Mixes
 

What are some of the most common mixes for pattern pilots? I think it would be pretty sweet to generate a list for the newer guys to see what the more experienced guys are doing.

Obviously the most important thing to do is properly trim out the plane, THEN make necessary adjustments. But, I imagine some things are inevitable even with a properly trimmed plane. I've flown all summer without using mixes, have been working on trimming my plane, and think I am ready to start using the tools of my radio, at least in competition. Also I think this is very appropriate and specific to pattern planes as they are designed to fly well and have less couplings than other aricraft.

Thanks for the input!

RE: Mixes
 

Welp...first of all, if you have a decent design, you're usually able to get it to darned near zero mix, depending on a number of factors, such as whether or not you have snaps and spins, how "hot" you like your set up, how much expo you can handle, etc.

Trying to answer this question is like painting with a VERY broad brush, but there are some similarites in most designs with most set ups. I may get poo-pooed for posting this, but what the heck.

First of all most people run thier CG too far back and don't have enough positive incidence. This was the trend a few years back as we transitioned from the ballistic style of flying to the more slowly constant speed larger planes. As with everything when you make a large change in total overall concept, there is a steep learning curve. A leading pilot/designer/builder made common a set up that used darned near zero on the wing, negative on the stab and the CG pretty far back. it worked, but with strange effects. Some of the problems associated with this carried over into modern day, but due to the work and guys like Bryan Hebert and myself to a much smaller extent, we're running somewhere around 1/2 degree positive on the wing, stab at zero or very close, and a much more forward CG.

This does a number of things, most good, but everything has a trade off. First it darned near nullifies mix, all lines track better, the plane is much more stable, and has a very locked in feel around neutral. This is a good thing! but we deal in balance, so here is the down side.

You usually end up running a good deal more throw for snaps and spins, but they do land much cleaner with a LOT less displacement. And since the planes are flying slower to begin with, this "problem" is compounded by a more forward CG. So if you're able to handle a hotter set up, with more expo, there is no "problem" to speak of. Most guys that fly masters and FAI have become accustomed to this hotter set up because that's what it takes to get through the patterns with snaps, spins, etc. you can use a condition switch to alleviate some of his but it's troublesome and slightly more work.

Rolls require a little more rudder input at slower speeds with a more forward CG so this is something else to get used to.

But I will say that this general set up theory is the best I have ever personally used and is well worth getting used to. I now fly my whole pattern with no need for throwing any switches, and that is also a plus. The other is in severe wind. if you run a lot of expo, you much more likely to hit that banzai curve in the throw that sticks an unexpected and very high rate of throw at you making it very hard to correct smoothly in the wind. The less expo you can run, the easier it is to fly consistently in high wind. Generally speaking that is....

Now with all that being said, and understanding that you CAN get most modern planes to zero mix if it is a good design, some people are very uncomfortable with the "feel" of this set up and seem to need to work into it. This approach is debatable, some will tell you just jump in and learn NOW. Easy to say at this time of year, much more difficult in say, June :D

So...what most people do is a bit of a compromise. They use the more forward CG, but not to the fullest extent. They run higher wing incidence, but not to the fullest extent. They run higher throws, but again....not to the fullest extent. What they end up with is a fairly nuetral plane that requires very little mix for thier set up. It's not perfect but most people live with it. The more "common" mixes end up being:

1 Rudder to elevator: usually the plane being tail heavy pitches to the gear on KE. This is easily fixed for KE flight, but at hard over extremes such as a KE loop, a lot of planes need the mix removed at the ends. So they use a curve or they don't fly FAI LOL

2 Rudder to aileron mix: Less common and dpepends on design, CG, Incidences of the wing. Roll coupling. You can get this out usually by adjusting your incidence, CG and retrimming from scratch. This may affect #1 though....since this is normally offset by dihedral, a good design needs little to none of this.\

3 Aileron differential. This will depend mostly on the design of the plane and the incidence. In order to get the plane to roll axially (and not wallow), it is sometimes necessary to move one aileron more than the other. This is fairly common but not always. A good design and careful attention to linkage gemoetry and symmetry and usually this is minimal or non existant with modern planes.

