Kitfox Series 7 Super Sport - Show Me Fox

[Jason Murphy]

Hi Jason,

I made some scuff plates for my floorboards out of 0.015" stainless steel shim stock. I think the material was "half-hard", so it is very durable & scratch-resistant, has a nice springy temper and cuts really cleanly & easily with smooth jaw hand shears. I put a "scuffed" finish on them with a scotch bright pad. After doing that I decided I really liked the look of the carpet from Kitfox, and ended up installing that.

Thanks John,

I will look into that material. The upholstery Kitfox sells does look pretty sharp. I am going to try and do my own with the goal of having an airplane that is unique and not quite like the rest. Admittedly I may have gotten in a little over my head on the upholstery side of the world.

I did meet a gentleman this year at the Reno Air Races who is now retired but did upholstery work for a living. I am hoping to lean on him and get some guidance when I get to that part of the project.

One benefit I can think carpet would offer is it would collect bits of dirt and debris which would otherwise work its way beneath the floorboards and possibly end up between the fabric and tubes.

[Jason Murphy]

Please excuse the terrible lighting on the photo of the underside of the wing tank. Sanded the Superfil used to dress out the false ribs bonded to the wing tank.

Flipped the wing with the assistance of my son. Sanded the top surface of the wing tank smooth. There were many imperfections from what looked like dust settling in the resin as it had cured. This tank is in much better shape than my other tank. The scallops which were quite noticeable on my other wing tank was not there. The leading edge of the tank is dished out so I applied Superfil to the leading edge. I will use the leading edge template to guide my sanding efforts and create a nice smooth transition between the leading edge material and the wing tank.

the inboard side of the tank required special attention, the leading edge on the inboard side was about 3/8” tall vs 1/4” on the outboard side. Using 100 grit I gently sanded the leading edge of the inboard side down with the goal of creating a smoother transition. I sanded about 3/8 inch back and about 1/16 down. There was approximately 1/2” of tank material that was not disturbed to ensure the tank would not develop a leak.

[jiott]

I'm not sure whether I should bring this up or not; maybe some others will say there is no problem. My concern is that the wing flexes a lot in flight and that is why Kitfox never had success with rigid aluminum tanks. That is also why they specify mounting the tanks to the spars with a flexible silicone non-hardening adhesive. I would be somewhat concerned in overriding this built-in flexibility by essentially gluing the tank leading edge to the front spar with SuperFill, which cures hard. Not sure if you are doing the same to the aft edge and rear spar. No problem with filling in low spots, roughness, fairing out the shape etc. but actually attaching to the spars could be a problem. Of course the new Series 7 uses the fiberglass Laker Leading Edge to cover the front tank to spar gap, so there is no issue as I describe. Someone who has done it successfully tell me I am predicting a tempest in a teapot.

[Jason Murphy]

Jim, Thank you for the comment. You do make a very good point regarding the flex of the wing... I bet it would be best for me to sand down until I see the fiberglass of the wing tank where the leading edge of the tank joins the spar.

The goal was to fill those low spots and make a nice smooth transition from the leading edge to the upper camber. The tank of my left wing had large scallops between the baffles and I ended up doing the entire top. I did not put anything on the rear of the tank because I figured that the fabric may not even be touching that part of the wing tank.

[Jason Murphy]

Once again it has been quite some time since I have been able to dedicate much time to the build.

Since my last posting I have received my flight instructor rating and I have started work on my CFII rating.

I have dedicated a lot of thought to the fitting my right wings flaperon. This evening I recruited my boys in assisting me with hanging the flaperon back on the right wing and taking measurements.

Using the No 3 rib as my Zero. The No 1 rib measures 35 1/2”. The No 5 rib measures 35 1/2” center to center. The No 7 rib measures 71” center to center. The No 9 rib measures 106 3/8” where it should measure 106 1/2. This falls within the tolerances outlined in p. 3 of the build manual.

I also have been working on a transition between the landing gear reinforcements at the bottom of the fuselage.

The tubing used on the fuselage is 1/2” with powder coating measures 0.515”.

5/8” tube with a wall thickness of 0.058” would have an internal diameter of 0.509 which should have a snug fit.

I also want to ensure there is plenty of fuselage tubing for the fabric to bond to when it is attached.

