Walk the start and shutdown sequences for three piston helicopters, see why each step is there, then drill them from memory. Tap any line to open the reasoning.
Gauge values and prime timings are illustrative, chosen to teach the sequence. They are not aircraft limits.
| FUEL INJECTED R44 Raven II · 300C | CARBURETED 300CB | |
|---|---|---|
| Metering | Fuel servo meters by airflow and sends fuel under pressure through a flow divider to a nozzle at each cylinder. | Float carburetor meters fuel through the venturi. Fuel and air mix before the intake manifold. |
| How you prime | Electric pump with mixture rich pushes fuel to the nozzles. Then mixture back to idle cutoff before cranking. | Primer or throttle (accelerator pump), as the installation provides. Mixture stays rich. |
| Mixture while cranking | Idle cutoff, then smoothly to full rich as the engine fires. | Full rich the whole time. |
| Hot start | The tricky one. Heat-soaked lines vaporise fuel. Little or no prime, crank with mixture at cutoff, feed it in when it fires. | Usually easy. Skip the prime; the bowl already holds fuel. |
| Flooded | Mixture idle cutoff, throttle open, crank to clear, then close throttle and restart. | Same idea: throttle open, crank to clear the cylinders, then normal start without priming. |
| Carburetor ice | No venturi, so no carb ice. Watch for impact ice on the air filter in visible moisture. | Real risk, worst at low power settings common in helicopters. Watch the CAT gauge and apply carb heat to keep it out of the yellow arc. |
| Carb heat at start | Not fitted. | Cold / off for start. Heated air is unfiltered, and a backfire through the carb is worse with it open. |
| Shutdown | Both stop the engine with mixture to idle cutoff after the cool-down, so the cylinders are left without fuel. | |