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Post Info TOPIC: Low-observable Rotorcraft


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Date: Apr 3, 2012
Low-observable Rotorcraft
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I've been trying to think of what general design principles could be used to make a truly low-observable (stealth) rotorcraft. Let's try to think up one, shall we? Here's a very basic (un-manned) concept that I sketched out roughly. The top picture is the basic overall shape and the bottom picture is a cut view of one side of the LO rotorcraft as seen from the front.

Might be hard to understand, but I might make improvements later.

It's a counter-rotating design, by the way, with a stealthy F-117-style grid on the top and the bottom to shield the blades from radar.



-- Edited by Kryptid on Tuesday 3rd of April 2012 09:43:10 PM

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Date: Apr 4, 2012
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What? You're doing it all wrong! This is what an LO rotorcraft should look like!  biggrin

boeingsikorsky-rah66-comanche_12.jpg


Nuff said!



-- Edited by Flyboy on Wednesday 4th of April 2012 05:27:38 PM



-- Edited by Stingray on Monday 10th of June 2013 04:25:32 AM

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Date: Apr 4, 2012
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The Comanche may have been stealthier than a conventional helicopter, but I don't see the big spinny rotor on top being very conducive to maintaining a low radar cross-section when compared to something like a B-2 or F-22.

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Date: Apr 4, 2012
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Generally I can't think of a rotorcraft being a practical stealth aircraft at all. Wouldn't the large blade radius (shrouded or not) create an equally large signature? As opposed to smaller lift-fans, or lift jets... at least those could be concealed in mid-flight as a compound aircraft, giving it smooth stealth without a huge rotor creating a signature. :P



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Date: Apr 4, 2012
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fluttercopter wrote:

 As opposed to smaller lift-fans, or lift jets... at least those could be concealed in mid-flight as a compound aircraft, giving it smooth stealth without a huge rotor creating a signature. :P


 

Now what about in hover mode? In which case your concept of 'concealed' lift systems would have to be in use, thus creating a large radar and IR signature, easily detectable. Correct me if I'm wrong, but I believe the mindset on a 'stealth rotorcraft' is having a VTOL aircraft that takes advantage of more versatility than a conventional fixed-wing, while maintaining a low radar signature! aww

With a rotor system, yes I can agree on the problem there. While the problem of an external rotor's emission is somewhat fixed by Kryptid's shrouded coaxial system, there's still another problem. The skin of a rotorcraft emits very high vibration due to the rotor and other moving parts. While still being steps ahead of a 'conventional' stealth rotorcraft (RAH-66), it still won't reach that of fixed-wing designs as the B-2.



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Pepper wrote:
fluttercopter wrote:

 As opposed to smaller lift-fans, or lift jets... at least those could be concealed in mid-flight as a compound aircraft, giving it smooth stealth without a huge rotor creating a signature. :P


 

Now what about in hover mode? In which case your concept of 'concealed' lift systems would have to be in use, thus creating a large radar and IR signature, easily detectable. Correct me if I'm wrong, but I believe the mindset on a 'stealth rotorcraft' is having a VTOL aircraft that takes advantage of more versatility than a conventional fixed-wing, while maintaining a low radar signature! aww

With a rotor system, yes I can agree on the problem there. While the problem of an external rotor's emission is somewhat fixed by Kryptid's shrouded coaxial system, there's still another problem. The skin of a rotorcraft emits very high vibration due to the rotor and other moving parts. While still being steps ahead of a 'conventional' stealth rotorcraft (RAH-66), it still won't reach that of fixed-wing designs as the B-2.


 

You don't have to be sarcastic, besides you just basically proved my own point in the end! evileye



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Date: Apr 4, 2012
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Cool concept, Kryptid! I think it might work having those concealed rotors. But what if you made it manned? How would you apply the same concept to a manned system without modifying it to accomodate as such? Just wondering.



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Date: Apr 5, 2012
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I've thought about how to make a manned version, but haven't done anything more with it than simple sketches. I know there are likely problems to be hammered out. Obviously, the grid would interfere with the airflow to the rotors so I imagine the thrust would be lower and specific fuel consumption higher. Achieving thrust for forward flight could be problematic unless one were to fit a dedicated turbofan in it. Channeling exhaust gases from the turboshaft probably wouldn't produce much usable forward thrust since the majority of the engine's power is used to turn the rotors. Perhaps some method of bleeding off rotor wash to generate forward thrust could work if I thought about it.

I suppose the Avrocar might be one of the best analogies I could go by. With modern flight-control systems, something like that might actually be feasible today. I believe the rotor would need to be larger than in the Avrocar in order to be closer with conventional helicopters in terms of specific fuel consumption.

Vibration is an interesting consideration, and I'm not currently well-versed in how much this affects radar cross section. I do see how that could be of concern when attention to detail is paid; stealth is largely determined by shape, and tiny changes in shape due to vibration could affect that.

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Date: Apr 5, 2012
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Kryptid wrote:

The Comanche may have been stealthier than a conventional helicopter, but I don't see the big spinny rotor on top being very conducive to maintaining a low radar cross-section when compared to something like a B-2 or F-22.


Well for your information, the Comanche actually had a radar cross-section the size of that of a 'small bird' (so I have been told). And the YF-23 for example, had a radar cross-section the size of a 'spider' (so I've heard). So, there's not much in it, is there?



-- Edited by Flyboy on Friday 6th of April 2012 11:14:51 AM

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If true, that's impressive. I imagine that the RCS of a helicopter is constantly changing as the blades spin, though. I wonder if it still maintains a similar level of RCS when the blades are in their worst and best radar-reflecting positions.

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Date: Apr 6, 2012
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Flyboy wrote:
 
Kryptid wrote:

The Comanche may have been stealthier than a conventional helicopter, but I don't see the big spinny rotor on top being very conducive to maintaining a low radar cross-section when compared to something like a B-2 or F-22.


Well for your information, the Comanche actually had a radar cross-section the size of that of a 'small bird' 


Actually not! Many reliable sources (including globalsecurity.org) say its cross-section is almost less than that of a Hellfire missile. The "small bird" claim sounds like an exaggeration, since these weapons give off a pretty obvious signature when launched. :P



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Date: Apr 8, 2012
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Oh no! Have I been owned by Leela!? Well let's just say that less than half the size of a Hellfire missile is still damn impressive for a helicopter. But the 'small bird' claim came from a guy who I have spoken to who worked on the Comanche program. He seems like a really sincere guy and I never sensed any hint of him feeding me inaccurate info. Why would he? He's moved on now and would have nothing to gain for exaggerating.

But to be fair, I don't think that either of us can claim supremacy as there is a lot of misinformation about the Comanche, even on so-called reputable sites.

Oh, and how dare you question your master!?  biggrin



-- Edited by Flyboy on Sunday 8th of April 2012 11:12:58 AM

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