Aileron Differential / Adverse Yaw and a touch too much cleverness – Hard Lesson Learned and

phoenix

 

Update – while everything below still stands the cause of the problem was worse than I thought. In introducing a curve for the aileron differential I had reversed the servos to make it work BUT I had not tested “basic or panic” mode afterwards – and so the aileron controls were reversed in that flight mode – which is kind of ironic. This has made me even more convinced that a basic / panic mode with no mixes is not necessarily a good idea or needs to be done and (re)tested with as much care as the other modes.

I read an excellent article in the BMFA journal ( issue 121 , unfortunately not on-line ) about Aileron Differential / Adverse Yaw but unfortunately never got around to doing much about it until this week. Essentially this is where symmetrical deflection of the ailerons causes too much drag on the lower aileron – just like dropping a flap on one side of the model only.

Last week when I set up my new Hobbyking Phoenix 2000 ( review coming soon )  with quite large aileron throws so that I could use crow braking / spoilers. When I looked at the amount of downward deflection of the ailerons it was very significant and alarm bells rang in my head. I used curves on the Taranis to reduce the downward deflection to 40% and this seemed to work really well.

curve5

In my Taranis setups I usually have a basic mode with no mixes as a fallback in case I have programmed something wrong. I have always been quite proud of this feature – until today.

As I circled around for landing I accidently knocked the switch into this basic mode. I wasn’t too worried as it was a simple landing and I didn’t need engine or braking. Unfortunately during the slow turn the model stalled, dropped a wing and dived into the long grass.

What had happened was that the 40% limit on the downward aileron deflection had been removed and the excessive downward deflection on the inside wing during the turn had created so much drag that the wing had stalled.

Thinking back to my first slope session a couple of weeks ago when a crashed another plane the symptoms were very very similar.

So the lessons learned :

1) aileron differential is very important

2) you can be too clever when programming transmitters sometimes

I will update the 6 channel Taranis eepe this week

V2 FRSky Taranis 6 Channel Configuration eepe with trainer, flaps, crow spoilers, reflex and instructions

Update – see this important article on Adverse Yaw. I hope to add this feature soon.

markedup v2

Here is version 2 of my 6 Taranis Channel setup for planes such as the Bixler. New additions include volume control, black box recording ( telemetry, switches and sticks ) and a timer.

This file is strictly for OpenTX 2.x and will not work for OpenTX 1.x

Files => eepe file and instructions

I have had my FRSky Taranis for a few months now and am loving the software side of it. My son has a 6 servo bixler and I have set up a configuration on the Taranis to support trainer ( buddy ), flaps, Crow Spoilers and Reflex – mostly just to experiment. You can download the eepe file, the sounds and the instruction pdf below. I will probably blog various sections too.  The latest version ( what ever that currently is ) can be found here => http://www.seancull.co.uk/taranis  The key features I wanted were :

  • A Motor Safety Switch
  • A trainer function so that I could connect the Taranis to another buddy box via a buddy / trainer lead. I wanted to have two modes – a partial mode where I retained throttle control and a full mode where I could pass across all 4 primary functions.
  • High, Medium and Low Rates with Expo
  • Rudder and Aileron mixing to smooth out turns
  • Flaps with elevator compensation
  • Spoilers / Air Brakes / Opposing Ailerons and Flaps or Crow as the glider folks call it. Also requiring elevator compensation
  • Reflex – positioning the flaps in a slightly up position – supposedly makes for more speed – I just like experimenting
  • A basic “panic mode” that removes all mixes
  • Dangerous functions such as flaps or spoilers should have repeating warnings to remind you they are active.
  • Occasional functions should have a once off voice alert to remind you what they are – e.g. the partial trainer mode selection.
  • Timer
  • Volume Control

If you are specifically after an F3 glider set up see Mike Shellims Configuration

Taranis / OpenTx 2.x – the difference between raw stick values and Inputs for rates

A quick note on something I have just realised.

When you look at the mixes screen in OpenTX 2.0 there are now options in the mixes to use Ail or [I4] Ail ( the number may vary )

These are VERY different.

[I4]Ail is the aileron stick value after the rate lines have been applied.

Ail is the raw stick value. If you use Ail then your Rates Switch will not make any difference – you will always be on Full Rates. So check these settings carefully when you upgrade or if you upload eepe files from other people.

There is a useful forum post here

raw