Throttle mixing with elevons?

[JustinMader]

Hey all,

I've been watching a ton of videos about throttle mixing, but almost all are for a normal elevator. The one elevon throttle mix vid I found used some proprietary radio system setting (Spektrum I think), but none for Otx/Etx.

On my Mini Q I'm looking to reduce the amount of reflex as the throttle goes up. In theory this would maintain level flight throughout the speed range. My thoughts are either to change the midpoint or add some down pitch to the throttle, but I'm having a hard time figuring out how to only affect pitch. Since both pitch and roll are mixed together in the radio for elevons, I'm kinda stuck.

I have a dual rate switch, so I can easily reduce the amount of overall throws at high speed, just need to get that midpoint down. I'm using a Radiomaster Boxer with Edgetx, but it seems to work just like Opentx (which I have on an old Qx7). Any advice (or link to a good tutorial) would be greatly appreciated. Many thanks!

Cheers,
Justin

 

[Wayne]

Hey Justin,

I'll always suggest going after the aerodynamic fix first. With this Mini Q this is a bit of a fine edge, but you may still have some aero tuning to cure this.

Basically 2 things will cause pitch up with throttle:
1- CG
2- Thrust Angle

The Mini Q has a very narrow CG range, so I am going to pretend you have that one pretty well dialed in. But a nose heavy plane will pitch up as speed increases. So this leaves us with the motor thrust angle. Most planes will need to down thrust to fight this pitch up under throttle. Adding one washer to the top motor mount screw is a good starting point. Test fly and adjust as needed.

Chasing this sort of setting with the transmitter mixing can be tricky. While it might be fine for a big slow trainer, it might be horrible for something fast like a Mini Q. It will typically involve some delays to make it feel sort of OK. Honestly, this is best done with a flight stabilizer that can read the pitch change and correctly adjust with the right amount of pitch correction.

Always go for the aerodynamic corrections first. Mixing or stabilizers last.

Hope this helps.

 

[JustinMader]

Thanks Wayne!

Can't fit a FC in here, otherwise this wouldn't be a problem.
Motors are already shimmed down so they point at the the nose, hesitant to go further down as this is usually how I set up my twins.
Will try to move CG backwards to see what happens. I know I'm a little on the nose-heavy side as I wanted to play it safe to get it flying. Currently at 21-21.5mm from LE. Will shift backwards a couple mm at a time, without going past 25mm.

I like to keep things simple, so the radio mixing isn't very appealing, but would do in a pinch. Many thanks for the advice!

 

[Wayne]

On this plane I'd only move a MM per flight to test the CG. The range of CG is VERY tiny on these planes. Many powered pilots prefer a nose heavy setup, and most glider pilots like a tail heavy setup. I'm a glider guy at heart, and I can tell you a lot of powered pilots never see the full potential of an airframe as they keep them so noseheavy. (A motor on a plane can really mask the nose heavy condition.)

 

[JustinMader]

On this plane I'd only move a MM per flight to test the CG. The range of CG is VERY tiny on these planes. Many powered pilots prefer a nose heavy setup, and most glider pilots like a tail heavy setup. I'm a glider guy at heart, and I can tell you a lot of powered pilots never see the full potential of an airframe as they keep them so noseheavy. (A motor on a plane can really mask the nose heavy condition.)

Follow up thought: if the motors are pointed too far downwards, would that also cause pitch up at high speed?

I know how pitchy and squirrelly a tail-heavy plane will fly. The Mini Q doesn't feel that way at all, so I may be too far nose heavy.

 

[Miami Mike]

Justin, you should definitely first go after the aerodynamic fix like Wayne says, but if all else fails and you want to do what you asked for, it's actually pretty simple with OpenTX or EdgeTX.

First create a curve, which will start out looking like one of the curves in the attached images. It might be the one that slopes up or the one that slopes down, depending upon your model setup, but in either case the X = -100 point will be at Y = 0 and the X = +100 point will determine the elevon position you want at full throttle. Your curve can have as many points as you like up to 17 and you can adjust it as you like until you get it just right.

Second, whatever mix lines you have for your two elevon mix channels, you only need to add a line at the end of each to add in the curve.

CH1:Throt     Thr Weight(+100%)

CH3:LElevn     I3:Ail Weight(-50%)
            += I4:Ele Weight(+50%)
            += Thr Weight(+100%) Curve(CV1:mot) [motor] <- added line for throttle mixing

CH4:RElevn     I3:Ail Weight(+50%)
            += I4:Ele Weight(+50%)
            += Thr Weight(+100%) Curve(CV1:mot) [motor] <- added line for throttle mixing

 

[Wayne]

If the motors have too much down thrust, then the plane will pull down at high power settings. This is pretty darn rare.

 

[JustinMader]

Quick follow up to close this out: moved the CG to 23mm and there was no pitch change throughout the throttle range. Only had time to make a few quick passes, but seems like that was the answer. Thanks everyone for the advice.

 

[Wayne]

Glad you got it sorted out!