Rotor vibrations

XXavier,

Those formulas are different by a factor of 2, have you got a link for those? D might be measured in peak to peak while V is measured zero to peak as shown below, that would explain the factor of 2.

(...)

I got the formulas from this site:

 
Xavier
It's good to see you're experimenting. However you cannot simply compare vibration acceleration amplitudes at different frequencies across the spectrum without first converting them to velocity (it's the only use of the conversion). It's how I try to decide from these spectra if there may be a rotor track/balance problem but the system is very ball^park and not to be considered as precise, it's just a pointer as to which direction to look.
Your data shows
1/rev at 0.015g which is 0.166 IPS.
2/rev at 0.0425g & 0.025g (there are two them) which equals 0.05g which is 0.25 IPS.
So the ratio of 1 to 2/rev is less than 1 in 2. That seems very low to me,
From Oskar's ratio of between 1 in 20 to 1 in 40 (which I agree with if we're comparing vibration velocity at the rotor head and not acceleration) it seems you have a serious rotor 1/rev vibration. If it were true I'd expect you to complaining about a very bad stick and/or cockpit shake. If you took the readings with your hand on the stick you've dampened the vibrations and probably dampened the higher frequencies more than the lower ones because the spring stiffness of your hand/arm is relatively high.
Your prop is at 0.025 g which is 0.044 IPS which appears to be negligible but you've measured your vibration at the stick which is a long way from the prop and is filtered & damped by all the connections in the stick linkage so the value is debatable.

The conclusion is that this method is not always reliable and needs experience to interpret which is another reason I try not to discuss the results on social media.

Mike G
 
Thanks, Mike.

I'll try to take new measurements, this time fixing the iphone to the gyro's frame.

This afternoon, I also took velocity measurements with a device that a friend lent me. I attached the sensor to a screw head of the mast and measured between 0,4 and 0,9 ips while in flight. The readings jumped a lot...

At the present time, I'm not specially concerned by the stick shake of my ELA. I had a real problem with the original rotor, but when I changed to a set of Averso blades & hub bar, the vibration sank to a tolerable level. In 'subjective units', I'd say that it's 'much less than half' what it was...
 
I got the formulas from this site:

That was it, displacement is measured peak to peak while velocity and acceleration are measured zero to peak.

Mike has lots of experience with vibration measurement, as he says where and how you measure is critical. You typically want to measure as close as possible to the source of the vibration. For horizontal rotor vibration the sensor should be mounted on the head at 90 degrees to the axis of rotation, and ideally pointing towards the axis of rotation. For prop vibration the sensor should be mounted on the gearbox as close as possible to the prop, again at 90 degrees to the axis of rotation and pointing towards the axis of rotation.
 
I have tried to find an external sensor I can use with my iphone so that I can use other than the stick to measure the levels, but, as yet, not managed to find one.

phil
 
I have tried to find an external sensor I can use with my iphone so that I can use other than the stick to measure the levels, but, as yet, not managed to find one.

phil


There's an app in Applestore [Vibration Analysis]. Once you have it installed, it gives you the option of buying an 'external accelerometer' for USD 2,99...

I've not tried, but it's a tempting offer, that...
 
it is funny because I found out that people were trying to tune their rotors to reduce vibrations 2 years after having bought my first Averso rotor with which I have never ever noticed any perceivable vib's

I am usually making rotors for fun at the averso factory owned by my mate it is really interesting to see the static balancing process which is totally simple.

they perform a dynamic in flight vibrex test but most of the time the corrections are nill or very reduced .

in fact the job becomes before they assemble rotors when the spend time looking for nearly appaired pairs of blades among the cent's of blades they buy from the extrusion company .

they appair them in weight , cg and twist so that the corrections to make are as small as possible

the more blade a maker have or make the easier it is to make good rotors .. and of course the non accetable blade are returned to the extrusion company ..

all of this is absolutely fantastic

It took Xavier Averso years to invent all the right methods, and Averso aviation have bettered the process in production capacity .

