Do you always reach best true airspeed in cruise? You should know this step to use aircraft momentum from slightly above a selected altitude to accelerate into best cruise speed. The procedure has at least 3 benefits:
- It’s a process check
- No delay – you don’t wait on engine power
- Cooler cylinder head temperatures
Here’s a process check using the GFC-700 autopilot in a Cirrus Perspective SR22TN Turbo.
In a full power climb from below, select an altitude 100 feet above the target cruise level, in this example 17,600 feet. Upon reaching 17,600 feet, reset the altitude select to 17,500 feet. Then touch the autopilot Vertical Speed (VS) and dial in a 400 foot per minute descent. This will set the plane in a slightly nose down position and use aircraft momentum to accelerate into best true airspeed (TAS).
Pull the throttle back as the plane is descending. You don’t have to stay at full power for several minutes. Use the operating manual procedure to set power and mixture for cruise (See last week’s article for instructions). In the Cirrus Turbo it’s called the “Big Pull.”
This procedure for getting “on the step” reduces pilot process variation associated with relying only on engine power to accelerate into best cruise speed from below. If you’ve sometimes reduced power too early you may find a better cruise speed. Compare your true airspeed results.
Cooler Cylinder Head Temps
Today’s GA aircraft have amazing engine monitors. Cirrus Aircraft measure each cylinder head and exhaust gas temperature, turbo inlet temperature, fuel flow, etc. If you’re entering cruise from below and remaining in a slightly nose up attitude that can contribute to a higher cylinder head temperature. Even more noticable after a long climb.
Try the “process check” to enter cruise from just above the selected altitude. With the nose slightly lowered and in a 400 foot per minute descent the cylinder head temperatures cool and the plane will be correctly positioned for cruise when leveling off. Your highest cylinder head temperature may be lower. Compare your results.
- If you’re on an IFR flight plan obtain ATC approval for deviations above your assigned altitude
- Getting an airplane into best cruise performance can be affected by several variables: weight & balance, density altitude, and pilot process variation.
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