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Clare,
You seem to be pretty well connected up there. And you concerns are (believe it or not) well taken. May I ask if it might be possible to collect whatever information IS available from that test? Initial assumptions, load distribution, deflections noted (preferably at any given load, if possible), etc. Last night there was a message on the Texas Parasol list that indicated that the spar tube in question had actually kinked. The only thing I'd heard before is that the rig was in danger of imminent collapse - but no details as to what was meant by that. I've never been offered even a scrap of this kind of information - only the final conclusion. And that rather loudly... If you really believe there is an issue here, what would it hurt? Thanks, Richard |
#2
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![]() All right, back to the beheadings! Four days, and not a mumblin' word. Makes a body wonder, don't it? Seriously, if the intent is to protect the innocent and unwary, why NOT respond (and show your work?). Or? Have I misinterpreted obviously altruistic motives? (huh!) I've been trying to raise the RAA web site for several days to see if they post their articles on the web. But it seems to be snowed under and won't be back up until the spring thaw. Fortunately (or otherwise, depending on your point of view?), I just happen to HAVE a copy of the magazine. It was sent to me by a Canadian fellow (who I'll not name to avoid allegations of international espionage). But here it is, and we'll let the reader decide for him/her/it self... http://www.home.earthlink.net/~tp-1/ page-1.jpg to page-6.jpg I particularly like the ripe irony of the last paragraph of the article. There are also a few of the stress analysis reports in pdf format. ul-spar.pdf The original preliminary report (corrected! The original original showed an 8 G limit(!), but it was a simple error) ul-redo.pdf Suggested upgrade to 4.4 Gs at 650 lbs fastner.pdf rivets, bolts, etc For what it's worth, none of these are my own works. They were posted to the Fly5k list by the author and are presented here for enlightenment and entertainment of (any?) interested readers... Richard |
#3
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Richard Lamb wrote:
I've been trying to raise the RAA web site for several days to see if they post their articles on the web. But it seems to be snowed under and won't be back up until the spring thaw. It works for me ..... And they don't post their articles. Rob |
#4
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On Sat, 25 Feb 2006 13:32:14 GMT, Richard Lamb
wrote: All right, back to the beheadings! Four days, and not a mumblin' word. Makes a body wonder, don't it? Seriously, if the intent is to protect the innocent and unwary, why NOT respond (and show your work?). I'm not involved, so I have no work to show. As for the "Canadian project" - it is basically DEAD. Or? Have I misinterpreted obviously altruistic motives? (huh!) I've been trying to raise the RAA web site for several days to see if they post their articles on the web. But it seems to be snowed under and won't be back up until the spring thaw. Fortunately (or otherwise, depending on your point of view?), I just happen to HAVE a copy of the magazine. It was sent to me by a Canadian fellow (who I'll not name to avoid allegations of international espionage). But here it is, and we'll let the reader decide for him/her/it self... http://www.home.earthlink.net/~tp-1/ page-1.jpg to page-6.jpg I particularly like the ripe irony of the last paragraph of the article. The artical was written by a Canadian who was looking for a good, cheap, safe way to get into the air. He was reporting on the early stages of the "Canadian project" and none of the problems with the wings had been uncovered yet, or at least the testing had not yet been done. There is also no indication that they were building a heavier version than yours, other than the mention of designing an all aluminum wing. The artical was written more about the Canadian ultralight regs than about the Parasol. As for the other attatchments, I'm not an engineer, so I can't speak for their accuracy - but at least it looks like whoever wrote them did have a very good understanding of the engineering involved. Myself ? - it was over my head. I have no idea who wrote them, or what his qualifications are. Neither do I particularly care. It's YOUR design. It's up to YOU to either make it safe, and provide accurate information, or to do one of two things: Remove the plans from circulation, or mark them clearly as being "proof of concept" plans requiring some extra engineering - and NOT FOR FIRST TIME BUILDERS. OK - 'Nuff said - I'm out here. I've let everyone on this list know the concerns that were raised, and the status of the plans. That's all I intended. There are also a few of the stress analysis reports in pdf format. ul-spar.pdf The original preliminary report (corrected! The original original showed an 8 G limit(!), but it was a simple error) ul-redo.pdf Suggested upgrade to 4.4 Gs at 650 lbs fastner.pdf rivets, bolts, etc For what it's worth, none of these are my own works. They were posted to the Fly5k list by the author and are presented here for enlightenment and entertainment of (any?) interested readers... Richard *** Free account sponsored by SecureIX.com *** *** Encrypt your Internet usage with a free VPN account from http://www.SecureIX.com *** |
#5
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![]() Such a shame, Clare, because the 4.4G upgrade is exactly what you've been asking for? Richard |
#6
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On Sun, 26 Feb 2006 00:14:19 GMT, Richard Lamb
wrote: Such a shame, Clare, because the 4.4G upgrade is exactly what you've been asking for? Richard I've forwarded the references to Gary, see if he says the issue is adequately addressed. If it is, I'll pass it on back to the group. *** Free account sponsored by SecureIX.com *** *** Encrypt your Internet usage with a free VPN account from http://www.SecureIX.com *** |
#7
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On Sun, 26 Feb 2006 00:14:19 GMT, Richard Lamb
