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Home✈️Aircraft🚁HelicopterHelicopter Main Discussion › Flight Characteristics of Damper Stiffness on a Helicopter
09-05-2006 11:23 PM  14 years ago
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AnnihilaT

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The Netherlands

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Flight Characteristics of Damper Stiffness on a Helicopter
Hey All,

We have a pretty heated discussion going on in the trex forum about the effects of softer and harder damping on RC helis. Some are of the opininion that changing the damping effects cyclic but not collective. Others are convinced that damping changes will change collective as well to the point of even needing to re-adjust pitch curves. Its an interesting theory and i wonder if some of you experts (or aspiring experts?) could chime in with your opinions on this.




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09-05-2006 11:28 PM  14 years ago
SteveH

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Texas

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I'm not going to claim to be an expert, but in cases of extreemly soft damping, it will effect the collective pitch range and accuracy. The older Hawks with the 5mm feathering shaft and worn out soft dampers are notorious for this.The government cannot give you anything without first taking it from someone else.
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09-05-2006 11:39 PM  14 years ago
3D WASP

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The subject was a good topic for debate. My theory is this...with softer dampening the spindle is allowed to move up in the head block. This causes a "smile" in the blades under hard loads. Briefly giving you that extra little bit of pitch. Creating very crisp collective response, resulting in very sudden stops when you want. Grab your heli and pull up on both blade grips. You can see the relation to pitch from the pitch links, watch what happens. I noticed this after trying hard dampening in my lil Rex. It absolutely killed collective response, the heli flew through a good couple feet. Much more so than with the stock dampening which is much softer.Timing is everything
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09-06-2006 12:07 AM  14 years ago
OICU812

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Well making the dampening stiff makes tic tocs, both elevator and aileron for example much more crisp. Banking in at high speeds does not seem to drift as bad as softer dampening. There has never been any notice of having to change pitch curves for a lack of feel, if anything other than the pyshical changeout of the dampner rings or delrin insert such as a carbon extreme and such the feel for 3D has been much better with stiffer dampening methods. I would think that the mass of pro pilots out there run it is hard as they can, not only for tight feel and crisp stop feel but also for the common knowns such as boomstrikes and tail strikes etc. This is also the obvious second best benifit. FOr sport flying and abit more stable bird the softer to mid grade dampners feel fine, for throwing the poop to it and wanting to carve things up nothing beats a super tight feeling head on the heli imho of course....Once upon a time there were Nitros, flybars and frequency pins...
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09-06-2006 12:21 AM  14 years ago
BJames111

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I don't mean to nit pick, but I want to address one thing:

the word dampening means to moisten, or wetten.

the word damping, is what you are referring to.

the parts are dampers, not dampeners.

The most important thing I know is that with soft dampers if you fly 3d you may get a boom strike. The harder the damping, the less likely this will happen.
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09-06-2006 12:36 AM  14 years ago
OICU812

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Ok dampers, not dampners lol. That is what I meant from my conversation, and also as you had mentioned I as well mean to dampen by the use of stiffer or less stiff dampers yes. As well I agree on the 3D and boom comment. The lift you see is not significant enough, more flex or concern would or should be given to the grade of the blade used, ie: cheap wood Align blades vs a super stiff blade like a Hyperion or a V-Blade for example. Yes the spindle will lift some giving the effect of a lift or movement in the linkages, however that is with a pyshical pull on the end of the tips of the blades, not in flight where there are no lifting pressures on the underneath of the blade and all force is given from the lift itself of the heli, this may not be the way to explain it but I mean by pyhsical force blah blah..etc...Super soft dampers would allow alot of movement yes, but if you are flying 3D of any sort or aiming for precision that would be the worst way to run your heli anyways so why would you??? And would the amount of movement actually cause a need for re pitching the helicopter? Well.... imho if it does it is way too sloppy and just plain wrong.

Softer dampening = softer dampers, sport mild flying
Harder dampening = hard dampers, 3D and aggressive flying

My translation
...Once upon a time there were Nitros, flybars and frequency pins...
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09-06-2006 12:42 AM  14 years ago
BJames111

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uhhh...DAMP, not dampen...

carbon extreme dampers...yes. Infinovation dampers...yes.

mushy dampers? bad...no.
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09-06-2006 12:45 AM  14 years ago
OICU812

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HAH !

...Once upon a time there were Nitros, flybars and frequency pins...
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09-06-2006 01:03 AM  14 years ago
SolarXtreme

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Arroyo Grande, CA

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Others are convinced that damping changes will change collective as well to the point of even needing to re-adjust pitch curves.
This depends on the design of the rotor head. Most traditional systems use a floating spindle design which all share this side effect. Hirobo heads however do not use a floating spindle design and thus damping can be chaged without effect on the collective response of the helicopter.
.
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09-06-2006 01:18 AM  14 years ago
BJames111

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I love the bunny, and pancakes too.
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09-06-2006 02:50 AM  14 years ago
JKos

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Redondo Beach, CA

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How dampers effect the collective response of a heli is going to depend on the head design. If the spindle has a ball or other such method in the middle which removes collective forces from the dampers, then the damper hardness should have little effect on the collective response.

