Rotor Track & Balance (RTB) training Australia

[Mike G]

I was asked by Rick Elliot of ASRA

to do 4 RTB (Rotor Track & Balance) training sessions across Australia teaching groups how to use the Smart Avionics PB4. We agreed a schedule that included me also running 2 “workshops” at the ASRA “Nationals” (their Mentone or BDs).

I recently married and my new wife, Dominique, who is a gyro pilot and keen photographer, decided she wanted to come along.

We flew into Perth and the first session was at White Gum airfield with a very warm welcome and active group led by Nick Buri. We tracked & balanced a Magni M24 and tried to balance a Niki Kallithea.


The Niki proved to be not very RTB friendly due to the teeterblock/hub bar design that was a mix of Tervamaki with the old “half-moon” tracking feature installed and the Averso/GyroTech style chordwise shifting barrel.

Next, we flew to Adelaide and drove out to Rollos field operated by Gary Williams.

Again a very welcoming and enthusiastic group who were very keen to learn. Here we successfully balanced a Magni M24, an ELA Eclipse and an ELA Scorpion.

Gary very kindly flew Dominique around the area in his beautiful Cavalon and then in his FW. All 3 rotors were successfully tracked and balanced and the PB4 allowed us to investigate a yaw problem that we traced back to the rudder.

Then off to Sydney and a long drive up to the Nationals at Quirindi. Here I gave the 2 “workshops”, one being a basic presentation on how to separate out different vibration frequencies (primarily 1 & 2/rev) and how to read a polar chart and the other being a presentation of my GWS (the same as at BDs last year). Both were well attended with about 30+ attendees and were followed by lively question sessions.

See following post for the rest
Mike G

 

[Mike G]

This was followed by the 3rd RTB training session where we tracked and balanced an MTO sport and a Magni M16.

The PB4 allowed us to pick up a 1/rev side to side vibration in the cockpit even though the rotor was excellent, we tracked this down to the rudder cable tension that were re-tensioned and that showed a small improvement and the owner said he’d continue to see if it got better. This session went very well and we even had time to balance both props.

Then down to Melbourne and a drive up to “Area 51” at Nagambi with Brett Perry the master of ceremonies.

Here we had about 10 participants, up from the original 6 or 7 as the word had got around that perhaps this training had some value. We tracked and balanced a Brako 2 seat a Brako single seat and 2 TAGs.

The single seat owner said that he still had a hell of a lot of stick shake even though the PB4 said his rotor was fine. I thought he was just being super fussy until he showed me a video. We went out to look and found the roll and pitch pivot bushings and control system generally with a lot wear. The owner was happy to now know what his problem was and announced that it gave him a “winter project”.

Dominique got mustering type flight in a TAG flying very low to see and photograph the kangaroos.

The TAGs also proved to be very RTB unfriendly. Initially giving us curved move lines and then often not responding to adjustments as we expected. In the end we managed to improve them and they were much better than when we started but not down to a level of vibration that satisfied me.

In conclusion a fabulous trip for Dominique and me, we met a ton of very nice and kind people who made us feel welcome and clearly wanted to learn anything they could about RTB.

A special thanks to Rick who saw the value in getting enough guys in Australia trained up to use the PB4. We met a few old timers especially a very impressive Kevin Traeger who, by the seat of his pants, told us what adjustment was needed and when we’d finished our calibration flights, he was spot on. This just goes to show that it’s possible to track and balance without modern equipment but you’d need Kevin’s 20 – 30 years’ experience balancing 100s perhaps 1000s of rotors.

Mike G

 

[Gyro_Kai]

Great adventure, enjoy the down-under!

Kai.

