LLE and Fuel tank

[alanr]

Hi all,

Just thinking about my yet to be ordered kit and the LLE option and if to go for this option at all.
I think I am correct in understanding that it comes in two pieces and joins at rib#5. Just wondering if folks are also cutting and making a join at the edge of the fuel tank (I think rib# 3)to make changing a fuel tank slightly easier if and when, heaven forbid, in the future a tank happens to leak. Or is this not the thing to do?
Also any comments for or against the LLE would be appreciated. The added weight v benefit v appearance etc.

Alan

[cap01]

alan , don't know anything about the leading edge kit but i have some experience with the gas tanks leaking . be sure to leak check them good before installing them . i had a new tank that leaked and luckily found it before i installed it . when the hole was drilled for the outlet , the drill had gone too far in the tank and cut into the tank on the other side of the little sump area by the outlet . being the standup people that they are , the mcbeans made it right .

[mr bill]

I don't know how much they improve performance, but they do improve the appearance of the wing. I installed them according to the instructions and would not cut them at the tank until repairs are needed.

[alanr]

Chuck/Bill, Thanks for the advice....much appreciated.

[jtpitkin06]

Part of the charm of a Kitfox is the rag wing appearance. Some paint jobs actually emphasize the scallops on the leading edge.

The leading edge kit has not been shown to be of significant advantage in performance. Adding weight just to make it look more like a metal wing is somewhat a move in the wrong direction. But that's why they make Fords and Chevys. Everyone likes something different. Maybe an all metal wing Kitfox will show up some day.

jp

[alanr]

Great thoughts John..Thanks.
I change my thoughts day to day on if going with the LLE option, with maybe slight performance gain and the smooth look is worth the extra weight and any issues with a tank change further down the line. Of course there is also the $1000 dollar saving if I don't go with it to consider!

[jiott]

A couple of thoughts on the LLE: I don't believe the weight gain is much at all because the LLE eliminates the full span plastic extruded leading edge which is quite heavy. Also, I agree with John in liking the ragwing look of the scalloped leading edge. There is also some thought that the scallops act somewhat like VG's, actually improving the wing performance, or at least offsetting any performance gain with the LLE.

[Esser]

I went with the LLE because I want to actually scientifically experiment with VGs. The LLE is quite light and I think adds very little weight over the extrusion piece.

That's just me

However, if you had a leaking tank, I would just cut the LLE at the time of tank removal. It will be a simpler job than the fabric patch.

[alanr]

I thought read somewhere the LLE added 2.5lbs per wing...is this not correct?

[HighWing]

Part of the charm of a Kitfox is the rag wing appearance. Some paint jobs actually emphasize the scallops on the leading edge.

The leading edge kit has not been shown to be of significant advantage in performance. Adding weight just to make it look more like a metal wing is somewhat a move in the wrong direction. But that's why they make Fords and Chevys. Everyone likes something different. Maybe an all metal wing Kitfox will show up some day.

jp

I agree with John somewhat. You can always recognize a Kitfox approaching by the way the sky reflects off the top of the wing. But....

The Harry Riblet airfoil only has its full cord design contour over the wing tank, rib cap strips and false ribs. This amounts to about 37 of the 156 total inches of leading edge per wing (24%). Airfoil designers will tell you that the most critical section of an airfoil is the leading 10%. of the top surface. One of my best Kitfox buddies has heard Harry Riblet himself comment on that when discussing the Kitfox wing.

I have mentioned that I have the poor mans leading edge - aluminum. I find that stalls are much more docile, especially full power stalls, than my first Model IV in which they were exciting to say the least. Stall speed is a couple of mph slower. I figure my added weight is about 10 lbs. as I eliminated the top false ribs. Would I do it again? Yes, but would have to think about the $$$ with the LLE.

[alanr]

Lowell and Josh, thanks for the input...all food for thought.
Seems to me the case is not totally clear cut either way so whichever way I go, LLE or not, I will probably wish I had done the other at some point down the line!

Alan.

[DesertFox4]

The LLE will be on my 7SS. I've flown two Kitfox with it installed and can tell the difference. Problem is no one has had time to do in-depth comparisons between with and without. I know that the wing behaves differently, better, with. Wish I could quantify my impressions with real data but alas, I can't. Just know I've flown a few "stock" Kitfox in my day and a couple LLE's. I'm going LLE.

As mentioned early, Harry Ribblet designed the wing for the model 4 ( which is the same wing used on the 5,6,7,& 7 SS). If you don't know the name and fly a model 4 on up, you should know his name. He's the reason we all have such great flying and handling aircraft.
His design had the "leading edge" as now available in the LLE. Denney Aerocraft and SkyStar never used the leading edge treatment for whatever reason. Maybe they couldn't figure out a way to make it work without incurring the problems resulting from the wing flex. Maybe monetary reasons. Dan Denney has it on his private "super stol" Kitfox but has aluminum instead of fiberglass. He has deformation from the wing flex but other than the fabric wrinkling he loves it. That says something right there.

Now that the flexing wing problem has been solved by the LLE, it completes Harry's vision for the best performing wing for our particular aircraft. We all know the Kitfox flies great without the LLE and thousands of aircraft flying don't have it. Also as mentioned earlier, maybe V.G.'s will have a measurable effect on this wing. Not sure yet. I think after some time and with many builders installing it, we may see in the future that those aircraft with the LLE may be in more demand over the Kitfoxs without. Of course my crystal ball has been a little off in the past.:rolleyes:

I love the look of the LLE Kitfox wing too over the scallops. :)

[alanr]

Steve..Thank you for the explanation and your experienced input. So for today it looks like I will be going with the LLE even if it does break the bank!

Also following your build with very keen interest..simply great!

Alan

[Flybyjim]

So how does the LLE work with the flex of the wing and not show up with wrinkles in the fabric as you indicated the aluminum does?

[HighWing]

A note on wing flex and aluminum leading edge skin deformation. One of our buddies from the Fly Idaho days had a Rans s-7 with aluminum leading edges. His would occasionally have the aluminum cave between one of the ribs. We would call it to his attention and he would grab his wing tip and with a grin, shake the wing and the bubble would pop out.

When I decided to to the aluminum leading edge, it occurred to me that it was on the ground that the aesthetic imperfection would occur and be visible. In the air, who knows - aluminum or composite. And I repeat, until someone mounts their GoPro looking outward on the top of the wing, who knows what the top surface looks like in flight with the outboard end flexed up.

I planned my installation in the ground configuration. My Rotisserie was modified to support the wing at the lift strut brackets. The wing would then hang as it would when on the fuselage on the ground. The only thing I would do differently if I were to do it again would be to put some weight in the tanks as they will warp the spars a bit when full. i will occasionally have s small barely visible four inch diameter dent near the outer edge of the third rib left side. It is impossible to see when on the ground, but if you look while filling the tank it sometimes appears.

For what it's worth, I rechecked my numbers and got a four mph lowering of stall speed at power off - 40 mph clean. These numbers are relative to my first Model IV.

At 4500 RPM, I could get 30 mph before stall and at full power 28 mph with no wing drop. (The "interesting" in my previous post referring to full power stall has always been previously referred to as violent. I was asked to do a full power stall during a BFR once. I did it and that once was enough for the CFI.) I procrastinated big time during Phase one on this airplane for obvious reasons.

[DesertFox4]

Good stuff Lowell. More info than I could give the group. All I could tell was that the wing behaved better in all speed ranges. Felt more reliable if that makes sense.

I'll do that GoPro thing but probably not for a while yet.;)