I love my averso rotors ... I have 4 !


They have a very good product, excellent service and reasonable prices. No wonder their rotors are selling quite well, worldwide...
 
I have tried to find an external sensor I can use with my iphone so that I can use other than the stick to measure the levels, but, as yet, not managed to find one.

phil

I contacted 'Mecanocaucho' yesterday, and they told me that they can supply an external accelerometer. They use to sell it only to their clients, but they could make an exception for us. But the price is 300 euro...
 
After reading Mike's comments, I clamped my IPhone to the instrument panel of my ELA, and I took a reading this afternoon. It's very different this time, with the 2/rev vibration prominent...

Captura de pantalla 2020-09-04 a las 21.53.43.png
 
@XXavier have you done any more trails tests with the programme ??

I have been unable to fly since early Sept. after an operation so not done a great deal.

I have taken the chance and had my blades overhauled/reviewed by someone with more skills than I with resin, he is replacing the protective strip along the leading edge and checking and filling the tiny dents/chips.

I will then be taking the chance to reweigh and balance the rotor bar. It is 7.1kg with an out of balance of 5g. Then when I get the blades back I will do the same with each one seperately (cg and weight) then together mounted on the rotor bar.

Whilst I cannot play out I might as well do what little I can.

phil (de fer)
 
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No, I haven't done it again. My blades have, for the time being, an acceptable level of vibration, so it's not a matter of much concern...

I hope you recover well from the operation, and may be happily flying soon...
 
I have often tried to help owners with vibration problems and have recommended the “Vibration Isolator Pro” app (there is another one that an owner has used called “myFrequency” it’s a bit more complicated) as a means of trying to detect if the vibration being felt subjectively was 1 or 2/rev. As most of you know rotor imbalance and out of track cause a 1/rev vibration and all our 2 bladed see saw rotors produce a 2/rev vibration. So we can reduce excessive 1/rev but can’t do much about the 2/rev.

By using this app the owner can send me or post here the vibration spectrum measured at the stick and I try to get a feel for the ratio between 1 and 2/rev to say if I think a track and balance would be useful or not.

I don’t have much data of stick vibration because it’s not something I usually measure when balancing a rotor and so it’s a bit of a guessing game for me to say if a balance is necessary. Added to that I have no idea about the accuracy of the telephone accelerometers or the quality of the connection between the telephone and the stick. So, as you can see in this thread, I cover my ass with words like perhaps, usually, maybe etc which is not very satisfying for me or the owner.

The ideal position to put the telephone with this app would be at the top of the mast were I measure vibration during balancing and I have a small database that would allow me to be more confident in my analysis. Unfortunately the telephone has to be near the pilot so that he can get it to push the buttons to record the spectrum so this option is out.

To get around this problem I asked Mark Burton of Smart Avionics to make me a simple 3D accelerometer that could be cabled to a telephone and to develop a simple app to record the vibration spectra. This he has done and I am testing the prototype at the moment.

Here are photos of this “widget” fixed to the stick and to the rotor head of my gyro.
IMG_20201214_155918.jpgScreenshot_20201016-163621.pngIMG_20201214_160608.jpg

If there is sufficient interest and I can persuade Mark to make and distribute these, I envisage this device being sold with one of the Smart Avionics PB3/4 accelerometer mounting brackets to be used by owners to keep a track of their vibrations to see if they are increasing or not. I have found from experience that, unless it’s enormous, it’s very difficult to “feel” if vibrations are actually increasing or not. After balancing many rotors I have learned not to trust my judgement because measured data has so often proved my subjective feelings totally wrong.

Again if there’s enough interest and owners invested in this I would propose that if they detect an increase in vibration they send me their measurements and because the measurements were made with the same bracket I use for balancing I will be able to compare the results with the same model that I have balanced. This would allow me to be much more precise about whether a Track and Balance is advisable or if the vibrations are typical for this model/rotor combination or not. Hopefully this would be more useful to owners than the current situation with the telephone alone.

