Building report Kosmo 3, Toni Bäuerle has built it

Toni Bäuerle: Ciao Kosmo! Sometime in the summer, Maurizio and I had the idea of building the KOSMO 3 model by Benito Bertolani.

The model, like Maurizio with Italian roots, was used successfully for several years in the 1970s by Benito Bertolani at Italian national championships and also with his colleagues in the national team in the then RC-1 class, now F3A, at world championships.

After a brief search on the Internet, we came across the Italian manufacturer Mantua Model, which was selling the Kosmo 3. As there were still 2 kits in stock, we quickly ordered them. The matching mechanical retracs was also added to the shopping basket. One week later, a large box arrived at the door.
A first inspection revealed a neatly packaged kit made of plywood and balsa with corresponding documentation. At first glance, it looked very promising.

Maurizio had already organised a 10cc OPS 60 Ursus engine with a red cooling head, which Bertolani had used for years in the Kosmo 3 before switching to the Italian engine brand Rossi.

Here are some technical data in advance:

Kosmo 3
Construction: Benito Bertolani
Length: 1344 mm
Wingspan: 1640 mm
Take-off weight: approx. 3400 gr
Engine: 10 ccm Methanoler
Distributed by: Mantua Model (Italy)

Many components of the kit are laser-cut, others are already sanded moulded parts. We started with the numbering of the components after the first photos of the kit were taken.

We started with the basic framework of the fuselage, which went quickly by hand. The enclosed plan is not true to scale, but is reproduced in large steps on a reduced scale. Parallel to the construction, we were supported by a construction report in the Italian construction forum Baronerosso. The first parts were quickly put together and the fuselage showed the first contours.

After the fuselage framework, we took care of the tailplane. This is made of polystyrene and already covered with a kind of paper. After gluing the two halves together, we glued and sanded the trailing edge and the wing tips.

So that’s it for today, we’ll start building the wings soon. You can look forward to it.

01.02.2022
We start building the wings. After sorting the wing ribs, they were threaded onto 2 round wooden sticks and assembled according to the grooved leading and trailing edges.

The distance between the ribs is thus automatically predetermined. The wing that has been threaded in this way can now be clamped in the supplied wing rig to create a wing that is ultimately straight during this construction phase.

It is important to ensure that you do not build 2 left or right wings, for example. I’ve seen and experienced it all before. It should also be mentioned that there are corresponding ribs for a rigid undercarriage (included in the kit) and for a retract. In our case, we were able to put aside the ribs for the rigid undercarriage. The raw construction was then quickly glued together using PVA. For initial stability, we glued the lower main spar and the rear auxiliary spar. Now the wing could be turned and the upper side was fitted with the spars. Now it was the first time to assemble the aeroplane with the components that had already been made and we got an idea of the dimensions and shape of the future model.
The next step was to assemble the retracts.

Plywood doublers were used here to support the retracts. Additional reinforcements were added at one point or another in order to better transfer the forces. I took care of the wheel houses. In this case in the old manner. For this purpose, 1 mm balsa sheets were cut into strips and soaked in water. After soaking, 2 strips were brushed with PVA and wrapped together around a spray can using rubbers. After drying, you get really stable wheel houses that have a nice round shape. These still need to be adjusted and placed in the wing with the built-in retracts.

A few more reinforcements on the wing and we were ready to cover the top of the wing with balsa sheets . To do this, 3 balsa sheets were joined together to one piece and attached to the top of the wing with PVA. This required a few pins.

The underside has not yet been covered with balsa until the installation of the mechanical retract has been realised, starting with the type of linkage and fine adjustment in the wing. We were already eager to finish the wings.
After a long break and Maurizio’s lack of time, I decided to continue the project on my own.
The wing mouldings were adjusted slightly and glued to the fuselage. This results in a large contact surface for the wing.

Next I took care of the nose retract. Here you have to use your own imagination, there is no material or suggested solution. The retract mount was realised with 2 beech boards.

Now I took care of the construction of the turtle deck. To do this, a moulding block is glued with subsequent half ribs and a spar construction, on which the planking is then mounted using individual strips. Now you can round off the back of the fuselage with a balsa plane and a sanding block.

The next step was the canopy area. Here you realise that this is not a plane for beginners. With a little brainpower you can imagine how it could be realised. It remains open whether you want a removable canopy, which is advantageous with an electric drive, or whether you want to glue the canopy and canopy frame to the fuselage.

The servo board in the fuselage is to accommodate 4 servos and be made in a screwable design. The servos for the elevator, rudder, nose landing gear and engine throttle for the Rossi 60 will then work there. The rudder will be controlled using cables (diamond steel wire).
To do this, I positioned the servo nicely in the centre. As an alternative to the elevator linkage using bowden cables, I created a pushrod for the 2 elevator blades using a carbon arrow and a fork linkage. The servo is centred above the rudder servo.

Now put the fuselage to the side and continue with the wing. The panelling is now attached to the underside of the left wing using PVA.

Things are progressing, more on the Kosmo 3 soon.

So, let’s continue:
In addition to the installation of the retracts, the design has already been considered.

The Kosmo 3 was to be decorated in the colours of the Italian flag. A chinese heat-shrink film was used, which was in no way inferior to its German competitors in terms of workmanship. A few stickers were created with my own cutting plotter and we had a great model on his own feet.

The first flight was relatively unspectacular and exceeded all expectations. The Kosmo 3 is a very fast model, supposedly the fastest at the time. Landings can be approached very slowly without fear of a stall.

It was a lot of fun to build the Kosmo 3 and Benito Bertolani succeeded in creating a perfect construction that was used in competitions for years. Unfortunately the kit is no longer available and so the Kosmo 3 has a special place in my collection of RC1 and F3A models.
With flying greetings, Toni

Text and photos: Toni Bäuerle