I bought a rossi .81 used in good shape ran like a champ. I had it in my Skyburner 60 that I scratch built from M.A.N plans with a ramtec fan unit and an unknown muffled pipe. I was running omega cool power 5% with 5 oz synthetic and 2 oz castor oil added on an OPS cold plug. When I tuned the pipe it maxed out at 19,700 rpm. Not rich, not lean, nice fat smoke trail, just right, ran like a champ. I had been flying all day yesterday and all day today. It was running great and hauling balsa. On the last flight of the day I was flying along and the engine started to run a little rich. So I banked hard left and came out of the turn in a dive to make a high speed pass to see if would lean out. It started to lean out a little and then poof, like it ingested something. It was still running although very rich, lots of smoke trail. I throttled back to half, dropped the gear, and made an emergency landing. When I chopped the throttle on final the engine died. When I got it back to the pits I found the sheared impeller shaft.

What happened?
Did I do something wrong?
Or is this a common problem with rossi engines?
Does anyone still sell the OS .91 vrdf?
If not, will the OS 46 vrdf work in a ramtec fan unit?

No you did nothing wrong, It's really the nature of the .81 Rossi, to just run itself into oblivion. The .81 Rossi's are terrible vibrators and combine that with a high revving fan unit and something is gonna give. I had many .65 rossi's in my DF's and every once in a while the crank would break. In the future make sure the rotor is well balanced, try to stay away from the .81's unless you are using a Byron fan, the .65 rossi's are just about indestructable and would probably work ok in the ramtec, though it may be a bit much for the .65. Forget the .46VRDF it's not going to spool up the ramtec. You may want to look into the classifieds for, O.S.91, 77 BVM .82, .91, 96 CMB .65, .91 K&B.82

Hope this helps

Thank you for the Info frankflyboy1.

I checked the balance on the rotor and found it to be very slightly off balance, but I guess at high revs just slightly off is enough. To bad... it was a great running engine in spite of all the bad reports I've heard about Rossi. I'm going to try and get my hands on an os .91. If not I've found some used bvm .91s but I've read that the bvm over revs in anything other than a bvm fan.

Just a few more questions though. What’s the best way to balance an impeller, scrape the blades like a prop, add led tape to the back side of the blades? I have a du bro precision balancer for balancing. Is there a better balancer to use for balancing rotors?

I hope to get my skyburner back in the air soon. It sure is a sweet flying design. Easy to fly, smooth as silk, and hauls some balsa across the sky. Not as fast as I was hoping though, about 85 mph tops if I had to take a guess. But it sure looked good doing it. If I could get my hands on a good os .91 and the right pipe and get about 22-23k revs I just might be able to reach that 140 mph mark the designer claims it will do. YEEEEEE HAAAAAA!!!!!!

Thanks again

The best way to balance is to drill the hub on the aluminum part. DO NOT scrape the blades or add lead to them. Don't drill completly through the aluminum just make pockets. I know BVM sells engines for the Dynamax and I believe it's the .91 or the .82 and either one would work awesome