I cut a piece of 5/8 tubing in half using a pipe cutter. With any luck I will be able to use my pull saw and cut it lengthwise. I need one piece approximately 19 inches in length and the other approximately 7 inches in length. I asked the local machine shop if they could cut it for me and they wanted $150 to run it through their band saw. I am going to give it a try with my pull saw otherwise I can buy my own band saw for that price and have a band saw after I'm finished.

I will need to mix up some SuperFil and make some transitions between my false ribs and the leading edge. Then I plan on sealing all of the wood with epoxy varnish and paint the aluminum with epoxy primer. I will need to make a trip back to St Louis to pickup epoxy reducer. I had two cans and they both developed a leak. I retained the chemical but one had developed rust inside the container and contaminated the clear one.

I will also be pulling the other wing down and sanding all the false ribs down with my sanding block like I did on the right wing. Then sand all the sharp edges and seal similar to the right wing.

[Jason Murphy]

Split 5/8” tube lengthwise

I plan to bond this to the lower longeron to streamline the landing gear bracing.

[Jason Murphy]

Fit 5/8” tube which had been previously cut in half around tubing of fuselage. This was quite the challenge as the tubing of the longeron was bowed as well as large weld beads present.

Used popsicle sticks to ensure the tube was flush outboard as well as vertical.

Longeron and aluminum tube were prepped with scotchbrite and denatured alcohol. I filled the pipe with hysol for 100% bond with the longeron.

I will come back in with hysol and make a nice clean fillet at the joints and ensure water will be unable to get between the aluminum and the longeron. I will likely use some SuperFil to make a transition between the landing gear brackets and faring tube.

[Jason Murphy]

Finished installing the split tubing along the longerons of the fuselage.

These will take the tiniest amount of SuperFil to blend all of the areas together.

I plan on revisiting my doorframes after this. I was advised by a very well informed builder that you should take a straight edge and run it from the door frame to the belly of the aircraft. You should tweak the door frames until they align with the straight edge.

[Jason Murphy]

I committed to the decision that I was going to attempt to move the No 9 rib to make it just right. I was gently heated the Hysol using a solder iron and gently picked away the hysol.

This was an exceptionally tedious process but I did not want to disturb the hysol bond between the spar and the drag / anti drag tubes.

While sliding the rib over the top of the hysol which remained on the spar the shear web fractured at the thin point just above and below the rear spar.

I entertained the idea of following the guidance in AC43-13b and creating a doubler for the shear web but decided that it would be best since the area was easily accessible to simply replace the part with new.

A call of shame was made and additional parts were ordered

[Jason Murphy]

I have been busy studying and training for a CFI-I rating so working on the airplane has been on the back burner.

The new parts arrived a while back. I ordered 2 new ribs, trailing edge, trailing edge reinforcements, and the appropriate rivets. I will fabricate new false ribs using an original factory rib as a template similar fashion to my earlier work.

Today actually went much easier than I thought it was going to. Using a coping saw the No 10 rib was cut away and the false ribs between No 9 and No 10 were cut away. The rivers heads of the stainless steel rivets were drilled out and the rivet shanks were knocked out using a center punch. The front of the No 9 rib was cut away and the No 9 rib removed.

Because the leading edge had been bonded on and dressed up I absolutely did not want to heat anything to remove the old materials. The spars were protected with tape and a dremel tool and flap wheel was used to remove the majority of the rib remnants. Then I finished cleaning up the old materials using a sanding block and 220 grit sandpaper.

Once again this was tedious work but I did not want to potentially disturb the bond of the leading edge. I worked through the day and into the evening and ran out of time to bond the new No 9 and No 10 ribs into place. I have made that mistake of trying to bond something in place and thinking everything was secure and walking away and I come back and it’s wonky.

The wing had been moved out of the basement to the living room because the floors are level. Before I bond the ribs into place I am doing to setup my wing jigs aka precision saw horses ensure they are level and square per directions in the wing assembly supplement to ensure everything is just right. I realize that 8 of the ribs are not disturbed and I could probably bond these ribs in place without taking these extra steps but this makes me feel better about the quality of work performed.

Regardless I have ran out of time in the day and so the wing will be living upstairs this week. My wife is going to be thrilled.