Physics question.. can you figure it out?

[Turbo Ryan]

I think your right

Ok, so if i get on the treadmill and run as fast as i can with a kite on a string it will fly, right???

This argument is flawed. This scenario requires you gain forward motion using the ground as resistance. The original argument use resistance with air (i.e.thrust) to gain forward motion.

As I sit and think about this, your scenario is the best argument for flight in the original post. The last time I flew a kite I didn't have to keep running all over park to keep it flying. In fact, my "ground speed" was stationary, yet the kite continued to fly. But how could this be? I'm not moving, but the kite is still flying. This doesn't make since according to some of you, I have to have ground speed in order to fly right? Well, I guess the answer is no.

Now, lets relate the kite to the plane. The kite gets it's air speed to fly from wind, where as the plane creates its own wind by pushing itself through the air, not across the ground. In both cases flight is not dependent on ground speed.


Ryan

P.S. If this is all just a big joke, then lets just end it now and have a big collective laugh. Somebody set up a poll and lets see what the general consensus is. I can only hope there is only a small number of you that are still not believers.

 

[jasonlachapelle]

Like Dan, I'm also a military pilot. (great explanation btw)

the plane will be able to take off.

this explanation is wrong:

Ok, so if i get on the treadmill and run as fast as i can with a kite on a string it will fly, right???

it's the equivalent of:
all forks have teeth,
I have teeth,
I must, therefore, be a fork.

Your feet are not freewheeling. You are putting power to the ground with them. People have a hard time visualising the plane moving one way while the conveyor moves the other.

 

[Pablo]

I think your right

Ok, so if i get on the treadmill and run as fast as i can with a kite on a string it will fly, right???

erm no

You get an F

 

[Big Stu]

erm no

You get an F

 

[rtviper]

Interesting thread. One question? If the plane is just sitting on this large treadmill and the treadmill starts moving at 100 mph will the plane start to move backwards at 100 mph? If so then with some thrust that would normally propell the plane at 20 mph would the plane move forward at 20 mph even though its was going backwards at 100 mph?

 

[chevyII]

No it wouldnt take off you still would be putting your cloths and shoes on from the strip search at the gate

 

[darkred87T]

Interesting thread. One question? If the plane is just sitting on this large treadmill and the treadmill starts moving at 100 mph will the plane start to move backwards at 100 mph? If so then with some thrust that would normally propell the plane at 20 mph would the plane move forward at 20 mph even though its was going backwards at 100 mph?

No

 

[turbobuickman]

Interesting thread. One question? If the plane is just sitting on this large treadmill and the treadmill starts moving at 100 mph will the plane start to move backwards at 100 mph? If so then with some thrust that would normally propell the plane at 20 mph would the plane move forward at 20 mph even though its was going backwards at 100 mph?

Not at first because it would have to overcome the momentum going backwards but yes the plane would start moving forward because it is "pushing off" the air, NOT the moving conveyor belt; therefore, the speed of the conveyor belt has nothing to do with the speed of the plane under power (other than a SLIGHT BIT of added drag from the wheels).

 

[rtviper]

Once the thrust from the engines exceded the necessary thrust needed to prevent the plane from being taken in the direction of the conveyer belt the plane would then start to move forward. It would just require more thrust then normal to exceed the drag from the conveyer belt and reach its lift off speed

 

[darkred87T]

Not at first because it would have to overcome the momentum going backwards but yes the plane would start moving forward because it is "pushing off" the air, NOT the moving conveyor belt; therefore, the speed of the conveyor belt has nothing to do with the speed of the plane under power (other than a SLIGHT BIT of added drag from the wheels).

What RTviper is asking is if the plane is movining 100mph backwards on a treadmill, will 20MPH worth of forward thrust move the plane 20MPH forward? It would move it 20MPH forward on the treadmill, but it would still be going 80MPH backwards. However, this does not pertain to the original question. We are making it out to be too complicated. The intended answer is simple, the plane will move forward because of thrust pushing it, not the wheels.

 

[turbot2496]

Geez are we still at this ...

 

[jpratt]

What RTviper is asking is if the plane is movining 100mph backwards on a treadmill, will 20MPH worth of forward thrust move the plane 20MPH forward? It would move it 20MPH forward on the treadmill, but it would still be going 80MPH backwards. However, this does not pertain to the original question. We are making it out to be too complicated. The intended answer is simple, the plane will move forward because of thrust pushing it, not the wheels.

20MPH of thrust would slow the plane down from -100 slowly and would eventualy begin to move forward at 20 if there was ZERO resistance created by the wheel bearings.

 

[fullahotair]

If you put the jet on a frictionless surface or even ice for that matter , lock the wheels, and turn on the engine, the plane will take off, even the wheels aren't spinning at all.

