Rotor Vibration Analysis

coyotekyk

Newbie
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Dec 22, 2015
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Borrastre
Hi all. I would like to smooth the operation of my rotor. Today I went flying with the "Vibration Isolator Pro" application and it gave me these results. I would like to perfectly understand the process and learn about it.
I understand that I have a vibration at 6Hz (1 per revolution) and a little higher vibration at 12Hz (2 per revolution).
It is a Magni rotor (no tracking adjustament).
Where should I start?

1.jpg
 

blw2

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my firts job out of college (mechanical engineering) was as a Maintenance Reliability Engineer at a large pulp and paper mill. Among other things, our primary role was doing regular vibration analysis of every piece of rotating machinery in the place.

Unfortunately, I can't help much with this... it has been many years since I looked at a spectrum like that..... for me it was back in the early to mid 1990's.
I do think I remember a 2x rotation being a typical indicator of shaft misalignment when it was a higher amplitude than the 1x like that.... but what that would mean in this application, I have no idea.
I look forward to following the thread!

Was this a radial measurement? Axial?
at the rotar head?
 

coyotekyk

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Dec 22, 2015
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I'm not sure how this application works, but I think the measurement is axial. I took it with the phone simply attached to the cockpit.
 

Mike G

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Lillebonne France
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Owned Magni M16 now ELA 07
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I've PM'd you my email, contact me and I'll see if I can help. No need to discuss this problem on the forum, we'll only get the thread polluted by opinions.
 

kolibri282

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Quote: we'll only get the thread polluted by opinions /Quote
It is sad to hear that other members of the forum have also come to the conclusion that quite often technical questions are not discussed using technical/engineering/scientific arguments.
 

Jincamty

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My opinion is that Chuck Beaty can offer short and accurate answers to most rotor related questions. (When can we buy the book Chuck? :) )
 

C. Beaty

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Sorry, Jincamty, too old, too lazy, too cantankerous to undertake what would be a labor of love. I doubt if sales would cover printing cost.
 

JETLAG03

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Virollet 17260 FRANCE
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@Mike G I can understand your point of view and wish to keep the reply crisp and free of noise but hope you could share an insight to rotor balancing. Phil
 

XXavier

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@Mike G I can understand your point of view and wish to keep the reply crisp and free of noise but hope you could share an insight to rotor balancing. Phil
And I second the motion... Mike's experience and knowledge on the subject are very valuable...
 

WaspAir

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Sorry, Jincamty, too old, too lazy, too cantankerous to undertake what would be a labor of love. I doubt if sales would cover printing cost.
Self-publish as a Kindle (amazon), Nook (Barnes & Noble) or Kobo e-book and there's no printing cost to recoup.
 

Mike G

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Lillebonne France
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Owned Magni M16 now ELA 07
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I'm in touch with Coyotekyk. If anything interesting comes of our discussions and trials he can tell you about it.
Mike G
 

bryancobb

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coyotekyk

Your curiosity on how to get a smooth flying rotor is commendable. I am by no means an expert but I have developed a pretty good understanding over the years and I'll try to pass on some of what I have learned. Forgive me if you already know some or all of what I say.

At the entry-level of understanding, an unbalanced, shaking rotor must have some mechanical change made to get it smooth. Among the list of things a person can do are...1) Dial-indicate and/or weight-match everything that rotates 2) Add weights to the rotating assembly somewhere 3) Twist or Change the Angle of Incidence of one or more blades 4) Add bendable trim tabs to the trailing edges of blades at some distance from the tip 5) Move the chordwise CG by adding leading edge or trailing edge weight or by carefully painting using paint weight to achieve the same thing.
There's more on the list but these are the most common things that folks usually measure and change.

All balancing attempts must have a means to take repeatable, consistent vibrations which I think you already have.

If you measure your vibrations in flight at the speed where you spend most of your time, and make an adjustment to ONE of the items in the above list and then go fly and measure again, you will gain experience and understanding about what adjustment fixes what vibration. If you are very lucky, someone has already done this for a machine just like yours and you don't have to start from scratch.

Most balancers or software packages use one or more accelerometers to measure magnitude of your vibe and either photcell pickup or Hall effect trigger to measure clock position where the vibration happens. The clock position can be like 1:00 -12:00 or 0-360 or 1:00 - 24:00, etc.

As an example to help you understand, Let's say...looking down on your spinning rotor from above, we draw a large circle that represents the rotor disk and we pencil-in the top view of a simple fuselage, fixed to the center of the circle. If we assume that 12:00 is the nose and 6:00 is the tail, that can be the seeds to label the sketch accurately around the 360 degrees. Now lets say that the big circle gets a number 1 and the center of rotation (mast) gets a zero. Divide this with 9 concentric circles. The smallest is 0.1, the next 0.2, etc. as you progress outward. These circles represent magnitude of your vibe and 1:00 -12:00 represent azimuth or clock position.

Now you can plot data points from your electronic balancer and change ONE thing at a time from paragraph 2. This moves your datapoint and you can begin to get a "feel" for what needs to change to get smoother. More later.
 

500e

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a lot more now
As bryancobb says, "weight-match everything that rotates" "make an adjustment to ONE of the items in the above list and then go fly and measure again"
With the helicopters we have found the above works well,
Blade weight end for end is important on helicopters whatever the opinions say, have made a small scale test rig to try & found that that a set of blades weighing say 1.0 Kg each can have a large variation at the root it will make a difference to overall smooth flight.
On what we balance the tips will be within 1 gram roots 4 grams have done enough to know it works.

Have never done a autogyro but cant see the basic difference other than unpowered & fixed pitch
 
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