How do I know it's me?

[ShawnK]

Every time I try to do axial rolls, the nose pitches skywards during the inverted section, and I come out of the roll with almost zero airspeed.

My assumption is that it's me dumb-thumbing it. Is there any test I can perform to verify that it's me, and not some kind of cyclic interaction?

[DavidH]

You use a Pmix. At full left cyclic you mix in some aft cyclic. At full right cyclic you mix in some fore cyclic.

I use about 10% fore/aft cyclic when using full left/right cyclic.
Only takes 1 Pmix to accomplish it.

David

[ShawnK]

Should I try to verify somehow that it's not me dumb-thumbing it before I use a P-Mix?

That's kind of what I was asking... I don't know if it's me or the machine that's the problem. I assume it's me, but I'm wondering if there's a way to find out first.

[ErichF]

Well, it could be a phasing issue with the mechanics, which can be compensated for by electronicall, as DavidH was explaining, or physically, as with some machines like Hirobo.

More likely, you aren't setting the machine up for the roll, or your balance is too far aft. You gotta make sure the tail is trued up behind the machine before the roll. I use the smoke trail as a guide. If the tail isn't straight behind the machine, you can get an ugly corkscrew effect. Also, you may be using too much negative collective at the top of the roll, introducing a pitching moment. Also, don't pitch the nose up as you enter the roll. That's a common mistake some people make when they first try rolling; they're affraid of altitude loss during the roll. I have done axial rolls at full speed with the nose pitched down 15-20 degrees at the start. With proper collective management, the roll stays straight with no altitude change.

So, check your balance and your mechanical phasing if your machine has that adjustment. Use less negative pitch in the roll, and don't pitch the nose up.

If you have CCPM, check for pitch excursions of the swash on your negative collective side. You may have an interaction going on, causing a virtual phasing issue.

Have fun,

Erich

[ShawnK]

Erich (and Dave),

Thanks for the advice! You may have a point with the negative pitch... my friend at the field had commented that the engine sounded like it was getting loaded down a lot on the inverted section. Maybe I was just being a little too apprehensive and holding too much negative, like you said. However, I don't understand what you meant when you said that too much negative would introduce a pitching movement. How does that work?

Speaking of mechanical phasing: Should the head be set up so that the flybar and both sets of balls on the swash all fall on the same line? When looking at the machine from the top, if I hold the flybar so that it's in line with the tail boom, the inner ball on the swash is about 1/2 ball width off from the outer ball. If I line up the balls (easier to see), the flybar looks like it's off about 5 degrees (or so) clockwise. I'm not sure how to compensate for that, though, unless I wanted to shave the washout arms enough to let the washout link move inboard a little bit. (This is a Bergen Intrepid 50... similar head to the MA Fury Extreme, I think? There should be a picture in my gallery... suffice it to say, there's no radius block like a Hirobo.)

I'll just assume it's me for now, and keep working on my technique.

I never realized how little I know about this stuff, until I tried doing it well. :mrgreen:

[TMoore]

Keep the nose down or level when you enter the roll.

[fitenfyr]

When I manage to do a very nice axial roll I am using so little negative I feel like it is going to fall out of the sky. :D

Seriously just a tad below 0 is enough to keep it from falling on most of my ships.

I move to negative as I am rolling (right or left) and then center at mid stick (0) until it goes inverted then just go down a nudge (estimated about 2-4 deg?) then start right back up into zero as it comes back up right.

If is miss the timing it will pull/push or nose up everytime. :D

[GM1]

Roll trim is one of those things that is somewhat akin to magic. I have had models that rolled perfectly with no adjustment and others that wouldn't roll true no matter what you did. Lets take a minute and talk about trim and then worry about the roll. A model with an incorrect CG will not roll true, period. How do you trim a model's CG? Statically balance the model with 1/2 tank of fuel so that the nose hangs slightly low. With 3/4 tank of fuel, hover the model with the swashplate ABSOLUTELY level. Add or subtract nose weight until the model hovers hands off in no wind with ZERO elevator trim. Once that's good, you can proceed.
Go into FFF and see what trim (if any) the model needs. If it noses up, remove some horizontal fin area or shorten the flybar. If it noses down, increase the horizontal fin area or lengthen the flybar. Just a touch of back trim is Ok but NO forward trim. With 1/2 tank of fuel fly across in front of you and roll to inverted with just enough negative to maintain altitude. The model should continue to cruise along with little or no tendency to nose up. If it does cruise along level then you are probably getting into the negative pitch way too hard during the roll. What I did was creat a special condition that has less negative pitch so that even if I get cheesed up with nerves at a contest, I cannot really pull too much negative as it isn't there.
Let me insert something here. I am assuming symmetrical non-washout blades. If you have semis or washout blades, you can get some really funky action as you go into negative pitch. Are you flying symmetrical blades?
If after Cging the model, it still noses up and tries to stop, it gets MUCH harder to fix. You probably will need two program mixes, an aileron to TR and an aileron to elev. You REALLY do not want to run these unless you have to as you can really screw it up if you don't have patience to do this 1% at a time and spend a whole day working on it. Hey Ben, tell him how to set up the p-mix as I think you have it done in a file somewhere.
Gordie