Assault on Bin Laden: mystery of the downed chopper

Mr London 24/7

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Not new, our Dear quellish posted and discussed before:

http://www.secretprojects.co.uk/forum/index.php/topic,12597.msg260144.html#msg260144
 

LowObservable

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Morning all.

"Among the classified products produced under his Boeing tenure were the stealth helicopters involved in the raid that killed Osama bin Laden, which were based on technology developed for the Boeing-Sikorsky RAH-66 Comanche helicopter the Army had canceled."

http://airforcemag.com/Features/Pages/2019/February%202019/George-K-Muellner-1943-2019.aspx?fbclid=IwAR1LiPAHlWNTRBWZvCff1lzP6zYPJGPTmEZNA8vL7-hVITrEUT2KfDy8bIk
 

TomS

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Now, that is interesting, and certainly lends credence to the position that the Bin Laden raid helos were a new design (presumably with parts adapted from the S-70 and possibly other aircraft), rather than being simply Black Hawks with minor modifications.
 

Sundog

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TomS said:
Now, that is interesting, and certainly lends credence to the position that the Bin Laden raid helos were a new design (presumably with parts adapted from the S-70 and possibly other aircraft), rather than being simply Black Hawks with minor modifications.
IIRC, the original LHX program also looked at a small utility version, besides just the scout. My guess is they took that work and scaled it up to fit the Blackhawk's mechanical systems, so in a sense, mainly just the airframe was new, in a typical "Skunk works" fashion. Or should I say Phantom Works? ;)
 

Flyaway

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Sundog said:
TomS said:
Now, that is interesting, and certainly lends credence to the position that the Bin Laden raid helos were a new design (presumably with parts adapted from the S-70 and possibly other aircraft), rather than being simply Black Hawks with minor modifications.
IIRC, the original LHX program also looked at a small utility version, besides just the scout. My guess is they took that work and scaled it up to fit the Blackhawk's mechanical systems, so in a sense, mainly just the airframe was new, in a typical "Skunk works" fashion. Or should I say Phantom Works? ;)
Are you saying it was a Blackhawk under the skin just with a different body?
 

marauder2048

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Could they really have achieved meaningful acoustic reductions with such an arrangement?
 

LowObservable

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Yes, according to most responsible and authoritative reporting going back to 1987.
 

Colonial-Marine

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In my opinion abandoning the light utility variant of the LHX was a big mistake and certainly didn't help save the RAH-66 from the chopping block years later. I'm glad it seems something came from all that work at least.
 

LowObservable

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The two versions would have had the same engines and rotor system.

What would have been brought over to the LO Hawk would have been flight controls and blade aerodynamics.
 

marauder2048

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LowObservable said:
Yes, according to most responsible and authoritative reporting going back to 1987.
Despite the absence of available noise reduction options/retrofits
for the S-70/UH-60 family + derivatives (S-76 and S-92)?

With ever tightening noise regulations, you should have seen something by now.
 

LowObservable

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Not necessarily. LO generally involves compromises and the civil operator may not care enough about noise to accept them.

And then there's the rather obvious point that "quiet" in an urban, civilian environment is not the same as "quiet" when you're trying to get the jump on a twitchy foe in the middle of the night, in a mid-sized town in Pakistan.
 

TomS

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marauder2048 said:
LowObservable said:
Yes, according to most responsible and authoritative reporting going back to 1987.
Despite the absence of available noise reduction options/retrofits
for the S-70/UH-60 family + derivatives (S-76 and S-92)?

With ever tightening noise regulations, you should have seen something by now.
I'm not super familiar with helicopter noise regs, but it looks like the new, more stringent Stage 3 rules only apply to new helicopter types, so there may not be a pressing market for hushkits on existing aircraft.

Also, the lack of commercial S-70s might be a factor -- there really don't seem to be any true civilian users at all, just military and a few paramilitary or police users.
 

TomcatViP

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And the S-70 is heavier. Built for the military. Heavier, more lift (at eq. representative rpm), more noise. It would be like comparing an armored car with a Prius.
 

marauder2048

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LowObservable said:
And then there's the rather obvious point that "quiet" in an urban, civilian environment is not the same as "quiet" when you're trying to get the jump on a twitchy foe in the middle of the night, in a mid-sized town in Pakistan.
The CRH-60 has no acoustic reductions; is there a third type of "quiet" for CSAR?
 

RavenOne

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TomS said:
marauder2048 said:
LowObservable said:
Yes, according to most responsible and authoritative reporting going back to 1987.
Despite the absence of available noise reduction options/retrofits
for the S-70/UH-60 family + derivatives (S-76 and S-92)?

With ever tightening noise regulations, you should have seen something by now.
I'm not super familiar with helicopter noise regs, but it looks like the new, more stringent Stage 3 rules only apply to new helicopter types, so there may not be a pressing market for hushkits on existing aircraft.

