A bit of backoftheenvelope calculation regarding overthecowl sightlines.
 My diagram of the B&S 810cc engine (attached) differs a bit from the measurements on the drawing by Hephaestus. By my measurement using a bright light and squinting old eyes, vertical distance from the crankshaft centerline to the topmost edge of the valve cover is 10.4". If we compare that to the given "down" (crankshaft centerline to bottom of case) distance (5.88"), then it looks like, if we keep the same prop location, the top of the cowl could be 4.5" lower if we flipped the engine to be headsdown (BTW, it looks like TiPi has taken the other approach and will keep the top of the cowling at about the same location and will use the extra clearance to bring the prop (and thrust line) higher by several inches).
If the top of the cowl is 4.5" lower, and the pilot's eyes are 60" horizontally from that high point in the cowl, the improved downward FOV equals 4.3 degrees. To get an idea if that is significantit's about 2" down at arm's length. Also, the 4.5" increased height for "headsup" orientation is a the top of the bumps for the cylinder heads, the SD1 cowlings dip down between the heads to provide a bit better visibility directly on front of the nose and to streamline things a bit (a large spinner also helps, as does their prop extension).
Prop clearance/ length/performance: For direct drive at 3600RPM and 30 HP, it looks like a 42" prop is all that is needed, at least from 70120 MPH ( a longer prop might be useful at lower speeds, esp to reduce takeoff roll).
Optimized for 70 MPH (approx climb)
40" dia: 62% prop efficiency, 100 lbs thrust
42" dia: 66.2% prop efficiency, 106 lbs thrust
44" dia: 66.6% prop efficiency, 107 lbs thrust
Optimized for 120 MPH
38" dia: 79.4% eff, 74 lbs thrust
40" dia: 80.2% eff, 75 lbs thrust
42" dia: 80.9% eff, 76 lbs thrust
44" dia: 80.9% eff, 76 lbs thrust
 My diagram of the B&S 810cc engine (attached) differs a bit from the measurements on the drawing by Hephaestus. By my measurement using a bright light and squinting old eyes, vertical distance from the crankshaft centerline to the topmost edge of the valve cover is 10.4". If we compare that to the given "down" (crankshaft centerline to bottom of case) distance (5.88"), then it looks like, if we keep the same prop location, the top of the cowl could be 4.5" lower if we flipped the engine to be headsdown (BTW, it looks like TiPi has taken the other approach and will keep the top of the cowling at about the same location and will use the extra clearance to bring the prop (and thrust line) higher by several inches).
If the top of the cowl is 4.5" lower, and the pilot's eyes are 60" horizontally from that high point in the cowl, the improved downward FOV equals 4.3 degrees. To get an idea if that is significantit's about 2" down at arm's length. Also, the 4.5" increased height for "headsup" orientation is a the top of the bumps for the cylinder heads, the SD1 cowlings dip down between the heads to provide a bit better visibility directly on front of the nose and to streamline things a bit (a large spinner also helps, as does their prop extension).
Prop clearance/ length/performance: For direct drive at 3600RPM and 30 HP, it looks like a 42" prop is all that is needed, at least from 70120 MPH ( a longer prop might be useful at lower speeds, esp to reduce takeoff roll).
Optimized for 70 MPH (approx climb)
40" dia: 62% prop efficiency, 100 lbs thrust
42" dia: 66.2% prop efficiency, 106 lbs thrust
44" dia: 66.6% prop efficiency, 107 lbs thrust
Optimized for 120 MPH
38" dia: 79.4% eff, 74 lbs thrust
40" dia: 80.2% eff, 75 lbs thrust
42" dia: 80.9% eff, 76 lbs thrust
44" dia: 80.9% eff, 76 lbs thrust
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