Originally Posted by
1QwkSport2.5r
Earl - those Drone diesels having a fixed compression ratio must be a little finickier to run in regard to fuel/props? Or I should say you might have to adjust the ether content for different props or do you just have a narrow span of props you can use with them?
Yes the engines were regulated to run a 11x10, 11x12 propeller for control line. A 12x8 is about the equivalent. Also the engines were originally setup for 75% ether and 25% heavy weight mineral oil. The motor oil is important as it has to burn, no synthetic oils, in order to moderate all that ether igniting and going off like a bomb.
Thus if you use our current model diesel engine fuel, you need to try some different propellers to get it to run OK. But even then it may not want to peak out with the needle valve setting and run with a bit of a miss to it. If you use a variable compression head then you don't have the problem. Some variable compression heads are more limited in the compression ratio range though than others.
There are some variable compression heads for them and there are even some glow heads too. The glow heads came out late when glow engines had taken over the USA market. I do have a copy of a old article about making a DIY variable compression head for the Drone engines too.
These two examples were made by someone in Italy of all places for a Drone .29 engine. Even way back in 1947 through 1949 the Drone engines had some international interest with people.
I am partial to the regular fixed compression heads as it confuses people a lot at the flying field.
