MICRO Helis:Hiller-Only VS. Bell Hiller-Which is really preferred by most RC pilots ? - RC Groups
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Nov 19, 2008, 02:50 AM
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MICRO Helis:Hiller-Only VS. Bell Hiller-Which is really preferred by most RC pilots ?


Lets discuss rotor head mechanics

For 200,400, and above series of helicopters, i noticed that the dominating design is bell hiller configuration and for micros (and mostly Fixed Pitch helis), i usually see at most the hiller-only design in their rotor head configuration. But what about micros with bell hiller heads ? The Walkera 4G3 is classic example of a Micro with a Bell Hiller head design.

Some may debate that they prefer Hiller-Only heads due to its rotor head configuration simplicity and lesser parts;



as against a bell hiller head where a couple of extra parts (mixing arms and additional pitch links) are present;



But what about controllability and crisp cyclic response ? We all know that a hiller-only configuration, a pilot has to wait for the flybar to react (T1) before the heli starts to move to the desired direction (T2). Thats roughly half a second to 1 second of delay from TX cyclics to the actual time the heli goes into the desired direction. Its like steering a car and the car reacting to the steer command 1 second after (now thats difficult driving).

With a bell-hiller head, the heli reaction time is almost instantaneous as the servo+swash has a direct influence on the main blade via the mixer arm (T1) and the flybar now becomes just a stabilizer for the main blade through the same mixer arm. (refer to the above figures)

UPDATE:

THE MECHANICAL MAJIC of "Bell Hiller" Mixing



Closeup of the mixing arms in action:

Micro FP: Bell Hiller Test 5 (0 min 55 sec)


Here is the "Magic" Mechanics behind the Bell Hiller mixing as demoed on the following video;

Without thinking of the complexities of the mixing arms + pitch Links on bell hiller mixing, imagine two independent systems (a) flybar+paddle and the (b) servo+swashplate dictating the pitch of the main blades. If you independently move the flybar, the main blade (pitch) goes with it. If you also independently move the servo+swashplate, the main blade ALSO goes with it. Now if you "mix" the two independent flybar and swashplate inputs, the pitch of the main blades correspondingly follow and is actually the average (depending on the mixing arm ratio) of the two inputs.

So technically, the swashplate is providing DIRECT cyclic inputs on the main blades for fore+aft controls (aileron/elevator) at the same time the flybar is also providing stabilizing inputs to the blades. The flybar actually STABILIZES the entire system whether there are (or none) cyclic inputs coming from the swash.

That DIRECT input from the swash going to the blades makes the heli's flight response almost instantaneous.


On the following video, watch the PITCH of the main blades as I apply the cyclics from the TX and as i independently move the flybar. Thats "bell hiller" mixing.

Micro FP: Bell Hiller Test 4 (1 min 12 sec)


In Hiller-Only, there is no DIRECT input from the Swashplate going to the main blades. Heli's flight direction is entirely dictated by the state and position of the flybar. The flybar has to change its position first before the heli could start to react on the final state of the flybar and that is the cause of the delay on the cylics which others term them as "sluggish".



Please post what you guys think and maybe post some videos of your heli in flight using the hiller-only or bell-hiller showing the advantages of one from the other.
Last edited by EQMOD; Nov 20, 2008 at 07:11 PM.
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Nov 19, 2008, 02:57 AM
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The Bell Hiller Ground Effect Hover

This one requires a LOT of cylic input commands to the heli but she is hovering close to ground on a very confined space overcoming ground effect

Micro FP: Bell Hiller Ground Hovers (0 min 59 sec)


I doubt if a hiller-only head can be managed to perform such flight sequence.


