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Quality of kitplane designs?
After reading
http://www.faa.gov/aircraft/gen_av/l...dia/Zodiac.pdf I'm wondering how much trouble is hidden in other kitplane designs? Obviously, the RV fleet seems to be rather untroubled, but the others? How much design work is really going into kit planes? Or is it eyeballing/judging from experience for the most part? Oliver |
#2
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Quality of kitplane designs?
Oliver Arend wrote:
After reading http://www.faa.gov/aircraft/gen_av/l...dia/Zodiac.pdf I'm wondering how much trouble is hidden in other kitplane designs? Obviously, the RV fleet seems to be rather untroubled.... Obviously? http://www.kalinskyconsulting.com/rvproj/nosegear.htm I've been looking at homebuilt accidents for quite a while now. I got into it hoping to find, among other things, common threads in accidents that might indicate design flaws. As it turns out, clear-cut cases are rare. One factor is probably the relative scarcity of most homebuilt types, which reduces the sample size. Its hard to spot trends from ~5 accidents per year for a given type, especially when over half of them are going to be due to pilot error. Ron Wanttaja |
#3
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Quality of kitplane designs?
"Oliver Arend" wrote in message ... After reading http://www.faa.gov/aircraft/gen_av/l...dia/Zodiac.pdf I'm wondering how much trouble is hidden in other kitplane designs? Obviously, the RV fleet seems to be rather untroubled, but the others? How much design work is really going into kit planes? Or is it eyeballing/judging from experience for the most part? Oliver Often the designs are performed by well meaning backyard designers that borrowed a design from another ship that they saw flying and assumed it to be good. In fact a noticeable test for reliability has been noticed occurring so often that I've coined an ancronym for it: NHFY. None Have Failed Yet. That is exactly the statement I've heard when reliability was questioned. I've heard people say things like "Herby has been flying his ship with that design for 5 years" A closer check shows that yeah Herby has been flying on the average 10 hrs/yr. and has accumulated the total of 50 hrs on that design. In some cases the shafts had very sharp stress risers machined into them but the NHFY said they were reliable. In one case a simple seal w/o the normal spring insert, chewed a 0.020 jagged groove in the shaft. The designer was aware of this problem for several years but elected to use the NHFY reliability test. It pays to look into the specifics of the design and might even pay to have an experienced engineer take a close look. Vans anodizes the RV wing spars. Anodizing aluminum reduces the fatigue life by as much as 50%. Van knows this and takes it into account in his design to achieve a safe aircraft. Other designers see the use of anodizing and use it without having the technical skills evidenced by the RV crew. Numerous examples of violation of "Good Practice" can be seen in numerous aircraft at various fly-ins. If some of the judges used at these events could be of higher technical and experience background, some of these things could be found and pointed out. E.G. A Oshkosh Grand Champion rotorcraft had anodized aluminum control tubes that failed in fatigue. The pilot survived. Up until then NHFY worked. |
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Quality of kitplane designs?
Oliver Arend wrote:
After reading http://www.faa.gov/aircraft/gen_av/l...dia/Zodiac.pdf I'm wondering how much trouble is hidden in other kitplane designs? Obviously, the RV fleet seems to be rather untroubled, but the others? It is not untroubled. Besides the nose wheel issues already mentioned by Ron Wanttaja, about three decades ago the RV-3 experienced at least four accidents in which in-flight wing separations occurred, and since some of the causal chains were speculated or unknown, the wing spar design was questioned, existing airworthiness certificates were suspended and new operating limits were placed on any reissued ones. The designer employed external reviewers who found no problems with the design, but nevertheless made changes to beef up the wing. (Does some of this sound familiar after reading of the Zodiac problems?) You can find some history on the RV-3 problems he http://www.romeolima.com/RV3hq/Info/info.html Scroll down to the "RV-3 wing spar background" section and review the documents at the three links provided for additional background and detail. |
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Quality of kitplane designs?
On May 20, 8:52*pm, Oliver Arend wrote:
I'm wondering how much trouble is hidden in other kitplane designs? Obviously, the RV fleet seems to be rather untroubled, but the others? It's not just problems with the design (if any). Plenty of instances of a design that has no problems *if built according to the plans* but have problems when builders make changes (even if it's just to make it 'stronger'). For example, on Ron's Flybaby page (http:// www.bowersflybaby.com/safety/index.html) there is discussion of wing departure accidents on Flybabys that builders changed. There appears to be nothing wrong with the Flybaby design, yet wings did come off. And others have mentioned the RV-3 'problems'. So pick a design that has lots of examples flying and build it according to the plans. Ross |
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Quality of kitplane designs?
