As we round the corner past the U.S. Labor Day weekend, thoughts of cold-weather operation begin to make their unwelcome presence felt, especially among operators of unhangared aircraft. Cranking up a mechanically complex aircraft on a subzero morning can put lifetime-limiting stresses on drivetrains. This is especially true when it comes to rotorcraft, with their high number of crucial moving parts. When rapid dispatch times are critical, as they are with offshore oil and, even more so, emergency aeromedical services, operators and the people who depend on them cannot wait. But machines often wake up and get into action more slowly than human beings.
That’s where preheating systems, long a staple of arctic bush flying, come in. Beginning with dangerously improvised home-grown attempts at only keeping engine oil sumps above freezing, or warming engine compartments with risky, jury-rigged arrays of electric light bulbs, the techniques of keeping aircraft safely and effectively warm have become the mission of specialty equipment makers such as Tanis Aircraft Services of Glenwood, Minn. Beginning modestly some decades ago with a product line warming only the engines of the most common types of fixed-wing piston singles, Tanis now manufactures or can custom design thermal blankets, coils and related heating equipment for just about every make and model of helicopter, from the Robinson R22 to the Sikorsky S-76.
One reason to preheat otherwise cold engines is engine wear and/or damage. Aircraft engines are built of a variety of alloys, with engineers balancing light weight against strength. The varying metals inside a modern engine expand and contract at different rates (for an extreme example, really cold aluminum shrinks nearly twice as much as steel chilled to the same temperature). At low temperatures, engine tolerances can vary widely. When all these parts start rubbing up against each other, minimally lubricated with oil that more closely resembles peanut butter, the result is excessive wear. Mechanics have long claimed that 80 percent of engine wear occurs during the first five minutes of starting, and that adequate regular preheating can go a long way toward lengthening engine and parts life.
Engine heaters are most commonly used for those who fly in chilly weather. But what is “chilly?” Most agree that whenever the temperature drops to below -5 degrees C (23 degrees F), engines should be preheated.
A growing acceptance of the need to preheat has led to increased demand for the heating kits made by Tanis, as well as renewed focus on the part of its new owner, Gary Schmidt. He recently acquired the heat-kit manufacturer from the Tanis family, and began developing preheating kits for larger turbine-powered helicopters.
“During the past year we have noticed a dramatic increase in interest in our systems for helicopters by both maintenance managers and operators,” said Schmidt. One of the reasons he cited for this was a growing acceptance throughout the aviation community of the need for preheating aircraft systems. “The word is really out on the benefits of preheating.”
Tanis claims to be the only supplier of preheat systems designed specifically for helicopters, owning several patents on rotary-wing preheat systems under Canadian law. “We design each system specifically for each make and model, applying exactly the amount of heat needed to effectively heat that specific component. On helicopters that includes transmissions, gearboxes, fuel-flow controls and batteries. Some of our helicopter installations even include cockpit preheaters to protect and improve the operation of cockpit instruments.”
Schmidt described a threefold system of advantages to the Tanis preheat system: “The first is the safety of flying a properly preheated aircraft. The second is the immediate availability of the aircraft. The third is the efficacy of applying just the right amount of heat where it needs to go.”
This final stage, that of getting the heat right where it needs to go, is especially challenging in the case of most turboshaft engines. These powerplants and accompanying components require a broader application of heat, an act performed chiefly in the form of electrothermal mats attached to interior structures such as engines, oil tanks, main and intermediate gearboxes and tail-rotor gearboxes. To retain this heat, Tanis offers a custom-made quilted blanket individually tailored to fit specific makes and models of helicopter. The blanket is usually attached to the helicopter using the same hinged closure handles securing the doghouse structure to the helicopter.
How much does this sort of protection cost? For a Bell JetRanger, the basic heating kit, including tail-rotor gearbox heat and cover, amounts to $1,945. For a light twin such as a BK 117, the kit price for heat to both engines, oil tanks, main gearbox, intermediate and tail-rotor gearbox amounts to $2,753. (Many of the larger turbine-powered helicopters do not need thermal blankets, owing to the insulating qualities of those helicopters’ doghouse-style engine and transmission housings.)
A preheat kit for a Sikorsky S-76 tops out at $3,726 with a heat-distribution scheme very much like that for the BK 117.