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HomeAircraftHelicopterAerobatic FAI F3C F3N Contest › Trim shifting in wind
06-02-2009 09:36 PM  9 years agoPost 1
fgf no

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norway

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Hi all
I have a Raptor 90se which I am trying to set up for contest flying.
When the model hovers nose into the wind,it`s fairly stable,but when I do a 180 pirouette,ending up tail into the wind,the model wants to back up against the wind and to the right.
Can anyone try to explain to me why this is,and how I can minimize this effect?
The model is balanced fore/aft with 3/4 full tank,and has no such tendencies in calm conditions.
I realize I will have to do some corrections, but would like advice on how to make the model a bit less sensitive to this effect....
The model is also a bit "bouncy" in windy conditions, any advice on how to reduce this is also appreciated....

My current setup is as follows:
- Radix 710 (tried SAB 690 fai and K&S 680 fai)
- TT black paddles (tried some K&S,but liked the standard TT paddles better)
- Infinivation dampeners (tried TT blue ones as well)
- 570 mm flybar (standard is 520mm)
- Inner hole on the mixer arms (0,85? flybar ratio,standard is 1:1)
- Headspeed in normal mode is around 1650rpm
- Metal blade grips (standard Raptor 90 se)

Any advice on how to make the model sit better in a hover would be much appreciated

geir

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06-02-2009 10:09 PM  9 years agoPost 2
Dr.Ben

rrMaster

Richmond, VA, USA

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I read you to mean it's tucking INTO/towards the breeze when tail in, right?

Ben

Peak Aircraft/Team Minicopter Team Futaba Team Kontronik USA

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06-03-2009 06:08 AM  9 years agoPost 3
fgf no

rrNovice

norway

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I read you to mean it's tucking INTO/towards the breeze when tail in, right?
Yes, it wants to tuck into the wind, when the tail is into the wind.
It does not do it, when nose into the wind....

geir

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06-03-2009 08:42 AM  9 years agoPost 4
Spacey

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Pretoria, South Africa

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Trim will change slightly as you piro the model in wind, mainly due to the change in drag induced by wind over the mechanics. Nose into the wind your model's most streamlined as far as the pod is concerned, tail into the wind and it's the complete opposite again. So the wind will literally blow the pod away more making the disc tilt into the wind.

Your delta mixing due to this scenario also gets interesting which is giving you the right trim change you're experiencing.

Slap a set of weights on the flybar and keep moving them out from the centre very little by little and keep flying the model after each change checking how the trim's now as you piro it. Find a middle ground and then work on stick skills. Sounds like your flybar length is already in the ballpark so a set of weights should to the trick.

Play with the pitch curves if the model's bouncy on the stick, just flatten the curve around the hovering area. Next thing to try is play with headspeeds to make the blades less bouncy in the wind, you need to find the blades's sweetspot.

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06-03-2009 12:29 PM  9 years agoPost 5
ErichF

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Sutton, NH

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If the heli counters into the wind, your flybar is working too much, as well. Try using a shorter flybar (500-ish mm) as well as the weights Spacey mentioned.

Erich

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06-03-2009 12:44 PM  9 years agoPost 6
Spacey

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Pretoria, South Africa

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I wouldn't go to a shorter flybar just yet, the fact that the model's ok nose into the wind leads me to think the flybar's pretty close to perfect. Of course Eric you're absolutely correct, we also can't be sure if the model's maybe been trimmed alot to get it sitting nose into the wind, which of course makes matters worse when it's turned around.

Either way I'd try the weights first, change one thing at a time and be sure of the results.

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06-03-2009 01:42 PM  9 years agoPost 7
ErichF

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Sutton, NH

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we also can't be sure if the model's maybe been trimmed alot to get it sitting nose into the wind, which of course makes matters worse when it's turned around.
That was exactly my thought. And yes, only change one major item at a time, because there will be trade-offs for each thing changed. For example, a shorter flybar will reduce your roll rate upstairs, requiring you to increase your servo rates, which will upset any mixes you may have programmed to fix a roll excursion. This is where it all gets fun

Erich

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06-03-2009 01:48 PM  9 years agoPost 8
Bruce Naylor

rrApprentice

Swindon, Wiltshire, UK

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So how does head teeter (soft or hard) come into the mix here?

