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Look Ma … No Hands

trim_tab

Photo courtesy FS-Force

As a kid, telling 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 flying students to try letting go of the control wheel or stick at times 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 put, 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 — come together. Alter any of the forces and you’ll need to re-trim the aircraft to reestablish that balance.

Failure to reestablish balance and the pilot’s forced to hold 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 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 won’t notice any change at all.

But if the airplane’s nose drops and the airspeed begins increasing, you’ve been holding the nose up. An opposite reaction means you’ve been holding it down. Again, that means you’re working too hard.

So how do you fix the problem? The worst thing you can do right now 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 in 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 quick solution.

The trick though, is to grasp the control wheel and set the 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 for that speed and trim just a bit nose up or nose down and let go. If you did it all correctly, that airplane will cruise just dandy at 85 knots until one of the forces changes. Same works to set up a descent. 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 final tip. If you haven’t yet earned an instrument rating yet, trust me … learning to properly trim the airplane will make your training a whole lot easier. Creating good instrument flying skills will at times seem to require every ounce of brain power your have. Now you’ll know how to tweak just a bit more from that gray matter when you just might need it.

Fly safe.

 

16 Comments

  1. “trim tabs help maintain an airplane’s state of balance where all four of those basic forces …”

    That’s an odd way of putting it. Even just in the case of pitch-trim set inappropriately, relaxing controls will generally result in a “balanced” (non-accelerating?) airplane, just at a different AoA / airspeed / climb-rate.

    • Which is not what you want…normally we want to maintain a set airspeed, altitude and heading. By having a trimmed aircraft it will help maintain those parameters…

    • I think I was trying not to let the entire discussion get too complicated, but Frank is right about trim being applicable to any state of flight. I simply ran out of time and space, but I should have made room for that sentence. The beauty of online communications is that when a reader points out a detail like this, I can go tweak it pretty easily for the next folks who happen along.

      • Yeah! I couldn’t think of a terse way of summarizing trim’s mechanical effect, except circularly with the article’s focus: “trim sets the plane’s neutral (hands-off) behaviour”.

  2. Good brief…as a Flight Examiner I often observe poor flight performance that is obviously caused my a poorly trimmed aircraft. I use the same technique and ask the applicant to release the flight controls to confirm my suspensions…

  3. I was lucky. Every instructor I’ve had has been a “bear” for proper trim. The first one told me he was just too lazy to work more than he had to, and enjoyed flying his aircraft in a “relaxed” state of being. Then, he’d chew on me for failing to keep the aircraft in proper trim.

  4. From the first flight in 1969, it was drilled into me that if you are flying with more then two fingers on the controls, you are out of trim. Then the instructor would roll in full up or down elevator trim (C150/PA-28). Same with maneuvers’ like steep turns (weren’t limited to 60 degrees of bank then). Now it’s just how I fly.

    If you really want some fun, try flying a “Heavy” like a P-3 with the alt hold off. Get everything trimmed out, relaxed and holding altitude and then the whole crew will “run the tube”. Without telling you when they were starting the fun. Figured if you could maintain +- 2500 feet at FL230, you were doing damm good as everyone ran from one end to the other of the tube, repeatedly.

    • 🙂 Thanks! Besides it’s nice to know some “Old Farts”, besides me are still out there.

      OBTW. In the beginning I was flying out of PAE. Same time as the 747 started the first test flights. Some of us learned about wing tip vortices behind a Heavy first hand. We were all lucky. Gotta give the FAA credit, Pilot Reports WERE acted on. No one knew about wingtip vortices then, between the FAA and Boeing it didn’t take long to figure out what was happening, and how to keep out of trouble.

  5. Why heck I’ve been doing that for the last 51 years of instruction. Nuttin new young man 🙂

  6. Excellent article. Trim is a flight control but so many Pilot’s, even ones you would consider Professionals don’t use it or understand it well. I see it all the time with the students I train in Tail Wheel and Aerobatics. The author is dead on. Good job!

  7. This is a great article! As a student pilot, I have had some trouble trimming and keeping straight and level. I always seem to be climbing and descending no matter what I do with the trim. My biggest problem is trimming the aircraft, then adjusting the speed with the throttle, which throws it all off again! Great job with the article, this will definitely help me out! 🙂

    • One thing to remember is that aircraft speed is controlled by the angle of attack, not the throttle. Throttle controls altitude/vertical speed…apply throttle in level flight without hands on the yoke and the aircraft will climb. Aircraft trimmed for a specific angle of attack will fly at a certain speed, even if you yank the yoke, the plane will settle back to the trim after a few
      oscillations. Pitch for airspeed, then trim off the control pressure.

  8. Everyone needs to read the article by Gene Hudson published in the Mar/Apr 2014 FAA Safety-Brief, page 13, the physiology of manual flight control. It outlines the reasons for turning the controls loose.

  9. I probably do everything wrong – but I’ve only been flying four years and I’m 77. I trim for takeoff because my plane needs all my strength to hold it, otherwise. I trim for cruise so I can let go of the yoke for the remainder of the flight. As the fuel burns off during those hours the altitude starts to wander, so continue to ignore the yoke and I barely touch the trim switch to make altitude stay where I want it. To descend I reduce rpm, hands off. To climb I increase rpm, hands off. The airspeed hardly changes. AP? What AP? It’s just a nicely trimmed aircraft.

  10. I like Mr. Hanson’s analogy. I would add a sentence or two (or three). I’ve always told my students that the aircraft is never finally trimmed (stabilized) until the power being used is in equilibrium with the intended regime of flight. The classic case is going from climb to cruise, using climb power after re-setting the aircraft pitch attitude to cruise. Initially (instantaneously) after dropping the nose, the aircraft will need little trim change, but as the aircraft attains the new cruise speed (holding forward pressure), one will need to keep adjusting the trim (rolling off the pressure, so to speak) until the new speed (regime of flight)) is in equilibrium with the power setting, whatever final power setting is used.

    This equilibrium concept is always true, whether it be climb, cruise, descent, or ‘slo-flight’. It should be ‘well-worn’ when flying on instruments.

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