Supertrim

Mike Shellim 23 July 2022
Last updated 30 Nov 2022

Supertrim provides a smarter, easier way of adjusting crow compensation. While not as flexible as my Crow aware adatpive trim, it does not require a Lua script.

Background

When using crow brakes, there are two components to pitch trim:

The Problem

Base trim and crow compensations are both about pitch trim, but they have different adjustments. This is confusing for the pilot.

The solution: Supertrim

Supertrim provides a single adjustment point for both base trim and crow compensation, using just the regular elevator trim:

This makes the process of trimming really easy. Brakes off, trim, apply brakes, trim. Done! When the brakes are deployed, the base trim is held at its last value, and any compensation adjustment is added to the base trim - exactly as it's supposed to. Once the brakes are retracted, the elevator trim resumes its normal function of adjusting the base trim.

When trimming with brakes on, the brakes should be at 75 - 100%, in other words near maximum compensation.

How it's done

Supertrim depends on a cool feature of OpenTX: a trim can be repurposed on demand, so that it updates a GVAR while holding the trim value. It's then simply a question of using the GVAR to supply the weight of the compensation mix.

The following are required:

Here's the code:

GVARS

GV1 - min=0%, max=40% -- supplies compensation value

 

CH2:elevator

+= Source=I2:Ele Weight=-100% -- elevator input + base trim
+= Source=Thr Weight=+GV1 Offset=−GV1 -- compensation

 

Logical Switches

L1 Thr < 100 -- true when brakes deployed

 

Special Functions

SF1 switch=L1 - Adjust GV1 Source=TrmE -- trim updates GV1

Here's how it works:

Adding a compensation curve

The amount of compensation is normally non-linear with respect to crow, so a curve will usually be included in the compensation mix. Nothing special here.

Use with flight modes

The example code above assumes a single flight mode. The technique is also perfect for setups with multiple flight modes which include a dedicated 'crow' mode. In this case, the base trim in crow mode should be obtained from another flight mode, normally 'cruise'. Sharing of trim settings between flight modes is configured in the Flight Modes menu. For more info see Advanced trims.

Demo file

A demo can be dowloaded here (X9D profile). If using the Companion sim, note that dragging the trim handle doesn't work when adjusting compensation. Instead, click on the arrowheads at each end of the trim sliders.

Integration in Pro templates

At the time of writing, Supertrim is integrated in the latest DLG, DLG6S and F3F templates. The plan is to include it future versions of the remaining templates, where applicable.

Links

For more info, see Advanced trims, in particular the section "Using a trim to update a GVAR".