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# Will it take off?

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posted on Feb, 17 2006 @ 04:49 PM

The point was made before, in prior posts, but to re-iterate: An aircraft's propulsion system acts against the mass of the Aircraft, NOT against the air surrounding the aircraft.

Technically this is correct. But air is the medium through which thrust is created and thrust is basically how much air you through backwards how fast and because thrust from propellors, jets and rockets are far greater than the friction of the wheels the airplane will have no trouble taking off. Its amazing how many people confuse themselves.

posted on Feb, 17 2006 @ 04:51 PM

Originally posted by orca71
No.

The jet engine/propellor pulls the aircraft forward, causing airflow over the wings.

Which would be true if the aircraft were operating normally (without the treadmill).

posted on Feb, 17 2006 @ 04:53 PM

Originally posted by robertfenix
Really amazes me at the length some people will go

Take a giant wind tunnel,

Put whatever plane you want inside the wind tunnerl and attach the plane with a cable to the end so that the plane has a full range of motion.

Now crank up the wind tunnel to generate the airspeed needy to get the plane into the air. No power, since the plane is held in place by the cable.

The plane is "flying" right... yes

Because the "airspeed" over the wing is at the right velocity to provide lift.

Consider this to be relative airspeed, with a 0 ground speed.

So you have your plane in the air in the wind tunnel, now turn on the power on the plane.

Let assume the force of the wind to equal our relative airpseed to keep the plane in the air is 50 units

50 counter untis are being imparted on the plane by the cable to keep it in place right. 50 pushing it 50 holding it back.

So now you turn the planes power on and make 10 units of forward power,

Does the plane move forward ... no

50 units pushing against it,, 40 counter units by the cable and 10 counter units by the plane

lets take the plane up to 50% so now

50 units against it, 25 counter units from the cable and 25 counter units from the planes power.

has the plane moved no, why because the plane still has to overcome the counter force keeping it from flying back that the cable is holding onto

Now lets crank the planes power up to 90%

Still the same force pushing against it (the wind) but now the cable is only imparting 10% to hold it in place and the plane is using 90% to push forward, without the cable though the plane would bo forced backwards because it has less forward force then the wind pushing against it

so now you are at 100% equal force from the plane as the wind against it, the cable goes slack and the plane is flying in place.

FOR THE PLANE TO FLY FORWARD INSIDE THE WIND TUNNEL IT MUST CREATE MORE FORCE THEN THE WIND FLYING AGAINST IT. REMBER this whole time the plane has 0 ground speed and the airspeed is only relative to the wing, the "object" has 0 forward momentum

You can not use the downwind turn example because a plane flying the air has postive forward momentum which is different then our example as well as the conveyor belt.

A plane flying at a true airspeed say of 80 knotts is traveling 80 knotts forward, if the plane flys into a wind blowing at 160 knotts the plane does not stall just the relative airspeed over the wing now becomes 240 knotts reletive to the wing and creates MORE lift as well as more pressue on the wing controls. If for example the controls or airframe is only rated for 165 knotts then the plane does not lose control because it stalls but because the total force imparted on the control surfaces is greater then it can handel. This is why planes can take off into the wind and why sometimes they crash after taking off into the wind. If for example your wing lift needs 100 knotts to take off and you have a 40 knott wind you could then accelrate to 60 knotts ground speed and take off but if the 100 knott wind layer was shallow and say a mere 50 feet up it was only 10 knotts instead of 40 knotts then as you rolled up at 60+ knotts but a relative 100knotts at the wingspeed sure you could be in the air but as soon as you hit that 10 knott layer your 60+ 10 knott wings speed being below the 100knott lift requirement would send you crashing into the ground.

And has happend to more then enough private planes, commercial planes, military aircraft etc.

You here it all the time, plane crashed after take off just 1 mile from the airport. Some of these case are on accent with not enough forward airspeed (true forward airpseed) and into the wind, where the plane meets a slower relative airspeed wind and being under powered for the condition, stalls at low altitude where there is not enough time to recover and crash.

It is safe to land into the wind but it is very tricky to take off into the wind

A plane then flying with the wind is still moving forward at the 80 knotts relative to the wind but the ground speed becomes increased slightly due to friction on the plane. Since the air mass as a whole is moving at 160 knotts and the plane is flying within the air mass is moving at 80 knotts. The plane could appear to be flying at 100knotts or more due to the position on the ground relative to it, but airspeed of the wing may still be 80 knotts.

Thats why the problem of powering down causes the plane to stall, the air mass over the land is moving as a whole but that is independant of the wing speed through that airmass which is required to produce lift.

Congratulations. You understand that aerodynamic drag is a significant force and can significantly counter thrust.

Now all you need to do is understand that wheel friction is relatively insignificant and cannot counter thrust.

posted on Feb, 17 2006 @ 04:56 PM

Originally posted by orca71

Originally posted by Kruel
Then what you're saying is, the jet engine/propeller creates the airflow which travels over the wings and causes lift.

