Kaos construction report

Years ago, our flying colleague Toni Bäuerle discovered the KAOS from the American Joe Bridi. No sooner said than done, it was easy to get the blueprint.

Egbert, his flying colleague, was enthusiastic about the project. Here is Toni’s test report:

Part 1:

15.01.2021

The Kaos 60 is a design by the American Joe Bridi. The model was released in February 1970. The design is now over 50 years old. WOW!!!

The Kaos is one of the most famous aerobatic aircraft ever designed. It was used in many competitions. Joe Bridi was a participant in the legendary TOC Las Vegas (Tournament of Champions), in which the world’s best aerobatic pilots were invited, for many years.

Technical data

Name: Kaos 60
Developer: Joe Bridi, USA
Wingspan: 59 inch (150 cm)
Length: 55.5 inch (141 cm)
Wing area: 647 sq. inch (41.7 dm²)
Weight: ~ 3 kg
Motor: Super Tigre G60 Blue Head with tuned pipe
Propeller: APC 11×7

The root rib is 19% thicker, the end rib 17% thicker.

At our club, the Kaos was often built and flown back then. My father had also built and flown this RC1 plane in the early 80s. Now I wanted to revive the model and enrich the retro scene. Before that, I had already built and flown the legendary Blue Angel 60.

The plan can now be downloaded from the internet (Outerzone, Aerofred). There are even plans that are CAD-compatible. So it happened that a club colleague had made me a set of ribs, in this case laser-cut. This saved me a lot of work. He was also able to provide me with the plan, printed out with his A0 plotter. Many thanks at this point.

After I had procured the necessary materials, I was able to start building. My two biggest helpers were a small disc sander (125 mm) and my Proxxon circular saw, which is great for cutting battens that are not available.

I started with the elevator. The plan was covered with a film and the mouldings could be produced and glued according to the plan. The basic framework as a lattice construction was quickly done, then the top and bottom sides were planked with 1.5 mm balsa wood, ready for sanding.

The hull frames were then made. The hull is built on its back. After the frames were glued in place, the side panels could be attached.

The area of the wing is reinforced with 1 mm plywood. The bottom of the fuselage remains open until the servos and Bowden cables are installed.The installation of the motor mount, made of beechwood in my case, took a little more work because there was a lot of measuring to be done. The side thrust and engine camber of 3 degrees each have to be taken into account here. The threads for the motor attachment were cut into the motor mount and the designated motor, also an old-timer (Super Tigre G60 Blue Head), was allowed to test-sit.

The two elevators were cut out and moulded according to plan. The parts for the rudder were also made.

Now the wing came into focus. I decided to create a so-called wing jig, an auxiliary jig for building a wing (building jig). The ribs were threaded onto carbon arrows and aligned at the appropriate distances using a template. This construction is fixed on the jig and the first main spar made of pine is glued. After that, the auxiliary spar and the landing gear mount in the form of a T-slot bar were installed. After the first half of the wing was finished on the underside, I was able to turn the wing and glue the spars on the upper side.

This is the current status and there will be more to report soon.

Part 2:

15.02.2021

After the construction of the raw frameworks of the 2 wing halves, the planking could be applied. These are attached to the upper and lower sides in the area of the leading and trailing edges. Before that, the landing gear mount for the 4 mm landing gear wire was appropriately reinforced.

A filling block for the holes in the wing mounting using a 6 mm nylon screw was inserted. A reinforcement for the wing dowel as a counter bearing was also glued to the main spar. A balsa wood block to finish the wing tips at the wing ends should finish building the wing halves.

Now the two wing halves could be glued together. To do this, the wing is placed on its upper side on the building board. This means that the wing has a 0-degree dihedral on the upper side.

After gluing, fibreglass reinforcement was applied to the centre section, with a slight excess of the fuselage width. After the resin had hardened in the wing, a small cutting disc was used to cut out the corresponding section for the aileron servo. The servo, in this case a low-profile version, was placed in the cut-out. The ailerons were also made and the hinge slots were set in the wing and the ailerons. As almost always, I used the good hinges from Kavan.

In the meantime, I had found a picture in an old photo album showing my father’s old Kaos. I think that was probably in 1981. We had been invited to visit the model flying club in our partner town of Istres (in the south of France, in Provence). It was a big deal with the press and radio. My father and I were able to achieve first place for the best flight demonstration with this Kaos and my Curare 60. The prizes at that time were pre-built fuselages of various types (motorised model, glider).

