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Old 03-24-2009, 01:12 PM   #41 (permalink)
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WOW... this thing just keeps going!
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Old 03-24-2009, 07:00 PM   #42 (permalink)
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Originally Posted by HELINHAWAII View Post
WOW... this thing just keeps going!
And how many times has it shown up in the past?...Search function?
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Old 03-24-2009, 07:29 PM   #43 (permalink)
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This is my final post on this thread, thanks to ALL who have contributed and I respect, in the true spirit of HeliFreak, each and everyone's views and opinions on this subject.

For the record, I'm 57 and started flying helis in the late 1970's (Graupner Bell 47G with a HB25 motor, fixed pitch and no gyro, MacGregor 27MHz, 4 ch. radio and a rotor with flapping hinges, unheard of today, and I still have this fragile old lady in my workshop!). Before that, I built and flew planks, free-flight and control line, from the age of about 9,but I always dreamt of having a model helicopter, way before they became a practical reality So you could say I've had a bit of practice!

To date I've built/owned/flown probably 35 or so machines, my current favourite (or at least the machine I seem to fly the most) is my Trex 500 which needless to say, has been built and set up properly with the benefit of about 30 years' experience.Over the years I have absorbed plenty of technical information on how our helis fly and are controlled, BUT..

I still feel uncomfortable with the word "stability" when applied to a helicopter in the hover.

Reading every reply in this thread, the overwhelming concensus is that a helicopter is inherently unstable in the hover - even Pinecone (my 'new' adversary? - I hope not!) conceded to this..

I would go further by saying that a helicopter's uncontrolled behaviour in the hover is in fact divergent.

So why do we persist in using the word "stability" to describe degrees of unstable behaviour, or, in other words, "instability"? An "oxymoron", perhaps?

I still prefer to use the word "controllability".

In my opinion, flybars add "controllability" to "instability"

They do not add "stability" to "instability"
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Old 03-24-2009, 08:04 PM   #44 (permalink)
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I am suprised that nowhere in this thread has anyone brought up bell/hiller control systems or gyroscopic precession. Now, I'd have to go and research these things to get absolutely right, but I choose instead to go from memory which may make all of the following an exercise in BS:

Our rotor disks can be viewed as a gyroscope. If you have ever pushed down on the edge of a spinning gyroscope, you will find that the effect of the force that you applied will manifest itself 90 degrees forward of where you applied the force in the direction of rotation. That is to say, if you have a clockwise spinning gyroscope and you press on the north side, the gyro will actually tilt down on the east side.

What does this have do with flybars you say? Well, flybars happen to be located 90deg ahead of the blades on a typical two bladed rotor. This enables the swash to tilt in the same plane that you want the cyclic response to be. Because the flybar partially controls the blades in a bell/hiller rotor control system, the maximum tilt of the swash drives the flybar 90deg ahead of the blade it controls in order to get the rotor disc to tilt exactly the way that you want it to. The flybar is like power steering for the rotor head.

I think that if you had vertical linkages from the swash to a non flybar head and you tilted the swash to the left (clockwise rotation), the rotor disk would tilt forward resulting in forward movement of the heli.If you tilt the swash forward in such a setup, the heli would tilt to the right. Now if you add the flybar with paddles 90 deg. ahead of the blades, the disk would tilt forward with a forward swash tilt, etc....

I realize that I'm not 100% correct on all of this stuff, but there is definitely some truth to it (in my head at least). If there is anyone on here that can clarify these issues, please speak up.

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Old 03-24-2009, 08:32 PM   #45 (permalink)
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Why the reference to the term "stability"? Because in full scale heli world this is most certainly a legitimate term. Or more specifically Static and Dynamic stability.

Static stability deals with the tendency of the helicopter to return to it's original position after a disturbance.

Dynamic stability deals with how successful the helicopter is in finally returning to it's original track.

Both Static and Dynamic stabilities apply to each of the three planes of movement, Longitudinal Stability, Lateral Stability, and Directional Stability,

And to specifically quote a gentlemen that formed the Nelson Aviation College in New Zealand and spent over 30 years giving instruction to flight and theory of flight of helicopters....

Quote:
At best, helicopters are statically stable and dynamically unstable in the longitudinal plane
Quote:
In the rolling plane, helicopters are generally statically stable but dynamically unstable
Quote:
In a hover, most helicopters are (directionally) statically stable but dynamically unstable
But then that really does open a can of worms, and a person could spend years researching each one. The flybar is simply gyroscopic mass that aids in the stability of the helicopter.
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Old 03-24-2009, 08:50 PM   #46 (permalink)
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Here's a pic of a Huey and you can clearly see the flybar (with weights). The head looks a lot like an RC heli head.
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Old 03-24-2009, 09:04 PM   #47 (permalink)
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I would like to say this about the subject...

