Model IV needed mods?

[Greg79]

What mods are a must on a classic model 4? Mine is a speedster but the only thing I'm really keeping from the speedster is the flight surfaces. I am adding the bay back into each wing and changing out the landing gear. I've never flown a KF and there's a lot of threads about adverse yaw and lack of authority on flight surfaces.
Do I need to add electric trim?
Lager elevator?
Lager rudder?
I'm pretty close to covering so I want to make any needed changes before. I would love any advice on anything pertaining to building a model 4
Thanks!

[avidflyer]

If it's a classic 4 with the 1200 lb gross weight, it should have the larger tailfeathers already. Also the mixer controls on the Kitfox 4 and later eliminate some of the adverse yaw that was more noticeable on earlier models. JImChuk

[Greg79]

Thanks, it is a classic 4.

[Wheels]

I would add the provision for a rudder trim tab to the tail before covering. Not an electric trim, just a place to mount a tab or wedge. I have a IV and its a classic IV no speedster mods. I also have the cargo pod and I use it although its harder to do as the stock configuration is just plain hard to access. I'm working on a quick release pin set up and some wheels to drag it around like luggage. I"ll still have to attach and detach for access.

[Greg79]

I would add the provision for a rudder trim tab to the tail before covering. Not an electric trim, just a place to mount a tab or wedge. I have a IV and its a classic IV no speedster mods. I also have the cargo pod and I use it although its harder to do as the stock configuration is just plain hard to access. I'm working on a quick release pin set up and some wheels to drag it around like luggage. I"ll still have to attach and detach for access.

I figured I was going to need a rudder trim tab. Seen several threads on here where they just adhesive them to the fabric but I'll add some tabs. How does yours fly without elevator trim?

[cap01]

yes, you do need electric elevator trim. i installed it on my IV 1500 and its one of the better mods I've done. the larger elevator would be nice to have on mine, I'm not sure if the speedsters have the large elevators.
if you have the old gas tanks be sure to replace them also both should be the 13 gal tanks.
if the wings aren't covered, install tubing for an aoa if there's a chance you might want that system

[Av8r3400]

I did some extensive modifications to the tail on my Classic IV-1200. It was an experiment to gain authority at lower speeds of the elevator and rudder. Thus far I have been happy with the mods and the handling compared to my IV-1050 I had previously.

I did add an electric elevator trim tab. IMO this is a good modification to make.

The rest of these are not necessary to do, but I wanted to do some experimenting and make the plane my own...

16568

This is a good before and after of the elevator. Also shown is the trim tab. If I could do it again, I'd make the tab larger.

16569

[HighWing]

One of the most frequently mentioned issues - elevator authority - can be helped a lot by simply closing the gap between horizontal stab and elevator. Most do it with tape after covering. You may want to look at the geometry and see if there might be something you can do before covering. I did it and it was pretty complex, but l am sure there could be simpler approaches.

[avidflyer]

Another thing I would do if I have an uncovered Avid or Kitfox is widen the fuselage before covering it. The Kitfox 4 I'm currently rebuilding is now 4" wider in the seating area. The Kitfox 3 I'm doing is 3" wider. Used steel tube on the 4, and glued on wood in the 3. The doors are bent to fit the opening when they have no windows or panels in them, and then installed with the doors in their final position. The Kitfox 3 was covered already when I got it, but I was able to undo the fabric enough to get the wood glued on, and then pulled the fabric back into place. Once again, I can't up load photos. JImChuk

[av8rps]

I would make any mods to fuselage necessary to install an extended baggage area with hard floor and sides. Probably just a few extra tabs? Av8r3400 did a really nice baggage area on his. Maybe he has a few tips for you on that.

I really don't think the average guy needs bigger tailfeathers, but if you have a desire to do some major refabbing, go for it. If you decide to keep the original tailfeathers, an elevator trim tab is good to have and so are gap seals so as to make the existing elevator fully effective.

I would also make sure you have a good plate for the com antenna ground plane, as that is hard to do once fabric is on.

And if you plan to do any booney bashing, one can never go wrong with adding a few gussets on the tailwheel attach area for a little extra pounding back there.

