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The fuel control unit is controlled with centrifugal bobweights. The throttle has three settings, namely off, idle and open. The idle speed is somewhere between 63-65% of engine RPM (or gas producer, as the Americans call it).
The engine starter is either a Bendix or a Ceco, the former giving you no control over the start process other than by opening or closing the throttle. The only way you can tell is look at the label on it in the engine compartment. The Ceco allows you some measure of control over the TOT during the start.
LongRanger
The C28 is larger and heavier, using up 135 litres per hour. The centrifugal compressor is probably the most obvious visual difference. Being wider but shorter, it gives the impression the engine is ‘shoved’ forward against the firewall. The accessory gearbox is squarer but the turbine is similar. There is also a bipod rear mount on the turbine to combustion case split-line.
The C28 does not need a particle separator, as the inlet to the compressor has a bulbous duct which houses an in-built extraction system. It was replaced on the C30, and such airframes can have a standard separator fitted. The exhaust goes out through a single rectangular duct.
The accessories are also different. The EDFP and FCU, for example, are ‘piggy-backed’ on each other and are driven from a common shaft.
The igniter plug is not next to the fuel nozzle, but is inserted in either side of the combustion can.
Transmission
Mounted forward of the engine and coupled to it with a short drive shaft, with heat detection strips that turn black when they get too hot. It is a reduction gearbox that transmits power from the engine through spiral bevel and planetary gears to the main rotors. It has a self-contained lubrication system with its own oil cooler, and the hydraulic pump and rotor tacho are also attached, so you still get hydraulics during autorotation (however, you still need power, so if the hydraulics fail, pray the electrics don’t go as well). It is secured by an isolation mount to minimise vibration.
The tail rotor drive shaft has eight sections, with the forward one connected to the back end of the freewheel unit. The second section is actually the oil cooler fan shaft, connected to the tail boom splice with the third section.
There are two spiral bevel gears inside the tail rotor gear box, which transfers the transmission forces through 90°.
In the LongRanger, a nodal-beam setup is coupled with an elastomeric restraint for a generally vibration-free ride. The chip detector on the free wheeling unit is electrically connected to the TRANS CHIP warning light
Rotors
The main rotors are a “droop-snoot” design, and semi-rigid, using an underslung-feathering-axis hub, which has only six grease-lubricated bearings (the grease, MIL G 81322, can make a real mess when you do the 50-hour service. It’s good down to –65F). They use North American rotation, that is, anti-clockwise when viewed from the top, and carry 24 lbs of weight each to help provide high inertia. In fact, it is possible to cut the engine on the ground, pull the machine up into a hover and (very quickly) spin through 180°, or more, before putting it on the ground again. The main rotor hub has a flap restraint system (the “bunny ears”) to prevent droop at low RPM. The maximum deflection applied to the blade is 24 inches, or roughly level with the bottom of the tail rotor cover.
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