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Oct 07, 2008, 07:52 PM
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"PUSH PULL" Interlocked Mixing Arms Bell Hiller Concept for Fixed Pitch Helis


After a successful experiment on applying a bell hiller mod on a fixed pitched heli;

https://www.rcgroups.com/forums/showthread.php?t=933715




I decided to tackle in detail the "push-pull" concept on bell hiller mechanisms for Fixed Pith Helicopters (whether its a Mini or a Micro heli).

The idea is to use an "interlocked" bell hiller mixing arms on FP helis having a "single" blade grip such that a "push pull" link arm mechanism can be applied. The advantage of having a "Push-Pull" servo linkages basically eliminates any slop and lessens the flexure on the mechanical arms.





The mixing arms on both side of the blade grip is locked together through a horizontal bar;






Here is a view of the the horizontal bar (above the blade) grip locking the two mixing arms together;





and view of the mixing arm on one side;





As the swash plate tilts to one side and "pulls" one side of the interlocked mixing arms, the other side "pushes" it to the opposite direction tilting the blade grip+blades with it. The horizontal bar actually now becomes part of the "push pull" mechanism as it reduces any error in mixing caused by flexure on the entire blade assembly.





The same case on the flybar as it also does a "push-pull" force on the interlocked mixing arms, it tilts the interlocked mixing arms and blade+blade grip with it ;




Here are some gif animations of bell-hiller push pull mechanism on a tilting swash;




and the tilting flybar;





And a couple of test flight videos using the "push pull" interlocked mixing arms bell hiller mixing concept;

Mixing arms in action;

Walkera 4#3 Bell Hiller Mod - Ball links closeup plus hover (1 min 4 sec)



Flight videos;

Walkera 4#3 Bell Hiller Mod - "Mad" Cyclic tests (2 min 50 sec)


Walkera 4#3 Bell Hiller Mod - Test flight video Part 3 (3 min 37 sec)


Walkera 4#3 Bell Hiller Mod - Test Flight Video Part 2 (4 min 16 sec)
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Oct 08, 2008, 09:54 AM
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From a mechanical and operational point of view what is the difference between this and dze's elastic string mod?

Also, is the original drawing correct or should the swash links be displaced 90 degrees?
Last edited by Martyn McKinney; Oct 08, 2008 at 10:20 AM.
Oct 08, 2008, 11:43 AM
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Quote:
Originally Posted by Martyn McKinney
From a mechanical and operational point of view what is the difference between this and dze's elastic string mod?

Also, is the original drawing correct or should the swash links be displaced 90 degrees?
Hi Martyn,

Yes thanks for illustration heads-up. I corrected it already;




As for the elastic string mod difference, mechanically it works as the swash has a direct influence on the main blade grips. However it is not a "push-pull" mechanism. Its more of a "pull down only" mechanism where one side of the swash can only pull down the grip through the string while the opposite side also with the elastic string does nothing.

Although the elastic string mod can reduce the delay in the cyclic response, there is some loss on the swash pull-down force as the elastric string has to stretch first before the main blade grips + flybar starts to react with it.
Oct 09, 2008, 05:34 PM
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Let me just add that the "interlocked" mixing arm has to freely see-saw on the blade grip itself
Oct 09, 2008, 09:08 PM
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Shouldnt this be in the micro area?
Oct 09, 2008, 09:17 PM
Was a lookin fer loomyum foral
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That looks complicated. Maybe just a flybarless FP would be really twitchy and simple.
Want to try a good one ? A variable pitch "FP". Modify a floating flybar head (like Esky, 22E, Axe Cp) to FP. Now mix the flybar into the blade grips. Set them with some positive pitch so as the rotor gains rpm, the flybar lifts up and increases the pitch, then drops back down and decreases pitch at lower rpm.
The lower rpm could be calibrated to have a good head speed to allow responsive hover control, more than currently available.
Swinging balls could do the same with a better tendancy to return to lower pitch.

A variable FP ?

HA HA

CH
Oct 09, 2008, 09:22 PM
Was a lookin fer loomyum foral
Chophop's Avatar
I think all we really need is an Align head for a 300 sized heli, a 570mm rotor, belt tail, and under 400g. I am waiting.

CH
Oct 09, 2008, 10:11 PM
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Quote:
Originally Posted by JustinMoore12
Shouldnt this be in the micro area?
Discussion is mainly on the bell hiller heads. It so happened that my test heli is only a micro.
Oct 09, 2008, 10:14 PM
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Quote:
Originally Posted by Chophop
That looks complicated. Maybe just a flybarless FP would be really twitchy and simple.
Want to try a good one ? A variable pitch "FP". Modify a floating flybar head (like Esky, 22E, Axe Cp) to FP. Now mix the flybar into the blade grips. Set them with some positive pitch so as the rotor gains rpm, the flybar lifts up and increases the pitch, then drops back down and decreases pitch at lower rpm.
The lower rpm could be calibrated to have a good head speed to allow responsive hover control, more than currently available.
Swinging balls could do the same with a better tendancy to return to lower pitch.

A variable FP ?

HA HA

CH
As you said it, it will be really twitchy if you remove the flybar.

Also, flybar is there to maintain flight stability. We cant just pitch it both at postive or negtive as the flybar disc will not tilt to pitch the main blades.
Oct 10, 2008, 02:24 AM
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Quote:
Originally Posted by EQMOD
As you said it, it will be really twitchy if you remove the flybar.

Also, flybar is there to maintain flight stability. We cant just pitch it both at postive or negtive as the flybar disc will not tilt to pitch the main blades.

Strangely enough - I was just thinking about it this morning - flybarless FP micro? Would that help?

If you put more weight (30g? - actually one is 19g + carefully measured cables ~25-30g) and comparison to weight of flybar plus flybar paddle's drag - would these two cancel each out? If so - that could be great mod (althoughwith current prices of flybarless systems it is a bit silly, still... )

After reading this thread I am seriously thinking of getting same micro only to experiment like that!


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