Does the helicopter take off?

[Leros]

Originally posted by: brikis98

Originally posted by: mordantmonkey

for ever action there is an equal and opposite reaction. the engine creates force the rotates the blades, but this force also pushes the body in the opposite direction. fortunately the body has much more mass than the blades. (think if the blades were held fast and the body suspended in the air, the body would be spun by the engine.) the tail rotor counter acts this opposite spinning force, so in order for the body to turn in the opposite dir. of the blades, the tail rotor simply yeilds to that force.

i'm still missing something in the picture. here's a simple experiment i did:

i have a ruler with a hole drilled right in the middle of it and a pencil. while holding the pencil upright in my hand, i place the ruler on it so the hole fits snuggly around the pencil tip. i can now spin the pencil with my hands, which turns the ruler. this is like the engine of the helicopter turning the rotors.

now, i happen to be sitting in a swivel chair. as my hands spin the pencil/ruler (which is right above my head) i can use my feet to spin the chair. now, my feet are acting like the turntable on the "body" of the helicopter (the chair/me). as far as i can tell, the ruler is definitely still spinning with respect to the air around it, regardless of which direction i'm turning in the chair. if it was a helicopter rotor, it would be generating lift.

perhaps the right way to put what i'm thinking is that the rotor is free spinning with respect to the turntable, and therefore the turntable has no effect on it.

what am i doing wrong?

(edited for clarity)

Are you spinning the ruler opposite of the chair?

Also, you need to be rotating around the pencil.

 

[Specop 007]

Originally posted by: jagec

Originally posted by: mordantmonkey
have you ever seen a heli lose it's tail rotor function? yeah the body spins wildly out of control and the blades do lose some of their lift.

Well, when I was shooting down Mi-24 Hinds in Afghanistan with the mujahadeen...

Originally posted by: brikis98
so then explain something i'm just curious about. say that in normal flight, the main rotor is spinning clockwise. say the helicopter (from an above view) wants to rotate in place counterclockwise, which i believe it should be able to do. if the main rotor isn't free spinning from the body of the helicopter, how would the body be able to turn rotate in the opposite direction of the rotor? i'm having trouble picturing it...

Easy, it decreases the force of the tail rotor, and the reaction force from the engine powering the rotor causes the helicopter to rotate.

Originally posted by: brikis98
now, i happen to be sitting in a swivel chair. as my hands spin the pencil/ruler (which is right above my head) i can use my feet to spin the chair. now, my feet are acting like the turntable on the "body" of the helicopter (the chair/me). as far as i can tell, the ruler is definitely still spinning with respect to the air around it, regardless of which direction i'm turning in the chair. if it was a helicopter rotor, it would be generating lift.

Sounds like you're just not spinning the chair fast enough, because you should be able to bring the "rotor" to a standstill, doing what you describe.

The axis's (axse? axsii? Whatever) would have to be diriectly in line with each other. Make sure your pencil on the ruler is above the hub of the chair.

 

[Mrvile]

This question is different than the airplane one. First, the airplane one is a "yes, it will take off" because the wheels of the airplane have nothing to do with the forward thrust of the airplane since they are freely spinning (the engines provide the forward thrust). However, for the helicopter, the blades provide the lift and since they are not freely spinning (they cannot be, otherwise the blades cannot move), they will always spin wrt the helicopter and will always remain at a speed of 0 wrt the ground.

There's nothing else to this. I don't see why either problem is discussed so much.

 

[imported_goku]

LOL @ this thread.

 

[ahurtt]

To me it seems like this scenario would be essentially the same as suspending the helicopter off the ground by fixing its main rotor to something immovable and then starting the engine. Obviously the cockpit part of the helicopter would then spin instead of the blades. No, it would not take off.

 

[ElFenix]

Originally posted by: Specop 007
I believe it would. The rotors would have no net speed in relation to the body of the helicopter, but they would have a net speed in relation to the ground and as such to the air around the helicopter. As long as you have air passing over the rotor blades you have lift, regardless of the body of the helicopter.

the only way the rotor could have no net motion in comparison to the body is if the engine was off.

i think what he is asking is if the turntable was spinning the opposite way at the same RPM, would it take off, and the answer is no, it wouldn't.

