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HelicopterOff Topics › To take off, or not?
09-02-2003 10:00 PM  14 years agoPost 1
TurboRacer

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The Task
"Take off or not Take off ?"

The plane (jet or screw) stands on a runway. The runway has a mobile covering (such as the tape conveyor). This mobile covering can move against a direction of plane running. Also, 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 . A question: whether the plane on this cloth can run up and take off?

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09-02-2003 10:17 PM  14 years agoPost 2
Hawk4flyer

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Deland,Florida

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Duh???!!!!! Yes!!!!

But only if the brakes are released. lol

Speed derived from trust is not dependent on the wheels.

Of course everything is relavant, if the cloth were traveling at 200mph then the wheels would explode and in that case no it won't take off.

But if you were to use Vx for takeoff, (the speed of the cloth + the speed of the aircraft) would be within the limits of the tires and you would take off normally.

For example, Vx for a 152 is 55mph twice this is 110mph. the tires on a 152 are rated for 150mph to 200mph depending on the manufacturer.

Likewise Vx for a mulit engine plane like the Seneca, is 80mph(?) that would be 160mph. the tires on a Seneca should be rated at 200mph.

Aircraft do something like what your describing already. A downwind takeoff or landing would be simular to your cloth idea.

A 30mph tailwind and a 65mph landing speed would equal 95mph ground speed.

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09-02-2003 10:47 PM  14 years agoPost 3
spurry

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I love these things, kinda like the hovering in space or jumping in a bus ideas.

If I understood it correctly, it would be a plane trying to take-off with full throttle on a runway which is like a conveyor belt but running in the opposite direction at the same speed as the plane would want to move forward at?

Anyways, for the plane to take off, it needs the lift, ie the airflow over the wings, which you wouldn't get if the plane was stood still reving its bollocks off. Even the propwash wouldn't pop the plane up as it would corkscrew applying as much upwards force as downwards to the wing in effect cancelling it all out. If somehow the plane did pop up then it would just hit the belt again, sort of like running on a treadmill fast then jumping off. What determines whether it flies is the airspeed. They fly with the wings not the wheels. Of course the wheels being able to manage twice the normal take-off speed is relevant, but I don't think it's the main factor.

Interesting to hear what others would have to say or at least hear some reasons why some people might think it would take off. Btw, it would have a 35mph ground speed with a 30mph tailwind. But a 95mph airspeed with a 35mph headwind flying with 65mph groundspeed.

Your runway too short? Bungee ought to do the trick.
James

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09-02-2003 11:23 PM  14 years agoPost 4
A. Bundy

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Aurora,IL. 30W/SW of Chicago

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Turbo...You need to find a better club.

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09-03-2003 01:28 AM  14 years agoPost 5
debogus

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Beauklahoma,peoples republic of mexifornia,USSA

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UH?

Conveyor belt going with the plane with the Brakes locked and all the passengers jumping at the same time.

POP Quiz Whats worse on a hangglider upon landing a 20mph tailwind or 20mph headwind
DAVE

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09-03-2003 05:15 AM  14 years agoPost 6
KC

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WA

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---

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09-03-2003 02:00 PM  14 years agoPost 7
ausheli

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Kalgoorlie, the gold capital of Australia, Western

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i have to agree with spurry, with no forward movement there is no lift

Drill it, Blast it, Bog it

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09-03-2003 02:07 PM  14 years agoPost 8
TurboRacer

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ausheli - we're talking thrust though, not powered wheels. The air is standing still, it's the ground that's rolling..

Thrust would move the plane down the runway, regardless of what the runway is doing.. The wheels will just be spinning a lot faster than they normally would.

This question always gets a lot of people coming up with different theories.

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09-03-2003 03:33 PM  14 years agoPost 9
Dragon2115

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New England

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No, it won't take off. Because of rolling resistance every time the plane tries to accellerate the mechanism controlling the speed of the cloth will accellerate in the opposite direction as well, cancelling out any forward movement. The cloth and tires will just keep going faster and faster until the engine runs out of thrust or the tires fail.

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09-03-2003 04:36 PM  14 years agoPost 10
skier

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New Jersey, USA

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It is not possible for the mobile covering to keep up with the wheels speed. No the plane won't take off, but that would require the plane to move forward and if the belt is moving back the wheels won't move forward therefore the plane isn't moving forward and the plane won't take off.

If you were using a prop plane then the air the prop pushes back may eventually get the wind under the wing moving fast enough that the plane will take off but the jet engines are mounted on the wing and don't push any wind pass the wing.

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

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09-03-2003 05:19 PM  14 years agoPost 11
Super Phreek

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THe propwash is very turbulant, you need a smooth airflow over the wing to get any lift. So with the prop going full bore, still no flying if the is no airspeed.

Derek

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09-03-2003 05:23 PM  14 years agoPost 12
CeeJay

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Alexandria, LA - USA

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I'm no rocket scientist, so this comes from a guess using common brain power.

It doesn't matter that the runway will move in the opposit direction of the thrust, at the same speed that the aircraft moves foward. This thrust is applied to the airframe, it's not to "Drive" the wheels to spin. Thusly, the airframe is going to react to thrust that is applied to it. If all that is holding it "Back" is air, still air at that. Well, put it like this, that airframe is going to move in the opposite direction of thrust, unless something other than air is going to hold it back..

