Stick shake

[Greg Vos]

Hi Mike,
Thank you for the reply. I am finding out the hard way that everything you say about stick shake is true!!! The learnings are good. I made the mistake of shifting the chord wise location in increments which were too large and missed the target big time. Looks like from your info above, I should be moving in steps of 0.05mm at a time followed by a test flight to measure progress.
John H.

I tried tracking by adding and removing shims…. It really is a time consuming job, also added reflectI’ve tape to the ends and used a sharp light to see the blades against a hanger door, ( cheap alternative to the LED lamps) Dave my partner in the gyro project agreed we got it as close as we could with minimum equipment and only basic knowledge, our video we placed could be as Mike says misleading as the phone software tends to smooth out shake, we do have slight cabin hop and I am hoping that we are not doing damage to the gyro by not having data on the vibration.

My concerns are that a xenon fell a while back with blades cracking as they exit the hub bar and this is on my mind during every flight

 

[JETLAG03]

Hi Mike,
Thank you for the reply. I am finding out the hard way that everything you say about stick shake is true!!! The learnings are good. I made the mistake of shifting the chord wise location in increments which were too large and missed the target big time. Looks like from your info above, I should be moving in steps of 0.05mm at a time followed by a test flight to measure progress.
John H

Hi John, how big were the increments? cannot be easy to make a step of 0.05mm. I am in the process of having shims created to give me steps of 0.5mm phil

 

[Eric S]

I have found tracking on the ground using reflective tape on the tips and my prerotator is only a starting point. In order to check my tracking while under flying loads, I wait until the sun is low in the sky, fly toward the sun and then make a slow, banked turn keeping the sun's reflection on the blade tips. It works well for me to see if the rotor tips are in the same plane.

I've also noticed it's hard to repeat changes, especially when it's by feel. Loosen or tighten a tracking adjustment nut by 1/2 or 1 flat (1/12 or 1/6 turn), then go fly to see if it's better or worse. If it's worse and I put it back where it was before, the stick shake doesn't always feel like it did before making the change. I can see the benefit of using accelerometers to remove subjectivity.

Eric

 

[Mike G]

Jetlag
If you're talking about 0.5 mm increments in chordwise "shift" along the teeter bolt that's much to big. 0.1 is the standard and 0.05 is preferable.
Are you going to Blois this year??
Mike G

 

[fara]

Hi John, how big were the increments? cannot be easy to make a step of 0.05mm. I am in the process of having shims created to give me steps of 0.5mm phil

0.5 mm ~ 20 thou ... that's a lot

 

[fara]

.......


So I've never fitted them to an Averso rotor but from memory they have a removable end cap that has some fixing screws that could be used to attach the standard Smart Avionics bracket. You could always make your own out of a piece of aluminium if you don't like plastic and Smart Avionics offer to make customized brackets.

Mike

I have fitted them on Averso on the end cap. There is I think a 5 mm (M5 or M6) screw that you can take out and use a longer screw of the same kind to install them. As I remember when you fly it, if you can see 2 different color LEDs, you are not in perfect track. When the two colors disappear and you see just a purple, they are in perfect track. Of course to see these the best way is to fly at sunset down the runway.

However, as Mike and other have mentioned perfect blade tip track isn't the target. Lower vibrations are and that can and do happen with slight out of track rotors

 

[JETLAG03]

Jetlag
If you're talking about 0.5 mm increments in chordwise "shift" along the teeter bolt that's much to big. 0.1 is the standard and 0.05 is preferable.
Are you going to Blois this year??
Mike G

Thanks Mike. Sadly, I cannot make Blois this year.

