Building the Kolibri Slow-Flyer

The Kolibri is a popular, inexpensive design that makes a great first time slow flyer. Follow the directions below and you should be flying in no time. There is a list of items required for construction at the end of this document.

The V-tail

Prepare 2 carbon rods Ø 1,3 mm and 720mm in length, two 1.3 mm thick balsa triangles (better if laminated from 2 x 0.7mm balsa) as shown in the drawing and 2 carbon rods Ø 1,0 mm and 50mm length. Glue the balsa triangles to the ends of the 1,3 rods with CA and let it dry well . Then bend the rods and glue the other end to the small side of the balsa triangle. Now you have to glue the 40mm long, Ø1.0 mm rods to the third side of the triangle.

Covering: Only the top side will be covered! Prepare an appropriate size piece of covering foil. Place the second frame on your table as mirror image of the other one. Rub the carbon rods with glue stick (‘UHU" recomended). Stretch the foil over the frame and rub it to the carbon rods with your finger. "Cut" protuding foil by moving around the frame with a "not too hot" small soldering iron tip. Finally you glide over the foil with a hot modelling iron (full heat) without touching the foil, in order to tighten and smooth it. Note: Avoid direct contact of the iron with the bent carbon rods - they will break with localised heat !!! Let some drops of thin CA flow around the rudder in the slot between covering and carbon rod in order to reinforce the adhesive strength. The control horns are then cut out of 0.6 mm plywood according to the plan and 0.6 mm holes drilled into them. The slits for the horns are cut into the balsa triangles carefully using a scalpel. They are then inserted, adjusted and glued into position.

The wing

The wing will be built very similar to the tail. Prepare 2 carbon rods Ø- 1,5 mm each 950mm in length . Glue the two rods together with CA by overlapping their ends 2cm. The joint is stiffened by wrapping a small tuft of carbon rovings around it and hardened with thin CA. Connect the open ends of the rods in the same way. Tie a thread between the two joints so that the joints have a distance of 265mm. You may need to tie extra threads 300mm from, and parallel to, the centre thread, to get the shape shown in the diagram. Now you have the flat skeleton of your wing in front of you. Glue four fittings (carbon or ply-wood) size 0,8x3x3 mm to their positions according to the drawing, with CA. Make sure they fit well! The two 5cm pieces left over from your 1,5 mm dia. rods are now glued perpindicular to the center of the wing structure with CA and wrapped with some rovings and thin CA (see photograph).

The upper side of your wing must now be covered with transparent or aluminum-coated condensorfoil in the same way as the tail. Note: Make sure you pull the foil tight while glueing. "Cut" protuding foil by moving around the frame with a "not too hot" small soldering iron tip.

In order to give your "flat wing" an airfoil you tie a thread around fitting 1 and fix it with CA. Now go with the thread to fitting 2, tie it around (do not glue yet) go to fitting 3 underneath the wing, tie it around and go back to fitting 4. Once you are sure that your wing tips are 90mm above the center of the wing you glue the thread to fitting 4. Now you still have the chance to adjust the twist in your wing at the fittings 2&3 where the thread is still not fixed. Once your wing is without twist, fix the thread to fittings 2&3 and a few minutes later (max. adhesive coherence) cut the unnecessary thread on the lower side of the wing.

Finally, glide over the foil with a hot modelling covering iron (careful until you work out what heat setting - my old iron needed full heat) without touching the foil, in order to tighten and smooth it. Note: Avoid direct contact of the iron with the bent carbon rods - they will break when heated !!! Now you can cut away the thread in the centre of the wing.

Fuselage and undercarriage

Use a thin walled aluminum tube with 5mm inner diameter and 2cm length as a stiffener for the undercarriage mount. Drill the holes for the tail (2mm), wing and undercarriage (1.5mm) and the tail skid (0,8mm) in the breeze tube fuselage to the correct position with the correct angle according to the drawings. The "legs" of your undercarriage are made from carbon rods Ø 1,5 mm and 150mm length. Bend piano wires Ø 1,5 mm and glue them to the "legs" according to drawing as wheel axles.

The wheels themselves are each made of two wheel discs glued together (ensure the grain of the two parts are at 90 deg. to each other) and finished with tyres made out of foam rubber. To make the tyres: stretch used model car tyres over a plastic or wooden cylinder. Cut the tyres out on a lathe (should one be so fortunate as to have one) or a drill attachment using a scalpel, and then sand round with 100 grade sandpaper. The wheel hubs are made from a piece of Bowden cable inner.

The guide tubes for the tail are also made from 1 cm long Bowden cable inner. They are glued into the respective fuselage holes.

Note: Undercarriage legs, wing support rods and tail parts are only stuck with a good fit and not fixed with CA so that they can be removed (adjusted) at any time.

Engine mount

The WES-Technik propulsion set 1a is mounted to the fuselage tube with a piece of Ø 5mm balsa rod (use some CA) as shown:

Servo / receiver mount

The wiring for the antenna must not be inside the carbon tube! This can cause interference.

Building Materials needed for the Kolibri