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Old 08-18-2017, 05:57 AM   #26
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Apples and Oranges. Stardusters are usually NOT flown like a Pitts so no reason to fail. And of coarse no drag wire blocks to fail either.


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Old 08-18-2017, 07:46 AM   #27
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Default High performance S1 wing plans

I figured the apples to oranges thing. But still...both are aerobatic rated (yeah yeah I know Stardusters are not "designed" for Acro even though they are stressed to +6 -6, it's a known story Lou Stolp didn't like Acro as he feared to many would die trying it but he did design the plane to take the G loads, so while it wasn't designed to be a top Acro mount it is indeed aerobatic and rated for such...same can be said for RVs.) one seems to have a fail problem of plywood wings one doesn't. If one is failing within it's gross Acro weight G rating then there is a design issue not a type of construction issue. Maybe the drag wires vs tubes IS the reason you don't see Starduster failures of the plywood wing ribs? Not debating the better or worse Acro machine here, interested in why one plane seems to have a higher failure rate of a type of Rib construction where another does not....Again, with both being flown within there design G limits. (I'm curious if the Sparcraft routed Pitts Rib failure is overly talked about and exaggerated the actual failure rate?) seems like if one is flown within its flight designed limits and has zero failures (or very few) and the other is flown in its limits but has higher failure rates there is bigger issue at hand... the drag wires might very well be the issue.



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Old 08-18-2017, 12:11 PM   #28
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I have no idea about the drag wire vs. tube has any relationship to anything but the "simple" fact is that 99% of SD2 are NEVER flown like the average Pitts is!

My Spezio is built like a tank and supposed to be stressed to +9 G's but that has about nothing to do with how they are flown. Yea I know some idiot managed to break one negative which led to the jury struts but it was never designed for aerobatics. That said, the Tu-holer wing with it plywood LE's is probably almost impossible to damage internally
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Old 08-18-2017, 12:37 PM   #29
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I'm thinking the S-2C rib design change was to make them cheaper to build, not lighter. I'll guess the ply web is 1/8" and there's no need for vertical spruce members or additional gussets -- notice the vertical grain on the plywood. The material costs would be higher with this design but the labor could be a lot less.
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Old 08-18-2017, 11:53 PM   #30
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The ply vs stick built rib failure comparison has little to do with G loads. When I first started to work for Ultimate the first thing Gord said to me was, my ribs are broken, why do you think that is, and can you fix it so it won't happen again. They were stick built, and broke just ahead of the rear spar. The problem was the ailerons were bigger & more powerful than standard Pitts ailerons, the load they placed on the hinges was twisting the rear spar, putting a compression load in the top and bottom cap strips. I placed a 1/2" sq. spruce strut each side of the ribs, top and bottom, 4 pieces per rib, near each hinge location. That became standard on the first commercial Ultimate wings. This wasn't my idea exactly, the Stearman has compression struts that do the same thing to stop any twisting of the spar. The Starduster does fine with ply ribs because the aileron load is less, if it was increased, something would have to be done to handle the twisting moment on the spar. There is no debate, stick built is lighter, but for all but the thoroughbred competition machines, ply works ok if the design is done right.
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Old 08-19-2017, 02:29 AM   #31
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Quote:
Originally Posted by planebuilder View Post
he problem was the ailerons were bigger & more powerful than standard Pitts ribs, the load they placed on the hinges was twisting the rear spar, putting a compression load in the top and bottom cap strips.
well that explains the the torque tubes in the S-1-11-B wings, spent 2-3 days making those dam things........1/2 inch wood struts would have been a lot easier to make....
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Old 08-19-2017, 03:27 AM   #32
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Ahhhhh. So it's a function of the rear spar twisting due to the Pitts having larger aileron loads that causes the more frequent failures of the Sparcraft Pitts wings vs Starduster Too ribs.

This was exactly the kind of detailed info I was curious about. I knew it had to be something other than "people fly one harder". It's actually the Sparcraft wings are not strong enough due to the aileron load constant acro applies to them. A easy fix of adding more compression struts would solve the issue but alas it would add more weight to a already heavier design than the original. Does anyone have any actual numbers of how much a set of Sparcraft wings weigh vs a set of stock stick built wings weigh? (Assuming both have plywood leading edges....as that the new standard more all agree is better, most. I'm sure someone will swear aluminum is still the cats meow but I'm just trying to see what the weight difference is if both are built with the same leading edges)

This is all strictly academic as I believe this is a no different than any other hobby where 99.8% percent of us can't get all the performance out of "the dog" of the two. Unless you weigh 130-150lbs vs 175-225lbs that most weigh now days it's always funny to hear people talking about saving ounces while they eat there second burger. Kinda like a 200lb jockey...the old nag with the 90lb child size jockey wins everytime. Anyway...it's all very interesting to me to understand the "why" something isn't as good vs just hearing it isn't and not really knowing a good reason.
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Old 08-19-2017, 04:48 AM   #33
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With due respect I think you are again confusing apples and oranges. What planebuilder was talking about twisting the spar was NOT a standard Pitts wing but the Ultimate with its huge ailerons. And it was stick built ribs that were breaking not plywood.

That said I bet you could break a Starduster wing.....if you rode it hard enough.
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Old 08-19-2017, 10:59 AM   #34
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The only thing that a spar craft wing and the s2c wing have in common is that they are both made from dead trees
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