# Stick shake

#### Mike G

##### Junior Member
Abid

What Jean Claude is saying is that, if the rotor blades are infinitely stiff torsionally and/or have the CofG exactly at the centre of lift point chordwise, then an increase in load (say 2 G) increases Rrpm by 1.414 (square root of 2) and that increase in Rrpm increases the centrifugal/petal (depending upon your religion) force by the increase in Rrpm squared (1.414 squared = 2). Therefore when you look at the coning angle triangle of forces the vertical load force vector has increased by 2 and the centrif force vector has also increased by 2 so the coning angle remains unchanged.

Now in reality blades are not torsionally stiff and the chordwise CofG is probably not at the CofLift. So an increase in load will increase Rrpm and hence centrif force and that centrif force that is offset from the CofLift will twist the blade giving a positive twist if the CogG is behind (nearer the trailing edge) or a negative twist if the CofG is in front of the CofLift. This means that the blade pitch angle will cause the Rrpm to be higher (if pitch is reduced) or lower if pitch is increased and the coning angle centif force vector will be longer or shorter than the theoretical one hence decreasing or increasing the coning angle.
Mike

#### Abid

##### AR-1 gyro manufacturer
Abid

What Jean Claude is saying is that, if the rotor blades are infinitely stiff torsionally and/or have the CofG exactly at the centre of lift point chordwise, then an increase in load (say 2 G) increases Rrpm by 1.414 (square root of 2) and that increase in Rrpm increases the centrifugal/petal (depending upon your religion) force by the increase in Rrpm squared (1.414 squared = 2). Therefore when you look at the coning angle triangle of forces the vertical load force vector has increased by 2 and the centrif force vector has also increased by 2 so the coning angle remains unchanged.

Now in reality blades are not torsionally stiff and the chordwise CofG is probably not at the CofLift. So an increase in load will increase Rrpm and hence centrif force and that centrif force that is offset from the CofLift will twist the blade giving a positive twist if the CogG is behind (nearer the trailing edge) or a negative twist if the CofG is in front of the CofLift. This means that the blade pitch angle will cause the Rrpm to be higher (if pitch is reduced) or lower if pitch is increased and the coning angle centif force vector will be longer or shorter than the theoretical one hence decreasing or increasing the coning angle.
Mike

Got it. I thought so but was not clear that is what he was getting at

#### Jean Claude

##### Junior Member
Mike's explanations are remarkably accurate.
Thanks for his help.

#### Tyger

##### Super Member
How is it that Mike G – a member for sixteen years with over 1,500 postings – gets a "Junior Member" subtitle?

#### lindandavid

##### Gold Supporter
How is it that Mike G – a member for sixteen years with over 1,500 postings – gets a "Junior Member" subtitle?
I was wondering how that works too. I've been a member for 6 years but I'm still a newbie.

#### WaspAir

##### Supreme Allied Gyro CFI
It used to be user modifiable, which is pretty obvious from mine. Haven't tried making any changes lately.

#### Smack

##### Re-member?
"Obvious", is it ?

#### Sv.grainne

##### Active Member
Not obvious to me!

#### Tyger

##### Super Member
Haha, did you guys imagine the title "Supreme Allied Gyro CFI" was granted by admin?

#### Burrengyro

##### Gold Supporter
If tracking with shims resolved your problem then it was 1/rev, no doubt about it.

AutoGyro use stainless steel shims for tracking, I use plastic shims, they're colour coded so that later I can see what thickness is there without having to take them out and measuring them.
Hi Mike G,
Bought a set of colour coded shims as per your comment above. Very handy!!! I used some of these shims to improve the blade tracking in my ELA07S. I also used a pair of these plastic shims to remove some slop between the hub bar block and the teeter tower. Do you have any concerns about the long term use of using these plastic shims to remove slop in the teeter tower? Have machined some stainless steel shims of the same size as replacements, just in case....
Many thanks, John H.

#### Burrengyro

##### Gold Supporter
Hi Mike G and all,
What is the optimum clearance between the teeter tower and the hub bar teeter block in a gyro such as an ELA07S?
Many thanks, John H

#### Abid

##### AR-1 gyro manufacturer
Hi Mike G and all,
What is the optimum clearance between the teeter tower and the hub bar teeter block in a gyro such as an ELA07S?
Many thanks, John H
Nothing. There should be no play side to side but it should not be so snug tight that the teeter operation has resistance.

