Horizontal Stabilizer vibration

[rocketman2tm]

I just installed an Airmaster propeller on my Kitfox. One of the things I noticed is that I'm getting some heavy shaking on the stick during takeoff. As soon as I switch the controller from takeoff to climb, the shaking stops. I looked at my Insta360 video and I think I've found the culprit. The horizontal stabilizer is doing a bunch of moving around right after I get airborne and goes until I switch to climb.

I know this is a common thing with super cubs but I've never heard of it with a Kitfox. One thing to note is that on my airplane I usually trim just nose down of neutral during takeoff. I have not flown the plane again since I've seen this video. I'm wondering if it makes sense to try more of a nose down trim.

Has anyone else experienced something similar to this. I'm running a 912is Sport.

[Shadowrider]

Prop-wash is hitting the tail. I think the play that is found in the trim motor and slider block makes this more problematic. More HP and higher RPMS at high AOA and this problem gets worse.

[Floog]

Not uncommon for tail vibration at high AOA. Reduce from Vx to Vy or less if you're not trying to clear obstacles. That's some serious vibration on the left stab! Don't be the first to have it come apart.

[n85ae]

With my IO-240B and 74" prop, I have this all the time at full power on takeoff. It's a momentary thing that passes pretty
quickly. It's disconcerting, but after 20+ years of flying I'm used to it.

Jeff

[Shadowrider]

Just figured out a hack for this. After watching Trent?s video I decided to try full nose down trim for takeoff. I agree with Trent it gets your tail off quicker and gets your tail wheel clear of obstacles it can hit. Also eliminates tail shake. A lot of the shake comes from play in the trim motor I think. When you trim it full nose down it reduces the play.

[Redline]

Just figured out a hack for this. After watching Trent?s video I decided to try full nose down trim for takeoff. I agree with Trent it gets your tail off quicker and gets your tail wheel clear of obstacles it can hit. Also eliminates tail shake. A lot of the shake comes from play in the trim motor I think. When you trim it full nose down it reduces the play.

I just tried this for the first time two weeks ago and also noticed it reduces the shaking. I like it much more than starting with neutral trim.

[Shadowrider]

Yeah sorry I meant to say it reduces it not illuminates it. I have always taken off with slight nose down trim, but now I am going to just go full trim down.

[rocketman2tm]

I ended up finding that there was a slight amount of play in my horizontal stabilizer. The play was coming from the rod end bearings. What I did to resolve this is to add a half turn clockwise on both rod end bearings. I am still able to freely slide the bolt through the rod end bearing and there is not any bending of the horizontal. Since making this adjustment there is no more play in the horizontal either on the ground moving it by hand or in the air.