Rotax engines have a gear reduction.general aviation engines (lycoming and continental )not.
This is a question that I ever wanted to ask: Why ?
I mean that I know a reduction gear box allows a fast rpm engine to let run the propeller at lower and more efficient rpm. I also know that in bycicle if you use a lower front gear and bigger rear gear you can better climb (same "monk" power but higher efficiency and lower speed).
does the gear box allows :
- increase power to the propeller and keep same torque ?
- increase torque at the same power ?
- increase torque and power ?
- non of above ?
Anybody is able to explain it to me ?
  • Re: gear reduction box

    by » 13 years ago

    I'm pretty sure the reason is that our propellers have to run at about 2000 to 2800 rpm and an engine designed to give max power at that sort of speed is going to be large, that means it's capacity, displacement or swept volume will be large. As a result the engine will be physically larger and heavier.
    A smaller engine developing the same power at 5500 rpm will be lighter but has to be geared down to 2000 to 2800 rpm for the propeller. So the reduction in weight by going to a smaller, faster engine is ofset by the extra weight and complication of the gearbox. Rotax have done a pretty good job at finding a good lightweight powerful solution.
    The Lycoming 235 engine develops about 115 HP and has a capacity of 235 cu ins whilst the Rotax 912S develops the same power with 82 cu inches of capacity.
    Mike G

  • Re: gear reduction box

    by » 13 years ago

    that is what I though and your explanation of lower weight in exchange of rpm appears reasonable.
    So you think that there no advantage in terms of torue or HP at out shaft level .

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