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Contest Flying Contest Flying F3C/AMA


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Old 05-25-2006, 04:32 PM   #1
ShawnK
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Default Too much flybar authority... now what?

While out at the field today with winds gusting 20-30mph, I got a very clear, unmistakable display of how a model behaves when it has too much flybar authority. Every time a gust would kick up hard, the heli would lean into it and take off (and I don't mean creep... I mean take off!)

So I understand now that I have too much flybar authority. My question is this:

* Do I simply change my Bell/Hiller mix ratio to decrease the flybar authority?
* Do I experiment with flybar weights?
* Do I change flybar length or paddle size?
* Do I do all of the above?

What is the relationship between Bell/Hiller ratio, flybar length/weight, and paddle size, as it pertains to overall flybar authority?
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Old 05-26-2006, 06:47 AM   #2
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Wow, I didn't know there was a stock machine that had that much flybar authority. Most of us are modifying the head to get more flybar not less. If the model is indeed working upwind and is stable when the air is calm then you would reduce the flybar authority by changing the ratio. Putting flybar weights on will slow the cyclic response, changing the flybar length will also change cyclic rates and affect aero trim. Paddles have an effect on how the model reacts to cyclic inputs but pretty much the flybar ratio controls the wind correction. You might try changing the delta ratio in the non correcting direction as that also has an effect (unless the head is rigid). This works pretty well when the amount of change is different with the wind from different angles.
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Old 05-26-2006, 09:56 AM   #3
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This is my Intrepid 50, running 85mm V-Paddles on a 502mm flybar (measured paddle end to paddle end). I don't know what the exact ratio is (never did the math), but the B/H mixer arm is mounted with the shorter side to the flybar, and the ball link mounted on the innermost hole (as much flybar authority as I can get on this bird in this configuration). I've since moved the Hiller link ball out one hole. We'll see how it goes.

All I know is, when the wind would kick up, she just nosed down and started off. I'd hold back cyclic to keep it still, and as soon as the gust let up, then it's backing up towards me. I didn't like it. :mrgreen:

Hell, maybe I should just fly the damned thing the way it is, instead of twiddlin' with stuff all the time...
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Old 05-26-2006, 10:43 AM   #4
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How does it act in a non-hurricane situation?
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Old 05-26-2006, 10:46 AM   #5
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Seems good to me, but then again, I have to get up on a ladder to lick Gordie's boots. :mrgreen: Maybe someday, I'll be good enough to give you a more subjective evaluation.

I'll put it this way... your average sport flier probably wouldn't think twice about it, but I don't want to be an average sport pilot. I want to learn how to actually build, setup, and pilot a helicopter for F3C. That's why I'm thankful that guys like Gordie and Dave are willing to entertain my questions.
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Old 05-26-2006, 11:49 AM   #6
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Chris will probably be able to explain this better than I, but here goes...

Each blade grip has a mixing arm connected to it. Hold the assembly so that the root of the grip is to the left and the mixing arm is facing you. The left half of the mixing arm should be longer than the right half. Both halves should have two threaded holes for the ball link.

If both ball balls are in the right hole of each pair, you'll get lower cyclic authority, which is good for beginners and aerial photography. If you use the left hole of each pair, you'll get greater cyclic authority. I don't know what the result of using both inner holes or both outer holes would be.

If you decided to move these, check your collective and cyclic pitches. They will change.
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Old 05-26-2006, 08:58 PM   #7
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Like Gordie, I see little way that you could have too much flybar authority. If you were truly well above 1:1, the model would likely be unflyable at anything approaching a hovering rpm unless you also were using a sig amount of neg delta and some seriously weighted up symmetrical blades.

The first thing that I would do is accurately measure your bell hiller ratio. After you determine that it is indeed approaching 1:1, you need to look at introducing neg delta into the system. To really see the benefit of the delta, you're going to have to have numbers well into the teens, an all metal head, and preferably a floating axle head design.

Once you get the delta up as high as possible without introduce a wicked oscillation at hovering rpm, you can play with flybar weight to further reduce the trim shifting depending on how the model is oriented to the wind.

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Old 06-25-2006, 09:34 AM   #8
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Buddy,

It should be easily managable at .7:1-1:1, Try smaller paddles and /or flybar weight. Maybe you have too much cyclic expo and not enough cyclic authority near center? Mixing ratio and delta changes are very subtle by effect under the conditions you mention.

Stephen
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Old 06-30-2006, 09:11 AM   #9
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How does the model fly in an 8-10 mph wind. The vast majority of all contest flights are flown in a moderate wind so we adjust and trim the model for that. The ideal situation is dead calm for hover, a good wind for downwind rolls and the auto, and never a crosswind. Unfortunately, that may happen once in a lifetime. :mrgreen:
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Old 07-01-2006, 10:29 PM   #10
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Well, now that I no longer have that particular model, this topic is kind of moot.

Now I'm playing with an Evo 50. Much more maneuverable upstairs, but the Intrepid kicked it''s arse in hovering maneuvers.

Now, if I could just figure out where my vibration problem is in the Evo (and get some decent friggin' blades... damned TT carbons), I'll be rockin'!
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