iron eagel

Dany03 Hit the nail on the head, all the belt will do is make the wheels spin faster.
I have stood by the wingtip of a J3 going into a 40 kph headwind at take off, it climbed out like a helicopter. Airplanes do not care about ground speed ( how fast they move relative to the ground) just air speed. And like I said before the belt moving under the aircraft will produce air movement of some kind. The wheels may spin like He## but the plane will fly! No mater what the airplane will respond to the thrust of the engine, the wheels just keep the prop from getting broke and the belly from getting dents.

starwoes

this focus on wheels i believe is getting outrageous. in fact, to see this clearly, i think you must discount the value of weight. for one, assume the plane is suspended on an infinite rope.......eg, a clothesline is hooked up where there's a pulley on the clothes line which is connected to the cg of the plane such that, the plane's wheels barely touch the threadmill...aircraft is perfectly balanced and suspended above the threadmill but with enough wheel contact (friction to spin the wheels). any increase or decrease in threadmill speed results in an increase or decrease in wheel speed.

spin the threadmill alone and see what happens. l'm sure the wheel will duplicate what the argument is about without a resultant increase in airspeed of the craft. now turn on the jets of the aircraft or the props of the aircraft and see what happens. the airplane will accelerate down the rope...threadmill or no threadmill. in fact, the wheels and threadmill can spin like mad and it wouldn't make a bit of a difference. i believe that's why we rely on wheels to propel cars and thrust to propel aircrafts.

in any case, i believe a seaplane trying like mad to match the current of a river will probably result in zero airspeed and thus...no fly..

iron eagel

Yes indeed the wheels and or how fast they turn are no matter to the airplanes movement.

da Rock

How on earth is the conveyor belt possibly going to do anything to the airplane. It has no purchase, no leverage. If it was going to hold back the a/c it would have to do it THROUGH the tire. And if it grips the tire, the tire will turn. No leverage to the airplane through the wheel bearings at all. AND the problem says the conveyor is going to try and keep up with the wheel! So it isn't even going to try and hold anything back.

But truth is, the airplane couldn't care less what the conveyor does or the tires for that matter. It's going to go where the thrust pulls it as soon as thrust > drag.

What actually happens in this "puzzle" is that the airplane starts to move forward as soon as thrust is greater than drag. When it begins to accelerate forward, the tire starts to turn, and the conveyor matches it's rotation by matching the turn and winds up accelerating along under the airplane. Hope the ground crew had walked back to the ramp.

BWooster

The airplane does not care what the wheels do: absolutely true, unless the wheels generate friction to prevent the airplane from gaining airspeed, i.e. hold the airplane back.

This thought exercise amounts to taking off with the brakes locked. In order for the aircraft to take off, its airspeed must rise. (Assuming calm air, its groundspeed will equal its airspeed. But if the conveyor turns only as fast as the wheels, it cannot gain any ground speed, unless it drag its wheels.

So, it can take off, but only if the propeller thrust is greater than the resistance of the wheel- conveyor friction.

da Rock

Actually the only direction the a/c could roll the tires would be clockwise. And when they start to roll clockwise, the conveyor is going to start running in the opposite direction. And that direction is the same one the a/c is taking off. So the wheels aren't going to turn and are going to sit still on a conveyor that's hauling a.... a couple of non-turning wheels that're attached to an a/c that's taking off.

da Rock

You know what's so funny about this puzzle?

It's original description is flawed.

Look at what it actually says about the direction of the wheel's rotation and what the conveyor does. I've been playing with it to stir the pot, but it's time to blow it out.

The original description says the tire's going to rotate clockwise right? A couple of problems with this. And it says the conveyor is going to match the tires direction in the opposite direction. An obvious problem with this.

da Rock

BTW, isn't it the F-14 that has an afterburner control with stages? It's like a gearbox with different gears, only 1st gear is less afterburner and 2nd is a little more etc. And the reason for this shifting deal is because if the sucker is firewalled while the a/c is sitting still the a/c will rip the gear off the plane even if the brakes are OFF because the drag on the wheels even when rolling free is greater than the strength of the gear!!!!!

Now we know where this teaser came from.

3dbob37n

This thing can drive you nuts!
Anyway, all of you guys are forgetting one thing: The conveyor belt is moving in the opposite direction from the rotation of the wheels and is automatically adjusting itself to the speed that the wheels rotate. This being the case, the model would not accelerate. Because of this, it can never reach flying speed.
Let's discount some of the super powered airplanes and just consider that this is an ordinary model airplane with normal power. We all know that if you have enough power the model will bounce a couple of times and break free. But this would not be as described.
Summed up, the converyor belt is moving at the same speed as the wheels which will give no forward motion to the model. It can't fly.
Ah gee, who started this????? Do we finally get an answer?????

3dbob

iron eagel

The typical glow powered model has a thrust to weight ratio of two to one, I do not care what the wheels are doing the airplane will move forward belt or not.
LOL

Phlip

Doesn't matter which direction the belt turns. Either the wheels will not turn, or turn faster. Doesn't matter. Plane accelerates and flys either way!