I must have had a "brain fart" on my last post #203 I am in the process of having some new caps made that will give me 0.1mm adjustments.

phil

 

[Burrengyro]

Hi John, how big were the increments? cannot be easy to make a step of 0.05mm. I am in the process of having shims created to give me steps of 0.5mm phil

Hi Phil,
I have the ELA threaded barrel chord wise adjuster in my hub bar block. I think one full rotation moves it 1mm chord-wise. There is no graduated reference with this system which is a pity. A 20 degree turn of the barrel should give a 0.05mm chord movement. Ultimately, what gives the least vibration is what I am look for. I made some stainless steel shims on the lathe to remove any chord-wise slop along the teeter bolt. What material are you using for your shim system. I was thinking of going to steel for ease of surface grinding the shims to a good accuracy but am concerned about inter metallic erosion of using steel next to aluminium.
Hi Eric,
Your "low sun" method of blade tracking is one I must try!
John H.

 

[Brian Jackson]

I have found tracking on the ground using reflective tape on the tips and my prerotator is only a starting point. In order to check my tracking while under flying loads, I wait until the sun is low in the sky, fly toward the sun and then make a slow, banked turn keeping the sun's reflection on the blade tips. It works well for me to see if the rotor tips are in the same plane.

I've also noticed it's hard to repeat changes, especially when it's by feel. Loosen or tighten a tracking adjustment nut by 1/2 or 1 flat (1/12 or 1/6 turn), then go fly to see if it's better or worse. If it's worse and I put it back where it was before, the stick shake doesn't always feel like it did before making the change. I can see the benefit of using accelerometers to remove subjectivity.

Eric

Cool idea about using the sun's reflection. Is there some optical trick to determining which blade is tracking high or low?

 

[JETLAG03]

Hi Phil,
I have the ELA threaded barrel chord wise adjuster in my hub bar block. I think one full rotation moves it 1mm chord-wise. There is no graduated reference with this system which is a pity. A 20 degree turn of the barrel should give a 0.05mm chord movement. Ultimately, what gives the least vibration is what I am look for. I made some stainless steel shims on the lathe to remove any chord-wise slop along the teeter bolt. What material are you using for your shim system. I was thinking of going to steel for ease of surface grinding the shims to a good accuracy but am concerned about inter metallic erosion of using steel next to aluminium.
Hi Eric,
Your "low sun" method of blade tracking is one I must try!
John H.

Hi John. I (my machinist) is using the same aluminium used for my teeter bolt bushes 2017A (au4g). Whilst there is aluminium/steel interface between the bush and bolt, I thought it easier to use the same material. I have 8 such bushes with the same 37.5mm shaft and shoulders which vary in increments of 0.5mm from 1.5mm to 3.0mm. By swapping the bushes and the shims mentioned in #208 (0.6mm to 0.9mm) I can adjust the position along the teeter bolt by +-2mm ie 4mm movement in 0.1mm increments.

phil

 

[Mike G]

Burrengyro John H
I think you'll find the thread on the ELA barrel is 1.5 mm pitch.
Steel shims should be OK (the teeter bolt is steel in aluminium) but make sure you protect it for rust, you're on the Atlantic coast. For that reason your plastic shims might be even better.
Mike G

 

[Burrengyro]

Burrengyro John H
I think you'll find the thread on the ELA barrel is 1.5 mm pitch.
Steel shims should be OK (the teeter bolt is steel in aluminium) but make sure you protect it for rust, you're on the Atlantic coast. For that reason your plastic shims might be even better.
Mike G

Hi Mike and all,
1.5mm ELA Barrel pitch explains a lot. So a 10-degree rotation gives approx 0.04mm shift chord-wise. No wonder I have been missing the target spot using 20 degree turns as a minimum. I started with the hub bar as close to the centre of the teeter tower as possible using shims, then using the barrel to move left or right and do a flight test to feel the results. Is there any particular flight manoeuvre I should use to best check for chordwise balance improvement without exciting some confusing input?

