Low Noise Helicopter

[GilTeva]

Hi, I would like to hear your opinion about my idea, how to make the helicopter more quiet. This is my idea:

 

1.A quiet helicopter that includes a long shaft between the body and the main rotor, and the main rotor generates an homogeneous equal thrust in all 360 degrees, and the movement is achieved by tilting the rotor blades in an angle in relation to the shaft.

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the rest is in a file

Quiet_helicopter.doc

[Corbec]

I'm not quite sure how changing the mast length would make the helicopter quieter. The only stuff I've seen to make a helicopter quieter was angled main rotor tip caps, and that only does so much.

[GilTeva]

What makes it quieter is that you don't change the attack angle of the blades as they rotate.

To enable such a rotor you need to use a long mast.

[Corbec]

So you are saying that you would keep the blades at a fixed pitch? Or are you saying that you would not allow flapping?

 

Fixed pitch blades wouldn't work, you wouldn't be able to control the helicopter. Flapping is there to keep the lift on the rotor disk even.

 

I'm sure that if the problems were that simple to overcome, that engineers would have come up with it over the last 70 years. It would cut out all the complex rotor systems we have right now, that add weight to the aircraft.

[Goldy]

What makes it quieter is that you don't change the attack angle of the blades as they rotate.

To enable such a rotor you need to use a long mast.

 

What makes a main rotor quieter would be composite blades....slowing down the rotational speed of blades ( especially tail rotors that spin much faster) and the tip changes that you see on the new style R44 blades ( reduces tip vortices).

 

Anyway, interesting concept...build a remote control version and test it out !

 

Goldy

Edited March 31, 2007 by Goldy

[brushfire21]

Goldy, you are right on that most of the noise comes from that little invisible tailrotor!

 

But to be honest, a completely quiet helicopter is like having a muscle car without a kick ass exhaust!

[GilTeva]

The noise from the tail rotor is at high frequency, but it does not give low frequency noise. If you will increase the diameter of the tail rotor you will decrease its noise.

 

Main rotor as I suggest, with fixed pitch as the blades rotate, will also not have low frequency noise. The flapping makes that noise and you can hear that the noise increases when there is more flapping. When the helicopter is in one place.

 

It will be possible to control to movement to any direction if you tilt the whole rotor in an angle. To tilt the rotor is possible, but I offer another methd. To use the swash plate to make an angle between each blade and the mast. The result is the same as tilting the rotor but the mast is fixed.

 

see here: http://www.gen-corp.jp/

 

The roto craft is a it like my idea. It has fixed pitch. The movement is done by changing the rotor angle. But they put the engine near the rotor and they have a short shaft. The weight of the pilot allow the angle of the rotor to be un-parallel to the gound. The weight pushed down.

 

I suggest that you put also the engine far from the rotor. Like this you can control the movement.

 

If someone can help me with building the r/c model it will be nice.

[GilTeva]

If the rotor is high above the central gravity point, you can use a fixed pitch blades, and change the angle of the rotor in relation to the body.

 

The gravity pushes the lower part of the shaft down.

[GilTeva]

Please see the animation that I made

[coanda]

fly the md520 notar. thats about as quiet as it gets. well done on that animation, i needed a good laugh.

[FauxZ]

Fixed pitch blades are going to require a change in RPM to operate, and the lower your RPM, the lower your available power. On top of that, how do you plan to autorotate with fixed pitch blades? Multiple engines won't help you at all if you manage to run out of gas, or get a batch of bad gas.

 

I'd like to know where you plan to park that sweet R44 in the animation.

[ChprPlt]

That would be a bitch to put the blade tie on that 44 haha

[Eric Hunt]

How do you tilt the disk to make it fly? You need some mechanism running up the mast to tilt it, and you are introducing a problem spot in the drive shaft by installing a gearbox that can tilt.

 

Long driveshafts need careful balancing, and bearing mounts in positions that do not induce resonance. You will also get large bending moments in the shaft by having the disk so far from the transmission.

 

How do you counter flapback? Inflow roll?

 

A lot of things work in small scale models that will never work in the real thing. A bamboo rotor blade on a toy, while seemingly rigid, will absorb and flex to cope with stresses and fly beautifully. A full-scale item made of real materials will not. And as Igor found out, it also will not fly, until a swash plate and feathering hinges are installed.