wrote: Such a shame, Clare, because the 4.4G upgrade is exactly what you've been asking for? Richard You want more input - you got it. OK, we are NOT engineers, but looking at this with a few more knowledgeable guys than myself the following observations and recommendations age just the beginning. The last PDF with the spar calculations is a problem. On the first page there is a basic math mistake. We did not go into the calculations to see if the rest was correct or not. 144 pounds per wing is 288 pounds total, not 244. The author then assumes that the lift distribution is equal down the length of the wing, and it is admitted that this assumption was made to simplify the math. Unfortunately this removes some of the lift load from the inner spar and makes the calculated G's quite optimistic. In real life the lift is usually assumed to center about 44% out from the root. A proper load test will have an elliptical distribution of sandbags for this very reason. The equal distribution assumption transfers a lot of sand out beyond the lift strut attach. This has two effects that give optimistic conclusions. There is less sand (lift force) at the weak point 40" out from the root. Also the equal distribution tends to straighten the inner section of spar, like a teeter totter, so that it would take more weight to get the spar to buckle between the root and the lift strut attach. The conclusion is therefore optimistic. Also it is premature to state from this spar analysis that the wing is OK. The calculation, even if correctly done, address only the strength of the front spar. The testing of the wing performed at Gary's hangar addressed this non-linear loading. Just a little more input from another more knowledgeable than myself. The material that the plans and the airplane use is 6061t6 correct? The calculations show the material or the identifier as being 6061. The problem in the shown calcs is that the numbers he is using at 68000psi tensile is higher than the ultimate strength of 2024-t4 which is given at 64000. 6061t6 is only 45,000psi ultimate and 39,900 yield. It's no wonder the wing was failing at 2g. *** Free account sponsored by SecureIX.com *** *** Encrypt your Internet usage with a free VPN account from http://www.SecureIX.com *** |
#8
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Hi Group:
Cla Looking at the calculations for the spar, spar.pdf I do not see your interpretation. The 67000 psi value is Bearing Ultimate, not tensile. A MATWEB lookup is in order: 6061-T6 Tensile ultimate: 45000 Tensile yield : 39000 Bearing ultimate: 88000 Bearing Yield : 56000 The values presented in the spar calculation are correct, and the bearing ultimate of 67000 is below spec. So where is the spar calc using bad values except, as you say, in the initial assumptions of 244 pounds versus 288? Curtis Scholl Just a little more input from another more knowledgeable than myself. The material that the plans and the airplane use is 6061t6 correct? The calculations show the material or the identifier as being 6061. The problem in the shown calcs is that the numbers he is using at 68000psi tensile is higher than the ultimate strength of 2024-t4 which is given at 64000. 6061t6 is only 45,000psi ultimate and 39,900 yield. It's no wonder the wing was failing at 2g. *** Free account sponsored by SecureIX.com *** *** Encrypt your Internet usage with a free VPN account from http://www.SecureIX.com *** |
#9
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On Mon, 27 Feb 2006 15:14:24 -0500, Curtis Scholl
wrote: Cla Looking at the calculations for the spar, spar.pdf I do not see your interpretation. The 67000 psi value is Bearing Ultimate, not tensile. A MATWEB lookup is in order: 6061-T6 Tensile ultimate: 45000 Tensile yield : 39000 Bearing ultimate: 88000 Bearing Yield : 56000 The values presented in the spar calculation are correct, and the bearing ultimate of 67000 is below spec. Thjat may well be true, but is "bearing strength" the proper charachteristic of the material to be used in this calculation? As I said - not an engineer - just asking. Please explain for the rest of us how the bearing ultimate and / or yeild values impact the calculation, vs tensile. *** Free account sponsored by SecureIX.com *** *** Encrypt your Internet usage with a free VPN account from http://www.SecureIX.com *** |
#10
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I've never liked powered ultralights that use the US part 103 definition of
ultralight. The FAA limited the empty weight to far too light a weight. They could have added a hundred pounds to the empty weight and kept the other limitations as they are. This would have produced a real viable airplane class. As it is, the structures are designed without a lot of redundancy. In the airplane in question here, the design is fine when it's new but if there's much hangar rash on the leading edge of the wing the load that the wing can take is greatly reduced. I read all of the screaming and shouting about this plane's wing and I finally decided to take a quick and dirty look at the stresses on the front spar. I choose the front spar arguing that it's going to take most of the loads anyway. Using a single spar unravels a knotty little problem of resolving the reactions from the fore and aft lift struts and the two flying wires. This was only a quick look after all. I just wanted to see if the wing was in the ball park. Please understand that the real airplane needs both the fore and aft spars and the fore and aft lift struts in order to react to the wings chordwise torsion. For convenience, I used a level spanwise wing loading. This is a conservative approach. We speak of conservative and non-conservative. A conservative error is one which leads to an over designed structure. A non-conservative error is one which leads to an inadequate structure. I used the drawings that are available on the web. They include the spar inserts. I have a slight problem with these inserts. Since they aren't a tight fit, its possible for the edge of the insert to cause a stress riser on the inside of the spar tube. It's something to keep an eye on. With my quick and dirty assumptions, I found that the spar would yield at 4.4 g's at 600 pounds gross weight. That is looking at bend moment stresses only. A betters analysis would raise that number. This includes the inserts. Without the inserts the spar yield at 2.3 g's at 600 pounds and 2.8 g's at 500 pounds. Per MIL-HDBK-5 the tensile yield strength 6061-T6 tubing is 35K PSI Rich |
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