Assault on Bin Laden: mystery of the downed chopper

[quellish]

There is some speculation over at the dark lair of our dire enemies, militaryphotos.net ( ;D ), that the bird that went down was actually a custom built close support bird, possibly around the size of the Kiowa. AFAIR, the 160th did have a small number a of a 'stealthy' version of the OH-58 (can't remember the exact designation at the moment) up to around the mid-90's (budget cuts), although that was apparently an infiltration and retrieval platform rather than armed support (no weaponry was normally fitted, IIRC). However, I believe that the general consensus over at our mortal foes is, for the moment, the same as over here, i.e. the crashed bird was a stealthy variant of, or a inflitration optimised design derived from, the Blackhawk.

I thought ATS were the mortal foes, and MP.net was neutral.
There was a "stealthy" Kiowa, but it was never produced:
http://en.wikipedia.org/wiki/File:OH-58X.jpg

The horizontal tail of the mystery aircraft seems to be in a very different position than on a Blackhawk. Of course, we're looking at a jumble of broken parts, so who knows.

 

[Grey Havoc]

I thought ATS were the mortal foes, and MP.net was neutral.

I'll update my recognition files. ;D

There was a "stealthy" Kiowa, but it was never produced:
http://en.wikipedia.org/wiki/File:OH-58X.jpg

The horizontal tail of the mystery aircraft seems to be in a very different position than on a Blackhawk. Of course, we're looking at a jumble of broken parts, so who knows.

No that's not the version I was thinking of. Now what was it's designation. Arrrgh!

 

[Mat Parry]

In Ed Lovick's excellent book "RADAR MAN" he briefly mentions some work he was involved with in looking at reducing RADAR returns from helicopters. As I recall, the gist was that with even numbers of blades on the main rotor and when spinning at the correct RPM (blades rotational frequency had to match the frequency of a hostile RADAR signal) a receding blade and its opposite approaching blade could combine to result in a kind of cancellation of the RADAR signal.

Obviously the application of this phenomena is limited, however anything Mr Lovick worked on is intensely interesting.

As I've pointed out before Mr Lovick finishes his book

THE END *


* for now

(maybe he'll be able to write another chapter soon)

 

[TomS]

There was apparently a batch of about 18 OH-58D ""Optimized Aircraft" that had some very minor stealth features (coated windscreen, a re-profiled nose, and RAM boots to cover the rotor joints). I had thought that they went to TF118, the unit of armed Kiowas for Operation Prime Chance in the Persian Gulf, but it looks like this wasn't so. Perhaps they went to TF160?

http://www.vectorsite.net/avb206.html#m4

The attached photo is of the OH-58X, which may be the same or may not. I remember seeing a more operational-looking image of the "stealth" OH-58 that had a more faceted nose and the usual low-reflectance paint. But you can see the boots and gold-tinted windscreen.

 

[Grey Havoc]

There was apparently a batch of about 18 OH-58D ""Optimized Aircraft" that had some very minor stealth features (coated windscreen, a re-profiled nose, and RAM boots to cover the rotor joints). I had thought that they went to TF118, the unit of armed Kiowas for Operation Prime Chance in the Persian Gulf, but it looks like this wasn't so. Perhaps they went to TF160?

Bingo! 'OH-58D OA / Optimized Aircraft' was the designation I was trying to think of. The 'later' OH-58X was a separate program (probably the company OH-58D Variant demonstrator).

 

[blackstar]

I recently read an article in a helicopter magazine (I forget which one) about the Papillon Whisper Jet, a modified S-55QT helicopter that was specially modified by the company owner for quiet operations over the Grand Canyon. Can't find much online, but here's a photo:

http://www1.airliners.net/photo/Papillon-Grand-Canyon/Sikorsky-S-55QT-Whisper/0918375/

It's not a pretty helicopter.

As I remember, the designer added a rotor blade, altered the blade tips, and put a heavy-duty muffler over the engine. He also did something with the tail rotor. They served to significantly reduce the noise. The company owner was a pilot and inventor and he said that he had a hard time convincing anybody in the helicopter industry of the need for quieter helicopters, so he built his own. He knew that noisy helicopters over a national park would put him out of business.

 

[Abraham Gubler]

The horizontal tail of the mystery aircraft seems to be in a very different position than on a Blackhawk. Of course, we're looking at a jumble of broken parts, so who knows.

Its in the same position as the Black Hawk relative to the counter torque rotor. Just that this helicopter has a large fairing extending aft from the horizontal tail. Which could possibly hold a Black Hawk folded back tail wheel for retraction.

 

[sublight]

Martha Raddatz of ABC news talked about the raid and said "The Blackhawk assault helicopters were in a stealth configuration" on the broadcast this evening. She doesn't usually embellish so I am thinking somebody at the Pentagon used that specific verbiage to her.