#### Burrengyro

##### Gold Supporter
Nothing. There should be no play side to side but it should not be so snug tight that the teeter operation has resistance.
Hi Fara,
Many thanks for the info. Any thoughts on the use of plastic shims rather than steel or stainless steel shims to eliminate teeter tower side to side play?
Thanks, John H

#### JETLAG03

##### Active Member
guessing my rotor head system may be different in design. The teeter movement is in bearings and the bushes are held static to the tower. In an attempt to give lateral adjustment I have designed "bush caps" that fit shoulders of the bushes giving +2mm -2mm (4mm) of adjustment in steps of 0.2mm. The "bush caps" in pictures 3 and 4 vary in thickness 0.6mm/0.7mm/0.8mm/0.9mm each with a wall of 1mmx2mm

phil

#### Jazzenjohn

##### Gold Supporter
Wait... What??? You're NOT the Supreme Allied Gyro CFI ????

#### Abid

##### AR-1 gyro manufacturer
Hi Fara,
Many thanks for the info. Any thoughts on the use of plastic shims rather than steel or stainless steel shims to eliminate teeter tower side to side play?
Thanks, John H

No need to use stainless steel shims to tighten the teeter bolt gap. If the play is slight which it should be, then simply tightening the teeter bolt and nut would be ok. If the play is significant, you need new shims made. Same on either end. In AR-1 we use 40 thou bent sheet shims and then tighten the bolt up. This is ok to do on teeter blocks like Averso but should not be done on rotor hubs like AutoGyro etc. However, some of this also depends on what and how big the flanged pressed in bushings are in your teeter towers. That is why this advice should come from ELA technically. I don't think what I am telling you will not apply to ELA but I am not an ELA expert or designer and if they have done something funky, my advice may not work. Teeter towers, teeter bolt, the flanged bushings pressed into teeter towers (or some have bearings in the teeter tower) all are airframe manufacturer's doing and they should be consulted while doing this.
To be on the record this advice is worth exactly what you paid for it

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#### WaspAir

##### Supreme Allied Gyro CFI
Wait... What??? You're NOT the Supreme Allied Gyro CFI ????
Of course I am. Just ask the United Nations High Commissioner for Rotorcraft. But it's not one of the default automatic titles in the forum software.

#### Burrengyro

##### Gold Supporter
No need to use stainless steel shims or tighten the teeter bolt. If the play is slight which it should be, then simply tightening the teeter bolt and nut would be ok. If the play is significant, you need new shims made. Same on either end. In AR-1 we use 40 thou bent sheet shims and then tighten the bolt up. This is ok to do on teeter blocks like Averso but should not be done on rotor hubs like AutoGyro etc. However, some of this also depends on what and how big the flanged pressed in bushings are in your teeter towers. That is why this advice should come from ELA technically. I don't think what I am telling you will not apply to ELA but I am not an ELA expert or designer and if they have done something funky, my advice may not work. Teeter towers, teeter bolt, the flanged bushings pressed into teeter towers (or some have bearings in the teeter tower) all are airframe manufacturer's doing and they should be consulted while doing this.
To be on the record this advice is worth exactly what you paid for it
Hello Fara,
Many thanks. ELA Aviacion use a threaded barrel in which bearings are mounted and this barrel is threaded into the teeter block, no bushings in the ELA tower. The threaded barrel can be turned to move the hub bar along the teeter bolt to find the best vibration-free location for the rotors. Am I correct in thinking that this location may not coincide with the centre point between the teeter tower sides?

I am currently using 2 plastic shims 0.25mm thick on either side of the teeter block to remove the side-to-side slop along the teeter bolt between the teeter block and the teeter tower sides. I have machined stainless steel shim washers to replace the plastic shims if this is what experienced forum members recommend. Maybe someone with hands-on experience with the optimum teeter tower setup for ELA07S gyros might be able to share their insights with the forum?

Many thanks for any info shared. John H.

#### Abid

##### AR-1 gyro manufacturer
Hello Fara,
Many thanks. ELA Aviacion use a threaded barrel in which bearings are mounted and this barrel is threaded into the teeter block, no bushings in the ELA tower. The threaded barrel can be turned to move the hub bar along the teeter bolt to find the best vibration-free location for the rotors. Am I correct in thinking that this location may not coincide with the centre point between the teeter tower sides?

I am currently using 2 plastic shims 0.25mm thick on either side of the teeter block to remove the side-to-side slop along the teeter bolt between the teeter block and the teeter tower sides. I have machined stainless steel shim washers to replace the plastic shims if this is what experienced forum members recommend. Maybe someone with hands-on experience with the optimum teeter tower setup for ELA07S gyros might be able to share their insights with the forum?

Many thanks for any info shared. John H.

The shims between teeter block and teeter towers ... we do them not quite as washers but this way and they are stainless steel not plastic

#### Attachments

• teeter-bolt-shim.JPG
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#### Brian P

##### Member
If you were to allow the teeter block some small movement between the towers...wouldn't it centre up where it needs to be?
Probably a stupid question.