Sig Mustang Stunter

I have one Mustang Stunter kit left. I've built two of them over the years. First one, too heavy for the Fox .35. If the winds kicked up even to 10 mph it was getting blown out of the sky. I also didn't know what I know now about the Fox .35. I built my first one at 15-16 yrs old. Also, in regards to building, I could've saved ounces on them. This is how you learn though. They don't fly too bad, my second one was powered by a OS FP-S.40. I purchased that engine in 1988 for $56.00. The receipt is still in the box. Much more oomph with the FP compared to the Fox. 1988 was the year the 40th Anniversary was introduced. What many didn't realize initially was the significance of the 40th anniversary.

The version prior to the 40th which is what I refer to as the red, white , black box 80's versions were hit or miss. Like most Fox's you purchased 10 ran them all, cherry picked the good ones and sold the rest to your competitors or friends. You either received a fair to moderate one or a real POS! Mostly were POS versions. In typical Duke Fox fashion, the machinery is outdated, the castings were wore out, quantity over quality and the price remained the same. Therefore, your engine had poor fits, the castings had more flash and slag inside the engine then outside. I had one engine where the head was installed 180 and the baffle of the piston was striking the top of the head. These engines looked so bad on the outside he just glass beaded them to make them appealing.

Enough people complained about this and the 40th was revamped with a cleaner casting, tighter fits in fact some were too tight and instead of black oxide finish on exterior parts, they were plated. The real problem though with the 80's version and the 40th is that Duke never revised the muffler mounts and it still used the POS method of the ears on the side of the case. These instantly broke off in a crash. If they didn't break in a crash, they broke from vibration.

Most were giving up on the 40th because they were not breaking in. I pretty much take them apart and polish and lap the piston sleeve and I generally can have one flying out of the box in less than a hour. So while most are trying to run a gallon of fuel through it, I was flying. The connecting rod looks like they were made by a caveman using period tools. It's imperative to insure that the engine isn't so tight that you damage the rod. Constant running on a tight engine beats the rod into submission so it's essentially wore out by the time it's broken in. A Fox that's not broken in will lean up, sag and then seize up. If this is constantly done, it's not very good for it.

The Sig Mustang also uses a inverted engine. If one isn't familiar with this, the end result is just frustration. Don't flood a inverted engine, not only will it not start, it will take out the plug instantly. In addition, if the tank height is incorrect, the case fills with fuel and the engine locks up. Start it upside down if needed. I personally wouldn't start it in the plane if you feel the engine is new or near new. It's not very good for the plane when it's shaking real bad. That's exactly what a new Fox is going to do.