The fuselage is where most of the work is to be done.
Firstly, the main Undercarriage and tailwheel will be tackled. With pretty much all F3A models it is recommended to reinforce the main Undercarriage area. This is particularly pertinent with BJ Craft as the UC plate is two pieces of light ply laminated together and the top layer has lightening holes.
My customer asked me to upgrade this area to avoid disaster with a busted UC plate or fuse side damage with a hard landing. Yes, we all have them now and then...
I’ve created an upgrade kit which is shown in the above gallery.
The kit consists of:
- 2mm Carbon Upper Brace.
- 1mm Carbon Upper Plate.
- 1mm Carbon Lower Plate.
- 50mm Carbon cloth.
- 12k Carbon Tow.
The factory applied adhesive on the top of the UC Plate should be removed. This will allow the upper carbon plate to sit flat. The lower plate spans the whole UC plate. To fit the carbon plate, the UC leg opening in the fuse side will need to be opened out a little.
The surfaces of carbon to be glued should be roughed up with sandpaper to assist adhesion. The upper and lower plates were glued in with 30 minute epoxy and the cloth and carbon tow was attached with Epiglass 9000 Laminating resin. This resin is lower viscosity and will wet out the cloth better. Depending on the hardener chosen (I use standard) the working time is about 45 minutes and cure time is 24 hours.
The Upper Brace is made from 2mm carbon fibre sheet. There is no need to glue this part in place. I suggest using M3 cone washers to help spread the load on all four M3 Undercarriage screws.
I found that the inner holes on the Undercarriage legs for mounting did not line up. The laser cut Lite Ply Undercarriage plate is accurate. I filled the existing inner holes with epoxy and glass rovings. Then drilled a new hole in each Undercarriage leg. The ply plates that carry the blind nuts for the Undercarriage screws are also out. I made new ply plates from aircraft grade ply and reused the blind nuts. The fit is now perfect!
The BJ supplied tailwheel was upgraded with a few small modifications. The factory supplied plastic tube spring was replaced with a brass coupler, piano wire and delrin post. I found the plastic tube supplied would split when threaded onto the long grub screw. BJ also suggest on his blog to re-bend the tail wheel to make the models stance lower. I didn’t do this and have since heard of failures after bending the wire.
A flat washer was soldered onto the spring wire for the tail wheel to push against. This prevents the chance of any binding against the radius in the spring wire.
A delrin Bush was made to support the tailwheel assembly. This Bush was glued into the fuse after drilling a 5mm hole of course.
My Customer wanted the factory supplied canopy latch system to be replaced. A number of people have lost canopies due to the default latch failing.
The two plastic pins at the front are retained but a spring latch system was used at the back of the canopy. Everything except the spring was designed and manufactured here at Precision Aero Products. The design mimics what has been used on the Allure/Alchemy with great success. I don’t know of a single canopy failure using this style of system. I think the pictures tell a better story than I could write.... :-)
Ventilation.... On a BJ model all the ventilation holes need to be cut by the builder. Templates should be supplied in your kit to do this. A number of Element kits were released without templates (including these two) but fortunately BJ was able to supply the CAD files which allowed me to make the templates locally on our CNC Router.
To cut the ventilation holes you’ll need a Dremel, cutting tools like ceramic cutoff wheels, sanding drums, files, masking tape and a marker.
I firstly place masking tape on the fuse where the cutouts are to be located. The ply templates can then be used along with the marker to mark out the holes. Then a sharp scalpel is used to cut around the marks just made and then pick out the tape. This gives you a nice line to cut to. Depending on the shape being cut, I would start with the cutoff wheel in the Dremel. Then final shaping is done with sanding drums and files. Sandpaper stuck to round tubes of various diameters also make great sanding tools.
The rear vents on the side and bottom of the fuse are elliptical in shape. I found a diamond burr in the Dremel made easy work of roughing out these holes. Final shaping was again done with files and sandpaper by hand.
First up will be the Plettenberg Advance. Below is a gallery showing the method used.
The Mounting System was supplied by my Customer along with the Plettenberg Advance. The mount is an MTS front and rear mount to suit the Element. We have since improved upon this mount to make thrust adjustment easier. I’ll document the improved mount later in this blog.
