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Richard May
 Post subject: Folding wing negatives?
PostPosted: Wed Mar 06, 2019 1:55 pm 
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I have always thought that a folding winged S-18 would be great. But it just occurred to me that a device similar to a rod end bearing is used at the rear spar to rotate the wing on and to act as the rear spar. It would surely provide enough strength to prevent twisting of the wing, but would seem to offer zero strength in resisting wing bending with G loads. And all of the wing bending resistance would be transferred to the main spar. The non-folding winged T&S-18's have a continuous rear spar that would no doubt share some of the wing bending loads during G load. I don't know if I'd want to give that up to get a folding wing. I also prefer the appearance of the mid wing dihedral break, instead of the break occurring near the fuselage side. The mid wing break reminds me of the F-4 Phantom's wing. I think that's one of the neatest aspects of the Thorps appearance. But for highway trailering that would make the mid wing section too wide, so there was really no other way to solve that one. I just wonder with the current S-18 kit, if one chooses to build a non-folding version of the wing, if the dihedral break can be put where the original wing had it? Or is the wing kit only made to use the inner version of the break made for the folding winged S-18? If a non-folding wing S-18 is built, there's really no reason for the dihedral break to be made at the inward location. Unless one prefers the appearance of that. And I know some do. To each his own in that regard. I do think the newer Sunderland airfoil is safer to use whichever way the wing is built.


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Rich Brazell
PostPosted: Wed Mar 06, 2019 2:22 pm 
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If you care not to fold the wing , just bolt it in place and leave it alone . I have had the folding wing version since 2011 (first flight) and have been very happy with it . I have had the AC stored at home here in San Diego for the last 8 years . Hangars are at a premium and years on a waiting list . After 8 years I finally broke down and rented a hangar at KSEE . Figure 8 years x $500.00 month (keeping AC at home on trailer) , that's $48,000 . A good investment in my book !

As far as the trailer my design came from Gus Gordon . With wings folded and on the trailer the whole rig is California street legal ! I am not an engineer but , the "universal joint" on the rear of the wing is more for transporting the wing than flying . I know the "pip pin" is not structural and can actually be missing . I'll let the engineers chime in regarding universal joint . If you do not want to fold the wing but , want the Lou Sunderlund wing use bolts to secure it in place . You may need NAS bolts or hand fit them to get a snug/no play in the wing at the wing attach point at the wing break .

RB O0


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Richard May
PostPosted: Wed Mar 06, 2019 3:03 pm 
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Rich, What I want is the wider and longer fuselage with the original T-18 wing. With or without the newer airfoil. Doesn't that Sunderland airfoil slow the plane down some? Seems like I heard only a knot or two if it does at all. Rich I remember talking to you on the phone many years ago, over at a friends house. I used to live out in San Diego also, in Pacific beach in my United airlines days. Until furlough in '81. Then to Piedmont.. you were furloughed from Usair if I remembered? I also remember how hard it was just to get a tie down spot at Montgomery field. A hanger was totally out of the question. But here where I am now, I rent a hanger for $225 a month south of Charlotte. So the folding wing thing isn't as needed as it would have been if I were still out there where you are. I finished my Glasair 3, and I miss having a project. So I'm looking at the S-18 again. It took me the same 27 years to build the 3 as your 27 years to build the S-18. But I'm sure I can build another one a lot faster! So we always think :) I don't have enough years left to let one drag on that long again!


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James Grahn
PostPosted: Wed Mar 06, 2019 3:44 pm 
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The aft spar has a pin in it to carry the loads. The universal is not for carrying that load. You can use an AN bolt there as well.
In your last post, you describe the T18W. Bottom line is that you can build it however you want.
Cubes


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fytrplt
PostPosted: Wed Mar 06, 2019 4:56 pm 
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I had a "T" wing on my plane for over 1,000 hrs. Then I put an "S" wing on it with aux fuel. I gained about three MPH with similar loading. The stall characteristics of the "S" are almost benign compared to sharp break of the "T". In my talks with Lu Sunderland, he explained these phenomena. They are attributed the more rounded leading edge (better stall) and the better alignment of the chord to the fuselage. The first wing coordinates are 0, -.5. This effectively lowers the leading edge or decreases alpha.

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jrevens
PostPosted: Wed Mar 06, 2019 9:49 pm 
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Richard,


The rear spar fittings on this airplane, folding or standard wing, are not designed for carrying bending loads at the joints between the fuselage, inner and outer panels. The main spars and associated fittings carry those loads.

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John_Arnold
PostPosted: Wed Mar 06, 2019 10:52 pm 
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Great photos Rich. Thanks for posting them. One picture etc. etc.


