Fuel Systems and Engine Indication
Fuel Systems and Engine Indication tests how fuel is stored, boosted, metered and sprayed, and how cockpit indications let you judge power and health. In a helicopter, torque is often the primary power indication, with N1, N2, TGT and fuel flow as supporting parameters.
Core rules
- Typical sequence: tank, boost pump, shut-off valve, low-pressure filter, high-pressure pump, fuel control unit, flow divider, nozzles.
- The fuel control schedules fuel against demand using N1, N2, TGT, torque and ambient conditions; FADEC adds electronic metering and protection.
- Fuel flow indication is a demand and health indicator, not a direct torque gauge.
- Torque is measured by a torque transducer or by engine or transmission pressure; it is the best direct measure of rotor load.
- TGT responds quickly; indications may lag or be damped.
- Water drains and filter checks are preflight-critical.
Worked example
Fuel flow is 300 kg/h and fuel density is 0.80 kg/L. Volume flow = 300 / 0.80 = 375 L/h = 6.25 L/min. If the same engine later shows 330 kg/h at the same torque and TGT, the change may indicate a density change, a leaking or fuel-rich schedule, or a sensor error. Density varies with temperature, so compare mass flow and volume flow carefully.
Traps
- Reading fuel flow as if it were torque.
- Ignoring fuel density when converting units.
- Assuming a high TGT is always a fuel system fault.
- Failing to drain water from low points.
- Mismatching nozzle flow numbers.