As with most designs, the nose ring is used to set the thrust. This build will be no different except that a little more clearance between the spinner and nose ring will be allowed. This will allow for thrust adjustment during the trimming process. The spinner used in this instance was a Falcon 3B Carbon Spinner. A spinner spacer was cut out of 2.8mm light ply on the CNC. This spacer was cut the same outside diameter as the spinner (82mm) and the inner hole was cut to be a neat fit over the Plettenberg thrust washer. This helps with trimming the carbon firewall to centralise the spinner/motor on the nose ring. Once happy with the fit of the firewall, sand the outside edge of the carbon to help the epoxy adhere. Also sand the inside of the fuse for the same reason. It’s also important to clean both parts with methylated spirits before gluing too. Next the motor, spinner spacer and spinner is assembled to the fuse. As you can see in the pictures, masking tape was used to hold everything in alignment. The adhesive used was Pacer Z-poxy which sets in 30 minutes. I also mix in some glass fibre rovings or powder to give the adhesive some body. With the motor in place access around the motor is limited. This being the case, a number of small blobs of epoxy was applied around the firewall to tack it in place. Once fully cured, the motor and spinner was removed and a full fillet of adhesive was applied to both sides of the firewall. This was done in two steps. I hung the model from the nose and tail to prevent the epoxy fillet running to one side.
An MTS rear support was also used. This version was the narrow one which suits the BJ Craft fuses. This rear support simply pushes onto the Plettenberg rear bearing boss and is attached to the fuse sides with carbon or ply side pieces. Reassemble the motor to the firewall. Dry fit the rear support and adjust the side pieces to get a neat fit to the fuse sides. Again, sand the carbon side pieces and fuse sides where they will be glued. Clean with methylated spirit too. Epoxy and glass rovings was again used to glue the side parts to the fuse sides.
That’s it. The Plettenberg is mounted!
Updated Plettenberg Mount - On a subsequent Element build, the mounting system was modified. The front carbon plate is completely new and the rear mount side pieces now have a slot in them to allow easier adjustments. The front mount has just four mounting screws which makes thrust adjustment simple with shim washers.
A Ply Firewall is used with this front mount as you can see in the pictures above. The alignment method was changed a bit to make life easier. A drill jig the same diameter as the nose ring makes locating the mount a breeze. Some small spacers were used to get the offset of the firewall correct for the Plettenberg Advance. A small spirit level was used to get the fuse level and then level the drill jig. Then drill one hole at a time and insert the screws after drilling each hole. These M3 screws will be replaced with countersink screws to clear the spinner backplate.
The Ply Firewall Can now be shaped to fit the nose. Just take your time here to get the fit a neat as possible for a better glue joint. Gluing was done with epoxy and glass rovings. An additional length of 12k Carbon tow was added around the front and rear of the ply firewall.
Adverrun XS Contra Drive System Mounting - The Adverrun will be mounted in the second Element which of course has a contra nose. The only difference being that BJ Craft has added a ply ring to the nose which removes the right thrust.
Mounting the Adverrun into the Element is arguably easier than mounting the Plettenberg Advance. As with the Pletty, a nose ring spacer was made to get the spinner to nose ring spacing right. With a contra you want a gap of 2.5-3mm to allow for movement of the drive system. Remember, the Adverrun is soft mounted front and rear!
Being the first Adverrun I’ve mounted, a dummy firewall was made from light ply. From this adjustments were made and then the real firewall was cut from 4mm AC Ply. The final part ended up with a 45° chamfer on the front edge. See the pictures above.
The firewall needs to be mounted as far forward in the nose as possible hence the 45° chamfer. This is due to the added thickness of the contra nose ring. You may need to remove some moulding bumps or flash to get the firewall fitting well. Once happy with the firewall fit, it was glued in with epoxy and glass rovings. You’ll end up with a small gap on one side between the firewall and inner nose ring. I just filled this with more epoxy and glass rovings once the initial firewall glue had cured.
The rear of the Adverrun is also soft mounted now. Small plywood side pieces were made to tie the rear of the drive to the fuse sides. Note that plywood was deliberately used for its superior noise absorption in soft mount systems. In the rear, using plywood allows blind nuts to be used as well for the retention screws. The side pieces were adjusted to get a perfect fit. The fuse sides are roughed up with sandpaper and cleaned with methylated spirit. Then both side pieces are again glued with epoxy and glass rovings. I normally just apply enough epoxy to tack things in place and then remove the drive and go over it again once cured with another fillet of glue on each side.
