Stealth Helicopter

American combat choppers are pretty quiet. A friend of a friend in the Canadian Army got surprised on maneuvers - one just popped up over some trees, without being heard until it was right on top of them.

 

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Nor was it actually what it claimed to be, I'm sure Dywyddyr can fill you in on the use of Jetrangers or somesuch.

 

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Bell 222.
Anyone can buy one... (provided you're rich enough).

 

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I can afford perhaps this

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...

 

I always loved the idea of intermeshing rotors (syncopters), but they got to be noise as hell with the shock waves of each rotor interacting with each other. Still good high speed potential because of even lift no matter the speed.

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The Ruskies produced a bhemoth with counter-rotating baldes, though the model defies my memory just now. It worked, but was extremely noisy and unpopular with pilots.
Quiet rotor technology had become quite advanced, as has exhaust cooling/flaring/porting technology. Often now fresh-air is mixed directly with the exhaust limiting its temperature to near-ambient, which is the goal. Porting the exit away from the engine also allows it to cool. It has the advantage of directing missiles away from the engine anyway. The comanche was designed to be able to take a direct hit from a 25mm AA round with armoured cables and multiple redundancies up to 4x.
The turbine can be made to run quietly now, leaving just the rotors as the main problem.
I wouldn't be surprised if a fault occured whilst hovering as this id the most difficult manoever a helio can perform (outside of a barrel-roll!).
They will definately wanted the black-box, and will have wanted to destroy sensitive electronics, radio, navigation and stealthy tech. I suspect some of these systems has RDX or something similar wired into them for this very purpose. The computers' HDD would also be an object to retrieve or destroy.

 

I'm sure they took the box and blew everything else to bits that could be used by others.

 

Thanks for that first pic of the Chinese one, Cosmic. I like it.

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If you're referring to post #13 that's a US Army (RAH-66) Comanche. And it's been cancelled.

 

Oh well, I was hoping for an anti - matter propelled one anyways.......thanks Dyw.

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Helicopters will always fail a mjor test with respect to radar returns. The returned signal has an advancing and receding velocity component. Even if you manage to make the blades from some form of material that can minimise the return yet is strong enough, you still get that unique signal.

 

Maybe you should do some Googling. Technology moves on.

And detection relies on the strength of the return signal as well as its "uniqueness".

 

So does receiver technologies.

 

So what?
The receiver only ever gets a reflection that's the 4th root of the outgoing signal at best.

 

Eh? 4th power of the range, it's proportional to the output power.

I've worked on systems that had to have digital filters added to them to reduce the false alarm rate against large birds, never mind helicopter rotor disks. The strength of the doppler shifted components in the return signal are even lower than then the majority of the return.

Receiver and stealth technology are in a similar race to the old armour - ammunition race. One side comes up with ways to defeat the other.

 

Yes, my bad. Brain fart.

And if you googled you'd see that the rotor turn rate is "tuned" to the expected radar system they're sent up against. Which will minimise returns.
Cutting-edge US stealth vs. Pakistani (largely ex-US Cold War period) radar? Not much of a contest.

 

But the rotation rates determine your lift, you can tune against a general band of radar fequencies, but it will never be exact. You'd get better protection just keeping low enough and using terrain analysis to get skirt known sites and use dead ground to hide in the clutter. The US has the most comprehensive supply of ground data.

I must admit that I'm finding it difficult to find anything to indicate that the RCS of the rotor blades themselves can be modified, and that's the part that returns the signature velocity components. I have found plenty about noise supression , but not radar suppression.

 

Er, you don't think extensive Elint would have been done before they even considered sending the helo in? They'd have known exactly which radars and frequencies they'd be facing.

There's not a lot available, just hints.

 

They might know the exact frequencies of the individual transmitters (I was amazed what a scientist from Qinetiq managed to dig out about one of our Rapier FSC systems), but the helicopter can't keep a constant rotational velocity. That's a factor that constantly changes as the lift requirement varies, though admittedly it will be within a small range of values.

I'm not saying that it's impossible. Just raising an observation that there are limits to what can be done with a helicopter because it has inherent identifing features. They were sufficent on the Rapiers to generate 'helicopter alarms'.