Topic: Can this airplane lift off?

[HavocTurbo]

Get on  a treadmill....

Wearing rollerskates.

Turn it on full speed.

Hold on to the handles.

You don't move right? Sure you are holding on.

Now move yourself forward and backward on the the treadmill using the handles to pull yourself forward.

Guess what ..... You move!!!

That's the effect the propeller or jet engine will have on the plane. The plane doesn't move because it is connected to the ground. It moves because it is "connected" to the air.

Gordon, you had me confused with your earlier posts. We got it straigntened out. I think sometimes I have to re-read everything just to make sure I don't see what I "want" to see. 

[my78k]

OK but what if the treadmill adjusts the speeds instantaneously to your new speed? Say for example the treadmill is at 4mph and you pull yourself forward at 2 mph....the treadmill automatically (and at the speed of light) adjusts to 6 mph. Do you move forward then? 

Dennis

[HavocTurbo]

OK but what if the treadmill adjusts the speeds instantaneously to your new speed? Say for example the treadmill is at 4mph and you pull yourself forward at 2 mph....the treadmill automatically (and at the speed of light) adjusts to 6 mph. Do you move forward then? 

Dennis

Yes because you are pulling on the handles.... not the belt.


OMG Dennis if you are jacking my chain I'm going to find you and.......

and....

Buy you a beer.

[MCRider]

OK but what if the treadmill adjusts the speeds instantaneously to your new speed? Say for example the treadmill is at 4mph and you pull yourself forward at 2 mph....the treadmill automatically (and at the speed of light) adjusts to 6 mph. Do you move forward then? 

Dennis

Yes the forward motion of the plane is 100% a function of the propellor. Whether the wheels are down or retracted, this is true.

The wheels are not "attached" in any way that will affect the rolling forward of the plane. They just roll.

[Inigo Montoya]

I think at this time, it is 99% jerking chains and 1% not getting it!

[my78k]

Count me in the 99%....although I usually hate being part of the majority!

Dennis

Edit- that above post was just to draw attention to the flaw in the original question. It mentions having the conveyor match the speed of the wheels...the 2 will never align!! As the conveyor speeds up to match the wheels....the wheels speed up too!

[MCRider]

Count me in the 99%....although I usually hate being part of the majority!

Dennis

Oh...you kid.

[mattcb350f]

What's up with this tangent about propellers moving air?  Of course propellers move air.  Who said they don't?  

Propellers move the plane, the movement of air is a byproduct of the downwash effect of the propellers creating lift.

Propellers and Helicopter blades are simply airfoils (the same shape as wings) and dont move air as a method of creating thrust, but rather create a lift vector. Helicopter blades create a lift vector up, and prop blades create a lift vector foreward.

...this thread is rediculously awesome. 

 Matt.

[Inigo Montoya]

OK now it is time to join the chain yankers!  The plane would never take off, the belt would pull it backwards! It just would!

[bunghole]

Planes can't fly.  They're too heavy.

[Inigo Montoya]

I thought planes flew thru water?

[Soos]

Isn't it that the plane simply pushes the earth under it away from the motor?
They don't really fly
It is simply repulsion created by the sphyncto hyperbarium effect of the internal combustion run rampant?
IE no wheels attached to the motor to harness the power into simple forward and reverse momentum?

Hence the reason cars, motorcycles, and boats do not fly.
They are harnessing this power through the wheels.

And we all know that it is near impossible to fly over water, and thats why it is soo hard to make a boat fly.
The only reason planes make it over the oceans is the height they attain, and they glide 'till they go over land again to gain altitude.


 



l8r

[Inigo Montoya]

AH So it is like the spaceship developed by Professor Farnsworth on futurama! The ship does not move, the engines move the universe around the ship!

[HavocTurbo]

AH So it is like the spaceship developed by Professor Farnsworth on futurama! The ship does not move, the engines move the universe around the ship!

bah you beat me to it you bastard. 

[Soos]

Exactly.
The motor manufacturers don't want you to know that you can hover by removing the attachments to your weedwacker......

[sangyo soichiro]

I think at this time, it is 99% jerking chains and 1% not getting it!

Sadly, it's the other way around...

This post is addressed to no one, and everyone in particular.

There are two problems here.  You've all answered the easy one and have now slipped into complacency.

I have hinted, and hinted, and hinted again, that there are two problems.
(Hey!  Remember me?!  I was the one that started this thread!)





Easy version:
In one interpretation, the conveyor ends up moving at twice the plane speed relative to the ground.  Thus the wheels turn at twice their normal speed.  This is not a big obstacle to overcome, and the plane will fly.  This is basically what Mythbusters did. 

That was the simple version.  Those that realized this, congrats.