Wing mounting and adjusters.
The wing tube socket it already fitted to the model as are the stab tube sockets. On this model, the datum is the stabs. In other words, the stabs are the zero reference.
Important! Check the alignment of both stab tube sockets and the wing tube. They all should be parallel.
On the last Element I Built, the rear stab tube was parallel to the wing tube. The front one was out by 0.8°. This resulted in a 0.4° incidence difference between the two stabs. A new socket was made to replace the factory installed one. The stab incidence error is now 0.04°. Well worth the effort to fix it.
Below is a gallery showing various pictures of the wing adjusters I made and also how they were installed.
The first thing you should do is set the model up in a solid cradle that will hold the fuse steady. Then set your datum to zero on the stabs. I use a DXL360 angle meter but a Wixey will do the trick too.
BJ normally provides a template for doing the wing alignment. The last Element kit I assembled was missing this template along with some of the other templates. That’s ok as some masking tape does a better job in my opinion. With the angle meter on the wing, move the wing to get +0.5° and tighten the wing retention screw to hold the position. The factory cut anti-rotation pin holes in the fuse side may need adjustment to achieve this setting. You should be able to slide some masking tape under the trailing edge and leading edge at the root. Mark around the wing LE and TE onto the tape. Remove the wing and apply a strip of tape where the rear adjusters will be fitted. You should then be able to measure and mark the wing root centreline onto the masking tape. This will be the adjuster mounting screws centreline. The screw hole positions can be measured and marked out. These are centre popped by hand and then drilled to suit M3 screws. Repeat for the other wing.
A ply backing plate is used with these adjusters. The ply is glued to the inside of the fuse. Countersink screws are used on the adjusters so an appropriate countersink drill bit was used on the fuse sides for each screw. The adjusters can then be fitted with a little locktite on each screw. The rear adjusters are done.
Refit both wings and check they are still at +0.5°. The adjuster will most likely need a small adjustment.
The kit supplied adjusters are used on the front Anti-rotation pins. I used a ply backing plate on these adjusters too. The adjuster is glued to the ply plate with CA. The adjuster is set to mid-range and then each adjuster is glued to the fuse.
If you’ve got everything square the wings should go on and come off with ease and have minimal slop if any.
Receiver Mount - The receiver mounts used in these two models were originally designed by Richard Hirst. I’ve modified the tray a little to include a position for a PowerBox Smart or Digi Switch. This saves cutting a big hole in the side of your fuse.
The tray looks to be an odd shape but this allows one of the receiver antennas to be cable tied to the tray facing backwards. The other antenna is routed up the side of the fuse.
The kit supplied balsa triangle stock was glued to the bottom of the tray. The whole tray was then levelled up and glued into the fuse.
The Digi Switch is screwed directly to the tray. The receiver and RX battery are attached with double sided tape (Receiver) and Velcro straps.
Battery Tray - A battery tray kit was supplied by my Customer. It was designed and manufactured by MTS. In theory the whole tray is adjustable to allow for CG fine tuning. The tray has approximately 1” of adjustment range.
For the second model I acquired some parts and then cut the Lite Ply on the CNC router. This keeps both models the same with respects to battery mounting.
Assembly is very straight forward. The lateral plates are cut to length once you’ve decided on a location for the tray. Each lateral plate is glued to the fuse sides and supported by a rectangular doughnut. The 6mm carbon tubes will need to be glued into the lateral plates with epoxy. Rough them up with sandpaper first. The actual battery tray can be attached with the screws to the 3D printed adjuster blocks.
Conventional battery straps are used to secure the packs to the tray.
Canaliser - The canaliser is attached to the top of the fuse with three M3 screws and blind nuts. The builder has to fit the blind nuts to the fuse. Round ply doughnuts are already fitted where the canaliser attaches. Holes for the screws are already drilled in the canaliser. Just locate them and remove the covering over each hole.
For whatever reason, the angle of attack (AOC) of the canaliser is negative to the wing. The incidence should be the same as the wing. Some packers will be needed under the canaliser to get the incidence identical to the wing. Also check the lateral alignment by measuring with a ruler down to the wing. The gallery below you can see the balsa packer used to get the alignment right.