Juggernaut

Juggernaut is Valkyrie Aerospace’s first complete electric-powered RC model, featuring a unique twin boom inverted V-tail airframe configuration and brushless motors upcycled from Ewaste. The build process is similar to that of our other models but incorporates new techniques that the builder needs to be aware of; in particular, you’ll need to follow the order of cutting, folding, and gluing the fuselage booms closely (as depicted on the plans and in photos below) for a strong and aesthetically pleasing aircraft.

If you are new to building your own airplanes (or to model aeronautics in general), we suggest you first develop your skills by constructing and flying some of our other design before making a Juggernaut, so as to build experience for this model.

The links to the plans are below:

 

Juggernaut three-view

Juggernaut plans

Let’s get started!

Tools:

  • Hot glue gun (preferably a 1/2 inch model)
  • Spare glue sticks (preferably the clear kind)
  • #11 X-actor knife blade with type A handle
  • Thumbtacks
  • Steel-edged ruler or yardstick
  • Soldiering iron (higher wattage units make things much easier)
  • Pen and pencil
  • DX-6i (or radio of your choice; just make sure your recievers are compatible)

Parts

  • Adam’s foamboard (three 20 x 30 inch sheets)
  • Two DVD drive brushless motors (or two 1450 KV brushless outrunner motors)
  • Two 18 amp brushless ESCs (consider buying a multicopter pack)
  • Four Hexatronic 9 gram servos
  • Y-harness
  • 1300 mAh 2S 25C LiPo battery (three cell battery would be even better)
  • Deans/T-plug connectors
  • 2 mm banana plug connectors
  • Heat shrink tubing
  • Soldier
  • Linkage stoppers
  • Music wire (or paper clips)
  • 2 inch packing tape
  • Coathangers or similar gauge wire
  • Wire cutters
  • Wire strippers
  • Lighter
  • Old credit cards, gift cards, etc.
  • 8.5 x 4 slow-fly propellers
  • 1/8 inch machine screws (1 inch long)

 

 

Plans

You will want to print the plans on 30 inch wide paper if at all possible, but you can use software to tile the PDFs, print them on 8.5 x 11 paper, and tape them back together if you have to.

We usually transfer the plans to our foamboard with a thumbtack, poking holes at corners and ever six inches or so along straight lines and every 1/2 inch or so along curved lines. When everything has been marked in this manner, we then “connect the dots” with a pencil and ruler and trace curves free handed. This method usually achieves satisfactorily accurate transfers, though we would still prefer to print directly onto the foamboard.

As with our other plans, black lines are cut completely through, red lines are 50% score cuts, and blue lines are guides for assembly and decoration.

 

Parts and their construction

The wing spars are a good place to start the build. Simply cut these out and set them aside, being careful not to confuse them with scrap, of course! You can then cut out the rest of the wing, bevel the leading edge, and glue down the spars inside the wing as shown below.IMG_0606.JPG

Test all of your servos, ESCs, and motors before installing them, as once the aircraft is build they will be very difficult to access. Route the wires out the center hole as shown.

Cut out the fuselage booms. For now, only cut the red score lines running the length of the boom and those on the bottom plate of the cowling; removing foam from other areas at this stage will cause trouble later. Make the booms by applying glue inside the gaps of the lower fuselage boom plate, then folding the side plates against it at a 90 degree angle; you may benefit from doing these one at a time. Continue by folding the upper fuselage plate on top on the two side plates, then gluing the angle cowling plate in place. Cut the hole for the servo lead on the aft end of the boom on the inner side of the A-tail and route the servo lead down the boom, up through the holes you cut in the boom and wing, and out through the middle of the wing’s wiring hole.

Ensure all wiring is correct before proceeding. To fold the wing, apply glue to the top of the spars already in place, the leading edge, and the top of the lower trailing edge, then fold the lower side of the wing down on top of the upper side (this is because the lower side is smaller and easier to manage). Make sure the lower and upper trailing edges have mated along their length and have dried thoroughly before releasing them.

Cut out the A-tail piece and slightly bevel the middle, allowing it to fold at an approximately 100 degree angle. You’ll also bevel the crease where the fuselage tab meets the aft end of the fuselage booms and make the 50% score cut for the ruddervators – but don’t cut the ruddervators loose yet.