Phlip

It's not this thing that's driving me nuts.

Or are you just playing with us?

iron eagel

Phlip, thanks for the drawing perhaps that will get the point across.
Although you are from MA maybe they will think it is just another "liberal" point of View
LOL

3dbob37n

So when do we get the answer?
Is the engine even running?
If you can open the doors after landing, it was a good landing.

3dbob

iron eagel

I like the way you think!
Keep the shiney side up. LOL

Flyfalcons

You can also think of it as an infinetely long runway with an increasing tailwind as you try to take off. For every knot of ground speed you gain, the tailwind picks up by one knot. You can be doing 160 knots over the ground, but with a 160 knot tailwind your true airspeed will be zero and you still won't take off.

iron eagel

I guess nobody read this !

iron eagel

There is no wind, it is just the wheels spinning keep in mind groundspeed mean nothing to an aircraft, besides the belt will cause the air to move due to friction at some point ground effect would come into play.

bentwings

Ok here is my $.02

The only way this plane is not going to take off is if it is hooked to a DCTD dually (Dodge Cummins Turbo Diesel) going the other way. Guess what kind of truck I drive.

What about a sea plane??? The ground (Earth) is rotating about 1000+ mph one way or the other and they still get off the ground. How about a ski plane??? same thing.

It doesn't matter squat which way the conveyor is turning or how fast. The jet engine (or prop engine) pushs against the plane not the wheels so it moves forward. When The air flow over the wing reaches flying speed , up she goes.

Aircraft depend on air speed not ground speed.
__________________________________________________ _____________________________________________

another dimes worth:

awright. One more time. How about if the pilot realizing there is a hoax going on here, locks up the brakes and puts on the parking brake for good measure. IE wheels are not going to turn no how.

The conveyor exactly matches the wheel speed. Wheels no turnee, belt no movee.

Give it the throttle and spool up the jets. 6 turning, 4 burning as they used to say in a B-36, Plane starts moving...wheels no move....belt no move to match. plane goes faster and faster. v1 is reached wheels still no turn because belt is matching wheels. Pilot pulls back on stick and ...zoom airplane flys. wheels still not turning, belt not moving with wheels.

air plane flys no matter what. Ie some planes don't even need wheel to take off ..just skid.

bentwings

ps the truck guys are up to 21 pages 3900+ views. keep it going. plenty of flames[sm=drowning.gif]

iron eagel

bentwings
You must have seen the beating we have all taken trying to explain the plain will indeed fly. Thanks for telling them that unless you got a force pulling the airplane back that it will fly. But I bet someone will say your wrong anyhow....
Gee you know about the Peacekeeper lol thought no one would remember that old cigar.

David Cutler

The runway takes no part in the change in the motion of the aircraft, so any movement of the ground there might be is irrelevant.

Once the airspeed is enough the plane will fly, whatever is happening to the wheels.

How do you reckon a plane with floats takes off water otherwise?



-David C.

BMatthews

All those in favor of banning bentwings for bringing this up raise their hands... or if you're on a treadmill wave them in circles either clockwise for yay or anti clockwise for nay so you'll all go in opposite directions and make it easier to be counted....

bentwings

Banhim
http://smiley.onegreatguy.net/banhim.gif
'Round and 'round 'till we all fall down. grade school days......or was that control line combat???

Maybe if we can find a big enough tow strap to hitch to my Dodge and the conveyor I can slow it down enough for everyone's plane to take off then we'll all be happy..

Do y'all think our 118" Z B-25 will get off the conveyor with g-45's ?? How fast will the wheels be turning if take off air speed is 40kts???[X(]

da Rock

Nope

Unless the tire moves forward or backward it won't rotate. Until it rotates, the belt won't move. The only way the tire can rotate is for the a/c to move forward. So if the belt is going to move in any direction, the wheel has to be moving in a direction so that the tire can rotate. The stated problem is simply a trap.

If the stated problem meant to say that the conveyor belt would move along with the tire, keeping the tire from advancing, then the wheel bearings are going to have to somehow stop the forward movement of the a/c without having any purchase. The guys who say the bearings are going to burn out are on this track.

Now, if the conveyor belt is supposed to be resisting the forward motion of the a/c by moving against the rubber of the tire and that's your argument, you're hanging your hat on the tire's traction to the belt being great enough to hold the a/c stationary. You're going to lose your hat. Ever seen a NASCAR stocker sliding sideways or doing a burnout? And about that F-15 pulling it's landing gear out by hitting the afterburner too quickly. It's tires were rolling, just not fast enough.

I'm guessing that this puzzle was thought up by an Aerodynamics professor and he used it to judge if a student had any real understanding of Thrust > Drag.

Phlip

I'm guessing that this is not really a puzzle. I made a new diagram to show what is really going on here.

Phil