Why Understanding the Trim Tab is Important to Become a Better Pilot
By Robert Mark on March 2nd, 2021 | What do you think? »Look Ma … No Hands
As a kid, when you told your mom you planned to try something without holding on was a tipoff that something dangerous was surely in the offing.
But when I tell flight students to try letting go of the control wheel or stick at times when we’re flying when I first get to know them, I’m actually trying to help them become better pilots. In my case, it’s all about learning to trim the airplane. Pilots who fail to learn the purpose of the trim tab – that little piece of hinged metal on the end of the elevator – or the movable horizontal stabilizer really are doomed to work way too hard at becoming truly good pilots. I often find though that many instructors don’t take enough time to explain the “why” behind trimming an airplane.
Most simply, trim tabs help maintain an airplane’s state of balance where all four of those basic forces we learned about as student pilots — power, lift, drag, and gravity — basically come together. Alter any of those forces and you’ll need to re-trim the aircraft to re-establish that hands-free balance. When the trim is set properly, the pilot can indeed let go of the wheel and the airplane will fly just fine.
Failure to re-establish that balance though and the pilot is forced to maintain back or forward pressure on the control wheel to maintain altitude or airspeed. That might not seem like a big deal, but it’s just one more brain function that’s not available for other important things like navigating, looking out the window for other airplanes or drones, or keeping an eye on the weather.
The Nuts and Bolts
Here’s how you can make your flight training and flying life a little easier. Next time you’re out solo in level flight, simply let go of the control wheel or stick and watch what happens to the nose of the airplane. If the airplane’s properly trimmed, you shouldn’t notice much of a change at all.
But if the airplane’s nose drops and the airspeed begins increasing, you’ve been holding the nose up yourself, fighting the trim tab itself. An opposite reaction means you’ve been holding it down. And all of this means you’re working too hard.
So how do you fix the problem? The worst fix you can try while you’re not grasping the control wheel is to begin fussing with the trim wheel. Trying to fix a balance problem by only trimming and you’ll end up chasing the nose through an endless series of up and down pitch changes. This happens quite a bit when the aircraft is equipped with an electric trim button on the control wheel because that seems like the best solution.
The trick is to grasp the control wheel or sidestick and manually set the airplane’s nose pitch where you want it first. THEN trim until you feel no pressure at all. If you’ve done it right, the pitch won’t change when you release the wheel. Still not quite right? Grasp the wheel again and trim just a teensy weensy bit at a time and let go again.
Want to hold 85 knots in level flight? Set the power and pitch attitude for that speed and trim just a bit nose up or nose down so the nose seems not to move. If you handled this chore correctly that airplane will cruise just dandy at 85 knots until one of the forces changes. The same works to set the aircraft up for descent or landing. Set the power, drop the flaps and trim until the airplane holds the speed without any pressure on the wheel from you. There shouldn’t be any configuration on any airplane that won’t allow you to trim off the pressure you’re holding unless something is wrong somewhere. Climb at 85 and trim off the pressure. It even works in a steep turn if you’re ready for it … turn and trim.
One configuration that could pop up is if the airplane is loaded with too much weight in the tail. It is possible to load the aircraft with such a rearward CG that the trim is unable to balance the airplane. That’s just plain dangerous and explains why keeping an eye on how you load the aircraft can become very important.
One final tip. If you haven’t earned an instrument rating yet, trust me … learning to properly trim the airplane will make your training much easier. Creating good instrument flying skills will at times seem to require every ounce of brainpower you have. Now you’ll know how to tweak your airplane in a way to free up just a little extra gray matter for when you’ll need it most.
Fly safely,
Rob Mark, Publisher
This article was reprinted with permission from AOPA Pilot
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