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HomeAircraftHelicopterMain Discussion › Are there any heads out there that are totally rigid?
04-25-2013 04:53 PM  5 years agoPost 1
Machinehead01

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Lower Michigan

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Are dampners really required? What are the pros and cons of a totally rigid head? I know blance would have to almost perfect, but what else might it need? I can build such a head, but was wondering would it be worth the effort?

Tom

"You judge according to the flesh; I am not judging anyone."

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04-25-2013 06:04 PM  5 years agoPost 2
MartyH

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USA

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In general a tighter head is going to react more quickly. I have had such hard bushings and shims in a head before that I wondered if they shouldn't just be aluminum slugs! I generally like a medium hard bushing to be easier on the control links and servos.

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04-25-2013 06:31 PM  5 years agoPost 3
Santiago P

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South West, Ohio

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Are dampners really required?
in some form YES
know blance would have to almost perfect, but what else might it need?
Is not just about balance, this is not a wheel spining around; there a whole lot more going on...

.

Gentlemen,

A rotor head is always going in and out of unsteady aerodynamic conditions that produce anywhere from mild to harsh vibrations.

ALL ROTORS, including full size, are designed with some dampening mechanism in mind. The dampening can occur in the head, or in some newer multiblade rotors with rigid heads, the dampening is designed in the blade root or shank. These would NOT be practical alternative for our 3D oriented toys.

For best maneuverability, a more rigid system is better, but still must be damped somehow.

Fully rigid rotor systems are intolerable of resonant nodes, so all related structures including how the mass of the helicopter hangs below has to be taken into account.

Fortunately, most of the higher amplitude nodes are lower frequency and can be avoided by turning higher RPM, but the rotor and the helicopter frame must STILL deal with transient vibrations that if not dampened, can & do accelerate material and component fatigue and cause failures.

Control systems don't like that either. Everything gets pounded down to control links, servos, MEMS, frames, fuel tanks, etc.

Aircraft systems design has always been a game of trades, you must give something to gain something else. Heli rotor systems are no exception.

your friendly shoe salesman

Santiago

Team Minicopter - PeakAircraft.com
bavarianDEMON- Team Kontronik - Scorpion Motors-

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04-25-2013 07:07 PM  5 years agoPost 4
dkshema

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Cedar Rapids, IA

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The head needs to be able to work with the constant leading,lagging, and flapping up/down of the rotor blades every revolution. The blade attachment bolts help address the lead/lag issue, but flapping is still a problem.

There are some videos out there where a heli manufacturer mounted a camera on the head of their helicopter, looking outward, at a single rotor blade. The one I've seen was on a Sikorsky S-55 many years ago.

The blade itself looked like a noodle as it went round and round, and the amount up up/down flapping excursion it saw was quite impressive. Somewhere, the head and/or rotor system needs to deal with that, otherwise you'll end up back in the development of the helicopter about where it was in the early 1930's, wondering why your heli simply disintegrated before your eyes.

-----
Dave

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

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04-25-2013 11:22 PM  5 years agoPost 5
fenderstrat

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Aston,Pa

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the Warp 360 has a rigid head with respect to the fact that there are no dampers.Cf grips provide a slight damping effect but there are no replaceable dampers.

I dont have one yet but reports are it flys well with high or low headspeeds

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04-26-2013 01:05 AM  5 years agoPost 6
cmsilvoy

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Durham, NC

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The JR MB series are rigid heads with absolutely no dampening.
I have flown others from 50 size down to a Gaui head for the 450 that had no dampening.

I will tell you that most of these systems worked great with glass blades, with the blades acting as dampeners.

Specifically, one MB head that I flew back in 2004 worked great with Funkey glass 550's and when I tried to hop it up with a set of custom Vblades it SUCKED because the blades were way too rigid.

The JR series that I am flying now seems to be working great, but then the blades are balanced perfectly and the machine is electric so there are less vibrations throughout the machine than with the old nitro stuff. I have to think that this has something to do with my current level of success.
The blade itself looked like a noodle as it went round and round, and the amount up up/down flapping excursion it saw was quite impressive. Somewhere, the head and/or rotor system needs to deal with that, otherwise you'll end up back in the development of the helicopter about where it was in the early 1930's, wondering why your heli simply disintegrated before your eyes.
Unfortunately, our models do not abide in any way to the rules of conventional rotor blade dynamics..In MANY ways we are blazing into new territory with our carbon blades and high headspeeds.

