A question for you aviators out there...

[Shab]

I was having a discussion with a mate the other day regarding helicopter speed, or rather their top speeds. I argued that the top speed would limited by the fact the rotor blade that was moving away from the direction of travel [if the blades were rotating clockwise as viewed from above this would be the righthand side] would eventually generate negative lift as the air passing over it would be faster than it's rotaional speed. At this point I supposed the aircraft would flip over.

Later, I thought about it and reckoned you could get around the problem by having two counter-rotating blades on the same prop shaft, but then I thought this would have been tried before if it was feasable.

Anyway, my question is, if indeed this is a problem, are there any ways to overcome it.

Hope I've explained what I'm on about...

Cheers,

Shab.

[chasharman]

chopper probs

When you say counter acting rotors on the same drive, is this not the same technology used on the Chinook (excuse spelling). The fact that the rotors are going in the opposite direction means there is no need for a tail rotor.
Don`t know about the speed problem though.

[M35A2]

Couldn't you use the rota's to keep the aircraft in the air, and a jet engine to propel it at vast speed forwards??

[That Ruddy Squirrel]

Why not build one of these - then problem sorted




Trev ps ever wished some cables would snap ?

[Shab]

Couldn't you use the rota's to keep the aircraft in the air, and a jet engine to propel it at vast speed forwards??

That's the problem though...if the rotor blade is rotaing at 100 mph and the airspeed of the helicopter is 100 mph, the air speed over the lefthand side of the blade would be 200 mph and as it traveled around to the other side the speed over the blade would be 0 mph, hence no lift...

Chas,

I think the Chinook does have counter-rotaing blades as you point out, but if you mounted them on a single shaft you could make it a lot more compact, and as you say, no need for a tail rotor.

[Shab]

Why not build one of these - then problem sorted




Trev ps ever wished some cables would snap ?

WTF is it!

[That Ruddy Squirrel]

WTF is it!

It's an Osprey - it uses the Tilt Rotor principle, take off vertically, then tilt forward to fly like a plane, tilt back to land vertically.


Trev

[CaptainBeaky]

The effect is called retreating blade stall, and it gives an absolute limit on the airspeed of a helicopter - once you approach this speed, the aircraft becomes unstable, and any sudden change in air speed will result in a snap roll towards the retreating blade side.

The end result is that you get the opportunity to road-test the afterlife of your choice...

Having 2 co-axial contra-rotating rotors (like the KA50-series Soviet helicopters) won't help much - you just get the effect on both sides, the blades will start to flap violently, and you get the same result as above i.e an once-in-a-lifetime, intimate sky-ground experience!

[Shab]

The effect is called retreating blade stall, and it gives an absolute limit on the airspeed of a helicopter - once you approach this speed, the aircraft becomes unstable, and any sudden change in air speed will result in a snap roll towards the retreating blade side.

The end result is that you get the opportunity to road-test the afterlife of your choice...

Having 2 co-axial contra-rotating rotors (like the KA50-series Soviet helicopters) won't help much - you just get the effect on both sides, the blades will start to flap violently, and you get the same result as above i.e an once-in-a-lifetime, intimate sky-ground experience!

Very succinct Peter. So...That would be my fledgling helecopter design career over then...

[CaptainBeaky]

Let's see if I can get this to work - this is a KA50:

[Shab]

Let's see if I can get this to work - this is a KA50:

It did indeed. Looks like a right mean bustard. How long have they been around?

[CaptainBeaky]

Quite a few years now. Seriously mean piece of kit, although possibly not quite a match for the AH64 - APache would probably be able to answer this, if he's allowed to

[Apache]

The effect is called retreating blade stall, and it gives an absolute limit on the airspeed of a helicopter - once you approach this speed, the aircraft becomes unstable, and any sudden change in air speed will result in a snap roll towards the retreating blade side.

The end result is that you get the opportunity to road-test the afterlife of your choice...

Having 2 co-axial contra-rotating rotors (like the KA50-series Soviet helicopters) won't help much - you just get the effect on both sides, the blades will start to flap violently, and you get the same result as above i.e an once-in-a-lifetime, intimate sky-ground experience!

The retreating blade stall is a limiting factor, as it compressibility. The faster you go, the higher the advancing tip speed. As you get close to the speed of sound, you run into all sorts of problems which are difficult to deal with on a rotary wing craft.

[Apache]

Quite a few years now. Seriously mean piece of kit, although possibly not quite a match for the AH64 - APache would probably be able to answer this, if he's allowed to

I dont think there's any attack helicopter out there that comes close to the WAH-64. Note the W, it's important. It means it's built by Westlands and therefore has rolls-royce engines (much better than the US version), better avionics, and a defensive aids package to die (or rather, NOT to die) for.

[The Lovely Boyo]

The retreating blade stall is a limiting factor, as it compressibility. The faster you go, the higher the advancing tip speed. As you get close to the speed of sound, you run into all sorts of problems which are difficult to deal with on a rotary wing craft.

Apache hits the nail cleanly on the head - basically the blades explode as the tip tries to go through the sound barrier but any part of the blade nearer the axis is travelling through the air (any air) at a slower speed.

The Soviet Bear bombers pushed thier blades to the limit. Apparently, NATO fighters that shadowed them during the cold war could only get so close due to the sonic booms coming off the blades - madness!