LLE Kit (Laker Leading Edge) Composite Leading Edge ??

[southwind32]

Has anyone installed the composite leading edge? What are the pros and cons on this? Thanks
Brian

[N213RV]

I installed them on my KitFox SS7.

Pros: should improve speed and I like the look of the smooth leading edge
Cons: more work to install vs not installing. Also, be careful of getting too much heat on them when covering. I had a spot that appeared to pull away and form a pocket which was noticeable and I had to adddress.


Has anyone installed the composite leading edge? What are the pros and cons on this? Thanks
Brian

[southwind32]

Looks really nice. Thanks

[efwd]

Hi Brian
I bought just about every upgrade available when I ordered my Kit. Although I like the smooth leading edge and almost dropped the coin for it, I keep seeing the photos of Ross' adventures across the "entire" continent down under. He doesn't have the LLE. If he's having that kind of fun without getting up off his wallet then I will too. I can buy a considerable amount of fuel for the 912iS for that money. :D
Eddie

[rosslr]

Hey Eddie - small correction - I DO have the LLE on mine.

cheers

r

[southwind32]

Hey Eddie - small correction - I DO have the LLE on mine.

cheers

r

Do you think it makes a difference? I looked at an S-5 yesterday that didn't have it, and as far as looks, I thought the wing looked fine without it. Do you think it's worth the extra $1000 in performance?

[efwd]

Oh, Sorry Ross. Thought It looked like it didn't in one of your photos. Damn, maybe I can't fly across the continent after all. :D
Eddie

[jiott]

Here's my take on it FWIW: The Laker leading edge keeps the wing rib profile consistent all along the wing. Without it, the fabric shrink changes the profile somewhat in between ribs, making the profile thinner in these areas. That thinner average profile would reduce drag and also reduce lift somewhat. Therefore you would have to fly at a small increase in AOA to recover the lost lift, but this would also increase drag probably back to the same drag of the thicker average Laker wing profile. I think the differences very likely offset one another. INMHO the main advantage of the Laker leading edge is the smooth consistent looks and a very small weight savings. To me its not worth $1000, I kind of like the retro look without it. I have heard it said that the small changing profile at the old style leading edge acts somewhat like VG's and that may be why the addition of VG's never seems to make much difference on a Kitfox. I have not heard of anyone, factory or otherwise, that has actually measured any performance improvement with the Laker leading edge. This is just my own blathering and am open to other ideas.

[rosslr]

Does it make a difference? I don't now for sure as I haven't flown the aircraft without it, however, I believe it was one of the mods made to improve the performance of the wing. I can understand the thinking behind it. It certainly provides a very consistent leading edge. Eddie, it wouldn't change my mind about flying anywhere if I didn't have it though! I have flown Craig's Model 4 across Australia in three days and it was just as much fun - just a bit slower.

But here is a much more intelligent response from a previous thread ont he topic by our Administrator.

[I]Jim- Yes that is Mr. Laker.

The composite is of a thickness that it would not interfere with the designed flex of the wing either at regular length or the "Speedster" length.

I've flown 3 Kitfoxs with this option installed, both regular wing and the Speedster length, and saw no wrinkles of any kind in the fabric or composite leading edge. The 3 have been in service for up to 5 years now. In that time and number of flight hours if there was to be a problem develop it would have shown by now. Also the LLE appears to be unaffected by our somewhat warm Arizona summer temperatures.

Aluminum has been tried with moderate success. However when the wing flexes from normal flight it does show oil-canning along the length of the leading edge. Dan Denney's bush plane has the aluminum leading edge and has oil-canning after flight. While it has no ill affects on flight characteristics or flexing of the wing, it is aesthetically less pleasing than the LLE. Our Kitfoxs are just too pretty to have wrinkles anywhere.

On an aerodynamic note- Harry Ribblet who designed the Model 4 wing, was never completely satisfied with the finished product that was sold with the Denney Aerocraft kits and consequently all others since. The model 4 wing is in principle the same wing used on all Kitfoxs since, including the model 4,5,6, and 7's. Obviously some design changes were made to increase gross weights in later models. Harry said that there was only about a foot of his actual design in that wing as sold. He intended there to be a D-section to get the full effect of his design. Now we all know how well the model 4-7 wing actually flies so obviously there was no problem with the wings sold, built and flown. It just wasn't precisely what Harry had in mind for the design.

So why am I installing the LLE on my last ever Kitfox. Again I've flown a couple LLE equipped Kitfoxs and maybe 30 give or take of the regular winged Kitfoxs and while I can't exactly quantify with hard numbers the perceived gentler stall characteristics, or the possible improvement in cruise speed, or the quicker take offs, I just really liked the way they all felt. It feels better to me and was so stated almost in the same words by the builders and owners of said equipped Kitfoxs. I think that in the coming years with so many new builders opting for the LLE that we will find out that what I and the others perceive will come to be more quantifiable. I really don't care as I like the way the aircraft feels with the LLE. Could I live without it? I am. I love the performance of my current wing. I think it could be better with the LLE. I'll let you all know sometime in the future just how much when I get some flight hours on my new SS7.