Spot Landing Exercises - Bell Hiller Style

Walkera 4#3 - Spot Landing Exercise (1 min 24 sec)


I think both hiller-only and Bell Hiller can do this but i think its much easier to perform this sequence on a bell hiller head configuration. Dont ask me how hiller-only spot landing performs as i have never tried it
Last edited by EQMOD; Nov 19, 2008 at 03:47 AM.
Nov 19, 2008, 02:58 AM
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I have always wondered about this. I have never flown a heli with the bell-hiller head. I will get my chance when the 4g3 gets delivered soon. But i have always wanted to try both so i can see which one i prefer.
Nov 19, 2008, 03:44 AM
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Quote:
Originally Posted by buster7467
I have always wondered about this. I have never flown a heli with the bell-hiller head. I will get my chance when the 4g3 gets delivered soon. But i have always wanted to try both so i can see which one i prefer.
Thats actually the purpose of this thread. Many RC pilots started flying on a specific configuration (hiller only , bell-hiller) without realizing what the other config can or may not offer. So basically, this should be some sort of "share-your-flight-experience" exercise.

In my case, i started learning on a heli with a bell-hiller head. A Hiller-only head trial flight came as a "shock" to me. I always thought that they are the same. You will never know until you try both or somebody tells you how it feels like to fly one from the other.
Nov 19, 2008, 12:02 PM
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Although I've been flying fixed wing RC for years, the one and only heli I've flown so far is a HBFP. Thus, I'm all too familiar with Hiller-only control.

Coming from a fixed wing background, I found Hiller control response very, very sluggish from the moment I first flew with it. Now that most of my flying is on the HB, I have found myself compensating automatically for the delayed and muted response of the heli to control inputs. So much so, in fact, that when I last tried to fly fixed wing, I over-controlled so much that I put the plane through comic cycles of oscillating pitch and roll.

Wanting better control of the HBFP, I attempted a Bell-Hiller modification. What I discovered is that BH control did provide the quick and precise response I was used to in fixed wing. However, I also found out that it's not easy to add a mechanically sound, precise, and reliable BH mechanism to the FP head. None of my attempts could stand up to vigorous flying for any length of time.

There are some inexpensive alloy CP heads available (with BH) and I might try to adapt one of those to the HB to gain reliable Bell-Hiller control. Or perhaps I can just take the step to flying a CP machine (with BH). In the meantime a longer flybar has increased responsiveness in the Hiller system. I'll might try lighter, bigger paddles too.

Andrew
Nov 19, 2008, 12:13 PM
dze
dze
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ive flown both .. to me its not a huge issue .. i have a 4#3b and hbfp with no bell hiller and 3 king2s' with the bell hiller ... the kings are definitely more precise but fp's are still controllable and responsive if set up correctly and for the general usage, which is learning on or playing around, the simplicity means more durability less down time and cheaper to maintain .. personally i dont think an fp is worth modding they fly pretty well the way they come and it still boils down to the pilot having good control .. when a person is ready for more precise control they are going to want better quality throughout and more power and collective pitch so the headspeed and tail are more stable, so then i think is when a bell hiller is really needed and most if not all cp helis come that way ..
.. another issue for me personally trying to mod an fp to a bell hiller setup, is a certain degree of improvment can be made in certain areas but it is usually detrimental in others .. i tried it on my 4#3b and it worked beautiful in perfectly still air and slow forward ... but outside in the wind and flying it hard and fast it became uncontrolable .. it would take several degrees in engineering i think to pull off a bell hiller mod on an fp and have it be a drastic improvment in all areas imo ...
Last edited by dze; Nov 19, 2008 at 12:18 PM.
Nov 19, 2008, 11:59 PM
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EQMOD's Avatar
Quote:
Originally Posted by landru
Although I've been flying fixed wing RC for years, the one and only heli I've flown so far is a HBFP. Thus, I'm all too familiar with Hiller-only control.

Coming from a fixed wing background, I found Hiller control response very, very sluggish from the moment I first flew with it. Now that most of my flying is on the HB, I have found myself compensating automatically for the delayed and muted response of the heli to control inputs. So much so, in fact, that when I last tried to fly fixed wing, I over-controlled so much that I put the plane through comic cycles of oscillating pitch and roll.

Wanting better control of the HBFP, I attempted a Bell-Hiller modification. What I discovered is that BH control did provide the quick and precise response I was used to in fixed wing. However, I also found out that it's not easy to add a mechanically sound, precise, and reliable BH mechanism to the FP head. None of my attempts could stand up to vigorous flying for any length of time.

