Pakistan Helo Crash Question

[Crusty]

Never having had the pleasure of helicopter groundschool, what is this helicopter stall thing the media is talking about in the Bin Laden capture? Can downwash be reflected back up in a confined space and radically modify airflow on a rotor?

[ipilot54]

It is being reported tonight that the rotor came in contact with a cement wall and "exploded" during landing. It did not specify which rotor but it is plausible; tight confines. My first thought this morning was it took ground fire as that was being reported first thing.

All said, the media will not be too reliable so lord knows what happened.

[bizjets101]

I've heard several versions, we'll see how it plays out, but here's a photo in the court yard.

[iflyforpie]

Never having had the pleasure of helicopter groundschool, what is this helicopter stall thing the media is talking about in the Bin Laden capture? Can downwash be reflected back up in a confined space and radically modify airflow on a rotor?

What it sounds like is 'power settling' or 'vortex ring state'. Vortices come off the rotor tips much like a wing from induced drag, but it forms a donut shaped region of turbulent airflow around the rotor disc with downgoing air on the interior side of it.

If the helicopter has low forward velocity and has a high rate of descent while carrying lots of power, the downgoing air in the vortex ring will be accelerated to the point where the helicopter is unable to stop decending.


What I think they are confusing it with is 'retreating blade stall' which results from high forward speed where the retreating blade can no longer compensate for disymmetry of lift by increasing angle of attack without stalling.

[Crusty]

Thanks Pie

I've heard of that 'vortex ring state' before but it was on one of those discovery channel nascar crash/police chase/airshow explosion mashup type shows so I didn't know if it was real.

[burhead1]

[sky's the limit]

Very difficult to say at this point.

Could it have been VRS? Sure. Under NVG I can see it happening, but it wouldn't be my first choice in this scenario with a machine such as that. Settling with power? Same.

Impact with a building or terrain? Again, sure. But once again I'd be surprised unless they were actually dropping guys on the ground. If it were a fast rope or rap situation I'd find it surprising.

My bet at this point would be RPG or small arms which are the bain of helicopter existence over there. It'll be interesting to hear what comes of it.

stl

[grimey]

How do you crash the helicopter like that with no injuries, or at least no major ones? Damn lucky on the part of those onboard.

[sky's the limit]

How do you crash the helicopter like that with no injuries, or at least no major ones? Damn lucky on the part of those onboard.

VERY lucky, considering nobody in the back would have seat belts on, just tethers. Maybe everyone was out and it was shot down, who knows at this point.

stl

[Inverted2]

I hear it got tangled up in Osamas clothesline.

[bizjets101]

Navy Seals reportedly torched/blew up helicopter before departing . . .

[Beefitarian]

That's a small dose of reality there. It's obviously still a hot zone post Osama.

[airway]

This is from a press briefing at the White House:

http://www.whitehouse.gov/the-press-off ... -bin-laden

During the briefing the officials say "During the raid, we lost one helicopter due to mechanical failure", but later when the press are asking questions, they say this:

Q Yes, hey, how are you doing? My question would be, what was the type of the helicopter that failed? And what was the nature of that mechanical failure?

SENIOR ADMINISTRATION OFFICIAL: Can’t go into details at this time.

SENIOR ADMINISTRATION OFFICIAL: We didn’t say it was mechanical.

[Expat]

The reaction here? Show me the photo of dead OBL, then I will begin to think it is not just a political ploy to justify drawdown in Af, and secure re election...

[Blakey]

Even more interesting than "what happened", are the questions being asked over at MilitaryPhotos.net about just what kind of helicopter this was. Nothing I've ever seen before.

http://www.militaryphotos.net/forums/sh ... Laden-raid

That's why it all got trucked away under tarps. Somebody has some nice new toys they didn't want us to see!

[bizjets101]

No mystery to me, just a tricked out UH-60 Silent Hawk variant . . .

[Blakey]

Never heard of it before. Every day is a school day! Thanks.

[Expat]

If the raid took place at night, and the Seals immediately blew up the damaged bird, which is standard practise here, where are these photos from???

[grimey]

The helicopter cracked it's tail over the wall when it crashed. Obviously the seal team torched to fuselage, and didn't get the tail, because it was on the other side of an 15 foot wall. Notice there are only pictures of the tail rotor, nothing else.

[r22captain]

No mystery to me, just a tricked out UH-60 Silent Hawk variant . . .

that was a drawing someone whipped up after the speculation.
http://defensetech.org/2011/05/04/what- ... look-like/
it's still a mystery for sure.

[sky's the limit]

It's interesting that the official explanation of the crash is now a density altitude one. I find it somewhat difficult to believe to be honest. They would know the numbers for hover performance in and out of ground effect for the given weight, and unless a pilot got a little hasty and came in a bit too hot, it's tough to buy the "pilot error" argument straight up. I think there's more to it than that, perhaps they just hit the wall. Maybe it took fire, be interesting to see what comes of this.

In touch with a few people in US Forces trying to get a better idea, see what I can find out.

stl

[ragbagflyer]

The May 2 raid on Osama bin Laden’s luxury compound in Abbottabad, Pakistan, had it all: painstaking intelligence-gathering, a heroic Navy SEAL assault team, satellite and drone surveillance, and biometric forensics.

And now this: a possible super-secret, stealthy helicopter, unknown to the wider world before one crashed during the assault.

Aviation specialists are picking apart pixel-by-pixel the dozen-or-so photos of the copter that have appeared online. They’re assembling digital mock-ups of the aircraft and comparing them to lost stealth designs of the 1980s and ’90s. Speculation abounds, and so far no one from the government is commenting. But depending on what the copter turns out to be, it could shed new light on everything from the abilities of U.S. commandos to the relationship between the United States and Pakistan.

Full Article here:

http://www.wired.com/dangerroom/2011/05 ... pter/all/1

[Beefitarian]

I would think they are working on things besides drones and don't feel like talking about it until they have something better. At that point you can declassify it and bring it to the airshow as "The new F-117." etc.

[justwork]

The reaction here? Show me the photo of dead OBL, then I will begin to think it is not just a political ploy to justify drawdown in Af, and secure re election...

I'm glad they're not releasing pictures.
The best thing America can do is Kill him and forget him. Dumping his body at sea, perfect - leaves no place for mourners to assemble. The sooner everyone forgets his name the better, he doesn't deserve to be immortalized with photo's and martyr fame. Forget the person, not the crime. My goal is to never use his name again, written or spoken. He doesn't deserve it. I hope in 5 years people have a hard time remembering his name, and 5 years from then they can't.

Those pilots are BAMF's, bringing two teams in that area at night... hats off. Too bad they lost a bird, but they destroyed most of it to preserve their technology. I wouldn't want a single piece of metal left in Pakistan after the most wanted man in the world was hiding under their nose... Or maybe it would be the best place to loose a piece of stealth technology, as they seem too incompetent to know what to do with it.

[Heliian]

Although that "silent hawk" rendering looks nice, it's pretty innaccurate. T/R on the wrong side, the fuselage would also be heavily modified, not like the photo and the M/R blades would also be more refined, not just winglets on the ends. Here's somone else's rendering which is somewhat convincing but without published proof it's all fantastic speculation.