The (Stealth) Blackhawk Crash

AvWeb ^ | 5/12/2011 | The AVweb Editorial Staff

[BwanaNdege]

The (Stealth) Blackhawk Crash The reason a stealthy version of the MH-60 Blackhawk crashed during the May 1 raid that killed Osama bin Laden includes the vortex ring state phenomenon, according to officials, but helicopter crashes in the Middle East are far from uncommon. Hot air close to the ground and the aircraft's proximity to the high walls of the compound could have caused that thin, hot air to be driven by propwash up the walls and then down through the rotor, causing the vortex ring state. With those conditions, the helicopter would have lost lift and settled with power, which is what officials say happened. The resulting hard landing immediately altered the original plan for SEALS to fast rope to the ground from a hovering aircraft. They fared better than they might have. In Iraq, only IED explosions and being shot by the enemy rank higher than U.S. helicopters for killing American soldiers, according to the Armed Forces Journal. And 80 percent of the helicopter accidents occur without the intervention of hostile forces. That said, the military helicopter crash rate is actually better than that of GA aircraft.

The non-hostile, non-combat accident rate for military helicopters currently stands near 2.1 per 100,000 hours while flying in some of the least hospitable conditions available to helicopters. Meanwhile, the accident rate for GA aircraft stands at 6.86 per 100,000 hours. The military helicopter pilots are most often brought down due to a combination of weather conditions and terrain. Night vision goggles have improved matters, but dust storms, brownouts caused by rotor wash, wire strikes and controlled flight into terrain are still problems the military and Congress hopes to better address. Proposed fixes include terrain avoidance avionics that would warn pilots of potential hazards. (cont)

[Cheetahcat]

How about coaxial rotors? that would cure the close ground vortex and eliminate the need for a tail rotor system.

[fso301]

The SEALS then had to blast though the outer wall.

If you ever come across a photo of a breaching hole, please let me know because I still haven't seen one.

[SoCal Pubbie]

Like I wrote on my post, that's what was stated was in the 20/20 report. They also stated that the power went out in the neighborhood at the time of the raid. There's been so many version of went down that one wonders what the truth is.

[Pentagon Leatherneck]

I believe this is the phenomenon that resulted in the loss of several V-22 aircraft, including one crash that cost the lives of 19 Marines. One V-22 was lost primarily to VRS at Marana, AZ in April, 2000. Following a long and detailed high rate of descent test program, it was learned that the V-22 VRS margin is actually greater than most conventional helicopters. One has to exceed 2400 FPM ROD to encounter torque bumps and roll-off. And tilting the nacelles forward forestalls VRS, whereas helicopters must drop the nose, lower collective, and fly out of the vortex. TC

[Steely Tom]

Thanks for the info, and for other things as well, both of you.

[Wuli]

“Hot air close to the ground and the aircraft’s proximity to the high walls of the compound could have caused that thin, hot air to be driven by propwash up the walls and then down through the rotor, causing the vortex ring state. With those conditions, the helicopter would have lost lift and settled with power, which is what officials say happened.”

A close friend who does know, and is in a position to know something about all this, says that the size of the opening of the compound and its high walls (& the altitude and air temperature) could have by themselves caused loss of lift, without the vortex ring state - simply collectively restricting how much air could be sucked how quickly under the main rotors, to provide, or to continue to provide the lift. He does not discount the vortex ring theory; he just thinks it is not the only possibility.

[Wuli]

"I got the impression by reading at Aviation Week that is was far from certain that the helicopter was truly some form of advanced, “stealth” helicopter. Covering the tail rotor has been applied elsewhere and the use of anti-IR paint is nothing special."

I know someone who KNOWS the Blackhawks; intimately. He says the tail rotor size and shape was "non-standard" for a "production" Blackhawk.

If the changes were actually stealth related, the tragedy is not the mere fact that it was left in the compound, but that in all likelihood it has left Pakistan, for China.

Make your own comparisons:

A tour from the maker of the Blackhawks (it's an Adobe Flash video and it starts slow). What is nice is it lets you alter the view of an operating Blackhawk, to see it from either side or either end; at:

http://www.sikorsky.com/Products/Helicopter+Tour

versus

http://cencio4.wordpress.com/2011/05/03/mysterious-helicopter/

which includes the comment:

"However, the depicted horizontal stabiliser and tail rotor of the wreckage don’t seem to be a any form of H-60. Both the shape and position are not common to either Black Hawks or Apaches helicopters. Noteworthy, the tail rotor has a weird cover that could be anything from a stealth cover, to an armour plate to a noise reduction device."