Breakdown of the Buildup

JournoDrone One began life as a foam glider called the "AXN CloudsFly," sometimes marketed as "Floater Jet." This powered glider has a 1.29-meter wingspan and a length of 0.86 meters. It shipped with a 2100kV motor already installed, which I complemented with a 20A Electronic Speed Controller (ESC) and a 2200mAh 3S LiPoly battery. Additionally four servos (one each for the elevator and rudder, and one for each wing's aileron) and a radio receiver and transmitter were required for operation.

The preferred started RC plane for the DIYDrones.com community seems to be the MultiPlex Easy Star. It's a robust plane with room to spare for the Arduino-based autopilot that the community frequently uses. Although it has smaller on-board storage, the CloudsFly had the added advantage of elevators. Some on FPV message boards mentioned that the CloudsFly was easier to pilot, as well.

In addition, there were numerous online guides and threads on message boards made by people who were experienced with this model of powered glider. The AXN Clouds Fly Wiki  not only had information about stock setup, but also listed tested and successful modifications to strengthen the airframe. An extensive, 3-part series on YouTube walks through the basic assembly of the aircraft and also makes recommendations for setup and mods.

 

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The glider did not take much time to assemble -- perhaps an hour at most. Construction mostly consisted of attaching/ connecting hardware to the control surfaces and mounting the four servos in the wings and in the fuselage (the latter was accomplished with a little hot glue). Some foam on the interior of the nose had to be removed to make way for the 3S battery, but this was a fairly standard practice for this powered glider. The instructions called for gluing the wings together inside the fuselage. However, as I needed this to be transportable, I chose to leave the wings unglued and detachable.

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I removed all the stock decals, which came off fairly easy with the assistance of a hair dryer. Then I gave everything a coat of Minwax Polycrylic, which I read would prevent the foam from melting when sprayed with paint (most spray paints contain propellants which will dissolve most types of foam), as well as enhance the rigidity of the aircraft.

I used a foam brush to apply the Polycrylic out of the can. When it dried, I then sprayed everything standard grey automotive primer. This was a no-frills paint job, and I wanted the color of the plane to reflect its current state of development.

While the Polycrylic provided a good surface to paint, and didn't add much weight to the craft, it most certainly did not make the plane more crash-resistant. A significant amount of paint and Polycrylic flaked off from anything but light handling. Attempts at masking certain parts of the aircraft in blue tape to paint designs resulted in the primer and Polycrylic coming off together, although this could be attributed to the qualities of the primer (a good primer theoretically should be susceptible to bonding as such).

Some RC forums recommend using cement-like coatings that went on thicker and required sanding afterward. While that may provide a good look for an impressive scale jet, I do not think it would be practical for a "workhorse" like a journalism drone.

For my next drone, if I should paint it at all, I would invest in a small, cheap spray gun and use common latex paint. Paint in aerosol cans are an expensive investment over several projects, and as mentioned before, the propellant can melt foam. Meanwhile, a spray gun can be cleaned and re-used after each use. Latex paint cleans up easy, it's available at almost every hardware store and in a near infinite number of color combinations. It also flexes better and is less likely to crack and flake, is resistant to many chemicals, and does not react with the foam beneath it.

   Modifying for Stability and Transport

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During the first crash of the drone, the wings had separated. So one of the first modifications I had made was to ensure the wings would stay together in-flight, and in the event of a crash.

The glider kit included a hallow carbon fiber tube that spanned most of the length of the two wings. This tube was designed to nestle in a groove on the underside of each wing, and the whole thing was to be glued and secured with a foam flap. As stated before, this would prevent the wing from being broken down for transport.

I set out to create a better option by cutting the existing CF tube in two, gluing one in each wing, and then finding a smaller CF rod that would fit snugly inside the tube and bridge the two wings.

Thus, when the wing flexed, it would still flex against a solid structure of carbon fiber, and that structure was secured to the wings. But when it came time to break the kit down at the end of the day, the wings would detach and the rod would slide out.

While this method proved effective for strengthening the wing, some modifications were still needed to ensure the wings would not try to separate from each other during flight. I found a common solution to this in the CloudsFly Wiki and elsewhere, in the form of cheap, disposable plastic wall hooks, and "hook and loop" tape (commonly known as Velcro).

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While these plastic hooks come with adhesive strips, and some RC enthusiasts use the strips, I recommend instead using foam-safe superglue or two-part epoxy to attach them to the airplane. The adhesive strips might be enough to hold the necessary force, but they're designed to detach from walls without tearing off paint or drywall and can only hold a couple of pounds (which is listed on the package), so they can't provide a bond as good as other adhesives.

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To give the adhesive for the hooks a proper surface to bond to, I sanded through the primer and Polycrylic coating down to the original foam. Additionally, I scuffed the bottom of each plastic hook to prepare those surfaces as well.

Pre-flight, several rubber bands are draped over the top of the fuselage and held by the hooks. In addition to providing elastic strength to keep the wings joined together, I found that it has the added benefit of making the joined wings more rigid.