Also, the lack of commercial S-70s might be a factor -- there really don't seem to be any true civilian users at all, just military and a few paramilitary or police users.
Yes there are a lot of former army UH-60A hitting the commercial marketplace ...in last few years.

And S-70i International Blackhawk entering service with likes of LA County FD, Polish Police etc

Here’s Heliops poster of all commercial UH-60A and S-70i

Cheers
 

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marauder2048

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TomcatViP said:
And the S-70 is heavier. Built for the military. Heavier, more lift (at eq. representative rpm), more noise. It would be like comparing an armored car with a Prius.
The S-92 has the same growth rotor blades as the UH-60M in part because they reduce approach noise.

But there's no gain in level flight and it's sort of the low-hanging fruit of acoustic signature reduction.

My suggestion is that the big gains you need to really improve survivability aren't attainable in a
derivative re-hosting of Black Hawk mechanicals/powertrain.
 

yasotay

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Of course most of the noise on a Blackhawk comes from the tail rotor. Followed closely at distance by the turbines, then the main rotor as you get closer. This is why I thought the very different tail rotor on the Bin Laden raid aircraft of interest.
 

TomcatViP

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True. Blackhawk are difficult to detect by sound only until you are to be overflown. Then the sound is very rough until the bird fly in the distance.

@Marauder: you are certainly right. With more power (ITEP) and redesigned blades, they might theoretically have to ability to gain a lower rotor diameter, hence lower tip speed. Something that will impact the high pitch part of the noise.
 

quellish

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yasotay said:
Of course most of the noise on a Blackhawk comes from the tail rotor. Followed closely at distance by the turbines, then the main rotor as you get closer. This is why I thought the very different tail rotor on the Bin Laden raid aircraft of interest.
As I would think most readers of this forum would know, RF stealth is based on directing energy away from the receiver. An F-117 is hard to detect because the energy sent to it is reflected elsewhere, with very little sent back to where it came from. The same amount of energy is at work.

Acoustic stealth is (conceptually) similar. In the Hawaiian islands there are many helicopter tour operators. For years several used A-Stars. Not too loud but you did hear them coming. A few years ago some of those operators switched to "eco-stars" - partly for noise reasons. When they are flying straight at you.... yeah they might be quieter. But when they are flying past you, are in the distance, are turning away from you, etc. they are VERY loud.

The sound energy is focused in specific directions. It ends up being quiet from some directions, much louder from others. The SHHHHH-60 probably works in much the same way. The tail rotor works to *shape* the noise signature. The bad guys do not hear the helicopter until it is too late.

What we saw of the wreckage of the SHHHHH-60 clearly shows UH-60 internals. The outer skin may have been too burned to draw useful conclusions about what the outer mold line may have looked like, but significant portions of the main rotor and transmission were clearly from recent UH-60 products. The lack of any significant changes to the main rotor/rotor head was very curious in light of the *extensive* changes to the tail rotor.
 

yasotay

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The rotor noise is a function of rotor speed (I believe) and is mostly generated off the tips of the rotor. So the faster turning tail rotor is propagating the sound fore and aft of the aircraft. Having been around Blackhawks for some time, i can tell you that you hear the tail rotor more pronounced than the main rotors even though on a quiet day you are likely to "feel" the low frequency of the main rotors near the same time. I believe this is why a MV-22 is very quiet compared to conventional rotorcraft in forward flight as the noise is propagating out the the side of the aircraft. In helicopter mode it is as loud as any helicopter I have ever been around.
 

Jeb

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Blackhawks also have that distinctive cadence to their rotor beats. I imagine that the redesign of the tail rotor for the SSSSHHHawk (whoever called it that, I salute you) is as much about changing up the sound signature as anything. Imagine if you were able to adjust a helicopter's sonic signature to something more indigenous to the area, so that local observers would think it's just another one of their own helicopters flying around? That's a lot cheaper than a full-on stealth treatment and it nets you the same result, which is getting by without setting off alarms.
 

Dynoman

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Interesting observations on stealth helicopter concepts from Vertical magazine. Covers the four signatures of radio frequency (RF), infrared (IR), acoustic and visual in the context of helicopter stealth.
https://www.verticalmag.com/features/hide-and-seek-html/
 

Dynoman

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I have not seen any good pictures of the main rotor blades that would indicate active rotor control techniques, such as harmonic pitch control (HHC) or individual blade control (IBC) through small outboard flaps on the main rotor blades. However, piezoelectric material or shape memory alloys could have been used in the MRB to actively reduce noise and vibration as these technologies were developed in the late 1990's. Blue Edge demonstrated both modified tip sweep and IBC technologies to reduce rotor noise. Maybe someone has better pictures of the MRBs to make an assessment. The rotor mast probably had some form of masking as well (like the anti-torque rotor) to reduce gearbox noise, possibly similar to the RAH-66 or S-92.
 

yasotay

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Main rotor hub that was standing in the middle of the wreckage appeared to be very much a standard H-60 rotor hub While there could have been much change to the blades they appear to have been mated to a standard hub.
 

marauder2048

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I suppose if these birds were always intended for SOF missions they may have traded off some of the
more exotic acoustic signature minimizations under the premise that these missions would have
planning times sufficient to accommodate (computationally) very expensive but high-fidelity acoustic route planning.