On the other hand, if the dampers have the job of fully supporting the spindle, then damper hardness would most likely have an effect on collective response. Movement of the spindle up and down could either add or subtract pitch from the pilots input. Which effect and how much is going to depend on the head geometry.

- John

EDIT: Sorry, somehow I missed SolarXtreme's post.
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09-06-2006 05:23 AM  14 years ago
OICU812

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Solar pretty much said it well too. But in "general" regardless of the specific heli or head design the same rule of hard dampers or damper system would be more set or adequate for 3D flying and of course on the other seat the softer setup for mild to moderate flying styles. Be well. ...Once upon a time there were Nitros, flybars and frequency pins...
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09-06-2006 05:37 AM  14 years ago
TMoore

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Cookeville, TN

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Wayne Mann would be the authority on this as would several others that come to mind. I still prefer to call the so called dampers/dampners, whatever, in the head "teeter rubbers" as that is what the feathering spindle is trying to do in flight and the orings are trying to constrain this action.

The Hirobo system in general is an underslung teetering hub and this reacts differently to a feathering spindle that is constrained by tetter rubbers.

TM
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09-06-2006 07:23 AM  14 years ago
nocontrol

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Cape Town, South Africa

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In my opinion, looking at Vibe head - Softer dampers less pitch under load conditions. Lets say: from ball on blade grip to servo's there is no play and spindel is solid mounted and you dump hard and then then give +10 degrees pitch you will have +10 degrees pitch. Now if the spindel is in very soft rubber and you do the same dump with stopping it with +10 degrees there will be load on this soft rubber, the spindle will be pushed up and you will have less pitch, The more the spindle moves up the less pitch you will have under load.
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09-06-2006 09:16 AM  14 years ago
CK_

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Redondo Beach, CA

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The dampers on our models work as both flapping springs and flapping dampers. The harder the damper, the higher the spring effect and the lower the damper effect and vice versa. A component of damping also comes aerodynamically from the rotor blades and increases as headspeed increases. If the ratio of total stiffness to total damping is too high, it will lead to oscillations or wobbling, especially after a hard cyclic input. (Think of stiff springs in your car when your struts are shot) This is why a stiff head will wobble at low headspeed but will smooth out at higher headspeeds. At higher headspeeds the aerodynamic damping increases and the ratio of stiffness to damping falls. Other things can affect stiffness or damping. With a flapping hinge offset like the old concept 30 head, centrifugal force will make a headspeed dependant flapping spring. The delta of the head also creates an aerodynamic flapping spring which is headspeed dependant.
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09-06-2006 09:25 AM  14 years ago
AnnihilaT

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Yes its an interesting point that this is affected by the design of the head as well. For example, on the Synergy you have a delrin sleeve which fits over the feathering spindle. This sleeve has a larger OD in the center of it than it has on the ends. Effectively what this does is support the spindle in the middle of the head and allows the spindle to teeter but prevents it from moving up or down when the dampers become loaded.

On the Raptors you have a different design of the same function. There is a ball raced pin / cog which goes thru the middle of the head with a hole in it. The spindle then fits thru this hole. This also allows the spindle to teeter only and not move up or down in height.

I guess more specifically the question should be, whether or not it could in fact be possible, that a spindle which is supported at either side by ONLY dampers, could actually cause a significant and noticeable change in collective response when the stiffness or durometer of the dampers are changed.




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09-06-2006 09:48 AM  14 years ago
Gyronut

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Martinsville In.

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My model 1001 xcell is only supported at the ends by 1 50D oring on each end and most definetly has plenty of room to move in the "Z" axis.Rick
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09-06-2006 04:19 PM  14 years ago
ChristianM

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Oslo, Norway

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JKos and SolarXtreme has got it right. If the spindle is supported in the middle of the hub then the load from changing collective pitch will not put a load on the dampers and thus have not effect.

However, in the original question it was referred to the Trex forum. I don't know about the 600 but the 450 does NOT have a support for the spindle in the hub so the dampers will have some effect on the collective pitch. The trex has non-corrective delta so if you add pitch, the spindle will move slightly upwards and compress the dampers as the heli accelerates. This movement will add a small amount of additional pitch. The softer the damper is the bigger this effect will be.

As others have discussed it does have a big influence on the cyclic. For 3D you want hard dampers.

Christian
Burn fuel, be happy
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