Stretching the tail?

[TJay 1041]

 This may come as a shock to some of you but I dont know how to quite.  I was looking at the kitfox today and thought to myself I bet that thing would look better If I added 10 inches to it.

So here is the math

Empty CG with adding 10 inches to the tail 13.16

Most forward 12.74

Most aft         14.14

How does that sound to you guys? Should I go longer than 10 inches Or does that sound about right?

[1avidflyer 1983]

What is the distance from your leading edge of wing to tailwheel center now?  I just did my Kitfox 4 last week, and it was 156.75".    Where are you thinking of adding the length?  JImChuk

[TJay 1041]

Right now its 155 I was thinking of going to 165 Mostly for looks and to get my numbers a little better I believe my empty cg is 11.9 Maybe I would have to look and with 10 inches back that would get me to 13.16. As for extending it I would just do the last bay in the tail that looks by far the simplest. Also keep in mind I am working on building a new set of wings with the newer airfoil. I love Airplanes.

Jim what is your empty cg?

[1avidflyer 1983]

TJay,  My empty CG on the Kitfox 4 is 12.55" and I'm at 644.6 lbs.  JImChuk

[ChrisBolkan 130]

I think extending the tail will lower your angle of attack unless you add larger tires or taller gear. But it is awesome if your engine is too heavy :-)

[Good old number 29 158]

I had been considering the same thing with my model 1. I think 10" sounds about right. My idea was to do that when I put a Phazer motor on it, but then I'd want to stiffen the wings, and then I'd want to strengthen the carry throughs accordingly. Might as well build new wings, with a cleaner airfoil, while I'm doing that. I got to the point that I figured I should probably fresh. Actually, I want to build a clean, composite cruiser. Something to pick up where the Kitfox leaves off, rather than trying to turn it into a Super Cub. Just thinking... But really, I think you have a good idea. Model 2 and later were 7" longer on the fuselage. 10" is probably better. You could try to compensate for the minimal difference in AOA, but it's probably fine, as is. I don't have any trim in mine. It requires constant back pressure on the stick to keep it level. It seems like a little adjustment on the tail, when you lengthen it, would fix that and address the angle of attack issue at the same time. 

[1avidflyer 1983]

Have you tried pulling just a little bit of flaps?  That will lower the nose and act as trim.  JImChuk

[Good old number 29 158]

I have to hold back pressure and hold the nose up. The flaps are already reflexed a little. Can't pull them up any farther. Pulling them down makes the nose go down more, as noted. I ought to try to take a measurement of where the stick is, in flight, and see where that puts the elevator. We could call it a weight and balance issue. Kitfox is known to be nose heavy, commonly, and mine would be one of the best examples of that, with the panel tank, no wing tanks,  no battery or header tank behind the seat, and heavier landing gear with bigger tires, on the shortest model. On the other hand, the elevator does what it's supposed to. Just a little better angle on the horizontal stabilizer, or a trim tab, and it would be fine. I'm starting to believe that the wings should have had a little more angle of attack built into them, in the first place, since it commonly touches down tail first, even with a fair amount of flaps bringing down the nose, and the 25" tires. The greater wing twist of my early model also decreases the angle of attack of the wings, overall. I should add that stretching the tail back 10" would resolve any issue my Model 1 might have with weight and balance, or trim.

Edited 7 Aug 2020 by Good old number 29
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[TJay 1041]

Another trick I found is push the front of your horizontal down till it hits the frame tubing and drill a new hole that helps lighten the back pressure and only takes about 10 minutes.

[1avidflyer 1983]

Have you tried pulling just a little bit of flaps?  That will lower the nose and act as trim.  JImChuk

Sorry, I was thinking backwards when I wrote this post.  And I haven't had a drink in weeks..... What I have done to lift the nose is a short length of 1/4" bungee cord tied to the seat truss that goes around the joystick, and goes back and is tied to the seat truss.  As you raise the bungee up the joystick, it puts more back pressure on the joystick, and that will act as nose up trim quite nicely.  JImChuk

[109jb 181]

On my Kitfox 4 I can trim it with flap for cruise but I've also been thinking about adding trim using a bungee, a piece of sailing rope, and a mini sailing quick cleat. Would cost only a few dollars and only take a few minutes to rig. A whole lot easier that cutting the back end of the plane off.

[Good old number 29 158]

I was thinking about my misuse of terminology on my previous post. Obviously, I meant to say angle of incidence, rather than angle of attack. It seems like my Model 1 could use a bit more angle of incidence, since the angle of attack is such that the tail touches first, even with the bigger tires. I've considered doing what TJay suggested, changing the angle of the little wing, I mean the horizontal stabilizer, to decrease the stick pressure in level flight, I just haven't gotten around to it. I'll probably make that adjustment when the fishing season slows down. I have a whole list of things I want to do to it, still. Like stretching the tail...

[akflyer 1427]

I was thinking about my misuse of terminology on my previous post. Obviously, I meant to say angle of incidence, rather than angle of attack. It seems like my Model 1 could use a bit more angle of incidence, since the angle of attack is such that the tail touches first, even with the bigger tires. I've considered doing what TJay suggested, changing the angle of the little wing, I mean the horizontal stabilizer, to decrease the stick pressure in level flight, I just haven't gotten around to it. I'll probably make that adjustment when the fishing season slows down. I have a whole list of things I want to do to it, still. Like stretching the tail...

Stretching the tail will make that tail hit first even worse.  Are you using full flaps for landing?  You can either drop the leading edge of the horizontal stab down or put a trim tab on the elevator and tweak it till she flys hands off at cruise.  A couple turns around the pattern will get you dialed in. 

What is your CG at?  Get it back around 16 or 18" and the plane will fly MUCH better and land SLOWER.

[Good old number 29 158]

The original numbers had the cg limits at 10-14.something. The slightly heavier tailwheel helps bring it aft a little, but the 25" tires bring it right back to where it was. Since I'm just running the panel tank, and don't have a battery, there's not much I can do to bring it aft, except add dead weight. If I do that, the cg is moving further aft as I burn fuel, so I pretty much left it to be what it is. The way they set the cg limit is a joke, in the first place. 120 pound pilot and full fuel sets the forward limit. Low fuel and two fatties to make it full gross sets the aft limit. 
My comment about stretching the tail and  touching down tail first was intended to say that you could make a slight adjustment to compensate for that, so it didn't get worse. 
Yes, I have been doing full flaps landings. Once you get a feel for how much much much adverse yaw that gives you, it's pretty great if you don't have a crosswind. I've read the comments that some people have made about always keeping the flaps up, that they never use them, but it does get a lot slower with full flaps. Plus, you land a lot flatter. 

For myself, my plan to stretch it is going to start at the tip, lengthening the rudder and elevator. That will give me some more control authority and move the cg aft a bit, in a way that keeps it controllable. 
I had a whole lot of fun the other day, with some strong, steady winds aloft. I backed the rpms down to 4,000 and gave it full flaps, making 15-20 mph, speed over ground. Looking down, I could hardly tell I was moving. These planes are a lot of fun to fly slowly.