Rotor Balancing training with Mike G (Goodrich) using PB-4 balancer

[Abid]

We finished the second day of training with Mike G for rotor balancing.
Mike started with general vibration spectrum analysis and what usually shows up in the gyroplane and went all the way into using PB4 to make move lines using dual axis accelerometer at the rotor-head (just above the pitch and roll block) to how to standardize installation and orientation of the accelerometers, and then using a second accelerometer in the cockpit and seeing its polar and balancing techniques and suggestions for many different rotors he has experience in.
The class was a treasure trove of conceptual and specific knowledge and it continues into tomorrow with more hands on balancing of rotors and propeller balancing. We had 6 people which is just about the right number for this class. Any more would be too many. 5 of the 6 were right from our airport and company. Only 1 person from Texas who is an AutoGyro dealer showed up from outside.
If you are a dealer, builder assist center or a manufacturer/oem and if you have not had this class or know what's in this class, I would highly recommend it. Otherwise you are just throwing darts in the dark and really don't know what you are doing when it comes to balancing and tracking rotors. Single axis balancers like Dynavibe with a single axis accelerometer are ok for propeller balancing but they are really honestly useless for balancing and tracking a rotor and only used when nothing better is available.
I want to thank Mike G. for coming over and sharing his knowledge with us. He will be hanging out in our (SilverLight Aviation) tent at Bensen Days if someone wants to talk to him.

 

[klyde]

We finished the second day of training with Mike G for rotor balancing.
Mike started with general vibration spectrum analysis and what usually shows up in the gyroplane and went all the way into using PB4 to make move lines using dual axis accelerometer at the rotor-head (just above the pitch and roll block) to how to standardize installation and orientation of the accelerometers, and then using a second accelerometer in the cockpit and seeing its polar and balancing techniques and suggestions for many different rotors he has experience in.
The class was a treasure trove of conceptual and specific knowledge and it continues into tomorrow with more hands on balancing of rotors and propeller balancing. We had 6 people which is just about the right number for this class. Any more would be too many. 5 of the 6 were right from our airport and company. Only 1 person from Texas who is an AutoGyro dealer showed up from outside.
If you are a dealer, builder assist center or a manufacturer/oem and if you have not had this class or know what's in this class, I would highly recommend it. Otherwise you are just throwing darts in the dark and really don't know what you are doing when it comes to balancing and tracking rotors. Single axis balancers like Dynavibe with a single axis accelerometer are ok for propeller balancing but they are really honestly useless for balancing and tracking a rotor and only used when nothing better is available.
I want to thank Mike G. for coming over and sharing his knowledge with us. He will be hanging out in our (SilverLight Aviation) tent at Bensen Days if someone wants to talk to him.

"Single axis balancers like Dynavibe with a single axis accelerometer are ok for propeller balancing but they are really honestly useless for balancing and tracking a rotor and only used when nothing better is available."
As a retired engineer, past editor publisher of Experimental Helo magazine, owner of a Safari and presently an owner of a Rotorway type helicopter as well as someone who has balanced main rotors and tail rotors on several helicopters, the DynaVibe works quite well. I was able to consistently balance rotors 1/rev to less than 0.1ips. Quite often it was no more than three start ups.
The Present Dynavibe includes a spectrum measuring capability. I don't know what "Magic" the PB4 has but the only thing that I would like to have for my Dynavibe is the ability to screen capture the vibration spectrum with a joystick mounted switch. As I understand it the Dynavibe guys have a method for measuring track on the middle of the blade as well as the tips in elite. I haven't got that capability yet. I have experience with 4 different balancers and had a balancer lab set up in my basement to look at 4 different balancers operating on a rotating test wheel. To date I like the Dynavibe best.

 

[Abid]

0.1 ips in which axis. Of course you can do things with a single axis accelerometer but with double or triple the work.
To make a move line in x and y at the rotor head and in vertical axis in the cockpit near the seat for span, pitch and chord/shift you need quite a bit more than 3 starts.
Anyway good that Dynavibe single axis gives you satisfactory results. Spectrum capture is on PB-4. We have 2 dual axis accelerometers with it and a remote capture switch
Gyroplanes and helis are not exactly the same in balancing it would seem to me but perhaps you have balanced some gyroplane rotors and know better than me.

