The Bobcat-75 Project

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Page 2

       It was time to mount the booms to the wing panels. The kit came supplied with some nylon bolts that were intended to hold the booms to the wing. I was not to keen on how weak they were or the fact they did not seem to fit the blind nuts very well so I used my own hardware. I found a few steel M4 x .75 metric bolts in my screw assortment that fit the blind nuts perfectly so I installed the booms with the steel bolts and some washers. I used a liberal amount of blue thread locking compound to keep them from backing out.

       I decided to thread the servo wires through the front hole in the wing root to be eventually run into the fuselage. I did have to trim a piece of balsa to fit them up front.

       As far as I can tell there was very little thought in the design on how the wings were going to stay on the spar. I can only assume that the horizontal stabilizer itself would keep the two booms together and thus keep the wings from flying off :0P I wanted something a little more secure so I opted to install a blind nut on the front part of the wing root rib. This nut will be used with a cap screw inside the fuse to hold the wing to the fuse.

       Notice the 5/8” hole I made in the fuse for the servo wires to pass through.

       I used a “fender washer” under a M4 bolt to secure the wing to the fuse. I also used a liberal amount of blue Loctite on the threads to keep them tight.

       I have heard of folks gluing the wing to the fuse using epoxy and even silicone which seems like a fair idea. Although I do not plan to break down the Bobcat for storage I still want to be able to replace a wing panel or be able to work on repairs in a modular form. This is why I like the blind nut setup :0)
       At this point I installed the nose wheel bracket. I must say this was incredibly difficult task with the stock hardware! Nothing seemed to fit unfortunately although I did get it done :0/ I did notice that the stock gear wire was a bit short for the job....

       The Bobcat was really taking shape now and almost on it’s own feet. I used the stock hardware to bolt the horizontal stabilizer in place using the blue Loctite on the treads as well.

       The rolling airframe really looked nice and I was getting excited about wanting to fly the Bobcat!!!

       The next step was to install the Super Tigre G-75 engine to the airframe. Because the engine will be mounted pointing backward I had to make a few adjustments. The muffler from the G-75 is a bit awkward and bulky as they are designed to be quiet. Unfortunately I could not stand using the muffler with the “square” end pointing into the wind as it just doesn’t look good. Besides it isn’t aerodynamic at all!!! Being the perfectionist I am I had to make a “new” muffler.

       Now before I go any further I want to assure you that this muffler will work as-is with maybe adding an optional silicone exhaust tube to point the exhaust away from the fuse. There are also several after-market mufflers (like Mac’s Mufflers cat # 6900) that would work just as well. What I did to this muffler may be above and beyond what anyone would want to do, I understand :0)
       I started out by buying some materials from
McMaster-Carr supply. I picked up a 1-3/4” 6061 aluminum rod, 3/8 OD X .028 wall aluminum tubing and a piece of 3/8 ID X 1/8” wall silicone tubing (high temp). With these parts I planned to make two custom exhaust pipes for the Super Tigres. (One for myself and one for my friend Andreas)

       I cut the end off of the stock exhaust pipe so I could measure the ID of the pipe body and get started.

       I then cut a couple of blanks to be used as the muffler cap bodies off of the 1-3/4” aluminum bar. I also cut a couple of short pieces of aluminum tubing for the exhaust “stinger” tubes.

       I was now ready to shape the rod blanks into the end cap parts using my 7 X 10 metal lathe. I started out by machining the surface that will fit into the end of the muffler tube. I then bored a hole in the middle to allow me to shape the inside of the muffler cap.

       A 3/8” hole was then bored into the side of the muffler cap for the stinger tube to be installed later.

The shaping process could now begin....

       After an hour or two in the garage I had finished the end caps and was ready to install them into the stock muffler bodies.

       I used some aluminum pop-rivets and JB Weld epoxy to secure the end caps into the muffler bodies. I also used some JB Weld epoxy to secure the stinger tube and exhaust manifold into the muffler. This makes the whole assembly very solid. After the modification I added about 2 grams of weight to the muffler. As a finishing touch I bead blasted the pipes for a finished look.

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