Propeller Operation

Magneto Drop & Leaning the Mixture

During the pre-take-off engine run-up, the magnetos are checked at around 1700-1800 RPM. At this stage the propeller pitch is at the fine/flat pitch limit stop and remains there during the engine run-up and until after the take-off is well under way. Therefore the drop in RPM will still be apparent and will not be masked by the CSU. The same applies to leaning the mixture if this is necessary before take-off, as would be the requirement when operating from a hot and high airfield. Lean the mixture until the RPM rises to its maximum peak. The exhaust gas temperature (EGT) will also be at its peak indicating the correct mixture setting for maximum power. When the RPM is at its peak, note the position of the mixture control and then quickly return it to ‘full rich’. The engine should continue to run smoothly without any surge in power. Continued smooth running indicates the chosen mixture setting was correct and the mixture control can now be returned to the continuously noted position