Hi Roy

Another convert from the air beaters???

An 18lb. bird and a BME 50 an unlimited vertical don't go together...

You may find a 15lb. model capable of this with the BME 50...

Your going to have to step up the engine size. At least a 3.7 or 60cc engine.

A few choices come to mind. I prefer the Taurus Engines... Lightweight, power, transition and simplicity second to none...
Taurus offers a 3.7 or 4.2 in this range.

ZDZ offers a rear intake 60 that is capable. Some like em some don't. These appear to work work best when matched with a tuned exhaust system.