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HelicopterOff Topics › To take off, or not?
09-05-2003 07:41 PM  14 years agoPost 41
spurry

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Reading, UK

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Ok, I know this is applying an outside force on the plane but theoretically, it should stay still. Tie a rope to the front (no, not the prop! ), then stand in front of the belt and pull, the belt Vs wheel motion will always keep it still right? And it will remain on the belt, but is this to say that it would be impossible to pull that small model plane forwards? This is assuming that the the belt speed is not limited and the wheels will survive any rpm.

Tom, I want to see that tape!

James

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09-05-2003 09:51 PM  14 years agoPost 42
Danny R

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Atlanta, GA

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I believe that the plane won’t take off, not because the thrust is being transferred to the belt, but because normal planes aren’t designed to take off without forward movement. And the belt is removing that.

Just to make myself clear, the thrust isn't really applied to the belt. It just appears that way to observers, because only the wheels and the belt are turning at a faster and faster rate directly proportional to the thrust given.

The motive force of the belt itself is a mystery and outside the scope of the problem.

this thread is a perfect example of how many RC pilots have NO CLUE as to even the most basic of aerodynamics !! i am embarased reading this crap !!!!

Do this mean that you think the plane will fly?

the speed at which the wheels trun is irrelavent. it's "air speed" moving over the air foil that ccreates lift.

Yes air speed creates lift. But with the conveyor moving counter to the plane, air speed will always be zero, not counting prop wash or turbine intake.

but is this to say that it would be impossible to pull that small model plane forwards?

Yup, impossible. Even though the force is external to the plane, the belt would match the wheel rotation, thus offering up an equal counter force keeping the plane still.

Remember that the trick of this problem is that the conveyor perfectly matches the wheel rotation. This physically impossible physics problem is what causes the strange results observed, because the only way to get any forward motion is to violate the main rule of the problem, which everyone who thinks the plane will fly is doing.

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09-05-2003 11:54 PM  14 years agoPost 43
Jagboy69

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Miami

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...And then one time, AT BAND CAMP.....

Jason /// Sceadu50/9chp WWW.Jagboy69.com

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09-06-2003 12:32 AM  14 years agoPost 44
spurry

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Reading, UK

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I stuck a trombone up my.....

Thanks Danny, I was thinking along the same lines as you right up until I thought about pulling the plane forward, but it just can't be done, sounds weird, but it must be true. Is this the end then? Will we all live happily ever after knowing the plane won't take off?

James


PS: Sorry, I meant flute.

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09-06-2003 12:50 AM  14 years agoPost 45
srslamalot

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Atlanta, GA

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Yeah, but do you think the plane will take off or not?

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09-06-2003 01:05 AM  14 years agoPost 46
spurry

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Reading, UK

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Not! This should be a poll now.

James

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09-06-2003 02:26 AM  14 years agoPost 47
KC

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WA

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----

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09-06-2003 03:56 AM  14 years agoPost 48
debogus

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Beauklahoma,peoples republic of mexifornia,USSA

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????????????

for food or as a pet

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09-06-2003 05:31 AM  14 years agoPost 49
KC

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WA

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09-06-2003 03:06 PM  14 years agoPost 50
AirWolfRC

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42½ N, 83½ W

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Cute problem, TurboRacer, but not that mysterious.

You have two points that come to bear here.

First, if the airflow over the entire wing is not enough (not just from the prop blast), the plane will NOT get airborne.

Second, the conveyor thing;
the covering has a control system which arranges speed of cloth movement so that wheels rotation speed of the plane was equal to speed of cloth movement
If your conveyor belt moves backward to try and keep the plane stationary and rotate the plane wheels forward without letting the wheel axel move forward, you will have a positive feed back loop in the control system that controls the speed of the conveyor belt and therefore a run-away condition.

Here's why. As the plane's thrust moves the plane forward, the wheels will start to rotate forward. The belt control system will make the belt move backward. That will make the wheels rotate faster. That will make the belt control system make the belt move backward faster. That will make the wheels rotate faster. .... and so on. Something's going to blow.

That's called a run-away condition in the control system, also known as positive feed-back. The instant the wheels start to move, you will have that condition. It's just like stepping on the gas pedal if the car is going too fast (instead of the brake).

Now, if you have a NEGATIVE feed-back condition, as the wheels start to move forward, the conveyor belt starts to move forward to keep the wheel rotation speed the same (zero). The plane is still moving forward and, if the belt is long enough, the plane will take off.

If your statement about the belt control system had said "to keep the wheel AXEL from moving forward", you would have no feed back at all. In that case, as the axel moves forward, the belt would move faster but since there is no solid connection between the belt and the axel (the wheel bearings), the belt speed would go to infinity (theoretically) but not be able to get the wheel axel back to its original position (again, because of the wheel bearings allowing the wheel to rotate freely).

It's all in the details.

Wolfgang

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01-30-2008 01:51 PM  9 years agoPost 51
cessna151

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Missouri... Originally Indiana

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The original thread!!!!!!!!!!!!!!!

IT FLIES!!!!!!!!!!!!!!!!!!!!!!

--Eagles may soar high, but weasels don't get sucked into jet engines!--

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01-31-2008 10:04 PM  9 years agoPost 52
srslamalot

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Atlanta, GA

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I was very excited to see them test this (and I know the RC plane would take off no matter what) But I think there was a problem with that experiment. The belt is supposed to move at the same speed at the plane, thus eliminating any forward movement the plane might produce while it’s still in contact with the ground. They only moved the belt up to the take off speed of the plane, but it didn’t take long for the plane to move faster then that speed. If you watch the clip, the plane starts to move forward on the ground before it takes off.

If you ask me, they need to do it again, and make sure the plane isn’t moving forward on the cloth.

Just my 2 cents.

Tom

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01-31-2008 10:07 PM  9 years agoPost 53
legoman67

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Nanoose Bay B.C, Canada

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the wheels dont move the plane, so no matter how fast that treadmill goes the plane will still move...

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HelicopterOff Topics › To take off, or not?
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