However...
Almost everyone, prematurely satisfied with their superior intellect, has overlooked the other way one can interpret this problem.  For this, you should be ashamed.  Especially those that have become arrogant.


The original question was purposely vague.  It's possible to interpret it this way. 
Here's the more difficult version:

Bunghole caught this part:

Hmmmm......

Upon re-reading the original wording of the question...

Wouldn't the conveyor and therefore the wheel speed accelerate to infinity.  Each time the plane moved forward relative to the ground (not the conveyor), the conveyor would sense an increase in speed and then match that speed. 

In this version, the conveyor speed goes to infinity (if you neglect relativity).

Combine that with the fact that wheels have a non-zero moment of inertia (a resistance to a change in motion), and this problem is not so easy anymore. 






So while you are all congratulating yourselves, and laughing at those with different answers, I'm sorry to say that you all fail for not realizing the problem to its fullest.  It's particularly disturbing to me because I gave the more difficult problem here and still, none of you grasped it.

Sorry to use red, but all my previous attempts to get your attention have failed.  I thought I'd try this to see if it would work.


Now... if anyone is still addressing the simple version and wondering why others are so dumb, I can only assume you cannot be bothered to read what I have written.

[Inigo Montoya]

What? I missed that.
Actually the wheels would not speed to infinity, just double what the plane is moving. Say takeoff speed 80 mph, if the plane is going 40, the wheels would be spinning like it is going 80. It just keeps doubling till the plane gets airborne.

Isnt this fun!

I still think the universe moves around my engine though!

[bunghole]

I think it WOULD go to infinity since it is a positive feedback loop between the conveyor and the wheels.

But I'm no physician

[mattcb350f]

...from pg2

Regardless of the speed or direction of the conveyor belt, as long as the aircraft is allowed to accelerate through the air it will take off.

However, I have a hard time understanding which way the conveyor is moving. If the conveyor matches the speed of the wheels to keep them stationary...it will take off no problem.

If the conveyor moves in the opposite direction to spin the wheels at twice the speed then they would likely fail prior to rotation (depending on the Vr speed and the speed rating of the tires) ...but it would still take off, just with blown tires.
 Matt.

The second paragraph makes reference to what you are saying. However, rather than spinning to infinity they would only spin to twice the speed that is required for takeoff.....like vinmans brew is saying.

 Matt.

[Markcb750]

soichiro

This statement:  

When the runway senses the wheels moving, the runway will match the speed of the airplane's wheels, but in the opposite direction.

this precludes your proposed second scenario.

Neglecting the above part of the thought experiment:

You might be able to accelerate the planes wheels t by quickly accelerating the belt to a high linear speed,  high enough to cause the friction in the wheel bearings to exceed takeoff thrust from the prop, (a functional equivalent to applying wheel brakes).  But you preclude this from the experiment with the above referenced codicil.


Of course you could make the belt move fast enough to seize the wheel bearings, again this is the functional equivalent of applying brakes, not something that would occur in the scenario you outlined.  



See my point?

[mattcb350f]

You might be able to accelerate the planes wheels t by quickly accelerating the belt to a high linear speed,  high enough to cause the friction in the wheel bearings to exceed takeoff thrust from the prop.  See my point?

I do. However the drag friction from the wheel bearings would have to exceed the thrust PRIOR to the velocity needed for liftoff, and no further. Once lift off is achived the drag is lost.

 Matt.

[TwoTired]

There was only one question in the original post.   And, one choice of two answers in the poll.

That was answered with a simple, yes.

The other "data" given was a distraction irrelevant to the ending question.  What's the point of discussing something irrelevant to the question to be answered?

We could all discuss that there was a stationary tornado in the airplane's area and if the spiral rotation of the air mass was clockwise or counter-clockwise, then make assumptions about which side of the eye the plane was on, and what sort of debris was spinning in the air mass.
If there was a 1500 lb cow rotating within it, the airplane would simply turn into debris on contact.  Then we could discuss where the debris would land and which bits would then "fly" about in the vortex, quite separate from the wheels or the conveyor belt.
And then, what if Godzilla was stomping about the vicinity?

Cheers,

P.S.
Johnny has a wart on his chin, and another on his bum.

Can Johnny still eat wheat cakes?

[mlinder]

Johnny has a wart on his chin, and another on his bum.

Can Johnny still eat wheat cakes?

Simple answer: Yes
Difficult answer: No, because he's dead.

[mattcb350f]

FORGET IT.........Forget everything I've said.

I've just seen the plane on the conveyor and have changed my mind. There is no way it will take off.

























 Matt. 

[HavocTurbo]

Sure that'll take off. Till it rips its wings off and falls back down.