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Extended Leading Edge rib stitching

skywagon8a

MEMBER
SE Mass MA6
My leading edge skin is extended 12-1/2" aft of the spar on the top and stops at the spar on the bottom. How is everyone attaching the fabric to the bottom cap of the rib in this area where you can't get a full stitch in place. Do you just run the stitch around the lower cap? or do you glue it in this area and start the stitching at the 12-1/2" location?
 
The way I did mine .....

Attach the front edge of the extended LE to the normal leading edge (1/2" overlap) then clamp it down to the ribs. Using a square, draw pencil lines that align with both edges of the ribs. Cross mark these lines where the normal rib stitches (spacing) would go. Remove the extended LE from the wing. Using a step drill, drill 3/8" holes (slightly to the outside of the line to leave some material in the center) at the rib stitch cross-marks.

The 3/8" holes are larger then needed to pass the rib stitch through but being "over-sized" insures that the you can easily pass the needle / stitch through the hole without getting it up against a sharp edge where it could chafe through. Also, about 1/2 the hole will be over the rib so the thread should not be shafed on the inside either.

Take care,

Crash
 
Both interesting ideas. I had not thought of stitching the upper surface over the leading edge. You are correct in making generously sized holes to prevent cutting the stitches. I was going to attach the top fabric the same as if it were a wood skinned wing, glued down to the edge. The concern with the lower surface is to hold it up tight to the rib because of the slight concave curve of the cap strip.

What do you think of just stitching the lower cap back until you can get a full stitch?
 
You're now in the lifting portion of the wing where the extended LE is being installed. I would NEVER just glue the fabric down. Rib stitch or use big headed rivets or some type of mechanical fastener in this area.

Setting the spacing and pre-drilling almost makes extended leading edges a "non-issue" when covering the wings. Every set I've ever seen, was done this way.

Take care,

Crash
 
Cuz at high AOA, the fabric will be pulling away from the wing structure on top. Glue MIGHT be fine, but if it's not - - -
 
Crash said:
Setting the spacing and pre-drilling almost makes extended leading edges a "non-issue" when covering the wings. Every set I've ever seen, was done this way.

Take care,

Crash

Setting the spacing and pre-drilling almost makes extended leading edges a "non-issue" when covering the wings. Every set I've ever seen, was done this way. DAVE
 
So has anyone ever tried running a 12" strip of fabric lengthwise down the wing instead of the extended metal? It seems that if the fabric was only glued at each end it would shrink tight in a lengthwise direction with no scallops and support the main covering layer. I was thinking of trying that to save weight and the rib stitch issue.
 
gpepperd said:
So has anyone ever tried running a 12" strip of fabric lengthwise down the wing instead of the extended metal? It seems that if the fabric was only glued at each end it would shrink tight in a lengthwise direction with no scallops and support the main covering layer. I was thinking of trying that to save weight and the rib stitch issue.

don't think that would work without a strong strip at back edge of fabric strip...

you could do some serious lightning holes in ext LE maybe, I have seen .016, but you must use angles under it....

if you shrink fabric right you will not have much scallops at all...

for top of wing you shrink in strips long ways of wing starting from center of wing & at high part of rib curve, out both ways, and then move an inch or two and do another stripe, tring to finish that forward curved area where scallops form before going near rear part of wing.... and at end do whole wing.... never front to back or you guarantee HUGE scallops

not sure if this shows well, but this is without extended LE, shrunk right to avoid scallops

01010013.JPG
 
The medium fabric being produced right now is a few ounces shy of the previous heavy fabric. It pulls tight with out much scalloping. I actually thought the scallops helped slow flight. I thought that is why the wood spar J3 with the 3/4 wrap leading edges flew better than the aluminum spars with full wrap leading edges.
 
I stitched around the whole rib up to the aft edge of the extended leading edge skin. Then I went around just the bottom rib cap to the spar. On top, I used fabric rivets through the extended portion of the leading edge skin up to the spar. I have photos somewhere.
J


fabricrivets.JPG
 
We use to put extended leading edge on almost every set of wings we built. If we didn't we would "pinch an inch". After gluing fabric on the leading edge of the top of the wing, we would gather, with clothes pins, an inch or more of fabric in two places length ways about 12" aft of the front spar. This would gather more length ways strands of fabric and when shrunk like Mike said it would make the fabric extremely tight over the area of the ribs that are most prone to scallop. I know the extended leading edge works, but on my wings that i am building now i think i will forgo the weight and "pinch an inch".
 
