Head damping - what does it do?

[sethml]

I've always been confused about blade grip dampers in R/C heli heads. It seems that multiblade scale heads are often rigid, while 3D two blade heads are damped. Yet it seems that for harder 3D people run harder dampers. Most heads have a single feathering shaft shared by two grips with dampers on each end. But SAB is proud of their new HPS2 and HPS3 heads with independently-damped feathering shafts for each grip.

Can anyone explain the trade-offs, please?

[sethml]

Found a reasonable answer: http://www.rcgroups.com/forums/showthread.php?t=1192960

[P@reez]

Nice explanation! Thanks for posting.

[Mateyhv]

Very interesting, I have always thought of the dampers as the equivalent of a cars suspension, the harder it is, the direct and faster control response is. They also absorb part of the vibrations from the blades that might damage the heli. Think of a car with a 100% rigid suspension, probably wouldn't last for long.

But I had no idea that dampers help to counteract the rise and fall in lift on both sides of the rotor disc in forward flight. And I can't grasp how this 'flap' motion occurs and how is it promoted by the dampers.

[extrapilot]

Guys

A blade is well damped in flap- it has a lot of surface area, and air is fairly sticky. Try flapping a 2’ x4’ board up and down and you will feel how much the air is resisting this. Try it in lead/lag, there is almost no damping. So these damper devices don’t do much with blade flap, but they may help with lead/lag. One thing they do without question is decouple the head from the main shaft to a degree. Softer dampers mean less cyclic force at lower cyclic values can be transmitted to the main shaft. Stiffer means more force.At high cyclic values, the spindle will lock in the housing (typically), and the damper is not allowing additional flex...

We have machines with very rigid spindles (DFC heads for example). The rotor works regardless, but the coupling to the rest of the machine is stiff. And, the rotor blades still bend/flap with cyclic- nothing is infinitely stiff.

When a blade flaps, while it sees relative wind (say, a wind from the front at 0 deg- parallel to the rotor disc, due to the blade’s rotation), the blade’s angle of attack changes. As the blade flaps up, the AOA decreases. As it flaps down, AOA increases. The idea here is that in turbulence, if you hit a pocket of faster air for example, the advancing blade will flap up a bit, dropping lift as it does, and the retreating blade will flap down, increasing lift. The process is called ‘flap to equality,’ where equality just means equal lift across the disc.

For us, it is not really needed on the main rotor. It can reduce cyclic performance, and adds mass/complexity. It can be useful on the tail, since it doesn’t have cyclic. As the machine accelerates in FF/FFF, the advancing side of the tail rotor generates much more lift than the retreating side, so there is a large imbalance there which = stress/vibration. Allowing some flap there with real hinges permits this ‘flap to equality’ process to happen- reducing the imbalance. It also provides motion that allows for a geometric trick, where the flap adds or removes some pitch at the blade root. That is a coupling called ‘Delta-3’, and it is talked about a good deal in this sub-forum if you care to read more about it.

Keep in mind, this is a very complex subject, and there are ways to have a constrained flap hinge while retaining good cyclic performance (with Delta-3, with changed blade CG, etc). All of this stuff is a tradeoff between vibration, performance at high cyclic values, cost, mass, blade instability, etc.

[SamCassidy]

Originally Posted by extrapilot

Guys

A blade is well damped in flap- it has a lot of surface area, and air is fairly sticky. Try flapping a 2’ x4’ board up and down and you will feel how much the air is resisting this. Try it in lead/lag, there is almost no damping. So these damper devices don’t do much with blade flap, but they may help with lead/lag. One thing they do without question is decouple the head from the main shaft to a degree. Softer dampers mean less cyclic force at lower cyclic values can be transmitted to the main shaft. Stiffer means more force.At high cyclic values, the spindle will lock in the housing (typically), and the damper is not allowing additional flex...

We have machines with very rigid spindles (DFC heads for example). The rotor works regardless, but the coupling to the rest of the machine is stiff. And, the rotor blades still bend/flap with cyclic- nothing is infinitely stiff.

When a blade flaps, while it sees relative wind (say, a wind from the front at 0 deg- parallel to the rotor disc, due to the blade’s rotation), the blade’s angle of attack changes. As the blade flaps up, the AOA decreases. As it flaps down, AOA increases. The idea here is that in turbulence, if you hit a pocket of faster air for example, the advancing blade will flap up a bit, dropping lift as it does, and the retreating blade will flap down, increasing lift. The process is called ‘flap to equality,’ where equality just means equal lift across the disc.