4. Throttle to elevator. A lot of people experience a pull to the canopy on the downlines. usually 1-2% down E at idle takes care of this, but be warned: this is one you need to fix without mix. because it will bite you all over the place in the upper classes especially. You hit idle, inverted, the plane doesn't need as much down to hold level...speed up and it changes...go into a 45 and it changes again...get the picture? It ain't good but you can get away with a very small amount with enough practice.

5. Throttle to rudder: a plane that has a wider speed envelope and a rearward CG will experience this fairly dramatically. You trim the rudder for level cruise speed, but a downline the plane yaws right. So people mix in L rudder to idle. Again not a good deal.

6. Down elevator to left rudder: This is a rare mix but depending on the design, prop, engine, set up and everything else, the plane might yaw hard in a push such as the double immelman. Some people mix in rudder to the elevator to "fix" this. Depending on the plane and set up, I have seen it work flawlessly, and I have seen it spell unpredictable disaster. Proceed with caution.

Now here's the rub: Most very good designs end up with a very minimal amount of 1-2, and occasionally 3-4. Some have mixes numbering in the teens and more...and some are unmixable/untrimmable due to inherent flaws in the design. if you're not flying the FAI finals sequence, you can get away with a lot more mix and a much less "perfect" airplane, but if you ever intend to fly on that level, you're not doing yourself any favors. 5-6 are usually sign that you have pretty severe problems elsewhere, and might be due to set up but more likely design.

So if I have any "advice" it would be the same as you're likely to hear from many others.

1. Take the time to properly trim the CG, incidences and engine thrust. if you do this your mixes will be minimal to non existant.
2. If you still have a few strange characteristics, go back and repeat step one. :D
3. Repeat step one again for good measure.
4. Add mix as necessary...but it needs to be VERY minumal and you need to fly your plane through everything imaginable to look for unintended consequences.
5. If after doing this you find the plane just "feels" too nose heavy or hot on the sticks, back off and compromise SOME for the time being until you get used to it...then at a slightly later date, ease back into it and "retrain" yourself.

Now anyone who wants to paint a broad brush and say "if a plane isn't perfect you gave up" or "there's no such thing as perfect", I'll go ahead and concede that you're both right. But I believe the best set up is the one you can fly and make it look good doing it....and the more "true" your plane flies, the easier that becomes. Start down the road to perfection and never give up and never get lazy or complacent. You don't HAVE to do it all in one swift stroke, but it's easier on you if you take as many steps on that journey as you're capable of. if some of this sounds contradictory, it's because it is. We're dealing with balance, and a changing balance at that. As your skill improves so will your "feel". What feels great to you today may not feel so great after a couple hundred flights. Do what is necessary to fly that elusive perfect sequence. And remember, the fun and reward is in the journey, the destination is it's own reward.

-Mike

RE: Mixes
 

Joe,
Even a "perfect" design may require some rudder - elevator mixes for knife-edge. This is because of the spiral slipstream from the prop. Each stab. half sees this and it makes it seem like they have different incidence settings when in fact they don't. If everything else is correct trim-wise you should end up with an equal amount of mix for both rudder directions. The plane will go to the gear in left rudder knife-edge and to the canopy in right rudder knife-edge so you will need to set up a small amount of left rudder -> up elevator and right rudder -> down elevator. You SHOULDN'T need throttle -> rudder mixes. Sometimes they're unavoidable but try to do everything possible (mechanically) to avoid using mixes.

John Pavlick
Team Black Magic, Tech-Aero Designs

RE: Mixes
 

Wow I guess Mike was typing while I was. Yeah - what he said! LOL I think you get the picture - try to avoid mixes especially "silly" ones like left rudder to down elevator for outside corners. At that point you just need to fly the plane. Really. :) Just try to get the plane to not fight you in the more common positions: vertical up and down lines, knife edge both directions and of course straight and level flight (upright AND inverted). Remember, you will need to hold some down elevator when inverted. That's OK. Just make sure the plane locks in and doesn't feel mushy. After that just practice a lot with your primary airplane. I'm going to try to do that this season (as opposed to what I've been doing over the last few years). Hopefully this will pay off.