 

[pnad]

Originally posted by: ahurtt
To me it seems like this scenario would be essentially the same as suspending the helicopter off the ground by fixing its main rotor to something immovable and then starting the engine. Obviously the cockpit part of the helicopter would then spin instead of the blades. No, it would not take off.

DING! I was waiting for the right visual.

Think old school cartoons. Imagine if God jammed his finger into the rotor blades of a hovering copter. The blades and rotor are made of ultra-unobtainium and will not break. Rotor stops and body spins at 1000rpms.

For the ruler/chair experiment:
You have to rotate your chair at an equal-opposite RPM. If you do it correctly the tip of the ruler should stay pointed at your monitor.

 

[brikis98]

Originally posted by: pnad

Originally posted by: ahurtt
To me it seems like this scenario would be essentially the same as suspending the helicopter off the ground by fixing its main rotor to something immovable and then starting the engine. Obviously the cockpit part of the helicopter would then spin instead of the blades. No, it would not take off.

DING! I was waiting for the right visual.

Think old school cartoons. Imagine if God jammed his finger into the rotor blades of a hovering copter. The blades and rotor are made of ultra-unobtainium and will not break. Rotor stops and body spins at 1000rpms.

For the ruler/chair experiment:
You have to rotate your chair at an equal-opposite RPM. If you do it correctly the tip of the ruler should stay pointed at your monitor.

ah, there we go, i finally have the proper visuals in my head.

at the cost of looking like an idiot in my cube, i redid this experiment as carefully as i could and as you said, the tip of the ruler does seem to keep pointing at my monitor.

so, i remove my objection and agree the helicopter will not take off. of course, as mentioned before, this neglects the (riduclous) torque forces, pilot passing out, tail rotor, etc. thx every1 for the explanations/help/etc... for some reason this one just took me a while to picture properly

 

[drinkmorejava]

If it spins with the blades it takes off. If it spins against the blades, it does not lift off as the blades will have no motion relative to the ground and thus there is no air flow over the blades. Course, there are a ton of other factors in this including the helicopter would slide off and the engine structure is not designed to be spinning like that.

 

[UCJefe]

Think of it this way.

@ t=0: Both helicopter and blade are pointed North |
@ t=1: Helicopter has rotated 90 degrees clockwise w/ respect to the ground (now pointing East), blade has rotated 90 degress counter-clockwise w/ respect to the helicopter. The configuration now looks like this: |--

Both the blade and helicopter have moved but since the blade did not move with respect to the Earth around the turntable (and consequently, the air as well), no lift is generated. Like others said, the moving of the helicopter body itself might move a little bit of air but it wouldn't be enough to take off.

Can't wait for the next thread.

 

[Number1]

The last time, I said the airplane would take off I got called an idiot. So at the risk of looking foolish again, here is my answer:

no net motion = no air movement over blades = not taking off.






By the way, I was right with the plane.

 

[hellokeith]

Originally posted by: Mark R
matches its speed so that there is no net motion

No net motion = no takeoff

 

[herbiehancock]

If I could choose the helicopter to be placed on the turntable, I'd almost guarantee it'd lift off.

Guess everyone forgot about the Boeing Chinook........twin counter-rotating rotors instead of a main and tail rotor. Both rotors provide lift but counter-rotate one another, which is why it needs no tail rotor.

So no matter which way the turntable turns, one of the rotors will be providing lift, and probably enough to get it off the turntable to allow the other rotor to then start producing
lift.


Here's a link to a neat photo of one........nearly vertical....... http://www.chinook-helicopter.com/Vertical.jpg



So, the answer to the OP's question is yes, depending................

 

[Smartazz]

I think it would be able to take off, but I'm not 100% sure how a helicopter works.

 

[flexy]

it takes off...or...UHM....

If the helicopter...or the rotor-motor (for that matter) spins AGAINST..would it actually mean the rotor-blades can not spin because of the retro-spin of the attached motor ??? It could also be the case the blades are able to spin regardless whether the motor/helicopter spins in whatever direction...than the question is already wrong to begin with since it would be IMPOSSIBLE to make the rotorblades STOP.