Chris

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04-26-2013 03:27 AM  5 years agoPost 7
Gary Jenkins

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Nowhere, US

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You should build a head with no dampers and you'll learn from experience. A monster truck without dampener would be a real thrill ride.

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04-26-2013 03:36 AM  5 years agoPost 8
GetToDaChopper

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Las Vegas , NV

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sure, they are called tail rotors ! lol

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04-26-2013 04:38 AM  5 years agoPost 9
Machinehead01

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Lower Michigan

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In defense of the tail rotor though...
The amount of pitch is consistent for the full 360 degress of rotation.

cmsilvoy. You are on par to what I was thinking. I have seen some of the multibladed heads out there and for the most part they don't appear to have any dampening either. The reason I asked this question is that I have a piece of titanium that is big enough to make a head block with an incorporated spindle. The head block would be threaded in the tips of the spindle but the head and spindle would be all one piece. I don't want to waste the material if it doesn't work.

Tom

"You judge according to the flesh; I am not judging anyone."

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04-26-2013 06:28 AM  5 years agoPost 10
DougPenhall

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San Jose, CA - USA

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I believe it would be prudent to make a prototype out of cheaper material and test it before trying it with your piece of titanium. Even if it would work, getting it right I'm sure would require a few itterations and experimentation.

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04-26-2013 06:56 AM  5 years agoPost 11
Chris.C

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Hong Kong

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I have the JR MB391 3 blades head in my Sylphide. Yes, the head is near complete rigid. I think part of the equation is in the blades that JR recommends to use. Even though these blades are carbon and take the shape like their F3C blades, but they have a little flex built into it lengthwise.

In flight(CGY750 with standard setting), there is no wobble, oscillation, pitching up & down in FFF. One thing though that the whole combo is not very sensitive to pitch change, meaning I have to move the collective pitch stick a little more to get the same response I want that similar to my Sylphide with fly-bar head, even though both heads are using 720mm blades.

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04-26-2013 11:25 AM  5 years agoPost 12
cmsilvoy

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Durham, NC

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Another thought.....
there was a Japanese pilot, circa 2003, who was flying a Raptor 90 in 3D masters with a completely rigid head.
I remember that being the hottest helicopter there.
Wish i could remember the pilot. I will try to check it out for you...

Chris

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04-26-2013 02:58 PM  5 years agoPost 13
Santiago P

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South West, Ohio

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Guys,

Like I pointed earlier.

A fully rigid head is possible, provided you do not operate within any of the entire machine resonant nodes. Even so, the compromise is that you will pound every rotor vibration to the entire heli.

It makes for a attention deficit disorder helicopter, where you constantly have to check it for parts fatiguing, or vibrate to failure, and electronic component hell.

The other options is to use flexible propellers like Chris mentioned with the systems using glass blades. Also, the more blades, the smoother the system.

a heli rotor is always in and out of unsteady conditions
they vibrate ALL THE TIME, some vibes are low amplitude, some higher
for the system to operate smoothly something has to give
If you make everything rigid
something eventually will give

.

FWIW:
In so many years participating in this hobby, I've seen nothing that gets more compliments than a smooth running and reliable machine.
But lately, in this era of rotor heads with hacked-jobs-control-arrangements that required stupid stiff dampeners, too many have lost perspective of what a proper 2 blade head should be designed like.

Santiago

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04-26-2013 06:31 PM  5 years agoPost 14
BobOD

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New York- USA

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Well stated Santiago. There are designs out there with no benefit that I can see except to save the difference of a few dollars of extra parts, at the expense of not having the option to dampen optimally. It works but isn't possible to be optimum.