 

Face it, son, it is a dream of someone who doesn't understand the larger picture. As a kid, I designed a helicopter pedal-powered by bicycle gears, and reckoned it would work, until the realities of Power Required and Power Available punctured my balloon.

[67november]

Face it, son, it is a dream of someone who doesn't understand the larger picture. As a kid, I designed a helicopter pedal-powered by bicycle gears, and reckoned it would work, until the realities of Power Required and Power Available punctured my balloon.

 

there was a $10,000 prize back in the 80's for anyone that could build a flyable human powered helicopter, I beleive that prize was never collected.

[GilTeva]

Only the cyclic pitch is fixed, the collective pitch can be changes, so you don't need to gear the engine.

 

The main noise of the main rotor, is when the helicopter advances, and the cyclic pitch starts, and the blades starts to wave, as they rotate. This is low frequency noise.

 

By eliminating this I reduce most of the low frequency noise. This low frequency noise travels for many kilometers since the air does not attenuate it, as it attenuates the high frequency sounds.

 

The girafee neck can be bent back without a problem, or we can make it telescopic, so it shrinks down. The blades can be bent to be attached to the neck.

 

There are two forces in aviation: one is the gravity force that pushes everything down, and one is rotor force, that is supposed to push up. If you make them far one from the other, the whole thing is more stable. I am sure that the new thing will be more safe to drive.

[GilTeva]

In order that I will be your son, you need to be at least 70...

 

 

You can tilt the axis of the rotor, or tilt each blade, using arms and swash plate. But you tilt the angle between the blade and the shaft, instead of tilting the attack angle of it.

 

You are right that the shaft might be the problematic thing. I think that is why they did not think about my idea before. Or did not want to think. life is already hard. But if you overcome this...

 

I don't think that the shaft needs to be that strong. but maybe if you use titanium, it is strong and not heavy. Maybe a composite material.

 

My last reply answers about stability. I think it will be more stable since you put the weight far from the rotor.

 

Not may years ago, people would only dream of flying, so I understand your difficulty to understand how this long neck helicopter can fly.

[ECD]

In order that I will be your son, you need to be at least 70...

You can tilt the axis of the rotor, or tilt each blade, using arms and swash plate. But you tilt the angle between the blade and the shaft, instead of tilting the attack angle of it.

 

You are right that the shaft might be the problematic thing. I think that is why they did not think about my idea before. Or did not want to think. life is already hard. But if you overcome this...

 

I don't think that the shaft needs to be that strong. but maybe if you use titanium, it is strong and not heavy. Maybe a composite material.

 

My last reply answers about stability. I think it will be more stable since you put the weight far from the rotor.

 

Not may years ago, people would only dream of flying, so I understand your difficulty to understand how this long neck helicopter can fly.

 

Hi!

Really funny that animation..

There are multiple problems with your idea. For one, it is trying to solve the wrong problem..

Cyclic input is made to create unequal lift on opposite sides of the rotor disk, this will make the helicopter move..

Flapping however takes place for the opposite reason, when moving from a hover (building velocity) the speed of the blades relative to the air is unequal on different sides of the rotor disk. This induces different amounts of lift on different sides of the helicopter, making it tilt over to the side.

To eliminate this problem the blades flap, up on the advancing side to generate a lower induced angle of attack and therefore less lift, down on the retreating side to produce a higher induced angle of attack and so more lift. The “sum” of the higher airspeed and lower angle of attack of the advancing blade is virtually equal to the “sum” of the lower airspeed but higher angle of attack retreating blade.

Problem solved (if we forget about the Coriolis effect, and I will for now..)

 

Notice that the flapping in forward motion takes place to the sides of the helicopter. And the tilt of the disk to create velocity is 90 deg off from this..

 

What you are suggesting only works with coaxial rotors(and you even give an example of a crazy man with a coaxial rotor on his head). Here you have two counter rotating rotors, and unbalance in lift induced by one of the rotors is cancelled out by the other. But as you notice, the idea already exists..

oh, and they still have cyclic input.. and noise as well.. lots of it..

 

Keap trying though..