So it the advantage of reducing/eliminating scallop based on performance or cosmetics? I remember disagreement about any benefit and have never heard anything conclusive to support extending the edges or even in attempting to eliminate scallop.

Is the FAA allowing you to extend? Three years ago I was told not to even think about it. The FAA would not even consider allowing it without engineering.

Thanks,

Stewart
 
I guess that's where I am at. I know the extended leading edge, if done right, works to eliminate scalloping. Whether or not this is a performance advantage, I'm not sure. I know it adds weight and the frost builds heavier on it then just the fabric.
 
I've read the 1927 report. I still can't help but wonder how it applies to modern 2000# Cubs with long props, VGs, synthetic fabric covers, and all the other things that have changed in the last 83 years. I know some really good Cub pilots who believe extending the edges improves performance. I mean guys who push performance to limits beyond my own. I've also read rebuttals. In the end I have more information about the topic yet I'm no closer to answering the question about whether there's a benefit. The good news for me is that in my use I'll never recognize such a benefit. That doesn't ease my curiosity.

Stewart
 
I remember talking to Dan of Dan's Aircraft repair (Anchorage AK). They used to put them on almost every Cub they rebuilt when the FAA allowed it.

He told me about Cubs they had recovered and the only mod was to extend the leading edges. The owners came back and said "wow, it feels like you installed a STOL kit or something". These were long time owners / Bush operators with thousands of hours in the same plane.

One day I was at the airport talking with a Cub pilot and commented on how nice the fabric job looked on a Cub. He said "ya it looks great but now it flys like crap, there's too much scallop between the ribs and it won't slow fly like it used to".

We've also seen pictures posted of Cubs in flight with the fabric on top of the wing billowed WAY up between the ribs. This has got to make for a very fat, slow flying wing.

So what is the correct fabric tension between the ribs? Extended leading edges removes that question for the most part.

I also feel they help improve cruise speed. Before, this Cub with big tires, Borer prop., etc. would curise at around 85 mph. Now it cruises at 105 to 110 mph.

IMG_2613.JPG


P.S. I weighed them before installation and they weighed 3 lbs.

Take care,

Crash
 
I think Paul Babcock at one of the LHV wing rebuild seminars mentioned something about a metal spared wing has a little bit more lift than a wood spared wing because the leading edge on a metal spared wing goes all the way to the spar, and a wood wings LE is shorter and leaves a 4 or 5 inch gap in front of the spar that is scalloped all the time and decreases lift.??

Glenn
 
Interesting to get two opposite views:

cubdriver2 said:
I think Paul Babcock at one of the LHV wing rebuild seminars mentioned something about a metal spared wing has a little bit more lift than a wood spared wing because the leading edge on a metal spared wing goes all the way to the spar, and a wood wings LE is shorter and leaves a 4 or 5 inch gap in front of the spar that is scalloped all the time and decreases lift.??

Glenn


Steve Pierce said:
The medium fabric being produced right now is a few ounces shy of the previous heavy fabric. It pulls tight with out much scalloping. I actually thought the scallops helped slow flight. I thought that is why the wood spar J3 with the 3/4 wrap leading edges flew better than the aluminum spars with full wrap leading edges.
 
cubdriver2 said:
But are we talking about 2 different area's, one is in front of the spar, and one is aft.

Glenn

Glenn-

You and Steve are talking about wood spar wings and how the leading edge on the bottom of he wing does not go all of the way to the spar. IE 3/4 wrap.

P2240544.JPG
 
From a previous thread....


