I’ve come to some conclusions about the OS 46 VX DF engine. Its power is truly awesome, easy to start, idle and transition. The engine has some definite things you must consider when it is to be used in a prop plane. This engine is very limited in the prop that you can use. In order to install a prop you must use a short shaft adaptor which means the hole in the prop must be 3/8” diameter this effectively eliminates safely using all 9”sport props with their small hubs, even if you intended to keep it in it’s safe speed range. I have not had much luck carving down 10” sport props with its much larger hub so that pretty much leaves the pylon props, the gray glass filled and the black carbon fiber types. I tried the gamut of the gray type from 9 to 9.75 pitches, all with the same result…the blade tips come off. I even trimmed the diameter some with the same end result. This engine has more then enough power to destroy all APC grey pylon props at will.
I had convinced myself that the Diamond Dust needed more diameter than the carbons came in but this is all that I now had left to try. So I shortened the pipe a tad so the 7.4 X 8.25 carbon prop could wind up to 24,500 on the ground and god knows how high it unloads to in the air. Well life is full of surprises because the DD is a heck of a lot faster than it was with any of the grey props, so much faster that I’m barely able to stay ahead of it. I never thought that day would come, but it’s here. The carbon has over 25 flights on it now and it looks great.
My conclusion;
Because of prop limitations, this OS 46 VX DF engine is best used in a very clean plane like a Strega 45 (Look’s project), Quickie 40 or a Clipped wing Diamond Dust (at the dirtiest). If one was to tone the engine down to lower rpm applications, it would be unpractical. A fast sport plane would be better off using a Webra, Rossi or Jett that have smaller prop shafts, more usable power band for available props, much lighter weight and better fuel efficiency.
Got another surprise, long life glow plugs!
The same glow plug has lasted me 17 flights and still counting, using up 8oz. per flight, that’s about 1 gallon of 30% nitro at over 25,000 rpm. The glow plugs are K&B, Type HP high performance Long Reach (#7300) Description: “This is a favorite for both Airplane and boat racers using more than 25% nitro. Works great in ducted fan engine too.” http://www.mecoa.com/acc/glowplug/glowplug.htm
This Diamond Dust now has over 50 flights on it, 25 with a new engine/carbon props. The other engine was used and got some lean runs/thrown tips and I guess it was just too much for the bearings. That engine is together again and waiting next to the other two.
The clipped wing DD is harder to launch than the standard version but I got it down to a science now.

Just some of the blown props and the good carbon.