I may revert to the plastic shims to reduce slop along the teeter bolt soon. We get a lot of salt in the air on the Atlantic coast.
All and any advice gratefully received.
John H

 

[JETLAG03]

Hi Mike and all,
1.5mm ELA Barrel pitch explains a lot. So a 10-degree rotation gives approx 0.04mm shift chord-wise. No wonder I have been missing the target spot using 20 degree turns as a minimum. I started with the hub bar as close to the centre of the teeter tower as possible using shims, then using the barrel to move left or right and do a flight test to feel the results. Is there any particular flight manoeuvre I should use to best check for chordwise balance improvement without exciting some confusing input?

I may revert to the plastic shims to reduce slop along the teeter bolt soon. We get a lot of salt in the air on the Atlantic coast.
All and any advice gratefully received.
John H

Morning John.

For my part, a test flight using only "feel" is not a good technique to create reference points.
Difficult (impossible) to verify vibration levels without a system of registering and recording them.

I use a free program (thanks @Mike G) AMC mechanocaucho on my iphone (#2) shows some simple mountings I created for my iphone.

Once I am again mobile enough, maybe 5 weeks I will be re-commencing my rotor adjustment using equipment previously mentioned giving me an adjustment range of +-2mm (4mm)

phil

 

[Chook]

Hi Phil,
I have the ELA threaded barrel chord wise adjuster in my hub bar block. I think one full rotation moves it 1mm chord-wise. There is no graduated reference with this system which is a pity. A 20 degree turn of the barrel should give a 0.05mm chord movement. Ultimately, what gives the least vibration is what I am look for. I made some stainless steel shims on the lathe to remove any chord-wise slop along the teeter bolt. What material are you using for your shim system. I was thinking of going to steel for ease of surface grinding the shims to a good accuracy but am concerned about inter metallic erosion of using steel next to aluminium.
Hi Eric,
Your "low sun" method of blade tracking is one I must try!
John H.

Burrengyro I also have an ELA 07S with an unlogged chequered history - suffice to say it had some awful shakes.
I manufactured a simple tool to track my barrel changes and found that i could feel changes of 2 to 3 degrees of barrel rotation never mind 20 degrees!
Unfortunately I also discovered that the barrel and bearing tolerances were way out which precluded me from reproducing accurately any changes that were done. I have replaced the teeter bearings with our tried and tested bronze bushings. Indeed the bearing receptors in the original barrel were different tolerances so that when my machinist turned the new bushes he had to fit them individually. Then also had to build them so that when they were pressed they caused to barrel to expand to remove the "looseness" in the barrel threads. Very ordinary on the part of ELA. I am now waiting for an opportunity with Wolfy to bolt the analyser back on.
I am busy at the moment planning for a trip with some of the local guys to fly some 30 hours over 2 weeks so I wont be able to follow this thread. I hope what I have written helps someone to correct their "shakes"

Regards.........Chook.

 

[Mike G]

Dave H & Phil
Here is the polar chart from an ELA Eclipse that I balanced today. It has an Averso rotor but with the ELA hub bar so is pretty similar to Dave's and Chook's ELA.
You can see that the initial measurements were points 5 & 6 at 0.45, 0.84 IPS respectively.
I rotated the "barrel" 90° and got points 14 & 17. The vibration was reduced but you can see that I have overshot the centre. and need to turn the barrel 15° back to get nearer the centre.

What I hope this demonstrates is that if you are trying to balance by feel or by simply measuring the vibration, then in this example, after the first adjustment of 90° you would have thought "It's getting better I must rotate even further" and that would have made the vibration even worse as point 17 would have moved off north east and point 14 would have gone north west.
I post this example because it was such a simple balance and there's no confusion coming from spanwise imbalance and tracking. This example gives a simple illustration of the need to measure the phase angle while balancing not just the vibration.
This must be the easiest balance I've ever done, I hope it clarifies things a bit for you.