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Rich Brazell
PostPosted: Wed Mar 06, 2019 11:26 pm 
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Richard...I do sort of remember you although my mind at this point is basically a big bowl of mush ! Like everyone else said about putting this wing on that and that on this wing . Not a big difference as as I can tell but, the LS wing does give a gentler break . When my brain has matured more maybe I can give a more intelligent answer . Motor on ! ???

RB O0


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Richard May
PostPosted: Thu Mar 07, 2019 9:26 am 
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Some good info from you guys, thanks much. I'm surprised at the mention that the sunderland airfoil actually increased speed. Good to know. From what I've learned that airfoil is the nose section of the GAW-2, same airfoil on my Glasair, except it uses it for the entire cord. One could easily think that the sharp leading edge of the original T-18 airfoil would slice through the air faster. But it doesn't seem to be that way. That GAW-2 is on the Piper Tomahawk, not a fast plane. And I always though that airfoil would put a lid on the top speed of Glasairs, then I see Jeff Lavelle doing laps over 400mph in his Glasair-3 in Reno with that wing, so that put that thought to rest. Airfoil shape is beyond us amateurs trying to figure out, who aren't talented engineers. I go with what I hear works best.


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flyingfool
PostPosted: Thu Mar 07, 2019 10:12 am 
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From what I understand. The folding “S” wing aircraft has a higher gross weight and higher G loading. Or at least the same G loading at a higher weight. Which suggests that the “S” wing is STRONGER than the original T wing.

While the dihedral being closer to the tip may make it look more F4 Phantom like. I believe the break point closer to the fuselage of the “S” wing makes it look more F4U Corsair like. Especially with the split flaps.

The F4 phantom seemed like nothing more than an academic aerodynamics riddle to prove that a brick with enough power and putting enough “do-dads” at every conceivable angle can fly.

The F4U Corsair on the other hand was one of the few propeller fighters that made it and used well into the “jet age” and this nearly the epitome of propeller fighter design.

Beauty is in the eye of the beholder.


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jrevens
PostPosted: Thu Mar 07, 2019 11:49 am 
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My understanding is that the weakest point on the standard wing structure is the joint/fittings between the inner & outer panels. When designing the folding wing, stronger fittings (steel vs aluminum) were required to handle the greater moment arm and bending forces at that joint. This also resulted in the greater load limits of the “S” wing - +6/-3 @ 1500# vs 1250# with the original wing.

I used the Sunderland airfoil on my “standard” wing, and I would rate the stall characteristics as pretty benign under normal, coordinated conditions. I had a conversation with Lu Sunderland once when he said that the center of lift of the LDS airfoil was shifted slightly. Supposedly the airplane will fly a little less nose-down, resulting in slightly less drag, potentially giving a little more speed.

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Richard May
PostPosted: Fri Mar 08, 2019 1:26 pm 
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Oh you are right about that F-4. I talked to one pilots that flew them with the Nevada air guard. He said they start the takeoff roll with the stick full aft and just sit and wait until it picks up enough speed to raise the nose. I told him "what a lead sled!", he said "oh yeah, it's nothing but that".. brute power for that bird to fly.


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fytrplt
PostPosted: Fri Mar 08, 2019 1:40 pm 
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That lead sled got me through 210 combat missions and a trip to Mach 2. Pretty bad ass in its day.

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Rich Brazell
PostPosted: Fri Mar 08, 2019 2:30 pm 
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One of the finest airshows I've seen was the Navy Blue Angles flying the F-4 at El Toro MCAS WAY back when ! I think it was their last show flying the F-4 before transitioning to the A-4 Sky Hawk . ;) If you wanted smoke and noise this was the AC to go see ! :P

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Richard May
PostPosted: Sat Mar 09, 2019 11:12 pm 
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That F-4 is still bad ass, once it gets moving with all that power. And I've always loved the looks of that airplane. Some people call it ugly, I've never understood that, it looks awesome to me. Makes me wonder if John Thorp wasn't inspired by it's looks when he designed the T-18's wing with it's mid-span break. The T-18's wing is what I think really makes it stand out above the looks of the Van's designs. Although, one remnant of the original T-18, which was designed to have the engine's cylinders hang out in the breeze, was the tapered cowl and front fuselage. And the cowl cheeks that attach to it. It does reduce the legroom somewhat. Once John abandoned the idea of the exposed engine, I'm surprised he didn't straighten out the fuselage sides to give more room inside. Although if it were like that now, it would look lot like an RV-6 or 7 in the front. Maybe some difference is better.


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