There are some inexpensive alloy CP heads available (with BH) and I might try to adapt one of those to the HB to gain reliable Bell-Hiller control. Or perhaps I can just take the step to flying a CP machine (with BH). In the meantime a longer flybar has increased responsiveness in the Hiller system. I'll might try lighter, bigger paddles too.

Andrew
Good info Andrew!

I actually had a good success in converting a FP head to bell hiller;


She flies great on FFs, banking, etc. You might want to take a look at it.


The approach was centered on an H-bar / Push pull concept:




While tilting the swash;



and the tilting flybar;




https://www.rcgroups.com/forums/showthread.php?t=935419
Last edited by EQMOD; Nov 20, 2008 at 01:45 AM.
Nov 20, 2008, 12:00 AM
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EQMOD's Avatar
Quote:
Originally Posted by dze
ive flown both .. to me its not a huge issue .. i have a 4#3b and hbfp with no bell hiller and 3 king2s' with the bell hiller ... the kings are definitely more precise but fp's are still controllable and responsive if set up correctly and for the general usage, which is learning on or playing around, the simplicity means more durability less down time and cheaper to maintain .. personally i dont think an fp is worth modding they fly pretty well the way they come and it still boils down to the pilot having good control .. when a person is ready for more precise control they are going to want better quality throughout and more power and collective pitch so the headspeed and tail are more stable, so then i think is when a bell hiller is really needed and most if not all cp helis come that way ..
.. another issue for me personally trying to mod an fp to a bell hiller setup, is a certain degree of improvment can be made in certain areas but it is usually detrimental in others .. i tried it on my 4#3b and it worked beautiful in perfectly still air and slow forward ... but outside in the wind and flying it hard and fast it became uncontrolable .. it would take several degrees in engineering i think to pull off a bell hiller mod on an fp and have it be a drastic improvment in all areas imo ...
Was this the rubber-band mod ?
Nov 20, 2008, 12:31 AM
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FP Bell Hiller Style Indoor and Outdoor FF/Banking


Here are test flight videos;

Walkera 4#3 Direct Drive DD Tail Test Flight (2 min 48 sec)


Micro Speedster : Walkera 4#3 with the Bell hiller Mod (5 min 11 sec)
Last edited by EQMOD; Nov 20, 2008 at 12:36 AM.
Nov 20, 2008, 12:34 AM
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landru's Avatar
Quote:
Originally Posted by EQMOD
... I actually had a good success in converting a FP head to bell hiller. ...
Hi EQMOD,

Thanks for posting those pictures and animations. I had seen your BH modification before and I was impressed with the strategy of tying the mixing arms together. I bet it offers increased rigidity and hence better durability and consistency.

The photo below shows my own first efforts. Later versions were improved by using more rigid GFK for the mixing arms and ball joints at all connections. The later version worked well for mild-mannered flying but just wasn't up to prolonged vigorous flying. Think mid-air self-disassembly. It also suffered from some inconsistency in control response, due in good part, I think, to the 'cranked' Bell linkages from swash to mixing arm -- a problem addressed by your tie-rod idea. Ball bearings on the mixing arms also seemed like a really good idea, if not an absolute necessity.

Regards,
Andrew
Nov 20, 2008, 03:39 AM
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EQMOD's Avatar
Quote:
Originally Posted by landru
Hi EQMOD,

Thanks for posting those pictures and animations. I had seen your BH modification before and I was impressed with the strategy of tying the mixing arms together. I bet it offers increased rigidity and hence better durability and consistency.

The photo below shows my own first efforts. Later versions were improved by using more rigid GFK for the mixing arms and ball joints at all connections. The later version worked well for mild-mannered flying but just wasn't up to prolonged vigorous flying. Think mid-air self-disassembly. It also suffered from some inconsistency in control response, due in good part, I think, to the 'cranked' Bell linkages from swash to mixing arm -- a problem addressed by your tie-rod idea. Ball bearings on the mixing arms also seemed like a really good idea, if not an absolute necessity.

Regards,
Andrew
Hi Andrew,

Yes. When I first tried the Bell Hiller Mod on the FP head, there was no horizontal bar and just pure mixers. It was difficult to achieve correct blade tracking. Also, cyclics are unstable and twitchy. The H-bar fixed that. The same Horizontal Locking bar actually kept the mixing arms in place and always "synchronized". The main blade grip is moving as a single system which means the bell hiller mixer arms on both side of the grip should also move as a "single system" thus reducing any cyclic pitch discrepancy.