For us, it is not really needed on the main rotor. It can reduce cyclic performance, and adds mass/complexity. It can be useful on the tail, since it doesn’t have cyclic. As the machine accelerates in FF/FFF, the advancing side of the tail rotor generates much more lift than the retreating side, so there is a large imbalance there which = stress/vibration. Allowing some flap there with real hinges permits this ‘flap to equality’ process to happen- reducing the imbalance. It also provides motion that allows for a geometric trick, where the flap adds or removes some pitch at the blade root. That is a coupling called ‘Delta-3’, and it is talked about a good deal in this sub-forum if you care to read more about it.

Keep in mind, this is a very complex subject, and there are ways to have a constrained flap hinge while retaining good cyclic performance (with Delta-3, with changed blade CG, etc). All of this stuff is a tradeoff between vibration, performance at high cyclic values, cost, mass, blade instability, etc.

[nightstalker]

If someone cant explain it in a way anyone can understand...it's probably wrong.
The right answer is that the dampers dampen the link between the rotor and the fuselage. The softer the dampers, the tamer it will feel - harder dampers will make it more solid and precise.
however, you wouldn't want to put hard dampers on an old Raptor, because it is a tame heli no matter what - - just like you wouldn't want to put soft dampers on a Goblin, because it's meant to be solid and precise.
That other stuff doesn't apply

[desertstalker]

Originally Posted by nightstalker

If someone cant explain it in a way anyone can understand...it's probably wrong.

I am sorry, but that is just rubbish. A person's inability to understand (or to explain) does not impact the validity of a concept.

[Fauropitotto]

Originally Posted by nightstalker

If someone cant explain it in a way anyone can understand...it's probably wrong.

I've met plenty of absolute morons that could not grasp concepts no matter how it was explained to them. Their brains turn off when faced with new information.

Likewise I've met plenty of intelligent folks (mostly Ph.Ds) that are absolutely brilliant in their field, but can't explain what they do to anyone that isn't already in the field.

[nightstalker]

Originally Posted by Fauropitotto

I've met plenty of absolute morons that could not grasp concepts no matter how it was explained to them. Their brains turn off when faced with new information.

Likewise I've met plenty of intelligent folks (mostly Ph.Ds) that are absolutely brilliant in their field, but can't explain what they do to anyone that isn't already in the field.

You be watching too much Big Bang Theory lol
For real though, I've got to interact with Ph.d's all day - in college - and trust me, the same rules apply! ... And it doesn't take a Ph.D to understand helicopters It's easy!

[Xrayted]

Originally Posted by nightstalker

If someone cant explain it in a way anyone can understand...it's probably wrong.
The right answer is that the dampers dampen the link between the rotor and the fuselage. The softer the dampers, the tamer it will feel - harder dampers will make it more solid and precise.
however, you wouldn't want to put hard dampers on an old Raptor, because it is a tame heli no matter what - - just like you wouldn't want to put soft dampers on a Goblin, because it's meant to be solid and precise.
That other stuff doesn't apply

"The right answer is that the dampers dampen the link between the rotor and the fuselage."

That is not an explanation of anything. Why do they need to be there and exactly what do they do? They help facilitate teeter of the spindle for blade flap, which in turn creates blade lead/lag which cancels out the dissymmetry of lift of the rotor. This is one of of the basic areo physic principles of how ANY heli works. Your heli would roll over into the ground without this happening.


"The softer the dampers, the tamer it will feel - harder dampers will make it more solid and precise."

That is a description of the resultant feel of using different damper stiffness, and not a definition or explanation of what dampers do and what they are there for. No matter more rigid or soft damping, the fact still remains of what is going on in the head. The question was what do dampers do and the difference between the different head designs and damping methods

"That other stuff doesn't apply"

Once again, "that other stuff" is the answer to the question and how helis work. How can one deny the basic physics of how a heli is able to even fly in the first place and claim it doesn't apply? You do realize this is the aerodynamics and physics forum don't you? People come here specifically for the deeper explanations that you seem to be so offended by

[Smoggie]

Originally Posted by nightstalker

If someone cant explain it in a way anyone can understand...it's probably wrong.

So that would make quantum physics and general relativity 'wrong' because very few can understand those fields of science. It even makes calculus 'wrong' too because lots of people cant do that. Heck a good many people cant even do basic algebra, so that must be 'wrong too'

'Anyone' includes some pretty thick people. On the basis of your theory only the things that the most dull witted can grasp are true.

Utter nonsense.

[extrapilot]

Have a look at another thread

https://www.helifreak.com/showthread.php?t=642335

Here was a summary of some of just a few of his insights from that single thread. It is frightening.

