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HelicopterMain Discussion › Hiller Vs. Bell Hiller
11-30-2007 12:25 AM  9 years agoPost 1
MMike

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Holland,Mi-USA

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In my limited experience, I found the Axe CP with the Hiller swash plate to have an unstable flying personality.

My 13" EP100, with a Bell Hiller is easier to fly being Bell Hiller.

Am I correct in thinking it's a "swash plate thang"?

MMike

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11-30-2007 12:33 AM  9 years agoPost 2
Zaneman007

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Texas - USA

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Although I never owned an AXE CP, I did have a blade CP. It is not so much a hiller thing as it is a cheap sloppy thing. When I added the bell hiller set up to my BCP, it did respond better, but anything would have been an improvement.

I have realized that plastic parts on small helis have big tolerances. Sloppy tolerances make for sloppy flying, no way around it.

If the AXE is anything like the CP, it is a handful to fly. A bell hiller set up will help, but..... you get what you pay for.

Type collin mill theorys in your googl search engine. They guy does a great job of explaining the two systems.

Old Guys Rule!

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11-30-2007 12:46 AM  9 years agoPost 3
MMike

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Holland,Mi-USA

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Zane

I agree

I find it ironic that the beginner, trying to hover, on an unstable inexpensive machine with just a rate gyro, has a harder heli to learn on than most of us with our $1000+ quality machines.

MMike

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11-30-2007 02:59 AM  9 years agoPost 4
dkshema

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Cedar Rapids, IA

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The difference is not a swashplate thing. The flybar and paddles represent the Hiller influence, and are part of the Hiller Rotormatic system.

The Bell part of the equation comes from the connection between the swashplate and the pitch links on the main rotor grips.

The two systems -- Bell and Hiller -- are combined in the mixing levers that are usually either mounted on the flybar seesaw or main rotor pitch links (depending upon the heli design).

Dieter Schluter is the fellow who combined the two systems and patented it as the "Beller" system.

The mixing ratio between the Hiller system and the Bell system is one of the determining factors of how responsive the heli is.

-----
Dave

* Making the World Better -- One Helicopter at a time! *

Team Heliproz

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11-30-2007 03:12 AM  9 years agoPost 5
ZXXflyer

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stone mountain, georgia, US

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So wether the mixers are mounted to the blade grips or on the flybar seesaw, it's the same system? I am comparing a Hawk pro rotor head to a stock ZXX head.

Believer in Weston motors!

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11-30-2007 03:37 AM  9 years agoPost 6
dkshema

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Cedar Rapids, IA

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Yes, the location of the flybar does not change the fact that you have a combination of a bell and hiller system.

Once upon a time when Dieter Schluter introduced the Schluter Champion, a heli with the underslung flybar, he was asked if putting the flybar below the blade axle made any difference over what was standard for the day -- above the feathering shaft. His reply was to the effect "yes, with the underslung flybar, we can hover inverted lower to the ground".

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Dave

* Making the World Better -- One Helicopter at a time! *

Team Heliproz

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11-30-2007 06:17 AM  9 years agoPost 7
spork

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Mountain View, CA

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Dieter Schluter is the fellow who combined the two systems and patented it as the "Beller" system.
I did not know that. I've learned my new fact for the day and can sleep easy now. Thanks.

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11-30-2007 01:43 PM  9 years agoPost 8
w8qz

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Grand Rapids, MI - USA

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The difference in my experience is control delay: the 'pure Hiller' system (swashplate drives only the flybar - for cyclic control i.e. std. Blade CP) adds a slight bit more delay in response. The 'Bell' system (well, only "sorta" - we almost never use a true 'Bell' control system on our models with the friction dampers and flybar weights {Vario scale Bell 47 head excepted}) as used on our models gives a much quicker response.

As pilots, we train our brains to compensate for a particular amount of control delay (between our inputs and the machine's response); switching from a 'slow responding' machine to a 'fast responding' machine (or vice versa) will throw us off - for a while. (More practice with one or the other will 'retune' the brain to the particular machine.)

In practice, the mixing of the 2 gives a reasonable compromise between the stabilizing action of the flybar, and the quick response of the direct input. Fine-tuning the mix one way or the other produces varying control responses (i.e. 3D wild contortions vs. FAI stable hovering).

