8KCAB Decathlon 8KCAB 1973

[Charks_Wilson]

really appreciate all the insight on this forum. I want to reach out about an vibration issue I’m experiencing on my decathlon.

1973 8KCAB
IO 320 E1A
Converted to christen inverted system
Hartzell propeller

Alieron spades
Wheel pants with 700 6s
Recovered in 2014
Flys straight and true with just a touch of right rudder in cruise but mostly hands off in smooth air.

Prop has been statically balanced last week and will get dynamically balanced in 14 days or so.

I’ve owned the airplane for 1 month.

I’ve noticed a vibration or “seat buzz” in mostly the front seat. It seems to increase with speed but it is hard to say. I know long term vibration can cause a plethora of issues so I want to remedy as soon as possible. Potentially below 80 MPH I notice a reduction in vibration. I have flown two other 150 hp decathlons and never noticed this much vibration. Looking at the tail as best I can while flying I see no noticeable vibration. I will be mounting a camera rear facing shortly to see if I can pick anything up on video. Tail flying wires seem to be taunt.

Engine mounts were replaced in 2020
No carpet on floorboards
Belly fabric seems to be in decent shape.
I’ve read missing/broken cross members on the belly fabric can cause drumming/vibration

Any insight would be greatly appreciated!

Please feel free to reach out!

Regards
Andy

 

[vupilot]

It's hard to understand what kind of vibration you are feeling through text, but I wouldn't consider any of these older Decathlon's as the smoothest running airplanes by any stretch. Fabric drums, heavy metal props, lots of draggy struts disrupt air, and that tin pan right under your feet. I just dynamically balanced to within 0.04 IPS. Started at 0.20. My phone mount running Foreflight still shakes a good bit, so does the hula girl on the glareshield but I can feel the improvement certainly as well. Do the balance, run the camera all directions, check for loose fabric, skylight, wheel pants, spinner wobble, a wheel rotating rather quickly inflight, etc.