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Old Aug 17, 2008, 02:27 PM
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BoneDoc's 3D Clinic #8: Knife Edge Mixing

Hey Gang,

"Welcome to another 3D Clinic Session with Josh "BoneDoc" Young and my lovely wife, Inn."

This has been hotly requested, so though the video is a bit "raw", I'd thought I'd post it now, and when I have the time, refine it so that it's clearer.

Let's jump in:

KE mixing IMHO is one of the most important mixing you can do to make your aerobatic aircraft flies better and truer. In reality, it's really TWO mixes, as you need to mix out the roll coupling (rudder --> aileron) as well as pitch coupling (rudder --> elevator). Of the two, the roll coupling is the harder to fly out, and so it should be the first to be mixed out.

Some basic info on Mixing:
BEFORE YOU START, YOU NEED TO MAKE SURE THAT YOUR PLANE IS PROPERLY TRIMMED, AND THAT YOU'VE SET YOUR CG AT THE DESIRED RANGE.

Mixes are just pre-programmed actions you tell your transmitter to do when a certain stick input is entered. In this case, the stick input is the rudder (MASTER), and the computer is entered to add a certain amount of aileron / elevator (SLAVE). When you're new at this, add FIVE PERCENT at a time until you've overcompensated, then come back a couple of percent. The AJ Slick did not require much, but I had a 50cc Lanier Edge that required 20% Rudder - Aileron mix.

Mixing out the Roll Coupling
Most aircraft's roll coupling will be in the direction opposite of the rudder input. When you set the mix out on your radio, first wiggle your aileron in the opposite direction of your rudder to get the correct direction, then figure out which mix (whether positive or negative) will produce that result. Do this until you get the mix right in BOTH direction.

Mixing out Pitch Coupling
Pitch coupling is greatly influenced by your CG because your CG determines your elevator trim for a straight upright flight. In general, the more aft your CG is, the more pitch to the belly you get (because your elevator trim will be deflected downward more). The opposite is true for a forward CG. In general, majority of aircrafts will pitch to the belly, and you'll need the elevator to deflect UP with rudder input. This will usually mean that your mix will be POSITIVE in one direction, and NEGATIVE in the other direction (you'll see in the video what happened when I forgot that fact ).


Concluding words

Once you mix out your pitch and roll coupling, you'll be surprised how easy it will be not only to do KE, but also to perform precision rolling maneuvers, in particular, the point rolls. I shot some footages doing 4 and 8 point roll, and I was pleasantly surprised how much easier it was to do them with the Slick mixed out...

Without further ado, here's the video

.
3D CLINIC VIDEO #8a: Knife Edge Mixing
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Old Aug 17, 2008, 02:43 PM
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Thanks, Josh. I was out playing around with my mixes just today and not getting anywhere, so I think this is going to help me a great deal.
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Old Aug 17, 2008, 02:51 PM
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Thanks Doc,

the file is HUGE 87 MB, but it's 12 min's worth of footage.
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Old Aug 17, 2008, 02:52 PM
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Great vid Josh -nice work, both of you!

You brought out a very important point here - LOOK at the surface you are applying a mix to! Which way is it moving? Is it the way you want it to move?

Usually, when (like Doc says) you "aren't getting anywhere" in mixing, it's due to one of two things:

1.You're not remembering what it is you need to do after you land.

2.Your mix is going the wrong direction and you don't realize it.

Handy tip: On virtually every 3D airplane set up for 3D flying, you need the elevator to move UP when the rudder is moving EITHER directions. I.E. - Right rudder gives you some UP elevator, and Left rudder gives you some UP elevator.
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Old Aug 17, 2008, 02:54 PM
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With most of my planes, the case is down elevator, and opposing aileron. I have no idea why it is always down elevator.

But good vid Josh.
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Old Aug 17, 2008, 02:59 PM
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More wisdom from the Pro.
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Old Aug 17, 2008, 04:28 PM
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BoneDoc,

That's an outstanding presentation.
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Old Aug 17, 2008, 04:32 PM
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Another very useful contribution to helping others learn 3D and set ups BoneDoc.

Thanks to the other poster for correcting there post .
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Last edited by Get Real; Aug 17, 2008 at 09:12 PM.
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Old Aug 17, 2008, 05:58 PM
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I haven't seen the vid but I'm assuming you are showing a linear mix? I have often been tempted to try a curve mix with more anti-coupling as rudder increases, I seem to note that you need progressively more mix as rudder increases, ie at the bottom of a KE loop using full rudder you have to override your mix and add more opposite aileron
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Old Aug 17, 2008, 05:58 PM
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I haven't seen the vid but I'm assuming you are showing a linear mix? I have often been tempted to try a curve mix with more anti-coupling as rudder increases, I seem to note that you need progressively more mix as rudder increases, ie at the bottom of a KE loop using full rudder you have to override your mix and add more opposite aileron? what do other people feel and has anyone used a curve mix?
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Old Aug 17, 2008, 07:51 PM
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Quote:
Originally Posted by blucor basher
Great vid Josh -nice work, both of you!

You brought out a very important point here - LOOK at the surface you are applying a mix to! Which way is it moving? Is it the way you want it to move?

Usually, when (like Doc says) you "aren't getting anywhere" in mixing, it's due to one of two things:

1.You're not remembering what it is you need to do after you land.

2.Your mix is going the wrong direction and you don't realize it.

Handy tip: On virtually every 3D airplane set up for 3D flying, you need the elevator to move UP when the rudder is moving EITHER directions. I.E. - Right rudder gives you some UP elevator, and Left rudder gives you some UP elevator.

By the one of two things :

1.You're not remembering what it is you need to do after you land.

Do you mean make adustment after observing your flight and making corrections in the mix ??
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Old Aug 17, 2008, 08:12 PM
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Joined Jan 2008
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Quote:
Originally Posted by goflyhighrc
By the one of two things :

1.You're not remembering what it is you need to do after you land.

Do you mean make adustment after observing your flight and making corrections in the mix ??
blucor_basher meant that when you land, you forget which way the plane was coupling so you end up making the wrong correction and worsening the problem, or you have to go up and try it again.

Great videos BoneDoc. They have helped me tremendously while learning 3d.
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Old Aug 17, 2008, 08:47 PM
flying yellow and black
Co Spgs, CO
Joined May 2008
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Great video Josh. The more of your videos I watch, the more I have been able to get out of them. I took my Velox out this afternoon and tried to mix out the very little coupling it has. I went the wrong way with a couple of settings but I figured out what I was doing and I think I have it right now. Either way it was a good learning experience. I brought the Velox home, which is always good I wish I could try to mix the coupling out on my SHP, but that is another story...
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Old Aug 17, 2008, 10:54 PM
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R/C Addict is correct, what I meant is that often, after we land, we don't remember what changes we need to make to our mixes. For the record, when mixing a new plane, I try to have a helper handy. Josh has done this job for me before - the helper scribbles notes while I fly so I can remember what it was I wanted to mix out.
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Old Aug 17, 2008, 11:12 PM
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Houston, TX
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Blucor Basher and Xpress,

I wonder if the reason why your planes need differing elevator mixing is due to differences in where you like your CG. I think the take-away is that the Rdr-->Elv mix should be in the same physical direction for both rudder deflections.

Alan
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