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John Watkins details the construction of his Kirby Kite
this building information is for the plan available from Traplet (QEFI) A long as I have known the Kirby Kite, I have regarded it as the most aesthetically appealing of all vintage gliders. Imagine my delight when attending the 1985 VGC Rally at the Long Mynd, there were three! Ted Hull's was the one I chose to extensively photograph after assisting many two-man launches from the Mynd's west face. An accurate three view drawing was acquired and plans prepared for a1/4 scaler, Ted Hull was a great inspiration and helped by providing some of the detail that I had missed. FuselageThe fuselage is constructed on a hard balsa crutch using 1/8" ply, half formers and 1/8" sheet balsa planking. Sheeting is strictly the word, as the rear end, being straight lined, is covered in three pieces, Fret out all the farmers from good quality 1/8" ply. Laminate the forward keel and upper centre strip. Note the latter extends from F1 to F5. Remove between F3 and F5 after planking. Glue the 1/8" ply laminations to the upper and lower 1/4" square hard balsa longerons and pin to the plan. Glue in all portside former halves and 3/1 6' square side longeron. Lift from plan and add the other former halves and side longeron. Make sure the two root ribs fit snugly across F5 to F8 and securely glue in position. Prepare all fittings that cannot be reached after planking, ie. 1/8" dural tailplane fixing straps, Graupner wing joiner tubes, wing strut anchorage points and tailplane strut press studs. Plank with medium grade 1/2" x 1/8" balsa strips between F1 and F6, working from side to side to prevent distortion The rear fuselage from F6 can be covered in three pieces of I / 8" lighter balsa sheet, one piece over the upper rear decking to each side longeron and one piece each side to the keel. The upper decking will require wetting and possibly pre-forming over a suitable core, ie. another fuselage! Avoid the use of pins by using adhesive tape to secure planking and sheeting while glueing. Add hardwood nose block, fin and rear skid and sand all to a smooth contour. The cockpit hatch can then be cut out and edges faced with 1/32" ply.  Ray Jones displays his Kite enlarged from the Watkins plan Wings
Prepare top and bottom spruce spars and rear spar webbing of horizontal grain 1/16" ply and balsa. (Steam the gull bend into the spruce spars). Lay the webbing strip onto the main spar plan, marking with a pencil the rib positions. Accurately glue in the top and bottom spruce spars, noting the spar taper is uppermos,. add the nose portion of each rib, joining together with the 1/4" x 1/ 8" hard balsa false leading edge. When dry place inverted on wing plan and secure firmly to building board, from R8 to R24; the root section remains inclined. Using suitable wood offcuts, chock up the prepared spruce trailing edge and ribs and glue all firmly in position, including the aileron ones. (The ailerons will be cut tree later). Cut oversize holes in the ribs for aileron and spoiler control wires and fit 1" x 1/2 "x 1mm ply guide plates to ribs in positions shown on the plan. Securely glue in the wing joiner steel strips and wire to give correct incidence angle. Glue on the I /8" balsa facing strip to the leading edge, sand to width in line with ribs and fit 1/16" leading edge sheeting top and bottom. Fit the 1/8" balsa capping strip to leading edge and sand in correct profile. Add all fittings for struts, spoilers, etc. this may be necessary before leading edge sheeting and webbing is added. Complete aileron structure and cut free as previously stated. Washout should be only slight from R13 to tip and equal on both wings. Tailplane and ElevatorsThe tail was purely a matter of keeping down the weight, using a basic structure of extremely light quarter grain 1/2" balsa sheet. Knew I'd find a use for it some day! The rudder is an outline of wound balsa strip........ shades of tree flight days! RudderLaminate the outline from 1/32" medium grade balsa strip around a hardboard or plywood inner former. Glue the strips using white glue and allow to dry overnight. Protect the former and building board with cling film or candle wax to prevent a glue-up! The remaining constructional work should be easily completed following the details shown on the plan. FinishingAfter careful preparation the fuselage was simply covered with while Solartex. Fuselage formers which show on the surface of the ply covered full-size were simulated by using strips of ironed on Solartex under the main covering. All flying surfaces were covered with 'natural' Solartex, using Balsaloc on the undercambered ribs and all other necessary areas. Following the full-size practise, the wing and tail open structures were masked and sprayed white on top of the covering and yellow on the leading edge: two hours of masking equalled two minutes of spraying! A Futaba flight pack was fitted as far forward as possible. The C of G positioned on the balance point, bringing the weight to 7 1/2 lbs, and a wing loading of a mere 16 1/2 or / sq.ft. and we were ready to go. FlyingFirst flight was at Walkers Hill in Wiltshire against a 21 knot wind. It just about held it's own with a fair amount of down elevator. This proved to be quite an unfair test as although rigging angles had been carefully monitored, adding much more nose weight became a danger of pushing the C of G in front of the wing! This is the result of using the scale Gottingen 535 wing section with the flat plate tail. Now that the trim has been sorted, the Kite is sheer relaxation to fly, albeit a bit sluggish in winds over 10 knots. She tows up predictably well in the lightest wind, and thermals willingly. This is a glider that seems more at home on the flat than the slope, showing up it's graceful lines and structure in the sunshine. Aerotow facilities are fitted and have proved very satisfactory, I've lost count of "hour plus" flights she's performed. Copies of the five sheet Kirby Kite Plans can be purchased from Double Digit Plans, See also Documentation for details of the full size |
The wings presented their own difficulties with compound trailing edge curvature in the form of root sweep back and gull effect. After careful thought, the wing spar was firstly constructed over the plan, glueing in the forward ribs and false leading edge strip, the remaining rear portion of the ribs were added with the wing in the inverted position, chocking up the per-formed spruce trailing edge to fit and glue in. The rest was simple, but a close watch was kept to prevent warps creeping in.