There are some variations of using elastic bands to secure wings to scale RC aircraft. One of the more common methods uses a rigid post that protrudes from either side of the fuselage, under the wing. In that configuration, the elastic band is placed over the top of the wing and fuselage, and is held against the post. I opted for the hook-and-band method because I believed puncturing the soft, foam fuselage with a strong post was risky and unnecessary.

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The instructions for the Clouds Fly also suggested gluing the tail surfaces to the fuselage. However, it's a common modification to leave tail wings unglued and attach hooks as well. For JournoDrone One, I left the elevator tail wing unglued and attached hooks, and then secured those hooks with packing tape. I similarly secured the hooks on the main wings with packing tape as well.

Instead of going over the fuselage, the elastic bands that secured the elevator/tail wing were secured over the rudder. After some attempts at flight seemed to show that these bands were in fact pushing the tail wing up and causing the nose to drop, a proper hook was added on the fuselage to ensure the band kept the tail level.

Next, I attached hook and loop tape to where the wings meet together. I found the stock adhesive on the hook and loop to be inadequate for my purposes, so I applied glue to the adhesive surface.

The hook and loop weren't so much meant to provide structural support as the were to add an extra layer of protection to keep the wings bounded. This, along with the hooks and elastic bands, I felt provided a good balance between rigidity, transportability, and setup time.

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A Solution for Takeoffs and Cameras


Although the Clouds Fly had been used before for FPV (First Person View) aerial photography, even using the same GoPro camera that DroneJournalism.org had, most configurations did not appeal to me for a number of reasons.

Many FPV enthusiasts, not just those using the Clouds Fly, place the camera in the "cockpit" of the glider. If the camera is small enough, servos are sometimes employed to allow the camera to pan to the left and the right, and even tilt down to offer a better view of the ground. More advanced FPV systems even have a live feed of the video to the pilot, which he uses to fly the aircraft, rather than observing it from the ground. But the primary objective of the FPV enthusiast is not to record the ground, but to provide the most accurate depiction of direction and heading -- as if a pilot were somehow in the aircraft.

FPV pilots sometimes elevate the cockpit camera for better ground coverage, but ultimately, the nose of the aircraft obscures view of the ground. Astute watchers of military drone technology will note that most of those drones employ gymbals and cameras in the nose of the craft, or beneath the craft, or both. Considering the likelihood of nose-in impacts with this prototype drone, then it would make sense for the camera to be placed on the underside of the fuselage.

At the same time this design solved a problem, it created another. Placing the camera on the underside of the drone would expose it to damage when the drone inevitably came in for a belly-landing. Additionally, a camera protruding from the base might make hand launching difficult.

After hand launching did prove difficult even without the bulk and weight of a camera, I decided to pursue a landing gear system that could solve both the camera and the launching problems simultaneously. That solution was a plate to which both aluminum camera gear, and a GoPro camera mount were attached.

 

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A section of 3-ply birch was cut to fit the width of the fuselage. Aluminum landing hardware was sourced that was wide enough not to obscure the camera's field of view, and tall enough to grant adequate clearance when landing.

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This landing configuration is known as "tricycle landing gear." As it stood with only the two wheels in front, the rear would drag. These aircraft are called "tail draggers," regardless if they employ a wheel.

Following the advice of an experienced RC enthusiast, I did not chose to employ a wheel, as I was told that a misaligned rear wheel could make a straight takeoff nearly impossible. I instead used a metal piece of hardware normally used to hold up curtain rods. This was then glued to the rear end of the craft and secured with copious amounts of packing tape. The height of this curtain rod hook was enough to ensure that the control horn wouldn't scrape the ground and become damaged.

There were two immediate drawbacks to this design, as testing showed. One wasn't so much the design, but an oversight in execution. During several attempts at takeoff with the new gear, the drone would pivot on its wheels and nose down after gaining speed. This was evidence that the gear were somehow not placed in a correct position on the fuselage. Further researched proved this to be the case; most proper tail-dragging craft have the axle of the landing gear coincident to the leading edge of the wing.

Some RC enthusiasts have placed the landing gear in front of the leading edge of the wing without problems, but to put the landing gear behind the leading edge is asking for trouble. Fortunately, my landing gear axles were only slightly behind the leading edge, and the tipping effect was mitigated by moving the drone's center of gravity aft (I simply moved the battery closer to the rear of the craft).

The second drawback to the design related to the strength of the birch wood being greater than the strength of the fuselage. By looking through RC message boards, I gathered that one major complaint about all tricycle landing gear was how easy the gear could damage the aircraft in the event of a hard landing.

It wasn't uncommon to hear that the landing gear would rip out the entire floor of a wood aircraft if the landing was harsh enough. This would complicate rebuilding or even make a rebuild unfeasible. This did turn out to be a major issue for JournoDrone One, as I'll explain shortly.

A third drawback of trike landing gear is the penalty in both weight and drag, compared to a smooth-bottomed, hand-launched drone. It lessens maneuverability and decreases flight time. However, this was not an immediate drawback, and I was able to get the drone airborne regardless.

 

Posted on October 28, 2012 .