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#101
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New trainer from SZD Bielsko
Mike Lindsay schrieb:
That's why the BGA has every ab initio in the UK religiously checking the flaps on a K13 every time they launch. I don't think I've ever seen a K13 with flaps. That was exactly his point. |
#102
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New trainer from SZD Bielsko
Ian,
Looks like we both recall correctly but incompletely. The AAIB report of the 1996 accident, at http://www.aaib.dft.gov.uk/cms_resou...pdf_502118.pdf states: "Several witnesses formed the opinion that this launch was faster and less steep than normal, the launches already being considered, by several witnesses, as being fast that day. One witness reported the presence of a strong wind gradient, the surface wind being 5/10 kt. At a height variously estimated by witnesses of between 600 and 700 feet the glider was seen to 'speed- up' and its climb angle reduce. At about this time, and whilst still in a nose high attitude and connected to the cable, several relatively rapid oscillations in pitch occurred. One witness estimated these to be as much as 15°, with the wings being seen to 'flex' correspondingly an abnormal amount. At about this point, the airbrakes were seen to briefly deploy. Almost immediately, they deployed again, this time coincident with the right wing failing in an upwards and rearwards direction, pivoting about its root end and releasing a cloud of debris." A doubled weak link was used, which could have allowed excessive loads on the airframe in previous launches and in this one. Part of the conclusion was: "In view of the fact that the corrosion had developed over a long period of time, during which the glider had been launched and flown without incident, and that the aircraft had been launched by winch earlier on the same day in similar conditions by the same pilot, it is considered probable that excessive loads were induced on this occasion. This, in turn, exploited the degraded strength of the wing spar, resulting in the upper spar boom collapse in the right wing." I read this as saying that continued overstressing on a weakened structure led to the failure, with that days's overstress being the final straw. The report says that other gliders flying from the same airfield had probably been overloaded. Only this one failed structurally, because of the corrosion. As I wrote before, flying outside the envelope takes one into uncharted territory. However, overspeeding on its own does not necessarily do so - it depends on how the pilot flies the launch and when the launch is abandoned. To summarise how I understand the UK training: 1. If overspeed is clearly excessive from the outset, release and land ahead if possible. If not possible to land ahead, see (3). 2. If moderately excessive in the lower 1/3 of the launch, give a chance for it to settle down and if not, signal too fast. 3. If it doesn't settle down, reduce the load on the airframe through a shallow rate of climb and release once a safe height is achieved. 4. Overspeed in the top 1/3 of the launch is potentially dangerous as the glider is under its highest load at that point, and cumulative overstress can lead to failure particularly if the structure is already weakened. 5. Too slow is more dangerous than too fast, provided you fly the fast launch so as not to overstress the airframe. I'd add that all suspicions of corrosion, overstress through excessive g, etc. need to be checked out by a qualified person. |
#103
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New trainer from SZD Bielsko
At 15:54 27 June 2007, Bruce wrote:
Mike Lindsay wrote: In article , Ian wri That's why the BGA has every ab initio in the UK religiously checking the flaps on a K13 every time they launch. My God! (that's the religious bit) I don't think I've ever seen a K13 with flaps. True, but they check them just in case... And they are checked in a K21... |
#104
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New trainer from SZD Bielsko
On Jun 27, 6:49 pm, Chris Reed wrote:
Ian, Looks like we both recall correctly but incompletely. The AAIB report of the 1996 accident, athttp://www.aaib.dft.gov.uk/cms_resources/dft_avsafety_pdf_502118.pd fstates... Sorry folks, I've just repeated some of what Chris posted, didn't notice that the conversation had "gone over the page". However, Chris does seem to be intimating that it's possible to structurally damage a glider during a winch launch from overspeeding. Providing the correct weak is used, that is not possible. Old myths die hard though. Dan |
#105
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New trainer from SZD Bielsko
Dan G wrote:
