I have a Futaba 9CAP super and there are some pattern guys at my field who are mixing for a straight knife edge. I understand that this corrects tendancies in the model when you do this but would I want to mix the rudder with elevator and possibly aileron for a straight knife edge if I do 3D? It seems that I would want all my surfaces totally independant of one another so if i am in a hover or something and I need a little rudde I dont get elevator and aileron also. Am I right or should I do a mix because it would be nice to have a knife edge that doesn't pull to the wheels (on my plane). I just dont want to do it if it will effect 3d'ing. Is it possible to put the mix on a switch so i can turn the mix on when i knife edge and turn it off otherwise?

Yep, that's how I do it. Just assign a mix to a switch that's convenient for KE flight and turn it off when you don't need it.
Even if you plan to leave a mix on full time it's a good idea to first assign it to a switch so you can turn it off if you need to.

The mix should be active at all times. The tendency to i.e. pull to the belly when rudder is applied, is not only present during knife-edge. But also in hover and all other maneuvers.

Yes and that was my main question. But say that you were good and stable on your lateral axis (elevator) in a hover but need a correction on your vertical axis(yaw/rudder) and when you add this correction wouldn't it throw you off because your elevators are moving when you didn't need them to? I do know that mixing corrects unwanted tendancies to pull... That's why I want to make a mix but I don't want it to interfere with my 3D.

As just said, if your model pull to the belly when you apply rudder in knife-edge.... it will also fall to the belly while you are hovering and apply rudder.

You can make the mix so that it is only active after reaching a percentage of throw. For example: in knife edge flight ...you usually have to hold at least 50% or more rudder. You can make the mix (say 5% up elevator) so that it only occurs when the rudder is past 50%.

I consider the use of mixing in a 3D plane to be somewhat akin to those horrible "snap roll buttons" that used to litter the escutcheons of transmitters in the 1980s -- they're really not needed and more of a gimick.

If you've got coupling in knife-edge flight then learn how to trim your plane better (reflex or camber the ailerons to reduce the effect -- experiment with your CG) or, if all that fails, just get a better plane or learn to fly it on the sticks.

Sure, some birds can be a real dog in KE and require a snot-load of elevator to keep them heading straight -- but that's why 3D is so challenging and so much fun -- because it's not always easy.

I've seen too many people spend more time fiddling with mixes, rates and other stuff than actually flying. If they'd spent that time in the air practicing then they'd actually be flying better (and with less hassle) than they are now.

Mixes are a crutch -- learn to walk without them and you'll be a much better pilot.

All IMHO of course :-)

There is a new thing out there... it's called evolution

Mixes are for reducing workload, and making your flying even better, maneuvers more precise. Of course, if you have no intentions doing so - by all means leave the mixes off...

...like driving a car with a steering that needs aligment, but hey.. "I can just correct it by turning the steering wheel an inch to the left - makes me a much better driver anyway"

Sorry, you hit a hobby horse of mine

Yeah I fly the sticks now and I think it's fun and I don't mind it and I agree it will make you better. Tomorrow we have an airshow that I will be flying at and I just want to be crisp is front of the crowd. Sometimes I can knife edge forever and other times it's real ugly I just have to find the sweet spot in the throttle.

Fair enough, I guess there are some who like to simply point their plane around the sky and some that want to "fly" it -- which means dealing with its imperfections and things such as turbulence.

Do you use gyros for hovering?

Of course (or at least I hope) not. However, using your rationale, why bother to learn to hover properly when you could just use some technology to make it easier?

That was my point -- if your plane pulls or pushes during KE, you really ought to either trim it out properly, get a better plane, or just practise until you can fly it on the sticks.

Some planes just have more coupling than others, based on the design. Using some mixing, you don't have to compromise your CG, wing incidence, etc, just so it flies straight in one condition (knife edge). Mixing for knife edge might be viewed as a crutch but all the IMAC pilots I know (including myself) have some mixing in our planes to help us fly better and more precise.

For 3D, I just leave my rudder-elev and rudder-aileron mixes on. If the plane has coupling, it's going to do it in all flight conditions, not just knife edge.

XJet, It sounds like your dream 3D airplane is a Cub with a big engine! I'm not sure that would make me a better pilot. Why fly a dog if you don't need to? Every good pilot I know takes the time to properly trim (this includes mixing) their planes. For wings19, if it's an aerobatic 3D plane, leave them on! The mixing is there to make the plane fly like all the controls are totally independent of each other. When you are 3D'n you want the plane to do exactly what you tell it to do and not have to compensate for any inherent coupling. Outside of pattern planes, there is very few that don't require at least some mixing.

XJet? That was your point?? If I have a car with a steering alignment problem, I drive to a garage and have them realign it. I don't just compensate, as it will wear out my tires, reduce safety etc. It certainly doesn't make me a better driving a broken steering. Quite an idiosyncratic point you make in my oppinion.

