Elektro Retro (oz16073)

About this Plan

Elektro Retro. Radio control sport model for electric power. Wingspan 2850 mm.

Quote (google-translated): "Elektro Retro. It looks like an old timer, but in reality it ios a very modern model. A real exercise in style invented by re-fishing the lines of old models for the sole pleasure of building with traditional techniques, where modelling marries the finest cabinetworking.

Having a complete motorization for 8s that was parked in a corner of the laboratory, I wanted to use it on a model with old timer flavor, one of those free flight models from the 30s and 40s with such atypical shapes and intricate structures, with a 'chubby' fuselage, with the fin wing sometimes perpendicular to the engine, and a very accentuated double dihedral. These retro models are coming back into fashion among the die-hard balsa slicers, as witnessed by numerous websites and the best forums such as RC Groups. On YouTube there are also many archive films that can serve as a real source of inspiration for everyone.

After examining quite a few drawings, I decided to make a 'mixed fry' of all these shapes. A few pencil marks... oops: mouse clicks later, and the model has already taken on its precise physiognomy.

The dimensions still need to be defined; for this I start from a hypothetical mass of 7.5 kg and a wing loading that does not exceed 70 g/dm2, for a surface of about 110 dm2, from which the wingspan and the chord can be established. The general appearance is caricature, almost cartoonish, with large wheels to take off even on rough terrain. The profile is the NACA 4415, with a flat belly and easy to build without the need for feet under the ribs, thick enough to fly slowly.

Not knowing where I would end up, I didn't have the courage to draw a section of the elliptical or polygonal fuselage; I limited myself to a simple rectangle, but with curved sides in laminated strips. For the empennage I chose the two rounded fins and a bit of dihedral for aesthetics. In the end I realized that it almost resembles a tow, so I will mount a tow hook. You never know. The design, as usual, is born and develops while I build, which allows, for each single element, to progress in a coherent and logical way and to make the necessary changes without wasting too much time thinking.

I start by drawing the wings: two meters and 85 of span for 43 cm of chord, and a surface of 112 dm2, no D-Box to remain in retro style, but 5x5 strips between the leading edge and the main spar to better follow the profile. All the wood was selected from red cedar strips purchased at the nearby DIY store. This is a relatively light wood, let's say like samba, and very fragrant; it reminds a bit of the smell of pencils from our childhood. If you can't find it, you can replace it with hard balsa or white pine, but not with fir which would be too heavy considering the quantity of strips planned.

The 'wing kit' was cut with CNC, all in 3 mm poplar plywood and very lightened. Eventually, you can replace the plywood with 3 mm balsa without drilling it or simply by making a few holes, since the first ribs that support the bayonet will still have to be made of plywood. The bayonet is a 14 mm fiberglass rod, while the 14/16 aluminum bayonet holder tubes were purchased at a DIY store. The rear alignment bayonet is made of 5 mm steel and is housed in a 5/6 mm brass sleeve.

Then, the leading edges of the external wing panels are prepared, made up of five 2x10 mm strips that will make up a 10x10 mm element. These strips must be soaked in water and then dried in the template. Finally, they will be glued with vinyl glue and tightened in the template for at least 12 hours. [The leading edge must be cut with the circular saw, on each side, so as to have a finished section of 5x10 mm up to the NI8 rib and then a 10x10 section to compose the terminal.

We proceed by gluing the extrados spars and the leading edge, the balsa filling between the ribs at the level of the trailing edge, and finally the 0.6 mm plywood that covers the extrados of the trailing edge. The bayonet holder tubes must be glued with epoxy after having checked that the two parts fit together well: The final gluing must be done at the same time as that of the plywood reinforcements on both sides of the spars.

The ribs are glued flat on the intrados spars and on the 0.6 mm plywood trailing edge. Nothing more classic. The N1 and N10 ribs are inclined for dihedral, with the help of the jig..."

Direct submission to Outerzone.

Supplementary file notes

Article.

Corrections?

Did we get something wrong with these details about this plan (especially the datafile)? That happens sometimes. You can help us fix it.
Add a correction