 

[LowObservable]

Blackstar - I took a flight on that thing. IIRC it still had the recip engine, and the slowed rotor was a big part of the concept.

 

[blackstar]

Blackstar - I took a flight on that thing. IIRC it still had the recip engine, and the slowed rotor was a big part of the concept.

The article mentioned that Papillon's owner flew it at Heli-Expo and had it hover over the entrance for over 30 minutes. Dunno what year, but it was in the last 15 years or so. He was trying to make the point that quiet helicopters were possible.

 

[Abraham Gubler]

The article mentioned that Papillon's owner flew it at Heli-Expo and had it hover over the entrance for over 30 minutes. Dunno what year, but it was in the last 15 years or so. He was trying to make the point that quiet helicopters were possible.

I had an MD Explorer hover over me a few weeks ago. So much for NOTAR being quiet it was like a hair dryer pointed right at you. Which kind of explains the system apart from the Coandă effect and all that.

 

[quellish]

Blackstar - I took a flight on that thing. IIRC it still had the recip engine, and the slowed rotor was a big part of the concept.

The article mentioned that Papillon's owner flew it at Heli-Expo and had it hover over the entrance for over 30 minutes. Dunno what year, but it was in the last 15 years or so. He was trying to make the point that quiet helicopters were possible.

Jane's has a blurb on it:
http://articles.janes.com/articles/Janes-Helicopter-Markets-and-Systems/Whisper-Jet-Sikorsky-S-55QT-United-States.html

I beleive he also started or owns Blue Hawaiian Helicopters, which may have also been Papillion at some point. They now operate the Eco-Star helo, which was designed to be quieter than the A-Star. Spend time near them though and you'll realize that from a number of aspects they're noticeably louder than the A-Star.

At some point during the 90s Hughes was showing off a quieting kit for the 500.

There was an AWST article in the early-mid 90s (1993-1996?) which talked about several different programs, including a helicopter with a variable diameter rotor (it was depicted as a spiral, as I recall. I believe the same issue had the first drawing of the Darkstar planform).

 

[blackstar]

I believe he also started or owns Blue Hawaiian Helicopters, which may have also been Papillon at some point.

They sold them off a few years ago.

 

[quellish]

WSJ reports that the mystery aircraft stalled in it's own vortex:

"One helicopter was badly damaged after hitting the ground hard in a "vortex" created by the high walls—a heart-stopping moment that encapsulated the U.S.'s biggest fears about the mission."

www.google.com/url?sa=D&q=http://online.wsj.com/article/SB10001424052748704569404576299500647391240.html?mod=rss_Earnings
(note: this link gives full access to the article if you follow the redirect)


I think it is important to note, however, that much of the reporting about the raid, and the helicopters, may actually be indirectly sourcing SPF. SomeNewsPaper or SomeReporter may reference stealth helicopters because they read about it on a site that was using SPF as a source. Take what you read with a grain of salt.

 

[Stuka]

The dreaded vortex ring state. UH-60 fastrope VRS video. "That's normal" lol

http://www.youtube.com/watch?v=tsDSvcEDCgg

 

[orko_8]

Comparing the photos of wreckage with the photos of H-60 and AH-64, my bet is on a highly modified AH-64..

 

[Stargazer]

It is more than likely that the destruction of the airframe resulted from not wanting sensitive stealth technology and avionics. However, Some people have raised the question of how the remains were carried away... it is a valid one I guess, but remember that one photo shows a completely burned out hull, so there may not have been much left in the end to carry.

As for me, I have three more puzzling questions:

1°) if the helo was shot down (or caught in a vortex, as some sources imply) what of the crew and how could they be safely evacuated before the crash?
2°) if the helo was THAT damaged by fire, why did U.S. soldiers leave the tail unit untouched? I know it was on the other side of the wall, but surely it could also have been destroyed before going...
3°) if the Pakistani population were so proud of their trophy, why did they cover it with a blanket instead of showing it off?

 

[Abraham Gubler]

1°) if the helo was shot down (or caught in a vortex, as some sources imply) what of the crew and how could they be safely evacuated before the crash?

Because it crashed while at low altitude and probably low speed. So the crash absorbing structure of the helicopter protected the crew.

2°) if the helo was THAT damaged by fire, why did U.S. soldiers leave the tail unit untouched? I know it was on the other side of the wall, but surely it could also have been destroyed before going...

It’s relatively easy to burn out a helicopter full of fuel with thermite grenades. As to the boom on the other side of the fence I think they had more important things to attend to.

3°) if the Pakistani population were so proud of their trophy, why did they cover it with a blanket instead of showing it off?

Because that would have been the Pak Army securing the site who did that. As to the competency of the site securing after the Army left with the boom that is the Pak Police and they were probably more concerned with keeping the peace rather than picking up bits of scrap metal that no one seemed to care about.

