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Mixes used to fly IMAC

Old 06-22-2003, 06:45 PM
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Geistware
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Default Mixes used to fly IMAC

I was wondering what mixes are used to fly IMAC sequences. I turn rudder-elevator coupling on and off for knife edge flight and I use the trainer switch for snaps. What others are used?
Old 06-23-2003, 01:07 AM
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Tim_Indy
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Default Mixes used to fly IMAC

My goal is to use the mixes to make the plane honest. When I command YAW (rudder) I don't want the plane to add PITCH or add ROLL, all I want is YAW. In your example, your plane probably pitches to the belly when you command YAW (rudder) so you've set up a rudder-elevator mix to counteract that. I understand that it doesn't just pitch to the belly only when I'm in knife edge, rather it pitches to the belly WHENEVER I ask for yaw. I can't think of a situation where I'd command for YAW and would desire to get YAW plus PITCH (or plus ROLL). An example would be when I'm coming in for a landing in a crosswind. When I correct for the crosswind with rudder, I don't want the nose to also pitch down. Since all I want is YAW when I move the rudder, I don't need to set up the mix so as to be able to turn it off. The same would apply if my plane rolled with rudder application, I'd use a full time mix to counteract.

I don't use a snap switch because my sequence has both positive and negative snaps.

My Great Planes Extra has zero roll coupling and small pitch coupling that remains consistent throughout the rudder travel. I've had a Cap that pitched differently depending on how far the rudder moved. A mix that worked at a low rate setting didn't work at high rates, so the best solution is a multipoint mix that had different values depending on stick position. If the transmitter doesn't allow for multi point mixing, then separate mix for low rate and high rate rudder is necessary.

Why different rates for rudder? My low rate rudder allows knife edge flight at 1/2 throttle, and half rudder stick throw. It's great tor 4 and 8 point rolls, knife edge flight, super slow rolls, and 3 or 4 turn rolling circles, stall turns, snap rolls, tail spins, torque rolls, and general flying. High rate rudder is called for for knife edge loops and knife edge Cuban eights, 1 or 2 turn rolling circles, high alpha knife edge flight, etc.

Again, I want the plane to be transparent. I want it to be obedient without adding anything on its own. This way, I can fly the MANUEVER, not fly the PLANE
Old 06-23-2003, 02:25 AM
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Flyfalcons
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Default Mixes used to fly IMAC

I use a rudder-elevator mix active full time. I also have a point mix so at the bottom 1/4 throttle the elevator goes down 1%. This allows the vertical down lines to be super straight. Not all planes need these mixes though.
Old 06-24-2003, 11:08 AM
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Sprink
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Default Mixes used to fly IMAC

Ideally you set up the plane by varying incidences etc so that mixes are not needed. But that usually means building loads versions of the same planes so you can make adjustments.

As with Tim_Indy and Flyfalcons I have my rudder mix on permanently. The coupling may be only visible when doing knife edge, but it is there whenever using the rudder.

Also use trottle to elevator if needed for up and down lines, but I turn this off for take off and landing.
Old 06-24-2003, 11:47 AM
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Sprink
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Default Mixes used to fly IMAC

Oh and use aileron differential to eliminate any yaw coupling from the ailerons.
Old 06-24-2003, 01:56 PM
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quist
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Default Mixes used to fly IMAC

I have decided to fly my downlines. I had a downline mix in my plane and I did not like it. I would have to counter the mix on 45 downlines and also on landing.

Part of the problem is that I fly a heli version WC2 and there is no wratched on the throttle so I can just go up one click of throttle
Old 06-24-2003, 07:35 PM
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Geistware
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Default Mixes used to fly IMAC

I find that during stall turns, my mix causes my plane to respond properly with the mix on. that is why I asked. I guess it is not set up properly!
Old 06-25-2003, 12:40 AM
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quist
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Default Mixes used to fly IMAC

during the stalled condition the mix shouldn't have much effect unless you have lots of mix.
Old 06-25-2003, 01:51 AM
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jelaird
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Default Mixes used to fly IMAC

What do you do when your rud-elev mix gets you perfect knife-edge flight but small deflections during level flight cause ballooning or whacky looking rolls when rudder is used?
I have another thread just started on this...
Other thread]
Old 06-25-2003, 11:38 AM
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rcplanefan
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Default Mixes used to fly IMAC

Here is a link to an article written by Gene Payson of Troy Built Models. Pretty well written bit and provides a look into what some of the "big guys" are doing.

http://www.troybuiltmodels.com/radiosetup.html

Ken
Old 06-30-2003, 10:49 AM
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Kris^
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Default KISS

I set my planes up for minimal pitch coupling with rudder-elevator on LOW rates in KE flight, then verify that during upright and inverted fight rudder-pitch coupling is lessened as much as possible. There will always be variances, depending on actual angle of flight, but for the most part, settling out a smooth, straight Knife-edge will carry over into less coupling during all other phases of flight. . I do this for LOW rates only, because when you get a fuselage really cranked over into the slipstream all sorts of strange things can happen. . IMHO it's not worth it to try to chase the coupling past where you will be doing precision sequence flying.

Roll coupling is pretty much a non-issue in most planes I've flown, and once you learn the planes characteristics its easy to manually compensate for roll-out/in during KE (where it usually occurs the worst). I've never felt it necessary to mix it out.

Off Throttle Downlines. . . . .most planes will pitch up, and require down elevator coupled to the low throttle setting. I have found this to be most prevalent on nose-heavy planes. I try to set the plane up so that it is hands-off pitch stable in both upright and inverted flight, by adding tail weight till the plane "balances" on CG for either direction and requires no trim changes/stick usage between upright and inverted. Then, I do not need a 'trim" from elevator to keep the plane straight in level flight, which translates to no trim in downlines and zero pitching out. One click of elevator trim is all it takes to make a plane pitch on downlines. I've found that by setting CG to make the plane go straight in level and straight down flight, 45's and uplines follow suit, with perhaps a slight, but easily manageable tendency to nose up on upline 45's, and good straight 45 degree downlines. About 90% of your straight lines are level, upline or downline, and 45's a lot less, so I consider it a good tradeoff. It also reduces necessary elevator and rudder inputs for the same amount of response, making the plane more sensitive to inputs, but allowing you to dial down the rates a bit. This causes less "binding" of the surfaces, which disrupts the flow of air less, and (in theory) makes the plane fly smoother.

I've added as much as 12 ounces to the tail of a plane to achieve this "balance", then shifted components to get the CG shifted and removed the lead weights. One advantage is that the plane becomes very 3D friendly as well, but not so much that you are pushing down elevator on landings. An added advantage is that stalls/spins require a lot less up elevator to hold the nose up at low speeds, and the plane tends to stall a bit harder and sharper at the break because it goes from flying to stalled/falling with a bit more authority.

These are just my personal observations. . trial and error will get you the best results for YOUR flying style.
Old 07-01-2003, 01:18 AM
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Geistware
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Default Mixes used to fly IMAC

I have to agree with your assessment of an AFT CG. I try to get my CG as far AFT as possible and still be stable. I don't do 3D but I like how crisp a plane flies when the CG is rearward.
Old 07-01-2003, 01:55 AM
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Default Mixes used to fly IMAC

The plane will stall better with a forward CG.

Craig.
Old 07-01-2003, 11:07 PM
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Geistware
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Default Mixes used to fly IMAC

Craig, I have heard this several times on the forum and have learned something new.

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