Lift Strut Harmonic

[Jmilless]

I have a harmonic in my left side lift struts when the throttle is at or close to idle and speed is below 85mph. It is definitely from turbulent airflow from somewhere, the only thing that has had any effect is a small slip and or the addition of flaps. When the power is at normal settings there is no harmonic. It also seems to only occur when I am in a nose level to nose down attitude, I can't say I have noticed it in a nose high attitude.

I have tried different rigging to match the lift strut angle of attack from side to side since I have no issue on the right side lift struts. I have adjusted the cable tension and have worked with shimming the cable guides, the increased cable tension offered a small improvement. When the increased cable tension helped I tried adding plastic covers to the cables that West Marine sells, this had no effect.
I have also tried some grip tape on the top and bottom of the lift struts with little effect. The prop is balanced, I balance it any time I change the prop pitch.
My left front jury strut did shear the solid rivets in the first 10hrs of flight, but since then I have replaced them with the Cherry Max rivets I have had no issues in 60hrs. I have a fuel pod but there is no difference on or off.

Anyone had a similar experience?


My setup:

• 88" Sterna Prop
• O-360 11:1 compression
• 3x3 gear which is covered
• 31" bush wheels
• Lew Aero Fuel Pod (On and Off)
• P-Stol Flaps

[Pete D]

If I remember right, you have an EX2? The larger, high compression engine and larger diameter prop most likely have something to do with it. You might see if you can borrow a different prop for a flight or two, see if that changes how it behaves.

The EX3 has different lift struts with the bigger engine/larger diameter prop and slightly different wing.