Stick shake

Mike G

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Jun 16, 2005
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Lillebonne France
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Owned Magni M16 now ELA 07
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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
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Tampa, FL
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AR-1
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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
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Jan 2, 2009
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2,349
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Centre FRANCE
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I piloted gliders C800, Bijave, C 310, airplanes Piper J3 , PA 28, Jodel D117, DR 220, Cessna 150, C
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About 500 h (FW + ultra light)
Mike's explanations are remarkably accurate.
Thanks for his help.
 

Tyger

Super Member
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Nov 25, 2017
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Clermont, NY
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How is it that Mike G – a member for sixteen years with over 1,500 postings – gets a "Junior Member" subtitle? :unsure:
 

lindandavid

Gold Supporter
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Jun 16, 2014
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Alto, NM
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Sparrowhawk
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How is it that Mike G – a member for sixteen years with over 1,500 postings – gets a "Junior Member" subtitle? :unsure:
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
Joined
Oct 21, 2006
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5,303
Location
Colorado front range
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Bell 47G-3B-1 / A&S 18A / Phoebus C, etc.
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stopped caring at 1000
It used to be user modifiable, which is pretty obvious from mine. Haven't tried making any changes lately.
 

Smack

Re-member?
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Georgetown
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"Obvious", is it ? :rolleyes:
 

Burrengyro

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Dec 15, 2020
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Ireland
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ELA07S and Montgomerie Bensen (project)
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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

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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
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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

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ELA07S and Montgomerie Bensen (project)
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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
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Jul 6, 2019
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358
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france
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300+ flexwing (pendulaire) newly trained on gyrocopter ((autogire)100h)
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
teeter bolt bush 2.jpgrotor head.jpg500size SHIM CARRIER 2.jpg500 size SHIM CARRIER 1.jpgshim carrier 2.jpg

phil
 

Jazzenjohn

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Milan Mich.
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I've designed, built, and flown 4 different ultralight gyros. Amassing parts for a 2 place now.
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Wait... What??? You're NOT the Supreme Allied Gyro CFI ????
 

Abid

AR-1 gyro manufacturer
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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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Burrengyro

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ELA07S and Montgomerie Bensen (project)
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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
Joined
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Messages
4,399
Location
Tampa, FL
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AR-1
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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
 

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Brian P

Member
Joined
Jun 10, 2019
Messages
52
Location
Nottingham UK
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.
 
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