I believe the bme 55 is now available, but would not recommend this large engine size to you for most current to 73" aircraft. Glow, use OS 160, mark 160, YS 140. Gas, check out the Evolution 26, 3W 28I, Martinelli. Some companys like QQ will not warrantee their aircraft with a motor larger than recommended, a 50 is out. Chip Hyde recommended a smaller motor than the 50 in his Cap X until DA came in as a sponser, now the DA 50 is recommended. DA does not have a smaller motor then the 50, sadly. The Elvolution 26 & 35 are front carb motors typical of glow engines and offer ease of installation. I have had SDS 160 and 180 from rc showcase, both have been good strong little engines, still running well after several years. They are a tad heavier than the elvo as is the 3w-28I, but thay have a little more power fdrom their rear induction design. Now have the Elvo 26 going into a QQ 73" yak 54. You can install them either with the typical beam motor mount, or back plate mount. The motor install is very good and simple. Their larger than usual ignition module poses some location problems. Choose your aprplane and then follow their engine recommendations as to size. Lots of great information here at RCU, and above all, great people typical of our hobby!!! Anyone being unkind or simply a jerk gets jumped on as they deserve. ENJOY.