How Does The Stealth Helicopter Work?

[thinker_jeff]

Here is where my question comes from -

 

Quote from Yahoo News: "A picture of the tail rotor of the chopper that the Navy Seals' Team Six detonated revealed unfamiliar features. Reports say it could be a new, secret helicopter.

 

When the Team Six members reached Osama bin Laden's compound in Abbottabad one of the choppers made a "controlled but hard landing," according to reports, probably due to higher than expected temperatures.

 

Temperatures affects the density of the air, and low density makes it harder for the rotor to sustain the weight of the chopper, especially if it was near its maximum weight (being packed with soldiers and fuel to fly in from Afghanistan). Abbottabad is about 1200 meters above the sea level, and altitude also affects air density. (See pictures of the elite force which killed Osama bin Laden.)

 

So what machine exactly experienced the hard landing described above? Short answer: we don't know for sure. Long answer: It seems that the tail rotor visible in the picture belongs to a highly modified version of the H-60, the chopper of choice of the special forces for more than 30 years. Aviation Week doesn't beat around the bush, claiming: "A previously undisclosed, classified stealth helicopter apparently was part of the U.S. task force that killed Osama bin Laden in Pakistan on May 1."

 

Link: http://news.yahoo.com/s/time/httpnewsfeedtimecom20110504couldthebinladenraidhaverevealedasecretnewhelicopterxidrssfullnationyahoo

 

 

 

[Airbrush]

I heard in the news this stealth chopper has more rotor blades which makes it quieter.

[thinker_jeff]

For the mission like this low noise is not enough. The low radar visibility was essential to pass through the defense system of Pakistani air force.

 

My knowledge about Stealth Airplane is very limited. It sounds that the shape of the Airplane and the coating on the surface are two of the most important features. B-2, F-22 and F-35 are the best examples for such features. However, to helicopter, the rotor blades may be the most visible parts by radar because they rotate to all the directions. Therefore, you cannot hide the blades by the shape but only can reduce the surface reflection by coating. The question is: is that enough to be Stealth Helicopter?

 

I'm waiting for a better explanation than mine.

 

 

 

[Airbrush]

Maybe the "stealth" chopper needs to fly under the radar?

[Brainteaserfan]

Maybe this will help.

 

http://webcache.googleusercontent.com/search?oe=UTF-8&hl=en&q=cache:kL7aKmOT9nYJ:www.bellinghamherald.com/2011/05/09/2006966/how-stuff-works-how-stealth-helicopters.html

[AlphaSheeppig]

In terms of radar invisibility, the blades need not be the classic airfoil shape. They can be angular or diamond shaped, which ruins their aerodynamics, but deflects the radar. You just put on a bigger rotor and more powerful engine, and it makes up for the reduced lift from the rotors. Look at the F-117, which is shaped such that it reflects radar, no matter which direction it comes from. There is no reason why you couldn't apply the same principles to a helicopter. The pics I've seen seem to show some sort of sharp corner on a surface of what seems to be a rotor blade. A big no-no in subsonic aerodynamics, because it reduces the lift and increases the drag drastically, but it would greatly reduce the radar cross section of the rotor blades. The tail rotor, which is much more clearly shown in pics, seems to be masked, and has stumpy blades with a very short chord - basically taking a minimalist approach. The helicopter must be a real bitch to control, but I guess that wasn't really one of the designers' priorities...

[thinker_jeff]

In terms of radar invisibility, the blades need not be the classic airfoil shape. They can be angular or diamond shaped, which ruins their aerodynamics, but deflects the radar. You just put on a bigger rotor and more powerful engine, and it makes up for the reduced lift from the rotors. Look at the F-117, which is shaped such that it reflects radar, no matter which direction it comes from. There is no reason why you couldn't apply the same principles to a helicopter. The pics I've seen seem to show some sort of sharp corner on a surface of what seems to be a rotor blade. A big no-no in subsonic aerodynamics, because it reduces the lift and increases the drag drastically, but it would greatly reduce the radar cross section of the rotor blades. The tail rotor, which is much more clearly shown in pics, seems to be masked, and has stumpy blades with a very short chord - basically taking a minimalist approach. The helicopter must be a real bitch to control, but I guess that wasn't really one of the designers' priorities...

Thanks for understanding my question.

The approach you explained should help to reduce the radar visibility. But, I still question if it can be as good as the F-117.

Mathematically, a curved surface can reflect radar wave back more than a flat surface unless the flat surface right agaist the radar. This is one of the reasons that a fixed-wing aircraft can be designed invisible by radar. The helicopter has to rotate its blades so that you must create a envelope of the blades all the time. This envelope is curved, no matter how you design it.

Edited May 31, 2011 by thinker_jeff

[AlphaSheeppig]

But, I still question if it can be as good as the F-117.

The F-117 is really in a class of it's own. They say bats fly into it at night because their echolocation can't pick them up...

 

It's not really any curved surface that is a problem, but rather concave surfaces, since these tend to reflect the radar waves straight back. In general, with modern stealth aircraft (now I'm talking along the lines of the F-35 and F-22), the approach is more to eliminate the concave surfaces (such as where the wings meet the fuselage) by blending these with a flat surface, or by making it a sharp corner. These have the disadvantage that at some critical angle they reflect the radar waves straight back, but if the angle is even slightly off, then the radar is deflected enough to be invisible, if it is detected, it would be pretty small, and would maybe be mistaken for a flock of birds or something. I guess it could possibly be the same with the rotor blades... If the rotor blades were made of a composite material such as carbon fibre (which is very likely) then they are semi-transparent to radar to start with...

[thinker_jeff]

The "concave surface" is better wording.

Another question - if the aircraft surfaces were made of transparent materials to radar and the internal materials were radar visible, is it the aircraft still visible to radar?

[raghavendrabsrg]

Guys Guys, chill.. i think the pakistan government does not have a good RADAR system ( or the radar watching guy was asleep).

 

Coming to the technology part,

Firstly: the kind of terrestial radar's that are used normally by any military will not be able to detect any low flying object

Secondly: yeah the coating helps to be invisible to RADAR.

Thirdly: I think the american helicopters rotors were tuned and modified just to reduce the sound levels.

Fourth: If the body of helicopter is "sharply" made, like the "APACHE".... RADAR signatures are reduced.. and as far as the MAIN ROTOR is concerned, if you see it in the "front view" the rotors are actually "flat".. so no problem with the RADAR.... (but if sophisticated spherical dome waveform RADARS were to be used.. then it would have been a problem..)

 

 

Conclusion: if you cant find the demon anywhere in the planet!! try searching in pakistan. "Anyone who is in pakistan is unsafe!!(osama)" LOL.. "anyone in INDIA is totally safe(Ajmal kasab- te terrorist involved in the mumbai attack)