 

[eddie]

I reported in another thread that My blades were balanced by the Gyro-Tech factory using the PB4 balancer,the employees there were trained by Mike

and the results were as expected,excellent..Also there is an Aussie who bought a set of GyroTech blades and reported having excellent results as I have.

 

[Abid]

We also started using a new unavailable to public data logger feature in PB4. Mike used it to do a test to see how much G induces how many RPM and 2/rev. This is the discussion I was having with Jean Claude, Chuck Beaty and me. There is more data to be collected. From the first sample and averaging data over a sample time period which showed somewhat stable G and RPM settled down in a steepish bank, what we saw was as follows:
1) 1 G normal rotor RPM ~ 352
2) average sustained G over sample: 1.288
3) RPM that this G load SHOULD have induced: 400.
352 x sq.rt (1.288)

4) Real Average RPM recorded over sample: 385

so difference of 15 RPM.

So the twist in Averso is not so much so the Beaty termed “collective pitch effect” has a minor influence not major. This is what it looks like from one sample. Further samples and averaging would have to bear that out. Mike said his ELA rotor seems to have more twist than Averso based on this result. It also seemed like it took 9 revolutions after application of G for the RPM to kick up. More on this with more tests. I am sure Mike will share these measurements with Jean Claude off forum anyway.
Feature like this is another great tool in PB4 though it would not be of interest or much benefit to a normal end user.

 

[klyde]

0.1 ips in which axis. Of course you can do things with a single axis accelerometer but with double or triple the work.
To make a move line in x and y at the rotor head and in vertical axis in the cockpit near the seat for span, pitch and chord/shift you need quite a bit more than 3 starts.
Anyway good that Dynavibe single axis gives you satisfactory results. Spectrum capture is on PB-4. We have 2 dual axis accelerometers with it and a remote capture switch
Gyroplanes and helis are not exactly the same in balancing it would seem to me but perhaps you have balanced some gyroplane rotors and know better than me.

No. I've never done balancing on autogyros. All my work has been on helicopters. I also have never had a polar chart to work from and just used what I call a physics approach. I was able to get my total 1/rev ips readings down to 0.05 ips in three passes knowing the wts/ips in the chord wise and span wise measurements. All though I've never done it there is a method using just a dial indicator to balance a helicopter main rotor in just a few starts. It was written up in the Experimental Helo magazine and used by one reader to successfully balance his tail rotor. My blade tracking is done with tip lights and link adjustments. To date I haven't needed to adjust the trailing edge. With the lights I can detect an ⅛" tip track error pretty easily. The 2/rev is another story. A rotor in forward flight will generate 2/rev changing forces.

 

[Abid]

No. I've never done balancing on autogyros. All my work has been on helicopters. I also have never had a polar chart to work from and just used what I call a physics approach. I was able to get my total 1/rev ips readings down to 0.05 ips in three passes knowing the wts/ips in the chord wise and span wise measurements. All though I've never done it there is a method using just a dial indicator to balance a helicopter main rotor in just a few starts. It was written up in the Experimental Helo magazine and used by one reader to successfully balance his tail rotor. My blade tracking is done with tip lights and link adjustments. To date I haven't needed to adjust the trailing edge. With the lights I can detect an ⅛" tip track error pretty easily. The 2/rev is another story. A rotor in forward flight will generate 2/rev changing forces.

Great it works for you. The only thing I know is that US military trained and capable teams for maintenance on helis take 6 to 15 hours to balance heli rotors and other systems with equipment with learning algorithms and HUMS. The central Florida trainer for a major supplier of Helicopter Balancing and Tracking equipment guessed that it would take a day or possibly more to properly balance our gyro rotor with multiple test flights. I reckon to balance AR-1 properly and to try and get it optimal would take 8 to 10 short flights and most of the day if Move lines have to be developed. If Move lines template is present after seeing trends then perhaps 2 to 3 hours with as many flights is possible.

 

[klyde]

fara: I can imagine that balancing autogyros takes a bit more. With the helicopter I can dial in my rotor rpm while setting on the ground. Hold it in hover, take my measurements, land and make an adjustment. On a strange ship, my first measurement and adjustment gives me a feel for the ips/gram for particular mounting place for the correction wts. I need an ips/gram for span wise and chordwise then the balancing operation goes fast. I have never needed anything like 2 hrs. to get the ips down below 0.1. I always track the blades first at flight rpm setting on the ground or in a low hover. I once discussed my methods with a person responsible for the balancing operation of the Silver State R-22s. He said my method was much simpler than his and in some ways more understandable. It is for sure less "Cook Book".
Now I did have a bunch of problems balancing the tail rotor on my Safari. The Kit factory finally gave up and balanced the tail rotor on the bench and shipped them balanced. I found there was a tail boom resonance and if I put the helicopter on vibration absorbing pads, I was able to use my technique with a modification. Normal balancing below any critical speed, I always added wts opposite the accelerometer. Above a critical speed I found I had to add the wts on the same side as the accelerometer. This idea was verified in an old MIT text on vibration.

