T-56 Allison
The Allison T56 family of turbo-prop engines are a constant RPM type. The engine drives a propeller via an extension torque shaft through a reduction gearbox. The engine at 100% RPM runs at 13820 RPM reduced to 1020 RPM at the propshaft using a 13.54:1 reduction gearbox. When the throttle is advanced from Flight Idle more fuel is scheduled and to maintain RPM nominally in the 100% range the propeller blade angle increases with the resultant increase in thrust. Although the propeller is fully reversible and constant speed there is no pitch changing lever. The throttle operates through a device known as a co-ordinator which combines outputs to both the engine fuel control unit and the propeller governor. Another lever known as the Condition lever can be used to feather the propeller, unfeather it and shutdown the engine. Earlier C130's did not have a low speed ground idle facility and it was not uncommon to close down the outboard engines to assist in controlling taxi speed after landing. As mentioned by Tree, up until the latest C130 (the J model) the operating crew included a Flight Engineer. The maximum torque allowed on all from the C130A to the C130H was 19600 inch lbs, this being an engine mounting limitation rather than an engine limit. The NTS mentioned by Tree is Negative Torque Signal which comes when ever the propeller tries to drive the engine, for instance on descent. The NTS system will cause the blade angle to increase so as to cause the engine to have to drive the propeller to maintain RPM. I have experienced a situation where the NTS system was mal-adjusted and prevented an air start being performed by driving the prop back toward feather whilst endeavouring to unfeather it.
The Lockheed Hercules is most certainly a true legend in it's own lifetime, even having been flown onto and from an aircraft carrier (the USS Forrestal) 29 times.
Last edited by Old Fella; 19th Apr 2008 at 05:59.