Art Hobby Scalar 4.0m f5j build log

Looking for a full size F5J model, 4.0m, quirky and original, for hobby and training… the Art Hobby Scalar could be the one.
I was searching for a nice f5j, and knowing the quality of AH’s models, I bought the Scalar on the spur of the moment when I saw it. Here is my build log.


You can find other builds here at the time I wrote this post:
From Patrick Sokol (designer of the Scalar, thanks!) on pfmrc-eu
and from another early builder: CJS on rc-network.de

I received the box pretty quickly, in stock at pp-rc Modellbau.

The kit

The fuselage, tail boom, rudder, stabiliser are highend parts, like my DLG, looks like Carboline and of course pretty light. Wings are big… 4 meters of wood veneer. Impressive kit.
It explains a lot of the price and it is the most expensive Art Hobby glider.
If you exclude the gorgeous Art Hobby “signature” wing panels, everything is exactly as you could expect it from a classic cfk/gfk 4m f5j model… which is nearly twice the price. The scalar seems a pretty good deal.

Experience

Having a bit of experience with my old Odyssey – I’ve done everything to it, from varnish to paint to epoxy. I can recommend to never paint it or you will perhaps regret it, give a try to the wood finish wings…
For the wood, you have mono-component varnish… with solvent like the Art Hobby varnish (the more risky for the foam) or water based like Marine varnish; And bi-components: epoxy – the wood is saturated, strong, showcases the beauty of the wood grain and gives you a good thickness.
You can do both starting by the epoxy.

A quick list of specific material for the build not included:

  • Epoxy Resin with UV protection – with low viscosity – mandatory
  • Matte Marine Varnish (I used Syntilor) – for extra finish
  • Some peel ply
  • Paper towel roller…
  • Fiberglass twill ~200g/m2 – for viable external wing panel joints – mandatory (provided fiberglass is too thin and only useful for the edge of the wings panels).
  • Not mandatory: Carbon twill ~200g/m2 to reinforce the bottom central panel joint more than the provided kevlar strips.
  • Carbon steel surgical blades like some Swann-Morton – ref 10 and ref 11.

You can find the classic AH build steps online, there is many video tutorials about AH gliders (like cutting the aileron/flap)… I am writing here about steps that make me lost a lot of time in error and trial. Here is my must-do things for AH gliders.

Wings

First of all, the wing panels are aligned, the joint is sanded to match the dihedral. The joint is simply epoxy glued as a first step to fix the two parts. The joint is strong enough to keep the right angle for the skin fiberglass/kevlar layup.

Always work at a good room temperature like 20 DegC at least, with the resin and the surface at the same temperature.

Wing panel joint

  1. Mix your resin (Epoxy Resin with UV protection – transparent stratification resin)
  2. Wet the wood with the resin
  3. Heat the wood (a hair dryer can do the job. I am using my heat gun soldering station at 120 DegC) – not too much, it is lowering a lot the viscosity – just enough to see bubbles popping, the resin is penetrating deeply in the wood.
  4. Apply your layers (carbon, fiberglass, …) and wet them completely with resin. A brush with vertical moves on the clothes or your finger (glove).
  5. Finally put the peel ply and pressure on it to wet it completely. You can use a credit card. The peel ply will suck the excess of epoxy. Check there is not a single bubble left between layers.
Central panel – botton: 200gr/m2 carbon patches + provided kevlar strip (200gr/m2 ?) + provided thin fiberglass.
Peel ply over to grab the excess resin and ensure there is not air bubbles between layers.
Raw result with peel ply removed. Really light sanding and wing surface resin layer will smooth it completely.
External wing panels with dihedral segments : epoxy glue on the joint to freeze the angle.
We will apply 200gr/m2 fiberglass here – not the light fiberglass provided.

Wing panel surface

  1. Sand the surface with 300 grit.
  2. Clean the surface and remove any dust
  3. Mix your resin (Epoxy Resin with UV protection – transparent stratification resin)
  4. Wet the wood with the resin (I am using my finger with latex glove here)
  5. Heat the wood (a hair dryer can do the job. I am using my heat gun soldering station at 150 DegC) – not too much! the goal is to lower the viscosity – just enough to see bubbles popping, the resin is penetrating deeply in the wood.
  6. Take a sheet of towel paper and remove all the excess resin by doing one movement from the leading edge to the trailing edge. Repeat with new towel paper. You can stop when you have a matte finish on all the surface.
  7. Leave it to completely cure for few days (depending on your resin).
  8. Lightly sand with 300 grit sandpaper and clean the surface
  9. Varnish one layer with a foam brush (Matte Syntilor Marine Varnish). It is a finish layer to perfectly fill the surface.
  10. Lightly sand with 300 -> 600 -> 1000 grit sandpaper.
Pre-Varnish : resin result
Pre-Varnish : central pannel top result – Kevlar + light fiberglass here.
Kevlar is more “yellow”
Pre-Varnish : Really discreet joint with the panel also epoxied with the same resin used for the joint.
Final result of the wing. The surface is flat and hard. The resin made the wood veneer reveal even more. Colors are stunning.
The wing is prepared for the aileron / flap cut.
I lay fiberglass under the servo frame
Servo frame fitting

My 3d printed servo frames

Provided horns Versus my home made horns = more grip and lower, allowing near seamless integration

Fuselage

Nothing fancy here. I added some carbon reinforcements in the fuselage on the joint between the fiberglass (top white part) and carbon (bottom black part).

It is stated that a 35mm nose cone should be use. My fuselage was a bit like 33-34mm and I was fitting a 28mm motor. I chose to left the fuselage cut untouched and simply make an adaptator to fit a 32mm nose cone perfectly. The weight is optimised (can not put the motor more forward) and the result is perfect.

The parts:

  • SunnySky x2220 iii 980kv – very efficient
  • ESC BLHeli-32 SucceX 55A Slick – (BLHeli-32 !!!)
  • Dual redundant Mini-560 BEC – 8V output
  • FrSky G-RX8 (2.4Ghz with Altimeter)
  • FrSky r9mini (900Mhz redundancy)
  • Hyper Spinner POWER 32mm, carbon blades…

HyperSpinner – 32mm. No gap with the 3d printed part.
Hand release plug – I don’t like fixed plugs on both ends because of mechanical stress.
Put two but it is too much force appllied on the servo. I removed one spring.
PTFE tube fitted to avoid friction with the line – trimmed later
Just two transversal piece of carbon 1.5mm to hold the servos.
Using fishing swivels for the pull line.

CG at 130mm for the maiden. No lead added with a 3s Tattu 2300mah in the nose. Everything looks good and I am pleased with the result. By design, not “competition light” (I am reaching 1750gr) but tough and easily repairable – exactly what I was looking at with this F5J, a nice reliable glider and perhaps a great performer. Waiting for the maiden now…

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