And also for the rough and tuff off airport stuff, you might want to add plates to the fuselage area forward of the seat, like they have on the Kitfox Super Sport.

And if you are concerned ever about flying over the 1200 gross, add a 4130 strap across bottom of fuselage that is attached to the lower wing strut attachment, providing extra strength to the wing attach during positive g forces. And while you're at it, put a couple extra gussets on the rear carry through spar (head rack) area nearest the rear wing spar bolt attach. These minor additions will make an already strong airplane much safer if flying heavy and in gusty conditions.

Oh, and on that subject make sure your horizontal stabilizer struts have the larger rod ends on them. The earlier 1/4 inch ones have a service bulletin on them to go up one size.

And last but not least, make sure you replace or strengthen the original rudder pedals so as to avoid broken pedal in flight. That can either be all new pedals from Kitfox, or modifying your existing pedals with strengthening gussets. That is all easier to do before fabric is on.

That ought to keep you busy for a while :)

[Greg79]

Yep that will keep me busy for awhile!! Thank you!!

[Guy Buchanan]

Go through all the Service Bulletins. Yes, I know it's a pain, but that's where all the safety issues are.
Decide what your goals are. Do you want an Oshkosh winner? Do you want it ultra-light? Do you want it super comfortable for long cross countries? Your goals will define many of your mods. For example, for my plane the goal was light, light, light, but still sexy. So:
All wood paneling was replaced with aluminum honeycomb.
The fiberglass seat pan was replaced with carbon. (Early seats had cracking issues at the forward attachment.)
The instrument panel and glare shield was carbon.
No silver UV protection was used, as the entire plane was painted with Imron, which had UV protection in it.
The tail surfaces were kept stock, with minimal airfoiling on the horizontal and vertical stab surfaces only.
The rudder was gap sealed with a simple carbon extrusion. The elevator with clear packing tape.
Lots of other mods to keep things light.
Everything was designed/built to make it easy to fold the wings: turtle deck, flaperon controls, fuel line routing, and I installed inboard valved tank vents to allow folding with full tanks.
My upper cowl was split at the firewall. This allowed a water-tight seal over the electrical and avionics, while still having easy access to the engine.
Next time I'd use piano hinges to attach the various cowl pieces.
Build a rigid baggage compartment. I made mine out of aluminum angles of various sizes and used corrugated plastic for the sidewalls and fiberglass honeycomb for the floor. All could be removed for access to the aft fuselage. Some have removed the two diagonal seat belt supports that intrude on the baggage compartment and moved the center seat belt support outboard to behind each occupant.
Build your own door latches.
Use bubble doors.
Make the rear triangle windows removable. Don't attach them to the fabric; they'll then be difficult to replace.
Put your door struts in front. That makes flying with the doors open much more pleasant.
If a 912 install, put the voltage regulator behind the firewall. It's not noisy and the heat reduction may save you some money.
I'd reinforce the landing gear attachments. They can rotate under load. (The pins move inboard.)
Put in the flap detent system.
If you feel like some fun, extend the legroom 3" by moving the seat back and the engine forward. You'll be happy you did. (Make sure the wheels stay in the same place relative to the leading edge.)

OK that's enough for now. Whew!

[Slyfox]

Good advice Guy, keep it light. the only Mod my 4 has is elevator trim. ya it's got grove gear, real nice. I put stats in the horizontal. has the standard elevator that came with it, I think it's the 94 1200. It started out long wing. I took a bay out and added two new tanks 13 gal. put vg's on it. now has 27.5 tires and T3 8inch matco double arm tail wheel.

I don't think mine needs the added supports, I learned to land it slow. many people make the mistake and come in over the numbers at 70mph or higher. be it scared or doing the Cessna thing, don't know. but a kitfox will bounce and go all over the place and ground loop with those speeds. I would just make sure the front mains are in alignment. that can make a squarely little machine.

what has made my fox special is the 912uls motor. that really changed the airplane. power when I need it and I don't have to worry about density altitude. I also love the inflight adjust medium Ivo. My 4 is a cheap fun flying machine. I love it.

[Greg79]

Thanks Guy!That is a big list!