i watched a youtube of john williams talking about the engines he has tried in the titan tornado . he did try a wankel and was impressed with it but it created too much exhaust heat . and that was a problem in the tornado. he also said he had a room full of engines that didn't work. even a 2 cyl inline rotax 4 stroke which was abysmal. then rotax offered him one the first 912s and said try it, if you like it pay for it. if not send it back. he now had the perfect engine. rip john. a great loss to experimental aviation, only a couple of weeks ago.