Question...

[AlaskaVX]

A plane is standing on a runway that can move(some sorty of conveyer).The plane moves in one direction,while the conveyer moves in the opposite direction.The conveyer has a system that tracks the planes speed and adjusts the conveyer speed to the exact same speed as the plane but in the opposite direction.
question is
will the plane take off or not?will it beable to run up and take off?

[BD-VX99]

No, lift is a function of air velocity (despite the wheels rolling at twice the speed). However, the conveyor would drag air with it and therefore create a small amount of wind in the opposite direction. I guess if you increased the speed enough you could drag enough wind to create lift but I highly doubt you you would ever be able to "drag" enough wind with the conveyor to allow the plane to take off (plus as soon as the plane gets out conveyor's wash it would plummit). Many automotive wind tunnels use moving floors and walls for the opposite reason (to simulate the walls being absent, and the vehicle moving at speed).

[volume311]

oh man I thought I was having a deja vu of a nightmare. There's an exact same thread over on NASIOC that was started yesterday and blew up to +1800 posts including MS paint diagrams and what not. Beleive it or not the debate is still going on.

For the curious
http://forums.nasioc.com/forums/showthread.php?t=891480

[mbeach]

I miss teh Nasioc OT. Sometimes.

Alan, where's that frequency? I'm getting some handhelds together for Caribou season and I want to get that freq on there as well.

[transio]

A plane's speed is generated by air thrusting devices (props or turbines). The wheels are freely rotating. A conveyor running opposite the plane will only double its ground speed, but will not significantly alter the air speed (I say not significantly because there will be some "drag" caused by the minimal friction of the rolling wheels. For the most part it's irrelevant though). The air speed is what is required for take-off.

Similarly, a plane in high headwind can take off at very low ground speeds. I've taken my model planes down to the airfield on very windy days and taken off almost without moving (relative to the ground).

Edit: Bleh, NOW I see BD-VX99's post.

[Triathlete]

Yes it can...



















































...if it is an AV8 Harrier! :yesy: :yesr: :yesg:

[Bulldoggie]

[QUOTE=transio]A plane's speed is generated by air thrusting devices (props or turbines). The wheels are freely rotating. A conveyor running opposite the plane will only double its ground speed, but will not significantly alter the air speed (I say not significantly because there will be some "drag" caused by the minimal friction of the rolling wheels. For the most part it's irrelevant though). The air speed is what is required for take-off.

Similarly, a plane in high headwind can take off at very low ground speeds. I've taken my model planes down to the airfield on very windy days and taken off almost without moving (relative to the ground).

A conveyor belt would only spin the wheels twice as fast as the thrust would move the plane forward even without the wheels. Some planes use skis as an example

[Maugan_VX]

No it would not fly because the generation of lift is only possible with apparent wind flowing over the wing surfaces.

(unless its a harrier, in which case its a flying Microwave, or a North Carolina Lawn Dart)

[Bulldoggie]

No matter how fast a conveyor travelled it would NOT stop the thrust from pushing the plane forward, unless it could excede the max. speed of the wheels or the wheels had brakes applied.
The trust would still push the plane forward, just as the thrust on a Harrier pointed downward is able to lift even if you took your hypothical conveyor and made it vertical and put the wheels of a harrier on it's nose the conveyor would only spin the wheel. the harrier would still climb because of it's thrust.

Not trying to offend

[BD-VX99]

Bulldoggie

I don't think you could offend anyone by being correct. In theory, if the aircrafts wheels were frictionless then the conveyor would have absolutly no affect on the planes ability to run up the runway and take off (Inertia would keep the aircraft still (with engines off) regardless of conveyor speed). I was assuming in this case that the wheels did have friction and thus the conveyor would be able to exert force on the aircraft. Is the question asking whether or not the aircraft could take of standing still (conveyor speed increasing to keep the aircraft still)? or if the aircraft could take off with the conveyor matching the wheel speed (obviously yes, but in its regular distance)?

[bobmumgaard]

A bicycle is on a treadmill and the treadmill runs at the same (but opposite rate) as the bicycle's speed (same situation as a runner on a treadmill, but riding a bike). Is the bike easy to ride?

[volume311]

Yea, the gyro-effect of the wheels keeps it balanced and since there's no drag, yea easier me thinks. The only opposing forces would be from the bike parts bearings/chain/tires low on air

[psychos2]

here is the answer (http://www.avweb.com/news/columns/191034-1.html)

[mbeach]

Thanks for the link -my head was starting to ache.

[Maugan_VX]

yeah after I posted that I gave it some more thought because the solution to the "riddle" was a bit too simplistic.

It would be a different story if the wheels powered the forward thrust or it was a car :)

[transio]

It would be a different story if the wheels powered the forward thrust or it was a car :)Not necessarily. Some planes (like biplanes) can maintain lift even when the wings are stalled (no positive airflow) because they have huge props pushing large amounts of air over big wing surfaces. That wouldn't be a riddle, though, but an engineering problem. I'd be interested to see a biplane do a stalled 0mph take-off. That would rock! :)

[transio]

A conveyor belt would only spin the wheels twice as fast as the thrust would move the plane forward even without the wheelsI'm not sure if you're agreeing or disagreeing with me, but that's pretty much exactly what I said (or was trying to say).

[Bulldoggie]

here is the answer (http://www.avweb.com/news/columns/191034-1.html)
Thanks for the link I could not word it better
And I was quoting Transio in agreement

[transio]

And I was quoting Transio in agreementOK... upon rereading my post, I realized it was ambiguously worded, so I wanted to make sure. :)