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JR-Spektrum . E-flite . Futaba-RC

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Aerobatic FAI F3C Contest > how to alter delta
 
 
Maxime
Senior Heliman
Location: Belgium

how do you change the delta offset on plastic blade grips?

I don't see any manufacturers who make parts or kits for this?

thanks
02-01-2008 09:15 PM
 
 
irocu88
Senior Heliman
Location: norfolk,va

Changing the delta is a matter of changing the length of ball stud on the grip in relation to the flybar (if I explained that right). Century sell various length ball studs depending on how far you want to go. At least thats my understanding of delta, if not someone will chime in.

Caliber 90 FT os91 c-spec
Caliber 50, OS50 hyper
Caliber 30 OS37
02-01-2008 09:38 PM
 
 
Wayne Mann
Senior Heliman
Location: United States of America

Hi guys,

It depends on a few things. If the bell mixers are bolted to the fly bar carrier like on a Hirobo head or a JR Vibe head, it is very easy to adjust the amount of delta. There is a ball in the end of the blade mount pitch arm. The push rod that controls the pitch in the blades hooks to this ball. To change the amount of and the type of delta (correcting or uncorrecting) you simply extend that ball further from the center of the rotor head in either direction, depending on which type of delta you desire. If the rotor head has no delta offset then the pitch arm ball will be directly over or under the fly bar.

If the bell mixer pivots on the blade mount pitch arm like on an X-Cell rotor head you have to move the pivot point of the bell mixer off center to one side or the other.

I hope this helps


Wayne Mann
02-02-2008 03:34 AM
 
 
jgoodsell
Heliman
Location: Sherbrooke, Québec, Canada

So a Picco heli, with it's 20 degre or so fly bar has lot's of corecting delta ?

Am I corect in this interpretation !??

It seams that Gravity is worst around here !
02-02-2008 12:01 PM
HOMEPAGE  
 
 
Wayne Mann
Senior Heliman
Location: United States of America

You would have to give me a link to a picture that shows the rotor head as I have no idea what the rotor head looks like.


Wayne Mann
02-02-2008 07:22 PM
 
 
Bruce Naylor
Senior Heliman
Location: Swindon, Wiltshire, UK

Question: If a spindle head is only supported by o-rings at either end, and these are both compressed holding the weight of the heli (either in the hover, or during aeros), is the centre of teeter the center of head, or is it offset towards one or other o-ring?

How does this affect ball lenghts to alter delta?

Are these style heads in fact displaying auto-adjustable delta?

Bruce.

"If you know what you're doing, you're not learning much"
02-03-2008 09:15 AM
 
 
Wayne Mann
Senior Heliman
Location: United States of America

Hi Bruce,

Yes the center of the axle is still the center of lift. Both O rings should be compressed evenly. Depending on how stiff the dampers are set up will determine how much the axle lags back into the dampers when torque is applied to the system. Even if you have no delta in the machine when it is sitting on the table it will have some delta once the rotor head is under load. How much depends on how stiff the dampers are and a few other factors.


Wayne Mann
02-03-2008 03:00 PM
 
 
Chris.C
Senior Heliman
Location: Hong Kong

Wouldn't it be better to have a pin in the middle of the axle like the 06 head so that the dampers are off-loaded of the weight of the choppers and do the work of damping?

So what is the advantage of full floating the axle?

Chris
02-04-2008 04:08 AM
 
 
Wayne Mann
Senior Heliman
Location: United States of America

Hi Chris,

No, having the axle supported by ball bearings like the 06 Caliber 90 does makes the model a lot less stable. Most of the competitors at the worlds in Poland were using a special made round 8 mm axle. The rotorhead is much more stable when you allow the axle to load up against the dampers.

Wayne Mann
02-04-2008 05:02 AM
 
 
Maxime
Senior Heliman
Location: Belgium

but this is only the case in the 06 caliber head, and so only with correcting delta(preferably hard dampers also)?

were the competitors in Poland using a center sleeve over the axle between the dampers? what about altering a center bearing support, with a damper in the middle of the bearing supported axle? that way it only allows the axle to free float to a certain amount, but the center damper restricts the vertical axle movement
02-04-2008 08:58 AM
 
 
Bruce Naylor
Senior Heliman
Location: Swindon, Wiltshire, UK

A model performing a loop with a floating shaft must excert more load on one rubber than the other since a blade will be creating more lift for part of the rotation of the head. The other blade will be in the same position some 180 degrees later, transfering the loading to the other rubber. Since this exchange of loading happens around 50 times a second, I would assume that the average lift would therefor mean to the centre of the head.

I too have noted the destabalising effects in the hover of a centre pivot over a floating shaft, but as Wayne notes, lead/lag starts to cause a problem (accuracy of loops, rolls etc). Stiffening up the teeter helps some - it's just another trade-off we have to live with, until some bright spark finds a simple solution.

Not sure whether a centre soft piviot would help or hinder - the harder it gets, the closer we get back to the destabalising effect of the hard center, so why should a soft one help?

"If you know what you're doing, you're not learning much"
02-04-2008 11:41 PM
 
 
Wayne Mann
Senior Heliman
Location: United States of America

Any type of center support will cause undesired effects on cyclic stability. When I was still using uncorrecting delta I ran two long set screws (one from each side) into the threaded hole in the center of the axle on the 06 head and tightened them up against each other. This gave the axle the ability to lead and lag and move vertically a small amount. I then threaded a short piece of of fuel tubing onto the exposed set screw from each side. If you are running uncorrecting delta with metal blade grips, with a free floating axle you must use the above method or either use a ball on the center of the axle to limit vertical movement.