The AH-64E was supposed to have a real-time acoustic footprint display which when combined with the
offline stuff from the planners could provide a real boost to survivability.
 

500 Fan

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I have done a little research into the various experimental and prototype versions of the Hughes/MD500 and H-6 helicopters and a huge amount of the various technologies developed and tested by Hughes and McDonnell Douglas Helicopters between 1970 and 1990 have direct applications for use in an LO helicopter. Things like;

Development and flight-testing of quiet rotorcraft with the "Quiet One/500P and NASA/Rotonet 500E

Higher Harmonic Control (can allow the noise signature of the rotor to be "tuned")

Flight-testing of composite main and tail rotor blades

Experiments with fuselage constructed from composites

Reduced radar signature with systems like NOTAR (although not employed on the Bin-Laden Raider)

Expertise in engine exhaust IR reduction

When Hughes were acquired by McDonnell Douglas and the Phantom Works joined up with the expertise at Hughes, it certainly seems likely that they would have done some work on LO helicopters. The 1995 article in Aviation & Space Weekly seems to infer that MDHC might have had two different LO rotorcraft flying in the late 80's and early 90's. One might be an LO version of the MD500 and this might be the TE-K project that crops up on the web. What configuration the other helicopter was in is anyone's guess. Could the Bin-laden Blackhawk be based on this prior test work? Have a look at the topic over on the ARC Air Forum in the helicopter section on the Bin-Laden Raid helicopter. There are some interesting comments there that indicate that the helicopter used in Pakistan was a modified H-60.

In relation to the rotor system on the H-60 and in particular the S-92, it is anything but quiet! The SAR S-92 in Ireland lands at a hospital near where I live and I can hear it at least a solid minute before it appears as a dot in the sky. I'm not sure if disc-loading has anything to do with it but I read somewhere that the S-92 should really have been fitted with a 5-blade main rotor instead of a scaled-up system from the H-60.

500 Fan.
 

RavenOne

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500 Fan said:
I have done a little research into the various experimental and prototype versions of the Hughes/MD500 and H-6 helicopters and a huge amount of the various technologies developed and tested by Hughes and McDonnell Douglas Helicopters between 1970 and 1990 have direct applications for use in an LO helicopter. Things like;

Development and flight-testing of quiet rotorcraft with the "Quiet One/500P and NASA/Rotonet 500E

Higher Harmonic Control (can allow the noise signature of the rotor to be "tuned")

Flight-testing of composite main and tail rotor blades

Experiments with fuselage constructed from composites

Reduced radar signature with systems like NOTAR (although not employed on the Bin-Laden Raider)

Expertise in engine exhaust IR reduction

When Hughes were acquired by McDonnell Douglas and the Phantom Works joined up with the expertise at Hughes, it certainly seems likely that they would have done some work on LO helicopters. The 1995 article in Aviation & Space Weekly seems to infer that MDHC might have had two different LO rotorcraft flying in the late 80's and early 90's. One might be an LO version of the MD500 and this might be the TE-K project that crops up on the web. What configuration the other helicopter was in is anyone's guess. Could the Bin-laden Blackhawk be based on this prior test work? Have a look at the topic over on the ARC Air Forum in the helicopter section on the Bin-Laden Raid helicopter. There are some interesting comments there that indicate that the helicopter used in Pakistan was a modified H-60.

In relation to the rotor system on the H-60 and in particular the S-92, it is anything but quiet! The SAR S-92 in Ireland lands at a hospital near where I live and I can hear it at least a solid minute before it appears as a dot in the sky. I'm not sure if disc-loading has anything to do with it but I read somewhere that the S-92 should really have been fitted with a 5-blade main rotor instead of a scaled-up system from the H-60.

500 Fan.
Thanks 500Fan, very in depth analysis. So conceivably with regard to the Little Bird airframe .....could it resemble what The Aviationist theorised ...

https://theaviationist.com/2011/05/25/a-stealth-little-bird/

In the 1998 Stealth Special of the Air Forces Monthly (Key Publishing)...in the section on RAh-66 and low observable helos....there was rumour about LHX competition and then MDH had tested a stealthy NOTAR but the Army picked the Boeing Sikorsky RAh-66 Comanche design instead. However officially as far anyone’s concerned the RAH-66 first flew in 1996.

I see a parallel with the Northrop B-21 and mystery triangles , Northrop won. So many a guess to see if the other OEMs must have built some prototype demonstrator ‘May the best man wins’.

The fighter like single seat fromBell-MDH team looks quite cool...as depicted by then MDH artists . This can be found in the late Bill Gunstons Future Warplanes.

Cheers



Cheers
 

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