I made a couple of head videos showing the arms in action;

Here is a demo of the head with the mixers, H-bar in action. The ball ended linkages for me i think is the best approach to a bind free movement. If there were binding in any of the links, the flybar will be actually "over the place" as we move the swashplate. In the video below, the flybar has even retained its "leveled" position even if made a couple of random cyclics. I also did a couple of flybar "tap" test to see if its still free to "see-saw"


Micro FP: Bell HIller Test 1 (1 min 32 sec)



Here is a rather "close-up" view of the mixers while i did a couple of cylic movements;

Micro FP: Bell Hiller Test 2 (0 min 36 sec)


And here is a rather unique H-Bar maneuver wherein i held the entire heli through the blade grip and attempted to move the H-bar to-and-fro across the blade grip. Watch the resulting effect on the heli's body


Micro FP: Bell Hiller Test 3 (0 min 23 sec)
Last edited by EQMOD; Nov 20, 2008 at 03:52 AM.
Nov 20, 2008, 07:16 AM
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chrise2's Avatar
I have Hiller FPs and Bell-Hiller CPs. I noticed a difference, but I don't know what I'm noticing more. The FP / CP difference or the Hiller / Bell-Hiller difference. I'm gonna guess its the FP / CP difference. With the flybar weights removed, I think my FP flies fine. For an FP.
Nov 20, 2008, 09:23 AM
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Quote:
Originally Posted by chrise2
I have Hiller FPs and Bell-Hiller CPs. I noticed a difference, but I don't know what I'm noticing more. The FP / CP difference or the Hiller / Bell-Hiller difference. I'm gonna guess its the FP / CP difference. With the flybar weights removed, I think my FP flies fine. For an FP.
The FP/CP difference mainly is on the blade pitch (lift) response, the rest (cyclic, directional) are Hiller-Bell Hiller difference.
Nov 20, 2008, 09:46 AM
Registered User
EQMOD's Avatar

THE MECHANICAL MAJIC of "Bell Hiller" Mixing


THE MECHANICAL MAJIC of "Bell Hiller" Mixing

Here is the "Magic" Mechanics behind the Bell Hiller mixing as demoed on the following video;

Without thinking of the complexities of the mixing arms + pitch Links on bell hiller mixing, imagine two independent systems (a) flybar+paddle and the (b) servo+swashplate dictating the pitch of the main blades. If you independently move the flybar, the main blade (pitch) goes with it. If you also independently move the servo+swashplate, the main blade ALSO goes with it. Now if you "mix" the two independent flybar and swashplate inputs, the pitch of the main blades correspondingly follow and is actually the average (depending on the mixing arm ratio) of the two inputs.

So technically, the swashplate is providing DIRECT cyclic inputs on the main blades for fore+aft controls (aileron/elevator) at the same time the flybar is also providing stabilizing inputs to the blades. The flybar actually STABILIZES the entire system whether there are (or none) cyclic inputs coming from the swash.

That DIRECT input from the swash going to the blades makes the heli's flight response almost instantaneous.


On the following video, watch the PITCH of the main blades as I apply the cyclics from the TX and as i independently move the flybar. Thats "bell hiller" mixing.

Micro FP: Bell Hiller Test 4 (1 min 12 sec)


In Hiller-Only, there is no DIRECT input from the Swashplate going to the main blades. Heli's flight direction is entirely dictated by the state and position of the flybar. The flybar has to change its position first before the heli could start to react on the final state of the flybar and that is the cause of the delay on the cylics which others term them as "sluggish".
Nov 20, 2008, 11:57 AM
dze
dze
Registered User
Quote:
Originally Posted by EQMOD
Was this the rubber-band mod ?
yes .. but honestly heres my hbfp with no bell hiller .. it flys just fine without it and i can fly it harder than my kings with bell hiller simply because im less intimidated coz i know if i crash it the max im going to spend to fix it is maybe 5$ ...
http://www.youtube.com/watch?v=pP5N8m0Olyw


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