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.
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.
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.