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HelicopterOff Topics › To take off, or not?
09-03-2003 07:52 PM  14 years agoPost 21
KC

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WA

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09-03-2003 08:09 PM  14 years agoPost 22
spurry

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Reading, UK

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The last thing that goes through the mozzie's mind as he hits the windscreen...

His Ass!

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09-03-2003 09:06 PM  14 years agoPost 23
Dragon2115

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New England

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Turboracer, CeeJay, and Augusto,

What you're saying would be true if there were a frictionless interaction between the plane and the moving conveyer belt. But that wasn't one of the conditions given in this brain teaser.

Think of it this way, if the conveyer belt were moving under the plane and the engine were shut off, the plane would start to move in the direction of the conveyer, right? Albeit slowly at first because the wheels would be spinning, but eventually catching up to the speed of the converyer due to the friction of the wheels against the belt, resistance of the tire to conforming as it rolls, bearing resistance, and maybe even a little brake shoe drag in there too. The only way the plane could stay in one spot is if it used thrust to maintain its' position. It would probably be some outrageous ratio to reach equilibrium like thrust that would normally produce 100 mph airspeed vs. 500 mph conveyer belt speed to keep the plane stationary, but belt speed wasn't limited on this.

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09-04-2003 03:16 AM  14 years agoPost 24
debogus

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Beauklahoma,peoples republic of mexifornia,USSA

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Hangglider answer

they have a stall speed of 18 so flying at 20 into a 20 headwind leaves you with a 0 ground speed .
20 tailwind + 20 airspeed = 40mph ++++++++
Concidering the landing gear is your feet not a good choice

Dave

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09-04-2003 06:13 PM  14 years agoPost 25
Augusto

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Dragon2115,

I don't agree with you. I stand for my answer but I'm not going to get into a never-ending story with this thread.

Augusto.

Avant Aurora Ultimate

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09-04-2003 06:31 PM  14 years agoPost 26
diZeaZed

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Bunnell, Fl.

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I agree that the plane would not actually fly, at best it would stay still. What would work is if you placed a large fan in front of the plane. If you brought the thrust of the plane up in relation to increasing the fan speed (wind speed) the plane could rise with no forward motion.
(hey, it sounds good to me!)
Jojo

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09-04-2003 06:34 PM  14 years agoPost 27
diZeaZed

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Bunnell, Fl.

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skuze me...just had a moment of clarity. Augusto is right, given that the drag created by the wheels is not to much to limit forward motion. I was thinking of a vtol.

oops

Jojo

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09-04-2003 08:06 PM  14 years agoPost 28
Danny R

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Sorry Augusto, but Dragon is right. A key element of the problem as listed is: "wheels rotation speed of the plane was equal to speed of cloth movement " Thus as long as the plane is on the ground (not enough lift to separate it), its locked to the conveyor which prevents any forward motion. Your contention that "The extra wheel speed will just add a little bit of resistance to forward motion that's all" is incorrect when given the wording of the puzzle. According the the puzzle, the wheel traction will always equal the thrust of the plane, because the conveyor will always keep time to the rotation.

Every inch the plane pushes forward, the ground moves that same distance backward. If the air surrounding the plane is independent of the conveyor (the conveyor doesn't generate its own wind via the movement), there will be no lift.

In such an environment the thrust of the prop or jet will in effect be simply transfered directly to the conveyor, causing it to move faster and faster.

If you think I'm wrong, then please describe exactly how the plane will move forward WITHOUT TURNING ITS WHEELS. Only if the interaction between the wheels and conveyor were entirely frictionless would that be possible (plane pushes forward with brakes on so wheels don't turn, and thus conveyor doesn't move).

Obviously of course a VTOL could handle this runway.

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09-04-2003 08:15 PM  14 years agoPost 29
TurboRacer

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CT

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Ok, you know what? I think this is going to take a real life experiment to settle.

Of course we can't do this with a fullscale plane, but we could do it with a model.

How can we go about doing this?

I'm thinking a treadmill, and a small, light electric plane that doesn't need a fast foward speed to go airborn?

Anyone have a treadmill and that type of plane?

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09-04-2003 09:33 PM  14 years agoPost 30
skier

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New Jersey, USA

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This would be in effect impossible to model in real life because the acceleration of the wheel speed and treadmill would have to be synchronized and the top speed of the ttreadmil would have to be near infinate.

-Dreaming permits each and every one of us to be quietly and safely insane every night of our lives.

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09-05-2003 12:15 AM  14 years agoPost 31
Dragon2115

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New England

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If you would like to simulate this simply put on a pair of roller blades and get on a treadmill. Start up the treadmill and hold on to the bar in front so you stay in one place. Now let go. What happened? Simple, after a short time you fell off the back of the treadmill. Why? Rolling resistance. Now hold onto a fan and adjust its' speed so that you stay still on the treadmill again. Do you have enough forward airspeed to take off yet? Not unless you can flap really really fast.

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09-05-2003 01:46 AM  14 years agoPost 32
spurry

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Reading, UK

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I can see this thread getting a couple of pages longer. And the more detailed it gets, the more I start to doubt my original thoughts, but my mind is going back and fro now.

