Horz stab vibrating?

[mmcgrew]

I think I am getting some vibration from my horz stab (from prop wash at high RPM). I used the 2 wire (each side) config per the plans. I am considering adding 2 more wires each side. I do not have a bushing installed in the leading edge of the vertical stab. This is either a 1/2" or 5/8" tube so I do not want to drill a #3 or #4 bolt hole for a wire tab. I am thinking about fabricating a double wire tab on the vertical tail post (in the current 1 wire tab location) and run the new wire up to the leading edge of the horz stab (larger tube). So both top wires would have a common attachment on the tail post, one going forward and one going back. For the lower wires I would do the same. Fabricate a double bracket where the single wire is attached and attach two wires at this location, one going back and one going forward.

How about some comments on this?

TKS
Michael
N9648B

[M Lightsey]

Michael,
What you're proposing is very common. Same as Pipers, TravelAirs and others that have adjustable horizontal stabs for trim.
Are you using round or streamlined wires on the tail.
If they're streamlined, you might try adjusting their angle of attack. Just like flying wires, they can vibrate if they're not perfectly lined up.
Just a thought,
Mark

[mmcgrew]

Good suggestion - I am using streamline. I need to check alignment

Michael

[Jackal]

For what its worth:

I've posted this before and been told I was mislead, but here it is anyway.

Lorin Wilkinson told me at Bartlesville in about 2001 or so as we stood near the tail of his Snooty Hatz and talked about the Stab and how he had a total of 8 brace wires on it (Two in place of each one shown on the plans) that his tail still vibrates in flight. He said he used the reduced dimension top longeron aft of the cockpit as shown on the early plans and he said he believed it was the ENTIRE AFT FUSELAGE which was flexing and allowing the stab to appear to shake. I think plenty of people have used the "full size" longerons all the way back and experienced the same thing though.

I've not yet flown mine (and won't for a couple years) so have no first hand info to pass on. Since I still have the opportunity to brace my Stab in various ways I am very curious as to what others report.

I've seen some use a streamlined tubing strut on the bottom of the H-Stab only (plus the standard per plans 4 wires). I wonder how this works. Anyone else flying out there with 4 or 8 brace wires with info to report?

The notion that the wires themselves are vibrating is very interesting. Yes, round wires probably wold not do that. Anyone flying with round wires?

[mmcgrew]

I am thinking about adding a lower strut on the tail????

[M Lightsey]

NX1279 has round wires, 8 of them. There's a double wire lug on the tail post. Wires run down to the hinge and to the leading edge of the horizontal where a bushing was added. The rear wire runs down to the stock location and the front wire goes to a tab that was welded to the lower longeron at the second to last bay.
Stock (reduced) size tubing to the tail. O-290 for power, never noticed any vibration of any kind coming from tail. Have had it up to 140 indicated.

[hatz215]

I added a second set of wires years ago after coming out of a loop and noticing leading edge stab vibration. I welded a bushing in the leading edge of both horizontal and vertical stabs and added another strap to the belly. Have had zero issues since.

Steve

[M Lightsey]

I'd be leery of adding a bushing to the leading edge of the fin for an extra wire. There's really nothing to support any load at that point. The rear wire attach point is loaded straight down into the tail post. Without any tubing to take the vertical load, I can see the leading edge of the fin getting distorted if much load were put on it.
The leading edge of the horizontal is much more substantial, so not a problem there.
Just my $0.02
Mark

[mmcgrew]

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

[stearmoth]

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