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Roll Trim Direction

design4p

Active Member
Hi,

I have a full suite of Garmin in my RV14A and just completed the build and now configuring the avionics- in particular the trim direction and related Autopilot movements. I have the roll trim servo in the wing.

This maybe a silly question but I am wondering which way the stick should move (on its own) when I press (say) the right trim button - should the stick move to the right or the left.

John
 
The stick should move to the right, when you push the right trim button.

Right. But how about elevator trim?
On a panel switch up, would be natural for nose up.
But on a stick, forward is nose down or nose up? I'd think nose down (same way as you push the stick -- but?

Finn
 
Right. But how about elevator trim?
On a panel switch up, would be natural for nose up.
But on a stick, forward is nose down or nose up? I'd think nose down (same way as you push the stick -- but?
Finn

It is your choice as long as it is labeled. With a rocker switch on the panel most people prefer pushing the top for down trim, similar to rolling a "trim wheel" forward. Remember, the elevator tab goes down for "up" trim and up for "down" trim. Believe it or not approximately 1/2 of the airplanes I inspect have at least one trim backwards.
 
Think of pitch trim like a trim wheel. Either on the stick or panel, the top or forward push of a rocker switch seems to mimic rotating a trim wheel for nose down.

That's how it feels to me.
 
I think of trim as what pressures I want to trim off to maintain level flight.

Elevator: If my nose is wanting to climb I need more nose down pressure to maintain level flight. I trim nose down (forward on the coolie hat trim switch) which in turn pushes the elevator trim tab up - which forces the elevator slightly down thereby lowering the nose of the aircraft to level flight conditions.

Aileron: Think about what happens to the aircraft when you make a turn. For a right turn I push the stick right which pulls the right aileron up (decreasing lift) and pushes the left aileron down (which increases lift).

Now let’s apply this to a situation where my flight today is solo so the right side of the aircraft is lighter than the left side (I’m a full figured guy). The left wing needs to generate a little more lift to compensate for my “heaviness ”. The right wing needs to generate less lift to maintain wings level flight.

So just like a “right turn” I need to move the stick slightly right. My trim setup is wired so that I apply “right turn (trim)” on my coolie hat switch. On my airplane I usually have to apply almost full right trim when flying solo and center the trim switch when flying dual. I burn initially out of the left tank when solo (5 to 10 gallons - depending on fuel load) then transfer to the right tank for the next five gallons then back left again. Airplane flys a really nice ILS with minimal trim changes. Of course as speed decreases and flaps are extended a little “nose up trim” (aft coolie hat trim) is required and nose down (coolie hat forward trim) when a missed approach is initiated and the airplane increases in speed with less drag and greater power application.
 
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