 

[Abid]

Sounds like a good trip Mike

The barrel roll adjuster for tracking is never going to be a good solution for proper RTB. I am not sure who originally came up with it in gyroplanes but when I first saw it, I was lost as to how it could give accurate results. There is no way to do the same thing twice reliably with it. It will just be a trial and error. One thousand of an inch makes the difference between a galloping horse and a sedan. How do you ever do that with a barrel and torque. I am not that smart or that good I guess.
For the chordwise balance the trunion is fairly good but one has to realize 10 degree turn gives a thousand of an inch adjustment. A full 180 degree turn will adjust 18 thou. That is a lot. One has to start by marking origin and move in reliable small increments.
RTB should not be seat of the pants black magic thing. It is a stepwise reduction to a solution by the numbers and adjustments that are known to move in known ways for the given rotor. Too much black magic going on in gyroplane world as is. RTB should not be adding to it.
Thanks for pointing out that even when some rotors were well balanced, the shake in the cabin was severe and people would always automatically say it is the rotor when it may completely have nothing to do with the rotor. It may be slop in control circuit. This is specially true when you have had a blade flap or blade strike on something and you have twanged your control system and rotorhead. You may think it looks good but it has developed slop and that will be felt. Rotors themselves may have zero to do with it.

Mike can you eloborate on this a bit more:
"The PB4 allowed us to pick up a 1/rev side to side vibration in the cockpit even though the rotor was excellent, we tracked this down to the rudder cable tension that were re-tensioned and that showed a small improvement and the owner said he’d continue to see if it got better."

Which make/model gyroplane was this? Did anyone check engine mounts on this gyroplane. If not they should and very carefully.

 

[Sv.grainne]

Mike:

I've found a PB4 locally and Dayton is going to let me use it. Going thru the tutorial and manual now. Can I touch base with you on questions?

Bobby

 

[Gyro Technic]

Just wanted to chime in and say how much I enjoyed Mike's class just before Bensen Days '22.
This man knows what he is talking about!

Do you see any vibration/ shaking here?

No.... That looks pretty smooth to me!

(Mike and his US-side protégé)

 

[Mike G]

Sounds like a good trip Mike

The barrel roll adjuster for tracking is never going to be a good solution for proper RTB. I am not sure who originally came up with it in gyroplanes but when I first saw it, I was lost as to how it could give accurate results. There is no way to do the same thing twice reliably with it. It will just be a trial and error. One thousand of an inch makes the difference between a galloping horse and a sedan. How do you ever do that with a barrel and torque. I am not that smart or that good I guess.
For the chordwise balance the trunion is fairly good but one has to realize 10 degree turn gives a thousand of an inch adjustment. A full 180 degree turn will adjust 18 thou. That is a lot. One has to start by marking origin and move in reliable small increments.
RTB should not be seat of the pants black magic thing. It is a stepwise reduction to a solution by the numbers and adjustments that are known to move in known ways for the given rotor. Too much black magic going on in gyroplane world as is. RTB should not be adding to it.
Thanks for pointing out that even when some rotors were well balanced, the shake in the cabin was severe and people would always automatically say it is the rotor when it may completely have nothing to do with the rotor. It may be slop in control circuit. This is specially true when you have had a blade flap or blade strike on something and you have twanged your control system and rotorhead. You may think it looks good but it has developed slop and that will be felt. Rotors themselves may have zero to do with it.

Mike can you eloborate on this a bit more:
"The PB4 allowed us to pick up a 1/rev side to side vibration in the cockpit even though the rotor was excellent, we tracked this down to the rudder cable tension that were re-tensioned and that showed a small improvement and the owner said he’d continue to see if it got better."

Which make/model gyroplane was this? Did anyone check engine mounts on this gyroplane. If not they should and very carefully.

Abid you have obviously understood, you must have had a good teacher

To answer you question:
This was an MTO sport and the side to side (X2) 1/rev vibration in the cockpit was higher than that at the rotor head. Since the source of 1/rev is the rotor the only way you can get a higher vibration elsewhere is if there is some sort of resonance. Using my smartphone and the Vibration Isolator app I blocked the tail so that it didn’t move and measure the natural frequency of the rudder. It came out at 6 Hz. Due to the combination of rudder mass and tension on the rudder cables the rudder was excited at its natural frequency by the very small residual 1/rev from the rotor. The owner tightened the cables and that reduced the 1/rev in the cockpit a little, I left him to continue because I was on a pretty tight schedule.

