Round Tube Spars with leading edge sheet

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PTAirco

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Apologies for the self-quote, but in engineering circles this rule is sometimes expressed more accurately as "if it seems stupid but it works, you just haven't analyzed it deeply enough yet."
My version: "If it's stupid and it works, it's still stupid."

Not that I think there is anything stupid about the Rans wing design. I had a friend who worked as a stress man for Pilatus and be built an S10. I asked if he ever did a stress analysis and said and no, he he was confident enough to fly it without delving into it too deeply. He didn't say though that it was a fine example of elegant and efficient engineering...it simply works.
 

Matt G.

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That leading edge skin is orders of magnitude less stiff than the tube spar, so it will react far less of the load than the skin.

I can't see in that picture what the rest of the wing looks like, but I'm guessing there's some diagonal bracing to take the torsion and drag loads, and as cluttonfred says, the leading edge skin is essentially a fairing.
 

jumpinjan

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I understand the front spar and the sheeted L.E. (good engineering), but that rear spar does nothing (unless its to strengthen the aileron attachment, probably so). Furthermore, I would add a sheet metal "C-channel" main spar around the 1/4 cord. For T.E. material, a 1/2" tube would be just fine and strong enough to resist the fabric tension. I cannot see how the tube ribs are attached to the front tube, but you don't want to just rivet the fish mouthed end of the rib to the tube spar either. There are better ways to attach the ribs to the tube spar.
Jan
 

BBerson

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image.jpg
That leading edge skin is orders of magnitude less stiff than the tube spar, so it will react far less of the load than the skin.

I can't see in that picture what the rest of the wing looks like, but I'm guessing there's some diagonal bracing to take the torsion and drag loads, and as cluttonfred says, the leading edge skin is essentially a fairing.
The diagonal bracing is for drag/anti-drag load but not torsion. The two spar with two strut is the torsion structure.
 

Matt G.

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Well, that's what I get for not looking much beyond the picture in the initial post and assuming it was a cantilever wing...:lick:
 

PTAirco

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I suspect that the shallow strut angle on a strutted shoulder-wing design means that the struts have a lower tolerance for negative g's.
As proven by that one that lost a wing during a negative maneuver (was it in Argentina?) , caught on video.
 

Marl

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Guys---

If you look into the S-9 that shed a wing you'll find that it was highly modified and had had the bugger flown out of it in airshows. It had a heavier than "approved" engine and was being pushed pretty hard. (Go watch some of those guy's videos---they'll make you hair stand on end with the things that they do!) It looks like he pushed it outside at a fairly high speed for a -9 and built some pretty high -G's before it fails.....

Just saying---the S-9 is a very good design---but this one (regrettably high profile and sensational) accident has been dragged out of storage many times to cast a shadow on the design. If the -9 is built as designed, flown within it's capability, and not abused, it is a wonderful, safe plane.

(And just like a Pitts--the plane can do more acro than prolly 90% of the pilot population can do!!---real bang for the buck if flown smart!!)

Oh--and the aluminum "wrap" on the spar---it's just there to smooth the leading edge of the ribs to get a more uniform airfoil. It is riveted to the ribs and bonded to the spar with a high tech, multi-component, steel-reinforced bonding agent (---ok, JB Weld :gig:). It serves no structural purpose. It is also thin enough that it can handle the bending of the spar that is present in flight (there's really not much bending due to the length of the wing and the location of the strut---it's a beefy sucker!).
 

proppastie

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the plane can do more acro than prolly 90% of the pilot population can do!!.
Any acro is more than 90% of the pilot population can do, and maybe that is a good thing.
 

bmcj

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Guys---

If you look into the S-9 that shed a wing you'll find that it was highly modified and had had the bugger flown out of it in airshows. It had a heavier than "approved" engine and was being pushed pretty hard. (Go watch some of those guy's videos---they'll make you hair stand on end with the things that they do!) It looks like he pushed it outside at a fairly high speed for a -9 and built some pretty high -G's before it fails.....

Just saying---the S-9 is a very good design---but this one (regrettably high profile and sensational) accident has been dragged out of storage many times to cast a shadow on the design. If the -9 is built as designed, flown within it's capability, and not abused, it is a wonderful, safe plane.

(And just like a Pitts--the plane can do more acro than prolly 90% of the pilot population can do!!---real bang for the buck if flown smart!!).
Hey Marl, welcome to HBA. I haven't talked to you in a long time! Did you get your Starduster back in the air yet? I'm still working on mine (actually, it's more like I'm wishing I could find the time to work on mine). If you stick around here, you'll find this forum is very active and interesting, with a good mix of members (engineers, designers, mechanics, pilots, wannabe's, and crackpots :gig:). We do have a group of members that have extensive engineering knowledge and they share it readily.

To address your post about the S-9, I don't see how any reasonable (maybe that's the catch) person could watch that video and jump to the conclusion that the S-9 was underdesigned. It was obvious that the pilot was asking too much of the plane, and that most planes under similar circumstances might suffer a similar fate.


Bruce :)
 

Autodidact

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To address your post about the S-9, I don't see how any reasonable (maybe that's the catch) person could watch that video and jump to the conclusion that the S-9 was underdesigned. It was obvious that the pilot was asking too much of the plane, and that most planes under similar circumstances might suffer a similar fate.


Bruce :)
Especially strut braced planes. I would expect a clip-wing Taylorcraft to do the same thing, or a Decathlon, if it's pushed too far... Never did I suggest that the S-9 was under designed. For crying out loud, he did a Lomcevak just before that!
 
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