You can build the Juggernaut’s nose now by cutting out the side plates and the curved top/bottom plate. Make sure to cut through the foamboard on the long cut on the side plates, leaving the shorted ones to free later. Cut the 50% score cuts where the fuselage door hinges into the top/bottom plate and where the nose comes to a point, then peel off its inner layer of paper, apply glue to the edges of the side plates, and wrap the top/bottom plate around the side plates, holding until dry. Set the nose aside.

 

Assembly

First, glue the fuselage booms onto the bottom of the wing, using the blue lines on the plans as a guide. The booms need to be square with the leading edge of the wing and parallel with each other; check both with a ruler while the glue is still warm.

You can then fold the A-tail and glue its tabs into their respective slots in the aft of the tail booms, then cut the ruddervators loose. Cut the slivers of foam marked on the inside of the fuselage boom and bevel the trailing edges of the boom’s side plates; this will allow you to fold and glue the aft end of the fuselage booms flush with the A-tail, decreasing drag and increasing strength.

On both the A-tail’s ruddervators and the wing’s ailerons, bevel the hinges, then reinforce them by bending them fully backwards, applying a small amount of glue to the hinge, and spreading this glue into a thin layer across the length of the foam. You may also need to cut a clearance gap on either side of the control surfaces to allow them to move freely.

The final step involving foamboard is to apply glue to the inside of the wing slot and slide the nose onto the wing, making sure all wiring gets tucked in and smoothing any excess glue with a piece of scrap foam. You can then cut through the aft and forward slots indicated on the plans to free the folding canopy door.

 

IMG_0723These salvaged motors are surprisingly powerful without any modifications, and although they don’t match the performance of hobby-grade motors, they should spin at a high enough RPM for fly-right-off-ground (FROG) takeoffs. The lower image is looking into the fuselage booms from the front, awaiting the motors and firewalls.

The Juggernaut is a fairly large model aircraft relative to other foamboard builds, but I have designed the nose to be huge. There is more than enough room inside for a camera or handheld transceiver (HT shown here), and the weight and balance works out well with a variety of combinations. I suspect that the nose itself will act as a lifting body, enabling a slightly further forward center of gravity than other designs considered, but have yet to verify this with a test flight.

I recommend gluing strong magnets into the foam at the rear of the hinged nose compartment. This is the best way I have found to keep the door shut when it needs to be while still enabling easy access between flights, and you can probably salvage tiny magnets during your search for ewaste DVD drive parts.

IMG_0713This is the base of the left side of the A-tail. Visible in this photo are the servo and its corresponding control horn, which I will connect with a control rod after centering, trimming, and attaching the servo horn. On the next Juggernaut, I will remember to route the servo lead on the other side of the tail through the boom.IMG_0717

My DX-6i, a six-channel Spektrum transmitter. The DX-6i is not a particularly expensive radio but it has the programming features needed for this project. A simple V-tail mix can be programmed quickly through the “MIX” menu, but you will also need to either mix the two aileron servos or yoke them both to one channel with a Y-harness.

Landing gear presents another problem. There are two options: mount two main wheels aft of the CG on the fuselage booms and place a nosewheel on the bottom of the canopy; or, mount two main wheels ahead of the CG on the fuselage booms (directly below the leading edge of the wing) and place either skids or tiny wheels on the very back of the fuselage booms. Option 1 is more stable, but some method of steering for the nosewheel needs to be devised. I will most likely implement option 2 on this prototype of the Juggernaut, as it will allow operations on rougher fields and will be easier to remove for storage.

 

Be aware that while summer is a great time to go flying models, there are some drawbacks. In south-central Kentucky the main problem is humidity; in July and August, the hygrometer regularly pushes 85% relative humidity and foamboard models left outside literally feel damp to the touch. This can cause warping in some sheets of foamboard and may result in the paper backing delaminating from others. Models have also been known to fall apart because they were left in hot cars and the glue holding them together melted. These issues can be combated to some extent by sealing foamboard with polyurethane Minwax and/or by building with Adam’s new waterproof foamboards. On especially hot days, you may still be able to fly early in the morning, but you should still watch for dew and fog – both of which tend to cause models to crash.

Happy building and good luck flying!

Creative Commons License
Juggernaut model airplane by Phillip Wilkerson is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

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