Aero-Tips!

A good pilot is always learning -- how many times have you heard this old standard throughout your flying career? There is no truer statement in all of flying (well, with the possible exception of "there are no old, bold pilots.")

Aero-News has called upon the expertise of Thomas P. Turner, master CFI and all-around-good-guy, to bring our readers -- and us -- daily tips to improve our skills as aviators. Some of them, you may have heard before... but for each of us, there will also be something we might never have considered before, or something that didn't "stick" the way it should have the first time we memorized it for the practical test.

Aero-Tips 06.20.06

One of the most important things to learn in the very first lesson or two flying an airplane is to make proper use of the trim.  This lesson will serve you whether you pursue a recreational or sport certificate, take the traditional Private Pilot route, or work your way up through the Airline Transport Pilot certificate. Trim will be one of your best friends in cruise flight, and is essential to successfully flying on instruments.

In a rather involved and somewhat math-heavy discussion, the National Aeronautics and Space Administration (NASA) tells us that "when there is no rotation around the [airplane's center of gravity] the aircraft is said to be trimmed." From the pilot's seat this means that flight controls are displaced to that the airplane is not pitching (nose up/down movement), rolling (wings changing their angle of bank relative to the ground), or yawing (swinging side-to-side relative to the airplane's vertical axis). Note that the airplane can be at any angle of pitch, bank and/or yaw relative to the horizon; it's the lack of change in the current angles that implies the airplane is "in trim."

Put it on my tab

You might be pushing or pulling hard on the yoke and/or rudder pedals to keep movement around the c.g. nil, and the airplane in trim. Most airplanes, though, have devices to reduce the amount of work you need to do to keep the airplane trimmed. Trim tabs are fixed or moveable parts of control surfaces that help relieve the pressure needed to displace the controls.

• Fixed tabs are attached to the trailing edge of controls, and are set during airplane production and adjusted as necessary afterward to apply control pressures normally seen in cruising flight. These are sometimes called ground-adjustable tabs. You'll usually see these thin metal fixed trim tabs on airplane rudders and sometimes ailerons.
• Moveable or in-flight adjustable trim tabs are hinged so you can move them using controls in the cockpit. These are most helpful when the trim requirement changes with airspeed, power changes and/or angle of attack. Almost all airplanes have a moveable trim tab on the elevator for pitch control.

Airplanes use different techniques for adjusting trim. Bungee chords might be used to put a load on control cables, deflecting the control surface without a trim tab. Most Beech Bonanzas use this for aileron trim. Some aircraft, for example the Piper Cub, have jackscrews that change the angle of incidence of the horizontal stabilizer to change pitch trim. In a few cases, including Mooneys through some large transport airplanes, the entire tail section of the airplane may pivot to accomplish pitch trim, a surprisingly reliable and effective system. Regardless of the design involved, trim systems do the hard work of maintaining trim so you don't have to.

Aero-tip of the day: Learning to trim the airplane is the first step in reducing pilot workload, and achieving consistent, predictable performance.

FMI: Aero-Tips