You will also note that a 90° rotation (0.375 mm or 15 thou) changed the vibration by 1.0 IPS (point 6 to 14). So if you want to work to less than 0.1 IPS (the industry standard) you need to be able to work to 0.0375 or 1.5 thou or less. Add that to my text about tracking in post 53 and you start to get a feel for how accurate you have to be if you're serious about rotor track and balance, shims made out of beer cans are good for bar talk but not for accurate RTB.

Dave H To answer your question "Is there any particular flight manoeuvre I should use to best check for chordwise balance improvement without exciting some confusing input?" I can only repeat what I've said before. There are guys out there who can track and balance without a balancer and I take my hat off to them, they have an experience and skill set that I don't have and I can only hope they'll come here to help you because I can't.
Mike G

 

[Burrengyro]

Dave H & Phil
Here is the polar chart from an ELA Eclipse that I balanced today. It has an Averso rotor but with the ELA hub bar so is pretty similar to Dave's and Chook's ELA.
You can see that the initial measurements were points 5 & 6 at 0.45, 0.84 IPS respectively.
I rotated the "barrel" 90° and got points 14 & 17. The vibration was reduced but you can see that I have overshot the centre. and need to turn the barrel 15° back to get nearer the centre.
View attachment 1153187
What I hope this demonstrates is that if you are trying to balance by feel or by simply measuring the vibration, then in this example, after the first adjustment of 90° you would have thought "It's getting better I must rotate even further" and that would have made the vibration even worse as point 17 would have moved off north east and point 14 would have gone north west.
I post this example because it was such a simple balance and there's no confusion coming from spanwise imbalance and tracking. This example gives a simple illustration of the need to measure the phase angle while balancing not just the vibration.
This must be the easiest balance I've ever done, I hope it clarifies things a bit for you.

You will also note that a 90° rotation (0.375 mm or 15 thou) changed the vibration by 1.0 IPS (point 6 to 14). So if you want to work to less than 0.1 IPS (the industry standard) you need to be able to work to 0.0375 or 1.5 thou or less. Add that to my text about tracking in post 53 and you start to get a feel for how accurate you have to be if you're serious about rotor track and balance, shims made out of beer cans are good for bar talk but not for accurate RTB.

Dave H To answer your question "Is there any particular flight manoeuvre I should use to best check for chordwise balance improvement without exciting some confusing input?" I can only repeat what I've said before. There are guys out there who can track and balance without a balancer and I take my hat off to them, they have an experience and skill set that I don't have and I can only hope they'll come here to help you because I can't.
Mike G

Hi Mike,
Thanks for the excellent real world example. The PB-4 looks like the real deal! John H.

 

[Mike G]

John
Don't get fooled by my example into thinking that track and balance with the PB4 is simple. I've tracked and balanced over a hundred rotors and this is the only time things have worked out so easily. It was quick because, with experience, I could see from the relative position of the first two points that the cause was probably mainly chordwise shift, that plus a lot of luck. If it had been earlier in my RTB experience it would have taken a lot longer. It was so quick I only asked the owner for half my usual fee.
Mike G

 

[fara]

Dave H & Phil
Here is the polar chart from an ELA Eclipse that I balanced today. It has an Averso rotor but with the ELA hub bar so is pretty similar to Dave's and Chook's ELA.
You can see that the initial measurements were points 5 & 6 at 0.45, 0.84 IPS respectively.
I rotated the "barrel" 90° and got points 14 & 17. The vibration was reduced but you can see that I have overshot the centre. and need to turn the barrel 15° back to get nearer the centre.
View attachment 1153187
What I hope this demonstrates is that if you are trying to balance by feel or by simply measuring the vibration, then in this example, after the first adjustment of 90° you would have thought "It's getting better I must rotate even further" and that would have made the vibration even worse as point 17 would have moved off north east and point 14 would have gone north west.
I post this example because it was such a simple balance and there's no confusion coming from spanwise imbalance and tracking. This example gives a simple illustration of the need to measure the phase angle while balancing not just the vibration.
This must be the easiest balance I've ever done, I hope it clarifies things a bit for you.

