Estimating % Power using Flight Test Data, Thrust HP, and Equivalent Flat Plate Drag

Objective The Objective is to generate a Chart that relates: RPM % Power Output True Airspeed Fuel Flow Range Cruise Altitude

Methodology Gather Flight Test Data for a variety of RPM settings (WOT thru economy cruise) For each RPM, record True Airspeed (TAS) at SL, 4000’ and 8000’ density altitude Calculate % Pwr for S.L. data Use the relationship between Density Altitude (DA) and Power Available to estimate % Pwr for 4000’ and 8000’

Assumptions Max BHP = 77 HP Prop Efficiency = 75% I don’t think I’m getting 80 HP based on my maximum RPM of 3300 Prop Efficiency = 75% Equivalent Flat Plate Area (fe) remains constant Changes in TAS are due to changes in engine power (% Pwr) Fuel Flow is proportional to % Pwr

130 mph & 58 THP intersect at fe=4 sq ft RPM = 3300, TAS = 130 mph % Pwr = 100% 130 130 mph & 58 THP intersect at fe=4 sq ft 58 THP = 77 BHP * 0.75 = 58

RPM = 3200, TAS = 125 mph 125 50 58 % Pwr = 50/58 = 86%

RPM = 3100, TAS = 120 mph 45 58 % Pwr = 45/58 = 77%

RPM = 3000, TAS = 115 mph 115 40 58 % Pwr = 40/58 = 70%

RPM = 2900, TAS = 110 mph 110 35 58 % Pwr = 35/58 = 60%

RPM = 2800, TAS = 105 mph 105 32 58 % Pwr = 32/58 = 55%

Findings Equivalent Flat Plate Area (Fe) = 4 sq. ft. RPM TAS % Pwr 3300 130 1.00 3200 125 0.87 3100 120 0.77 3000 115 0.70 2900 110 0.60 2800 105 0.55

Findings (cont) Measured WOT Fuel Flow = 5.7 gph Calculate fuel flow based on % Pwr RPM TAS % Pwr Fuel Flow 3300 130 1.00 5.7 3200 125 0.87 5.0 3100 120 0.77 4.4 3000 115 0.70 4.0 2900 110 0.60 3.4 2800 105 0.55 3.1

Effect of Density Altitude on Power Output

Findings (cont) Power Output falls with DA At 4000’ DA, max power output is 87% of S.L. output At 8000’ DA, output is 77% of S.L.

Conclusion From here, we can do the math and complete the % Power Table