Originally Posted by wrongway john
David, thanks for getting those numbers for us. I’m always interested in efficiency. Do you remember the rpms’s for any of those settings?
Here are the rpm numbers added plus a 3 GPH line.
7 GPH = 130 KTAS = 149.6 MPH = 21.40 MPG = 2180 RPM
6 GPH = 124 KTAS = 142.7 MPH = 23.80 MPG = 2090 RPM
5 GPH = 117 KTAS = 134.6 MPH = 26.90 MPG = 1930 RPM
4 GPH = 100 KTAS = 115.0 MPH = 28.70 MPG = 1740 RPM
3 GPH = 78 KTAS = 89.7 MPH = 29.9 MPG = 1590 RPM
One of the guys in our geezer lunch group is a retired Navy flight test pilot and we talked about min L/D which is max endurance and from that point on a graph, determining best range. He showed how they would extend a line from the left bottom corner of the graph to where it touched the curve coming down as speed is reduced to the bottom of curve (min L/D). The point where the line touches the curve coming down represents best range. In most cases it is just a bit above min L/D.
At 3 GPH, this airplane is very near the bottom of the curve. At one point speed bled off and I thought I would have to add power but it came back, it probably was caused by the unsettled air. I should have tried 2.5 GPH but it was getting time to talk to SUS tower. Next time I will see if this thing will fly at 2.5 GPH.
My opinion on max endurance and max range is that they are a function of angle of attack. When the weight of any aircraft changes as fuel is burned off, these speeds are less than at the starting weight. Fuel flow and speed are the variables, AOA is the constant.