I reading the specs on engines they all report rpm range, say 2500-17000, and then list practical range, 2500-13000. What does this mean?

Curt

Curt,

That should indicate the normal operating range from idle up to maximum rpm.

So often, what a manufacturer has to say about his engine, rpm wise, is not reliable. The maximum attainable rpm listed by any manufacturer is completely unrealistic. The engine would have almost no torque at that speed.

A general rule would be to prop the engine, to turn on the ground, halfway between the torque peak and the horsepower peak.

I sure, with your experience with boat engines, that once you get started with airplane engines, you will know what sounds about right. However, with a boat engine, you are trying to turn the maximum rpm if you can get it up on the step with just the lower tip of the prop in the water?

Also, go out to the flying field and observe others and listen. Ask questions.

Good luck,

Jim

Usually they'll give a practical range of for instance 2,500 to 17,000 and that it develops peak HP at 16,000. Really all that means is that if you've got a big enough prop on it then it'll idle at 2,500 and if you've got a small enough prop it'll safely run at 17,000. But the chances are you'll never see both figures with the one prop

However, in the case of the one running at 17,000 revs then it's past the point of max HP so it's a waste of time. No manufacturer gives any idea of where the peak torque figure is so it's a little difficult to prop for halfway between but for most engines, somewhere around 12k to 13K is more than adequate for a sport type or trainer.