Hatz Biplane Association

The Fix

Horz stab is vibrating. I took a small hand mirror along and could see the right side vibrating in the wind. I am going to add a stramline strut on the bottom of the leading edge back to the fuselage. I think this needs to be a plan change on all future plans.

Michael
N9648B

We have 170 hours on our Classic and so far have never noticed any vibration of the horizontal stabilizer. On an early flight there was a lot of vibration of one of the streamlined cabane wires. After turning the wire slightly to conform to the slipstream the vibration stopped. I would expect that a misaligned tail wire could cause some vibration to be felt.
John Hanson HC-012

BTW, I didn't build my first Pitts...just wanted to clarify that.

I have 8 wires on my tail, top wires streamlined and round on bottom. Yes, the extra Brunton wires are an extra $700. I'd rather have gone with a streamlined tube brace off of the lower longeron up to the leading edge horizontal stab. I did the strut method on my 2nd Pitts because my first Pitts experienced a completely severed front horizontal stabilizer tube due to a crack that formed at the front stab mounting bolt hole. That Pitts had no front stab support. I think a dull bit was used to drill that bolt hole and then the hole was not deburred and chamfered. What kept the leading edge tube from sliding off of the inner H tube assembly in flight, thus causing a snap roll that wouldn't have ended till I hit the ground, was about 5/8" of tubing overlap. Again, I think the crack started due to a badly drilled bolt hole but then propagated due to vibration and stress. My preference is a tube brace over wire brace, and would do it that way if I had to do it over again. But the wires looks good in my opinion and it works to reduce/eliminate vibration.



Just my opinions based on my experience and submitted FYI...

I'm using 1/2" 4130 round tube for braces as shown in the attached pictures. Pretty much duplicated what's on the Acro Sport II plans. It's a proven and very inexpensive method to add support to the stab. If I used 4 wires with terminals from Bruntons it would cost about $700.

-Scott

Hi Steve,

Very nice Hatz by the way! I really don't think it's a problem with the vibration, but Michael's Hatz has an 180hp engine, which will yield in a few more mph!

Hans, Switzerland

Given the fact that most Hatz's are flying with single wires, I don't think there is much of a load on the front wires. They are there to dampen vibration. Certainly no distortion issues on my airplane. I just finished recovering last year and everything was good inside.

Steve

Hi all,
We more or less duplicated the late Mehlin Smith tailplane layout with the standard 4 wires and a streamline strut from the lower longeron up to the tailplane leading edge. Mehlin used streamline wires on top and bottom, wheras we will have streamline on top and round on bottom. But one has to consider, that our tail planform is elliptical (not standard taper Hatz tailplane).
To our knowledge (Bill Rusk knows this best of course), there wasn't any vibration.
We hope to report our experiences this year after the first flight is over.
We would recommend adding a strut instead of extra 4 wires attached to a relatively week fin leading edge. The question is also which solution is easier to execute...

Best regards
Hans & Sam, H.C.#78, Switzerland

I saw a biplane at the EAA meet tonight that had a very small dia streamline tube attached below the leading edge of the horz stab and back to a attachment on the lower fuselage. Very neat and sturdy detail?

Michael