Diesel engines

[DIX]

I have used model airplane diesel engines for years but one question about them I still don't understand and that's the compression adjustment. I can set it and all works fine but lately I've started wondering why it is this feature only shows up on model engines. Can some one here explain to me why variable compression is used on some engines and what does it "buy" me to have variable compression. If anyone remembers the old Drone diesel it didn't have adjustable compression and it ran just fine.

Dick

[Doug_C]

The contra piston is mostly for starting at a higher compression ratio. This helps a cold engine fire off easier.

Although the Drone not having one. It may not have put out as much power as it could have.

DC

[DIX]

Thanks Doug,
That explains why the Drone was always hard to start the first time out that day. I also had a Mills diesel which had the contra piston. That started and ran just like a glow plug engine. I screwed the contra piston down until the engine fired. After it was running it didn't seem to make any difference where the contra piston was set. Of course screwing it up would eventually cause the engine to stop.

Dick

[allanwaterfall]

The variable compression tolerates different fuel mixtures,different props and weather temperature variations,summer to winter. Can also be used as a crude throttle by backing it off if you want a slow flying free flight model.

Allan