I think what isn't mentioned here is that the Rotax uses a much smaller prop which will result in much lower performance on a larger airplane. For example, a 220 Stearman hauls its heavy weight briskly into the air with a 108 inch McCauley steel prop. Put a shorter wood prop on it and it's a dog. Put a tiny prop on a Rotax powered Bearhawk, and I have serious doubts. Another example was the old OX-5 powered planes like the Waco 10 and, Lincoln Page and Brunner Winkle Bird. 90HP and carrying 3 people. They turned 1300 revs on a good day, according to my grandfather, but that long prop pulled them into the sky. I don't know of any Rotax powered planes that have big props. Great on a Rans, but it's a light machine, appropriate to the prop length and high revving engine.
As for the lead issue, .. please tell me where the Mayo Clinic report says anything at all about AvGas being a source of lead poisoning? Did they forget, or is it actually a non-issue. 100LL, yeah we all laughed when "high lead" LL100 came out. Only 4 times the lead of 80 octane. So full of lead they had to design new spark plugs for C-150's. Somebody had to come up with an answer to the California granola set, so good for GAMI. That said, you can bet they'll keep scratching and digging to shut us down. today I got a notice form SNG Barret, makers of parts for vintage Jaguars. The newly formed Alliance for Historic and Classic Vehicles is fighting against restrictions in Europe on operating and restoring old cars. That is coming our way as well, so we need to prepare. GAMI's work is a step in the right direction.
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