Cold Climate Helicopter Operations

Electric preheating of driveline components helps cold climate starts.

Any aircraft mechanic that has watched a turbine engine slowly spool up on a cold winter day has likely experienced anxiety relating to possible engine temperatures exceeding published limits during start. Exceeding the published limits can result in damage to the combustion chamber or hot section of a turbine engine caused by extended spool up times — a real concern to those operating in cold climates. The combination of cold thick oil being asked to lubricate driveline components and gearboxes, and the effect of low temperatures on battery efficiency is a formula for achieving a temporary spike in engine start temperature or, worst case, a hot start.

Aircraft mechanics and pilots both know that the best solution is a heated hangar, but this is not always possible. In the case of a helicopter, preheating of specific components such as gearboxes, transmissions, and other complex components can eliminate these potentially damaging conditions by lowering the viscosity of cold soaked fluids. One method of preheating is to install an electric preheat system.

The electric preheat system

To learn more about electric preheat systems, AMT turned to Tanis Aircraft Products in Glenwood, MN. Tanis electrical preheat products have been used in reciprocating aircraft engines for decades. Much of the same technology is currently used on helicopters to transfer heat from an electric heat pad into an engine’s oil, oil sump, hydraulic reservoir, reduction gearbox, accessory case, fuel control unit, tail rotor gearbox, or most any complex component.

Jim Conn, business development manager for Tanis, says, “The preheat technique is quite simple to explain in words: that is to raise the temperature of all helicopter critical fluids and components to a warm steady state. Over time, the temperature will stabilize similar to the internal temperature of a nominally heated hangar.”

Conn goes on explain, “Electric preheat systems are shoreline (hangar or ground outlet) powered by 115v or 230v AC and designed to draw between 5-13 amps per helicopter. Because the system operates on shoreline power and is not operated in flight, the installation does not require Supplemental Type Certificate (STC) approval but is regarded rather as a minor alteration, even though we maintain a current Parts Manufacturing Approval (PMA) from the FAA. Additionally, battery heaters can be installed into the main cabling for the component heat pads which will improve the efficiency of cold batteries during engine start.”

Thomas Judge, executive director for LifeFlight of Maine, says, “We work in an extremely cold climate and have the heaters installed on the main rotor gearbox, tail rotor gearbox, both engines, hydraulic oil tanks, and battery on our Agusta fleet. The electric preheat system increases our operational readiness and shortens take off times.”

Design, maintenance, and inspection

Conn says, “The heat pads contain resistance elements which are sandwiched and vulcanized between two sections of flexible heat conducting pads. These pads are affixed with a cold cure bonding agent to specific heat conducting locations on fluid reservoirs and components that if preheated will enhance the starting process.”

Conn explains the older style harnesses used high-temp silicone insulated wiring and spade type connectors. Feedback from aircraft mechanics in the field indicated that technicians were not always satisfied with the original spade type connectors. As a result of this type of feedback, they upgraded the design to use Mil-Spec Teflon insulated cable, the connectors are environmentally sealed and include a self-locking feature, and a quick disconnect feature was included using MIL-C-39029 connector technology. The latest SWAMP (severe wind and moisture problem areas) design parameters are used to develop and manufacture all helicopter systems.

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