Personal experience with my setup seems to suggest that a softer head helps in gusty conditions - I run zero delta offset. Is that true for all setups? (ie +delta, -delta, head speeds etc)

B.

"If you know what you're doing, you're not learning much"

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06-03-2009 03:48 PM  9 years agoPost 9
fgf no

rrNovice

norway

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Thanks for your replies

A little more info on my setup:

I already have weights installed on the flybar (the ones that come with Stubz paddles). All the way out seems to be more stable than all the way in....
The model hovers well with no elevator trim,and 4-6 clicks of aileron trim. (I have used weigths up front to eliminate elevator trim)
Swashplate is perpendicular to mainshaft,and all levers is level.

I would prefer to not go to a shorter flybar,as I feel the rollrate would be to slow (currently about 2 seconds to complete a roll).I currently run 6,5 degrees of cyclic pitch in idleup.

As for headspeed, I would not mind going lower than 1650,but lower will induce oscillation (very visible in the landing gear),with my current setup
Find a middle ground and then work on stick skills.
This is most likely where the answer lies lol

geir

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06-04-2009 01:43 AM  9 years agoPost 10
Dr.Ben

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Richmond, VA, USA

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Nothing beats practice, but be aware that the flybar ratio of that RSE model can be as high as 100%. Ratios this high will often cause the model to tuck into the wind as you're noting. I would be highly inclined to reduce the flybar ratio in 5-10% increments until you see the model just start to drift with the wind in a good breeze. You can set it to hold its position, but what you'll find is that neutral trim may be highly wind speed sensitive and in a stiffer breeze the model might try to tuck again. A slight drift gives you a little leeway.

Ben Minor

Peak Aircraft/Team Minicopter Team Futaba Team Kontronik USA

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06-04-2009 06:01 AM  9 years agoPost 11
Spacey

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Pretoria, South Africa

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Geir,

You could also perhaps go back to playing with different paddles if you're worried about roll rate vs stability. The size, shape and design will all play a part in these factors. Why alot of guys love the newer K&S F3C paddles so much, very stable and easy to use in hovering but still good roll rates. I believe the Rotortech's may be even better.

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06-04-2009 03:54 PM  9 years agoPost 12
fgf no

rrNovice

norway

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Thanks again for your replies

I went out to the field yesterday evening to practice,and it blew pretty hard.
I decided to lower the headspeed quite a bit,and it seemed to help a lot.I did not tach it, but I would guess it ended up below 1500rpm.
The model was a lot "calmer", which gave me more time to input corrections. I might have to go back to the softer blue TT dampeners, so I can run the headspeed this low without getting oscillation.
Another thing I noticed,was that when nose into the wind, the model wanted to back up, but like I said, it was quite windy, and it is OK in calmer conditions.....
As for paddles,I will probably get a set of the Rotortech paddles to try out.
but be aware that the flybar ratio of that RSE model can be as high as 100%. Ratios this high will often cause the model to tuck into the wind as you're noting. I would be highly inclined to reduce the flybar ratio in 5-10% increments until you see the model just start to drift with the wind in a good breeze.
As far as I know, the R 90se only has two available flybar ratios,giving either 1:1 or around 0,85:1 (Please correct me if I am wrong, but flybar ratio is determined by which hole on the seesaw the mixer arms are attached to, with the outer hole giving a 1:1 ratio?)

geir

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06-04-2009 04:10 PM  9 years agoPost 13
Dr.Ben

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Richmond, VA, USA

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85% might work quite well. The other choices are created with a drill bit <g>.

Ben

Peak Aircraft/Team Minicopter Team Futaba Team Kontronik USA

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06-04-2009 04:46 PM  9 years agoPost 14
fgf no

rrNovice

norway

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The other choices are created with a drill bit <g>.
That would include modyfying a set of mixerarms, but could be done...
Did it to my R50 titan with great success....

Do you think an even lower mixer ratio would be better?

geir

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06-07-2009 05:36 AM  9 years agoPost 15
Dr.Ben

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Richmond, VA, USA

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Interestingly enough, 100% flybar authority is often not the key to the best hovering model because such set up often tucks into the wind as you're seeing on your model. The SSR-VII is another example of what too high a f/b ratio can do to the way a head works in the wind.

I've personally seen everything from 65% to 90+% work well depending on the head design, so don't be afraid to dial your f/b back just a bit and see if the model becomes more predictable in the wind.