If you want to know what a flybar does, use your home's ceiling fan for an experiment. (if it's the kind that can 'swivel' from side to side)
Turn it on high and then try to move it from pointing one direction to the exact oposite direction.
You will notice that it won't follow a straight line. It will want to make an 'arc' instead of simply moving from blowing down-right to down-left.

So if you go flybar-less, and apply right roll, you might get right roll AND some pitch in there.


thats the best I can explain it to people when they ask me about it.
I hope this helps more than hurts...
hope its a correct description too.
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Old 03-24-2009, 09:48 PM   #48 (permalink)
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X-GEAR:

All 2 bladed helicopters have flybars. Just called STAYBARS or stablization bars. Go look at a UH-1H huey you will see them they just dont use paddles they use weights. On a UH-1H huey (If memory serves me correct) they are 8 lbs each.
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Old 03-25-2009, 07:44 AM   #49 (permalink)
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You are also missing the idea that you can improve stability, but still not have a stable system.

You can go from more unstable to less unstable and this is increasing the stability.

You seem to be hung up on stable. Stable and Stability have the same root, but do NOT mean the same thing. You can have negative stablity.

And helis have some stability, other wise, they would be impossible to fly. As in that case, every control input with generate a greater and greater motion, even if removed. Sort of like trying to fly a Heading Hold gyro with the gyro reveresed.
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Old 03-25-2009, 08:40 AM   #50 (permalink)
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Quote:
Originally Posted by fireplug1111 View Post
X-GEAR:

All 2 bladed helicopters have flybars.
?que?
http://www.innovator.mosquito.net.nz.../delivery7.asp
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Old 03-25-2009, 08:47 AM   #51 (permalink)
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http://www.heli-rnd.com/Flybar_and_flybarless.html


I have something in this page
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Old 03-25-2009, 12:00 PM   #52 (permalink)
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Originally Posted by HoverHeaven View Post
They do not add "stability" to "instability"
I disagree. They buffer the chaos of real world forces that come to play on the rotor disc. Which leads to controlability. A gust of wind might cause the heli to roll in one direction. The flybar disc wants to stay in plane thus introducing a change in the main blade pitch. Weather or not its hovering, forward flight or control changes.
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Old 03-25-2009, 12:15 PM   #53 (permalink)
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Quote:
Originally Posted by Mike SVOR View Post
That rocks
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Old 03-25-2009, 03:10 PM   #54 (permalink)
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Quote:
Originally Posted by fireplug1111 View Post
X-GEAR:

All 2 bladed helicopters have flybars. Just called STAYBARS or stablization bars. Go look at a UH-1H huey you will see them they just dont use paddles they use weights. On a UH-1H huey (If memory serves me correct) they are 8 lbs each.
Nope. SOME do, many don't.

Bell 206 and Huey do, but R-22 and R-44 don't.
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Old 03-30-2009, 09:00 PM   #55 (permalink)
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This is a topic about Helicopters, not sure what that was----- kinda cool I guess... Go do a google search or some research on IGOR SIKORSKY, He has several FAILED attempts until he added a staybar. It sloved all his problems in 1 flight in regards to the stability of a heli.............

Also The heli in the video looks to be a fixed pitch system. Just cyclic is used. No collective.....
When I was in the Army as a UH-1H crewchief I flew in a OH-58 once..... ONCE...... that was all it took too small, no protection, and didn't like the fact that you can carry a OH-58 turbine engine on your shoulder and walk off with it.....
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Old 03-31-2009, 08:23 AM   #56 (permalink)
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Quote:
Originally Posted by fireplug1111 View Post
This is a topic about Helicopters, not sure what that was----- kinda cool I guess... Go do a google search or some research on IGOR SIKORSKY, He has several FAILED attempts until he added a staybar. It sloved all his problems in 1 flight in regards to the stability of a heli.............

Also The heli in the video looks to be a fixed pitch system. Just cyclic is used. No collective.....
When I was in the Army as a UH-1H crewchief I flew in a OH-58 once..... ONCE...... that was all it took too small, no protection, and didn't like the fact that you can carry a OH-58 turbine engine on your shoulder and walk off with it.....
naw dude, that is a Mosquito helicopter without it's body on it.
It has full collective controls just like a real R/C hellicopter.
look em up.

I'm really wondering why you would say that when you can clearly see the collective handle and the dude operating the pitch from it.
strange, huh?
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Old 03-31-2009, 01:44 PM   #57 (permalink)
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Igor's first helicopter the VS-300 had a 3 blade head and no stabilizer bar. The change that gave him an overnight change in control was the addition of cyclic pitch on the main rotor. Up until then he had been using horizontal tail rotors for pitch and roll control with limited success. There are no Sikorsky helicopters with stabilizer bars, at least none that I know of. The stabilizer bar was invented by Arthur Young who patented it and sold it to Bell Aircraft who developed the Bell 47 and the Huey.
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Old 04-01-2009, 04:10 AM   #58 (permalink)
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And even in RC, multiblade setups don't use flybars.
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