Quote:
Originally Posted by nightstalker
For arguments sake, our blades don't lead/lag. They do have a lead or a lag in regards to the chord wise cg, but their position does not change in flight. Only fully articulated heads will allow this; due to the flapping hinge. Flapping is another thing our RC helicopters do not do.
Quote:
Originally Posted by nightstalker
The lead/lag and flapping action is ONLY on FULLY ARTICULATED rotor heads. It's all to counter the effects of dissymmetry of lift when using 3 or more rotor blades
Quote:
Originally Posted by nightstalker
I will concede that the blades flex, but they don't flap. Flapping is there to deal with dissymmetry of lift! Moving the cyclic on the ground doesn't show this at all.
Quote:
Originally Posted by nightstalker
Also, there is no such thing as ground resonance on an RC helicopter! That is unless it has a FULLY ARTICULATED rotor-head.
Quote:
Originally Posted by nightstalker
Ha ha ha ha!!!!! Listen to someone that says that dissymmetry of lift doesn't occur in " conventional" flight because of pilot induced cyclic??? WRONG!!!
Quote:
Originally Posted by nightstalker
RC rotors don't have a flap hinge. So guess what? They don't flap!
Quote:
Originally Posted by nightstalker
Have any of you flew straight and level and considered how much the blades are flapping with relatively little force on them? Seriously. Where's this happen- if not due to dissymmetry of lift? Experts?

[Xrayted]

Ah yes, I remember those conversations now. The heli mechanic that somehow denies the established aero physics that all helis are bound by only exist on fully articulated heads despite known and well established fact otherwise. Many of his own statements contradict one another. Its like one guy screaming that gravity doesn't exist simply because he says so, and getting upset because everyone else doesn't respect his opinion no matter how obviously incorrect it is to anyone else.

Now the snippy response to extrapilots post here makes perfect sense. Its nothing but a jab at EP due to prior exchanges from threads in the past where his theories of how things work were challenged and shot down by EP.

Thank goodness the OPs question had already been answered. Move along.......nothing new to see here

[nightstalker]

Ha ha You guys make it too difficult. It's head dampers. Not flap hinges or lag hinges. I don't mind busting people down, but not so you don't learn something.

[Xrayted]

Originally Posted by nightstalker

Ha ha You guys make it too difficult. It's head dampers. Not flap hinges or lag hinges. I don't mind busting people down, but not so you don't learn something.

Yes, you schooled everyone

What is sad is the fact that the average person who truly wants to learn something or understand the truth would typically go and read up and research for themselves if they were told by multiple people that something they believed in error was wrong.

We have all done it......thought something was fact because of a simple misunderstanding of how something works or because we were told something that was incorrect and simply repeat it, but a wise man when confronted with the truth and evidence of it everywhere is willing to reconsider, read and and learn, however a fool will never change his mind or accept that he is wrong no matter what.

These are well known and documented facts in literature for years nowNightstalker, and you could have easily researched this for yourself since that last thread in October, or ask someone with more experience than you since you claim to have been a mechanic on these machines, yet the fact that you refuse to do this and continue on with a false narrative that is opposite all literature and established physics speaks volumes.

I also noticed something odd in retrospect about that other thread only because you used a sarcastic reference to the "Big bang Theory" in post number #10 here, and then I noticed that one member in that old thread had used the same reference. That same person just happened to be the only one in that thread that didnt disagree with you and wouldnt listen to reason of any kind either. Then he just stopped posting at all ever since that thread faded away

[Fauropitotto]

It's probably better not to waste time engaging folks that have no interest in the 4 values that built this site.

Fun, Learning, Friendship, and Mutual Respect.

[KSHeli]

I teach Physics at the high school level you can't believe how hard it is to get students to unlearn misconceptions about our universe. It doesn't matter how many times they see in an experiment the actual effect they while relapse to what they understood from some earlier experience. I still replay the lunar hammer and feather experiment and some still question the results.

[R_Lefebvre]

So that must mean the feather experiment is wrong, because some don't understand it? LOL

Besides, the moon landings were faked.

[KSHeli]

Originally Posted by R_Lefebvre

So that must mean the feather experiment is wrong, because some don't understand it? LOL

Besides, the moon landings were faked.

You can't believe some of the justifications I get for their answers. Some I chuckle about for hours afterwards, some of their replies are just to try and get a rise out of me, but I learned a long time back how to turn it back on them with some one liners. The kids that have been around a lot me laugh at their classmates and reply you can't get him, when are you going to learn. We all have a good laugh for some small town entertainment, not much else going on here so we make our own.