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From the Army Times article: That crash landing might have been caused by a phenomenon known as “settling with power,” which occurs when a helicopter descends

by rkon 15y ago

From the Army Times article: That crash landing might have been caused by a phenomenon known as “settling with power,” which occurs when a helicopter descends too quickly because its rotors cannot get the lift required from the turbulent air of their own downwash. “It’s hard to settle with power in a Black Hawk, but then again, if they were using one of these [low-observable helicopters], working at max gross weight, it’s certainly plausible that they could have because they would have been flying so heavy,” the retired special operations aviator said, noting that low-observable modifications added “several hundred pounds” to the weight of the MH-60, which already weighs about 500 to 1000 pounds more than a regular UH-60 Black Hawk. http://www.armytimes.com/news/2011/05/army-mission-helocopter-was-secret-stealth-black-hawk-050411/ http://www.armytimes.com/news/2011/05/army-mission-helocopte...

nradov 15y ago
A WSJ article stated that the high walls around the compound induced a vortex ring effect. http://online.wsj.com/article/SB10001424052748704569404576299500647391240.html http://online.wsj.com/article/SB1000142405274870456940457629... In a normal landing the rotor downwash would spread out across the ground but in this case the walls channeled the moving air back up and into the rotor again, causing it to lose lift. Of course I don't know whether that's true or not, but it seems plausible. https://secure.wikimedia.org/wikipedia/en/wiki/Vortex_ring#Vortex_ring_effect_in_helicopters https://secure.wikimedia.org/wikipedia/en/wiki/Vortex_ring#V...
- ratsbane 15y ago
  There's also Loss of Tail Rotor Effectiveness[1] (LTE), caused by the tail rotor entering a vortex ring in much the same way the main rotor is affected in settling with power. LTE will cause a helicopter to yaw sharply in a direction opposite the main rotor's rotation. The position of the wreck, with the tail broken over a wall, makes me think there might have been a yaw problem. Or they might have been in a high hover, had a problem, and hit the wall on the way down. [1] http://en.wikipedia.org/wiki/Loss_of_tail-rotor_effectiveness http://en.wikipedia.org/wiki/Loss_of_tail-rotor_effectivenes...
- lotusleaf1987 15y ago
  The layout of the compound definitely had some design or goal to it. To my eye I couldn't tell what the effect was--religious was my first guess, but what you're saying makes sense. After all, he was 1800 yards from the Pakistan ~WestPoint. Coincidences of that magnitude don't occur flippantly.
  - lotusleaf1987 15y ago
    I'd love to know why this was downvoted. Sometimes HN is a really hostile and narrow-minded place.
    - prewett 15y ago
      I can't say why it was downvoted, but my reaction to your comment was that it was completely off-topic to the post you replied to: the parent post was talking about vortex rings off the wall and your post speculated about architecture. Also, you made strong claims with no evidence (religious motivation for the walls); the stronger the claim, the more support it needs.
      - lotusleaf1987 15y ago
        Please reread the comment "To my eye I couldn't tell what the effect was--religious was my first guess, but what you're saying makes sense." Which is pretty inconsistent from what you said "made strong claims with no evidence (religious motivation for the walls); the stronger the claim, the more support it needs." I made no claim whatsoever, I divulged my first guess/naive speculation and said at first glance from my uninformed perspective I did not know exactly what the intentions were behind the architecture, but that I thought maybe it had to do with religion--him being a religious extremist. I replied to the parent comment because I thought maybe the architecture was designed with the goal of producing vortex rings--making it harder for a helicopter to allow to allow people to repel. You're also a hypocrite considering the comment you made previous to the one I'm replying "This is kind of off-topic, but I've always wondered...:http://news.ycombinator.com/item?id=2515028 http://news.ycombinator.com/item?id=2515028 How is that any different than what I did, if not worse? Sometimes HN is just looking to be overly critical and point out flaws that only exist if you obsess over being pedantic.
- ra 15y ago
  Given the level of skill, training and experience a pilot would need to be allowed to fly that thing, and after rehearsing the raid in a life size replica of the compound - I think it's unlikely. Even doing a PPL you learn about the effects of vortexes, wind shear, turbine wash etc. And these guys have many, many, many orders of magnitude more training than that. More likely some combination of weight, altitude, excess speed... but I guess we'll never know.
  - astrodust 15y ago
    Apart from the obvious, such as landing under fire, dealing with the effects of the other helicopter in a confined area, or simply pilot fatigue after the fast, low flight to get to the compound, it could be some freak effect like that. Flying deep into Pakistan undetected and landing in Bin Ladin's backyard is a hell of a trick, no ordinary pilot could do that.
MichaelApproved 15y ago
"working at max gross weight" unlikely since the other heli would've been over weight (carrying both teams) and surely suffered the same fate. I heard it was hot and high conditions that forced it to go down http://en.wikipedia.org/wiki/Hot_and_high http://en.wikipedia.org/wiki/Hot_and_high
- hammock 15y ago
  I did read at first that one second heli evacuated both teams after the first one crashed. But I also later read somewhere else that they dispatched a third heli after the crash?
  - larrywright 15y ago
    The articles I saw indicated there were four choppers total. I'm not sure whether they were right there or just nearby, but the article gave the impression that they were there in case they had to engage the Pakistani Air Force.
    - hugh3 15y ago
      Surely if they did need to engage the Pakistani Air Force (and it's claimed that they had Pakistani permission for the raid) they'd want fighter jets, not extra helicopters?
      - showerst 15y ago
        Presumably they had those too, we don't know. It does make quite a bit of sense to have a backup in case something goes wrong, even under the high-stealth circumstances. Remember that we have no idea what was in those helos, they could've held more SEALs, or sophisticated medical equipment, or even heavy weapons (although if they were also blackhawks that's less likely.)
        hugh3 15y ago
        Oh, certainly. I agree, the extra helicopters would have been kept at a safe distance just in case one or more of the others had a problem. They've obviously learned a lot from Operation Eagle Claw (this is required reading for understanding this raid): http://en.wikipedia.org/wiki/Operation_Eagle_Claw http://en.wikipedia.org/wiki/Operation_Eagle_Claw
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by rkon 15y ago

