TM 1-1520-238-10 7A-4 Change 2 Section II. MAXIMUM TORQUE AVAILABLE 7A.9. DESCRIPTION. The maximum torque available charts shows the maxi- mum specification torque available per engine for 30 min- ute operation (fig 7A-2 sheet 1) and 10 minute operation (fig 7A-2 sheet 2) at various conditions of pressure altitude and free air temperature. Both single and dual engine op- eration limits are shown. The maximum torque available for 2.5 minute operation (fig 7A-2 sheet 3) shows the maximum specification torque available when one engine is inoperative; only single engine operation limits are shown. The torque factor charts (figs 7A-3 and 7A-4) provide an accurate indication of available power for the engines installed in each individual aircraft. 7A.10. USE OF CHARTS. The primary use of the maximum torque available charts (fig 7A-2 sheets 1, 2, and 3) is illustrated by the example. To determine the maximum specification torque available, it is necessary to know pressure altitude and free air tem- perature. Enter the left side of either the 30 minute or the 10 minute chart (fig 7A-2 sheets 1 or 2) at the known tem- perature and move right to the known pressure altitude, and then move down and read the maximum specification torque available. This is torque per engine. For dual en- gine operation, if the torque per engine exceeds the two engine limit, the maximum torque available must be re- duced to the two engine limit. For one engine inoperative, enter the left side of the 2.5 minute limit chart (fig 7A-2 sheet 3) at the known tempera- ture and move right to the known pressure altitude, and then move down and read the maximum specification torque available for one engine. If the torque exceeds the one engine limit, maximum torque available must be re- duced to the one engine limit. 7A.11. CONDITIONS. The maximum torque available charts (fig 7A-2 sheets 1, 2, and 3) are based on 100% rotor rpm, zero airspeed, JP-4 fuel and ENG INLET anti-ice switch OFF. With ENG INLET anti-ice switch ON, available torque is reduced by as much as 19.3% for 30 minute operation and 18.6% for 10 minute operation. For example, if value from the chart is 90%, with anti-ice ON, torque available would be 90 – 19.3 = 70.7%, 30 minute limit. 7A.12. TORQUE FACTOR METHOD. The torque factor method provides an accurate indication of available power by incorporating ambient temperature effects on degraded engine performance. The torque fac- tor method provides the procedure to determine the maxi- mum dual or single engine torque available for the en- gines installed in each individual aircraft. The specification power is defined for a newly delivered low time engine. The aircraft HIT log form for each engine provide the en- gine and aircraft torque factors which are obtained from the maximum power check and recorded to be used in calculating maximum torque available. 7A.12.1 Torque Factor Terms. The following terms are used when determining the maximum torque available for an individual aircraft: a. Torque Ratio (TR). The ratio of torque available to specification torque at the desired ambient tempera- ture. b. Engine Torque Factor (ETF). The ratio of an in- dividual engine torque available to specification torque at reference temperature of 35 C. The ETF is allowed to range from 0.85 to 1.0. c. Aircraft Torque Factor (ATF). The ratio of an in- dividual aircrafts power available to specification power at a reference temperature of 35 C. The ATF is the average of the ETFs of both engines and its value is allowed to range from 0.9 to 1.0. 7A.12.2 Torque Factor Procedure. The use of the ATF or ETF to obtain the TR from figure 7A-3 for ambient temperatures between –15 C and 35 C is shown by the example. The ATF and ETF values for an individual air- craft are found on the engine HIT log. The TR always equals 1.0 for ambient temperatures of –15 C and below, and the TR equals the ATF or ETF for temperatures of 35 C and above. When the TR equals 1.0 the torque available may be read directly from the specification torque available scales. When the TR is less than 1.0, the actual torque available is determined by multiplying the specification torque avail- able by the TR (example for TR = 0.98: 90% TRQ X 0.98 = 88.2% TRQ). The torque conversion chart (fig 7A-4) is provided to convert specification data to actual torque available. The single and dual engine transmission limits are shown and should not be exceeded.