Finally hit the combination for a solid running Fox 35 w/muffler - RMS 10x6 and free airstream vent!! In one of the Brodak Controlline World issues (the one with the big Fierce Arrow on the cover) there was and article, by D Hill and Joe Gilbert, comparing 10x6 prop brands. They tested something like 50 different props. There choice for best overall performance was the RSM 10x6.

I have been working with the Fox 35 for several years in OTS and had very inconsistent engine runs. I thought it was due to the muffler holding heat. I also cut the prop down to a 9x6+ size to reduce the load (and heat) on the engine. Although the muffler does hold heat it was not the cause of the run issues. By chance I remembered some advice given at one to the GSCB forums back in the late 60's to always locate the tank vent on the circle inside in the free air stream (about 3/16" off the fuse side). I had been running the uniflow vent line up in back of the engine thinking it would be in a dead pressure zone and reduce the upwind/downwind effect on the engine run in windy conditions. This was the big mistake, it caused all kinds of erratic pressure fluctuation and engine runs. I tried muffler pressure but the Fox didn't like that and gave the same erratic runs.

On a whim I remembered the old advice and built a vent tab that went under the back engine mount bolt on the circle inside and held a small piece of copper tubing in the free air stream that I connected to the uniflow line. I flew the ship with the 9x6.6 prop I had been using and noticed the run was unusually solid from the launch. I wanted to get a little more pull through the vertical 8's and since the engine was running very solid tried a 10x6 Power Point (narrow blades lower load). The PP loaded the engine a bit more but the run was solid. Next flight I richened the needle to get a lean 4 stroke and once again very solid run.

At this point I felt I could now set the engine anyplace I wanted and it would just hold. After reading the 10x6 prop article I ordered one of the RSM 10x6 props. The article said it had very good level flight stability and drive out of the corners (they tested it on a Twister/Fox 35, PA pattern). Reading the information on the RSM site they indicated that their prop has a 0.020" undercamber. This would account for the drive off the corner (the pipe guys found this out quite a while ago with I believe the Bolly props). I flew the RSM prop today and BOOM they were so right. That prop just drives through the consecutive verticals like it was in level flight. Great Great prop for the Fox 35.

Bottom line is position the tank uniflow vent in the inside free airstream, use fuel with 26 -28% (50/50) oil and the RSM 10x6 prop and go fly.

Best,   DennisT