Stealth Helo

[Dame]

Radar signature considerations aside, can any passenger helicopter be relatively quiet I wonder?

Can helicopters be stealthy? Of course, there are a lot of details and nuances to this topic which, for understandable security reasons, are not likely to be available.

Will the U.S. Army's New Helicopter Go Stealth?

 

[JedisonsDad]

A lot of research has gone into making helos more and more quiet. Typically you add more blades to reduce the amount of air getting hit between rotors blades. Think of a 2 blade Huey versus a 4 blade Black Hawk. Also, there are devices/designs that can go on the very tips of the blades to help reduce the sound, as the tips are traveling significantly faster than the central hubs. But overall, nothing groundbreaking has been accomplished in the rotary world, like was accomplished in the fixed wing world with the YO-3 during Vietnam.

 

[DA SWO]

Radar signature considerations aside, can any passenger helicopter be relatively quiet I wonder?


Will the U.S. Army's New Helicopter Go Stealth?

View attachment 35905

Blades create a huge RADAR signature.

 

[Dame]

A lot of research has gone into making helos more and more quiet. Typically you add more blades to reduce the amount of air getting hit between rotors blades. Think of a 2 blade Huey versus a 4 blade Black Hawk. Also, there are devices/designs that can go on the very tips of the blades to help reduce the sound, as the tips are traveling significantly faster than the central hubs. But overall, nothing groundbreaking has been accomplished in the rotary world, like was accomplished in the fixed wing world with the YO-3 during Vietnam.

That's the sort of thing I was looking for.

ETA: Do coaxial rotors make this worse? Can they be counter rotated?

 

[policemedic]

 

[Kraut783]

Still wondering about this one.....



EDIT: I have not seen anything new about this unique helo used in the Abbottabad raid....we see pics of pieces of it, but nothing solid. Said to be a stealth version of a UH-60....

 

[JedisonsDad]

That's the sort of thing I was looking for.

ETA: Do coaxial rotors make this worse? Can they be counter rotated?

Coaxial rotors might help with RADAR cross section because you are removing a reflecting disk from an additional angle caused by the tail rotor, but the same could be done by going with a NOTAR system, which is essentially using the directed exhaust as the counter thrust. I don’t know how much RADAR would be effected by stacking the disks though. And I have no idea how coaxial rotors compare in noise level versus traditional rotors.

For clarification, I assumed you meant something along the lines of the Ka-52 when you said coaxial, rather than a MH-47 which is a tandem rotor.

 

[Dame]

Coaxial rotors might help with RADAR cross section because you are removing a reflecting disk from an additional angle caused by the tail rotor, but the same could be done by going with a NOTAR system, which is essentially using the directed exhaust as the counter thrust. I don’t know how much RADAR would be effected by stacking the disks though. And I have no idea how coaxial rotors compare in noise level versus traditional rotors.

For clarification, I assumed you meant something along the lines of the Ka-52 when you said coaxial, rather than a MH-47 which is a tandem rotor.

Yes, I was more thinking of the Sikorsky S-97. When I was searching for information, I found an interesting paper on just this sort of difference.
https://cdn.intechopen.com/pdfs/57483.pdf

 

[AWP]

A bit of history for everyone:
Air America's Black Helicopter

 

[Arf]

This is one of those topics that is going to be highly protected. If I were a Nightstalker I would stay away from this post.

I’m just a boat guy so for anyone one in the internets who reads these just learn that this is a airplanes dumb people speaking these post.

 

[AWP]

This is one of those topics that is going to be highly protected and the worst thing we can do is acknowledge that this is possible at all. If I was a Nightstalker I would stay away from this thread.

I’m a boat guy so for anyone one in the internets who reads these just learn that this is a airplanes dumb people speaking these post.

100% agree and the UBL raid was 9 years ago.

Think of what we learned and are capable of now.

I wouldn't want to be a target on the "X", but everyone's mileage may vary. Even "just" our 11B's would frighten me, but other elements? I'm all about peace, son. Shit...even Ft. Hood's body count rivals ST6. Imagine what they could do if deployed...

 

[Dame]

A bit of history for everyone:
Air America's Black Helicopter

Awesome article.

 

[Ranger Psych]

Coaxial rotors do counter rotate. That's how coax birds like the russians have can go faster than your average helo, and how a Chinook can fly faster than your average helo... they avoid the phenomena known as Retreating Blade Stall.

Losing a tail rotor for cross-section sake but gaining a larger main rotor probably doesn't do it any favors, and NOTAR's nice but it doesn't do well with FOD ingestion (or just sand/dust for that matter) and it also has reduced authority compared to a tail rotor, which can be a deal breaker if you need that authority to point things in directions quickly to go waaaaWAAAAAPSHEWPSHEW.