The Lycoming 720 has been around for a long time, but it doesn't have a very good track record. It was used in a few Piper airplanes. The Brave 375, 400 Comanche, and a version of Navajo. This engine has been shoe-horned into a Pitts before I think. Now for aerobatic airplanes with greater than 1:1 power. Henry Haigh had an airplane called Rarsrepus with a Tierra Lycoming engine that had greater than 1:1 power. One of these airplane was lost due to aileron flutter. Wayne Handley had an airplane called the Turbo Raven, that could stop and go on a vertical up-line. He also used this airplane to set some time to climb records. This airplane was lost to a air-show accident, and Wayne nearly lost his life. Now for turbine engines. They are lighter weight for the same power as a piston engine, but when trying to adapt to a piston aircraft you have to have a longer nose moment or add weight for balance. Tom