I won't even begin to muddy this discussion by layering in how negative delta will contribute to the cyclic stability of the model......

Ben Minor

Peak Aircraft/Team Minicopter Team Futaba Team Kontronik USA

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08-10-2009 09:18 PM  9 years agoPost 16
R.J.

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SF bay area, CA USA

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Dr. Ben,

Is the flybar ratio a personal preference, or for hovering does one try to run as high a flybar ratio as possible without having the model tuck into the wind?

Is there a disadvantage to a high flybar ratio in the forward flight maneuvers?

The model I am working with is a MA Fury with Hirobo FFZ-III head, SSR-V #60 dampers, old Hirobo paddles with sticker covering from Tsurugi, and longer TT Raptor 90 flybar. Thanks.

Regards,
Rick

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08-11-2009 04:46 AM  9 years agoPost 17
Dr.Ben

rrMaster

Richmond, VA, USA

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Is the flybar ratio a personal preference, or for hovering does one try to run as high a flybar ratio as possible without having the model tuck into the wind?

>>Taste does play into it, but most of us will try to have the model sit reasonably still in a good breeze and maybe drift a little in less of one. I can tell you that it is thoroughly unnatural to have a model go INTO a stiff breeze. The needed correction feels pretty weird. Most of us have learned from day one to hold a model against the wind, not with it.

Is there a disadvantage to a high flybar ratio in the forward flight maneuvers?

>>Within reason, no. The reason part of this relates to the inherent stabilizing effect of the flybar when the ratio gets higher. You may find a need for more cyclic pitch range, paddle deflection, or even paddles area to correct for this and thus achieve the roll rate you require. At least with a contest model, you'll RARELY have a situation where a flybar ratio optimized for correct hovering performance then has to be itself retweaked for the aeros. ALSO, if you make a change which increases flybar ratio, most head designs with a sliding swashplate and mixers mounted elsewhere besides pivoting on the flybar will see a corresponding decrease in cyclic pitch and collective range. So, to keep the model's pitch and roll rates the same as they were before you raised the flybar ratio, you'll need to increase the cyclic and PIT AFR's. The nice things about a good flybar ratio upstairs are that it improves the straight line tracking and resistance to wind induced course deviations, pitchiness, and so forth.

The model I am working with is a MA Fury with Hirobo FFZ-III head, SSR-V #60 dampers, old Hirobo paddles with sticker covering from Tsurugi, and longer TT Raptor 90 flybar. Thanks.

>>With that head, we generally ran with the ball in the outermost hole in the bell mixer an the second hole out from the one closest to pivot bolt of that bell mixer. The hole closest to the pivot bolt tends to kill too much collective and cyclic range for what you can reasonably recover with more swash travel. The long flybar is not often asset in hover with that head, esp in the wind. A 480-490mm flybar works well. Make sure those paddles weigh about 40g for best hovering. The head has enough control authority upstairs to maintain good pitch and roll rates with that paddles weight and 6 or 7 D of cyclic.

Ben Minor

Peak Aircraft/Team Minicopter Team Futaba Team Kontronik USA

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08-11-2009 05:41 AM  9 years agoPost 18
R.J.

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SF bay area, CA USA

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Dr. Ben,

Thank you for the detailed explanations and recommended settings. I will try to achieve the setup criteria you outlined. Thanks again for your help.

Regards,
Rick

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08-11-2009 04:57 PM  9 years agoPost 19
teamdavey2001

rrApprentice

Sunnyvale, California, USA

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"I won't even begin to muddy this discussion by layering in how negative delta will contribute to the cyclic stability of the model......"

Dr. Ben, which way round are you using "negative" here. That is: do you mean reducing pitch as the blade rises or.....

Regards

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08-12-2009 01:56 PM  9 years agoPost 20
Dr.Ben

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Richmond, VA, USA

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Neither.... "negative" is another term for noncorrecting delta. You can have either kind of delta (positive or negative) with both LE and TE head designs depending on where the pick off on the pitch arm lies relative to the center of the rotor head. Noncorrecting/negative delta favors cyclic stability over collective stability. Correcting delta is the other opposite. Lots of either are rarely a good thing overall.

Ben Minor

Peak Aircraft/Team Minicopter Team Futaba Team Kontronik USA

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