Unkowns stealth helicopter downed in Bin Laden raid

[gunnergoz]

It seems from the photographic evidence that the helo that the US spec ops people lost during the raid had a very different pedigree from known aircraft.

This link http://www.aviationweek.com/aw/blogs/defense/index.jsp?plckController=Blog&plckBlogPage=BlogViewPost&newspaperUserId=27ec4a53-dcc8-42d0-bd3a-01329aef79a7&plckPostId=Blog%3a27ec4a53-dcc8-42d0-bd3a-01329aef79a7Post%3a275902dd-e7a2-40fd-ab78-d46e3bf922b1&plckScript=blogScript&plckElementId=blogDest and others have photos that lead me to believe that the downed bird may have been some sort of extensively modified MH-60 variant never seen before.

I was a maintenance officer on naval H-60's at one time and see the similarities but at the same time, this a/c has Skunk Works (or a similar secret sweat shop) written all over it.

[Magpie_Oz]

Perhaps they should have worked on the engine more than stealth ?

Why would they need a stealth helicopter?

The Pakistanis knew they were there and OBL doesn't have a lot of air search radars, or if he did spotting his house would have been pretty easy.

[Stalins Organ]

The engine didn't fail mechanically - it apparently stalled due to the complex wash generated by its own rotors ansd the high walls.

Turbine engines do this occasionally - even big jet engines - it can create a massive "backfire" & seriously damage an engine. Turbulent airflow into an engine can be a factor so a lot of design work goes into smoothing the airflow into the engine to prevent it.

I don't have any personal knowledge of such a thing happening, but it doesn't seem outlandish to me that a helicopter coming into a complex airflw envirnment might suffer a compressor stall, and have no room to recover before hitting the ground too hard.

[Magpie_Oz]

The engine didn't fail mechanically - it apparently stalled due to the complex wash generated by its own rotors ansd the high walls.

Turbine engines do this occasionally - even big jet engines - it can create a massive "backfire" & seriously damage an engine. Turbulent airflow into an engine can be a factor so a lot of design work goes into smoothing the airflow into the engine to prevent it.

I don't have any personal knowledge of such a thing happening, but it doesn't seem outlandish to me that a helicopter coming into a complex airflw envirnment might suffer a compressor stall, and have no room to recover before hitting the ground too hard.

True enough but I am thinking that for all the money spent on making it invisible to radar, which they didn't need, they could have perhaps worked on the engine airflows or what have you, that they did need.

[gunnergoz]

True enough but I am thinking that for all the money spent on making it invisible to radar, which they didn't need, they could have perhaps worked on the engine airflows or what have you, that they did need.

I think the purpose of most of these modifications was probably noise and heat abatement, not necessarily radar "invisibility." It's almost impossible to mask spinning helo blades from radar, at least as much as you can say, a fuselage. Its much easier just to jam radars and that may in part be the purpose of the weird dome structure on the end of the vertical tail, just above the tail rotor hub. But a relatively quiet helo with a low infrared signature would be worth its weight in gold in some scenarios like this one.

As to "engine airflow", it is a complex enough subject with turbine engines but a well known one anyway. I doubt that intake issues were at fault here. The problem with rotary wing aircraft near the earth is that the cushion of air under the aircraft can be disrupted due to environmental factors like high walls and then flight characteristics can go sideways in a hurry. Once you lose lift, or a substantial portion of it, the helo drops like a rock. One web source I saw is theorizing that there was a lot of heat buildup in the confines of the walled-in courtyard, sufficient to cause a differential in the lift generated by the blades once the a/c was over the yard. Could be.

[Affentitten]

Why would they need a stealth helicopter?

The Pakistanis knew they were there .

Nope.

From BBC

Mr Panetta said the Pakistani government was also not informed of the operation in advance because the CIA feared that word of it might have been leaked.

"It was decided that any effort to work with the Pakistanis could jeopardise the mission. They might alert the targets," he told Time magazine.

[gunnergoz]

The LAST people to be informed would have been the Pakistanis. They've sheltered Bin Laden for years, why forewarn them and let him bug out before we get there?

[abneo3sierra]

Aff and gunner beat me to it, yes, the Pakistanis were not informed, and were probably even quite misled.

[dieseltaylor]

The "Pakistanis" - the quote is actually "the Pakistan Government were not informed of the operation in advance" which is a different meaning to the Pakistans were not aware that the US had found the target.

Or to be more precise sections of the Pakistan intelligence service might have known more than their Government. ....

Now does anyone but me find calling the target Geronimo a little bit too reminiscent of "the only good injun is a dead injun". Would it have been better to go for a neutral name like Pacific or is that frowned upon in military circles.

Secondly I really do think that the US heads goggle-boxing whilst the raid occurred to be an unfortunate photo. It can be seen as macabre. Alternatively that there was nothing better to do in running the country. Or there was long range quarter-backing going on. My preference would be that the world is told " the President was advised that the operation had been successful".

