Zlin Z-XII (oz14946)
About this Plan
Zlin Z-XII. Peanut scale rubber model.
Quote: "Zlin Z-XII, by John Berryman. Ready to try a low-wing Peanut? This month's featured model may be just what you're looking for. The full-size Zlin Z-XII was a pre-WWII design by the famous Czech manufacturer and can be considered to be the predecessor of today's high-performance Zlin aerobatic aircraft.
No airplane nut needs to be introduced to the Zlin family of aircraft. These nimble Czech stunters have delighted air show audiences the world over for many years. The Zlin modeled here is a pre-war version, and could in some sense be called the granddaddy of the modern Zlins.
I first saw this Zlin presented as a quarter-scale VC ship. It possessed the kind of angular grace common to many pre-war designs that I find very appealing. In addition, it seemed to have reasonably good moments, and was quite colorful. The designer/builder, Mr Dennis Tapsfield, was kind enough to present a three-view with his construction article, and after a midnight raid on the office Xerox, a set of Peanut-sized reference drawings were produced.
After I took a look at the larger drawings, a lot of my enthusiasm evaporated. The wings really tapered, the fuselage was really skinny, and of course, the tail was too small. On the plus side, the ship had a long nose and some sexy exposed cylinders that could further aid the CG, and it also had quite a bit of dihedral.
To overcome some of the problems I found in the prototype, I made the following deviations from scale in designing my version of the Zlin:
• The tail surfaces are enlarged by 30%.
• The amount of taper in the wings is reduced slightly - by just over one-eighth inch at the tips.
• The dihedral is roughly 50% greater than that exhibited by the prototype.
• I made no change in the fuselage dimensions, and this means that it's snug in there. I simply decided that the thin fuselage was part of the charm of the ship, and should not be altered (it would be like putting dihedral on a Fokker Tripe). This means build lightly, because there's not a lot of room in there for rubber, folks!
Let's get your Zlin flying!
FLIGHT SURFACES: No surprises here. The tips are laminated balsa, and the ribs are sliced in Mooney fashion. The dimensions shown for the spar are approximate. I personally tend to cut my ribs a bit fat, which means that they don't always clear the spar. I cut tiny notches in the spar to correct this, and rationalize the procedure by telling myself that this helps lock the structure together. Build the wing flat, and add the dihedral (the breaks are outboard of the root ribs) after the glue has dried. For my own peace of mind, I also added gussets at the dihedral breaks. Make sure the root ribs are truly vertical, so that they will mate properly to the wing saddle... and don't forget to add the LG mounts before you remove the wing from the building surface!
FUSELAGE: Again, we'll follow standard Peanut practice, building one side on top of the other (separated by waxed paper, of course), and taking great pains to make each side exactly, I mean exactly, like the other. A little time now will keep alignment problems to a minimum later. I used firmer stock for the longerons, and lighter stuff for the cross pieces. To avoid wavy stringers, I find it much easier (and neater) to notch the rear formers after they're glued in place. I use a piece of taut thread to establish a straight line, and use a new, sharp, double-edged razor blade to cut the notches. After the stringers have dried, I then 'scallop' the formers between the stringers. A small drum-shaped bit in a Dremel works well for this. When I mated the sides together, I used "false bulkheads" (located at stations 3 and 4) to preserve alignment..."
Direct submission to Outerzone.
Quote: "Hi Mary & Steve, Please find attached plan and article for the Zlin Z-XII by John Berryman. From Model Builder, Volume 20, Number 215, January 1990... Thanks again for all you do. Kind regards, Ian Salmon."
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