Do You Really Know Your Aircraft’s Lifting Capability and Its Limitations?

Know Your Capabilities and your Limitations

Scenario:

You are doing a lift job with little margin. The Load calculation indicates the load is within 200 lbs of the aircraft’s maximum lifting capability for the altitude and temperature. As the lift is attempted, the pilot increases power to 50 psi on the torque meter, the load does not move, and the lift is aborted.

The flight manual supplement indicates that the maximum torque is 50 psi, which translates to 1100 horse power, and we should have been able to lift the load according to the performance charts. So why won’t the aircraft lift what the charts indicate it should be capable of lifting?

The FMS states in paragraph 2-16 and 5-7 that the helicopter is torque limited by the transmission to 1100 HP, which corresponds to 50 psi on the torque gage at 6600 engine/324 rotor RPM. However in paragraph 7-13 there is a notation that states “the power output capability of the T53-L-703 engine can exceed the transmission structural limit (50 psi calibrated) under certain conditions.” The key word here is “calibrated.”

In the TCDS for our aircraft, R00005SE, under note 12, it states “torque pressure output by the torque sensing system varies with the individual engines. The calibration of this value is required on each engine and the value corresponding to take-off power, is stamped on the engine data plate.” This statement applies to both the L-13 and the L-703 engines.

In the installation documents of the 703 engine STC, there is reference to TM55-1520-210-23-1/2/3, which is the UH-1 maintenance manual. In book 2 Section I, paragraph 8-6 (d), there is a procedure for marking the maximum torque limit by using the information on the engine data plate and a conversion chart in that paragraph.

So 50 psi on the torque gauge does not necessarily equate to 1100 SHP. As stated above, the torque sensing system varies with every engine, and therefore every engine will produce more or less power at a specific torque setting, and thus the need for calibration of the torque gage

How do we know how much power our engine is making?