Team POP Secret

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04-26-2013 10:09 PM  5 years agoPost 15
Daved Gutierrez

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Chicago, IL

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Here's a video of Kazuya Yamaguchi(from Taiwan) flying his Raptor 90 with no dampening, very high headspeed judging by the sound.
http://m.youtube.com/watch?v=AgBYC3...feature=related

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04-27-2013 12:04 AM  5 years agoPost 16
GetToDaChopper

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Las Vegas , NV

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hacked-jobs-control-arrangements that required stupid stiff dampeners
And god help your heli if those dampeners should start to loosen up and you don't notice it ! bye bye heli starting with it's boom first !!!

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04-27-2013 01:31 AM  5 years agoPost 17
BobOD

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New York- USA

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Are there any heads out there that are totally rigid?
Start a thread titled, " (Blank) helis are the best".

Just fill in the blank with manufacturer of you're choosing.

You'll find a plethora of rigid heads.

Team POP Secret

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04-27-2013 01:33 AM  5 years agoPost 18
cmsilvoy

rrKey Veteran

Durham, NC

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Here's a video of Kazuya Yamaguchi(from Taiwan) flying his Raptor 90 with no dampening, very high headspeed judging by the sound.
That's it Daved!!!
So, I was a year off, but you knew just what I was talking about!!!

And, to think, he WAS running a high headspeed at the time (probably 2200 rpm), and everyone thought he was insane...
Flashback to IRCHA 2012 runnning 700mm blades at 2400 rpm

This guy was ahead of his time, for sure...

Chris

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04-27-2013 02:33 AM  5 years agoPost 19
Daved Gutierrez

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Chicago, IL

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He sure was ahead of it's time.

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04-27-2013 11:59 AM  5 years agoPost 20
icanfly

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ontario

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A ridged head might be less attractive if weight is a concern. When you remove the dampers the shoulders of both clamp and head body can bind under load, Alas there is a solution but adds weight.

On a ridged head a clamp bolt will flex under load much like a bolt will stretch under torque. An assembly without dampers would have to be heavier, larger clamp bolt, feathering shaft, bearings, to withstand loading. The shoulder of a clamp bolt should be recessed into the head and not have threads where the two meet.

You see, I have a bent feathering shaaft. If it had no dampers all the stress in a swash event, crash, or blade strike with earth/object, would transmit somewhere. Dampers allow the feathering shaft to absorb load flex while putting space between the parts and removing stress from the bolt.

When you're building a multi blade head STUDS are the best way to to fasten clamps to the body.

Consider harmonic nodes. When you add pitch to one half of a disc revolution at 2400 rpm for example, you are inducing a 2400 cycle per minute vibration to the entire heli. Add blade wake slap aka blade farts, and the harmonic is increased in intensity.

Why a softer blade is slower? A; it twists. When the blade is pitched nearest to the main shaft pitch actuation is immediate. Further out toward the tips pitch is delayed. It's possible to correct for this by rotating the swash events in advance slightly. The blade also flexes up more at the tips while bringing it back to level 2400 times a minute is no easy feat and takes time.

In many machines, full size helis whatever, many parts have a limited lifetime. Remember, the harder a steel is (blade clamp bolts) the more brittle it becomes and failure is immediate and disastrous.

Dampers add a soft shock absorber to the head and permit smaller components utilizing softer steels in rc heli rotor head construction, and the use of stiff blades. A case of less rotating head mass equals simplicity and weight savings in it's present form.

Something I didn't see earlier till I reviewed a thread on blade balancing, was that dampers also dampen vibration from out of balance blades. After all 5/10s of a gram difference will not be visible to the naked eye nor appear to have an effect but put that .5 gram in the wrong place and one blade will be behaving differently than the other like pulling the main axis to it or pushing it away slightly, pitching a blade up or down prematurely, etc. Basically you CAN run a ridged head as long as your blades are matched to absolute perfection. A micro gram difference on a mini heli would be huge when scaled up.

A ridged high rpm twin blade rotor system might suffer from ULTRA SONIC vibration.

And if you want to go nuts and test an absurd rpm for limitations, couple a motor directly to the main shaft but remember the manufacturers recomendation,

DO NOT EXCEED THE LIMITS OF YOUR "TOY", CATASTROPHIC FAILURE AND EVEN DEATH MAY OCCUR AS A RESULT, other wise, your own your own babee.

Can you imagine 12000 rpm?

2cs

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