The laws of physics dictate that the airframe WILL move foward, it's AIR speed will increase, and with enough AIR SPEED the wing is going produce lift and the bird will fly.

Now, probably by the time the bird is flying, that conveyer belt is going to be moving at some extreamly high rate. Tires survive? Probably not. Hell, I'd love to be the man that could create "Belting" that could with stand what that belt is going to be going through! I mean, not only is it going to have to be tough, it's going to be one long puppy, too! That or the airframe will run off the end of the belt, and then all things will be normal again for the airplane. The wheels will be turning at ground speed, the airspeed will still be increasing, and as long as the airframe doesn't hit something to stop it, the bird will fly.

Dam I hate these kind of questions....

However, I bet someone out there knows what the last thing is that goes through a mosquito’s mind just as he splats on a car's windshield. And, does the mosquito's inpact have any resulting effect on the foward motion of the car?

(Now that ort'a stir up some poo!)

CeeJay

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09-03-2003 05:32 PM  14 years agoPost 13
Fraz

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New Market, MN

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So what about the Hanglider????

If they fly at 20, no problem, head wind is ok. But if they fly less then 20 then thats a problem and i'll take the tail wind.

Just a guess.

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09-03-2003 06:01 PM  14 years agoPost 14
spurry

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Let's just forget about the wheels for now, the point is there will be no lift without airspeed, and there'll be no airspeed because the plane isn't moving through the air.

It does matter about the runway moving in the opposite direction at the same speed. If it wasn't then it would just take-off as normal. The thrust generated is being used just to keep the plane 'stationary' relative to the pilot (assuming it's a model, if not relative to the ground).
Well, put it like this, that airframe is going to move in the opposite direction of thrust, unless something other than air is going to hold it back..
The belt is what is holding it back, the air is just still as usual.

There is no way that is would gain airspeed at all, execpt for the propwash, but like Derek said, it's just very turbulent and leaves the prop in a corkscrew manner so it wouldn't provide any lift.

If you're flying along in a lovely 182 at about 90 knots and you have a 90 knot tail wind, you'd stall, it's irrelevant that you are travelling over the land at 90 knots. Just like the model scooting across the belt. Ever seen a plane fly backwards, pretty neat?

To put it another way, imagine holding a large wing/handglider. To take-off you run to gain airflow over the airfoil, even more efficient when running into the wind. Now run on a treadmill whilst holding the wing, you'd just be using all your energy to keep up with the speed of the belt and the wing might as well not be with you, you'd just look a bit of a wally!

It's a simple no, for this Q.

James

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09-03-2003 06:04 PM  14 years agoPost 15
Jagboy69

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Miami

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This is the kind of stuff I ponder when the power goes out... no airflow over the wings equals no lift.... Remember what bournelli and newton taught us??

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

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09-03-2003 07:06 PM  14 years agoPost 16
CeeJay

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I knew better.... SIGH! !


Spurry, how is the belt holding the airplane back? In his query the wheels are turning on that belt, rotating, and the belt will match in it's speed the rotation of the wheels.. There would NOT be any "Holding back" There is no force there, other than the weight of the airframe on them wheels. The BELT is what's turning them, not the airframes power, supposedly to prevent the airframe from reacting to the foward thust. (It doesn't matter if it's a big fan up front, a suc-n-blow at the rear, or a pair of either out on the wings, thrust is thrust.)

With nothing physically "Holding" the airframe at rest, it's going to react.
Them turning wheels aren't going to hold it.


Enough for this debate..... Your right, and all others are wrong.

CeeJay

CeeJay

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09-03-2003 07:13 PM  14 years agoPost 17
TurboRacer

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Spurry said

"To put it another way, imagine holding a large wing/handglider. To take-off you run to gain airflow over the airfoil, even more efficient when running into the wind. Now run on a treadmill whilst holding the wing, you'd just be using all your energy to keep up with the speed of the belt and the wing might as well not be with you, you'd just look a bit of a wally!"

The problem with this is it is totally different than the scenario I first posted. In Spurry's example, power would be coming from your legs (equivelant of wheels) not thrust. If plane's wheels were powered, and they were what propelled the plane to take off speed, then you'd be right.

Take that same glider, same treadmill, and tape a bottle rocket to the glider (thrust). Run the same speed as the treadmill, then light the rocket. It will go foward because it now has thrust.

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09-03-2003 07:26 PM  14 years agoPost 18
CeeJay

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Alexandria, LA - USA

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BTW


What about them dam mosquitos ?


CeeJay

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09-03-2003 07:43 PM  14 years agoPost 19
spurry

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Reading, UK

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Good point about the rocket, but when it pushes you forward on the treadmill, wouldn't the little electronic gadget just increase the speed of the belt to make sure you stay put? I've got a nice cessna, I'll try it next time I go to the gym!

CeeJay, sorry, when I said 'holding it back' I was meaning the belt was holding it back in the same position relative to the ground to stop it thrusting forwards faster than the belt is going backwards, rather than some resistance.

Whoa, these mozzie Q's get u thinking!

James

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09-03-2003 07:43 PM  14 years agoPost 20
Augusto

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US

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Assuming that the wheels are designed to withstand the excessive rpms the airplane will take off without any problems.

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. The extra wheel speed will just add a little bit of resistance to forward motion that's all.

Augusto.

Avant Aurora Ultimate

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HelicopterOff Topics › To take off, or not?
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