 

[LowObservable]

Stuka wins 2 internetz. Had the incoming helo done that + hit the fence with the tailboom the outcome would have been much like that.

To AG's comment, I would add that the clean-up crew anywhere in the world would be unlikely to say "'ere, guv, that's a funny looking 'elicopter we've got".

On Whisper Jet - it received an STC in 1999 and was demoed at Heli-Expo in January 2000. It was claimed that noise would be below 80 dB at a distance of 500 feet.

It had a five-blade main rotor and a redesigned tail rotor, and was powered by a Honeywell TPE331-10 engine. In the cruise, engine and rotor speed were reduced to 92 per cent of normal. (So no recip - but the engine was direct-drive, not a free turbine, and they said this gave them more flexibility over rpm).

More here....

http://verticalmag.com/control/news/templates/?a=16656

 

[Grey Havoc]

The layout of the tail rotor, based on available photos and reconstructions, reminds me a bit of the tail rotor of the Naval Frigate Version of the NH-90. Or am I mixing up my helicopters?

 

[Mat Parry]

Inevitably there are many questions.

Occams razor would dictate that helicopters with stealth technology were used to insert a SF team, and the mission occurred as discribed (and this is what I believe), however...?

1/ What is the range of these stealthy helicopters? (presumably enough to avoid in-flight refulling over Pakistan)

2/ How many helicopters were involved? (using occams razor, to avoid detection all would have to be stealthy)

3/ What is the troop carrying capacity of these helicopters? (clearly however many were used there was enough redundant carrying capacity to absorb the loss of one helicopter and still get all the troops, aircrew and OBL out)

The US had a long time to plan this raid, and any associated deception / capability masking tactic's.

Just for fun, donning tinfoil shower cap (NB// I don't actually believe this is what occured)
RQ-170 capabilities beyond eye in the sky? If the US had the ability to electronically invade Pakistan's air defence network / computer systems AND fool them into not seeing conventional helicopters and C130 Communication nodes flying in their airspace then this would be a capability that would be highly sensitive and as a result an elaborate deception plan may be required... such as deliberatley crashing a mocked up "stealth body kit" blackhawk as a "false trail" explanation of how the interdiction was achieved. Tinfoil cap off (but still close at hand)!

EDIT
typo corrected

 

[negoshi8or]

check this book for a good description of what the CIA did to quieten the Hughes OH-6 (page 239 onwards)

SPYCRAFT
The Secret History of the CIA’s Spytechs from Communism to Al-Qaeda
Robert Wallace and H. Keith Melton
Published by Penguin Group (USA) Inc

 

[blackstar]

I think it is important to note, however, that much of the reporting about the raid, and the helicopters, may actually be indirectly sourcing SPF. SomeNewsPaper or SomeReporter may reference stealth helicopters because they read about it on a site that was using SPF as a source. Take what you read with a grain of salt.

This is a good point, but it does not only apply to SPF.

Keep in mind that many reporters are not getting new information, but repeating something they read elsewhere, often without indicating the source. The result is that you can have five stories all repeating the information, implying that it is solid and factual, when in reality the first reporter got the detail wrong and everybody else has been repeating it. This echo chamber effect happens a lot.

 

[Deino]

Just found that "reconstruction" at the German FlugzeugForum .. sadly without a source !

Deino ???

 

[overscan (PaulMM)]

Not accurate, IMHO.


I'm pretty sure it just has 4 blades, judging from the notches in the central hub. The blades are bent out of position.

The shaping of the bulges certainly looks like stealth.

 

[flateric]

sadly without a source !

militaryphotos.net - and much more reconstruction attempts are there

 

[overscan (PaulMM)]

Rotated - this shows the other side from previous pic.

 

[overscan (PaulMM)]

Notice that the fins, vertical and horizontal, have no taper, so their leading and trailing edges are at the same angles.

http://www.militaryphotos.net/forums/showthread.php?197635-The-mysterious-helicopter-involved-in-the-Osama-Bin-Laden-raid&p=5624026#post5624026

Other reconstruction:

 

[TomS]

About helo numbers:

Everything seems to agree that there were two assault helos performing the fastrope insertion. That means they probably launched three assault helos in order to have a spare en route. THe spare would likely have turned back part way along the route, once it was clear that the two primaries were going to make it. These are our mystery birds -- presumably modified H-60s. Their capacity is right -- a dozen assault troops each with relatively light gear.

Reports also seem fairly consistent that some MH-47s also participated. They would likely be carrying the security force that would set the perimeter and cover the extraction. I'd expect that they landed somewhere not too far outside the compound after the assaulters went in (it looks like there was open space across the road). Each would also be carrying around a dozen troops, to leave room for assaulters during the extraction phase. Again, they probably launched three with the goal of having two on the ground during the operation.

