RE: Nitroplanes Skymaster 337, Build Tips
<div style="text-align: center;"><span style="font-size: larger;"><u>Field Assembly</u></span></div>
In previous threads I learned that it is difficult to assemble the plane at the field. The nylon bolts that attach the TE (trailing edge) of the main wing are under the air scoop on the rear cowl. I solved this problem by building new, wider, mounts inside the fuse. This places the nylon bolts outside the scoop. Too bad you can see these bolts but it sure beats having to remove the spinner, prop and cowl every time you want to get at these bolts! I added plywood and mahogany to the outer skin of the fuse to reinforce the area where the new wing mounts attach. To make this wing modification complete I epoxied the dowel rods provided with the kit for the wing’s LE (leading edge). Then cut off, drilled and tapped them for ¼ x 20 nylon bolts. New TE bolt holes were drilled into the wing and wood was cut out from the under side to access the wing cavity. I then inserted and epoxied as much plywood as I could into this space to give the new holes some strength. Now wing attachment is simply to slide the TE under the scoop and drop the LE down to the fuse. Add four nylon bolts and a few screws for the canopy and you’re done!
Wing tubes are cut to almost perfect length to fit inside the wings. With the tail booms temporarily in place, see how well the wing parts seam together. I had to trim about 1/16” off the end of one tube to get it right. The instructions make absolutely no reference as to how the tubes are attached. There is a pilot hole under the central wing for the larger tube. I used this hole and also scouted out where the smaller tube was sitting. I was confused with most of the hardware that came with the kit so I drilled and tapped these wings and tubes for 6-32 machine screws. I did this for the wing extensions and the central wing section as well, so each tube is held in place with screws at each end (8 screws total for wing tube assembly). Thread locker is used for the wing tube screws. For storage and transportation I leave the tubes in the wing extensions and just add four screws to the central wing section at the field. If a hard landing causes the wings tubes to bend just replace them with 5/8” and 3/8” aluminum or brass tubing.
I also trimmed away some wood at the top of the rear bulkhead. It was right in the path of the air flowing in through the scoop to cool the rear engine.
BTW: If you make this wing mounting mod with 1/4 x 20 blind nuts do not use the nylon bolts that come with the kit. They are NOT 1/4 x 20.