John Pavlick
Team Black Magic, Tech-Aero Designs

RE: Mixes
 

Mike or John

I have a Zen 30. Good flyer until time to land. It has to come in pretty fast. Trying to come in slow and it is a tip stall disaster. I watched the pattern planes in Ohio and they come in like a feather. I'm building my second one as tip stall landings has finally taking it's toll. I would like to practice, practice, practice with this plane and then go on to my Osmose 70. Is it OK to put ailerons in a little up position on a switch for some washout and get the nose up and speed down a little? Would this also help with the tip stalling?

RE: Mixes
 

Your problem is more likely wing loading, compounded by a smaller plane with short snappy wings by nature.

Sure give it a try, and try it up high and slow first. Your descent rate will become steeper with spoilerons and flaperons. it's better to keep some speed on it until you know where that point is where it stalls or tip stalls. Then back down the speed slowly. Your descent rate will inscrease as speed bleeds off. So don't get it dropping like a rock and flop it onto the runway. try flaperons as well, they are similar yet different. They will require you to keep the plane a bit more level with a little more speed. but it will come on down for sure....preferrably under control LOL

The first thing to do is try and get as much weight off the plane as possible. THEN go from there.

-Mike

RE: Mixes
 

What you are talking about is a spoileron as Mike stated, if you have them drop instead of going up they would be flaperons. Either way, a flap or spioler is going to increase the rate at which the model descends. You might be better off using a flaperon instead of a spoileron if stalling is your issue.

Washout is bit of twist in the wing where the trailing edge of the tip is higher than the trailing edge of the root.

RE: Mixes
 

OK Mike. See what I can do and Thanks for your answer.

RE: Mixes
 

One more thing and this can be common in ARF designs...check the wings and stabs for even the most subtle warps. It doesn't take much to ruin your day. then you'll be chasing your tail.

I probably should have mentioned that first, but.....

Good luck, let us know how it goes!

-Mike

RE: Mixes
 

Mike
Don't worry. When petec gets a hold of me I'm sure to receive some solid direction.

RE: Mixes
 

Hi Garcfield,

I think the basic goal is to have a plane that does not roll, or does not pitch, with application of rudder. How aggressively you get this solution figured out depends on your skill level and sequence requirements. Flying wings-level is fundamental #1. If you are getting to this point, and now attempting wind correction and thus using the rudder; rudder-bad-effects can start to change your lines and wings-level work.

1. When you use rudder - you are inducing pitch and roll on most planes until you figure out how to get rid of it either with airframe adjustments or mixing.

Why do you need to get rid of it? Because bad tendancies will fustrate your efforts to fly better and make better use of your practice time. Most of all pattern flying does not need high inputs of rudder so for normal flight or knife-edge, you may be in low mix numbers. If you are flying rolling circles or F09 with the centered 2-roll loop, you will be frustrated greatly if rudder input is changing the pitch and roll or the airplane. In this instance, mix and airframe adjustments has everything to do with helping us "human" pilots make a clean precision maneuver. If bad things happen at higher rudder inputs, use the "curve" or "point" mixes rather than linear.
Thanks,
Jim

RE: Mixes
 

John,

I hate to disagree with you, but you almost always need some sort of throttle rudder mix to compensate for torque. If you put right thrust in you will need some on the downlines. If you go back and read some of Chip's trimming method's he can explain it a lot better than I can. Some people mix rudder to idle. I personally mix a little rudder with the addition of power, simply because I like my rudder neutral at idle. I had a VERY long discussion with Chip in Iraq over this very point (was amazing to have a guy who has seen and done as much as Chip being able to answer any question I had for 2 months). I actually had read his notes previously and had taken his advice, and loved how the plane felt. One problem is with todays designs running much larger props, you can't put enough right thrust in to totally fix the problems. Dave Guerin suggested when I talked to him a couple of years ago in Phoenix on some electrics you would need 5+ degrees of right thrust to totally compensate for the torque factor. This would cause the plane to yaw horrible when flying straight and level, so the compromise is mixing some rudder to throttle.

