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#21
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Glider crash near Reno yesterday
This is actually quite helpful. "Loops" means up and down, not spiral dive, and paraglider pilots know the difference. Nobody does multiple loops to the point of structural failure intentionally or unintentionally. That pretty much screams elevator control failure, and somehow getting stuck in a rearwards position. It also explains why the pilots might not have been able to bail out. Yes, I'm speculating, but that's likely all we'll get.
John Cochrane I agree. Ripping off the wings in a loop means going up to close to 10 g (5..6 g on the flight envelope, plus a demonstrated security factor of 1.75). Going close to that limit can't be done repeatedly without blacking out (I regularily do aerobatics with sailplanes between -3.5 and 6 g), so this can't have happened intentionally or unintentionally. Bert TW |
#22
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Glider crash near Reno yesterday
On Thursday, September 27, 2018 at 8:45:16 AM UTC-7, John Cochrane wrote:
On Wednesday, September 26, 2018 at 10:12:39 PM UTC-5, Ramy wrote: NTSB preliminary report: https://app.ntsb.gov/pdfgenerator/Re...=HTML&IType=FA Ramy This is actually quite helpful. "Loops" means up and down, not spiral dive, and paraglider pilots know the difference. Nobody does multiple loops to the point of structural failure intentionally or unintentionally. That pretty much screams elevator control failure, and somehow getting stuck in a rearwards position. It also explains why the pilots might not have been able to bail out. Yes, I'm speculating, but that's likely all we'll get. John Cochrane If I was purchasing a new glider today, I would be getting it with a NOAH system installed. As for the accident....I still don't have any words, I just can't believe it, just... |
#23
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Glider crash near Reno yesterday
On Thursday, 27 September 2018 19:28:44 UTC+3, Tango Whisky wrote:
This is actually quite helpful. "Loops" means up and down, not spiral dive, and paraglider pilots know the difference. Nobody does multiple loops to the point of structural failure intentionally or unintentionally. That pretty much screams elevator control failure, and somehow getting stuck in a rearwards position. It also explains why the pilots might not have been able to bail out. Yes, I'm speculating, but that's likely all we'll get. John Cochrane I agree. Ripping off the wings in a loop means going up to close to 10 g (5.6 g on the flight envelope, plus a demonstrated security factor of 1.75).. Going close to that limit can't be done repeatedly without blacking out (I regularily do aerobatics with sailplanes between -3.5 and 6 g), so this can't have happened intentionally or unintentionally. Bert TW What if wing was weaker than intended (ref. DuoDiscus wing spar AD years back)? Ripping of wings is impossible at max. rough air speed or less as wing stalls before it breaks but I think is possible at higher speed. |
#24
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Glider crash near Reno yesterday
On Wednesday, September 26, 2018 at 8:12:39 PM UTC-7, Ramy wrote:
NTSB preliminary report: https://app.ntsb.gov/pdfgenerator/Re...=HTML&IType=FA 2 to 3 seconds per loop? G'eeeees!!! a = v^2/r so r = v^2/a. Based on a 40 knot stall speed, a glider would pull 9G before stalling at about 120 knots, 60 m/s. 9G is 88.2 m/s^2. So loop radius about 41m, circumference 256m, time for a loop 256/88.2 = 2.9 seconds. All neglecting gravity and speed increases and decreases. Repeating for 10G gives 126 knots, 65 m/s, 43m radius, 4.16 seconds per loop. Repeating for 8G gives 113 knots, 58 m/s, 43m radius, 4.7 seconds per loop. Seems the paragliders' reports are plausible if they lost elevator control at a highish but nowhere hear Vne speed. Ouch. |
#25
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Glider crash near Reno yesterday
I agree that this appears to be an elevator failure. What pieces of the wreckage were retrieved? Was the horizontal stabilizer/elevator retrieved? Was the elevator bolt located (ripped out of the elevator, found in a side pocket, found in the trailer, etc). I have the ability to fly my Phoenix low level over the site on a suitable light east wind day and do a close search for the horizontal stab if it is missing. Finding the stab may be the key to solving this tragedy.
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#26
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Glider crash near Reno yesterday
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#27
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Glider crash near Reno yesterday
The Duo stab is held on by a sprung bolt which is retained in the fin. Care can be needed to ensure the bolt is fully engaged when rigging but the bolt could not be left out. Anyway, as already said what the paragliders reported is not consistent with a lost stab.
As an Arcus owner I am disturbed by this tragedy which may involve a back end control problem on an S-H 2 seater coming sòon after the loss of Dave Nadler's Arcus. I hope for more information about the Arcus accident in due course. |
#28
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Glider crash near Reno yesterday
On Thursday, September 27, 2018 at 10:53:23 AM UTC-7, krasw wrote:
What if wing was weaker than intended... The NTSB preliminary report makes it clear that very high load factors were applied to the wings. One witness reported the wingtips at or near vertical, another reported the wingtips almost touching. Even allowing for some exaggeration, it appears that the wings supported loads well above limit or even ultimate load rating. I agree that this is a very distressing accident. The facts in evidence suggest some sort of pitch control malfunction. But of course there is no proof one way or the other, and the post-accident fire has likely erased the evidence. Though perhaps the cause will be revealed by interference signatures on metal parts. --Bob K. |
#29
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Glider crash near Reno yesterday
I've got a question - let's assume that the speculation going on here is right and that the elevator control was locked in a full nose-high station - what is the optimal thing to do if you are ever faced with this? Am I right in assuming that it is to bail as quickly as possible before you start building G-loads which would make bailing impossible? If you somehow got yourself into a scenario where you were endlessly looping the glider, would deploying full airbrakes bleed enough energy to stop the looping (and maybe induce a spin instead)?
This is certainly a nightmare scenario. My condolences go out to the friends and family of the departed. |
#30
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Glider crash near Reno yesterday
On Thursday, September 27, 2018 at 8:58:23 PM UTC-7, James Betker wrote:
I've got a question - let's assume that the speculation going on here is right and that the elevator control was locked in a full nose-high station - what is the optimal thing to do if you are ever faced with this? Am I right in assuming that it is to bail as quickly as possible before you start building G-loads which would make bailing impossible? If you somehow got yourself into a scenario where you were endlessly looping the glider, would deploying full airbrakes bleed enough energy to stop the looping (and maybe induce a spin instead)? This is certainly a nightmare scenario. My condolences go out to the friends and family of the departed. If you are being subjected to 10 g's it would be very difficult to raise your arm to pull the handle - your 10 lb arm suddenly becomes 100 lb. Tom |
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