Crow brakes are virtually essential for F3X models. They allow you to bring your model down quickly, without building excessive speed. 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 - you have to cook them yourself! (A few of us do enjoy cooking...)
Aileron diff suppression
First a quick recap. When crow brakes are deployed, the flaps go down, and the ailerons go up, creating extra drag and reducing the glide angle.
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| F3F model with crow brakes deployed |
Now consider what happens if full crow is deployed. At this point, both ailerons will be raised. If you now apply a roll command, the upgoing movement will be limited by the hinge geometry. Just as bad, the downgoing movement will almost certainly be insufficient, depending on the amount of diff.
The result will be poor aileron response!
We can't do anything about the upward limit. However we can improve the downgoing travel.
The first line of defence is "aileron diff suppression". As crow brake is deployed, any aileron differential is reduced until - with full crow brake applied - the downward movement of the ailerons (in response to a roll command) is then the same as the upward movement. This will provide at least some improvement in roll response. If more downward movement is required, then we're into reverse diff territory.
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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