Arch

Here is the link to Chip's comments. This is a MUCH shorter version, but you get the idea.

http://www.rcaerobats.net/trim_chart.htm

RE: Mixes
 

Re: Throttle to rudder:

Ok I'll submit. LOL

With one more thought: The more forward you run your CG the less this effect is noticable, of course depending on the design and prop size etc. In all conditions where the rudder is involved you're dealing with the spiral slipstream. That is screwey by nature. This is one reason if you fly electric you'll REALLY notice the torque/yaw effect if you get rearward on the CG. And even forward it's there.

But to fully cover this it would take a novel.....because for everything there is an exception and everything affects everything else. if we take this to the enth degree the guys that need this info will be extremely confoozed by all of the contradictions and generalities. Which is why I just remembered my rule about posting on the subject of aerodynamics....ask 100 people and you'll get 100 different answers. And more than one are "right". It's all in the approach....airframe trim vs mix. A comfortable set up usually needs some of both, usually a lot of one or another.

I hate mix but I grow tired of trimming to get rid of one last 1% of something so yes, I will compromise. a 5mph wind will do more to upset a plane than that 1%. At some point you just have to know when enough is good enough and get up on the sticks and fly. That is usually where my theory takes a left turn from other's.

Bleah this could get really deep. LOL

-Mike

RE: Mixes
 

Hi Mike,
I've been flying for a good few years, and have heard most theories.
For CG I always have, probably incorrectly,used the feel I get as my guide.
Things like nose drop into rolls ,hold for spins ,stability etc.
It always comes out at between 30% and 35% of MAC, typically 32 TO 33.

What do you and B.Hebert regard as 'good' forward for CG.

Brian

RE: Mixes
 

Fairly certain Bryan's CG's are usually up around ~25-30% MAC

RE: Mixes
 

Bryan would tell you further forward than me...but I run around at 28-30% MAC or thereabouts. I like the way the plane feels there. I have tried it between 25-28%, and although it was VERY locked in and had almost zero mixing issues whatsoever, it just felt sluggish to me without a LOT more control throw. Digging the nose a little harder in rolls was the one thing that I never really got used to. We're only talking maybe a small "bump", but it's so much easier with the CG back just a touch from there. Not WAY back, and still a lot further forward tham most, just not as far as some others run thiers.

The other thing is the spin breaks. The further forward your CG, the harder it drops into a spin. One slight problem: the rules say you need to have a simultaneous rotation of the wings with the break. If your plane is set up darned near perfectly trimmed, that ain't gonna happen. It's going to drop like a rock...straight down. I used to try and compensate for this by leading with a little more rudder, but...that can bite you hard in certain conditions. Only speaking for my own plane, somewhere around 30% seems to be the sweet spot where I have darned near nothing in the way of mix, but the plane doesn't dig and need quite so much throw to do the snaps and spins on one throw condition.

heck I could be and probably am "wrong" to a lot of folks, I just know what I like to feel, and it's not always the same thing as others like all the time. And with this I also have to say that a few months from now my answer may be different still LOL

truth is I haven't been flying masters and/or FAI for years and years, but I have been designing for a long time now. I can tell you one thing that I think is probably more true than not: An intermediate level pilot is NOT doing himself any favors by using an FAI set up. A top level set up is hot by nature and not quite as easy for the beginner/intermediate to do the necessary line/radius/roll work. By the time you get to FAI it's pretty much second nature. But if you're still working on it all, you need to be very critical of what YOU need the plane to do. my answer in October is not the same as my answer in June. in June, don't make any drastic changes, because it's probaly too late unless you're at the bottom of the pack and have very little to "lose". This time of year? Set up hotter and above what you need and fly it that way. Start tuning it in to your skills at the first of the year, then go after that last couple of polish points.

it's a learning curve and the best use of practice time is by pushing yourself to your limits. Otherwise just sport fly and forget all this competition stuff [8D] LOL

-Mike

RE: Mixes
 

Brian,

An observation for what its worth.

