Mixture control: leaning procedure
Mixture control sets fuel/air ratio to the cylinders.
- Air thins with altitude, fuel drawn in does not.
- Unleaned mixture grows progressively richer in climb (TP 1102).
Setting by phase:
| Phase | Setting | Reason |
|---|---|---|
| Takeoff, climb, inside airport traffic pattern | Full rich | Runs engine cooler at high power. Lean only at unusually high-elevation airports, some over 5,000 ft |
| Cruise at altitude, power fixed | Lean (steps below) | Optimum power, no overheating |
| Before routine descent | Full rich, ideally enriched gradually as descent progresses | Avoids too-lean mixture if power suddenly needed; set for approach |
| No fuel/air ratio instruments fitted | Rich side | Default |
Leaning steps (cruise, power fixed):
- Move control slowly toward lean until RPM peaks.
- Move back toward rich until RPM just perceptibly drops.
- Result: slightly rich, optimum power, no overheating.
Wrong mixture:
| Effect | Too rich | Too lean |
|---|---|---|
| Power | May not develop rated power | Power loss |
| Running | Runs unevenly | Rough running, vibration |
| Temperature | Runs cooler than desired | Runs hotter than desired |
| Fuel/plugs | Wastes fuel, more spark plug fouling, reduced range | - |
Trap: staying leaned into descent. Sudden power need then finds mixture too lean.
References
- TP 1102 Ex.3 Ancillary Controls, Mixture Control