Fuel Tank Rebuild, new Trailer and Firewall rebuild

During the initial engine run up, a number of problems became apparent. The engine head was cooling properly, but the rest of the engine compartment was overheating. It also became apparent that I had too much pitch in the propeller. I reduced the pitch to the least angle available and I will use this setting for the retest. According to Leon Massa of Compact Radial Engines, the engine will really heat up at 6200 RPM. I have yet to see more than 5400 RPM. The tuned pipe I designed, was sized to start delivering a secondary boost at 6200 RPM. So hopefully the increased prop inflow will deliver more airflow for greater cooling at the higher output. The under cowl temps were getting too high after shut down, I recorded  300 degrees surface temp on the upper surface of the cowl. I have no doubts about the composite being post cured now!! As I outlined in the previous posts, I removed the fiberfrax from the firewall and then re-coated it with Fiber Frax and then a shield of .012 aluminum. I reinstalled the engine and added another heat shield between the exhaust and the fuselage fabric. Another problem with my original design was mounting the instrument panel permanently to the canopy. This turned out to be unsatisfactory because I cannot run the engine without the cowl installed. I am revising the design such that the instrument panel is on a separate hinge and will swing out of the way when the canopy is opened up. I have decided to use an original Fournier RF4D canopy in the future. I found a very good source who can make them for a reasonable price. Even though the canopy is thicker than the Lexan I am using, the elimination of the frame and housing will result in a net weight savings. Speaking of the Canopy Frame. I modified it to remove the solid bulkhead, this will interfere with the seat head rest, so I had to cut the foam core and complete a "corner Closeout"

the exposed pink foam shows the area I cut away.

the pink area was where the bulkhead was. I cut it out and then knife cut the pink foam away. I made a cut parallel to the existing laminate along the surface and then cut in at 45 degrees to remove a foam wedge approx .25" x .25" The exposed inside laminate was sanded with 180 grit paper to roughen it up so it can be secondarily bonded.

cut foam and sanded inside laminate

this shows what the edge looks like before dry Micro was troweled into the cut. Dry Micro was used, but that by itself has very poor adhesion properties. The technique here is to paint the surface first with raw resin and then trowel the Micro in.

Dry Micro

Dry Micro has a consistency similar to cool whip, its about as lite too. The key is that the mixture has a dull, non shiny surface.

laminate added

 
2 plies of 8 oz fiber glass was added over the micro and exposed foam. Its only necessary to wet out only 1/8" beyond the edge. In approx 12 hours the epoxy will be cured to a semi hard state that allows easy knife trim. after trim, the edges can be slightly rounded over because the micro will be exposed.
This is a common technique that is used to finish out a structural edge. Sometimes, the foam us routed out flush down to a 1/4" and unidirectional roving is added in place of Microballoon, this would greatly increase the bending stiffness of the canopy frame. It is not required on an Ultralight however.

The next big job was to redesign the fuel tank, again this is a temporary solution. I am going to adapt an off the shelf polypropolyene tank, this will offer the maximum resistance to Ethanol. Its unreasonable to assume that pure gasoline will only be available in the future. I need to talk to Leon about revising the carb and Engine seals.  I am really amazed what happens to epoxy when exposed to ethanol in gasoline. 20 years ago when I made fuel tanks similar to this for my old Wren, Ethanol was not used in fuel and I never had any issues. Because of this, I would NEVER consider buying a home built composite airplane that uses Mogas. Wet wings especially like the Lancair would be destroyed.

existing fuel tank mold

The rebuild started by laying up 3 ply's of 8 oz and one face ply of 120 glass in the existing mold. The mold was prepped with 5 coats of mold release wax. This mold is well seasoned, so 3 coats is sufficient

existing mold

3 plies of 8 oz and a surface coat of 120 glass were laid up.  All seams are overlapped a minimum of 1.5 inches

Bottom surface mold form

Instead of laying up the bottom surface on a flat plate, I decided to make a foam and Bondo sump. This will become the low point of the tank. This is a temporary one time tool.

lower surface mold form

I added bondo to fill the foam surface, and then sand able primer over the top of the mold form. 10 coats of mold release wax was added and then a coat of spray able PVA water soluble release. After the mold was treated, I laid up 3 plies of 8 oz fiberglass and one surface coat of 120 glass.



bleed air being added to aid the cure of the sloshing compound


After the bottom surface was cured and released, I bonded a glass bearing block into the base of the sump. This will be drilled and tapped to accept some barbed nipples for the fuel line and primer line.  I rough sanded the inside of the main tank and the bottom surface. I mixed up some epoxy and cotton Flox to a peanut butter consistency, its very important that this mixture have a shiny surface. I then bonded the upper surface to the lower surface.  After the tank bond cured, I drilled a 3/4" hole where the fuel gauge will go and started the sloshing process. I am banking on this sealant to give me enough life of this new tank for the flight test program. I will constantly check the tank for signs of ethanol degradation

And Finally!!! The reason I was late in updating this blog was a trip I made to Pearson Georgia to South Georgia Cargo. I got a hell of a deal on a 24' enclosed cargo trailer. I will convert the interior into a camper and a hauler for my plane. The trailer was sold thru Allpro Trailer out of Florida http://www.allprotrailers.com/  Ask for Brian Robison  brianr@allprotrailers.com The price was $3800 base , but I ordered 5200lb axles, the final price came to $4300. After my buddy Ed and I picked up the trailer, we immediately headed north to Wilson, North Carolina where Ed bought a very nice Piper J3F cub project. Ed started a blog similar to this, http://nc35447.blogspot.com/2012/06/data-plate-confusion.html  give him a visit sometime.

Robins new Home away from Home