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HelicopterMain Discussion › OK, I'm confused now....! Blade balancing question for the engineers out there.....
11-26-2007 09:05 PM  9 years agoPost 121
spork

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How do you propose to acomplish this ?
Just like in BillieBob's pics.

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11-26-2007 09:12 PM  9 years agoPost 122
AirWolfRC

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I don't follow you on that one, what pics ?

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11-26-2007 09:19 PM  9 years agoPost 123
Mark C

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The machines in BIlliebob's pics only show a flybar system. That aint gonna do it.

Don't think you are gonna be able to eliminate the wobble on a one-bladed heli. The wobble is the result of the lift moment transferred to the main shaft. To remove that is to remove the lift. And, that lift moment occurs all the way around the rotation. There is nothing to "teeter" or at least no way to "teeter" it.

And consider the situation where you apply aileron or elevator - you have situations where there is no lift applied to one side of the rotor and extra lift added to the opposite side. The "wobble" then becomes non-symmetrical about the main shaft axis. There is no simple solution for counter-weighting that would be able to account for all situations.

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11-26-2007 09:24 PM  9 years agoPost 124
spork

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Sorry guys, I don't have it in me to debate physics with Mark and Airwolf for another 40 pages.

It's been done, and works fine.

This is not a typical flybar system. You might notice a blade on one side and counterweight on the other.

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11-26-2007 09:28 PM  9 years agoPost 125
Mark C

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This is not a typical flybar system.
I can see all the components of it. Looks completely typical to me.
You might notice a blade on one side and counterweight on the other.
Ya man. That is what we are talking about - one-bladed helis. We are at least on that page!

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11-26-2007 11:18 PM  9 years agoPost 126
spork

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Yes, it's a one bladed heli in which the blade and counter weight teeter to eliminate the vibration that would result from the cyclic lift. I misunderstood your comment to mean "that's no one-bladed heli - it's just a typical flybar system"

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11-27-2007 12:26 AM  9 years agoPost 127
Mark C

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Yes, it's a one bladed heli in which the blade and counter weight teeter to eliminate the vibration that would result from the cyclic lift.
Yea Sporky but that would only work on a fixed pitch heli. If you only wanted a fixed pitch helicopter then you could make the blade and counterweight one solid piece and you could indeed teeter them on the top of the head to counteract some of the effects of the vibrations caused by lift. You could even angle the counterweight downward slightly to counteract the coning of opposing blade. You could probably get it all to balance out in a hover on a windless day.

But it would all begin to vibrate again once you begin to move forward and there is any dissymmetry in lift along the rotor disk - which has to happen in order to achieve forward flight or even a nice breeze. God help you if you had to auto rotate in a fixed pitch helicopter.

If you attempted to anchor your counterweight to the far side of the spindle on a variable pitch helicopter, there is no way to have the counterweight counteract all the varying forces that the blade exhibits during pitch changes, feathering and forward flight. The best way to achieve that is to hang another blade over there that exhibits the same forces on the opposite site of the mast.

The real puzzle here (at least my understanding) is how to eliminate the wobble caused by a one-bladed heli that has all the benefits of variable pitch.

Mark C.

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11-27-2007 01:09 AM  9 years agoPost 128
AirWolfRC

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There's only one way to counter the rotating lift vector of a one bladed heli,

Add the second blade , fixed pitch, variable pitch, whatever . . . .

The real question is does the rotating lift vector cause enough vibration to be concerned about ?

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11-27-2007 01:54 AM  9 years agoPost 129
spork

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If the blade and counter weight can teeter they can't put a moment on the main shaft except through a second order mechanism. This mechanism being non-vertical lift vector. With sufficient head speed this becomes insignificant, and you can do cyclic, collective, etc.

There are plenty of reasons not to make a one-bladed heli, but that's not one of them.
You could even angle the counterweight downward slightly to counteract the coning of opposing blade.
Having the C.G. offset from the teeter hinge would be an extremely poor idea.

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11-27-2007 02:16 AM  9 years agoPost 130
Mark C

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If the blade and counter weight can teeter they can't put a moment on the main shaft except through a second order mechanism. This mechanism being non-vertical lift vector.
If you can't put a moment on the main shaft then the main shaft and hence the helicopter body are not going to follow the rotor disk. That ain't so good. And if it is a non vertical lift vector then how is it going to lift the helicopter?
Having the C.G. offset from the teeter hinge would be an extremely poor idea.
Since the blade is going to cone to some extent then your CGs are going to get offset anyway. May as well counter that effect.
There are plenty of reasons not to make a one-bladed heli, but that's not one of them.
Since it is universally agreed that one blade is substantially more efficient than 2 then what is the reason?
With sufficient head speed this becomes insignificant, and you can do cyclic, collective, etc
I believe this is the case anyway. The power of the "wobble" is related to the amount of lift on the one blade but as you increase the head speed the amplitude of the wobble decreases as it's frequency increases maintaining the same power.

