Engine Construction
Engine Construction tests how modules are built, aligned, sealed and mounted, and why material choice and clearances matter. In a helicopter, the engine is attached through mounts and a drive coupling; construction details affect vibration, fire safety and maintenance access.
Core construction rules
- Modular design separates compressor, combustor, turbine and accessory gearbox so modules can be removed and balanced as units.
- Casings carry structural loads and form the gas path; split casings use controlled torque and locking.
- Bearings locate the rotor axially and radially: a ball bearing usually takes axial load, while roller bearings allow thermal growth.
- Seals control internal leakage; orientation and clearance are critical.
- Mounts and flexible couplings isolate engine vibration and accommodate misalignment.
- Materials: titanium or aluminium in cool compressor areas, nickel superalloys and cooled blades in the hot section.
Worked example
A steel compressor casing 0.50 m long rises 200°C in operation. With a coefficient of expansion of about 12 times 10 to the minus 6 per °C, growth = coefficient × length × temperature rise = 12 × 10⁻⁶ × 0.50 × 200 = 0.0012 m, or 1.2 mm. That is why one bearing is allowed to slide and why pipe unions and mounts use flexible sections. If the bearing arrangement were reversed, thermal growth would load the bearings and distort tip clearances.
Traps
- Reusing lockwire, self-locking nuts or seals beyond approved limits.
- Fitting bolts of the wrong grip length or grade.
- Damaging seal faces during assembly.
- Ignoring FOD in open casings.
- Assuming a visually identical part is interchangeable without approval.