Jim, I hope my long winded response shines some light on my decision to opt for the LLE. For me, the LLE and the Quick Build wing options were must haves along with the four stroke Rotax of course.

[jiott]

Thanks Ross for your informative response. For you it was a must have, for me it would be a nice to have.

One other comment from me on the leading edge, last summer I tangled with the top part of a christmas tree on landing rollout on a friends tree farm. My leading edge being old style is very solid and strong with that sturdy plastic extrusion running full span of the wings. When it smacked the tree, it did not even leave a dent or damage the paint, however the tree top then bent over and slid under the wing (again leaving no scratches or damage) and badly dented the front of my flaperon, which I replaced. My point here is that I believe if I would have had the Laker leading edge the thin fiberglass would have been badly crushed, unless I was lucky enough to have the impact occur over one of those few short pieces of plastic extrusion used under the fiberglass. I'm not going out looking for bird strikes, but if it occurs I may come out fairly good.

I would also like to pass on an interesting flight test I did the other day regarding gentleness of the Kitfox wing stall. I read somewhere, not Kitfox related, that the "falling leaf" maneuver was good practice to get the feeling of your aircraft in a full stall. You go up high and then throttle to idle (I also used 1/2 flaps like a typical landing approach) and pull the stick all the way back into your lap and hold it there. Keep the ball centered and wings level with rudder only. It should stall, drop the nose and recover, then stall again, drop the nose and recover, etc. while you lose altitude like a falling leaf. I did that and was very impressed by how gentle the Kitfox stall is, and how easily the ball and wings are centered. I could have stayed up there all day (given enough altitude) with the stick in my lap and the nose slowly nodding up and down, stalling and recovering all on its own without any other input or throttle from me except occasional rudder inputs. Its really quite amazing. Now I can see why, Floog I believe it was, actually used this method to lose altitude quickly instead of the usual forward slip. Quite a lot of tools we have at our disposal in these amazing airplanes.

[rosslr]

Agreed Jim - and if I was really trying to save some dollars I would not sweat leaving it out of the mix in preference to going flying!

I liked your description of the leave fall stall Jim. I too did it during the testing phase - and a few times since. It really builds confidence in the plane. I think I ay have had the pleasure of experiencing Floog's unique "altitude adjustment" technique! Not exactly textbook but it does keep the aircraft pointed towards the target!

Hope all is good up there with you guys - I still have fond memories of your generosity and look forward o repaying it some day!

cheers

r

[HighWing]

I put an aluminum leading edge on my 2014 completed Model IV, about the time the LLE began development. A comment on the oil canning. Back in the day we flew very often along side a Rans S7 - an earlier model - and oil canning was a frequent event when it was on the ground. The guy, Hal, a name familiar to many, would just grin and walk up and shake the wing and presto "pop" and all was well.

With that in mind, though, when I was installing mine, I decided.to support the wing during leading edge installation as if it was supported by the fuselage and lift struts. In other words, supported by a saw horse like stand at rib #1 and a similar stand at the lift strut attach bracket. I am not sure if this had any effect, but I have never seen any oil canning while on the ground. I guess I need to do some in flight video testing - though it flies without any apparent downsides.

[southwind32]

I put an aluminum leading edge on my 2014 completed Model IV, about the time the LLE began development. A comment on the oil canning. Back in the day we flew very often along side a Rans S7 - an earlier model - and oil canning was a frequent event when it was on the ground. The guy, Hal, a name familiar to many, would just grin and walk up and shake the wing and presto "pop" and all was well.

With that in mind, though, when I was installing mine, I decided.to support the wing during leading edge installation as if it was supported by the fuselage and lift struts. In other words, supported by a saw horse like stand at rib #1 and a similar stand at the lift strut attach bracket. I am not sure if this had any effect, but I have never seen any oil canning while on the ground. I guess I need to do some in flight video testing - though it flies without any apparent downsides.

What thickness aluminum did you use? What technique did you use to shape it? Thanks

[David47]

Just some thoughts on the Aluminium vs fibreglass LLE. The reason you get oil canning with the Aluminium leading edge is that it is quite stiff compared to the rest of the wing structure so it's picking up more load. Oil canning, or more correctly buckling, is a symptom of that. The fibre glass LLE is relatively flexible so you won't see the same effect. So to answer your question Highwing, about whether by supporting the wing at the root and strut attach points in the build you've overcome the oil canning issue, I doubt it. It all depends on the thickness of the Aluminium LE you put on. If it's thick, it may be that the loading it picks up isn't sufficient to cause buckling. If it's thin, it may buckle in flight without you noticing, but not sufficient to stay buckled when you get back to ground.