"The helicopter is much easier to design than the aeroplane, but is worthless when done."

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11-30-2007 03:02 PM  9 years agoPost 9
SSN Pru

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Taxachusetts

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I have realized that plastic parts on small helis have big tolerances.
This isnt so much the case. On smaller parts, unless the tolerances are held to a smaller number, compared to larger parts, the ratio of the tolerance dimension to the parts physical dimensions will be larger. This will show as slop and crappy fitting parts

Stupidity can be cured. Ignorance is for life!

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11-30-2007 05:34 PM  9 years agoPost 10
MMike

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Holland,Mi-USA

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This discussion has gone WAY over my head.

MMike

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11-30-2007 09:55 PM  9 years agoPost 11
Autoeject

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Ashtabula, OH, USA

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As pilots, we train our brains to compensate for a particular amount of control delay (between our inputs and the machine's response); switching from a 'slow responding' machine to a 'fast responding' machine (or vice versa) will throw us off - for a while. (More practice with one or the other will 'retune' the brain to the particular machine.)
Of that there is no doubt. I did an install on a JR voyager that had very heavy paddles and mixing toward the Hiller end of control. I almost crashed it just because it was so slow to respond to the stick. Felt like a noob again. Ended up only flying it just as long as required. Give me a faster heli any day!

Mark Webber
wai-rc.com
Spartan RC Distributor
Outrage Helicopters

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11-30-2007 11:19 PM  9 years agoPost 12
MMike

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Holland,Mi-USA

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Dave

I'm thinking it is a swash plate thang, Respectfully, where am I wrong?

Are you saying it's about HOW the swash plate is linked to the fly bar and / or blade grips?

MMike

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11-30-2007 11:44 PM  9 years agoPost 13
Autoeject

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Ashtabula, OH, USA

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In a Bell version, the swashplate is directly linked to the grip. Cyclic inputs are immediatly transfered to the blades. In a Hiller head, the inputs are slowed via the flybar. Using a mixing arm allows us to have the best of both worlds.

In a flybarless heli, the links go directly from the swashplate to the grips. A heli equipped in this manner will be very responsive to cyclic inputs.

If it's a swashplate thang, it's got to be due to poor quality control. If you've got a smooth/tight swashplate, the above control version will provide the appropriate responsiveness.

Mark Webber
wai-rc.com
Spartan RC Distributor
Outrage Helicopters

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11-30-2007 11:51 PM  9 years agoPost 14
MMike

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Holland,Mi-USA

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So the Axe is slow responding, and thusly, in my opinion, hard to fly with a hiller "swash plate"? or is there a better word here than swash plate?

MMike

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11-30-2007 11:55 PM  9 years agoPost 15
Autoeject

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Ashtabula, OH, USA

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The swashplate in not specific to the Bell or Hiller. The control is managed at the head. The axe is slow to respond for a variety of reasons. Most of which are probably associated with the manufacturing quality. I learned on something similar and was quite suprised when I moved to a quality machine how much easier it was to fly.

Mark Webber
wai-rc.com
Spartan RC Distributor
Outrage Helicopters

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12-01-2007 12:32 AM  9 years agoPost 16
spork

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Mountain View, CA

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Yup, as Mark says, the swashplate is no different on a Bell, a Hiller, or a Bell-Hiller design. Everything that distinguishes these heads is related to the mixing that takes place above the swashplate.

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12-01-2007 01:23 AM  9 years agoPost 17
dkshema

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Cedar Rapids, IA

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I took a look at the AXE CP manual and pictures of the head, as well as the swashplate.

If you look at your swashplate and compare it with a Trex swashplate, you'll see the same basic design. An outer ring that is fixed, an inner ring that rotates, and the whole shebang pivots about the main shaft using a uniball bearing.

The upper, rotating part of the swashplate is identical to that of many other helis, it has four balls on it, placed 90 degrees apart.

