Installation, Ground Operation & Storage
Engine mounts and cowling, the run-up mag check, shock cooling, ground-running care and preservation.
Installation, ground operation & storage, summary notes
- The engine is carried on mounts that absorb vibration and carry thrust and torque into the airframe, behind a firewall, inside a cowling with baffles that direct cooling air; flexible lines and connections allow for movement.
- Ground operation follows a set procedure: start, warm-up until oil temperature/pressure are healthy, run-up to check each magneto (the dead-cut/RPM-drop 'mag check') and cycle the propeller, then monitor temperatures and pressures, avoiding prolonged ground running, which overheats an air-cooled engine.
- The magneto (dead-cut) check confirms both ignition systems and their plugs work, that the RPM drop on each mag is within limits and roughly equal, and that the switch grounds the mags correctly.
- 'Shock cooling', a rapid power reduction that cools the cylinders too quickly (e.g. a fast descent at low power), can crack cylinders and is avoided by gradual power changes.
- Storage and preservation protect an inactive engine: inhibiting oil, dehydrator (desiccant) plugs, sealed intakes/exhausts and periodic turning; CORROSION (from moisture and inactivity, attacking cylinder walls and the camshaft) is the chief enemy, the engine must be de-preserved before flight.
- ⚠ Exam trap: the run-up mag check verifies each magneto/plug set and that the switch grounds the mags; the main threat to a STORED piston engine is internal CORROSION from inactivity/moisture, hence inhibiting oil and desiccant plugs.
During the run-up the RPM drop on the left magneto is far larger than on the right (and near the limit). What does an excessive single-mag RPM drop suggest?
A large RPM drop on one magneto means that ignition system is not firing all its plugs properly, commonly a fouled or dead spark plug, a faulty HT lead, or a magneto timing/internal fault on that side. Because dual ignition also aids combustion, running on the weak mag is rougher and slower; the fault must be investigated before flight.
Installation & care concept map
Installation, Ground Ops & Storage
Installation, ground operation & storage quiz
Installation, Ground Operation & Storage, quiz
1. Excessively rich mixture is indicated by:
Low cylinder head and exhaust gas temperature, rough running and black smokeA high exhaust gas temperature with smooth running, since the extra fuel raises the combustion temperatureA rise in oil pressure and temperature, as the unburnt fuel washes past the rings and thins the oil2. Detonation in a piston engine is:
Uncontrolled, spontaneous burning of the charge after ignitionNormal progressive flame-front burning, spreading outwards from the spark plug electrodesA failure of the ignition to occur at all, leaving the charge unburnt as it passes to exhaust3. Pre-ignition differs from detonation in that it:
Ignites the charge before the spark, from a hot spotOccurs only in turbinesCannot damage the engine4. Engine mounts are designed to:
Absorb vibration and carry thrust/torque to the airframeCool the cylinders by conducting heat from the crankcase out into the airframe structureStore a small quantity of fuel close to the engine so that the supply is never interrupted5. The run-up 'mag check' confirms:
Both magnetos/plug sets work and the switch grounds themThat the oil level and pressure are sufficient before the engine is run up to full powerThat the correct fuel grade has been uplifted, by comparing the power developed against the datum6. An excessive RPM drop on one magneto indicates:
A fault in that ignition system (e.g. fouled plug)A healthy engineCorrect leaning7. Prolonged ground running of an air-cooled engine risks:
Overheating (little cooling airflow)OvercoolingBetter performance8. 'Shock cooling' is avoided by:
Gradual power changesRapid power reductionsLeaning aggressively