First answered on Quora May 6 2018.

Yesterday afternoon while practicing circuits in a Citabria for my tailwheel endorsement I went to put the carburettor heat on to start my descent, keeping my eyes outside like a good stick and rudder pilot to make sure I didn’t drop the nose on my turn to base — and instead pulled back on the nearby elevator trim which is pretty direct in a Citabria. The next thing I knew I was squished in my seat with the horizon nowhere in sight. Immediately realising what I’d done I wrestled the nose back down to somewhere more reasonable, accompanied by a few choice invectives. The instructor laughed and said “I’m glad you did that, another student did that a few months ago but on short final (i.e. much closer to the ground) and came close to stalling onto the runway — now you’ll remember”.

The point of this slightly embarrassing anecdote is that control forces in a non fly-by-wire aircraft are a lot more powerful than you might expect from experience with a simulator or game. In fact when first learning to fly I often asked whether or not the instructor was on the controls with me. Where constantly holding a bit of pressure on the elevator or rudder to keep going where you want to go in a simulator is quite possible indefinitely, in a real plane it can quickly get exhausting and demand a lot of attention, as well as making it quite difficult to use equipment or write something down.

Correctly trimmed an aircraft like the Citabria really will fly itself. When taking off, after the aircraft wants to fly I’ll pull back on the stick and line up the top of the engine cowling with the horizon, glance at the airspeed to see that it’s around 70 knots and keeping my right hand on the stick to hold the sight picture, briefly take my left hand off the throttle and slide the elevator trim lever until I feel no force on my hand from the stick. At that point I can take my hands off the stick and the aircraft will happily continue to climb out with no input from me, and most importantly the airspeed will be very stable and not require much attention. I usually do a little “jazz hands” moment for the instructor in the back to show that things are trimmed out nicely.

In an extreme scenario if I tried to take off with the elevator trim stuck full forward or backward it would take almost all my focus and strength to keep the plane in the attitude and speed I wanted, and I think my arms would start to tire in less than a minute. More normally, flying without trimming is considered bad airmanship because there’s plenty of better things to focus your attention on than wrestling the controls.

Elevator is the most important trim control because of its tight relationship with airspeed. Aileron and rudder trim are also a thing but in the light singles I fly I almost never touch them, except perhaps on long cross countries when I develop a feeling that the plane wants to slowly turn one way or the other. In a multi engined aircraft rudder trim becomes critical for engine out scenarios.

Picture from Tailwheel fun in a Citabria showing (top to bottom) throttle, carburettor heat and elevator trim.