Extended Leading Edge skin(ELES)

I spoke with John Roncz, probably the leading airfoil engineer in the US. He is the one who has designed all of Rutans airfoils and others like john Sharp's Nemesis (dominated Formula 1 for many years). The guy is no yahoo, he knows airfoils and aerodynamics. I asked him about the Extended LE skin (ELES). After a long dissertation on the 35B airfoil origins etc his response was that he did not know of any wind tunnel tests, so take it with a grain of salt, but based on what he knew about airfoil performance, he did not think it would have any positive affect. At high AOA the air is only attached at the LE edge of the wing forward of the front spar. Thus any airfoil deformation aft of the forward spar is in dirty air and basically has no affect.
All that said, the ELES, remains an unknown because we have no wind tunnel testing, and furthermore we must add the VG's to the equation.
It does add rigidity, and strength, to the wing. Makes it easies to clean the frost off, and minimizes the scalloping. But it adds weight, 4 to 6 pounds.
Steve Tubbs, Jerry Burr and John Roncz all have expressed reservations as to its effectiveness at high AOA.

Bill
 
behindpropellers said:
cubdriver2 said:
But are we talking about 2 different area's, one is in front of the spar, and one is aft.

Glenn

Glenn-

You and Steve are talking about wood spar wings and how the leading edge on the bottom of he wing does not go all of the way to the spar. IE 3/4 wrap.

Steve may be talking about J3's with wood spars, NOT J5's. The J3 wood spar used the short LE, (like a PA18 outboard skin), full span. I've heard the same thing as Steve from the old timers that made a living dusting with J3's. The argument has been made before....

It seems the only reason the metal spars had the skin extended back to them was to keep the spar from twisting. That makes sense. If you really think bending some tin farther back will make it fly better....have at it.
 
SuperCub MD said:
behindpropellers said:
cubdriver2 said:
But are we talking about 2 different area's, one is in front of the spar, and one is aft.

Glenn

Glenn-

You and Steve are talking about wood spar wings and how the leading edge on the bottom of he wing does not go all of the way to the spar. IE 3/4 wrap.

Steve may be talking about J3's with wood spars, NOT J5's. The J3 wood spar used the short LE, (like a PA18 outboard skin), full span. I've heard the same thing as Steve from the old timers that made a living dusting with J3's. The argument has been made before....

It seems the only reason the metal spars had the skin extended back to them was to keep the spar from twisting. That makes sense. If you really thing bending some tin farther back will make it fly better....have at it.

Well obviously I was wrong here, I have not taken apart a wood spar J-3 wing and thought it was similar to a J-5 wing. Regardless, they both have exactly opposite ideas on the subject, which was the main point.

Tim
 
I believe it is difficult to compare the effectiveness of extended leading edges between an old fabric job and a new fabric job, on the same cub, with the extended edges. A cub with new fabric properly applied flies differently than it did with old fabric. I have talked with accomplished cub fliers and there is not a consensus on whether the edges are an improvement or not. What I have seen is the dents, between the ribs, in the trailing edges of these edges from snow loads, as the fabric is attached to the to the edges during the recovering process. I have seen some edges that were braked on the trailing edge and some that were not. I do think that the scalloping when kept to a minimum probably has not effect on the flight characteristics. Too much scalloping may lead to ballooning, which is a performance killer.
 
Sorry Tim, I didn't read the second half of SP post " sorry Steve " Tim that pix is of your J5 wing, same LE as my J4, LE goes from top of spar to a couple inches short of the bottom spar, the J3 wood spared wing the LE stops short of both the top and the bottom of the front spar, what I was referring to was that the gap between the shorter J3 LE and the spar is always scalloped and is not as good as a full LE like on a metal spared wing at producing lift or the scalloped one kills it. so if your wrong it's because I may have lead you astray :lol: not on purpose of course :roll:

Glenn
 
cubdriver2 said:
Sorry Tim, I didn't read the second half of SP post " sorry Steve " Tim that pix is of your J5 wing, same LE as my J4, LE goes from top of spar to a couple inches short of the bottom spar, the J3 wood spared wing the LE stops short of both the top and the bottom of the front spar, what I was referring to was that the gap between the shorter J3 LE and the spar is always scalloped and is not as good as a full LE like on a metal spared wing at producing lift or the scalloped one kills it. so if your wrong it's because I may have lead you astray :lol: not on purpose of course :roll:

Glenn

No....I was mistaken..... I thought the J-3 wood spar wing LE was the same as a J-5. Got to learn something today, I'm sure somebody else did too.

Regardless...you and Steve can figure it out. I should go home and blow the dust off of the J-5.
 
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