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HelicopterMain Discussion › Does a fly bar always remove cyclic pitch?
10-21-2004 11:54 PM  13 years agoPost 1
TurboStew

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Ft Collins, CO

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In all my research, the common explination says cyclic rate (not acceleration) can be increased by lowering the flybar ratio, ie, less blade angle change for a given flybar tilt. If this is true, it implies that the flybar always "removes" cyclic pitch from the blades. If you put enough paddle area ,make the flybar/paddle light enough, and add enough "paddle pitch", can the flybar be additive to blade pitch? I notice on Askcurtis that Curtis states (more than once) that he likes .65 for FAI and .85 for 3D. His definition of ratio is the same as the one I describe here. This seems backwards to the general rule unless the flybar can be additive to blade pitch.

Any thoughts or experts on the subject?

Link to Curtis and flybar ratios:
http://www.curtisyoungblood.com/faq...ry=Flybar ratio

8.5 pound 90 birds Rock!

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10-22-2004 03:01 AM  13 years agoPost 2
TurboStew

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Ft Collins, CO

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Hello?

8.5 pound 90 birds Rock!

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10-22-2004 03:20 AM  13 years agoPost 3
eric_b

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Denver, CO, USA

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Confucius say:

Ah, Grasshopper.... You need drink more bourbon, spend less time on whirlybird analysis....
In all my research, the common explination says cyclic rate (not acceleration) can be increased by lowering the flybar ratio, ie, less blade angle change for a given flybar tilt.
I always thought that a higher flybar ratio (more Hiller input versus Bell input) would lead to a more responsive cyclic. Many of the old-school choppers had ratios around .50 - .80, or so. When the Raptors came out, they boasted a 1:1 ratio ( 1.0 ) (the blade pitch changes the same angle as the flybar deflection) and thus, the Raptor was quite responsive in cyclic control. So given this, wouldn't a higher ratio give a more responsive bird versus a lower ratio?

Mebbe I'm wrong... James Wang you listening out there?? Taya? Dieter? What's the scoop?

On the other hand, a flybarless setup can also be VERY responsive in cyclic, which would have 0% Hiller input and 100% Bell input.

There was an article that I just read (or re-read) somewhere, maybe in Model Heli World.... about flybar issues and setup. I'll try to find it again.

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10-22-2004 04:20 AM  13 years agoPost 4
MJA

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UK

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If you read a little further down he states that the .65 ratio
"sits better in the wind" for FAI.
By this i take that to mean that when the heli is hit by wind gusts during precise hovering manouvres it tends to stay nailed
put over one point more
rather than the flybar responding too aggresively (heli moving into the wind direction) or not enough (heli moving away).
I think that's the right way around

It may be the same paddles/flybar setup used for his 3D
respond a little
too agressively to wind gusts at the .85 setting (or the correction is too powerful)


So to get the machine good to go
for both disciplines
without changing the flybar length or paddles, he just changes the ratios,because
at the ratio nearer to 1:1 it corrects (flybar responds )too agressively into the wind gust direction and over compensates (like a gyro with it's gain too high)

So the ratio you think is more stable for FAI .65 is actually less stable but he could be using it for different reasons than you think or with a heavier setup on the flybar that differs to his 3D setup.

When thinking about this stuff it's best to think in terms of how a heli reacts to a deliberate control input vs how it reacts to outside influences
The flybar damps both, or slows down the reaction of the blades to more manageable levels (speeds)

If it were a perfect setup,an FAI flyers dream (or even a 3D flyers dream)
you'd have a heli that had total
neutral instability,it stayed nailed over one spot when the sticks were left alone and it was trimmed neutral cyclics
,moves directly in full proportion to the stick input and start stops moving exactly in time
with the stick input,as fast or as slow as you wanted.And if it got hit on all 4 sides it would stay exactly over one point,even while pirouetting on the spot
in a 30mph wind .But i think it'd make flying heli's too boring/predictable


Martin

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10-22-2004 04:46 AM  13 years agoPost 5
eric_b

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Denver, CO, USA

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that would be awesome

But i think it'd make flying heli's too boring/predictable
I seem to remember (back in the day) people saying that about heading hold gyros.... and look where we are now!

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10-22-2004 05:15 AM  13 years agoPost 6
the collective

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Bayside, NY, U.S.A

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But i think it'd make flying heli's too boring/predictable
I doubt it. I wouldn't be surprised to see a system like you describe in a few years. I don't think it will keep a heli nailed over a spot, they'll always drift with the air movements, but you'd pretty much have the cyclic trim NAILED to lock the attitude right in.

Basically a fly by wire system for the cyclic working much like an HH gyro does now on the tail. It will happen, in fact, if you have a couple of extra 401's in your stash you could probably roll your own... hmmm...

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10-22-2004 03:06 PM  13 years agoPost 7
TurboStew

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Ft Collins, CO

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eric_b, thanks for getting the ball rolling on this topic. I appreciate everyones input here, but I still wan't to know if the accepted given range of flybar lengths, paddle areas and masses can be additive to cyclic pitch or it is always subtractive (steady state conditions, disregard cyclic acceleration). Am I asking a viable question here? If I take the flybar ratio to zero, it will be flybarless, then won't the heli have cyclic out the wazzoo?

8.5 pound 90 birds Rock!

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10-22-2004 04:54 PM  13 years agoPost 8
eric_b

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Denver, CO, USA

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Perhaps your question should be then: Does a higher flybar ratio (more hiller input versus bell input) always increase the dampening (in other words: reduce the responsiveness) of cyclic pitch?

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10-22-2004 05:54 PM  13 years agoPost 9
TurboStew

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Ft Collins, CO

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Yea.

8.5 pound 90 birds Rock!

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