Correct me if i am wrong, but I think biggest hang up is thinking that the mph of the wheels is equal to the mph of the plane. If you were standing off of the "conveyor belt", you would still see the plane moving like it was taking off even if the belt was moving the same but negative speed of the wheels.

My 2 cents:

N8

 

[83hurstguy]

20MPH of thrust would slow the plane down from -100 slowly and would eventualy begin to move forward at 20 if there was ZERO resistance created by the wheel bearings.

Correct. Nothing is instant, will begin to slowly accelerate forward as thrust is built. Thrust is always measured in pounds, b/c it is a force producing an acceleration (good old Newton's 2nd Law, F=ma).

Interesting thread. One question? If the plane is just sitting on this large treadmill and the treadmill starts moving at 100 mph will the plane start to move backwards at 100 mph? If so then with some thrust that would normally propell the plane at 20 mph would the plane move forward at 20 mph even though its was going backwards at 100 mph?

The plane will move backwards on the conveyor provided that the conveyor does not accelerate the plane at a rate that exceeds the capabilities of the static friction in the wheel bearings. If the conveyor just suddenly took off, it is very possible for the planes wheels to start spinning and the plane to not move along with the conveyor. (Newton's 1st law: Law of inertia, objects at rest tend to stay at rest, those in motion tend to stay in motion) You can rip a tablecloth out from under a table loaded with china without any of it moving when you pull fast enough, I've seen it done :biggrin:

 

[turbobuickman]

What RTviper is asking is if the plane is movining 100mph backwards on a treadmill, will 20MPH worth of forward thrust move the plane 20MPH forward? It would move it 20MPH forward on the treadmill, but it would still be going 80MPH backwards. However, this does not pertain to the original question. We are making it out to be too complicated. The intended answer is simple, the plane will move forward because of thrust pushing it, not the wheels.

Sorry, but wrong. The given thrust will slow the planes backward momentum down and eventually start moving it forward because the thrust needed to move the sheer mass of a plane is SO much greater than the frictional drag on the wheels. Again, the wheels spin freely and thrust is applied to the stationary air around the plane (not affected by the conveyor belt).

 

[corsair231]

the plane will be able to take off.


it's the equivalent of:
all forks have teeth,
I have teeth,
I must, therefore, be a fork.

.

As far as this thread is concerned, I say,

Put a fork in it. It's done.

 

[darkred87T]

Sorry, but wrong. The given thrust will slow the planes backward momentum down and eventually start moving it forward because the thrust needed to move the sheer mass of a plane is SO much greater than the frictional drag on the wheels. Again, the wheels spin freely and thrust is applied to the stationary air around the plane (not affected by the conveyor belt).

But in HIS question, the plane is already moving 100MPH backwards afixed to the treadmill. The treadmill is not just spinning the wheels under the plane in rtviper's question, it's moving the entire plane backwards at 100MPH.

 

[V6 Beast]

The plane would take off... the moving runway would only make the plane's tires spin twice as fast! :biggrin:

 

[KEVINS]

I can't believe how fast this question is spreading thru the BB's..

Another way to look at it is to tie a chain to the nose of the plane then let the conveyer belt turn. The Chain does the exact same thing the Thrust does by keeping the plane in one place in relative to the ground. Now will the plane try to fly?...Nope.

ks

 

[1ARUNM]

I'm enjoying this side of the debate

One more time. From original post:

"This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction)"

"This is simple, don't over complicate it."

Every scenario you "fly" guys have presented has involved the plane moving faster than the conveyor. You can forget all the thrust, physics rules, Newtons third law etc. to explain it except for wing aerodynamics. I'm not saying you can suspend the rules of physics but they are limited by the condition that the plane is rolling on the conveyor at the same speed opposite the conveyor belt. You are supposing things that aren't given in the original condition. It doesn't say whether the plane is an F-18 or the Wright flyer.

If you were standing next to the conveyor as this happened, the plane would appear to be standing still with the wheels rolling on the conveyor as long as the conditions were met. For it to move forward in relation to you and the air, it has to be moving faster than conveyor speed. The instant it does that it violates the original condition.
Would real planes take off on a real conveyor in the real world? I'm sure that most could, but not until they are moving faster than the conveyor belt. That's a Violation of original condition

I know it seems impossible but even though a jet might fly 1,400 mph and most conveyors only move inches per second. It's clear in the original post that the opposite speeds neutralize each other and that is the limiting factor. The plane is not allowed to go faster than the conveyor, and therefore is not moving through the air and will not fly.

I'm sorry that some of you did not detect the sarcasm in my Kite post If you gave me a "F" that means you agree with me