If the motor is, say, touchless and the rotor/spindle basically sitting in a magnetic field...would it matter whether the motor itself spins ? Or would the motor movement negate the movement of the spindle/rotor ???

Question here first whether the rotors actually SPIN...its totally irrelevant what the helicopter does ...IF the blades spin, yes, then they provide lift and the helicopter lifts off...

 

[flexy]

Originally posted by: Number1
The last time, I said the airplane would take off I got called an idiot. So at the risk of looking foolish again, here is my answer:

no net motion = no air movement over blades = not taking off.






By the way, I was right with the plane.

"NET" or not is irrelevant...."NET" in regards to the air ???? Of course not, if no motion in regards to the air..NO LIFT....NO LIFTOFF

Question here whether its possible to stop the blade's movement *in relation to AIR* by moving the heli/motor-housing in the op. direction ?

This should be a simple thing for an engineer to know ?

 

[flexy]

Originally posted by: herbiehancock


So no matter which way the turntable turns, one of the rotors will be providing lift, and probably enough to get it off the turntable to allow the other rotor to then start producing
lift.

interesting. but i dont know whether it provides lift...thats the point.

Lets say one axle of that heli is over the center of the TT, and spins backwards...so the motor/heli spins backwards..would it still provide lift ?

 

[Midlander]

*slowly shakes his head and hopes that most of these posts are satire*

 

[Howard]

I don't know, but the pilot would be dizzy as hell.

 

[Shadowknight]

If the helicoptor was on a turntable, the pilot must have been really hammered from crashing it into a local club.

 

[Injury]

Originally posted by: ScottSwingleComputers

Originally posted by: Injury

Originally posted by: ScottSwingleComputers

Originally posted by: ThePresence

Originally posted by: ScottSwingleComputers

Originally posted by: Specop 007
I believe it would. The rotors would have no net speed in relation to the body of the helicopter, but they would have a net speed in relation to the ground and as such to the air around the helicopter. As long as you have air passing over the rotor blades you have lift, regardless of the body of the helicopter.

You got that a bit backwards.

No, I think he got it right. Air passing over the blades of the rotor provide lift, regardless of what's powering the rotation, be it the turntable or the engines.

But the blades would NOT be moving in relation to the air or ground. The turntable would negate the movement of the blades.

Negative. The turntable would not change the fact that the blades are turning at a certain speed. The turntable could not match this speed because the turntable is ADDING to it, not catching up to it.

It's just like if you are in a moving car and throw a ball up a few inches... the ball doesn't go flying backwards as if it had suddenly left the car. If you were to throw the ball towards the front of the car, it is moving at it's rate + the rate of the car. We know this, again, because the ball does not go flying backwards. The ball's movement is relative to the car.

Now an even better hypothetical question would be "If you were in a helocopter in a tornado that spun at the exact same speed as the helocopter's blades in the opposite direction, could you maintain lift?"

Read the freaking OP. The turntable is going in the opposite direction. That does not add to, it negates the motion of the blades.

Maybe YOU should read the OP, because NOWHERE in the OP does it say or even IMPLY which direction it is turning. Even still, no matter which direction it is going, the direction the helocopter's rotor is relative only to the turntable.

Just like my car scenerio, if the car is going backwards, the ball will still go in the direction thrown, whether you throw backwards or fowards.

 

[her209]

REPOST

 

[Nyati13]

A single rotor helicopter would not be able to take off, if the turntable was spinning opposite of the direction the rotor spins.

This helicopter would be able to take off no matter which way the turntable was spinning. It's got two rotors that spin counter to each other.

 

[91TTZ]

Originally posted by: brikis98


so then explain something i'm just curious about. say that in normal flight, the main rotor is spinning clockwise. say the helicopter (from an above view) wants to rotate in place counterclockwise, which i believe it should be able to do. if the main rotor isn't free spinning from the body of the helicopter, how would the body be able to turn rotate in the opposite direction of the rotor? i'm having trouble picturing it...

Because the blades aren't solidly anchored to the ground or the air. The whole helicopter would pirouette.

 

[91TTZ]

The answer to this question depends on the type of helicopter. Most helicopters, like the Apache, would not take off. Some, like most Kamov's, would take off.

I am familiar with helicopters. I fly RC helicopters and built my Raptor from each individual part.