Chris W

Getting back to the original question of what attracts people to diesel engines in model airplanes.
I can see three major advantages that diesels have that would attract niche modellers.

1. You can entirely build or manufacture a model diesel engine in your own garage with a lathe and a mill, not so with spark or glow as I have yet to see anyone make a glow plug or spark plug in their own home.
2. A model diesel with variable compression allows the user to change the ignition point at will, and here you might quip "So what?" But consider something as simple as altitude changes, the thinner the air the more blade area a model needs for comparable performance to sea level and here a diesel excels as its not as fuel/air hungry as other systems and will happily pull helicopter size blades around in a slightly decompressed state. I have seen a pylon racer with a diesel head conversion on it at a meeting here called the "Oily Hand" and the pilot said it was slightly down on straight line speed but he was curious to see when the engine would quit if he went vertical for as long as possible. (Apparently this 'test' was done quite a few times just for the heck of it.) The model went straight up and was barely in sight when he commented that "right about now the glow engine would quit but the diesel just kept on going up, and up and up. It simply would not quit. And after speaking with a competition control line stunt flyer from South Africa who has to contend with massive altitude changes that vary with venue he settled on an MVVS 49 with a diesel head with the reasoning that altitude changes needed blade area changes, and guess what - the diesel out performed the glow when tasked with this issue. The venier screw changes the ignition advance or point, as does oil content or any other non compressable fluid.
3. Fuel economy and hot engine restarts, specifically F2C events or indeed or other fun fly event that requires the same.

What I don't see is a claimed 'maximum' torque advantage as a petrol or methanol engine with a tuned exhaust will easily out perform a model (non turbo) diesel. And what I dont see is that simply bolting on a diesel head onto a glow engine equals a guarantee of success.

And I will make a controversial statement here "I predict that when electric engines totally eclipse IC engines as a viably commercial powerplant and they cease to be made, the diesels will still be around long after that point."

Cheers.