Bill wrote:
>>>>>>>>>>>>>>>>>>> The 48" pitch refers to the theoretical 48" the prop (and thus plane) moves thru the air in one revolution. So 48" x 2400 rpm=115200 inches per minute x 60= 6912000 inches per hour / 12 = 576000 feet per hour / 5280= 109.09 miles per hour. This is in a perfect world. <<<<<<<<<<<<<<<<<<< Yeah. With Coupes, the percent of drag seems to be around 5%-maybe 4%. So, take your theoretical 109.09 mph for the 48" prop time .95 and you get 103.6355 or about the 104 mph most owners actually see. Now, let's see with a 52" prop and 2350 rpm . . . 52" x 2350 = 122,200" 122,200" perminute x 60 = 7,332,000 inches per hour 7,332,000 inches per hour / 12 = 611,000 feet per hour 611,000 fph / 5280 = 115.72 mph 115.72 mph * .95 = 109.93 mph more or less So, I conclude Al is missing about 5 mph. That's either instrumentation or real. I wonder if 2350 is Al's chosen power setting. If so, it makes sense that he'd set it the same in summer and winter - and, thus, get about the same true airspeed out of it. The engine should have more power available in the winter than in summer. Ed