The TS Composites Oxalys that I flew at this year's Triple Crown had the CG fairly far forward - at around 28% MAC. It was good to fly, but there were some downsides. In PO9, it required a fair amount of correction to fly the 3 Horizontal Rolls (Manoeuvre No 3) and the 4/8 Roll in the Top Hat (Manoeuvre No 5) was also difficult to fly. It was also reluctant to stall cleanly into the 2-Turn Spin (Manoeuvre No 14).

When I built my new TS Oxalys for the 2009 season, I decided to experiment with the CG slightly further back - at around 32% MAC. All of the above manoeuvres became easier to fly. At 32% MAC, I don't believe that the CG is too far back as the model still tucks slightly to the canopy on Right Rudder Knife Edge - requiring a small amount of R to DE mix to rectify.

I have heard it said that you can't have the CG too far forward on a pattern model. However given the choice, I would much rather fly the TS Oxalys at 32% MAC than at 28% MAC.

Other airframes may well be different.

Regards

Bob

RE: Mixes
 

Hi Mike,
That's interesting, 25% seems very forward.
However I must say I do not like the wing sections that have very rearward high points.
I now fly electric so moving CG significantly is not an issue, so I will try some this winter.
Thank you.

Brian

RE: Mixes
 

I personally am not a fan of throttle to rudder mixing, far to complicated to properly setup to use in all speed/throttle combination's IMO. Even with electric I don't think its required, and proper trimming/thrust adjustment will get you there. That includes any addition of left rudder at low throttle, never felt or saw the need for it.

On my Integrals I only run two mixes, rudder to aileron which is a flaw in amount of dihedral in the wings, and couple % of low throttle to down elevator for downlines. I run no other mixes on that model.

I think one thing overlooked (or maybe I just missed it) in all this is downthrust. No matter what your wing incidence and CG is, if your downthrust is not correct the 1/2 positive in the wings/forward CG will likely result in upline issues. 1/2 deg down or less seems to work well.

RE: Mixes
 

Probably your R/T must be more than 3 degrees.

VB

RE: Mixes
 

I don't know what stock is on the Integral, but its just ever so slightly less than what is molded into the fuse.

The folding props have a big influence on that though.

RE: Mixes
 

Arch,
Yeah I hear ya. Just transitioning from a re-pitched 3-blade to an APC 18.1x10 made me notice just how much of an affect different props can have on trim and outside corners. I'm sure with electrics there's even more to deal with (bigger props). Also, I fly with a somewhat more "forward" C.G. so that makes things a bit less critical. I guess I don't notice it as much as some people so I don't use throttle - rudder mixes. Also, I'm not flying Masters yet. Maybe that will make me change my mind.
The only mix I have on my V2.2 is a small amount of rudder -> elevator to trim the knife edge. The plane is fine on uplines and downlines so no throttle -> elevator mix required. I dialed this in with wing incidence and C.G. (which also minimized the pitch coupling in knife-edge). Until I get really good at trimming I just try to watch the plane very carefully and give it what it needs. As long as I get plenty of practice this seems to work. :)

John Pavlick
Team Black Magic, Tech-Aero Designs

RE: Mixes
 

Hi Bob,
I've only ever flown where it feels right. I have of course,with new models,tried options but I always end up at 32/33%.
Its the first thing I adjust, then work on the rest.
Maybe its time to rethink, but I think speed/style may have a role in this.
I may be wrong,as I have not yet tried, but I feel a forward CG will require more speed,
Also positive wing versus 0-0 debate is involved.
A few years back it was different as the entire schedule was from upright with only a little inverted work.
Now if any more inverted is added in we will have to put wheels on top as well. LOL
Take care Bob.

Brian

RE: Mixes
 

Brian,

I used to the think the same way....years ago however I went to the .5 on the wing and 0 on the stab and liked that, but also flew with my CG back some....After flying this year with it forward I really like it. Mike basically moved the CG when I had been gone for a few months on my black magic, so I had kind of forgotten how it flew before and bam....it flew significantly better, all of the mixes were GONE, and the one that really surprised me was the snap was better with the CG forward...I'm now convinced...

Arch

RE: Mixes
 

Increasing the incidence allows to get the CG back without affecting tracking. I can not explain why. Rolls are a lot easier in this condition and tracking and other characteristics remain equal. Try around 1 degree or more.

VB