David, you remind me of myself 25 years ago! I too was excited about the DeltaHawk engine. It "checked all the right boxes" (e.g. no ignitions, no carburetor, runs on jet fuel, etc.). Now, 25 years later I see that DeltaHawk has a new web site, probably new investors, but the same promise. "Pricing and availability will be announced soon." says the web site. I think I first read that in 1999!
Meanwhile, I've been flying ahead of (and behind) various Lycomings for those 25 years. Expensive, ancient technology, sometimes cantakerous but they work well in airplanes. I see it all too often: a builder "ages out" before he ever realizes his dream if the scope is too large.
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Joe