Years ago my Sonerai 2 had the VW 2180 cc. 54x44 Sterba propeller. Top speed was 150ish. Climb..times was 1400 fpm if I remember correctly. The high speed numbers were really ambitious. Maybe their climb was minimal. When talking to other Sonerai 2 pilot's...I was told their were inline with mine. Still, not bad but no where near the 200 mph that was supposedly possible.Thatcher CX4, 2180 cc and a Sensenich 60"x44". I climb at 80mph and see 2900 rpm there. My home airport is at 5,200' and I often climb to 11,500' or so to clear the local mountains. I don't have a VSI but I typically climb from takeoff at 5,200' to 10,200' in 7-1/2 minutes which averages out to 666 fpm. Wot in level flight at 8000' or so trues out to 137 mph or so at 3200 rpm.
The interesting thing is that last year I borrowed a Sensenich 54"x44" that came off a Sonex. Speeds and climb rates were virtually identical. The difference is that the 54"x44" took 400 rpm more to reach the same numbers.
Assuming we're talking about direct drive . . .What about 63" - 65" prop? Does anybody have power/torque curves of VW 1700ccm and 1835ccm ?
Does anybody have drawings of newer airfoils and shapes for wooden props ?
I think You're not right - most VW engs producers are pushing RPM at 3400-3600, but SAUER S1800 gives 68hp at 3200 and 65hp at 3000RPM - 253m/s , so pretty lower under 0.8M (272.24m/s). Then 63" prop could work with 62hp at 2800 (236m/s). S2100: 85hp / 3000rpm, 80hp / 2700rpm. Also prop blade mustn't be so narrow, as could see.Assuming we're talking about direct drive . . .
The tip speed of a 65" prop will be 888 FPM (at 70 MPH) at just 3100 RPM (thus leaving a lot of HP on the table--these engines are fine at 3600 RPM). 888 FPM is faster than a wood prop should be going. Also, with these small HPs and a long prop, the prop blades necessarily have very small chords (the engine doesn't have enough torque to turn anything beefier). Too-fast tips and too-wispy thin blades are a recipe for a thrown bade and all the drama that follows.
Example: >If< you can make 50 HP with an 1835cc engine at 3100 RPM and wanted a 65" Dia prop optimized for 100MPH, the prospective blade width at 75% radius would be less than 2" and the blade thickness would be about 1/4". I wouldn't recommend anyone fly behind a wood prop like that under those conditions.