Buying a used kitfox

[peanut]

I'm going to Florida for work. I will also be looking at a KF5. The space frame/ fuselage is factory build and jig built. Do I have a good reason to be concerned with a home built wing? After all, expoxy brand, application, etc means a lot! I've seen some very messy hysol jobs on the ribs from various web builds. Do I have good reason to question some basement builds? Or am I over thinking this? Are there any inspection plates to check this stuff out? I think I will hire an experimental A and P guy... Thanks a lot for your opinion.

[avidflyer]

I had to rebuild an Avid after flipping over while landing in deep snow with skis on, and when I pulled the old fabric off the wings, I was surprised by how poor the glueing job looked on the ribs to spars joints. The glue was way to runny when applied and it had ran down and off the joints in places, you could even see light through in places. None off those joints were broken however by the plane flipping over. I did clean up the joints and add more hysol before I recovered the wings just to be on the save side. There is also a story about Kitfox once making a wing without the joints being glued and supposedly the fabric once glued up made the wing structurally strong enough. I can't swear to this story as being true, but I did read about it somewhere. At any rate, I wouldn't be overly worried about the glue joints. Look in the inspection holes if you can and go from there. Take care, Jim Chuk

PS Kitfox also had some trouble with some of their quickbuilt wings glue joints back around 1994. They sent out a type of thin glue to pour into the joints that were cracking away from the spars. The Kitfox 4 kit that I have came with that factory repair kit

[peanut]

The wood and glued wings are really the only thing that kind of makes me hesitant on the KF line. All of the other stuff looks like "a real" airplane. I've gotten over the flaperon / ailerons of this type. I used to think it really took away from the looks of the plane but its grown on me.. It's just these wood/glued wings built by a guy who didn't know what was going on.

[HighWing]

Keith,
What is the vintage of the V? I built two IVs (1993 and 1992. I built the first set of wings and a previous owner built the second. Then, the factory supplied a 3M "Structural Adhesive". We were to thicken it by adding some cotton flox. It was pretty easy to get a good fillet by mixing it accordingly and then after applying it with the jumbo syringe use a wet finger to smooth the adhesive. It could be done progressively as the adhesive hardened. It was a dark grey in color. There were occasional issues with the early quick build wings - mostly with misaligned ribs with the ribs not vertical resulting in capstrips that were not flat to the wing surface. Guys would heat the adhesive with a hot air gun and clamp them in the right alignment to cool. I would think that the real issue might not be readily apparent until the wings are mounted and possibly flying. There needs to be some washout for desired stall performance. If I was planning on buying a previously started kit again, I would look at the overall build and check the attention to detail. I think this would give a good indication of how much attention was paid to the instructions. It is all in there and if followed, should be better than a factory built wing - in my opinion. I sometimes worry about stuff that is put together as a matter of routine rather than a one off by the end user - consider the misaligned ribs in the old days. One thing you can check in that regard - The flaperon hangars are mounted to ribs 1,3,5,7 and 9. The centers of those ribs should measure 35.5 inches to align with the slots in the flaperon for the hinges.

Another note. In the hangar where I was based as I flew off the 40 hours, there are two Pitts with all their clothes off being restored. Looking at those uncovered wings - the Kitfox wings look pretty robust.
Lowell

[peanut]

Lowell, he claims it is a 1994. Can I assume this falls in the correct era to be a legit KF5? He's owned it for a few years and he only flew 9 hours. He's near palm beach. Anyway... I've built a number of giant scale RC airplanes. Most of the big planes I built were 110" or so wingspan with twin cylinder 15 hp 2 cycles. My planes were always lighter than most who built the same kit. Sadly, I was an epoxy slinger until I realized more isn't always better! Hahah I am a pretty meticulous person with my toy cars and whatever. I just wish I coul see inside that wing. Also, what covering do most use and what is its life expectancy when flown average hours and hangared? Thanks, Keith

[Av8r3400]

... what covering do most use and what is its life expectancy when flown average hours and hangared? Thanks, Keith


Keith - the kits come with the Polyfiber/Stits system for covering and I believe always have. Lately there are a few builders using the Stewarts system with good results, but I would say the vast majority of Kitfoxes out in the world have Polyfiber/Stits covering.

