A quick re-calc to see if I could make a more sensible HP calculation:
Even then it's still uncertain as big slower-moving prop giving X amount of thrust will do better for takeoff than a smaller faster prop giving the same thrust.On the subject of horsepower:
"Horsepower" is a slippery subject. One wants to consider "Thrust", more than calculated horsepower.
An example: the Curtiss OX-5 was rated at 90hp. The Continental C-90 was rated the same. If One mounted a C-90 in a Curtiss Jenny, it would not fly.
More closely related to your project, let's compare the larger Mosler 40hp, and a Rotax 447 with a 2:1 reduction drive. Both are "rated" at 40hp. The Mosler turns a 54x24 prop at about 3200rpm. The 447/2:1 combination turns a 54x30 at 3250rpm. There will be a significant difference in thrust generated. You begin to see why "horsepower" is a less than perfect means of calculating speed/load-carrying capabilities.
Hope this is of assistance.
Are you saying that two airplanes with equal thrust will accelerate differently just because of a difference in prop diameter and RPM? Gee whiz, Mr. Wizzard! I thought that thrust was thrust.Even then it's still uncertain as big slower-moving prop giving X amount of thrust will do better for takeoff than a smaller faster prop giving the same thrust.
At this point I’m working out of Beaujon’s book, which is more or less an extremely simplified approach to UL design. Maybe too simple. I’ll have to look for a proper tail volume formula and see how it compares.What is your reference?
I didn’t recall using weight for this either. I wonder what the intention was when it was put in Beaujon’s formula, maybe it originally had wing loading (for some reason) but after a bunch of simplification gross weight was left?Vertical tail area is based on wing span, not weight.
I couldn’t agree more with your whole post and thanks for bringing it up.On the subject of horsepower...