But am I being sensitive to image management?

[Affentitten]

Secondly I really do think that the US heads goggle-boxing whilst the raid occurred to be an unfortunate photo. It can be seen as macabre.

Although the White House was connected to real-time information during the raid, neither Mr Obama nor Mr Panetta saw bin Laden's shooting as it happened, Mr Panetta told PBS in a separate interview taped on Tuesday

[gunnergoz]

"Geronimo" was the historical battle cry of US WW2 paratroopers, usually yelled out as they left their aircraft. I think there's reason other than "good injun is a dead injun" for using the phrase in a spec ops context. It's unique, an easy word to discern and not something the locals are likely to understand or come up with in advance. However, those who like to attach arcane meanings to everything the military does, will likely agree with you.

[womble]

I thought code words for things were randomly assigned these days. I know they are for ops.

[Affentitten]

I sense a conspiracy given that the word "Geronimo" has been used repeatedly in the last series of Doctor Who.

[dieseltaylor]

I know of its history of "Geronimo" in the US Army. : ) Perhaps it was remiss of me not have indicated the use in my original post but then I assume we are all grogs enough to know!!!

I will bear it in mind for the future. However on the basis that most of the world will not know its Army use it does mean the name does have a significance in the white US Army going out killing Indians even in fact this guy was Arab. Great of course for US audiences but not subtle.

The Doctor Who connection of course explains a lot.

*P.S. Geronimo was not killed by the US army but died of old age.

[Vanir Ausf B]

I rather doubt any "audience" was in mind when they chose the code word. I think you're reading a whole lot into it that was never even considered.

[dieseltaylor]

VAB - I am positive you are right.

However it is beginning to get a little murky with the new story. It irks the hell out of me that getting wrong stories out quickly seems more important than the correct story in due time.!!! Who the hell is responsible for the "stories".

I had looked up the helicopters for payload and range as I was wondering what fallback plans were in place. However given the huge range of variants I was at a bit of a loss!.

[Michael Emrys]

The engine didn't fail mechanically - it apparently stalled due to the complex wash generated by its own rotors ansd the high walls.

I wonder if the same thing happened as did to those Ospreys that crashed a few years back. Namely, rapid descent into their own downwash column caused a catastrophic loss of lift. Making an assault landing might increase the likelihood of this happening.

Michael

[gunnergoz]

I wonder if the same thing happened as did to those Ospreys that crashed a few years back. Namely, rapid descent into their own downwash column caused a catastrophic loss of lift. Making an assault landing might increase the likelihood of this happening.

Michael

As far as I can tell from a bit of wiki'ing, the April 2000 V-22 crash was caused by vortex ring state, which is pretty much what it looks like happened here with this new bird. Other V-22 crashes were for other, usually mechanical problems.

Interestingly, the V-22 is said to suffer less from vortex ring state than other rotary wing platforms. However, at the height and under the conditions this accident seems to have happened with in Pakistan, no rotary wing a/c could have readily avoided crashing once the right conditions appeared.

What is really a testament to modern construction is the fact that it seems that no one was killed during this apparent very hard landing. I know that seats in particular are made to cushion hard landing impact forces. In this case, the design (and perhaps a bit of luck) also managed to keep the main rotors from hitting the ground and shredding everything and everyone in the compound. That makes me think that the fall was short - perhaps 2-3 meters at most, and was partly cushioned by the impact of the rear fuselage against the wall (thus cutting off the tail rotor section and horizontal stabilizers) and also by the landing gear. There is one recent satellite photo taken of the compound and it fairly clearly shows the 4-bladed main rotors were burned in a normal pattern, and not broken up all over the place as they would have been had they impacted the ground while still turning. An H-60 type has a very wide, flat belly and this would have tended to keep it from rolling over once it landed.

Regardless, it must have been a very hairy moment for all involved and that they made it out and completed the mission is a real testament to the team's professionalism.

[SD Smack]

Vortex ring state or settling with power is a condition that results from a rotory-wing aircraft settling into its own downwash. Normally the induced flow from the blade (downward wind created by the blade as it creats lift) is highest at the blade tip and decreases along the blade as it nears the center of the disk. When entering a near vertical descent the induced flow near the center of the disk can actually become up flow (wind velocity is now up through the disk). There is still induced flow at the blade tip and some portion inward from there. If there is not enough power to slow the descent then the point along the blade where the induced flow and up flow meet cause vortex rings to form along the blade span. These vortices, which form normally at the tip of the blade, are now occuring along the blade itself causing a loss in lift.

The only way to get out of settling with power is to transition into lateral flight and based on the way the compound looked they may not have had the room to do that...but that is only speculation, I wasnt there, and I dont know what really caused the aircraft to crash/land hard.

Steve-o