Measurements could be made at the rotor and at the stick and even somewhere in the cabin that we could decide was our standard position for the particular gyro model in question. I wouldn’t charge for this analysis because I will be getting an important vibration database out of it. Eventually, with a big enough database, I would hope that we can include the analysis in the app so that the results would be instantaneous and I can go and do something else.

This device could also be put on the engine/gearbox to check if the prop needed balancing and even on the engine for some engine diagnostics.

You wouldn’t be able to balance a rotor with it.

The question you’re all going to ask is “how much?”. The prototype was cobbled up out of bits Mark had laying around the workshop so if he went into production he’d have to source better quality parts, organise manufacturing, develop the app, plus write the manual and I’ll have to do the testing to ensure that the app was user friendly in the cockpit. So we don’t know how much but have agreed that if the price exceeds 100 pounds/Euros/US dollars it would be too much and we’d not go any further.

So how much interest would there be in this?

Mike G
 
I have often tried to help owners with vibration problems and have recommended the “Vibration Isolator Pro” app (there is another one that an owner has used called “myFrequency” it’s a bit more complicated) as a means of trying (...)
(...) (...) (...)
If there is sufficient interest and I can persuade Mark to make and distribute these, I envisage this device being sold with one of the Smart Avionics PB3/4 accelerometer mounting brackets to be used by owners to keep a track of their vibrations to see if they are increasing or not. I have found from experience that, unless it’s enormous, it’s very difficult to “feel” if vibrations are actually increasing or not. After balancing many rotors I have learned not to trust my judgement because measured data has so often proved my subjective feelings totally wrong.

Again if there’s enough interest and owners invested in this I would propose that if they detect an increase in vibration they send me their measurements and because the measurements were made with the same bracket I use for balancing I will be able to compare the results with the same model that I have balanced. This would allow me to be much more precise about whether a Track and Balance is advisable or if the vibrations are typical for this model/rotor combination or not. Hopefully this would be more useful to owners than the current situation with the telephone alone.

Measurements could be made at the rotor and at the stick and even somewhere in the cabin that we could decide was our standard position for the particular gyro model in question. I wouldn’t charge for this analysis because I will be getting an important vibration database out of it. Eventually, with a big enough database, I would hope that we can include the analysis in the app so that the results would be instantaneous and I can go and do something else.

This device could also be put on the engine/gearbox to check if the prop needed balancing and even on the engine for some engine diagnostics.

You wouldn’t be able to balance a rotor with it.

The question you’re all going to ask is “how much?”. The prototype was cobbled up out of bits Mark had laying around the workshop so if he went into production he’d have to source better quality parts, organise manufacturing, develop the app, plus write the manual and I’ll have to do the testing to ensure that the app was user friendly in the cockpit. So we don’t know how much but have agreed that if the price exceeds 100 pounds/Euros/US dollars it would be too much and we’d not go any further.

So how much interest would there be in this?

Mike G

I am interested...

Regards


Javier
 
@Mike G Morning. yes, depending on final costs I will certainly be interested. My initial work with vibrations has certainly whetted my appetite.

phil (de fer)
 
I have often tried to help owners with vibration problems and have recommended the “Vibration Isolator Pro” app (there is another one that an owner has used called “myFrequency” it’s a bit more complicated) as a means of trying to detect if the vibration being felt subjectively was 1 or 2/rev. As most of you know rotor imbalance and out of track cause a 1/rev vibration and all our 2 bladed see saw rotors produce a 2/rev vibration. So we can reduce excessive 1/rev but can’t do much about the 2/rev.

By using this app the owner can send me or post here the vibration spectrum measured at the stick and I try to get a feel for the ratio between 1 and 2/rev to say if I think a track and balance would be useful or not.

