CHC AS332L Stavanger
Joined: Apr 2010
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From: Lost again...
Folks... have some humility. Everyone can have a bad day and make a screw up. Do not for one second imagine that you are not one of them.
Joined: Nov 2004
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From: OGE
As a pilot i'd love to be able to say i'd have spotted this but i'm not certain i would have (and any pilot who is "certain they would have" is kidding themselves - really!)
Folks... have some humility. Everyone can have a bad day and make a screw up. Do not for one second imagine that you are not one of them.
Folks... have some humility. Everyone can have a bad day and make a screw up. Do not for one second imagine that you are not one of them.
Let those without sin….
That said: I’d like to think I would pick it up. One of mine, and I’d expect most pilots, preflights is to carefully Inspect each blade for damage, including “hangar rash”. (Almost impossible to miss with down swept tips like on an AW189)
Don’t rush your preflight, no matter what time pressures your Company puts you under in the name of “maximising profits” (“Sweating the assets”)
Joined: Dec 2005
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From: England
You are quite right.
Let those without sin….
That said: I’d like to think I would pick it up. One of mine, and I’d expect most pilots, preflights is to carefully Inspect each blade for damage, including “hangar rash”. (Almost impossible to miss with down swept tips like on an AW189)
Don’t rush your preflight, no matter what time pressures your Company puts you under in the name of “maximising profits” (“Sweating the assets”)
Let those without sin….
That said: I’d like to think I would pick it up. One of mine, and I’d expect most pilots, preflights is to carefully Inspect each blade for damage, including “hangar rash”. (Almost impossible to miss with down swept tips like on an AW189)
Don’t rush your preflight, no matter what time pressures your Company puts you under in the name of “maximising profits” (“Sweating the assets”)
I have also seen tail rotors on back to front on a Hiller and a BO105. The 105 was spotted by me the Hiller got to ground run stage.
A personal check in respect of tail rotors was to rotate in the directon of rotation while ensuring the main rotor responded accordingly.
Joined: Aug 2006
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From: Hedge
On a similar note a certain operator in the Pacific region managed to install Jetranger Blades onto a Longranger.
Despite reports of "low power", I belive it flew for some significant time before being picked up.
Despite reports of "low power", I belive it flew for some significant time before being picked up.
Joined: Oct 1999
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From: Den Haag
I know of one operator that fitted a MR servo upside down in an AW139. Only spotted when the aircraft tried to roll over when the crew tried to lift into the hover. The fact that none of the disconnected pipework would line up didn’t seem to raise any alarm bells. Brute force and ignorance always wins…..
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From: Australia
Anyway, now we all know for sure that a blade flying in reverse at high speed is unstable...
Joined: Oct 1999
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From: Den Haag
Oh, s##t! It took me a while to spot it, I was zooming in on the dangling 'wire' (is that lightning strike protection??), then pitch link, then on damaged tip then the penny finally dropped! But what is that seemingly strange discontinuity at the break in the spar(?) near the leading edge? Almost looks like a Lego brick connection!?
Anyway, now we all know for sure that a blade flying in reverse at high speed is unstable...
Anyway, now we all know for sure that a blade flying in reverse at high speed is unstable...
Joined: Nov 2010
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From: Australia
Ahh, makes sense, thanks. Just had the photo in original post in mind and it looked like the damaged blade had lost part of its span. But looking again, it is just the trailing edge that was lost outboard hence why it seems short in OP.
Thread Starter
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From: After all, what’s more important than proving to someone on the internet that they’re wrong? - Manson
.......................and who would have spotted all 4 on backwards! Kind of "ups the ante" and in hindsight they were probably "fortunate" only one was on backwards.
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From: UK
Joined: Oct 1999
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From: Den Haag
Joined: Nov 2010
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From: Australia
Yes, I meant 'trailing' in the traditional sense of the blade profile.
