At 75% a 100hp Rotax will burn 18.5lph, and this normally coincides with 5000rpm so looking at the numbers above you could choose to go a bit quicker if you wanted to stick at 75% which works well on the Rotax. Provided you do not run them on 100LL more than 30% of the time the engine maintenance will not be an issue. If you are planning on running on 100LL more than that then you ½ all the maintenance periodicity which will bring gearbox work into play as well as introducing a 50 hour oil and filter change.
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