An OS.91 will turn more than 21000 in a Byron Fan. In a Dynamax I've seen almost 24000 on the ground and it unloads some in the air. I've owned a dozen or so OS.91s and I've flown them hundreds of flights and I've never broken a rod. I've always used 5% fuel and the for the last 5 years I have used either Wildcat Jet-A or PowerMaster ducted fan fuel. I have seen the OS.91/Dynamax fan combo fly a 30# T-33 with authority.