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#51
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Andor Holtsmark wrote:
Just to clear some things up: The Antares family of gliders has been designed with a safety cell and energy absorbing nosecone. In order to facilitate this, the cockpit was extended forward at approximately zero aerodynamic loss. The whole cockpit is using a special carbon-carbon technology (no kevlar or dyneema), and was designed mainly by a F1 crash structure designer. This is really very interesting. Are there test results that you can share with us, or perhaps videos of crash tests? Is there an article on the use of carbon-carbon technology in crash structure design you can recommend? I'd like to know more about that technology. -- Eric Greenwell - Washington State, USA * Change "netto" to "net" to email me directly * "Transponders in Sailplanes" http://tinyurl.com/y739x4 * "A Guide to Self-launching Sailplane Operation" at www.motorglider.org |
#52
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On Oct 12, 11:09 pm, Eric Greenwell wrote:
Even glider trailers can differ markedly from one another, so it's no stretch to imagine caravans (less than half the length, 30% wider, and twice as tall as a glider trailer of the same weight) might act very differently behind the same tow vehicle. One of the findings I remember from the Bath University study was that aerodynamics had little effect on stability - it was all about weight distribution. Shame the research is "pre-internet" - though maybe it got published in some engineering journal somewhere. However it doesn't really matter what shape, size or weight your trailer is, the basic rules always apply. You could never recommend having a negative noseweight or towing with a vehicle lighter than the trailer, for example. Dan |
#53
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On Oct 13, 3:14 am, Eric Greenwell wrote:
To the contrary, Schleicher and the others have chosen not to use a "safety cell" design. No, the ASW safety cockpit is a "safety cell" design, but your legs occupy the crumple zone. The idea was it was better that you broke your legs than died. Reinforcements - material irrelevant - in the cockpit walls and canopy frame stops the cell from collapsing into the space your torso occupies. The nose would have to extend several feet beyond were it does now to have sufficient crush distance, and they do not believe pilots will buy such a glider. Research has shown that only a modest - less than 50 cm - extension of the nose is sufficient to absorb enough energy that a safety cell in a glider can be effective up to at least 25 g: http://www.ostiv.fai.org/CkptRoeg.pdf As has been pointed out by others in this thread, Lange have used this research and so developed the extended collapsing nose-cone of the Antares. On Oct 13, 5:32 pm, Eric Greenwell wrote: It looks like a good design; still, an additional 4" over a "normal" fuselage is not much compared to the several feet of crush zone available in an automobile. The human body can easily survive 45 g with a good harness: http://csel.eng.ohio-state.edu/voshell/gforce.pdf So only a few tens of centimetres are required to reduce the acceleration in a glider crash to survivable levels. Is it intended that the [Antares] cockpit function in the "safety cell" manner that Dan G was describing...? Yes: http://www.lange-flugzeugbau.com/htm...0e/safety.html I wish there indpendent tests of glider crash protection that were released to the public, because it is very difficult for us to determine the effectiveness of a design, especially new designs that have not had any crashes yet. There has been lots, see the link I posted above and also the DG website for some overviews. Tony Head first conducted crash testing in 1988 and did lots more. TUV Rhineland did testing throughout the 1990s. Dan |
#54
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Dan G wrote:
On Oct 12, 11:09 pm, Eric Greenwell wrote: Even glider trailers can differ markedly from one another, so it's no stretch to imagine caravans (less than half the length, 30% wider, and twice as tall as a glider trailer of the same weight) might act very differently behind the same tow vehicle. One of the findings I remember from the Bath University study was that aerodynamics had little effect on stability That would be my guess for a caravan, as it's area is relatively close to it's axle. My guess for glider trailers is their relatively greater length would make it a factor. The "tail fin", since it is mounted far from the axle (much farther than the end of a small caravan is from it's axle), seems like it could have a noticeable effect. A number of pilots have reported putting spoilers on the trailer fin improved the stability. - it was all about weight distribution. That is what I was thinking about when I mentioned the big differences in shape between a caravan and a glider trailer. In addition to weight distribution, geometry is very important (such as distance from the tow vehicle's axle to the hitch), as are tires. -- Eric Greenwell - Washington State, USA * Change "netto" to "net" to email me directly * "Transponders in Sailplanes" http://tinyurl.com/y739x4 * "A Guide to Self-launching Sailplane Operation" at www.motorglider.org |
#55
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Dan G wrote:
Research has shown that only a modest - less than 50 cm - extension of the nose is sufficient to absorb enough energy that a safety cell in a glider can be effective up to at least 25 g: http://www.ostiv.fai.org/CkptRoeg.pdf A very interesting report! I'm pleased to see cockpit design has progressed this much. As has been pointed out by others in this thread, Lange have used this research and so developed the extended collapsing nose-cone of the Antares. I was impressed by the design before; now, even more so. On Oct 13, 5:32 pm, Eric Greenwell wrote: It looks like a good design; still, an additional 4" over a "normal" fuselage is not much compared to the several feet of crush zone available in an automobile. The human body can easily survive 45 g with a good harness: http://csel.eng.ohio-state.edu/voshell/gforce.pdf So only a few tens of centimetres are required to reduce the acceleration in a glider crash to survivable levels. This was surprising to me. Also surprising was the statistic that 76% of the accidents have impacts less 101 kph. I would have guessed much higher, and I know much higher impact speeds were part of the "several feet of crush zone" discussion that took place about 15+ years ago. Is it intended that the [Antares] cockpit function in the "safety cell" manner that Dan G was describing...? Yes: http://www.lange-flugzeugbau.com/htm...0e/safety.html I wish there indpendent tests of glider crash protection that were released to the public, because it is very difficult for us to determine the effectiveness of a design, especially new designs that have not had any crashes yet. There has been lots, see the link I posted above and also the DG website for some overviews. Tony Head first conducted crash testing in 1988 and did lots more. TUV Rhineland did testing throughout the 1990s. And also by a group at MIT: R. John Hannsman, Edward F. Crawley, and Karl-Peter Kampf, Experimental investigation of the Crash-Worthiness of Scaled Composite Sailplane Fuselages, Technical Soaring, volume 14, number 4, 1990, page 111 But, what I was wishing for was standardized testing of production sailplanes, similar to what is done for automobiles. An expensive wish, I know, but perhaps soon standardized computer calculations could replace full scale testing sufficiently well to make safety comparisons. -- Eric Greenwell - Washington State, USA * Change "netto" to "net" to email me directly * "Transponders in Sailplanes" http://tinyurl.com/y739x4 * "A Guide to Self-launching Sailplane Operation" at www.motorglider.org |
#56
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OK--I'll supply one.
