Design Group, August 1993

Vernon Blomquist

Originally published August 1993

The Ideal Aircraft Engine

This month I would like to talk about engines. The ideal engine would, of course, weigh nothing, use zero fuel and produce infinite horsepower. Since we can't have any of those things, how about a look at the direction we would like to go. For instance, low weight per horsepower is good. Reducing weight does wonderful things for overall performance and cost, both building and operating cost being to some degree related to how much the airplane weighs. In a similar vein, small size, which would tend to go with low weight, is highly desirable to reduce frontal area and drag.

An efficient engine, using the least fuel to produce the most horsepower is important. You want good gas mileage so you don't have to carry much gas or don't have to fuel up as often. This again reduces your weight, for a given range, giving those same good results for both building and operating costs. This efficiency would be especially nice if it also meant that the engine didn't produce much pollution, since that is going to be more and more a consideration. The frosting on the cake here would be if this efficient engine could also burn just about any fuel while it was getting all these good results.

Finally, it would be nice for the engine to produce it's horsepower at low RPM so that you wouldn't have to use a gearbox to get the propeller RPM low enough for efficient, quiet operation.

So where do you find this engine? I would like to toss out an idea, just for something to think about. How about a steam engine? Since this is just a newsletter column, I don't have to worry about practical matters of actual construction and there may be some considerations that make this a bad idea. However, I'd like to present some of the things I do know about steam engines that make them at least worth considering.

In case you hadn't guessed, steam engines fit all the characteristics that I have mentioned above. The actual engine for the Stanley Steamer automobile was a two cylinder opposed engine that you could hold in one hand. The boiler and water are a major consideration, of course. It would have to be a closed system with a condenser to recycle the steam to keep from having to carry a lot of water. I'll freely admit this is the one area most likely to kill the whole idea. As to the other areas, steam engines produce maximum torque at low RPM and are good low speed engines. I believe the Stanley engine turned at something like 900 RPM. This engine could also burn almost any liquid fuel with minor adjustments to the burner. You could even buy home heating oil for cheap and burn that. Steam engines are also supposed to be more thermally efficient and much less polluting than internal combustion engines. As an added bonus, a steam engine can be pumped up to a high pressure for a short burst of power by sitting and letting the pressure build up. This would be ideal for the take off run, allowing shorter fields to be used.

Since you don't generally jump into an airplane and just take off, the fact that the boiler has to be brought up to temperature isn't as much of a problem as it is in a car. You just fire up the boiler first before you go off to check on the weather and file your flight plan.

"Casey 01, no delay on the runway please...heavy jet traffic two mile final" "I'm shovelin' coal as fast as I can!!!!"

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Revised -- 22 February 1997