However, Chris does seem to be intimating that it's possible to structurally damage a glider during a winch launch from overspeeding. Providing the correct weak is used, that is not possible. Old myths die hard though. Apologies - didn't mean to intimate that. All I was trying to say is that overspeeding is not dangerous per se, but might become so depending on the condition of your glider, where you are in the launch and how you fly it. So far as structural damage is concerned, the only example we have is from an already damaged glider, so you may well be right that with the correct weak link you're protected from structural damage. However, I still refuse to accept overspeeding in the top 1/3 of the launch because (a) the glider is not designed for it, even if it won't fall apart, (b) I don't know whether my glider's structure has been invisibly weakened by past overspeeding, groundloops, etc, and (c) I can safely do something about it (bye bye cable). Below that, I'm prepared to try to sort out the situation unless it's clearly irredeemable. Of course, much depends on what you mean by overspeeding. 2kt over max winch is within the margin of error. 20kt over is far too much to live with all the way to the top. |
#106
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New trainer from SZD Bielsko
At 08:54 29 June 2007, Chris Reed wrote:
Of course, much depends on what you mean by overspeeding. 2kt over max winch is within the margin of error. 20kt over is far too much to live with all the way to the top. Debatable safety considerations aside, there's no benefit in fast winch launches anyway- there's just increased drag and therefore reduced final height, along with the possible distraction and discomfort of excessive acceleration at the beginning. |
#107
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New trainer from SZD Bielsko
Sally W wrote:
At 15:54 27 June 2007, Bruce wrote: Mike Lindsay wrote: In article , Ian wri That's why the BGA has every ab initio in the UK religiously checking the flaps on a K13 every time they launch. My God! (that's the religious bit) I don't think I've ever seen a K13 with flaps. True, but they check them just in case... And they are checked in a K21... ....and in an SZD Junior, Discus and Pegasus at my club, at least by me - and in my Standard Libelle. I see no reason to deviate from the standard CBSIFTCBE checklist, so "Flaps: not fitted" accompanied by a glance to see that there is indeed no flap handle is part of my checklist for a non-flapped glider. This has the benefit of keeping instructors happy on check rides without straining my brain to remember what checklist is expected as compared with what I might do or say when no instructor is present. -- martin@ | Martin Gregorie gregorie. | Essex, UK org | |
#108
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New trainer from SZD Bielsko
On 28 Jun, 21:23, Dan G wrote:
However, Chris does seem to be intimating that it's possible to structurally damage a glider during a winch launch from overspeeding. Providing the correct weak is used, that is not possible. Old myths die hard though. Why, then, is the winch launch maximum speed not Vne? Ian |
#109
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New trainer from SZD Bielsko
structurally damage a glider during a winch launch from overspeeding.
Providing the correct weak is used, that is not possible. Old myths die hard though. Why, then, is the winch launch maximum speed not Vne? If I understand it correctly, flying at maximum winch speed or below ensures that you won't lose your wings even if you use a wrong weak link or no weak link at all. Bartek |
#110
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New trainer from SZD Bielsko
"Martin Gregorie" wrote in message ... Sally W wrote: I see no reason to deviate from the standard CBSIFTCBE checklist, so "Flaps: not fitted" accompanied by a glance to see that there is indeed no flap handle is part of my checklist for a non-flapped glider. This has the benefit of keeping instructors happy on check rides without straining my brain to remember what checklist is expected as compared with what I might do or say when no instructor is present. Perhaps it is just the way that my mind works, but I have to respectfully disagree. If you fly something with fixed gear for your first 1000 flights, each time dutifully reciting something unnecessary like "UNDERCARRIAGE" and each time DOING NOTHING but just skipping on to the next item, then when you finally get in something with retractable gear, you are liable to do the same thing you have always done and land gear up as a result. I believe that checklists should be ideally posted in the cockpit and should be made specific to each aircraft so that each step on the list has real meaning each and every time. Vaughn |
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