Harmon Technologies, Inc.

Throttle Quadrant

The throttle quadrant has three levers and is used to control the engine and propeller.  Each lever on the throttle quadrant is described below:

Throttle

The throttle is the larger black lever on the left side.  This lever is similar to the accelerator pedal in a car.  It controls the engine power setting.  The level is shown in the idle position (toward the tail of the aircraft).  Full power is achieved when the lever is in the full forward position.  Unlike the accelerator in a car, the throttle stays where you put it.  Sometimes vibration can cause levers to creep slowly and the silver lever on the right side of the quadrant (it is pointing down) can be used to adjust the friction for all three levers.  This can make the levers easy or more difficult to move (and in the tighter position can reduce vibration creep). 

When setting power, the pilot normally looks at the manifold pressure gauge.  25 inches of manifold pressure is used for climbs, 24 inches for normal (75% power) cruise, 23 for economy cruise, and between 18 and 20 for slower flight (in the airport traffic pattern, etc.) or descents.

Propeller

The center blue lever is the propeller control.  In many ways, this level acts similar to a standard transmission gearshift level although it is continuous instead of having a fixed number of settings.  During ground operations and during takeoff and landing, this lever is in the full forward position.  This equates to first gear.  It is good for situations where maximum power output is needed but would not be efficient for cruise of descents.  During cruise, the lever is moved back by the pilot.  This increases the pitch of the propeller blades and so the prop takes a bigger bite out of the air.  This loads the engine more and is similar to shifting to t higher gear in a car.  As in a car, the pilot must avoid high power (lots of accelerator) and a low rpm setting (high gear).  just like in a car, this causes the engine to lug down and is not a good mode.

Because of the way the propeller mechanism works, it will attempt to maintain a constant speed.  The pilot looks at the tachometer when setting this lever (the tachometer is visible to the left of the quadrant in the picture).  Typically, full increase is used for takeoff and landing, 2500 RPM is used for climb, 2400 is used for cruise and descent.  During the pre-takeoff cockpit check, the pilot will exercise the propeller control two or three times and will make sure that the system is operating correctly.

A slower propeller causes less noise than a fast one.  When operating at high RPM, the propeller tips are near the speed of sound and generates much more propeller noise.  A lower RPM setting helps produce less noise and vibration so pilots tend to use lower RPM settings when appropriate.  In addition, N4907J has a three bladed propeller.  Using three blades (instead of the factory standard two blades) allows each blade to be slightly shorter.  This reduces the tip speed even more and causes less noise and vibration as well.

Mixture

The red lever on the right is the mixture control.  It controls the proportion of fuel being sent to the engine.  Full forward is a rich mixture (more fuel).  This is normally set to the appropriate mixture setting for sea level operation.  As the aircraft climbs, the air gets thinner and the mixture will become too rich since there is less air for the same amount of fuel.  The pilot can adjust the mixture so that  fuel is not wasted and the engine runs at maximum efficiency.  The pilot normally refers to the EGT (Exhaust Gas Temperature) gauge when setting this control.  Normally, we run N4907J at maximum power mixture.  This means that when cruising or operating in any mode above 5,000 feet MSL the mixture is slowly moved back until peak EGT occurs and then increased slightly (about 50 degrees of EGT).  This causes the engine to be slightly rich.  In an air cooled engine, the additional fuel helps to cool internal engine parts.  Leaning strategies are good topics for hanger talk since many pilots have strong opinions on the exact technique to be used.  The technique described above is conservative and is recommended by Textron/Lycoming, the engine manufacturer.

By the way, pulling the mixture control all of the way back is how an aircraft engine is shut down.

Copyright © 2004 Harmon Technologies, Inc.