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#61
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Texas Parasol Plans...
Cla
Bearing strength is for the Connecting Points of all those items you mentioned. And the engineer stopped the test before complete failure from what I read. Excessive deflection is not a failure mode unless the engineer states it is out of spec. And again, what was the sandbag testing weight at which the testing was stopped? And again, excessive deflection where? In the skins? In the Spars? in the struts? You stated: ** "No- Gary built a wing according to plans and sandbag tested it under an engineer's supervision. The engineer stopped the loading before failure because of excessive deflection IIRC." ** And I have a set of plans, and I recall seeing the sleeves being called out in the manual. And I don't see where aluminum skins are in the plans. Again, deflection where? "And sleaves in the spars by your own admission. Which are NOT in the plans." See wing plan D-WING3. It clearly shows what to do on the wing as for the sleeve inserts to reinforce the connecting points, wing to cabane, and strut to wing. Look, this aircraft flies, in it's designed weight class, it has worked for many years. The designer flies it. There are many copies flying, and the death rate is not "significant" considering what happened in the accident reports. As you said, Clare, you are not an engineer. And you don't have current validated DATA to back you up. I have stated instances of you being incorrect in your assumptions. And in one of the instances, given you the reference for corrections of your statements. We are done. No response is necessary or wanted. This will be an agree to disagree situation and no further contact is warranted. Curtis Scholl |
#62
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Texas Parasol Plans...
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 |
#63
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Texas Parasol Plans...
On Tue, 28 Feb 2006 09:50:32 -0500, Curtis Scholl
wrote: Cla Bearing strength is for the Connecting Points of all those items you mentioned. And the engineer stopped the test before complete failure from what I read. Excessive deflection is not a failure mode unless the engineer states it is out of spec. And again, what was the sandbag testing weight at which the testing was stopped? And again, excessive deflection where? In the skins? In the Spars? in the struts? The wing was tested to 2 G's at 600 lb gross. At that point the spars were ready to fail if I recall correctly. You stated: ** "No- Gary built a wing according to plans and sandbag tested it under an engineer's supervision. The engineer stopped the loading before failure because of excessive deflection IIRC." ** And I have a set of plans, and I recall seeing the sleeves being called out in the manual. And I don't see where aluminum skins are in the plans. Again, deflection where? The wing was tested with NO ALUMINUM SKINS. There are doublers at the arttach points in the plans, but the spars are not doubled between the root and the struts, which is where the spar is not up to the job from what I gathered. I'll be talking to Gary tomorrow "And sleaves in the spars by your own admission. Which are NOT in the plans." See wing plan D-WING3. It clearly shows what to do on the wing as for the sleeve inserts to reinforce the connecting points, wing to cabane, and strut to wing. Look, this aircraft flies, in it's designed weight class, it has worked for many years. The designer flies it. There are many copies flying, and the death rate is not "significant" considering what happened in the accident reports. As you said, Clare, you are not an engineer. And you don't have current validated DATA to back you up. I have stated instances of you being incorrect in your assumptions. And in one of the instances, given you the reference for corrections of your statements. We are done. No response is necessary or wanted. This will be an agree to disagree situation and no further contact is warranted. Curtis Scholl *** Free account sponsored by SecureIX.com *** *** Encrypt your Internet usage with a free VPN account from http://www.SecureIX.com *** |
#64
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Texas Parasol Plans...
Earlier, Richard Isakson wrote:
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. Interesting. When I run the moment of inertia for 2" tubing of .058" wall, I get 0.1667 in^4. Using that number and a yield strength of 35 ksi I get a yield moment of 5833 in/lbs. Do those numbers agree with yours? Of course, those figures disregard cripling or buckling, which I've not seen mentioned in this thread. I suspect that this whole thing will come down to a somewhat subjective matter of distributions and deflections. The distribution of loads between the forward and aft spars will make a big difference, and I think that the wing deflection will start to look scary before the spar tubes reach yield. But those are just more non-engineer's guesses, and there's been plenty too much of those already. Taking this out on a tangent, one thing about little airplanes like this that I don't understand is why so many of them use tubular spars. It seems to me that you can get so much better strength/weight and stiffness/weight using a built-up I-beam or C-section spar. Yeah, it's a bit more trouble. But the result is either better strength and stiffness for the same weight, or the same strength for less weight. But again, that's just my non-engineer wing developer perspective. Thanks, and best regards to all Bob K. http://www.hpaircraft.com/hp-24 |
#65
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Texas Parasol Plans...
"Bob Kuykendall" wrote ...