The AXE only uses two of those four balls, and those balls are 180 degrees apart. Those two balls hook to the hoop-like pushrods that connect to the rectangular flybar control cage. The other two balls on the swash are not used. Tilting the swashplate tilts that control cage, causing the paddles to tilt, eventually causing the flybar to change the tilt of the plane that it is rotating in. As the flybar itself tilts, the two short links connecting the flybar seesaw to the main rotor pitch arms on the grips, finally affecting the cyclic pitch of the two blades, eventually causing the plane that the rotor disk is rotating in, causing the heli to change direction. There is no direct connection between the swashplate and the main rotor pitch control arms. As a result, you'll find that the control response lags behind the control input because in order for the cyclic pitch to change, you're dependent upon how fast your flybar changes the tilt of the plane that it is flying in. You can fly the heli, but do not get a nice, crisp, instant response to the control inputs. The stock AXE lacks the "Bell" half of the "Beller" system. It only has the Hiller half and that half has a slow response time with regard to changes in control inputs. That is how Stanley Hiller managed to get his Rotormatic system to be so stable and forgiving for the new pilot.

In helis having the Bell part of the "Beller" system, those two unused balls on the AXE swashplate have control links attached. These control links end up going directly to the pitch control arm on the main rotor grips. Yes, the flybar and paddles still act exactly as they do in the Hiller system and still have that lag time between control input and control response.

However, since the Bell part of the system directly affects the cyclic pitch, the controls respond nearly immediately to control inputs. The Hiller system and the Bell system are mixed together up in the head. By playing around with the design and placement of the mixing levers that mix the Bell and Hiller controls together, the heli designer can control how much influence the Hiller Rotormatic system has on the heli's control, and how much influence the Bell portion of the system influences the controls.

If the Bell system inputs dominate the control influence, then you'll have a very responsive control system. If the Hiller system dominates, you'll have a very docile control system.

-----

The AXE with its Hiller only system is not unstable, what you're experiencing is control lag. Until you get the hang of it, the heli will always be a little bit behind your thumb inputs. Since your brain knows you've moved the controls, it expects the heli to respond immediately, but it doesn't. The heli responds maybe a half-second later than your brain thinks it should. You hover and want the heli to start moving forward. You feed in a bit of forward cyclic, your brain wants the heli to move. But the controls lag maybe a 1/2 second before the heli starts moving. This lag makes you put in a bit more forward because nothing "happened". When the heli DOES respond, you've added more control than you needed to, so the heli starts going faster than you expected. Now, you pull back on the stick, the lag is still there, you pull "more" and the heli catches up -- eventually.

Until you learn to anticipate the control inputs correctly, you'll always be a bit behind or ahead of the heli and the heli will just seem to be squirrely.

-----

With the Bell part of the system in the mix, when you move the stick, you see an immediate response. Your brain is happier, and you seem to be able to stay on top of the controls a lot better.

-----

The collective pitch system is fairly straightforward, you raise the swashplate, you raise the flybar control cage, and those two short links lift both blades simultaneously. Collective response should feel pretty solid and immediate.

-----

As you can see, this control problem really has nothing to do with the "slop" in the parts of the assembly, it has everything to do with the physics of how the control systems react. It's not a QUALITY problem, its a physics problem.

-----
Dave

* Making the World Better -- One Helicopter at a time! *

Team Heliproz

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12-01-2007 01:23 AM  9 years agoPost 18
SSN Pru

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Taxachusetts

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Its all in the head...

Stupidity can be cured. Ignorance is for life!

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12-01-2007 01:31 AM  9 years agoPost 19
Yug

rrMaster

UK. Herts

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The combination of the two systems makes it hard if not impossible to tune it for the optimum performance criteria of stability, zero pitchness and snappy roll rate while maintaining these in different wind conditions. It's all such a big trade off and quite a challenge if you're happy to spend hours tweeking stuff like, paddle types, weights, flybar ratios, delta settings and so on. Very good results can be achieved but understandably, a flybarless system employing gyros is so much more straight forward albeit significantly more expensive.

Vegetable rights and Peace

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12-02-2007 11:27 AM  9 years agoPost 20
MMike

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Holland,Mi-USA

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So one would not say, "It's a swash plate thang", but rather,
"It's a head unit thang"

Thx to all, I certainly learned something here.

MMike

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HelicopterMain Discussion › Hiller Vs. Bell Hiller
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