Aircraft taking off from a treadmill: Debate

[shreck]

what is the relative speed of a treadmill tossed out a window while the tread spins 100mph in reverse 


This thread has got to be the dumbest ever

[mechanic]

What about a hovercraft on a giant cattle grid??
 

[flight17]

While we are at it lets put a fan on our sail boat to make it go faster.

http://answers.yahoo.com/question/index?qid=20080506234729AApZqDe

http://www.youtube.com/watch?v=0CrXvOKPymk

lmfao

i read that and laughed for about 2 mins and dont know why lol. then watched the video. I actually didnt think the "boat" would move. if i wanted too i could think it out but dont really want too. instead will think out the helicopter one.

[Curlew]

While we are at it lets put a fan on our sail boat to make it go faster.

http://answers.yahoo.com/question/index?qid=20080506234729AApZqDe

http://www.youtube.com/watch?v=0CrXvOKPymk

I will admit that I posted this thread as an almost trolling joke, but this i actually can speak on, I have been sailing for many years, and have been teaching sailing for 6 years now, The yahoo answers are an absolute joke, mostly cause they never once recognize a sail as a airfoil WHICH IT IS



the diagram above shows the forces at work in a sailboats movement, air passing over the sail creates lift like a wing heading in the direction of the red arrow, this force can be divided into two vectors as shown by the blue arrows labeled A and B, Force A is negated by the keel underneath the ship as shown with a green arrow. If the force of the green arrow negates the force of arrow A then only arrow B's force remains thus producing forward motion through the lift of an airfoil. If the keel did not exist all sailboats would travel in the direction of red arrow. With that said producing a greater force in direction of the wind would produce greater lift that could be easily negated by the keel in the water. But to make this work you would have to  place the fan at an angle to the ship as a wind force coming directly on the bow of the ship would produce a red arrow that runs perpendicular to the ship and therefor be completely negated by the green arrow.



So if we add a fan into the equation, as shown here, we can see that the force of the air from the fan is shown in purple pushing backwards should have 2 effects, one shown in light purple is the vectors of the increase in force of the sail due to increased airflow, and once again the force perpendicular to the ship is negated, The second is the force produced by the fan pulling air like a propeller would shown in yellow, and once more we devide the force into vectors shown in light yellow, and of course the perpendicular force is eliminated by the keel. Notice how with both the light purple and light yellow arrows pointing in the direction of boats travel are not negated. and therefor indicate an increase in speed.

None of the yahoo answers mentioned this and the video supposedly "proving" the concept doesn't even use a sail, just a flat area for the wind to blow and that is not how a sail works, but it does prove that a parachute in a zero g environment could be pushed by a fan held by the user in the direction of the fan.


As for the hovercraft, now thats funny, and idk, ill have to ponder that one

[sluggish]

Is it possible for a B17 to back-up under its own power?  The answer is yes.  But how?

[kotrenin]

Back to the airplane/conveyor belt issue.
Here's a wrench to toss in.  

http://www.fanwing.com/pix.htm

creates it's own lift 

[mechanic]

Is it possible for a B17 to back-up under its own power?  The answer is yes.  But how?

using independant engines and wheel brakes to walk backwards step by step?

[redman555]

Mythbusters tested it... it worked..with a real plane...


right here. 

http://www.youtube.com/watch?v=YORCk1BN7QY&feature=related

-BigBOBCH

[jimson]

Easy way to prove it, put a toy car on a treadmill. Simulate engine thrust by pushing on the back of the car. It moves forward.

Plane may not take off unless the treadmill is as long as a runway but the motion under the free spinning wheels has nothing to do with it. Unless the wheels come off due to increased spin.

[oakranger]

No, the plane needs the lift by movement. 

[Dragon]

What about a hovercraft on a giant cattle grid??
 
(Image removed from quote.)

(Image removed from quote.)

I've seen demonstrations where one goes over telephone poles spaced about 3-4 feet apart and they didn't roll, so I'll assume that the flat tops of the cattle grid would provide enough surface area to keep it afloat.



Edit: And no, the plane will not take off without enough forward movement to provide the necessary lift.

[jimson]

The treadmill only causes the free spinning wheels to spin faster and does not act against forward motion unless the propulsion comes from the gearing of the wheels, therefore the plane gets forward motion to create the lift.

If you push on the toy car like a jet engine would push on the plane will it not move forward?

[Hap]

Easy way to prove it, put a toy car on a treadmill.

right

[druski85]

I will admit that I posted this thread as an almost trolling joke, but this i actually can speak on, I have been sailing for many years, and have been teaching sailing for 6 years now, The yahoo answers are an absolute joke, mostly cause they never once recognize a sail as a airfoil WHICH IT IS

Beat me to it -- absolutely speeds up the boat.  In that youtube flick the paper is basically a really inefficient spinnaker, but with a real spinnaker you are still treating it as an airfoil.  Whereas the main fore/aft sail is creating leeward and forward motion, the spinnaker is angled in such a way to create lift with the force vectors pointed forward and up.  Hence, by creating this vertical airfoil up front, you can move faster than the wind when it is at your back. 

Hovercraft - I don't believe it would work, particularly going over that deep of a pit.  If the pit were more shallow, (and therefore had less air to pressurize in order to maintain the pocket) perhaps that would make a difference.  I'd imagine it would be a mighty messy splatter either way.      I'm not entirely sure on this one though.

Helicopter - No idea, but the image is hilarious.

Plane - Biiiiiig old face palm. 

[Sonicblu]

The Myth can't be tested in real life guys. It makes a hidden claim that is violated the moment the aircraft moves forward.

You cant maintain the same wheel speed  and move forward at the same time. As soon as the plane moves forward you can no longer match the exact speed of the treadmill.

It violates the law of non- contradiction.

However the plane will take off as tested by the myth busters. But you will never be able to match the wheel speed as soon as it mover forward.

Ask youself match the wheel speed "compared to what"?