Last time, I covered the rubbing down of the Twin-Jet components in preparation for painting and assembling them into an airframe.
Now I move to the motivation, servo & radio gear installation.

Supplied with the kit are 2 Permax-400 motors. I have seen Choddys Twin-Jet fly quite nicely on these but as I was adding weight by filling in gaps and holes & painting the model I wanted some more clout from the propulsion system. I also wanted to be able to remove any motors fitted without damage to the engine necelles. Using .8mm veneer sheet I made motor mount liners.
This gives three advantages from my point of view.
1. Epoxy can react badly with EPP and trying to hold anodised motors with cyno is a dark art I have no knowledge of, so the beech wood allows epoxy to be used for the motors.
2. Additional heat from 480 motors was considered and this also helps protect the necelles from heating up.
3. If at some point a motor fails or I decide to try Cobalt or Brushless motors the foam will not be damaged during removal of the motor/s.

The odd shape of the mounting sheet can be seen here.

Cyno'd into place and a motor put in situ' to hold it in place.

Both mounts secured in place and ready for the thrust blocks.

One thing a few people have mentioned regarding the Twin-Jet is the large degree of up thrust. This is very apparent in Choddys plane & shows most notably when flying inverted. Much like the Picojet-Combat lots of forward stick is required for fly-bys and flying inverted.

Wire loom soldered directly to the motor terminals.

Terminal wires thick heatshrink coated

Motors secured in mounts & wires fitted to pre-cut wing grooves.

Motor polarity has been wired red to positive as one mod I am trying to get parts for is using pusher props. Wiring some 480 motors in reverse reduces the output RPMs and as with the JP-pros cannot be dial tuned like some. As I am having trouble sourcing 6" & 7" pusher props I will have to wire the speed controller end of the motor harness to be reversable. This will allow me to chop and change as needed. To begin with FK 6x4 props will be used on reversed motors. Still trying to get a second Graupner 6x3.
Why is it when you see props you never need that size or type but when you try to find them they are as elusive as rocking horse foot prints.

Thrust altered with small blocks.

Prop adapter fitted and secured.

Motor, adapter & prop all fitted.

Small blocks of beech 1/8 x 1/16 places at back edge of veneer mount to bring the motor thrust angle down to about half of the original. I will of course report fully on this action in case it is a lemon of an idea.
MFA Rocket 400 motor adapters used. I tried to find the nice domed ones like I have on my Pico-Jet & Choddy has on his Twin-Jet but they were taking ages to arrive so I got alternates. Will use the domed versions if they arrive soon with the pusher props.
Kavan FK 6x4 (the now nfamous) yellow bendy props used, with motors wired for reverse running.

Elevon mixing is required for this model. If you don't have a mix setting on your radio you can buy seperate mixer (Overlander do one)

Servo secured with blocks of beech & cyno. Glass tape keeps dirt out.

All wiring tested & secured. Glass tape keeps the wires safe.

Hinge area strengthend with wide glass tape ready for cutting.

Control horns need to be cut down to fit the slots provided. Make sure these are well glued in place with cyno, they are all that keeps the Twin-Jet from being an expensive lawn dart. Make sure servos are centred when fitting as a mistake at this point is hard to alter once servos are secured. Using small blcoks of beech to pack out the servo mounting hole these are cyno'd into place. A few minor mods were required to fit the Protech servos, a 10mm square block was removed whis allowed the sero arm free movement towards back of plane. V slots cut in forward edge to allow arm to travel forward fully. The servo is slotted in and a few drops of cyno at each of the blocks hold it in place. A large square of glass reinforced tape keeps the servo mostly free of moisture and dust.
Servo wires extended and a few small drops of cyno hold them into the pre-cut channels. Narrow tight weave glass tape keeps them in place and protects from damp and dirt.
Hinge area is also rienforced with wide glass tape as per instructions. It says use stickers provided actually, but as I am painting and not using provided decals this was a better plan.

Jeti 50A speed controller, Hi-Tec HS-4 reciever and 9.6v 2400Ni-Cad & 3000Ni-mh flight packs ordered especially for this project. (at some considerable cost I might add)

Speed controller wired for reversable power.

Mega high capacity 9.6v flight packs from Overlander.

Everything fitted to achieve correct C-of-G.

Speed contoller fitted with 4mm gold bullets. On motor side bullets are same way round so motor can be reversed easily. Power side of speed controller & Battery packs fitted with opposing connectors to avoid polarity reversal on the wrong side. Foam pads added either side and behind battery pack to keep in place as it is key to the C-of-G. Wooden blocks can be added more permanently. Reciever fitted with velcro so it can be moved around and the aerial fitted to pre-cut slot in wing. Secured with drops of cyno. All testing so far has shown no problems. Motors sound in tune & I will conduct a thrust test during the next week and report on the results.

All ready to paint and finish.

Part 3- preparation and painting


Article by Chinman from Bumpy Green Model Aerodrome
13th August 2001