nradov 15y ago

A WSJ article stated that the high walls around the compound induced a vortex ring effect. http://online.wsj.com/article/SB10001424052748704569404576299500647391240.html http://online.wsj.com/article/SB1000142405274870456940457629... In a normal landing the rotor downwash would spread out across the ground but in this case the walls channeled the moving air back up and into the rotor again, causing it to lose lift. Of course I don't know whether that's true or not, but it seems plausible. https://secure.wikimedia.org/wikipedia/en/wiki/Vortex_ring#Vortex_ring_effect_in_helicopters https://secure.wikimedia.org/wikipedia/en/wiki/Vortex_ring#V...

ratsbane 15y ago
There's also Loss of Tail Rotor Effectiveness[1] (LTE), caused by the tail rotor entering a vortex ring in much the same way the main rotor is affected in settling with power. LTE will cause a helicopter to yaw sharply in a direction opposite the main rotor's rotation. The position of the wreck, with the tail broken over a wall, makes me think there might have been a yaw problem. Or they might have been in a high hover, had a problem, and hit the wall on the way down. [1] http://en.wikipedia.org/wiki/Loss_of_tail-rotor_effectiveness http://en.wikipedia.org/wiki/Loss_of_tail-rotor_effectivenes...
lotusleaf1987 15y ago
The layout of the compound definitely had some design or goal to it. To my eye I couldn't tell what the effect was--religious was my first guess, but what you're saying makes sense. After all, he was 1800 yards from the Pakistan ~WestPoint. Coincidences of that magnitude don't occur flippantly.
- lotusleaf1987 15y ago
  I'd love to know why this was downvoted. Sometimes HN is a really hostile and narrow-minded place.
  - prewett 15y ago
    I can't say why it was downvoted, but my reaction to your comment was that it was completely off-topic to the post you replied to: the parent post was talking about vortex rings off the wall and your post speculated about architecture. Also, you made strong claims with no evidence (religious motivation for the walls); the stronger the claim, the more support it needs.
    - lotusleaf1987 15y ago
      Please reread the comment "To my eye I couldn't tell what the effect was--religious was my first guess, but what you're saying makes sense." Which is pretty inconsistent from what you said "made strong claims with no evidence (religious motivation for the walls); the stronger the claim, the more support it needs." I made no claim whatsoever, I divulged my first guess/naive speculation and said at first glance from my uninformed perspective I did not know exactly what the intentions were behind the architecture, but that I thought maybe it had to do with religion--him being a religious extremist. I replied to the parent comment because I thought maybe the architecture was designed with the goal of producing vortex rings--making it harder for a helicopter to allow to allow people to repel. You're also a hypocrite considering the comment you made previous to the one I'm replying "This is kind of off-topic, but I've always wondered...:http://news.ycombinator.com/item?id=2515028 http://news.ycombinator.com/item?id=2515028 How is that any different than what I did, if not worse? Sometimes HN is just looking to be overly critical and point out flaws that only exist if you obsess over being pedantic.
ra 15y ago
Given the level of skill, training and experience a pilot would need to be allowed to fly that thing, and after rehearsing the raid in a life size replica of the compound - I think it's unlikely. Even doing a PPL you learn about the effects of vortexes, wind shear, turbine wash etc. And these guys have many, many, many orders of magnitude more training than that. More likely some combination of weight, altitude, excess speed... but I guess we'll never know.
- astrodust 15y ago
  Apart from the obvious, such as landing under fire, dealing with the effects of the other helicopter in a confined area, or simply pilot fatigue after the fast, low flight to get to the compound, it could be some freak effect like that. Flying deep into Pakistan undetected and landing in Bin Ladin's backyard is a hell of a trick, no ordinary pilot could do that.

MichaelApproved 15y ago

"working at max gross weight" unlikely since the other heli would've been over weight (carrying both teams) and surely suffered the same fate. I heard it was hot and high conditions that forced it to go down http://en.wikipedia.org/wiki/Hot_and_high http://en.wikipedia.org/wiki/Hot_and_high

hammock 15y ago
I did read at first that one second heli evacuated both teams after the first one crashed. But I also later read somewhere else that they dispatched a third heli after the crash?
- larrywright 15y ago
  The articles I saw indicated there were four choppers total. I'm not sure whether they were right there or just nearby, but the article gave the impression that they were there in case they had to engage the Pakistani Air Force.
  - hugh3 15y ago
    Surely if they did need to engage the Pakistani Air Force (and it's claimed that they had Pakistani permission for the raid) they'd want fighter jets, not extra helicopters?
    - showerst 15y ago
      Presumably they had those too, we don't know. It does make quite a bit of sense to have a backup in case something goes wrong, even under the high-stealth circumstances. Remember that we have no idea what was in those helos, they could've held more SEALs, or sophisticated medical equipment, or even heavy weapons (although if they were also blackhawks that's less likely.)
      - hugh3 15y ago
        Oh, certainly. I agree, the extra helicopters would have been kept at a safe distance just in case one or more of the others had a problem. They've obviously learned a lot from Operation Eagle Claw (this is required reading for understanding this raid): http://en.wikipedia.org/wiki/Operation_Eagle_Claw http://en.wikipedia.org/wiki/Operation_Eagle_Claw

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