Brain Teaser

[Randy]

So. . .IF the plane is moving under the force created by engine thrust AND the wheels are not skidding, it is not possible for the conveyor belt to match the wheel speed.

No one said the wheels couldn't be skidding. If the engine, be it a prop or jet, created enough thrust to overcome the resistance created by the conveyor, then it would result in the wheels breaking traction and the plane would propel forward enough to create enough speed that would create the lift that would allow the plane to take off. Right?

btw - I agree it's a bullshit question, but, still fun to discuss

 

[galxy5]

Twowheelnut

ever been on an aircraft carrier

thrust x calapult = airspeed and lift ,, engines at full thrust and the cat throws the jet into the air ,, then the thrust takes over ,,

and just so you know they are loud as hell if you are in the forward conning station ,, just under the cat stop ,, with a hangover from drinking Marines under the table all night !!

 

[twowheelnut]

btw - I agree it's a bullshit question, but, still fun to discuss

Not as fun as:

The correct answer (question) is: Who cares? It's an improbable scenario anyway. Why would anyone build a runway as a conveyor belt? Now re-suppose the question moving the whole scenario to an aircraft carrier and hooking up an F16 backward on the catapult and I think you'll find the discussion much more interesting.

 

[twowheelnut]

Twowheelnutever been on an aircraft carrier

thrust x calapult = airspeed and lift ,, engines at full thrust and the cat throws the jet into the air ,, then the thrust takes over ,, 

and just so you know  they are loud as hell  if you are in the forward conning station ,, just under the cat stop ,, with a hangover from drinking Marines under the table all night !!

Re-read my post and quit drinking... :****:

 

[Just Plain Dave]

Me thinks the guy with signature of:"You say you're an electrical engineer and you can't even tell me how many amps are in a gallon??"

would HAVE to have the correct answer..

The plane will fly, however the only way we will see proof is when Wiley Coyote orders an Acme supersize, industrial strength treadmill, straps a rocket to his butt, gets on the treadmill and lights the rocket in an attempt to catch the roadrunner. At the last second that sly roadrunner hero of mine flips the reverse switch on the treadmill and we watch the results.

 

[galxy5]

twowheelnut

ahh yes ,,, backward !!! :headbonk:

 

[Bike Effects]

ToeCutter is right too--you may burn up the wheel bearings if the ramp going backwards causes them to turn faster than the max RPM they are spec'ed at.

Wheel bearings are not a limiting factor for aircraft, but aircraft tires have a max TIRE GROUND SPEED limit. It depends on the aircraft in question.

 

[Rogue]

ToeCutter is right too--you may burn up the wheel bearings if the ramp going backwards causes them to turn faster than the max RPM they are spec'ed at.

Wheel bearings are not a limiting factor for aircraft, but aircraft tires have a max TIRE GROUND SPEED limit. It depends on the aircraft in question.

Speed is allway a factor with any bearing... It's just aircraft take off speeds are well below the bearings rating. Spin those bearings at the equivelent of 10,000 mph and the bearings will go.... and the tires aren't rated for that either!

I still like my answer the best!

 

[FJRocket]

Yeah, ok, I get it. Thrust will move the plane forward and overcome wheel speed no matter what. So the plane will take off. I'm a convert.

 

[RadioHowie]

Just like in the two other forums I've seen this question posted, the original poster misleads the responders by mentioning the speed of the wheels.

The proposition is that the conveyor belt prevents the airplane from moving forward by matching the forward speed of the plane regardless of the amount of thrust.

The boat moving at x mph in a current moving x mph in reverse is the perfect analogy.

Liftoff is not a matter of thrust...it's a matter of ground speed. No fixed-wing aircraft (plane) can achieve takeoff until the entire aircraft has attained a speed at which the air passing over the wings creates enough lift to get the aircraft airborne. A given airframe will achieve takeoff at a given ground/airspeed, regardless of the thrust applied to the airframe. In other words an aircraft that achieves liftoff when the lift created by the air passing over its wings at 100mph will NOT achieve liftoff at a lower speed just because more thrust is applied to the airframe, so the answer is NOT thrust. The only advantage of increase thrust is the ability to get to 100mph sooner, but the limiting factor in this example is still 100mph. If the runway is moving backwards at 100mph while the plane attempts to move forwards at 100mph, then the plane is essentially not moving at all, hence no airflow over the wing surfaces, hence no liftoff.

The entire premise of the brain teaser is the conveyor belt negates the forward speed of the aircraft. The speed of the wheels is unimportant. They have nothing to do with lift or takeoff. It's ONLY forward speed of the aircraft that creates enough lift to get the craft airborne.

Just like walking up the down escalator, it doesn't matter how strong you are, if the speed of the escalator, inverse to the direction you're traveling, exactly matches the speed you're going UP, then you go nowhere. If you are an airplane, standing dead still in relationship to your surroundings, you go nowhere. Doesn't matter whether you're a 98 pound weakling Cessna or a Hulk Hogan F-16.

However...

 

[fretbender]

So. . .IF the plane is moving under the force created by engine thrust AND the wheels are not skidding, it is not possible for the conveyor belt to match the wheel speed. 

No one said the wheels couldn't be skidding. If the engine, be it a prop or jet, created enough thrust to overcome the resistance created by the conveyor, then it would result in the wheels breaking traction and the plane would propel forward enough to create enough speed that would create the lift that would allow the plane to take off. Right?

btw - I agree it's a bullshit question, but, still fun to discuss

Right!

And yes, it was fun right from the get go. Good one Randy.

Thrust will move the plane forward and overcome wheel speed no matter what. So the plane will take off.

yeah. . .but if the tires are skidding, will the tires pop? Will the wheels spark away to nothing? Will this result in the landing gear breaking and dropping the plane on it's belly? Huh??? Would it??? I think we should try this. Who has a spare aircraft (any kind) and a conveyor belt to suit? Let me know when it's ready to go and I'll do the filmwork. B)