At some point the frequency of the vibration is above the resonance of the blades, body, etc. and you can live with it.

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11-27-2007 02:25 AM  9 years agoPost 131
spork

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I'm bowing out. I'm not up for another 40 page pissing match. You get the last word.

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11-27-2007 02:52 AM  9 years agoPost 132
Mark C

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Ok... Thanks I guess. Didn't realize it was a pissing match to you. I thought it was just another discussion.

Adios.

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11-27-2007 08:52 AM  9 years agoPost 133
Hamo

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Ireland

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Last Saturday I did try to fly with a single wooden blade and a metal tube as counterweight. The heli was a Raptor 30 V2, wooden blade, 550 cm long, the metal tube was about a foot long, 12 mm diameter and I had to file opposite sides flat so I could get it into the blade grips. I drilled the end of the tube and added more weight so that the wooden blade and the metal tube would balance as a see saw. When finished balancing, the wooden blade was about 112 grams, the metal tube was about 150 grams. One thing I noticed after fitting to the heli was that the tube was rigid in the blade grip, not able to swing because of the flats I made on it. I should have used washers. I will next time.
I was excited and a little scared, but I am one of those crazy guys who is prepared to destroy a heli just to learn something new.
Well, as I slowly increased the engine speed, the side to side shaking was too severe and I had to stop. The helicopter was hopping from one skid to the next. I will do more testing, weather permitting and let you know. I will post pictures of it tomorrow.
Hamo

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11-27-2007 02:06 PM  9 years agoPost 134
Mark C

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Man that sounds like fun stuff! Please get someone to video it!

What I would suggest is:

A. Using the oldest, most worn out flap dampers you have.

B. To get it off of the ground, set one of your flight modes so that the pitch curve to absolutely 0 pitch all the way until the headspeed is well up at takeoff speed before any pitch gets applied. Set it up to fly/hover at 2/3 stick.

I guess that is one thing we haven't discussed yet is that if you have more drag on one side of the head than the other, you will get an additional component of wobble caused by troque drag that (I think) is exactly in phase with the wobble created by lift making matters even worse.

EDIT: Strangely, the "lift wobble" causes a force that results in a rotating tilt of the disk where as the "torque wobble" is on somewhat of a different vector - it wants the disk to travel in a circle around the mast (I hope that isn't too confusing).

Cool stuff Hamo! Please do get some photos.

Mark C.

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11-27-2007 03:36 PM  9 years agoPost 135
AirWolfRC

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To be a good demonstration, that tube needs to be shorter, heavier and less drag . . . . and a pivoting joint like a real blade.

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11-27-2007 07:12 PM  9 years agoPost 136
Hamo

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Here's a picture of my heli with a wooden blade and the metal tube on the other side. The wooden blade weighs 106 grams and has its CG 11.25 inches from the root. The metal tube weighs 156 grams and it's CG is 7.5 inches from the root. As I said in a previous post, as I increased the engine speed, there was too much vibration and I had to stop. I will keep working on this and let you guys know the outcome.
Hamo

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11-27-2007 07:19 PM  9 years agoPost 137
Hamo

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Don't know why the pictures didn't upload.

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11-27-2007 07:57 PM  9 years agoPost 138
Mark C

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That large round pipe may be causing too much aerodynamic drag on that side which could be the cause of your wobble.

As AW says, use a short heavier weight that has less drag.

Really intresting stuff.

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11-27-2007 07:59 PM  9 years agoPost 139
AirWolfRC

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There appears to be a slight problem,

106 x 11.25 = 1192.5
156 x 7.5 = 1170

1192.5 <> 1170

These numbers should be equal.

But your second photo shows all is good ?

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11-27-2007 08:02 PM  9 years agoPost 140
TachyonDriver

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AWW!
Airwolf RC beat me to it - different weights.

Little Spinning Bundle of Joy® DON'T DISS THE DINO!!

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HelicopterMain Discussion › OK, I'm confused now....! Blade balancing question for the engineers out there.....
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