Wayne Mann
02-05-2008 01:15 AM
 
 
RCHelicopterGuy
Veteran
Location: Michigan

Wayne,

Unless I misunderstood what you said, didn't you just describe the Raptor 90's head axle design?

The head axle is supported by large dampers on each side of the head block, but the axle itself runs through a solid shaft that has a hole drilled through the center which allows the axle to pass through. This shaft extends out through the sides of the head block, and pivots in two large bearings.

As such, the axle can only pivot along the blade grip axis. It's physically restrained from having any lead-lag motion in the head block.

I'm trying to picture in my mind the way the 06 Caliber's head is designed, but I've never seen one up close.



EDIT: I had to re-read what's been written. Are you saying that you want lead-lag but not vertical restraint?

I'm so confused!
02-05-2008 02:25 AM
 
 
Wayne Mann
Senior Heliman
Location: United States of America

Hi Shawn,

I want the axle to be able to lead and lag, but I do not want the center of the axle to be able to move up and down as this causes collective problems.

The Raptor rotor head that you have pictured is the same in principle as the 06 Caliber 90 head and nobody likes the way it flies with the ball bearing pivots.


Wayne Mann
02-05-2008 05:36 AM
 
 
Wayne Mann
Senior Heliman
Location: United States of America

Hi Bruce,

No actually when I run a good amount of uncorrecting delta I use very soft dampers which allows the axle to lag into the dampers quite a bit. This has no ill effect on the way the model does aerobatics. Actually I think the model rolls a lot truer with that set up.


Wayne Mann
02-05-2008 05:40 AM
 
 
F3CWNB
Senior Heliman
Location: Napier, New Zealand

Wayne

Quote 
Any type of center support will cause undesired effects on cyclic stability.

can you please explaine what you mean by this esp with regard to the Hirobo type head.

Regards, Colin

'Life' is Looking Up!!!
02-05-2008 06:23 AM
 
 
Wayne Mann
Senior Heliman
Location: United States of America

Hi Colin,

I should have made it more clear that I was strictly talking about an axle head with either ball bearings in the sides of the rotor head yoke that the axle pivots on or a free floating axle design that may or may not have a ball or piece of fuel tubing on the center part of the axle which would be put there to support the lifting loads and take those loads off of the dampers.

The Hirobo heads are of the off center teeter type where the head yoke itself teeters relative to the head block. Also the teeter bearings are off center relative to the through line that would extend through from the center of the blade grip bearings from one grip to the other. The off center teeter rotor heads respond differently to delta inputs. These type of rotor heads fly very similar to a solid axle head with correcting delta and stiff dampers. What this means is that there is a lot of trim change when the wind hits one side of the model verses the other. Example: If the model is trimmed so that it hovers hands off in calm winds and you turn the model sideways to the wind with a steady breeze blowing the model is going to want to nose down and go into forward flight with the wind hitting the right side of the model and it will nose up and back up at a fairly quick pace if the wind hits it from the left side. If the model is mechanically balanced (nose weight) so that it hovers on fore and aft cyclic in calm winds with a perfectly level swash plate it will try to go forward or backwards depending on the wind direction, at the same speed. It is because of this characteristic that I do not like off center teeter heads. Although I should mention that my Caliber's in Poland were set up with correcting delta and very stiff dampers to help me with the very strong winds that we were flying in. That set up is much easier to hang onto when the conditons are brutal. I wish that I had had a couple more months to get used to that set up prior to the worlds as the trim change during pirouettes in that much wind was very difficult to handle.

I hope this helps.


Wayne Mann
02-05-2008 07:31 AM
 
 
F3CWNB
Senior Heliman
Location: Napier, New Zealand

Thanks Wayne

I always appreciate the input from experienced F3C Pilots like yourself, Thanks for your time...

The characteristic of moving to the left of the wind is one that has caused me to scratch my head in the past with not only the Hirobo heads but also the Concept heads (completely different animal I know) were very bad for this and for that matter so was my Caliber M50 (generally these heads have correcting delta –although the early Eagle has non-correcting delta and still suffers from this problem). On the other hand my X-spec with the FFZ-II head does not suffer from this 90* drift, and it has non-correcting delta. Your comments on this matter lead me to think that I may have to live with this characteristic on the Hirobo head, but somehow I don’t think that Hashimoto would accept this sort of behaviour from his heli’s.

I know this is a leading question – but is there another avenue to alleviate this problem (does heavier blades help? Blade profile?)...

Thanks once again...

...Next time you are in New Zealand I will buy you a beer of something....

Colin

'Life' is Looking Up!!!
02-05-2008 08:26 AM
 
 
Wayne Mann
Senior Heliman
Location: United States of America

Hi Colin,

You would be very surprised about Mr. Hashimoto's model. He flies it with no program mixers and the model is quite tail heavy in the air. The pilots in Japan do not use the same methods of set up that a lot of the pilots in the rest of the world use. I have flown one of Mr. Dobashi's machines and Mr. Sensui's machines and they goth fly like crap compared to my machines, but this is because they do not add nose weight to get the machines to hover with a level swash plate and they do not use mixers to fix roll problems. They fly the sticks and fix everything MANUALLY. After flying their machines I now have an extreme amount of respect for their piloting abilities.

Can you take a better picture of your FZZ-11 rotor head and put it either here or in your gallery as I would like to see how it is made? It is the normal off center teeter hinge or has Hirobo changed the damping arrangement?



Wayne Mann
02-05-2008 02:28 PM
 
 
RCHelicopterGuy
Veteran
Location: Michigan

Wayne,

If I'm not mistaken, I think this is the partial metal version of the FFZ-II (picture taken from Erich's gallery)

02-05-2008 08:26 PM
 
 
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Aerobatic FAI F3C Contest > how to alter delta
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