Hi All

I'm wondering if anyone has any thoughts or experience with installing a variable incidence stabilizer trim system, similar to a J-3 or other Cub.

At least some WACO's originally had this system. This system might help me with my concerns about the change in thrust line associated with the R3600.

Thanks
KurtisA
HC-040

Hi Kurtis,

If you need to change the angle of attack of the horizontal stab to correct a weight and balance and thrust differential problem arising from using a bigger engine, then making the leading edge of the stab adjustable by putting washers between the stab and the fuselage mount works good. The adjustment is made during the first few flights so that the Hatz flies good with the trim tab able to handle the different power settings. Then there's no more need to adjust for the life of the plane.

For a thrust line fix, you can mount the motor so that the thrust line of the motor intersects the CG at the aircraft's recommended line of thrust.

Just some thoughts that might save you a lot of reengineering work if you change from the plans. Personally, I like my tail bolted on securely and a little trim tab doing my stick lightening duty. I feel that the more fittings there are, the more things there are to come loose, fail, crack, go uninspected, etc. Probably just my goofy way of thinking.

But then, the beauty of the experimental category shines with the ingeniusness of builders and their ideas.

Hatz away!

Mark T

The prototype Hatz CB-1 uses a Cub jackscrew for trim. Has worked well for 37 years!

Lyman

I owned a clipped wing Cub for a coupla years...wrung it out regularly..it was built in 1940! I guess it's not really the safety aspect that steers me away from this type of set up, but more of an engineering and time saving thing. My frame was already welded up when I got it and it was easier and quicker for me to cut the forward stab attach points and reweld for an adjustable set up (with washers) than to engineer in a Cub jack screw support system and the cables, pulleys and guides needed to operate such a system.. And my frame has bracing wires on the front as well as rear stab spars, and an adjustable front stab spar can't be braced.

Mark T

Thank-you

I have the classic plans, and they don't have an adjustable stablizer such as you are all describing.

I guess you would fashion the mount so that instead of welding in place the horzontal stab tube receivers, you make up a fitting so that a couple of bolts hold it together?

That sounds like a good solution..

Thank-you

Kurtis A.
HC040

Kurtis,

Before you go off and engineer this thing, look over the Hatz 535 (Randy Brooks) Hatz in the website's Builder's Pages.

Randy did just that (added the capabilitiy of ground adjusting the incidence of the stab by adjusting the vertical location of the front stab spar.) The last photo in his Builder's Page shows the lashup, and I have his drawings somewhere on my desk. He used a stack of washers on the bolts to create the variable geometry for the mounting location of the front spar.

Caasi
#777, HC-026

Dear Caasi,
We are also engaged on this task of an adjustable stab. We intend to consider Randy's and Lorin's approaches. Randy's sketches are in the HBA website (construction tips). There are two sketches. The front spar mounting is clear to us, but we wonder why the rear spar has to be adjustable: We assume that the stab could pivoting around the rear spar just one or 2 degrees. Or what is the reason for an adjustable rear spar?
Hatzy building!

Hans & Sam, HC #78, Switzerland

I went back to the sketches, and yes, those are the same ones I have in hardcopy.

I do not understand your question. The front spar is adjustable vertically, via washers in two places. The rear spar support is fixed vertically, but the rear spar tube must be free to rotate as the incidence is changed. The options specified are for various tube thicknesses to support the rotation of the rear spar.

???

Caasi

Thanks Caasi

I had a look. and that's basically what I was thinking about doing.

I should have my fuse upright by next week - and can start on it then

Kurtis A
HC-040

Thank-you for all your help with the design.

I have built and installed the system now. Like everything else it took longer than I thought it would.

In the end I sprung for the Certified Jack Screw and yoke. They worked very well. My only complaint is that they yoke is very wide and necessitated a little extra work to fair them into the tail.

I have some pictures, and if someone could tell me what I have to do in order to post them, that would be great!

Anyway, if anyone wants the pictures, e-mail me and I'll send some pictures.

tigermoths@rogers.com

Kurtis Arnold
HC-040

Hey Kurtis!

'Crazy' Mike here!

Attaching Pix is/are easy...

You MUST edit them so that they are less than 100KB!

Then, just follow the instructions in the 'Attachment' - 'Choose your file' box.

My 'Other' bi-plane has an adjustable horizontal stab, not unlike a Cub... Prior to restoration, I had had either a weight & balance and/or an aerodynamic issue, which resulted in a lack of sufficient nose down trim. My post restoration W&B is right where it should be and unfortunately, after flying, I STILL had a lack of sufficient nose down trim. Appears that the original builder established the Trim Travel Range below where it belonged, i.e. 'had an excess of nose up trim and no nose down trim! After correcting the Trim Travel Range, what was previously my MAX nose down trim, will become the CENTER of my trim range! 'Just waiting on the NEW jack-screw from the machine shop, and warm enough weather to do the fabric and paint ;(

Looking forward to seeing your photo's,

'Til then,

Happy Landings!

CM

Michael R. Devroy
P.O. Box 974
Lake Geneva, WI 53147
H: 262-248-4190
C: 847-224-5192
mdevoy@earthlink.net

Here are some pictures of what I came up with.

(I think I got this right this time... )

Kurtis A
HC-040