Sig J-3 1/4 Scale Cub Build Series – Part 11 – Cutting Cowl for DLE 40 Twin

In part 11 of the Sig J-3 Cub Build series we will take a look at cutting out the cowl for the DLE 40 twin.  (NOTE: At this point, the cub is actually finished and has already had it’s maiden flight both off land and water!  The DLE 40 Twin Engine is a great match for a 25% size J-3 Cub – balancing out the plane out perfectly!)

The DLE 40 engine is a larger engine and will require you to cut out a significant portion of the cowl on each side.  Also note that the cylinders are offset from one another so you will need to measure and mark out each side as needed.

Glue the two cowl halves together using the provided plastic strip and thin CA.  Roughen up the inside of the cowl where the bead of glue will be applied helps the CA glue adhere much better than on a smooth surface.

Next, determine where you want the prop hub to come through the front of the cowl.  Use a hole saw to make a nice clean hole.  Clean up the edges by hand and some 120 grit sand paper.

One each side of the cowl I placed a few strips of masking tape and using a ruler and a square I marked out the approximate cut lines of the shape of the cylinder and muffler locations on each side of the cowl.  Be sure to take into account how much the cowl will “overlap” onto the nose of the airplane!

With the locations roughly marked out, I used a jigsaw to rough cut the cowl on the marked locations.  The cutouts were quite rough but using a Dremel with a sanding drum you can smooth the edges quite nicely.

The paint used to paint the cowl was from a spray can called VHT.  This is an automotive based enamel paint that you can get in a spray can form.  It sprayed nicely and evenly!  This paint is heat and fuel resistant and has held up nicely so far! They have it available in a number of colors.  The white color seemed to match fairly closely to the white covering I used on the rest of the plane.  I also used their “bright red” color for the floats (covered in part 14 of this series)

https://www.vhtpaint.com/

Sig J-3 1/4 Scale Cub Build Series – Part 10 – Cabin Access Door

In part 10 of the Sig J-3 Cub Build series, we will be taking a look at adding an access door on one of the  fuselage sides.  This will allow easier access to the inside of the cabin when bolting on the wings and connecting servo wires.

The window outline comes as part of the printed balsa sheets included with the kit.  Cut this out using a band saw or tool of your choice.  Instead of gluing this directly to the cabin formers, we will hinge this to the rear-most cabin former.

Start by tracing the shape of the hinges on the cabin window. Then, remove the material in the traced area to the same depth as the hinge thickness.  This will allow the hinges to set flush with the inside of the material.  For added strength, the hinges should be pined in place.  I used toothpicks for this and epoxy.

Mark the locations for the hinges on the rear most former and pin and glue the hinges here as well.  Make sure to get the placement correct as not to cause binding.

The access door can then be secured in place during flight using magnets or a latch. I intend to use a small neodymium magnet for this purpose which will be installed later in the build.

The hinged area can be sanded flush with the side of the fuselage for a nice fit! Leave some extra material for final finishing and fit.

Sig J-3 1/4 Scale Cub Build Series – Part 9 – Fuselage Strings and Cabin Floor

In part 9 we will take a look at installing a miscellaneous items such the fuselage stringers, some additional window framing and also the nose flooring.

Included with the are a number of 1/8 x 1/4 long balsa sticks  for use as strings.  Reference the included place for their orientation and placement along the fuselage.  One helpful tip to make sure you get the stringer that is placed in the middle of the fuselage is to use a long straight edge as you glue it in place.

With the strings now in place we can turn our attention to the window framing that needs to be done. These are included as balsa sticks so you will have to measure and cut these as needed.  They will be a bit over sized and stick out over the sides of the fuselage, but they will be sanded smooth later.  Part of the metal bracing that secures the nose to the main former gets in the way of the 5/16 stock.  See the photos below for how to shape the stock so it fits nicely around the metal bracing.

To get the curve I just placed a small piece of sand paper over the wire and ran the 5/16 stock back and forth several times until it had carved out the center of it as shown below.

The fuselage flooring pieces are included as printed balsa parts that will need to be cutout at a band say or hand saw.  Also there is a large piece of balsa that will be used for the cabin floor, this is cut over sized and will need to be fitted as shown in the photos below.  I used a number of clamps here to make sure the glue joints will be strong.  I also added some additional triangle balsa inside the nose to help further secure the floor pieces.

Once everything is dry, the cabin floor can be sanded to match the shape of the fuselage!

Sanding the main floor to match the rest of the fuselage shape.

In Part 10, we will look at installing and fitting the cowl around the DLE 40 Twin motor!

Ultra-Tote Field Box Modifications

In this write up we are going to take a brief departure from our J-3 Cub Build series and build the Hobbico Ultra-Tote Field box  – but with a few customizations!

The Hobbico Field Box has been around for a number of years and includes some great equipment that compliments anyone with a nitro RC plane.  When I purchased my first glow-fuel plane, I also purchased the Hobbico Ultra-Tote field box.  It includes a number of necessary items; an electric starter and a glow plug wrench to name a couple.  The kit also includes a nice 7Ah 12 volt lead acid battery for powering the included electric starter and wired glow driver.

However, I decided I wanted to make a few modifications along the way!  Once the basic box was built according to the manual I came up with a better way to secure a gallon of glow fuel in the caddy.  I started by adding a one inch high by 3/8 inch thick piece of basswood that serves to keep the fuel jug from being able to slide out of it’s intended location.  To hold this securely in place a simple zip tie was used to secure the handle of the jug near the top of the tote box.  Using a zip tie in this location, helps to “wedge” the fuel jug in place preventing it from slipping or sliding around during transport.

Next, I came up with my own design for a “power panel” of sorts.  I added an “always hot” charge plug so I could charge the lead acid battery without having to remove it from the field box.  I also added a couple of voltage meters, a current/amp display for the glow driver and a master switch that powers the entire panel.  There are two main 12 volt power sources, one of which is tied to the master switch but the one on the far left is always hot – directly tied to the battery which can be used for charging or as a power source for an external charger at the feild!

I also installed a current limiting device that allows me to adjust the amount of current (amps) the glow driver is allowed to use.  More amps equals a brighter glow.  I set my current to be a little brighter than a standard 1 cell NiMh glow driver is able to deliver.  I added a deans plug to the included wired glow driver so I could use this as needed and unplug it when I was done using it.  I also added a two foot extension to the glow driver cord for a little more length. To wire everything together, I used a power distribution board.  (Any distribution board suitable for a mini quad copter will suffice.)

I also opted to mount a 4 cell (yes that’s right – a 4 cell) lipo to the included Hobbico starter.  Going the “wireless” route here means you won’t have to worry about any power cords getting caught in the propeller.  The 4 cells gives a little more power and RPM for the starter to use.  The jury is still out on the long term effects of essentially overdriving the motor by a few volts. It usually just takes a blip or two of the switch before the motor is running.

Another modification I made along the way, was to add a screw to the carry handle, which will serve to hold the transmitter in a convenient location when starting the plane.  This allows me “hands free” access to the transmitter while starting the plane so I can run up the throttle trim during startup.

The ultra-tote also includes a nice electric pump in the kit.  I mounted this on the side of the Ultra-Tote and used a servo extension to wire it to the power panel.  If I ever need to replace the pump, I can just unplug it and wire up a new lead and plug it back into the power panel.

So far these modification have been working quite well and is making my plane fueling/starting procedures much more convenient!  Much of the fun with this hobby is making things work they way YOU want them to!  I’ve included a gallery of photos below.

Until next time, happy flying and RC’ing!