Appendix G G-2 percent of the part 25 limit (i.e., 135 lbs after amendment 25-42; 162 lbs prior to amendment 25-42).
G.1.5.1 At any convenient airspeed (typically 1.13 VSR with minimum takeoff flaps), shut down the critical engine, and leave it windmilling (propeller feathered if autofeather is required), apply maximum available power/thrust to the operating engine, and while maintaining constant heading, vary the bank angle from 10° to less than 5° in approximately 2°-3° increments, noting the rudder force at each stabilized bank angle.
G.1.5.2 Plot the rudder force versus Wsin Ø for each of the test points. See figure G-1.)
Figure G-1. Rudder Force Versus WsinΦ FR=166 lbs Wsin = 784 lbs -50 0 50 100 150 200 250 400 800 1200 1600 Wsinlbs Rudder Pedal Force (FR) - lbs
G.1.5.3 Calculate WS sin 5° where WS is either the average test weight, or the lightest weight scheduled in the AFM, and define standard day rudder force (FRs) as the intersection of this value of WS sin 5° and the curve from step (2). For example:
𝐹𝑛𝑎𝑡 = 2600 𝑙𝑏𝑠 𝑉 = 1.13 𝑉𝑆𝑅 𝑊𝑠 = 9000 𝑙𝑏𝑠 G.1.5.4 Determine the maximum allowable asymmetric thrust from the relationship:
Appendix G G-3 𝐹𝑛𝑎𝑚𝑎𝑥 = 𝐹𝑛𝑎𝑡 ⋅ ( 150 𝐹𝑅𝑠 )1 Assuming a 180 lb force limit:
𝐹𝑛𝑎𝑚𝑎𝑥 = 2600 ⋅ (180166) = 2820 𝑙𝑏𝑠 G.1.5.5 Plot the maximum scheduled AFM thrust versus airspeed (see figure G-2), and determine VMCA at the intersection of this curve and Fnamax:
Figure G-2. Plot to Determine VMCA
80.5 KEAS 2820 lbs 2600 2650 2700 2750 2800 2850 2900 2950 3000 60 80 100 120 140 160 Ve - kts.
Fna - lbs.
G.1.6 If the force limited VMCA value is high enough to adversely impact the takeoff speed schedule, it can be reduced to an acceptable value by derating takeoff power or thrust.
For example, if the standard day rudder force (FRs) was 140 lbs on an amendment 25-42 airplane, the maximum allowable asymmetric takeoff thrust would be:
𝐹𝑛𝑎𝑚𝑎𝑥 = 2600 ⋅ 150140 = 2686 𝑙𝑏𝑠
1 (180𝐹𝑅𝑠) prior to amendment 25-42.
Appendix G G-4 G.1.7 Using the same maximum asymmetric thrust available versus airspeed as before:
Figure G-3. Plot to Determine VMCA for an Amendment 25-42 Airplane 172 KEAS 2686 lbs 2600 2650 2700 2750 2800 2850 2900 2950 3000 60 80 100 120 140 160 180 200 Ve - kts.
Fna - lbs.
G.1.8 Because of the shallow thrust lapse rate with airspeed, the force limited VMCA for these conditions would be 172 knots, which is obviously unacceptable. To reduce this value back to 80 knots (or any other speed), takeoff thrust should be derated to a level that provides a maximum asymmetric thrust value of Fnamax at the desired VMCA (80 knots in this example). The amount of derate required can be determined from the following plot:
Appendix G G-5 Figure G-4. Plot to Determine VMCA for Derate Thrust Maximum Thrust Derated Thrust (5%) 80 KEAS 2686 lbs 2400 2500 2600 2700 2800 2900 3000 50 100 150 200 Ve - kts Fna - lbs
G.1.9 For a given weight and bank angle, rudder pedal force is determined solely by asymmetric thrust; consequently, takeoff thrust should be limited to a value that results in a pedal force no greater than 150 lbs (180 lbs prior to amendment 25-42).
Appendix H
APPENDIX H. ADVISORY CIRCULAR FEEDBACK If you find an error in this AC, have recommendations for improving it, or have suggestions for new items/subjects to be added, you may let us know by (1) emailing this form to 9-AWA-AVS- AIR-DMO@faa.gov or (2) faxing it to (202) 267-1813.
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