Sundownee,
I had the same concern about the UMS 735 - bottom line, it has to turn much more than 5200 rpm. Maxam (post 2664) ran his up to 7,500 rpm with an APC 17x8, which ThrustHP computes should give 2 Hp for 14 lb thrust at 57 mph. Only question is reliability - where does that 5,200 rpm limit come from? The larger engines?
Quote is from post 2519.
ORIGINAL: redball8
UMS Seidel dropped their posted pricing on the 7-35 below $1200, so I started looking at the specs in earnest. They state a maximum rpm of 5200, and suggest props like 16x8, 18x6, 18x8, and 20x5. A few calculations with ThrustHP has me wondering how this engine could fly your average 120-size airframe. Optimistically assuming the 18x8 would turn at 5200 rpm, the 3 lb engine would develop 8 lb thrust and fly an aircraft at 40 mph. We euphemistically call that ''scale'' power in my club.
Am I missing something here? I recall an ST735 mounted in a SIG Waco SRE (70'' span) - will the engine fly such an airframe? Can someone suggest the sort of airframe that is suitable?
Thanks so much,
RB8