I mentioned it because it shows that with a good dynamic balancer, once you’ve tracked and balanced your rotor to a very low level, you know that any 1/rev in the cockpit/frame is due to something else and you can stop messing about with the rotor.

I have not found an example of loose engine mountings, I imagine that it would be at a different frequency but if you've had that experience and know the frequency of loose engine mounts please advise us it would be a great parameter to now when looking at the frequency spectrum.

Mike

 

[Mike G]

I really want to point out to any Australians on the RWF what a great organisation you have in ASRA. I'm sure you all bitch about the fees etc but I can tell you that I've tried to work with the PRA (US), BRA (UK), LAA (UK), SAGPA (SA) & the french FFPLUM. None of them had the imagination or organsation competence to do what Rick Elliot and ASRA did.
Australia now has a network of trained PB4 users and PB4s to oan out and they are thinking of organising a database of all balancing done so that anyone about to balance a gyro can download the balancing files of the same model to see what was done and how the move lines are orientated.

Now that PRA is under new management, I hope we can do something similar for the US.

Mike G

 

[Mike G]

Just wanted to chime in and say how much I enjoyed Mike's class just before Bensen Days '22.
This man knows what he is talking about!

Do you see any vibration/ shaking here?

No.... That looks pretty smooth to me!

(Mike and his US-side protégé)


View attachment 1158169

Thanks Denis I enjoyed our session together as well.
Mike

 

[Mike G]

Mike:

I've found a PB4 locally and Dayton is going to let me use it. Going thru the tutorial and manual now. Can I touch base with you on questions?

Bobby

Bobby
Of course no problems.
Mike

 

[Mike G]

While I'm logged in
I thought I’d try to clarify why I said that the Niki proved to be not very RTB friendly. The teeterblock/hub bar design is a mix of Tervamaki with the old “half-moon” tracking feature installed and the Averso/GyroTech style chordwise shifting barrel. I felt that adding the half-moon feature was particularly unfortunate because it meant that you had to loosen and re-tighten the 4 bolts fixing the teeter block to the bearing to adjust the track and those bolts take the entire weight of the gyro, unlike the classic half-moon on the Bensen style where these bolts take very little actual load. Tightening these bolts to the required torque while maintaining whatever tracking adjustment we were trying to achieve proved very difficult, added to which the half-moon was the wrong way around causing each tracking adjustment to create a secondary chordwise movement. This design also means that there is no reliably accurate means of measuring the tracking adjustment that you’d just made. Added to that there was no way of measuring accurately the rotation of the chordwise barrel.

I was unhappy to leave the owner with the job half-finished but he clearly understood the weakness of the design and told me afterwards that he’d created a set of shim blocks to be able to accurately measure the adjustment and that allowed him to tighten the 4 bolts solidly and not rely on the half-moon to hold the tracking adjustment. I gave him a simple design solution to resolve the problem in the hope that Niki might listen to him rather than me.

The 2 TAGs also proved to be very RTB unfriendly. Initially giving us curved move lines and then often not responding to adjustments as we expected. In the end we managed to improve them and they were much better than when we started but not down to a level of vibration that satisfied me.

The TAG rotor head and hub bar is based on the Tervamaki design using titanium for the two hub-bar side plates. The TAG rotor blades are similar in concept to the Tervamaki original design with the blades held in by 2 simple horizontal bolts, which made more sense to me than the Niki design which needed an adapter from 2 horizontal bolts to the classic cluster plate vertical bolts.

The teeter block uses an ELA style chordwise adjustment barrel in the central teeter tower and adjusts the pitch/tracking by shimming the teeter block. Getting the shims in wasn’t easy and like the Niki meant releasing and re-tightening the 4 teeter block bolts that carry the entire weight of the gyro; bolts that I’d rather leave torqued up once and for all. It also meant that we needed to lift the rotor to separate the teeter block from the hub bar so that we could install the tracking shims. It was impossible to accurately measure the chordwise adjustment because the special protractor and adjustment bar (that I know exists at TAG) was never supplied to the owners so we were forced to guess the angle based on the assumption that there were 6 equally spaced holes in the barrel and tried to use a digital protractor (smartphone) to measure the angles.