On Thu, 20 May 2010 06:49:58 -0700, Ron Wanttaja
wrote: Oliver Arend wrote: After reading http://www.faa.gov/aircraft/gen_av/l...dia/Zodiac.pdf I'm wondering how much trouble is hidden in other kitplane designs? Obviously, the RV fleet seems to be rather untroubled.... Obviously? http://www.kalinskyconsulting.com/rvproj/nosegear.htm I've been looking at homebuilt accidents for quite a while now. I got into it hoping to find, among other things, common threads in accidents that might indicate design flaws. As it turns out, clear-cut cases are rare. One factor is probably the relative scarcity of most homebuilt types, which reduces the sample size. Its hard to spot trends from ~5 accidents per year for a given type, especially when over half of them are going to be due to pilot error. Ron Wanttaja oliver's thread should be titled 'quality of kitplane design' because this really hits the black hole in most of aviation. nobody ever publishes the design calcs so you have absolutely no way of knowing what assumptions the designer made, you have no idea where they may have made a calculation error and you have no idea what the designer simply forgot to do. of course even if you actually saw the calcs would you even recognise a problem? as it happens I have seen chris's design calcs for the UL. they are many pages of tightly written calculations. I didnt fully understand what he'd calculated. it took a very experienced and schmicked up aero engineer to say 'hang on a mo' there's a calc error there'. ' gee that bit of the structure looks a bit flimsy'.'hang on that isnt the way to calc that'. in the meantime dozens had been built. the schmicked up aero engineer tells me that the corrections the poms made and the corrections described on the EAA website dont actually fix all of the problems that he is aware of. the short answer to oliver's question is that you will never know. calculation competence isnt the full answer either. The W8 Tailwind had no design calcs done that I'm aware of and yet the TLAR approach has produced a competent aircraft. My copy of Wittmans W8 is 25 years old. 750 or so hours and decidedly airworthy. The truth is that this design competence problem wont go away until design calcs are published so that some sort of peer review can occur. can anyone see that happening anytime soon? I cant. we also need a history of published design calcs out there so that people can build up the competent review skills. the solution in the meantime is to wear a parachute during test flying. actually fly a full test program including a dive to VD and a 60 degree banked turn both to the left and to the right at Vne. it wont prove everything but it will give you some increased confidence. btw I saw a really beautifully built RV6 landed a kiss on greaser on its test flight then go plonk on to its nose as the nose leg broke off. vans denied a problem. tisc tisc. Stealth Pilot |
#7
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Quality of kitplane designs?
On May 21, 7:44*am, Stealth Pilot
wrote: btw I saw a really beautifully built RV6 landed a kiss on greaser on its test flight then go plonk on to its nose as the nose leg broke off. vans denied a problem. tisc tisc. Yeah, and a buddy of mine saw an RV land on its nosewheel when the pilot made a bad approach and forced it on. Porpoised down the runway and broke the wheelpant. That sort of piloting is really common and regularly breaks nosegears on Cessna 150s and 172s. That RV pilot flew away again with the busted nosehweel in the baggage compartment, but what damage has been done to the leg now, and when is it going to snap off and cause a serious accident? And who will get the blame? Van's of course, not the clumsy pilot who failed to get the thing NDI'd after the incident. How often are RVs flipping over busted nosegears that were abused by their owners? Can Van's be expected to produce idiot- proof airplanes? Aren't we supposed to learn to fly so that fragile structures like airplanes don''t get broken and don't need redesigning to the point they're too heavy to fly? Dan |
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Quality of kitplane designs?
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#9
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Quality of kitplane designs?
wrote in message ... On May 21, 7:44 am, Stealth Pilot wrote: btw I saw a really beautifully built RV6 landed a kiss on greaser on its test flight then go plonk on to its nose as the nose leg broke off. vans denied a problem. tisc tisc. Yeah, and a buddy of mine saw an RV land on its nosewheel when the pilot made a bad approach and forced it on. Porpoised down the runway and broke the wheelpant. That sort of piloting is really common and regularly breaks nosegears on Cessna 150s and 172s. That RV pilot flew away again with the busted nosehweel in the baggage compartment, but what damage has been done to the leg now, and when is it going to snap off and cause a serious accident? And who will get the blame? Van's of course, not the clumsy pilot who failed to get the thing NDI'd after the incident. How often are RVs flipping over busted nosegears that were abused by their owners? Can Van's be expected to produce idiot- proof airplanes? Aren't we supposed to learn to fly so that fragile structures like airplanes don''t get broken and don't need redesigning to the point they're too heavy to fly? Dan Dang. As a pilot with a few hours in the Cessna products which included hauling sky divers with an avg of 15min between landings, I never saw or even heard much of people losing Nose gears. The Cessna was just very easy to land without getting the nose gear in the way.. |
#10
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Quality of kitplane designs?
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