Mini Arrow Build

After seeing a number to scratch builds from flitetest, and having a friend recommend giving it a go I thought I'd attempt my firs scratch build. The mini arrow seemed a good choice, the amount of building required is relatively small the techniques straight forward and not too complex so it seemed suitable for a first attempt at scratch building. Also there are fewer moving parts than some other designs, as it is a flying wing there are only two elevons.

Preparation

The main preparation involves getting your foam board, tools and the plans for the Mini Arrow. The planes can be downloaded from Flitetest and are available in two formats, tiled and full. The full contain the full plans on one large piece of paper which you can print on a large scale printer or have them printed at a printing shop. The tiled version of the plans breaks the plans up to A4 size so you can print them on a regular printer and then stick the pages together.

I chose to use the tiled plans and once I had glued the individual pages together to make the complete full plans I decided to make templates from the plans. The reason I decided to make templates was that I thought the templates could be reused if I want to build another Mini Arrow, or build specific parts if I need to make repairs. Also I though having card board templates would be easier to work with as the would have some thickness to them which would make tracing around them and cutting around them easier as opposed to paper plans. On the down side this does mean a little more work as you first need to cut out the templates from cardboard before using them to cut the foam parts.

To make the templates I simply used a spray on glue to stick the plans to some cardboard and then cut out the templates from the cardboard.

Tools for templates:

• MiniArrow plans
• 2mm think cardboard - to stick the plans to
• Spray on glue - this makes sticking the plansts to the cardboard easy, alternatively a glue stick could be used
• Scissors - to cat out the cardboard templates

Build

Cutting out the parts and assembly

The first part of the built is to cut the parts out of foam using the templates. To do this I pinned the templates to the foam board and then cut them out using a stanly knife. For internal cuts for scores I put pin holes on the cut lines then removed the template and made the cut/score using a stanly knife and a metal ruler as a guide.

Once the parts are all cut out the next step is gluing the parts. Follow the plans and take your time, make sure you have a triangle on hand to ensure 90 degree joins are straight and true.

Tools used in the build include:

• Foam board - I picked up my foam board from a riot craft store
• Pins - to pin the templates on to the foam
• Stanly knife - these are cheaper than an exacto knife and you will need fresh blades for clean cuts
• Exacto knife - used when needed in tighter spots, curves or internal cut outs where the stanly knife is not so good
• Steal ruler - for drawing straight lines and cutting straight lines
• Triangle - to check right angle glue joints are at 90 degrees
• Hot glue gun - for gluing the foam parts together
• Clear packing tape - for re-enforcement

Regarding the hot glue gun, my hot glue gun is just a basic one (ie $15 from hardware store) and is not an industrial one but this was sufficient for this build.

Protection and paint

After building the Mini Arrow I applied a coat of oil based polyurethane which is a clear coat. I did this to try and protect the foam board and make it a little water resistant. Following the clear coat I painted most of the wing orange after masking the center fuselage which I then painted black. As you can see in the photos after I masked off the orange to apply the black paint and then removed the masking tape some of the orage paint lifted, hence why I have a white showing around the black paint edges. The paints I used were enamel spray paints.

Electronics fit out

There's not a lot of room in the Mini Arrow, and under the hatch its a very tight fit for all the components. A small receiver such as the Frsky D4R-II is definitely required. It might be possible to use a larger receiver if the underside pods are used however you would need to carefully think about how leads and connections are made.

Room for batteries is also limited and as these are heavy it probably best to put them in the main fuselage so the weight is in the middle. plus you can then easily move in backwards or forwards as needed to adjust COG (Center Of Gravity). I found the 3S Nano-Tech 850mAh LiPo battery a good fit.

Servos and control horns are fitted to the top side of the wing so that they are protected when landing. Servo leads are routed through the wing spare into the fuselage. The servo leads on the HXT500 servos were just long enough to reach the fuselage and connect to the D4R-II receiver.

The motor was directly soldered to the ESC and bolted to the firewall of the mini power pod. The ESC was positioned in side the power pod just behind the motor.

Parts:

• Multistra Elite 2204 2300kv motor
• 12A blue series ESC
• 2 HXT500 servos
• Frsky D4R-II receiver
• 3S Nano-Tech 850mAh LiPo battery
• 5x4.5 prop

Flying

It is very important to ensure that the CoG (Center of Gravity) is correct, in my case I had to add some weight in the front of the nose to get the Mini Arrow to correctly balance.

Initially I flew with a 5x3 prop which was also a bit flexible (thought this could be good it if gets snagged on landings), however this did not seem to have enough thrust especially for hand launches. A stiffer 5x4.5 was prop was much better.

At low throttle the Mini Arrow seemed to drop the nose a bit so its best to keep the speed up on this wing, and for landing only cut the throttle just before touch down.