Yes some people do use gyros to hover and fly - helicopter people! I guess your point to them would be "why use gyros in helicopters, when you can just learn to hold it on heading yourself?"

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Anyway, there are actually good reasons not to "learn" to compensate for coupling errors. In the words of one of you esteemed contrymen, Peter Goldsmith (whose merrits count for alot more than yours or mine):

I suggest you read the intire document, as I am sure you will have alot to learn from it.


Edit: sorry Peter Goldsmith is Australian. But I am sure if you ask Frazer Briggs, he will tell you to set up your plane correctly and use mixes aswell.

Tor, while I can see both sides of this conflict it's your attitude that turns me off. "learn to fly on the sticks or get a better plane" That seems a little harsh. I can fly a knife edge all day long on the sticks. But I still use a mix on certain models. It makes the maneuver cleaner and more precise. Not trying to start a fight but people come hear for help not attitude.
To answer the first posters question. I have the mix on a switch. Most of the time I have it off. Certain things like a stall turn look terrible if your coupling is on. So I just turn it on for knife edge. If you are a thumb flyer put the mix on your spring loaded trainer switch. This way you can turn it on/off cleanly.

David

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daveopam, the lines you quote was written by XJet, not Tor (me). I agree with you on XJet's attitude.

I am sorry. I read through the post quickly. Opon reflection I should have sent a PM anyway.

No hard feelings,
David

I guess I'm spoilt because I fly mainly very well designed profiles -- most of which have virtually no coupling in knife-edge, which means that they're really quite easy to fly on the sticks.

I have to admit that flying a plane that kife-edges very poorly can be a handful -- but I only ever had one plane (a fatty) that flew like that and I got rid of it.

We've got a guy in our club who can fly almost anything knife-edge -- he delights onlookers by doing an entire (dead straight) KE pass along the runway with his CMP P51 Mustang. No mixing either :-)

You just don't get it. The mixing should be on at all times, because the coupling you see in knife-edge is just a symptom that... well the plane coupling issues. Coupling is not knife-edge specific, it will be present at all times. Try flat turns using rudder only and you will see that exact same coupling your model displays in knife-edge flight.

This is not about knife-edge, but correcting a bad behaviour of the model to improve every manuever where rudder is appliede. Be that pointrolls, harriers, hover or whatever.

Somehow a have a feeling you just want to stir things up. The give away is you been spoilt with great flying planes that all have virtually no coupling. Because about all planes does have coupling. Identifying it and knowing how to correct it is another thing

If we want to get into a measuring contest, I too fly only superior airframes, I fly $5000 pattern planes of the highest quality with the best equipment and compete at the masters level. ( I hate that statement, but my point is that it really doesnt make me a better pilot) I fly Composite airframes that are at the top of the line, straight true and as neutral as they come,, and they STILL need a little mixing.. For IMAC 3D I fly a 35% custom built 23 pound Extra 260 designed by Mr Von. If high quality airframes made me better, I would be the greatest pilot in the world.

Mixes are an ESSENTIAL part of a good setup once you have found a compromise on where you want the CG and have done all you can do to perfect setup mechanically. After that you are left with the inherent deficiencies of the airframe and that is where mixing comes in. There are so many mechanical mixes built into our RC planes it is ridiculous.

If you really mean what you say then take the right thrust out, set your trims at neutral on ALL controls and get after it. but dont you trim to compensate when the plane climbs rolls or dives,, you just learn to fly it like it is.... There is NO difference between this and mixing. Once you take it to that level, then you can condescend about being a purist. Until then, you are just talking smack on something you dont really understand just to try to make yourself feel better than everyone else when I am sure you are just like everyone else[8D].

SMART pilots do their homework and understand the purpose of mixing and what a truly great flying airplane is supposed to do. That is, Fly neutral. If you can get no coupling without mixes that is great. But 99% of airframes require some mixing to correct roll coupling and rudder to elevator coupling (which by the way is always occuring therefore always useful not just on knife edge). Smart pilots know when they have done all they can do mechanically and all they are left with is airframe deficiencies. Even the best airframes typically have a little coupling. In 3D typically you are flying scale aerobatic planes which REALLY have some bad coupling tendencies or airframes that are specifically designed to do certain things 3D that inherently carry bad tendencies with them.

Look, bottom line is if you do not want to fly with mixes that is fine, but trying to say that better pilots dont use mixes is not only untrue, its just a plain ignorant.

Sorry, I am off of my soapbox now.

Tor, you really dont need to defend yourself.. You are 100% right on the money. That is exactly how it works.

Well, looks like you guys have had some fun in this thread Our airshow was awsome today, HUGE turnout, the rc jets were sweet (first time seeing them). I ended up not using any mixes as I didn't have time to set em up and I locked in every single knife edge! I was flying the Matt Chapman CAP 580 and it flew like a champ today. I think for now I will leave the mixing out, maybe I'll throw a mix into the showtime once I get that going.