Throttle, Prop or Mixture?

Throttle, Prop or Mixture?

Throttle, Prop and Mixture – or short TPM – are typically three levers in an aircaft cockpit to manage the power of combustion engines. Taxiing on ground only needs very little power and actually when the aircraft engine runs on idle, the pilot already has to apply brakes to prevent rolling. When taxiing from the parking position to the runway, very little power is needed too.


Model of a Flight Simulator Throttle, Prop and Mixutre arrangement

Fixed pitch propellers

For fixed pitch propellers, the pilot will only have two levers: Throttle and Mixture. Throttle in an aircraft is like the accellerator pedal in a car. The Mixture lever is used to adjust the fuel/air ratio. With increasing altitude the air gets thinner and less fuel is required for optimal combustion. The pilot leans the engine(s) with the Mixture lever by pulling it backwards until reaching Exhaust Gas Temperature (EGT) peak. Afterwards he pushes the lever a little bit forward to run on the “rich” side (cooling of engine). On ground, during takeoff and landing the Mixure typically is rich – lever full forward! When the aircraft is lined up on the runway and ready for takeoff, the pilot needs maximum power to accelerate and lift off. He pushes the lever forward – full Throttle! After takeoff the throttle is slightly pulled back to set the required climb power.

Constant speed propellers

Engines are deisgned to perform maximum continous power at a given RPM. Fixed pitch propellers are directly connected to the crank shaft without a gear box. They are deisgned either for an optimal climb performance resulting in a slower cruise speed or vice versa. To overcome this problem, constant speed propellers were developed. A typical RPM during cruise flight is 2300 RPM. During takeoff run and climb, maximum thrust is needed to lift off as soon as possible and to climb as fast as possible until free of obstacles. At idle and at maximum climb performance the prop blades have the smallest angle of attack. With increasing speed of the aircraft the angle of prop blades increases and at safe altitude the pilot pulls back the Prop lever slightly to reduce RPM, followed by the Throttle lever to reduce manifold pressure. Constant speed props make aircraft faster, allow them to better climb and save fuel because prop and engine operate at optimal conditions during cruise.

FSX BOX – The portable Flight Simulator

Besides Yoke, Rudder Pedals and an Instrument Panel, Throttle, Prop and Mixture levers are one of the most important items in an aircraft cockpit. Item no. 2 in following image shows the integration into a portable Flight Simulator.

Karsten Reichart

Pilot and Engineer

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