Another thing that was surprising was the level of 2/rev vibration at the rotor head. In the TAG with a split mast, the side to side (X) direction the 2/rev was as high as 7 IPS, normally in typical tandem Eurotubs (ELA, Magni, AG) it is between 2.7 and 4.0 IPS. The solid mast TAG had 2/rev vibrations more in line with what we usually see. The split mast TAG also had significantly higher 2/rev vibration in the cockpit compared to the solid mast.

Before I get accused of only knocking Niki and TAG, they were both very comfortable and extremely well finished but remember I’m very focused on RTB and therefore critical of what I see as short comings in design that make RTB unnecessarily awkward, imprecise and non-repeatable. I could equally list the short comings of every gyro rotor design out there; they could all be better and more precise with a little effort but most gyro “designers” seem very reluctant to change when you try to tell them that their design could be better.

Mike G

 

[Georgi]

This was followed by the 3rd RTB training session where we tracked and balanced an MTO sport and a Magni M16.
View attachment 1158153
The PB4 allowed us to pick up a 1/rev side to side vibration in the cockpit even though the rotor was excellent, we tracked this down to the rudder cable tension that were re-tensioned and that showed a small improvement and the owner said he’d continue to see if it got better. This session went very well and we even had time to balance both props.

Then down to Melbourne and a drive up to “Area 51” at Nagambi with Brett Perry the master of ceremonies.
View attachment 1158154
Here we had about 10 participants, up from the original 6 or 7 as the word had got around that perhaps this training had some value. We tracked and balanced a Brako 2 seat a Brako single seat and 2 TAGs.
View attachment 1158155View attachment 1158156View attachment 1158157View attachment 1158158
The single seat owner said that he still had a hell of a lot of stick shake even though the PB4 said his rotor was fine. I thought he was just being super fussy until he showed me a video. We went out to look and found the roll and pitch pivot bushings and control system generally with a lot wear. The owner was happy to now know what his problem was and announced that it gave him a “winter project”.

Dominique got mustering type flight in a TAG flying very low to see and photograph the kangaroos.
View attachment 1158159
The TAGs also proved to be very RTB unfriendly. Initially giving us curved move lines and then often not responding to adjustments as we expected. In the end we managed to improve them and they were much better than when we started but not down to a level of vibration that satisfied me.
View attachment 1158160
In conclusion a fabulous trip for Dominique and me, we met a ton of very nice and kind people who made us feel welcome and clearly wanted to learn anything they could about RTB.

A special thanks to Rick who saw the value in getting enough guys in Australia trained up to use the PB4. We met a few old timers especially a very impressive Kevin Traeger who, by the seat of his pants, told us what adjustment was needed and when we’d finished our calibration flights, he was spot on. This just goes to show that it’s possible to track and balance without modern equipment but you’d need Kevin’s 20 – 30 years’ experience balancing 100s perhaps 1000s of rotors.

Mike G

Mike, how much does Kevin Traeger charge for his pants (including seat spot)? What brand? Thanks.

 

[Abid]

Abid you have obviously understood, you must have had a good teacher

To answer you question:
This was an MTO sport and the side to side (X2) 1/rev vibration in the cockpit was higher than that at the rotor head. Since the source of 1/rev is the rotor the only way you can get a higher vibration elsewhere is if there is some sort of resonance. Using my smartphone and the Vibration Isolator app I blocked the tail so that it didn’t move and measure the natural frequency of the rudder. It came out at 6 Hz. Due to the combination of rudder mass and tension on the rudder cables the rudder was excited at its natural frequency by the very small residual 1/rev from the rotor. The owner tightened the cables and that reduced the 1/rev in the cockpit a little, I left him to continue because I was on a pretty tight schedule.

I mentioned it because it shows that with a good dynamic balancer, once you’ve tracked and balanced your rotor to a very low level, you know that any 1/rev in the cockpit/frame is due to something else and you can stop messing about with the rotor.

