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So i've been having troubles with my slave struts vibrating in very specific regimes sometime while flying aerobatics but mostly if i get a bit of sideslip on the plane in level flight below 125 MPH or so. I have tried trip strips of strings, rods and the like at lots of locations on one side, on both sides of the slave strut. Neither of which ever completely solved the problem. Actually in the the case of the trip strip on both sides of the slave strut it caused a flutter just after takeoff (which will really get your attention) and a quick abort to the runway.
Its important to note that there can be two things that cause a vibratory mode in the slave strut 1) could be there is a dynamic alignment of the natural frequency of the slave strut and the engine or propeller imbalance. or 2) Aeroservo elastic response (flutter) where the strut builds up lift then stalls and sheads it causing the flow to reattach and build again in a fairly high frequency oscillation. Typically You can sort out which one you have by changing the RPM of the engine if it goes away by adding power or reducing power its likely a dynamic response. It it comes on with sideslip or if you can get it to go away with reducing or increasing side slip its likely flutter. Its important to know that one could feed the the other as well.
Anyway I've been living with this issue for many years and have always messed around trying to find something that fixes it. One day I was watching a video that Francois Marquis posted of the good old days before he sold out of the biplane world and into the monoplane world. He had a beautiful Christen Eagle. I noticed in the video that he had a zig zag strip on the slave strut and I asked him about it he said it worked great i pulled screen grab to remind me for later. The stuff is commonly used in the sailplane/Glider world to lightly add energy to the flow with micro vortexes i've seen them for rotor blades, props but never thought in those applications it worked or at least not measurably. In the low reynolds number applications just as on my struts I thought they had a chance. Besides i've tried everything else worst thing that would occur is they don't do anything.
I looked up online to buy the stuff and it was available from a number of resources but under the term turbulator tape Zig Zag & Dimple Turbulator Tape
There are number of different research articles on the subject and I have nearly always thought their advantages were snake oil. Anyway I looked at what they were selling and I thought hell it kind looks the size and rough shape of my pinking shears. So I took my Frost King tape (seriously love this stuff and its really inexpensive) and marked a center line on it then measured over 5/8" on both sides of the tape and pinked as straight a line as I could then applied them to the leading edge such that it wraps around to about the point of max thickness or maybe just beyond on both sides.
On my flight I test was not able to induce a flutter at any speed from 80-130 MPH which was always very reliably repeated. I haven't tested high speeds side slips yet but I never had problems there. So I'd say this is a dramatic improvement and I'm fairly happy as they are difficult to see and drag should be less than a rod/string or other trip strip. Your mileage may vary, but if you get desperate you can try this instead of the trip strip. If you do try this I would love to hear about your results as well. To be honest I'm still skeptical of them but hey if it works it works. (shrug)
Its important to note that there can be two things that cause a vibratory mode in the slave strut 1) could be there is a dynamic alignment of the natural frequency of the slave strut and the engine or propeller imbalance. or 2) Aeroservo elastic response (flutter) where the strut builds up lift then stalls and sheads it causing the flow to reattach and build again in a fairly high frequency oscillation. Typically You can sort out which one you have by changing the RPM of the engine if it goes away by adding power or reducing power its likely a dynamic response. It it comes on with sideslip or if you can get it to go away with reducing or increasing side slip its likely flutter. Its important to know that one could feed the the other as well.
Anyway I've been living with this issue for many years and have always messed around trying to find something that fixes it. One day I was watching a video that Francois Marquis posted of the good old days before he sold out of the biplane world and into the monoplane world. He had a beautiful Christen Eagle. I noticed in the video that he had a zig zag strip on the slave strut and I asked him about it he said it worked great i pulled screen grab to remind me for later. The stuff is commonly used in the sailplane/Glider world to lightly add energy to the flow with micro vortexes i've seen them for rotor blades, props but never thought in those applications it worked or at least not measurably. In the low reynolds number applications just as on my struts I thought they had a chance. Besides i've tried everything else worst thing that would occur is they don't do anything.
I looked up online to buy the stuff and it was available from a number of resources but under the term turbulator tape Zig Zag & Dimple Turbulator Tape
There are number of different research articles on the subject and I have nearly always thought their advantages were snake oil. Anyway I looked at what they were selling and I thought hell it kind looks the size and rough shape of my pinking shears. So I took my Frost King tape (seriously love this stuff and its really inexpensive) and marked a center line on it then measured over 5/8" on both sides of the tape and pinked as straight a line as I could then applied them to the leading edge such that it wraps around to about the point of max thickness or maybe just beyond on both sides.
On my flight I test was not able to induce a flutter at any speed from 80-130 MPH which was always very reliably repeated. I haven't tested high speeds side slips yet but I never had problems there. So I'd say this is a dramatic improvement and I'm fairly happy as they are difficult to see and drag should be less than a rod/string or other trip strip. Your mileage may vary, but if you get desperate you can try this instead of the trip strip. If you do try this I would love to hear about your results as well. To be honest I'm still skeptical of them but hey if it works it works. (shrug)
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