Interesting. When I run the moment of inertia for 2" tubing of .058" wall, I get 0.1667 in^4. Using that number and a yield strength of 35 ksi I get a yield moment of 5833 in/lbs. Do those numbers agree with yours? Of course, those figures disregard cripling or buckling, which I've not seen mentioned in this thread. For the spar alone those numbers are right and result in the poor spar performance without the inserts. The maximum bending moment happens at the strut attach point. This is where the insert sits and that increases the moment of inertia to 0.3155. This results in the improved load handling ability. In the interest of laziness, I didn't look at spar buckling nor did I look at negative loading. There is a potential for column buckling of the spar between the root and the strut attach point. As the wing is lifted, the strut is placed in tension. This places the inboard portion of the spar in compression. The combination of the compression load and the lift load could potenially cause buckling. Maybe I'll look at that sometime. I suspect that this whole thing will come down to a somewhat subjective matter of distributions and deflections. The distribution of loads between the forward and aft spars will make a big difference, and I think that the wing deflection will start to look scary before the spar tubes reach yield. But those are just more non-engineer's guesses, and there's been plenty too much of those already. Reading what little has been said about the load testing, I suspect there's a problem in the way the wing was held. It almost sounds like they didn't have the rear lift strut attached Taking this out on a tangent, one thing about little airplanes like this that I don't understand is why so many of them use tubular spars. It seems to me that you can get so much better strength/weight and stiffness/weight using a built-up I-beam or C-section spar. Yeah, it's a bit more trouble. But the result is either better strength and stiffness for the same weight, or the same strength for less weight. But again, that's just my non-engineer wing developer perspective. I think it's to keep the labor costs down. You might ask Chuck. Rich |
#66
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Texas Parasol Plans...
("Richard Isakson" wrote)
[snip] 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. Agreed, almost. 350 lbs would have been great (without floats). Low stall number is fine, but let's remove the speed limit on the upper end. If it weighs X and stalls at Y, carries one person and (8g) gallons of fuel ...who cares about its top-end speed! Montblack Hell ...I'M not 103 legal !!! :-) |
#67
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Texas Parasol Plans...
On Tue, 28 Feb 2006 19:31:30 -0800, "Richard Isakson"
wrote: "Bob Kuykendall" wrote ... Interesting. When I run the moment of inertia for 2" tubing of .058" wall, I get 0.1667 in^4. Using that number and a yield strength of 35 ksi I get a yield moment of 5833 in/lbs. Do those numbers agree with yours? Of course, those figures disregard cripling or buckling, which I've not seen mentioned in this thread. For the spar alone those numbers are right and result in the poor spar performance without the inserts. The maximum bending moment happens at the strut attach point. This is where the insert sits and that increases the moment of inertia to 0.3155. This results in the improved load handling ability. In the interest of laziness, I didn't look at spar buckling nor did I look at negative loading. There is a potential for column buckling of the spar between the root and the strut attach point. As the wing is lifted, the strut is placed in tension. This places the inboard portion of the spar in compression. The combination of the compression load and the lift load could potenially cause buckling. Maybe I'll look at that sometime. I suspect that this whole thing will come down to a somewhat subjective matter of distributions and deflections. The distribution of loads between the forward and aft spars will make a big difference, and I think that the wing deflection will start to look scary before the spar tubes reach yield. But those are just more non-engineer's guesses, and there's been plenty too much of those already. Reading what little has been said about the load testing, I suspect there's a problem in the way the wing was held. It almost sounds like they didn't have the rear lift strut attached It WAS attatched. It was attatched as if it was on the plane but upside down. Taking this out on a tangent, one thing about little airplanes like this that I don't understand is why so many of them use tubular spars. It seems to me that you can get so much better strength/weight and stiffness/weight using a built-up I-beam or C-section spar. Yeah, it's a bit more trouble. But the result is either better strength and stiffness for the same weight, or the same strength for less weight. But again, that's just my non-engineer wing developer perspective. I think it's to keep the labor costs down. You might ask Chuck. Rich *** Free account sponsored by SecureIX.com *** *** Encrypt your Internet usage with a free VPN account from http://www.SecureIX.com *** |
#68
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Texas Parasol Plans...
Richard Isakson wrote:
In the interest of laziness, I didn't look at spar buckling Without the jury struts, IIRC, it cripples long before anything else fails. Deflection at the jury strut attach point to the strut , during the load test was, 2 or 2.5 inches when really loaded down. hth Rob |
#69
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Texas Parasol Plans...
"Montblack" wrote in message
... ("Richard Isakson" wrote) [snip] 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. Agreed, almost. 350 lbs would have been great (without floats). Low stall number is fine, but let's remove the speed limit on the upper end. If it weighs X and stalls at Y, carries one person and (8g) gallons of fuel ...who cares about its top-end speed! Montblack Hell ...I'M not 103 legal !!! :-) I'm not sure that the subject is worth discussing further at this late date. But, since we are--the stall speed number is definitely *not* fine! The problem with the unreasonably low stall speed is that very modest surface gusts can easily upset an ultralight while taxiing; or worse yet, while taking off or landing. 350 lbs, one seat, and the speeds now authorized for LSA would have *dramatically* improved safety with only very modest training--although any maximum speed of at least 80 Kts would have worked. Peter Flagellation of a deceased equine is unsatisfying! |
#70
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Texas Parasol Plans...
Curtis Scholl wrote: Cla Bearing strength is for the Connecting Points of all those items you mentioned. And the engineer stopped the test before complete failure from what I read. Excessive deflection is not a failure mode unless the engineer states it is out of spec. And again, what was the sandbag testing weight at which the testing was stopped? And again, excessive deflection where? In the skins? In the Spars? in the struts? I disagree. Excessive deflection is a failure mode if it has sufficient adverse impact on function or safety, without regard to whether or not any particular engineer realized it and said so. That is more a criticism of the wording you used, than it is of the implied question--How do we know the deflection was excessive? (And what was it that deflected?) -- FF |
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