I have not found an example of loose engine mountings, I imagine that it would be at a different frequency but if you've had that experience and know the frequency of loose engine mounts please advise us it would be a great parameter to now when looking at the frequency spectrum.

Mike

Haha. Yes I had a very good teacher.
I know of at least one case in an ELA where it seemed like it was the rudder cables that needed to be tensioned and the owner tensioned them and then even tried making new set of cables but the whole time the actual problem was a cracked or broken engine mount allowing the thrust line to sway making a yawing motion. Eventually the gyro had to be crash landed and this discovered. Thus my warning. Similar thing happened in an AG915 which was made by the same people who make Argon. The 915 engine is heavier with more torque and they initially used the same exact engine mount and firewall to take the load of 915 as their 912 based engine. That resulted in a firewall/engine mount that moved changing thrust line. They eventually solved the problem but not before a few of them were in the field being used by customers.
I am surprised MTO Sport whose rudder's natural frequency is 6 Hz. I would have tried to make it so it was not 6 or 12 Hz but we have been through that. Hopefully rudder attached to the tail with cables tensioned to 45 to 50 pounds changes that frequency and he solves the issue.
ASRA did good by arranging training courses in different parts of the country. Buying a PB4 is the easy part but actually knowing how to use it and conceptually understanding RTB is the more difficult part. There is so much mythology in the gyro world at least in the US that if you actually start quantifying and reducing things down logically you will always find someone who is well known who will put out something to the effect that you don't know what you are doing and they have a better way even though the numbers show something else. But it is worth trying to get some people trained around different parts of the country who can actually help and willing to help.
You have already done training multiple times in Florida, then I think once in Texas and once in California (?). What I realized is that if the guys who took training did not use it in a year, its gone. They would have to review the material or have a manual to guide them through particular steps on PB4. Conceptually though they understand RTB. That does not go away.
The other hurdle is gyroplane manufacturers. AG for example has their own thing going on. As I know in the start they were using a balancer that did not even have multi axis accelerometers (or maybe I am mistaken). But basically the point being an end user is likely to get conflicting information even from manufacturers when in RTB there is no conflicting information necessary. It is not an opinion. It is purely a logical step wise reduction to a solution.

 

[Sv.grainne]

Bobby
Of course no problems.
Mike

Mike:

I started on the tutorial and got thru entering the span points OK. When I get to chord portion I enter points and nothing looks right. my lines are not intersecting and they appear on the X and Y span lines as short red lines? What's the best way of communicating with you?

Bobby

 

[Abid]

Mike:

I started on the tutorial and got thru entering the span points OK. When I get to chord portion I enter points and nothing looks right. my lines are not intersecting and they appear on the X and Y span lines as short red lines? What's the best way of communicating with you?

Bobby

Bobby
You can probably communicate by e-mail with Mike but I think it would be better if you also put the screenshots and discussion here. Someone will search PB4 use someday after training and have the same questions as you. They can find it thanks to search engines. You are making move lines I am guessing

 

[Sv.grainne]

Bobby
You can probably communicate by e-mail with Mike but I think it would be better if you also put the screenshots and discussion here. Someone will search PB4 use someday after training and have the same questions as you. They can find it thanks to search engines. You are making move lines I am guessing

Will do, I'm going to start over tomorrow and will post the results. Yes move lines. Sample points plot fine for span then when I move on does not look anything like the example.

 

[Mike G]

The ASRA newsletter has come out with yours truly on the front cover.
A reminder of a really rewarding visit for me, thanks again to those down under and ASRA for the outstanding organization.
They have a very informative and interesting quarterly magazine that other gyro Associations could learn from.
Mike G

 

[Bri350fly]

While I'm logged in
I thought I’d try to clarify why I said that the Niki proved to be not very RTB friendly. The teeterblock/hub bar design is a mix of Tervamaki with the old “half-moon” tracking feature installed and the Averso/GyroTech style chordwise shifting barrel. I felt that adding the half-moon feature was particularly unfortunate because it meant that you had to loosen and re-tighten the 4 bolts fixing the teeter block to the bearing to adjust the track and those bolts take the entire weight of the gyro, unlike the classic half-moon on the Bensen style where these bolts take very little actual load. Tightening these bolts to the required torque while maintaining whatever tracking adjustment we were trying to achieve proved very difficult, added to which the half-moon was the wrong way around causing each tracking adjustment to create a secondary chordwise movement. This design also means that there is no reliably accurate means of measuring the tracking adjustment that you’d just made. Added to that there was no way of measuring accurately the rotation of the chordwise barrel.