But I am curious how that blade would have behaved in this incident. A brief search of the internet found a discussion on aerofoils flying in reverse (https://aviation.stackexchange.com/q...lown-backwards). It drifted off topic but there was a useful plot of the lift on various aerofoils with AoA ranging from <0 to +180 degrees. So the data approaching 180 degrees gives an appreciation of lift vs AoA of an aerofoil flying in reverse. While a NACA 0012 profile has a fairly linear L vs AoA range up to around +/-10 degrees in forward flight, the linear range of L vs AoA in reverse flight seems less at only around +/-7 degrees:
But I doubt it was the L vs AoA characteristics that resulted in the description of the blade behaviour provided by Smokeyboy (#8). Lift on a wing is typically centred at around the quarter chord from the leading edge. When flying in reverse, that would remain the case but it is now located near what should have been the trailing edge and so no longer close to the axis of rotation in pitch of the blade. Once RRPM increased enough, or with some collective added, the outer tip of that rotor probably twisted into a higher AoA until the stored energy in the twisted blade 'let go' and made the blade tips twist back in the opposite direction. I guess it could be described as an aerofoil flutter behaviour(?). The sudden change in lift at the rotor tip (with no further control input required) could explain the blade flying up first then down before taking out the tail boom.
But I am curious how that blade would have behaved in this incident. A brief search of the internet found a discussion on aerofoils flying in reverse (https://aviation.stackexchange.com/q...lown-backwards). It drifted off topic but there was a useful plot of the lift on various aerofoils with AoA ranging from <0 to +180 degrees. So the data approaching 180 degrees gives an appreciation of lift vs AoA of an aerofoil flying in reverse. While a NACA 0012 profile has a fairly linear L vs AoA range up to around +/-10 degrees in forward flight, the linear range of L vs AoA in reverse flight seems less at only around +/-7 degrees:
But I doubt it was the L vs AoA characteristics that resulted in the description of the blade behaviour provided by Smokeyboy (#8). Lift on a wing is typically centred at around the quarter chord from the leading edge. When flying in reverse, that would remain the case but it is now located near what should have been the trailing edge and so no longer close to the axis of rotation in pitch of the blade. Once RRPM increased enough, or with some collective added, the outer tip of that rotor probably twisted into a higher AoA until the stored energy in the twisted blade 'let go' and made the blade tips twist back in the opposite direction. I guess it could be described as an aerofoil flutter behaviour(?). The sudden change in lift at the rotor tip (with no further control input required) could explain the blade flying up first then down before taking out the tail boom.
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From: HLS map - http://goo.gl/maps/3ymt
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From: Sweden
Joined: Oct 2005
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From: Anglia
..always has been a massive Murphy for two reasons:
1. The two pins are the same
2. The blades rotate the wrong way around! (To avoid Bell/Sikorsky patents, I’m told)
That’s what doing a Type Course is supposed to emphasise and I’m still not sure how ‘they’ managed to complete the installation and inspections.
I have seen almost as bad on Puma Tail Rotor controls too. Can’t do this on a Chinook as the Lag Damper won’t fit!
1. The two pins are the same
2. The blades rotate the wrong way around! (To avoid Bell/Sikorsky patents, I’m told)
That’s what doing a Type Course is supposed to emphasise and I’m still not sure how ‘they’ managed to complete the installation and inspections.
I have seen almost as bad on Puma Tail Rotor controls too. Can’t do this on a Chinook as the Lag Damper won’t fit!
Joined: Dec 2005
Posts: 1,581
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From: England
..always has been a massive Murphy for two reasons:
1. The two pins are the same
2. The blades rotate the wrong way around! (To avoid Bell/Sikorsky patents, I’m told)
That’s what doing a Type Course is supposed to emphasise and I’m still not sure how ‘they’ managed to complete the installation and inspections.
I have seen almost as bad on Puma Tail Rotor controls too. Can’t do this on a Chinook as the Lag Damper won’t fit!
1. The two pins are the same
2. The blades rotate the wrong way around! (To avoid Bell/Sikorsky patents, I’m told)
That’s what doing a Type Course is supposed to emphasise and I’m still not sure how ‘they’ managed to complete the installation and inspections.
I have seen almost as bad on Puma Tail Rotor controls too. Can’t do this on a Chinook as the Lag Damper won’t fit!
Assuming that this hasn't been modified out I wonder what happened there. One appears to be visible on the adjacent blade aft.
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From: USA