I don’t have much data of stick vibration because it’s not something I usually measure when balancing a rotor and so it’s a bit of a guessing game for me to say if a balance is necessary. Added to that I have no idea about the accuracy of the telephone accelerometers or the quality of the connection between the telephone and the stick. So, as you can see in this thread, I cover my ass with words like perhaps, usually, maybe etc which is not very satisfying for me or the owner.

The ideal position to put the telephone with this app would be at the top of the mast were I measure vibration during balancing and I have a small database that would allow me to be more confident in my analysis. Unfortunately the telephone has to be near the pilot so that he can get it to push the buttons to record the spectrum so this option is out.

To get around this problem I asked Mark Burton of Smart Avionics to make me a simple 3D accelerometer that could be cabled to a telephone and to develop a simple app to record the vibration spectra. This he has done and I am testing the prototype at the moment.

Here are photos of this “widget” fixed to the stick and to the rotor head of my gyro.
View attachment 1150095View attachment 1150094View attachment 1150096

Si hay suficiente interés y puedo persuadir a Mark para que los fabrique y distribuya, imagino que este dispositivo se venderá con uno de los soportes de montaje del acelerómetro Smart Avionics PB3 / 4 para que lo utilicen los propietarios para realizar un seguimiento de sus vibraciones y ver si están aumentando o no. He descubierto por experiencia que, a menos que sea enorme, es muy difícil "sentir" si las vibraciones están aumentando o no. Después de equilibrar muchos rotores, he aprendido a no confiar en mi juicio porque los datos medidos a menudo han demostrado que mis sentimientos subjetivos están totalmente equivocados.

Nuevamente, si hay suficiente interés y los propietarios invirtieron en esto, propondría que si detectan un aumento en la vibración me envíen sus medidas y, debido a que las medidas se hicieron con el mismo soporte que uso para equilibrar, podré comparar los resultados con el mismo modelo que he equilibrado. Esto me permitiría ser mucho más preciso sobre si es aconsejable un Track and Balance o si las vibraciones son típicas de esta combinación de modelo / rotor o no. Es de esperar que esto sea más útil para los propietarios que la situación actual con el teléfono solo.

Las mediciones se podían hacer en el rotor y en la palanca e incluso en algún lugar de la cabina que pudiéramos decidir era nuestra posición estándar para el modelo de giroscopio en particular en cuestión. No cobraría por este análisis porque obtendré una importante base de datos de vibraciones. Eventualmente, con una base de datos lo suficientemente grande, espero que podamos incluir el análisis en la aplicación para que los resultados sean instantáneos y pueda ir y hacer otra cosa.

Este dispositivo también podría colocarse en el motor / caja de cambios para verificar si la hélice necesita equilibrarse e incluso en el motor para algunos diagnósticos del motor.

No podrías equilibrar un rotor con él.

La pregunta que se van a hacer todos es "¿cuánto?". El prototipo se improvisó con las piezas que Mark tenía en el taller, por lo que si entraba en producción tendría que obtener piezas de mejor calidad, organizar la fabricación, desarrollar la aplicación, además de escribir el manual y yo tendré que hacer las pruebas. para garantizar que la aplicación fuera fácil de usar en la cabina. Así que no sabemos cuánto, pero hemos acordado que si el precio supera las 100 libras / euros / dólares estadounidenses sería demasiado y no iríamos más lejos.

Entonces, ¿cuánto interés habría en esto?

Mike G
me podria interesar.
 
Wolfy,
don't forget, you understand what I'm talking about, unfortunately most people find it too complicated.
Mike
 
Mike it would probably be good if you could post some more footage of the lack of joystick vibration on a good set of rotors to give these guys something to aim for. Never mind the damage to the rest of the aircraft that these vibrations cause. Once you have flown on a good set of rotors its hard to accept anything less and lets face it - its just hard work flying with anything less.

Regards..........Chook.
 
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