 

[cmb]

I was unable to attend the balance class at SilverLight as I "thought" I was mainly curious about the balancing process and could not make the trip to Florida early enough to attend anyway. I'm glad Fara hosted Mike so close to Bensen Days as I did get a chance to meet Mike there. After talking for a while he offered to show me the powerpoint that he'd hoped to present to a wider audience at Bensen Days. I must say I was very impressed with how Mike was able to convey rotor balancing in simple terms that were easy to understand. So impressed in fact that I'm ordering a PB-4 and plan to work with Mike to learn the process.

I agree with fara, this is a must have for those who wish to understand dynamic balancing and I'd like to thank Mike for taking his time to show me the presentation one on one. The knowledge and hands on experience Mike has, specifically with gyroplane rotor balancing, is best summed up as a "treasure trove" and I highly recommend anyone with an even passing curiosity in balancing, or understanding rotor vibration in general, attend one of his presentations if they have the opportunity. Whether or not you plan to balance your own rotors the presentation provides an excellent primer to understanding how the process works.

It was immediately clear to me that Mike is very passionate about his craft and his willingness to share the information he has acquired is a valuable asset to the gyroplane community. Without his willingness to share I likely would not embark upon the process of learning how to balance rotors.

Thanks to SilverLight aviation for hosting Mike G. and facilitating his presence at this years Bensen Days, I would hope to see him back next year so that others might attend one of his presentations.

Thanks to Mike G. for sharing a bit of your knowledge with me, I'm looking forward to learning more!

By the way I got a chance to fly the AR-1 for the first time with Greg at Barry Daze and the rotors were very smooth.

-Chris Buchanan

 

[Abid]

Mike is a treasure trove, you are right and I tried to empty him out as much as I could here
Engineering is an applied science and what Mike does beyond pure balancing and PB-4 is to gain data on all these different rotor systems quietly on validating or invalidating some of the theories put forth for different subjects that are relevant to vibrations on rotors. We all have our ideas and opinions and the data collection filters them out.

We will do another 2 day full course around Sebring Expo 2019 (probably right after Sebring Expo) and I will also arrange the one hour class presentation (intro) for $50/person at Sebring in the evening probably on Friday or Saturday so people coming there can stay for the expo and get to taste intro to vibrations and balancing after 5 pm at an educational tent. Refreshments will be served.
Keep this in mind
Sebring Expo is Jan 23 - 26 (Wed through Sat).

https://www.sportaviationexpo.com/

 

[cmb]

Thanks Fara, I've marked my calendar!
I agree, gaining real world data is what's important here, and anytime the understanding of any topic can be advanced objectively rather than subjectively I'm all for it.

Stick shake, mysterious vibrations and little knowledge of their long term effects on metal fatigue other than the attitude of relying on "past performance" partly led to my not remaining involved with gyroplanes when I started back in 1999. I see all that is about to change, and that's very exciting!

 

[Mike G]

Chris
I don’t visit this forum much now so thanks for bringing this thread to my attention and thank you and Abid for your kind words.
It was a pleasure meeting you because, along with the guys in Abid’s training session, you were just about the only people at Bensen Days who showed any real interest in what I’m doing and actually wanted to know more.
That’s the main reason I don’t bother much with this forum any more. I don’t expect everybody to be as concentrated on rotor track, balance & vibration as I am but I’m surprised that at the “Mecca” of American gyrocopters there was so little interest to at least learn some of the fundamentals of the causes and cures and how to identify the different vibrations we experience with our gyros.
You have my email so keep in touch and we’ll work something out for you if you do buy a PB4.
Mike G

 

[Abid]

The market for gyroplanes is growing and changing from the stagnation it suffered for a bit from what I can see. But the growth is also with a changing scene.
I am quite sure I already have enough people to do the full course once. the question would be can we do it twice in Jan.