Having said all this though, there are advantages to an Aluminium LE. One is durability from smashing bugs and anything else coming your way, perhaps with the exception of a tree as in Jim's case, the other is it provides a nice smooth aerodynamic surface at the LE which, incidentally, carries the majority of the aerodynamic pressure loading on the wing - around 50% or so over the first 30% or thereabouts, of the wing chord. So all in all, some form of LE skin that maintains profile is a good thing. But that's not to say that it will materially improve stall characteristics, because there's more to it than that.

For my build, I've gone with the LLE fibreglass option. I thought about using an aluminium alloy LE as well, but decided against it because I wasn't comfortable in handling a long length of aluminium sheet without creasing it. I also suspect I would have to have joined it it somewhere along the span because of the limitation on sheet lengths.

In summary, for mine, investment in some form of LE skin is worthwhile, whether it be aluminium or fibreglass. But then aeroplanes have flown for decades without them so it comes down to choice. And I don't think there is a right or wrong answer either way. They're both relatively safe, performance issues aside.

FWIW.

[HighWing]

I appreciate the comments. I am in Chandler, AZ for a grand-daughter's HS graduation and time is limited - more when I get home. I purchased the leading edge material from Aircraft Spruce. Search Leading Edge. It comes in 12 and 18 inch widths and lengths that will accommodate our wings. Thickness is .016" it is shipped rolled - no creases or dents. Installing was a challenge - more on that later.

[HighWing]

I have to apologize for not fulfilling my promise for more info. Busy busy with returning home from Chandler and diving into a community yard sale all day tIinitialoday. Will respond as promised, but will likely take another day.

[HighWing]

At the time I was building, there was talk about a leading edge modification using aluminum. A buddy and I were building at the same time and we both talked about trying it. The aluminum (12"X144"X.016") was ordered from Aircraft Spruce and sent coiled. My aluminum had taken a set during storage or shipping and to help getting a snug fitting of the aluminum to the spar, it was placed along the leading edge of the wing with concave curvature up. Trial fitting showed that the aluminum didn't want to lay firmly against the decreasing curvature of the rib from spar to the end of the false ribs. Also, it wasn't long enough to cover the entire length of the wing. Those issues became the challenges.

The length issue was solved by cutting the strip so that it would terminate over the #2 rib. and when all was installed, using "Micro" to fair the surface into the wing tank surface. What eventually worked for getting it to lay firmly against the ribs was a series of - one on each rib - ratcheting tie-downs that extended over the leading edge, then sidestepping the rib at the trailing edge of the aluminum and around the aft spar and return. The aluminum could then be forced to conform to the surface curvature. The first thing that was done after the experiments was to rivet an aluminum "Z" shape near the trailing edge of the aluminum strip between each rib that would capture the wood stringer that the false ribs were designed to rest on. (For weight conservation, I decided not to use the false ribs.) The "Z"s were used to maintain the straight - level - surface of the aft edge of the aluminum while under stress from the shrunk fabric and the possible lift while in flight. A note on that. A neighbor and friend had built two Pitts and a Christen Eagle. In discussing the trailing edge "Z" he mentioned that on his builds, the manual called for using a "Joggle Tool" for rolling the trailing edges of the aluminum to essentially accomplish what I did with the Z.

The aluminum was scuffed in the areas of the leading edge and the rib capstrips and a hole cut out that would accommodate the fuel tank filler neck. It was positioned and Hysol 9430 was used to glue in the leading edge along the front spar. Several bar clamps were used to secure the leading edge temporarily while the tie-downs were positioned over each rib starting at the inboard end. Once the Hysol cured, the straps were loosened and Hysol was applied to the remainder of the capstrips - starting aft and working as far forward as possible, the"Z" strips were snapped over the stringer and the straps re-tightened. Early morning or the cool of the day will give more working time with the Hysol.

For aesthetics, I extended the rib lace tape and finish tapes to the front spars. This also helped mask the inboard termination of the aluminum leading edge at the second rib.

That's about it.

Internal showing one bay with "Z"
13332
Wing
13333

[David47]

Nice job Lowell. That "z" former you've attached at the aft edge of the LE with help maintain profile of the LE really well. I don't think I'd like to be trying to form a "z" section on the aft edge of the LE skin as in the other builds you mentioned. I think your solution is way better and you didn't have to fiddle around with recessing the "z" to clear each rib. In a way I wish I'd gone down this path.

[av8rps]

I agree that the Riblett wing works well as it is and therefore the LLE option is probably more for aesthetics than anything. Ive flown Avids with tbe same basic mod as the LLE and frankly couldn't decide if it did anything or not? But I have to admit they sure make tbe wing look better.

A comment just made about the newer wing being beefed up by adding ribs... can someone confirm the Model 5, 6, or 7 having more ribs than say a Model 4-1200? I've never known that, so I'm curious more than anything.

Paul