A2A Comanche 250 is on its way! (Released! July 2023)

Start with the concept that pitch + power = performance.

You trim for the airspeed you want to maintain with your hands mostly off the elevator. This in turn results in a particular pitch when combined with actual airspeed (performance) and power when the controls are neutralized. You can rearrange that equation to solve for the other variables.

The other concept is that lift is a function of velocity and angle of attack. More of either equals more lift (and of course too much AoA will produce a stall, and there are other changes in drag happening… but I digress).

Getting more in the weeds, but more accurately, the tail section provides a counter lever for the airplane’s tendency to nose down due to the center of gravity (CG) being ahead of the center of lift (CL). The horizontal stabilizer is designed to provide lift downward - when increasing lift on the tail, it pushes the tail down and raises the nose. Back to the equation - if you change airflow over the tail without touching the flight controls, it wants to re-stabilize to neutral pitching moment and after several oscillations (called phugoids), it will stop pitching at wherever the set trim re-establishes that balance.

Example, if you slow down, the tail produces less tail down/nose up force, so the nose falls. But the rate of descent increases and the airplane accelerates, once again providing more lift, increasing the counter lever and raising the nose again. Undampened, the pitch will usually overshoot, going too high and start to slow the aircraft again, repeating the cycle. Provided you have enough altitude over the ground, it might do this several times before it stabilizes. As a pilot, you can help by dampening the oscillations - that’s literally one of our primary functions at a base level (we just don’t often acknowledge it directly in this manner).

So back to the main point, trim for the airspeed that is prescribed for the phase of flight in the particular aircraft and configuration (including weight). If you find yourself descending too rapidly, you need to add power and once again dampen the changes (oscillations) with the elevator, then re-trim.

We don’t necessarily shoot for a particular elevator trim setting when airborne - we just use whatever is necessary. However, the caveat is you shouldn’t really change it once established on final unless it’s really out of trim and you’re fighting it with the elevator. Generally do not use trim in the flare (that’s a contentious debate), but make sure you do reset it to takeoff trim once you’re firmly on the ground - usually after exiting the runway, but also could be part of a touch and go process.

The Comanche is a relatively “slick” or “slippery” design and really wants to speed up as you descend. You have to stay well ahead of it to get it down. The old “you can go down or slow down, but not both (at the same time)” adage comes to mind. But there are ways to mitigate that, using a forward slip, configuring with flaps and gear when feasible, or changing the geometry of your approach.