Stabilizer Streamline Strut Vibrations

[Steve W]

And Brooks, yes, I’ve seen the video which made me such a believer in streamlining everything I could. I do believe, however that the streamline stuff I had on the tail wires was a direct cause of the forged end breaking as quick as it did.
I used coverings everywhere I could which helps the final airspeed, shock tubes etc.

[whee]

Streamlining is great but you have to make sure it is online with the airflow. If not then it adds drag and may induce flutter.

For my round shock struts I plane to glue some profiled wood to the back of the struts. This solution could be used on a round tail strut.

Steve, You should call Bob. He’s always been helpful when I wanted to change something.

[svyolo]

I really wonder what is the axis of excitation. Bending, or twisting. The clevis end would have little to no added stiffness, in twisting. The stab end with the bolt is doing all that work in that axis.

[Steve W]

Whee, I used plastic streamline covers for my lower strut tubes. I had to shape the ends around the weldments but was happy with the final look. I filled the open ends with some caulking adhesive.
I used the small sized tubing and had it cut to a rough length for shipping. Go to the Aerolite 103 website and see what they have there.

[Steve W]

Just a pic of the plastic tubing

[svyolo]

A lot of higher performance hang gliders have very slick airfoil shaped external tubing. It forms the triangle that you control the glider with, and supports positive G air loads. The better stuff is pretty thin and low drag. The vast majority of them have what is essentially a full length stall strip or strips on both sides of the tubing, full length. It has been a while but I remember it was there to solve a lot of potential problems, including bending from generating lift and maybe flutter. 10 - 40% MAC from the leading edges.

[Walt Plentis]

Try taping a 1/16” piece of music wire on one side of the strut. This is commonly done on Pitts aileron interconnect struts and works well. It changes the lift on one side of the surface and the strut will tend to pull slightly in one direction rather than vibrating back and forth

[robcaldwell]

I had to Google "Music Wire". Never heard of it before... https://www.hobbylobby.com/Crafts-Ho...039%22/p/25259

[Steve W]

Thanks Walt. That’s a great way to troubleshoot. I would make another set if I could determine which way it needs to go to be more inline with the airflow.

[Walt Plentis]

Start with the tape and if you like the results you can weld the wire on if you want but I’ve never had one that’s taped on come off

[Bcone1381]

Streamlining is great but you have to make sure it is online with the airflow. If not then it adds drag and may induce flutter.

For my round shock struts I plane to glue some profiled wood to the back of the struts. This solution could be used on a round tail strut.

Steve, You should call Bob. He’s always been helpful when I wanted to change something.

Regarding Shock Strut Streamlining.....I'll add that on the Patrol Plans (before the Shock Strut went to a round tube) Bob allowed for an 8 Degree twist so that the strut was streamlined with airflow.
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The experts say that the ideal length of streamlining is 3.7 times the diameter with thickest part at 37% aft of the leading edge. I spent I think 3 months making these gear leg fairings for the round tube shock strut. It was my first fiberglass project. Only started over once. In the end I learned about vacuum bagging too. Those fairing from aerolite will save you time. Bob has a fairing for the shock strut tube available. Don't make your own. Putting weight in the leading edge like we do our control surfaces would help accommodate flutter.

If you make the lower part of the fairing as a separate piece and attached it to the round lower tube of the shock strut with a round hose clamp, it would be adjustable to align with the airflow.

I might make mine over. Maybe chop off the lower part and rework things. Who knows.....actually....Brooks, don't do that until after its flying.
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[svyolo]

Wow, that does look like a lot of work. Nice.

[Steve W]

Just an update on the vibration, I haven’t received the turbulator tape yet so I tried the 1” strips like Mike S tried. I flew yesterday for an hour without ballast in the back up to speeds of 155 mph and the vibration is gone. Everything I could see remained calm, struts and wires.
Thanks to all that assisted on this issue. Appreciate the forum and it’s value for the shared info.

[svyolo]

Glad something worked. Thanks for the update.

[Mark Goldberg]

Please post a picture of the tape on the hor stab struts to see what it looks like and where you placed it Steve. Mark

[Steve W]

Sure will Mark. It will be a while. The plane is an hour away and will be sometime before I’m up there again unless the weather warms up.

[Steve W]

Picture of the velcro strips used to stop vibration

[Nev]

Good to see you got it sorted. I was wondering if that could be the cause of fatigue issues on the threaded portion inboard, if the vibration is left to continue.

[Mark Goldberg]

Thanks for posting this Steve. You put more velcro strips than I imagined. I wonder if fewer strips would accomplish the same thing? Maybe someone will play with it and answer this question. Mark