Sunday, 26 October 2014

Reverse Diff - or how to improve your landings

Crow brakes are essential for bringing a model down quickly. However, deploying crow brakes can adversely affect roll response. In this post I'll examine the reasons behind it and describe a couple of techniques for improving roll control.

The techniques are particularly relevant for OpenTx which does not provide these features built in.

Aileron diff suppression

First a quick recap. As you apply crow crow, the flaps go down, and the ailerons go up.



Consider what happens if full crow is deployed, and you apply a roll command. The upgoing movement is limited by the hinge geometry, and the downgoing movement will be limited by the differential value. Depending on the amount of diff, and the crow configuration, the result can be poor aileron response.

The first line of defence is "aileron diff suppression". Most high end radios have this built in. As crow brake is deployed, differential is reduced until - with full crow brake applied - diff is zero. The downward movement of the ailerons (in response to a roll command) is then the same as the upward movement.

However this in itself may not provide sufficient movement for decent roll response. This where reverse diff comes in.

Reverse Diff

Reverse diff is an extra adjustment which can increase the downward movement beyond that provided by diff suppression alone. Using reverse diff, you can ensure that the aileron can deflect at or below the aileron centre position. I find this provides good roll control even with full crow.

This feature which is included F3F setup for the Taranis v. 3. The adjustment is via a single menu point.

F3F Setup for Taranis v. 3.0 can be downloaded from OpenTx Clinic.

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