The BME twins are not for those uninitiated to big gas engines. They produce awesome amounts of power, and due to the lighter weight of the 110 and 115 they effectively have more power than others of similar size due to weight alone. The 115 is an awesome piece of machinery by anyone's description.

As for cooling, they do require that the owner pays attention to airflow into and out of the cowl. I've already met one that has been severely cooked due to an improper installation and being run so hot the coating on the cylinders smoked. It still flys a 35% Katana even after a tremendous compression loss but it's unreliable until it gets fixed. What a shame for a relatively new engine. I've also seen another 115 where the intent of the baffle was good, but the design did not permit the exit air to flow anywhere near as well as it could and should. That engine is doing just fine to date and the baffle is being changed to a much simpler design that will provide much better cooling. The lesson here was that no baffle was much worse than a less than effective one.

All engines need airflow through and around the head(s) to remove waste heat from the combustion process. Most big twins, and some singles, end up fully cowled requiring that the the airflow into the cowl be directed through the engine heads rather than left with the ability to flow around the head. That's where many people make their mistake. They fail to design and construct simple lightweight baffles that send the air through the head and out of the cowl. It's really too easy. In the simplest form all one has to do is think of a pipe, with one end fit to the front of the engine and other end at the bottom rear of the cowl. It doesn't need to be anywhere near that tight or sophisticated. That representation was so people could mentally picture the way air must travel, not the relationship of inlet and exit sizes or super human fit tolerances. In the cowl, through the head, out the back of the head, exit the cowl. That's it.

As for installing one in a 91" Cap. I suppose it could be done, but I don't know how you'd land it. The previously noted Katana with a sick engine takes off at about 1/2 throttle and the 35% Sukhoi at 25 pounds and a good engine uses less power than that for the T/O. Landing approaches are at minimum throttle with a blip of the throttle once in awhile to control the sink rate. You'd need a three blade prop for sure since the 115 will rip any 27" prop out there while the recommended size of two blade props are from 28-30". It would have the power to weight of a foamie for sure. I know the 115 hauls a 35%, 24 pound Extra like it was a foamie, especially out of a hover. Think winged rocket...

RTK has the all up weight of his engine setup, but I believe it came out all up about a pound and a half lighter than a DA100