After this little detour, I will now continue reporting. The production of the servo board went quickly and then, as a result, the installation of the Bowden cable tubes followed. Since the bottom of the fuselage had not yet been glued, everything was still easily accessible for the installation.

I decided to control the elevons separately and not to connect the two halves of the elevons with a pine strip as planned. The wing mounting board was then glued into the fuselage.
The Bowden cable tube for the engine throttle was also laid. An old tank (400 ml capacity) from Graupner, but still in its original packaging, found its place in the front part of the fuselage after assembly.

I added a ‘soldering bead’ to the end of the brass tubes so that the silicone tubing would not slip off the tube.

The fuel cap was still being made and to fix it, I inserted two beechwood dowels into the cap to hold the Allen screws.

The provisionally installed motor for the installation of the Bowden cable has a side pull and a camber of 3 degrees each due to the installed motor mount. This is how it was planned.
The elevator was finally sanded and ironing could begin. The hinges were set here beforehand. For the underside, I chose a blue and white checked pattern, and for the top side, a gentian blue.

I designed the rudder in red to match the red spinner that will be used in the future.

In the meantime, I had built a new engine test stand to adjust the engine used here, in this case a Super Tigre G60 Blue Head, also a real classic.

Preview:

– Ironing the wing + fuselage

– Measuring and gluing the elevator and rudder to the fuselage

– Assembling the landing gear

– Finishing the linkages

– Assembling the engine incl. the tuned pipe

Part 3:

26.05.2021

In the meantime, the Kaos has already made its maiden flight and several more flights (4 litres of fuel). But one thing at a time.

Last time we left off, we were covering the wings. We applied a blue and white checked pattern to the underside of the wing. The film comes from Hobbyking and is excellent to work with. The films can certainly keep up with those from other manufacturers. The upper side was given a foil in gentian blue, decorated with the design used in the 70s for the Kaos. The wingtips were given a bright red colour. For the screw connection of the surface, brass sleeves were added to the through-holes. This prevents the openings from becoming worn.

Next, the fuselage was tackled. In order to achieve a clean finish here, special attention must be paid when cutting the film. The result is impressive. The canopy in the shape of a drop, available from PAF, was glued to a corresponding balsa board and placed on the fuselage. I have dispensed with a pilot here, as it is a purely functional model.

The next step was to align the unit of the already ironed rudder with the tail boom and glue it to the fuselage. This was followed by the installation of the aileron servo. As shown in the plan, a central servo is used here. Care must be taken to ensure that the linkage is free of play and that good (hard) wood is selected when using the strip-type ailerons. After completing the aileron linkage and installing the rigid main landing gear, the wing was ready as far as it went.

The next step was to assemble the engine unit, including the manifold and the resonance pipe. The installation of the silicone hoses from the tank to the engine unit and the attachment of the resonance pipe to the fuselage completed the assembly of the engine unit.

As a power switch, I used an electronic switch from Hacker, which is switched on and off by a magnet. The receiver was installed and the antennas were routed to the outside. A 4-cell Eneloop battery in the AA version is used.

The final step was to complete the linkages for the elevator and rudder.

So nothing stood in the way of the first flight. The first flight was scheduled for 3 March 2021. A few more pictures and off we go. With a dry weight of 3 kilos, a normal standard motor is sufficient; it doesn’t always have to be high-tech. The Blue Head is a great match for the model and its design. With the Kaos, all figures of the Classic Pattern (RC-1) can be flown.
And there is a motto: loud, low & fast! 😉

The model brings back memories from the early days of my modelling career and is almost a virus. Let’s see what else it brings. Some new projects are already in the planning and implementation stages, so stay tuned!

A friend and fellow model pilot from a neighbouring club built his own Kaos after I had finished mine. Thanks to the experience I had gained, he was able to build it quickly. He chose red as the base colour, also with a checkered pattern on the underside of the model, and used an HB61 red head as the motor. So we were then able to swirl through the air together with our two Kaos models and have a lot of fun together. We also took part in a retro meet in Pfäffikon (Switzerland) together. One day, my flying colleague Egbert lost his Kaos due to a comprehensible receiver battery failure. A cell had given up the ghost. A new Kaos was quickly built and is now flying again. It’s just a quick job.
I hope you enjoyed the report and that it has inspired you to rummage through your plans and look in your box of engines to see what else you can do with your vintage models.

In line with the motto:

‘Stop talking – start flying!’

With flying greetings, Toni

Text und Images: Toni Bäuerle