Posted on 05/12/2011 7:58:29 AM PDT by 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)
(Excerpt) Read more at avweb.com ...
I've only encountered it twice, both times above 4500 feet when trying a high hover & backwards flight while filming a moving train. thankfully, I had enough altitude to dive out of the descending column of air and regain lift.
That makes sense. I wonder if the fact that it was a “stealth” helicopter makes any difference as far as losing lift is concerned?
This was discussed in some publications earlier. The stealth birds are heavier, harder to see out of, and would have been coming in pushing max weight capacity. Still, I’d hate to be the pilot of that bird.
I don't know much about helicopters, and even less about "stealth" helicopters, but 30 years of engineering intuition tell me that whatever they're doing to make that machine stealthy is probably not helping it's flight characteristics.
It might “sound right” but consider that the aviators of the 160th Aviation Regiment (Night Stalkers) would have anticipated this and planned accordingly. My guess — and it is a guess — is that the chopper was ‘sacrificed’ as part of the tactical assault plan.
If they really were planning to fast-rope there likely would have been a lot of injuries among the passengers. I’m thinking everybody was strapped in anticipating a hard landing — a la the Son Tay raid (Vietnam).
You run a chopper into a walled compound & assault from the inside out.
I could be wrong because of 2 factors — we left a significant portion of the chopper intact, and (2) there was no followup airstrike to waste what was left.
I saw footage of one of those Sikorsky Sky Cranes do a that a few years ago. He was operating for a logging outfit, tried to land in a small field surrounded by tall trees. Slammed in pretty hard.
The Stealth treatment probably slowed max airspeed and the changes to the tailrotor probably affected anti-torque authority, but hover lift should not have been affected, unless main rotor blade tip changes screwed thing up.
From a picture in the compound it looked like the tail section landed on a wall. Whether that was due to pilot error or a malf is not known.
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.
It may well be a stealth helicopter, but the evidence we have is not sufficient to reach this conclusion. Aviation Week tends to be a quite reliable source in the aviation industry, so I would definitely take the stealth claims with a grain of sale.
Consider the EH-101 with its advanced rotors.
Its rotors are configured to provide the most lift at the tips, which has been reported to decrease rotor wash and mitigate RVS/Settling. With the greater lift at the rotor tips, the rotor speed is decreased and the rotors may not need to break the sound barrier - sound reduction (one component of “stealth”). That also means less torque (due to lower rotor speeds) and may account for the smaller tail rotors seen in the wreckage photos.
If, as has been suspected, the modified Blackhawk was outfitted with such rotors, I would think that RVS/Settling would less of a concern, but not impossible.
According to the article referenced in your earlier post, vortex ring state results from “upflow” near the rotor mast and blade grip region, a region of the rotor disk that provides no lift. When hovering, this region of the disk can stall; vortices shed by the stalled parts of the blades can propagate toward the outer circumference of the blade disk and disturb lift and control authority.
If they have to put strict limits on blade tip speed for stealth purposes, this problem would be exacerbated, I should think. Add in the environmental and load factors listed above, and it’s fortunate the pilot was skillful enough to save the mission, if not the helicopter.
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.
Some reports were it was more of a “modified” model. That tail section though, indicates some fairly serious modification.
I love you.
Interesting. If I ever got shot down though, I’d sure set her inside those walls.
I wonder if the fact that this was a super secret helicopter and that it is probably brand new left the pilot with very limited flight time with it. That would leave the pilot without the experience to overcome or avoid this type of phenomenon.
I still don’t understand why that tail was left behind for our enemies to study. Were they taking fire from outside the compound? Seems like it should have been fairly easy to blow up.
Isn’t the real point of this that the Pakis may have recovered this and already handed it over to the ChiComs?
The guys might have been in a bit of a rush when they left. They did their best in the time they had, which was probably about thirty seconds.
Rules of engagement may have inhibited bombardment options from the air. Can you just imagine the response from that team of nitwits in the WH Situation Room when some bomber pilot, orbiting nearby, offered to drop 500 pounders on the wreck?
Consider the source but that was their report.
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