The Pitch/Power Debate: It’s the Trim, Stupid

Posted by in Aviation

John over at Aviation Mentor recently posted an excellent article on the whole pitch vs. power debate.

I’ve never understood the dogmatic attitudes you’ll find among some pilots on this issue, although I’ve definitely seen those vociferous arguments out in the real world.

You can’t say it’s JUST power which determines altitude, because let’s face it, some aircraft don’t even have engines. And those aircraft happen to fly higher than aircraft which do have engines.

And it can’t always be pitch which determines altitude. One look at Sean Tucker flying the Oracle Challenger in level flight with a 45 degrees of pitch is enough to demonstrate that.

John’s longer and more detailed analysis came to the same conclusion I did. I’ve been saying forever that it’s not one or the other. It’s both. The pilot is simply managing the aircraft’s energy state. Those who insist it’s one or the other are taking a narrow-minded view, to say the least.

It pains me to see students get so mixed up in this debate, because it’s pointless, and it places so much emphasis on the topic that a more important element is left by the wayside: trim.

Students tend to think of trim as a secondary control, something relatively minor which is used for pitch. In fact, the control is even referred to as “pitch trim”. But unless you’re behind the power curve, it’s more directly related to airspeed than pitch.

Example: you’re cruising along at 160 knots in level flight and drop 10″ of manifold pressure. The airplane will begin slowing almost immediately. Less air over the wings means less lift. Since it’s trimmed for 160 knots, it’ll start to descend in an effort to maintain 160 knots. You didn’t change the trim, yet the pitch angle did change. What the airplane tried to do was maintain the same airspeed.

Oh, it’ll hunt around a while, but eventually, if the airplane is dynamically stable, it will return to the trimmed airspeed.

The same thing is true of climbs. The airplane is in level flight at 160 knots and you add 10″ of manifold pressure, the airplane will accelerate. This added airflow creates additional lift and the airplane starts to climb. The airspeed drops off again, the airplane’s climb rate decays a bit, the airspeed builds slightly, and the cycle repeats until the aircraft is established in a stable 160 knot climb.

This is an eye-opening event for many students. Yet even among those who “get it”, the importance of trim isn’t always fully apparent until it comes time for instrument training, because precision instrument flying requires pilots to be capable of climbs and descents at constant airspeeds. Without exception, they always have a much easier time of it once they ensure the aircraft is trimmed for the desired airspeed and let the inherent stability of the aircraft work on their behalf.

From where I sit, this tends to relegate this whole pitch/power debate to its proper place: an obscure message forum thread somewhere on the internet.