Mixing question

[thurmma]

Here we go. I have a 3DHS 330LX that is balance neutral on the center of the wing tube. Any time rudder is applied more than a few degrees, it starts tucking to the gear. The more rudder you add the harder it tucks to the gear. In knife edge flight from both directions, same thing. I have tried mixing it out and as long as you are not inverted and try to do a rudder correction, it all works out great. If you are inverted and apply rudder for course correction you are having to push up elevator to maintain level flight, more than normal.

I am at a loss on how to make this plane fly precision easier. I can fly it without the mixes just fine but, would like to be able to do a course correction without having to throw in up/down elevator to keep it in level flight.

My 42% Pilot Edge couples but, nowhere near as bad as this plane.

 

[Pistolera]

Mark....on a no-wind day, and trimmed for hands-off straight and level upright flight, what does it do on an inverted 45 deg upline, after releasing the sticks....nose creeps to the sky or ground?

Ideally you want it to creep toward the ground (slight nose heavy), or at most stay on track (neutral). That will give you a good CG to start looking at mixes, etc.

My Raven will just creep toward the ground. When inverted level, it needs just a touch of down elev to maintain that. Even so i still have some rudder to elev mixes as well as rudder to aileron, to remove the tucking tendancies.

 

[thurmma]

The plane will stay on the 45 until I pull it away. I have let it fly at that attitude for a long time to see if things would change after a bit but, it just stays there This plane has coupling issues bad. A friend has the same plane in a different scheme and the same thing with his. Almost identical setups also.

 

[Pistolera]

My friend Chris Thorpe has been flying his 3DHS 330LX in IMAC advanced and now unlimited for 3-4years. DA200 on cans.....not sure where his CG is or tracking, but I'm guessing it's set up a touch nose heavy.

As the plane CG goes toward nose heavy, it takes a bit more up elev trim to maintain level flight, which of course will reduce the amount of tuck with rudder. Still....mixing is usually required to some degree even then.

On my Raven I have;
Rud to Elev.....L Rudder 8% up elev, R Rudder 6.5% up elev
Rud to Ail........L&R rudder... 9% Aileron in direction opposite rudder (to keep it from rolling towards the rudder)
Thro to Elev.....1% down elev at idle (keeps vertical track down perfect)
Thro to Rud......1% R at full throttle (helps tracking on up lines)

All of these mixes are, of course linear.

 

[thurmma]

I am going to add a little bit of weight and tip it a touch nose heavy to see how it does. Thanks Earle for the input. It is REALLY appreciated Good luck this season!

 

[Bunky.F.Knuckle]

Instead of adding weight, move your heaviest item forward. Moving your engine fwd 1/8" will change your cg, but not drastically.

I dont like adding dead weight to an airplane.

 

[Pistolera]

What Bunky says.....try some washers between your engine and firewall, if you can't move batts etc.

Other than increasing the spinner gap a tad, it's the easiest way to get CG forward.

 

[yakken]

You dont have an engine thrust problem do you??

 

[Bartman]

what are the aerodynamic forces that are causing the nose to tuck in response to rudder? or is it gyroscopic precession?

@thurmma does it happen regardless of if the rudder input is quick or slow?

just trying to understand what is happening to make the nose tuck with rudder input

 

[TazmanianDevil]

Coupling can be a really pain in the ars sometimes.
The mix for the coupling should be checked when you are in a straight and level flight and then using your rudder to see how much it pull to the wheels or canopy, and then add the percentage to the ele mix.
The same method for the ail...

The rudder shouldn't be more then holding your plane on a knife on 3/4 throttle that being said, if you're having a big amount of travel to your rudder it will effect your ele and ail travel, their travel is derivative from the rudder travel so the more percentage you have in your mix and the more travel you have on your rudder will eventually cause the mix to be very sensitive.

Although I need more, I don't use more then 5%.

3D I don't use coupling at all.