No.

The jet engine/propellor pulls the aircraft forward, causing airflow over the wings.

The propellar is trying to pull the aircraft body forward but the body can not roll forward in "position" since the ground under it is moving in the opposite direction at the same rate.

So even though the propellar jet etc is pushing pulling the plane "forward" since it can not change its ground position there if no airflow over the wing.

posted on Feb, 17 2006 @ 04:57 PM

Originally posted by Kruel

Originally posted by orca71
No.

The jet engine/propellor pulls the aircraft forward, causing airflow over the wings.

Which would be true if the aircraft were operating normally (without the treadmill).

There are two main components to consider.

Theres one force trying to make the airplane move forward, and thats the thrust from the engines. This uses the air, which is unaffected by the treadmill.

Theres another force trying to make the plane move backwards, and thats the treadmill, which is limited by the amount of wheel friction.

Now which force do you think is greater? Thrust or wheel friction?

If the thrust is greater the plane will move forward, if they are the same the plane will stay in one place, if the wheel friction is greater than the thrust, then the airplane will go backwards.

posted on Feb, 17 2006 @ 04:59 PM

Originally posted by robertfenix

Originally posted by orca71

Originally posted by Kruel
Then what you're saying is, the jet engine/propeller creates the airflow which travels over the wings and causes lift.

No.

The jet engine/propellor pulls the aircraft forward, causing airflow over the wings.

The propellar is trying to pull the aircraft body forward but the body can not roll forward in "position" since the ground under it is moving in the opposite direction at the same rate.

So even though the propellar jet etc is pushing pulling the plane "forward" since it can not change its ground position there if no airflow over the wing.

It cannot change its ground position? Are you saying that the wheel friction is equal to thrust generated by propellor, jet or rocket engines?

posted on Feb, 17 2006 @ 05:02 PM
FORGET THE STUPID WHEELS, put skids on the plane, it does not matter, the plane sliding over the conveyor belt at the same rate as the conveyor runing under it in the opposite direction will still not fly into the air

put a box on a moving conveyor where does the box go....

pretend the box can move on its own by some power source, a mini jet engine lets say.

If the conveyer is moving at 3ms in one direction the box has to push forward with a force of 3ms in the opposite direction just to stay in one place relative to the ground

DONT YOU GET IT.

Substitue the plane for an abstract item its the SAME THING. no forward movement when the forces equal each other

3ms one way 3ms the other way equal 0 positional movement

0 positional movement means NO AIRSPEED OVER THE WING, NO AIRSPEED ON THE BOX, NO DRAG ON THE CAR. ZIPPO

[edit on 17-2-2006 by robertfenix]

posted on Feb, 17 2006 @ 05:03 PM
Oh, and if the engine thrust is no greater than wheel friction it has no business being on an aeroplane in the first place as a light aircraft can be pushed along on its wheels by a man.

That is why the belt moving backward does not keep the plane in the same place.

Robert fenix. forget the wheels? put it on skids? That is the whole point. If it was on skids then friction through the weight of the plane would certainly prevent its fortward motion, it the the very fact that the wheels are freely rotating of their own accord with no direct influence from the Aeroplane itself that allows this friction to be overcome so easily.

[edit on 17-2-2006 by waynos]

posted on Feb, 17 2006 @ 05:06 PM

Originally posted by orca71
There are two main components to consider.

Theres one force trying to make the airplane move forward, and thats the thrust from the engines. This uses the air, which is unaffected by the treadmill.

Theres another force trying to make the plane move backwards, and thats the treadmill, which is limited by the amount of wheel friction.

Now which force do you think is greater? Thrust or wheel friction?

If the thrust is greater the plane will move forward, if they are the same the plane will stay in one place, if the wheel friction is greater than the thrust, then the airplane will go backwards.

The logic you are applying here would work for submarines and space vehicles, not airplanes. You have to factor in the wings, and how air has to move over them to cause lift. If an airplane engine was powerful enough to generate the airflow required for lift... well it wouldn't need the wings for anything but changing direction (similar to a sub).

posted on Feb, 17 2006 @ 05:09 PM
Kruel; are you taking the P on purpose here?

Nobody claims the plane is stationary, nobody claims the airflow over the wings is from the propeller. Is that clear?

The notion is that the conveyor moving backwards at the same rate that the plane is moving forwards does not cancel out the forward speed of the aircraft because the wheels are simply rotating, not driving, the propeller is driving the plane forward so the belt has little effect and what little effect there is is quickly overcome anyway and the plane just takes off.

For the belt to keep the plane in the same place the friction acting on the wheels from its movement would have to be of an equal force to the thrust generated by the propeller, this would then cancel out any movement. However the thrust of an aircraft engine/propeller combination is MUCH greater than this force so forward motion is not cancelled out at all.

