SOB your right, well enough beer for one night I'm off to be too.

 

We've had it out on this one before...

I think it went about 50/50. Some aviation website said the plane would eventually take off...

Without sufficient air over and under the wing (ground speed, translating to air/wind-speed over the wing) I don't see how this would happen..

But, anyhoo, that was done before.. Then, I asked the question about to 3 guys, the belhop, and the 30 dollars becoming 27, and where'd the mystery $1.00 go?

 

This comparison eventually convinced me that the plane takes off:

Picture a hovercraft moving upstream. How does it move upstream? Well it has nothing to do with the direction of water flow and everything to do with the interaction of the horizontal thrust fan blades and atmosphere. Same thing with the treadmill and plane. However, as Bighersh alluded to, the plane would have to eventually get up to speed to create lift.

BTW, what is KTS? Knots?

 

KTS = nautical miles per hour, and the airplane will always take off. If you are thinking about ground speed then your are going down the wrong path. The only speed that matters for flight is airspeed. In fact single engine aircraft do not have a ground speed gauge. To obtain ground speed the pilot must do the math.

 

I've flown backwards in a Piper Super Cub.... just to prove this point.



In the other forum, the argument eventually progressed to whether or not the wheels and bearings on the landing gear would explode.

 

Fell backwards, or flew backwards?

OK, lets just say the plane can take off. If it never moves, how will it build groundspeed, to make airspeed, to make wind, to create lift, to get off the ground?

I don't deny that the propeller, jet, etc can keep the plane airborne once it's airborne, but if it never gets lift- I don't understand how it can fly...

I don't profess to be an aeronautical engineer, NASA scientist or anything, but I do know air aircraft requires air under the wing (or lifting body) to create lift.

It'd be easier to believe a rocket propelled plane (X-1) could potentially have enough thrust to create lift from a stand still, but not a jet or a prop.

 

Well, just think about this... does how fast the wheels spin have anything to do with airspeed? (remember, the runway is moving, not the air)



And yes, I set a super cub up for a landing (with instructor, who was having me do this because it was cool), in a 45 KT headwind, while slowing the plane down to where we were actually flying backwards, with an airspeed of about 40 mph (supercubs' airpseed indicator is in mph, not KTS) and a groundspeed of roughly -5.

 

Airspeed is your speed in relation to the air around you.

Wind is a factor. Depending on the direction you are facing relative to the wind, it can increase or decrease your groundspeed.

For example... If your plane needs to be at 50kts airspeed to create enough lift to fly, and you are facing into a 60kts wind, you can actually seem to move backward compared to the ground. That is why aircraft carriers always face into the wind for launches, and why airports have runways going in so many directions. Planes need less runway to reach the airspeed needed for lift if facing into the wind, and more if they have a tailwind.

Hope this helps.

 

Hersh, you are sooo close. If you would erase the word "ground speed" from your head you would be there. Let me explain a little about aircraft.

Airspeed is the term given to how fast the air is moving across the wing of the aircraft.

Groundspeed is the term that defines how fast the aircraft is moving in relation to the ground below it. It is more or less an average of distance vs. time not a true measurable quantity.

So ground speed has absolutely nothing with flight. The aircraft could be parked brakes locked not moving at all. Given a gust of wind 1mph higher than the stall speed the aircraft would take off. The wind moving across the wing created the airspeed necessary for flight. This is how the airplanes can fly backwards. The wind is blowing faster than the aircraft is flying. So in relation to the ground you are moving backwards but the speed across the wing is enough to maintain flight.

 

Cool... Thanks guys...

I tel you what though, I think we could get this put on Mythbusters, if we all wrote in and asked for it.

Those guys will try anything...

 

as soon as i went to bed last night i though of another humorous one.

You are hunting with your dog at the edge of a nearby forest.
The dog hears a noise in the woods and runs in.

How far can your dog run into the woods?


And on the airplane one, i think i have figured out a good sceneario to give the guys that still think it wont fly.

i think we all agree that an airplane moves because of its engines moving air in front of it, creating thrust and pushing out the rear. therefore giving the aircraft momentum and airspeed over/under the wings.

take this scenerio. you are on a treadmill, with you arms out.
you start to run as the treadmill keeps up. you stay in the same position . You feel NO air under or over your arms because you are using your feet and GROUND speed to stay up with the reverse-traveling treadmill. this is what woud happen to a car because it is propelled forward by its tires.

Now lets take this situation...
You are on a treadmill, arms spread out again. you have two friends, one holding you up on each side and you tell them to run forward. The treadmill is furiously spinning to keep you held back, and you are running and kicking like crazy but your still going forward. The force moving you forward is not your own feet and is not on the treadmill. Your friends are acting like engines that are propelling you forward. Regardless of wether or not you can go that fast on the treadmill, they are still pulling you forward.
So imagine that your friends are the engines and your the plane.
Hope that helps you skeptical ones.

 

Your dog can only run halfway into the woods... after that he's running out of the woods.


As for the airplane and treadmill, i think there might be some confusion as to the length of the treadmill. If its 5000 feet long like a runway, then the plane will be able to power up its engines and build up speed to generate the required lift to take off. If the treadmill is short, like one you might use in the gym, there's no way to generate lift, so the plane cannot take off.

- NCSU

 

The length isnt going to matter.

You are running on a tread mill. No matter how fast your feet move the tread mill is going to match your speed. Now you are carrying a nato rocket pack on your shoulder. You ignite the rocket.... what happenes? Tbe rociket pushes you forward, you run to keep up tread mill is running to keep up with you yet the rocket still moves forward, you are attached to the rocket so you move forward anyway.

The only thing the wheels of an airplane do is reduce friction between the plane and the ground until there is not friction. The only way you could prevent and airplane for taking off would be to strap it in a stationary position. The the wheels nor treadmill would move and the engine(s) would be running at mach 10.

 

The length DOES matter, because the plane is moving forward just as if it were on a regular runway.

Hersch, there is lift created under the wings because even though the wheels are rolling on a treadmill, there is still forward motion of the plane relative to the ground. No different than if it were starting on a regular runway...

 

So it's not going to hop off the tread mill and take off on a shorter one?
Or the longer one will slow it down longer???

No and no

The plane will take off in the same distance regardless.

The treadmill/conveyer is just there to mess with your mind. Neither one will have any affect on how fast the plane is moving, nor how long it takes to get moving. It's a zero factor.