So, the assaulters fast-rope in, do their job, and extract through the only easy route -- the main gate. They cross the road, board the exfiltration helos, and depart. The tail boom of the mystery helicopter appears to be on the other side from the main gate, so the assault team would have had to circle the compound to get to it and destroy it. Not a good idea under time pressure.

 

[tacitblue1973]

I'm pretty sure it would be at least 5 blades, there's a general rule of thumb to avoid 90 deg angles and the attendant double bounce radar reflectivity issues.

 

[Mat Parry]

Why use a mix of stealthy helicopters (assumed to be modified MH-60's) and non-stealthy MH-47's, kind of defeats the point of stealthing the MH-60's.

Stealthy MH-47's would seem to be stretching things too far even for me ;D

 

[Orionblamblam]

Why use a mix of stealthy helicopters (assumed to be modified MH-60's) and non-stealthy MH-47's,

Theoretically: stealthy chopper gets there first. Once the ruckus starts, when avoiding detection is no longer an issue, the more capable, less-stealthy choppers show up.

 

[Orionblamblam]

I'm pretty sure it would be at least 5 blades...

It is. Take a look at the half of the disk that's clearly visible: three notches are clearly visible. If there were four blades separated by 90 degrees, then if you colud only see half of a circular rim, you'd be able to see no more than two notches clearly, or one clearly and two right on the edge.

 

[Mike Pryce]

One thing that occurs is that there may be additional/other benefits from 'tricking out' a stealth helo.

A few years ago I spoke to the UK EH101 project manager and he pointed out that although the BERP rotors were designed for greater efficiency, and produced lower noise too, an unexpected advantage was they hugely reduced the likelihood of 'brownout' in hover/landing. He mentioned this included the insertion of troops - makes hovering safer so you can do it to reduced limits (e.g. at night), and inside the rotor disc (IIRC) the air is clearer, for the troops to see the ground etc.

So, although stealth may be a factor, maybe the 'tricked out' MH-60s (if so they be) were used because they offered additional attributes than low noise. Could explain why other, noisy, helos were used too, if they were.

 

[Deino]

;D

http://www.top81.cn/top81bbs/thread.php?cid=1&rootid=2989189&id=2989189

 

[Stargazer]

A daring and interesting stealth Black Hawk development has been imagined by David Cenciotti on his blog, and here it is, shown with a regular version for comparison. This has no value other than to add to the reflection on what a stealth Black Hawk could look like, it is not real nor supported by any substantial information:
http://cencio4.wordpress.com/2011/05/04/black-helo-down/

 

[Stargazer]

Here's my reinterpretation of what a stealthy Sikorsky CH-60 « Silent Hawk » could look like, using a profile I found at militaryphotos.net as a basis. I modified the nose's shape, made the landing gear retractable and removed as many appendices as possible for cleaner streamlining. I also added the tail fairing at the rear and blended the tail unit a bit more into the dorsal spine. Again, this image is purely hypothetical and should not therefore be taken as an authoritative source.

 

[flateric]

NASA/TP-2000-210083
AMCOM-AFDD/TR-00-A-007
Exploratory Investigation of Aerodynamic Characteristics of Helicopter Tail Boom Cross-Section Models With Passive Venting
Daniel W. Banks
Dryden Flight Research Center, Edwards, California
Henry L. Kelley
U.S. Army Aviation and Missile Command (AMCOM)
Aeroflightdynamics Directorate
Join t Research Program Office
NASA Langley Research Center, Hampton, Virginia
National Aeronautics and
Space Administration
Langley Research Center
Hampton, Virginia 23681-2199
June 2000

An exploratory wind-tunnel investigation was
conducted to determine the effectiveness of passively
venting two representative models of helicopter tail
boom shapes to reduce side force and down load during
simulated hover and sideward flight conditions. A
two-dimensional tail boom model with two different
cross-sectional shapes was used. One shape was oval,
representative of a UH-60 (medium size, single main
rotor helicopter with a tail rotor) tail boom, and the
other was a trapezoidal cross section, representative
of a potential low-observable shape.

Two 1/2-scale, two-dimensional models representative
of helicopter tail boom cross sections were
tested. Sketches and photographs of the models and
test apparatus are shown in figures 2 and 3. One
model, oval in cross section, was representative of a
UH-60 helicopter tail boom (fig. 2(c)) and the other
model with a trapezoidal cross section was representative
of an advanced low-observable configuration
boom (fig. 2(d)). Each model also had a simulated tail
rotor drive shaft cover (TRDSC) on the top.

 

[TomS]

Passive venting? Basically, building the skin out of mesh, right?

 

[fightingirish]

OBB, thanks for posting some info about "Stealthy Blackhawks" at your blog!
Link: http://up-ship.com/blog/?p=9714