[edit on 17-2-2006 by waynos]

posted on Feb, 17 2006 @ 05:14 PM

Originally posted by robertfenix
FORGET THE STUPID WHEELS, put skids on the plane, it does not matter, the plane sliding over the conveyor belt at the same rate as the conveyor runing under it in the opposite direction will still not fly into the air

put a box on a moving conveyor where does the box go....

pretend the box can move on its own by some power source, a mini jet engine lets say.

If the conveyer is moving at 3ms in one direction the box has to push forward with a force of 3ms in the opposite direction just to stay in one place relative to the ground

DONT YOU GET IT.

Substitue the plane for an abstract item its the SAME THING. no forward movement when the forces equal each other

3ms one way 3ms the other way equal 0 positional movement

The rocket thruster will move the box forward and no matter how much the conveyor speeds up all the conveyor determines is not the speed of the box but the amount of friction.

So lets say the rocket imparts 3ms speed to the box, and the conveyor is sliding in the opposite direction at 3ms, the amount of friction on the skids will be equal to what would be if the rocket were traveling at 6ms on a normal surface because thats the speed difference between the box and the conveyor.

Similarly, the aircraft is gong to move forward in position regardless of which direction or how fast its wheels are spinning. This is a simple point you seem unable to grasp.

posted on Feb, 17 2006 @ 05:14 PM
Ok, I give up. I can't explain things any simpler than I already have. They're all yours RF.

posted on Feb, 17 2006 @ 05:17 PM

Originally posted by Kruel

Originally posted by orca71
There are two main components to consider.

Theres one force trying to make the airplane move forward, and thats the thrust from the engines. This uses the air, which is unaffected by the treadmill.

Theres another force trying to make the plane move backwards, and thats the treadmill, which is limited by the amount of wheel friction.

Now which force do you think is greater? Thrust or wheel friction?

If the thrust is greater the plane will move forward, if they are the same the plane will stay in one place, if the wheel friction is greater than the thrust, then the airplane will go backwards.

The logic you are applying here would work for submarines and space vehicles, not airplanes. You have to factor in the wings, and how air has to move over them to cause lift. If an airplane engine was powerful enough to generate the airflow required for lift... well it wouldn't need the wings for anything but changing direction (similar to a sub).

Ive been extremely patient thinking I could help you understand something but if youre not going to be serious then its a waste of time.

posted on Feb, 17 2006 @ 05:18 PM
Kruel, did that last attempt of mine make no impression at all? Can you not see the different levels of force that the propeller induces by comparison with a free wheeling undercarriage?

posted on Feb, 17 2006 @ 05:20 PM
No I think it doesn't take off because the force against the wheels is equal to forward momentun ,therefore it can't take off i.e. it is static.

posted on Feb, 17 2006 @ 05:21 PM

Originally posted by orca71
Ive been extremely patient thinking I could help you understand something but if youre not going to be serious then its a waste of time.

How do you think I feel?

Originally posted by waynos
Kruel, did that last attempt of mine make no impression at all? Can you not see the different levels of force that the propeller induces by comparison with a free wheeling undercarriage?

Like I said, I already explained it in the simplest way. robertfenix also elborated on it quite a bit. I'm not going to repeat what I've already said.

posted on Feb, 17 2006 @ 05:22 PM
Fair enough kuhl, if thats what you think, at least its from a point of logic. I would just say that that would have to be one feeble engine that could be counteracted by a freely rotating axle on a belt.

posted on Feb, 17 2006 @ 05:26 PM
My arguement is that (If I understand this thread properly?) No matter how fast the wheels go (i.e. forward motion) there is an equal force counteracting this hence no air flow hence no lift?

posted on Feb, 17 2006 @ 05:31 PM
well at the risk of starting up all over again (please no!) the belt matches the speed of the plane, yes. If the wheels were geared to the engine like in a car then yes, the plane would remain stationary because the output force of the engine is being directly counteracted. However the propeller is acting on the air, this pulls the plane forward, the belt goes backward at the same speed but as the wheel are free spinning the net result is only that the wheels are rotated faster and the plane itself is not impeded.

This makes perfect sense to me but I see there are many who are having a hard time understanding the difference

posted on Feb, 17 2006 @ 05:53 PM

Originally posted by waynos
well at the risk of starting up all over again (please no!) the belt matches the speed of the plane, yes. If the wheels were geared to the engine like in a car then yes, the plane would remain stationary because the output force of the engine is being directly counteracted. However the propeller is acting on the air, this pulls the plane forward, the belt goes backward at the same speed but as the wheel are free spinning the net result is only that the wheels are rotated faster and the plane itself is not impeded.

This makes perfect sense to me but I see there are many who are having a hard time understanding the difference

Thats well put.

I also hope youre right that they are simply having a hard time understanding the issue.

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