1999 Chev Tahoe 1999 ASW27 + Cobra Tongue weight about 9% all tires new Begins sway at 68mph--diverging oscillation above 70 mph. Tried spoilers on vertical fin--no help Used nails as wedges to stabilize hitch in the receiver--no help. Attached same setup to a Ford Expedition--stable at up to 110 mph! Bought 2003 Chev Avalanche Stable at any speed traffic allowed! The difference---The 1999 Tahoe had a soft suspension and "vague" steering. The Avalance and the Expedition are much more stiffly suspended and the steering more precise. All three vehicles are massive compared to the Cobra+'27 The answer--IMO the "natural frequency" of the suspension no longer resonated with the trailer suspension "natural frequency" at highway speed. -- Hartley Falbaum "KF" USA "Dan G" wrote in message ps.com... On Oct 12, 3:57 pm, "01-- Zero One" wrote: So to say that "Towing is simple. Follow these rules, and your rig will be stable in all conditions and not need stabiliser hitch." is in my experience a gross oversimplification. Think we'll have to agree to disagree - but I'd like to know of examples where these guidelines were met, but the rig was still unstable. One thing I don't mention which could be called an "oversimplification" is weight distribution within the trailer, mass should be concentrated low and over the axle. However you don't usually have much choice about that with a glider. Dan |
#57
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Dan G wrote:
On Oct 12, 3:57 pm, "01-- Zero One" wrote: So to say that "Towing is simple. Follow these rules, and your rig will be stable in all conditions and not need stabiliser hitch." is in my experience a gross oversimplification. Think we'll have to agree to disagree - but I'd like to know of examples where these guidelines were met, but the rig was still unstable. My '89 Dodge Caravan and ASH 26 E trailer meets all your rules and is stable at 60 mph. At 70 mph, it's starting to quiver, and I've never dared go faster. So, is the rig "stable" or "unstable"? -- Eric Greenwell - Washington State, USA * Change "netto" to "net" to email me directly * "Transponders in Sailplanes" http://tinyurl.com/y739x4 * "A Guide to Self-launching Sailplane Operation" at www.motorglider.org |
#58
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Dan,
Indeed, from reading many posts on the stability issue, it seems that a precise, stiff suspension is what makes the rig stable. I recall one poster saying his rig was not very stable till he fixed a somewhat worn and loose joint in the front suspension that was barely noticeable when driving normally, but it improved the stability of the rig enormously. I suspect that when the tow vehicle itself is heavily loaded, making it less stable, it can have the same effect and cause the rig to be less stable than when the tow vehicle is more lightly loaded. The Honda Accord I used to tow had a Iow cg and a fairly stiff suspension compared to many large tow vehicles. The Astir CS and heavy trailer were clearly stable to 80MPH, which is as fast as I ever went. Never tried faster as I never trusted the small tires on the trailer too much. I doubt stability is about the weight of the tow vehicle. |
#59
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tommytoyz wrote:
Indeed, from reading many posts on the stability issue, it seems that a precise, stiff suspension is what makes the rig stable. And this explains partly why Americans tend to think they use trucks to tow. US cars have had a reputation for poor suspensions. Poor suspension means poor towing stability. Imagine someone towing with a large V8 with poor suspension. The tow will be unstable. Now try to tell that guy that towing with a smaller car will yield more stable results! No way, his logic will tell him he needs an even bigger car, i.e. a truck. As my girlfriend always said: It's not the size, it's the stiffness which matters. |
#60
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On Oct 16, 3:35 am, "HL Falbaum" wrote:
OK--I'll supply one. 1999 Chev Tahoe 1999 ASW27 + Cobra Tongue weight about 9% all tires new Begins sway at 68mph--diverging oscillation above 70 mph. Tried spoilers on vertical fin--no help Used nails as wedges to stabilize hitch in the receiver--no help. Attached same setup to a Ford Expedition--stable at up to 110 mph! Bought 2003 Chev Avalanche Stable at any speed traffic allowed! The difference---The 1999 Tahoe had a soft suspension and "vague" steering. The Avalance and the Expedition are much more stiffly suspended and the steering more precise. All three vehicles are massive compared to the Cobra+'27 The answer--IMO the "natural frequency" of the suspension no longer resonated with the trailer suspension "natural frequency" at highway speed. Of course different tow vehicles will tow differently, particularly with SUVs, many of which use suspension which can only be described politely as being "agricultural". My point (which I did not explain clearly) was that I doubt that if you had, for example, tried a negative noseweight or stuck a bunch of lead acid batteries in the end of the trailer your Tahoe would have towed at high-speed with stability. Dan |
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