The finished Gull airframe, ready for covering and finish.

The Kirby Gull

Fred Slingsby’s gorgeous gull-wing at 1:3.9-scale.

This is my second foray into the world of the Slingsby Gull, the previous being a much larger version of the Gull 4 replica. I’ve kept pretty much to scale, other that the fact that the blue of the full-size is lighter than I have used, due to the fact that the film that covers the flying surfaces is available only in a limited range of colours.

Left: The basic structure of the first of the fuselage half-shells is where it begins. | Centre: The front half of the fuselage is planked with 1.5mm ply: tedious but strong! | Right: The second half is built over the first, making sure to keep it all straight.

Construction is Williams-conventional, with the fuselage being built in two halves before being clad in plywood.

Left: View of the tailplane mount. | Centre: Basic tailplane assembly. | Right: Inner fuselage structure completed, now for all the plywood skinning The temporary formers have yet to be removed.

The wings are built with my current format of using a relatively small main spar, which is tied together at the front with ply web plates, and then reinforced for a good part of the wing by dropping in an equally size sub spar, thus to form a very strong I-beam.

Left: The nose block is made up from polyester filler. | Centre: The front end complete and smoothed with filler The temporary formers will be removed and the interior glassed with wing joiner tape and polyester resin. | Right: The components of the joiner box for the fuselage.

The wings are in one piece, with the gull break being achieved by bending the 5mm by 5mm spruce spars over a simple jig.

Left: Tailplane complete. | Centre: First stages of the fin construction. | Right: Setting up the rudder cable guides before sheeting the rear of the fuselage.

The wing joiner box in the fuselage allows the 15mm steel bars to overlap each other to give the maximum depth and strength.

Left: he lower canopy frames are laminated against the fuselage sides to induce the necessary curve. | Centre: “Canopy frame completed. | Right: First stage of wing construction: the 5mm square main spar is bent over a jig to induce the gull shape.

The airfoil section is my standard HQ35/14 for the inner panel, transitioning to HQ35/12 out to the tip.

Left: Sixteen millimetre brass wing joiner boxes between the sub spars: on the other wing they are between the main spars to allow for the staggering of the joiner blades. | Centre: Sub spars added and the wing ready for sheeting. | Right: Setting up the wings to the fuselage.

Thanks very much for reading and if you have any questions, please don’t hesitate to leave then in the Responses section which you can access by clicking the little 💬 below.

Left: Smoothing the joins between wing and fuselage. | Centre: Job done! | Right: View of the completed tail group.

Good luck with your project and see you next time.

©2023 Chris Williams

Resources

• Airborne with the Gull Replica on YouTube. — First flights with the Kirby Gull replica featured in this article.
• The Williams Anthology — The collected works of Chris Williams as found in the pages of the New RC Soaring Digest.

All images and videos by the author. Read the next article in this issue, return to the previous article in this issue or go to the table of contents. A PDF version of this article, or the entire issue, is available upon request.