Mike G
Junior Member
- Joined
- Jun 16, 2005
- Messages
- 1,917
- Location
- Lillebonne France
- Aircraft
- Owned Magni M16 now ELA 07
- Total Flight Time
- 550FW + 500 gyro
I have recently tracked and balanced three gyro rotors and all of the owners expressed disappointment in the lack of impact of tracking and balancing on “stick shake”. Added to that, TexasAutogyro’s recent post implies that you can cure stick shake by using a dynamic balancer.
Experience makes me believe that stick shake is primarily a problem of control system damping and that unless you have a major 1/rev vibration due to unbalance or tracking (perhaps TexasAutogyro’s initial situation), then the usual stick shake vibration is 2/rev and cannot be reduced with a balancer.
To demonstrate this I took a couple of videos of the Smart Avionics test bed gyro and flew two flights, one with the roll pivot bushing and roll control tube friction clamp “squeezed” tight and another with these loose. I also recorded stick shake with a PB3 but dropped my tablet and no longer have the data. However I think the videos speak for themselves.
The thing to notice is the frequency at which the stick is shaking; this clearly is not “ketchup bottle” 1/rev frequency. This is 2/rev and the frequency spectrum (now lost) clearly showed this.
https://youtu.be/Vwd5g8o9yCw
In this video there’s virtually no shake, but the difference is nothing to do with tracking or balancing.
https://youtu.be/eAzHjj-W-bI
The “improvement” was exclusively due to increasing the friction damping of the control system by “pinching” the roll pivot and roll control tube friction clamp. I tried to tighten the pitch pivot but due to the design I couldn’t get it any tighter.
Perhaps using a hydraulic damper would have the same effect as friction damping.
The one thing that isn’t obvious in the video (probably due to the cameras inbuilt stabilizer) is that with the friction increased the stick shook less but the cockpit vibrated more.
There’s no such thing as a free lunch.
Mike G
Experience makes me believe that stick shake is primarily a problem of control system damping and that unless you have a major 1/rev vibration due to unbalance or tracking (perhaps TexasAutogyro’s initial situation), then the usual stick shake vibration is 2/rev and cannot be reduced with a balancer.
To demonstrate this I took a couple of videos of the Smart Avionics test bed gyro and flew two flights, one with the roll pivot bushing and roll control tube friction clamp “squeezed” tight and another with these loose. I also recorded stick shake with a PB3 but dropped my tablet and no longer have the data. However I think the videos speak for themselves.
The thing to notice is the frequency at which the stick is shaking; this clearly is not “ketchup bottle” 1/rev frequency. This is 2/rev and the frequency spectrum (now lost) clearly showed this.
https://youtu.be/Vwd5g8o9yCw
In this video there’s virtually no shake, but the difference is nothing to do with tracking or balancing.
https://youtu.be/eAzHjj-W-bI
The “improvement” was exclusively due to increasing the friction damping of the control system by “pinching” the roll pivot and roll control tube friction clamp. I tried to tighten the pitch pivot but due to the design I couldn’t get it any tighter.
Perhaps using a hydraulic damper would have the same effect as friction damping.
The one thing that isn’t obvious in the video (probably due to the cameras inbuilt stabilizer) is that with the friction increased the stick shook less but the cockpit vibrated more.
There’s no such thing as a free lunch.
Mike G