Ok, so the plane will only take off with airspeed so it HAS to move forward faster than the belt is moving backwards.

Take a minute now, get a piece of paper and actually draw it all out. Imagine the plane sitting there on a table-high conveyor belt going god-knows how fast. So the plane will have to stay still relative to you (spectator) because whatever the wheels want to go forward, the belt will go backwards. It's there revving like hell but it can't move from that point (assuming this gadget detects the slightest de/acceleration). So it's STILL, no airflow over the wings so the wheels are always in contact.

All that seems fine to me. I think Danny R's post is saying the exact same thing. And I understand Dragon's post also to be the same sorta thing and I couldn't really see Augusto's point. So that's when I drew it all down and this time I thought about standing there next to this plane (lets say a model) watching it fight against itself, BUT, what about you actually pushing the plane forward?

Could you pull/push it forward? I know it's not the same as the plane's thrust, but this is what got me doubting my first thoughts. Try to pull it forward and the wheels would go faster and the belt would counteract but I think you could still pull it forward and re-position it there on the belt. To me that is along the same lines as Augusto's point:
The prop traction is derived from the interaction of the prop and the air so the prop pulls the airplane regardless of whatever is happening down there at the wheels.
BUT, if the wheels aren't leaving that belt, then how can it move forwards? This one's a corker!

James

PS: If I fly at 3D Masters next year can I use my metal blades?

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09-05-2003 01:50 AM  14 years agoPost 33
srslamalot

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This is just a guess from some things I’ve observed in life, but I would like to think that if the plane could generate enough thrust from it’s propeller, then it wouldn’t even require air to be moving over it’s wings to generate lift. It would just launch off the ground like a rocket. (But in my opinions, that would require a butt load of thrust, probably not possible from a prop plane) I like the idea of an experiment with a model airplane and treadmill, but the problem is that a model airplane’s weight probably isn’t close to scale. It would be like taping a bottle rocket to a paper airplane. (I’m pretty sure that would take off without any airspeed, I used to do it when I was a kid). I also think about those guys that can make their R/C plane hover in one spot. Those planes look like they have enough power to take off with out much if not any airspeed, but then again, there probably not to scale when it comes to power to weight ratio.
Therefore, in my amateur/expert opinion, the chicken came first.
Tom

So, is there an answer to this question, or not? I really want to know.

Actually, who cares, Planes suck, Helicopters Rule!!! (If the question involved a heli, then we know it would take off)

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09-05-2003 01:57 AM  14 years agoPost 34
spurry

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Reading, UK

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ah ha, but where did that bloody chicken come from?

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09-05-2003 04:52 AM  14 years agoPost 35
Super Phreek

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You can not generate enough airflow over the wings with only propellor thrust to provide the lift necessary to just fly off. The pro-wash is just to turbulent to provide enough lift. Even if you have engines on the wing, (assuming it is a nice smooth ariflow) the prop-wash is only passing over a small portion of the wing thereby reducing the overall effective wing area.

In respect to aircraft hovering in place, the prop is providing the lift. But if you lay it down horizontaly, the treadmill runway takes affect thereby canceling the prop thrust. No flight.

On the hovering airplane again, they usually have symetrical airfoils, so all the lift is derived by angle of attack, which still needs airspeed ( a little more) to provide the lift.

Derek

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09-05-2003 06:15 AM  14 years agoPost 36
Rick_H

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Boulder City, Nevada

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Common, put wheels on your heli an take off already. Who cares of the ground is moving.

Rick

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09-05-2003 06:23 PM  14 years agoPost 37
Danny R

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BUT, what about you actually pushing the plane forward?

It makes absolutely no difference where the horizontal thrust is coming from... engines on the wheels, a prop, someone pushing, or a jet engine. As long as the wheels are matched exactly to the conveyor, the thrust will always be transfered to the belt.

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09-05-2003 06:56 PM  14 years agoPost 38
srslamalot

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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. Think about it, there are planes that can take off without forward movement. (Harrier, or that other plane that has props on it’s wings, and the wings can aim vertical or horizontal) But they are designed completely different. The have more powerful jet engines and can aim the thrust down, to counter act the force of gravity, which is ultimately what is keeping the plane on the ground.
Now that I look back on the question, TurboRacer never specified the type of plane, (just jet or screw), so therefore my answer is Yes, a Harrier could take off if it was on a mat that removed it’s forward movement. But I don’t think a normal plane could.

Tom

And the chicken was just there, in the woods, making a sound. ( I can prove it, I have it on tape)

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09-05-2003 07:11 PM  14 years agoPost 39
heliVoY

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NJ

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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 !!!!


Wojtek

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09-05-2003 07:32 PM  14 years agoPost 40
TroyE

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Orlando, FL.

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the speed at which the wheels trun is irrelavent. it's "air speed" moving over the air foil that ccreates lift.
matbe you could read up on the theory of flight .

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HelicopterOff Topics › To take off, or not?
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