I was unhappy to leave the owner with the job half-finished but he clearly understood the weakness of the design and told me afterwards that he’d created a set of shim blocks to be able to accurately measure the adjustment and that allowed him to tighten the 4 bolts solidly and not rely on the half-moon to hold the tracking adjustment. I gave him a simple design solution to resolve the problem in the hope that Niki might listen to him rather than me.

The 2 TAGs also proved to be very RTB unfriendly. Initially giving us curved move lines and then often not responding to adjustments as we expected. In the end we managed to improve them and they were much better than when we started but not down to a level of vibration that satisfied me.

The TAG rotor head and hub bar is based on the Tervamaki design using titanium for the two hub-bar side plates. The TAG rotor blades are similar in concept to the Tervamaki original design with the blades held in by 2 simple horizontal bolts, which made more sense to me than the Niki design which needed an adapter from 2 horizontal bolts to the classic cluster plate vertical bolts.

The teeter block uses an ELA style chordwise adjustment barrel in the central teeter tower and adjusts the pitch/tracking by shimming the teeter block. Getting the shims in wasn’t easy and like the Niki meant releasing and re-tightening the 4 teeter block bolts that carry the entire weight of the gyro; bolts that I’d rather leave torqued up once and for all. It also meant that we needed to lift the rotor to separate the teeter block from the hub bar so that we could install the tracking shims. It was impossible to accurately measure the chordwise adjustment because the special protractor and adjustment bar (that I know exists at TAG) was never supplied to the owners so we were forced to guess the angle based on the assumption that there were 6 equally spaced holes in the barrel and tried to use a digital protractor (smartphone) to measure the angles.

Another thing that was surprising was the level of 2/rev vibration at the rotor head. In the TAG with a split mast, the side to side (X) direction the 2/rev was as high as 7 IPS, normally in typical tandem Eurotubs (ELA, Magni, AG) it is between 2.7 and 4.0 IPS. The solid mast TAG had 2/rev vibrations more in line with what we usually see. The split mast TAG also had significantly higher 2/rev vibration in the cockpit compared to the solid mast.

Before I get accused of only knocking Niki and TAG, they were both very comfortable and extremely well finished but remember I’m very focused on RTB and therefore critical of what I see as short comings in design that make RTB unnecessarily awkward, imprecise and non-repeatable. I could equally list the short comings of every gyro rotor design out there; they could all be better and more precise with a little effort but most gyro “designers” seem very reluctant to change when you try to tell them that their design could be better.

Mike G

Hi Mike
Thank you for your time whilst in Australia I can now accurately shim the pitch on my Kallithea and I have also a spanner I can measure degrees of rotation on, and 6 degrees is a 1 thou shift. It is now an easy process!

 

[Mike G]

Hi Mike
Thank you for your time whilst in Australia I can now accurately shim the pitch on my Kallithea and I have also a spanner I can measure degrees of rotation on, and 6 degrees is a 1 thou shift. It is now an easy process!

Well done Brian, thanks for keeping us all updated. Glad the PB4 training helped, as I said in earlier post I was really unhappy leaving you without finishing the RTB but without your mod we couldn't go any further. Perhaps you can now teach the manufacturer how to do it.
Mike

 

[Bri350fly]

Well done Brian, thanks for keeping us all updated. Glad the PB4 training helped, as I said in earlier post I was really unhappy leaving you without finishing the RTB but without your mod we couldn't go any further. Perhaps you can now teach the manufacturer how to do it.
Mike

Hi Mike
Thank you we are working together with this