estimating % power using flight test data, thrust hp, and equivalent flat plate drag

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

– 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

58

130

THP = 77 BHP * 0.75 = 58

% Pwr = 100%

RPM = 3300, TAS = 130 mph

130 mph & 58 THP intersect at fe=4 sq ft

50

RPM = 3200, TAS = 125 mph

% Pwr = 50/58 = 86%

58

125

45

RPM = 3100, TAS = 120 mph

% Pwr = 45/58 = 77%

58

40

RPM = 3000, TAS = 115 mph

% Pwr = 40/58 = 70%

58

115

35

RPM = 2900, TAS = 110 mph

% Pwr = 35/58 = 60%

58

110

32

RPM = 2800, TAS = 105 mph

% Pwr = 32/58 = 55%

58

105

Findings• Equivalent Flat Plate Area (Fe) = 4 sq. ft.• RPM TAS % Pwr

3300 130 1.003200 125 0.873100 120 0.773000 115 0.702900 110 0.602800 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 5.73200 125 0.87 5.03100 120 0.77 4.43000 115 0.70 4.02900 110 0.60 3.42800 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

ALT RPM TAS % BHPFuel Flow

(gph)Endurance

(hr)

Range No Reserve

(mi)

Range 1 hr Reserve

(mi)

SL 3300 130 1.00 5.7 2.8 365 2353200 125 0.87 5.0 3.2 403 2783100 120 0.77 4.4 3.6 437 3173000 115 0.70 4.0 4.0 461 3462900 110 0.60 3.4 4.7 515 4052800 105 0.55 3.1 5.1 536 431

4000 3300 140 0.87 5.0 3.2 452 3123200 135 0.76 4.3 3.7 501 3663100 130 0.67 3.8 4.2 545 4153000 124 0.61 3.5 4.6 572 4482900 119 0.52 3.0 5.4 640 5212800 113 0.48 2.7 5.9 663 550

8000 3300 151 0.77 4.4 3.6 550 3993200 145 0.67 3.8 4.2 608 4633100 139 0.59 3.4 4.7 658 5193000 133 0.54 3.1 5.2 693 5602900 128 0.46 2.6 6.1 778 6502800 122 0.42 2.4 6.6 809 687