As to longevity, a properly applied covering that is maintained and hangared, should last indefinitely. 20 years plus is not uncommon.

I chose to recover my project plane because it was stored outside for 10 plus years, so the airframe needed to be inspected in detail. Plus the paint and covering job was seriously ugly. The fabric itself was still intact and usable, just embarrassingly ugly.

[HighWing]

Keith,
I guess I misunderstood the progress of the airplane. If it is flying, not to worry about the rib spacing as the flaperons are already hung. I thought it was a project. 1994 sounds good for a V. Unlike today the IV, a very popular model was continued after the V was introduced. There were a lot of Vs under construction as I was building my first Model IV. As you have some experience with large scale RC, you should get a good first impression how it was built. There should be a at least one inspection cover near the Pitot Tube for plumbing assembly for inspecting at least that portion of the wing interior and it is likely that the wing tips are removable to at least check the outboard two or three ribs. 9 hours? What engine does it have? Is the current owner the original builder or a second owner. The reason I ask this is; has the forty hour Phase I flight testing been completed?

I agree with the covering comment, but even Polyfiber has its variations. I used the Aerothane both times which is a proprietary 2 part Urethane product from Polyfiber and it is very flexible and tough. The other option was Polytone. It is a solvent based top coat, is easier to use and repair, but will crack over time as it hardens, but there are rejuvinators available to help prevent that. It has a more dull appearance than the Aerothane and looks more like the dopes used in the classics. Aerothane can be quite glossy if applied carefully.
Lowell

[peanut]

Well it's like 200 TTAF , had a 582, he bought a mount for a 912, lost interest. Been kept inside the whole time. I wondered about how watertight the covering really is seeing that the wing has wood in it.

[Av8r3400]

My project plane lived outside (upstate New York) it's entire life from '97 first flight to when I bought it in '09. The sealant on the ribs is still shiny and undamaged.

It may seem odd, but it would be best that the wings are not "water tight". Air circulation, drainage and ventilation is needed for the wood to have a longer life.

I would not worry about the wood in the wings.

[peanut]

Yeah I understand about trapping water. I had the pleasure of putting a new transom in my boat from the PO drilling a hole for a depth finder 10 years ago... Arggg thanks for the help guys. If its worth looking at, I might post some pictures of the KF5 if the owner ok's it. I have a buddy going north with a sprint car trailer too. Extra tall enclosed trailer .... This might just work out.

[jiott]

Regarding the glue joints ribs to spars: The only real purpose of the wing ribs is to support the fabric and give the proper airfoil shape for efficient flight and to hold the two spars parallel at the proper distance apart. None of this has much of anything to do with the glue joint; it totally depends on the strength of the wood rib itself. Where the real important strength is in the spars themselves, held in position by the struts and root anchor bolts and the anti-drag cross-bracing tubes to prevent parallelogramming. None of this relies on the glue bond, which only helps keep the ribs in relative position on the spars. I do believe a wing built without glue, with just the shrunk fabric to hold the ribs in place would safely fly. Of course over time the small relative motion between ribs and spars and fabric would cause chaffing, wear and eventual failure.

Jim

[ken nougaret]

peanut,
if your coming through central florida, feel free to stop in zephyrhills for a cold one. i'm in the middle of my ss7 build.
ken

[peanut]

Ken! I go to Sebring 5 to 6 times a year. I'll look you up! Thanks.

[avidflyer]

Just going back to the worry about the wings and the type of construction used in them, I have an old picture from when Avid did stress testing on these wings. Of course Kitfox uses the Avid wing design in their planes as well. Hope the type below the picture is readable. At any rate, Avid tested the wing to 5.7 G's with no negative effects. As you can see in the picture, the fabric wasn't on the wing and I would think that would also make it somewhat stronger as well. I think the newer Kitfoxes have a stronger stiffener inside the spars also. Take care, Jim Chuk