Hatz Biplane Association

I do not know if I should rib stitch the two horizontial supports on the vertical stab on the Hatz classic. The fabric is about an inch off the lower support. the top support is much closer. To rib stitch the lower support the fabric would be pulled in a good deal. I like the non stitched look. Looking thru the pics - it appears some have stitched and some have not. Any suggestions will be appreciated.

Michael
N838MM

I built an LB-1 but the same thoughts should apply to either.
My thinking was if I didn't stitch the bottom rib the offset in the vertical stab would be for naught. The fabric would go where it wanted and I would have lost the effect of the bottom half of the offset. It seems to me I used a 1" spacing in that area and I did it before I shrunk the fabric.

Jeff Moore

Hi Hatzers,
I seem to remember someone saying that not stitching the base of the vertical stab can cost more speed than one would guess. It does look prettier without the stitching, but I am going to stitch mine.
Al

I covered one side of my vert stab/fuselage with a garbage bag taped in place. I drew a line down the centerline of the lower vert stab rib channel and marked off 1" increments from front to rear. I measured the distance from each mark to the garbage bag covering and recorded it. Then I removed the plastic and taped it to the other side taking the same measurements and recorded them. I used these measurements to make a rib out of 3/8" balsa and epoxied a thin ( 1/64") strip of ply to the outside edges so that when I rib stitched, it didn't cut in to the balsa. The rib has different airfoils on each side because of the offset fin. I used #8 screws with large diameter washers and locknuts to fasten the balsa rib to the vert stab steel rib channel. When I covered and rib stitched my fuselage, it gave a pretty nice curve with no tucking.

Mark T
#493

Thanks - I have shrunk my fabric - but my very experienced tech guy say I can stitch and the fabric will pull in with no problem. I see what you mean by the off set being negated

Michael
N838MM

For what it is worth? The prototype and more than a few others are stiched top rib only.

Lyman

Hi,
Previous to Marks response I was only using a scrap piece of fabric or stretch wrap taped over the fin to see the lay of the fabric. I used a piece of plastic the way Mark did (It shrinks some with a heat gun). I too like the look better with the lower rib brought out to the fabric line. Using a rib there may prevent the fabric from ballooning at our scorching speed. Thanks all for this thread.
Al

Mark,
Not to beat a dead horse, but would your balsa rib put the fin rib out of line with the rudder rib?
Al

Good question, Al. I'll find out when I fly it. The rudder is in a trailing position in flight, so I don't see how it would have any adverse effect. Since the rudder is tapered from the leading edge to the trailing edge, a more tear dropped shape on the vert stab would better blend the airflow with the taper of the rudder. And like you said, at our blazing speeds, proper airflow is everything! (I may install an airbrake under the belly)

Mark,
I should have made it more clear, I meant in height. My fuse and surfaces were made by Weld-Tech. I have the rudder stored elsewhere. I will get it and see how it looks. I may make an aluminum rib to straddle the channel so as to be at the same height.
Al