I found if you look online for (Air Trails Magazine) It says at the bottom shoo-fly 1960, I cant believe that, That's when i was born HA!, Sorry i ment HB 61, You can find them on MECOA.com, Very strong and reliable engines, My other 2 bud's have the same, With a 12X6 master airscrew, It will stay in a hover, I'll have to go through some disks to find it, I'll send one when i do. jc