Agusta-Bell 206B RC Helicopter in Scale 1:5.7 of the Greek Army Aviation




Introduction

I have started this blog as an english-text alternative to a thread that I have opened in modelclub.gr (modelclub forum in greek) regarding my project to build an RC scale model of an Agusta-Bell 206B Jet Ranger II of the Hellenic Army (see unofficial site).


Now a few words about the project itself. The model is based on the fuselage provided by Vario (model 1004) in scale 1:5.7. There are very little differences between a Jet Ranger III (model kit) and an Agusta-Bell AB-206B Jet Ranger II that I needed for the project, so I decided to get the kit from Vario. The kit has been bought from one of the best specialists and professionals in the field, Mr Thomas Baumann who has helped me with making my choice of the model and its accessories (Helikopter Baumann). Thanks Thomas! I would also like to thank the team of eflight for their professional support not only for this construction but for all my RC models and accessories. In addition, I would like to thank the team from Innoflyer and especially Mr. Christophe Raible for the help with the lighting system and for letting me test a new CPL model before its official launch. I would like to add here the biwix.com RC helicopter store and Johnny Trolliet at my hometown Renens for his exceptional service, availability and prices!

The particularity of this project is that the mechanism that I fit in the fuselage is not the one from Vario but a modified Align T-Rex 700E (Align RC Helicopters). I will give here details on the way that this is done with diagrams, photos, tips and tricks. This will cover the first part. The flight tests of the modified T-REX 700E have been conducted at the RC model field in Dizy, Switzerland that belongs to the Dizy RC Modelling Group (GAM Dizy). Big THANKS to all the members of the Club for the great friendliness since the first day I started there and for their help with advice and tips!

The second part will be dedicated to the scale model itself. Some photos of the Greek AB-206B can be found on the internet but they do not cover all the details. More photos of the aircraft with the Greek colors may be requested in the forum of modelclub.gr where I have gotten most of them thanks to the team spirit and great friendliness of the members (THANKS^1000 dsamba!!!). In order to complete the photographic part of the project I managed to get my own photos of a Jet Ranger III. This has been made possible thanks to the courtesy of the people from Heli-Lausanne (Heli-Lausanne) who have immediately accepted my request to get there and take as many photos as I needed. A big THANKS to them too!!!
At the last phase of construction, I have got invaluable help for the dimensions of the AB-206B landing gear from Iraklis Karailidis. Many-many thanks to you Iraklis!

So after this short introduction I will start publishing the steps I have already taken and will take during this quite challenging project (at least for me, it is my first scale RC helicopter).

I hope that you will find this blog helpful if you have a similar (or the same) project as mine and you will enjoy it as much as I do!

Welcome!
Hellenicopter

04/12/2017

The landing gear... again

OK, this time it should be correct. I have revisited the whole landing gear as the geometry before was not so satisfactory and the heli was sitting a bit too low. The angles of the geometry have been slightly changed but this forced me to do everything from the beginning, cross-tubes, fairings, landing skids, steps...

The cross-tubes are now made of steel tubes of 10mm diameter and 1mm thickness. After bending them a slight annealing took place to relax a bit the stresses.

The skids are now made with my Zortrax out of ABS and then reinforced from the inner side using 3 layers of 245g/m2 carbon fiber and the L285 resin in a vacuum bag.

The cross-tube cuffs have been redesigned as well as the fairings as the geometry has been modified.

The Zortrax has been used to print the new horizontal stabilizers as the ones before were too short. I will cover this part in another article.

Below some photos of the new adventure with the landing gear, hopefully the last one.

Cheers,
Hellenicopter

 

 The landing skids have been 3D-printed with my Zortrax M200, 4 pieces for each skid. They have been made with a 390μm vertical resolution in about 12 hours (each piece is 16cm long). Then they have been glued together with CA glue. After that, the carbon-fiber sheets (3 in total for each skid) have been cut to fit in the interior of the skids.

Printing at 390μm creates a lot of scalloping on the sidewalls of the pieces. Normally, this is a problem for the surface finish. Nevertheless, for laminating, this is mostly a feature as it increases the surface of adhesion between the resin (L285) and the ABS plastic.

It's even better to slightly sand the surface and clean it with isopropyl alcohol (IPA) beforehand for optimal grip of the resin on the plastic. Even without this surface preparation this type of resin adheres very well on the 3D-printed ABS.

The laminated skids are then put into vacuum bags (I used my Solis vacuum machine), sealed and left for 24h to cure at room temperature. By the way, some models of vacuum machines from Solis (like mine) are relatively low cost and perfectly adapted for small to medium sized laminated pieces.



In the pictures below you can see the method I used for drilling correctly the mounting holes in the cross-tubes. The cross-tubes of the Jet Ranger have about 12 degrees forward inclination (projected angle when viewed from the sides) and it is crucial to get the drilling as precise as possible.



To do the drilling, I have designed (with Autodesk Fusion360) and 3D-printed guides (Zortrax M200). The cuboid pieces are used to hold firmly the cross-tube in the vice. The other part that looks like a prism, once fitted at the right place on the cross-tube it creates the 12-degree slope with respect to the horizontal flat surface (glass or marble is best).

Once all the 3D-printed pieces sit correctly on the flat surface, I tighten the screws of the cuboid pieces and I install the hole assembly in the vice for drilling. The middle stock is designed longer in order to guide correctly the drill straight onto the cross-tube and avoid any slipping of the drill tip on the curved surface. The other two are not necessary but help for installation on the vice. Their second use is also to perform pre-drilling installation tests on the helicopter (that's why you see two M4 threads pointing out from them).

In the two pictures below you can see the crosstubes installed. Their length is not the final one as I need to trim them to get the correct height.



The pictures below are about the making of the updated cross-tube cuffs and fairings that needed to be slightly redesigned to fit the new geometry as the curvature of bending has been adapted from 10cm to 7cm and the dihedral angle of the cross-tubes from 60 degrees to 50.  (measurements done on photos, hopefully not too far from reality).
For the cuffs I 3D-printed the molds, waxed them and then covered with many layers of glassfiber patches. This patch work is needed to correctly follow the curved surfaces of the cuff mold. I used this method and not a negative mold because it's easier to make solid and sharp trailing edges for the cuffs. Nevertheless, a lot of sanding is needed after curing to get a smooth surface. I could put an additional layer of resin before full curing of the main laminate to get a smoother surface finish and avoid too much sanding, but anyway, now it's done, next time I will be less lazy :P...





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