Author Topic: Will the plane fly? (Brain teaser) (Read 10848 times)

Pride · « **Reply #30 on:** December 30, 2005, 08:14:19 AM »

Without movement, no air goes over the wings to provide lift. Plane is stationary.

kona · « **Reply #31 on:** December 30, 2005, 08:19:52 AM »

Just as I said.....................

Pride · « **Reply #32 on:** December 30, 2005, 08:28:26 AM »

Please note.. I love to debate... so dont take anything personally...

Quote from: "Biggles"

Put simply, the conveyor ain't doing s*** cuz of the whizzles.

good quote from MasterYoda:

Quote
Look at it this way. Stand on a treadmill going full speed while wearing rollerblades, tie a rope around your waste, and have someone standing in front of the treadmill pull on the rope...will you move forward? yes

The problem with this quote is the fact that there isnt "grounded" adding force to the plane. The plane's only force is the jet thrust which is counteracted by the wheels going the same speed in the opposite direction because of the treadmill.

Sure, in this example, if you tie a rope to the nose of the plane, and pull on it, with everything else being constant.. the plane would indeed move forward.. but that is not part of this situation.

llDayo · « **Reply #33 on:** December 30, 2005, 09:39:01 AM »

Quote

Look at it this way. Stand on a treadmill going full speed while wearing rollerblades, tie a rope around your waste, and have someone standing in front of the treadmill pull on the rope...will you move forward? yes

Actually, Pride, thinking about it more now I have to agree that it WILL take off. Think about it this way. If the plane is providing thrust to move at 5mph the treadmill will counteract that by moving 5mph. The wheels however will be moving at 10mph. Why is that? Like has been mentioned by others here the wheels are basically frictionless in regards to the thrust of the plane. They will not slow it down. The engines on the plane will push through the air while the wheels do no pushing at all. They merely keep the planes fuselage from sliding on the ground. As the plane and the treadmill move faster the rate the wheels are traveling will be the combination of both the speed of the plane and the treadmill.

In your picture you drew (quite nice btw :bigsmile: ), where it says the thrust is pushing backwards it is doing so in regards to the air. The treadmill is not applying any force against the plane to slow it down, all it is doing is making the wheels spin faster (in this case they're moving at 400 mph). Does this help make more sense of the problem?

Pride · « **Reply #34 on:** December 30, 2005, 10:03:04 AM »

I fully understand your point... and I have thought of it from that angle.. however...

Think of it this way...

Take away the jet thrust for a moment... turn the engines off. If you turn on the treadmill... the plane will slide off of the treadmill at 200 MPH. Now... restart the plane... put it back on the treadmill... turn the thrusters up to 200 MPH.. and the plane should (in theory, when not taking into account friction) stay stationary on the treadmill.

If you want to factor in friction of the wheels... then remember that the treadmill will adjust to any speed necessary to counteract whatever force is being put on the plane.

The problem remains then... if the plane is stationary, no air is moving over its wings, and no lift is achieved.

llDayo · « **Reply #35 on:** December 30, 2005, 10:19:24 AM »

You're missing the part about friction on the wheels on the plane. It's basically non-existent. If the treadmill started going at 200mph the plane wouldn't immediately slide off the back. Its wheels would start spinning first and any friction produced by them would slowly accelerate the plane backwards until it fell off. The thrust from the engines would more than counteract this friction (if the wheels had that much friction on them then a plane would never be able to take off, even from a stationary runway).

However, the engines displace the air in front of the plane providing thrust. The push off is not on the wheels. The plane would have enough thrust to move forward and eventually have enough air passing the wings to provide lift. No matter how fast the treadmill is going (as long as it is matching the speed of the plane) the wheels would just spin. To stop the plane the wheels would have to produce enough friction to counteract the thrust, without brakes this would be impossible.

On a side note, how much are hotel rooms for the LAN party?

Fabio · « **Reply #36 on:** December 30, 2005, 11:10:01 AM »

llDayo · « **Reply #37 on:** December 30, 2005, 11:37:00 AM »

Thank you, G!

Pride · « **Reply #38 on:** December 30, 2005, 12:04:40 PM »

you do realize that if you had told me prior to registering... i would have given you admission for free right?

llDayo · « **Reply #39 on:** December 30, 2005, 12:08:04 PM »

Crap. Well, I'm not decided on getting a room yet anyhow as I don't know if the wife is coming with or not. If she decides not to then I won't get one. I kind of forgot about the waiving thingy. Thanks Mr. Funkalicious

Pride · « **Reply #40 on:** December 30, 2005, 12:14:53 PM »

i'd make a deal with ya that if you had a friend sign up... i'd give them free admission, and they can just pay you the 20

Biggles · « **Reply #41 on:** December 30, 2005, 07:22:22 PM »

Quote

If you want to factor in friction of the wheels... then remember that the treadmill will adjust to any speed necessary to counteract whatever force is being put on the plane.

Err, ok, if you look at the runway not being calibrated to the speed of the plane but instead to any force being applied to it...then yes. Your treadmill would be spinning insanely fast, but it would keep it from going anywhere.

If it's only spinning as fast as the plane is trying to move, it won't do anything, because the wheels don't allow it to hold back the plane.

.:F3ar0n:. · « **Reply #42 on:** December 30, 2005, 10:18:36 PM »

Quote from: "Pride"

i'd make a deal with ya that if you had a friend sign up... i'd give them free admission, and they can just pay you the 20

I'll take a deal of a friend coming sign up (have 3 coming)

Pride · « **Reply #43 on:** December 30, 2005, 11:41:52 PM »

F3ar0n..... you find a fourth, and he can give you his 20 bucks instead of to me!

sully! · « **Reply #44 on:** December 31, 2005, 02:50:53 PM »

THe plane will take off. Period. End of discussion. The engines push the plane forward. When the treadmill tries to counteract the force of the engines, it has no way of "grabbing" the plane and pulling an equal and opposite force upon it, the wheels will simply spin. Since the treadmill can only cause the wheels to spin and not "pull" the plane backwards, the engines will continue to push the plane forward, creating lift over the wings (not the flaps, BTW, they create more drag on the plane when it is landing, you generally have your flaps in a neutral position when taking off and extended when landing) and causing the plane to lift.

There are 4 forces at work on an airplane at all times. An imbalance in these forces causes movement of the plane in the direction that is stronger than it's opposite force.

1. Thrust of an engine (pushing forward)
2. Drag of friction (usually of air, and in this case the treadmill)
3. Lift of the wings (lifting upward)
4. Pull of gravity (pulling towards the earth)

Looking at these four forces, the engines thrust forward, the treadmill tries to increase it's opposite pull, but it can't because the wheels will just spin and it can't transfer its energy to the plan itself. Thrust is the greater force and will propel the plane forward. As the plan moves forward, air begins to move over the wings and through the magic of the curved surface of the wings and Bernoulli's principle, lift greater than the pull of gravity is created, and the plane takes off.

The only way this plane would not take off is if the plane were on skis or the wheels were locked in place, or some other method of the treadmill to transfer its forces into the body of the plane, none of which is presented in the original question.

I won state level awards in school for my presentation/reports on airplane flight and balsa wood gliders I made and flew. Heck, I even got 9th at nationals one year. Just thought I'd throw some credentials in there.