You will also note that a 90° rotation (0.375 mm or 15 thou) changed the vibration by 1.0 IPS (point 6 to 14). So if you want to work to less than 0.1 IPS (the industry standard) you need to be able to work to 0.0375 or 1.5 thou or less. Add that to my text about tracking in post 53 and you start to get a feel for how accurate you have to be if you're serious about rotor track and balance, shims made out of beer cans are good for bar talk but not for accurate RTB.

Dave H To answer your question "Is there any particular flight manoeuvre I should use to best check for chordwise balance improvement without exciting some confusing input?" I can only repeat what I've said before. There are guys out there who can track and balance without a balancer and I take my hat off to them, they have an experience and skill set that I don't have and I can only hope they'll come here to help you because I can't.
Mike G

I can confirm the point Mike is making.
We just balanced an old AR-1 that was put out of balance (long story) today. Took a few hours. But it had been tried to be balanced by feel or by partial use of spanwise balancing (single axis accelerometer).

In the end we took out all the shims put in it for tracking (by feel). They were way too much at 8 thou +. That actually took away half of the problem right there. In the end following the process

1) Install the accelerometer(s) and RPM optical measurement sensor appropriately and in the sense/orientation, that makes sense within your system
2) Make move lines (X and Y) for each

Chord
Span
Pitch

in 6 short flights but with adding washers, trunnion movement, shims deliberately for move lines.

3) Reduce it to a solution using PB-4 or another tool's sub-menu and then select and apply one of the recommendation of the solution. In this case with PB-4 move chord -0.8 which in our case is 12 degrees rotation on the trunnion on Averso Stella as we defined 1 in chord units as quarter of the flat turn on Averso 6/hex trunnion and quarter turn then is 360/6 x 0.25 = 15 degrees. Thus 0.8 would be 15 x 0.8 = 12 degrees

3) Took another measurement after the trunnion movement in chord to get another point, reduced to a solution again in PB-4 and added 2 thou Aluminum shim to reduce pitch of the master blade.

The IPS came down to under 0.07 in both X and Y

Feel does not work generally. You can go from one side to the other and it feels the same and you have no clue you have overshot it by far. 12 degree rotation of trunnion and a 2 thou shim would be minor changes according to some but that is all it takes to get rid of things. You can also measure 2/rev by putting 2 reflective tapes instead of 1.

In my humble opinion, all the stuff about tracking on the ground for an autorotating rotor (like with flag), your feel, and the stick not shaking does not really mean too much. I have seen 0.8 IPS with stick not shaking and 0.2 IPS with stick shaking a bit like a yoyo. Stick shake could simply point to slack or looseness in control circuit and nothing more or it could be imbalance or lack of tracking. You really don't know till you have the numbers. Get the numbers. That does not mean your gyro's structural elements are not getting vibration. It just means your stick is not getting the 1 per rev shake. You may be happy but your gyroplane isn't. In the end the only proper scientific way to do this is to get the darn numbers, use the numbers and do a systematic approach to reduce them. To do that you have to have the equipment, know how to use it and know how to make move lines, understand how to reduce to a solution in a stepwise manner. And do this in flight not on the ground.

 

[DavePA11]

Mike, I don’t think you should reduce your fee if the job is accomplished in less time. Paying for the end results, and not how long it takes. IMO. Nice work!

 

[Mike G]

Fara
thanks, it's good to have a user come on with experience that confirms what I've said in some of my posts. Otherwise I get the impression I'm a lonely voice in the wilderness.

Dave
This might surprise you but I don't actually make any money at this, I don't even come close to breaking even. I'm retired with a reasonable pension and my aim is to make friends, meet and if possible help fellow gyro pilots. I'm doing fewer rotors in France since I've been kicked out of the French autogyro forum for disagreeing with one of the movers and shakers but this rotor was at a base near me and the guys there have become friends over time so I was happy to help.
Mike G