Tail Shaking Problem....

A friend with a newly acquired newly restored PA 12, called me early last winter and was concerned his
Horizontal stabilizer doing some unusual shaking during climb out AND in level flight
So we started looking into possibility's to include detailed inspection of the jack screw ( that has less than 200 hrs since new), the yoke link bolts. The engine mount
bushings, changed propeller's and nothing made any difference. He was very concerned and we never were able to stop this unusual shaking He is running the new Airglas Retractable 3000 Wheel Skis, with 8:50 tires. A few days ago he removed
The skis and installed his 31" Bushwheels.
Ran it around the patch a few times and discovered that there is now: ZERO tail shake?????
It is total tied to the skis. So if anyone else has experienced anything like this?? with those skis on Cub or Cruiser it would be good to hear about it. His 12 does have 3"
Extended gear.
E




Sent from my moto e5 go using SuperCub.Org mobile app

;-) When you fly in dirty air you shake. The tail has to fly in whatever happens in front of it.

Are there any flaps on this -12. If so, is there a difference up or down? There is no shake on my -18 with the long flaps.

Were the skis rigged correctly? Too much nose up or down?

When my 12 was rebuilt not far from where you live one of the mods done at that time was the addition of flaps. I had a similar, noticeable shake as you described. The addition of a gap seal, cover, on the flaps eliminated the shake.

Darn good question Pete! Because it now has no shake with tires. It is most certainly tied to those skis. His 12 has stock wings with 18 flaps. And it shook the worst on climb out and wide open. Those are big skis and I suppose if the tips were rigged to high that could contribute to that problem?
I am thinking he used Atlees rigging instructions when they installed them, but maybe should double check that???
Thanks for responding
E

Sent from my moto e5 go using SuperCub.Org mobile app

In general, it seems to me that a lot of mechanics have a tendency to rig skis too nose up. I don’t know whether they think that’s safer or perhaps that’s the the most “conservative” of rigging instructions. In any case, I like skis rigged almost level.

MTV

Good point Mike. If they are rigged nose up, then they will have a lot of air moving around their sides creating a large mass of turbulent air for the tail to fly through.

Worst "tail shake" We ever had was in a C120. Three of us took off from Bay Bridge Airport, Md. Climbing to gain altitude before crossing the bay and then up the bay toward Aberdeen the whole airplane started shaking. We were over the middle of the bay and I was hoping to make the shore on the North side. Marcia and I both opened the windows and tried tobserve the tail, wheels, cowl, anthing....

Then it stopped and all seemed normal. We kept climbing and I headed toward Martin State airport just in case but all was still. Then it started again but worse. I wondered for a moment how our parents would feel if our new family met it's end while trrying to figure what the h... was going on. Then it stopped. I decided to land at Martin State and called them on the radio.. Then it started again. Marcia tapped me on the sholder and pointed backward. There was baby Carla in the child's seat/car seat rocking her little body forward/aft as hard as she could laughing all the way. Amazing how hard that little body could rock that little airplane.....Called the airport and told them we changed our mind not mentioning I almost needed to change my drawrs.There renained a crease in the middle of my seat fabric...Carla turned her big 40 last Sept.

Jack

I have that same ski set up on a PA -18 and the only time I ever had any “tail buffeting” is climbing steeper than normal with t/o flaps and the skis In the retracted position. After installing them I climbed to altitude and flew it in various configurations including slow flight and stalls. Keep in mind they are prerigged pretty nose up when not deployed. So much so I discussed it with a Airglas rep. When deployed they are damn near perfect very little nose up. I realize some like more nose up or rocker? But even in deep snow I’ve never had a problem. Slow flight and stalls with those skis retracted are not worth repeating BTW.

I have heard that people with 180hp cubs look back and are alarmed at the tail shake in the wind stream....true??

I presume that the Charlie Center stab leading edge strut mounted to the jack screw was made to address this issue....

fobjob said:

I have heard that people with 180hp cubs look back and are alarmed at the tail shake in the wind stream....true??....

Click to expand...

Mine does not.

skywagon8a said:

Mine does not.

Click to expand...

Mine either

On a supercub if you look out the back window with full power in a climb it does shake a lot. Want to be terrified? Watch a carbon cub do a run up, right FMD? He said the whole fuselage aft of the windows were moving. Side note, with the flaps extended to the fuselage the stick will move fore and aft when coming in to land


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RaisedByWolves said:

On a supercub if you look out the back window with full power in a climb it does shake a lot. Want to be terrified? Watch a carbon cub do a run up, right FMD? He said the whole fuselage aft of the windows were moving. Side note, with the flaps extended to the fuselage the stick will move fore and aft when coming in to land


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Click to expand...

It will remind you of a Jerry Lee Lewis tune......[video]Carbon Cub Shake[/video]

RaisedByWolves said:

On a supercub if you look out the back window with full power in a climb it does shake a lot. Want to be terrified? Watch a carbon cub do a run up, right FMD? He said the whole fuselage aft of the windows were moving. Side note, with the flaps extended to the fuselage the stick will move fore and aft when coming in to land


Sent from my iPhone using Tapatalk

Click to expand...

It will remind you of a Jerry Lee Lewis tune......[video]Carbon Cub Shake[/video]