Introduction

Wingspan:	76"
Wing Area:	634 sq. in.
Weight:	48 oz. (target), 46 oz. (as reviewed)
Length:	45.4"
Wing Loading:	10.9 oz/sq. ft.
Servos:	3 Hitec HS-81
Transmitter:	Multiplex Royal Evo 9
Receiver:	Hitec 555
Battery:	7 Cells CP1700
Motor:	Mega Ac 22/30/3
ESC:	Castle Creations Phoenix 60
Manufacturer:	Cox Models
Available From:	Cox Models

I had heard about the Cox Dust Devil from a good friend and president of NEAC, Ric Vaughn. At the AMA Nationals, this model had been entered in the electric sailplane contests, and performed quite well. He described the model as a 2m ARF with a poly wing and RES (rudder/elevator/spoiler only) controls - ideal for high altitude thermal hunting yet with spoiler control for spot landings. I was intrigued, as I had not heard of this model prior to this event, and had been planning to modify one of my existing 2m models to include spoilers or flaps.

Kit Contents

The box

Contents are well packed to avoid damage

The model is packaged in a sturdy cardboard box, each part packed individually in sealed plastic bags. The wing panels are separated by a thin sheet of protective foam. The parts count is extremely low, as can be seen in the picture below. There is a detailed, well-illustrated instruction manual, which covers additional equipment, the assembly sequence, and control setup and balance before the first flights.

Low parts count made for quick assembly. Small parts bag included two different motor mounts.

The wing panels and tail are pre-covered in Sig AeroKote, and I know from previous experience that this color scheme (using transparent red covering on the wing) is quite visible at altitude in most weather conditions. The fiberglass fuselage is strong, yet light for this size model, and finished in white; the wing and tail surfaces are built up from balsa and ply.

I weighed the major components and included hardware before assembly:

• Wing Center Panel: 182g (6.4 oz)
• Wing Tip Panels: 65g (2.3 oz) each = 130g (4.6 oz) total
• Fuselage: 164g (5.8 oz) + canopy: 11g (.4 oz)
• Tail surfaces: 45g (1.6 oz) total
• Hardware including pushrods, wing joiners: 58g (2 oz)

Total weight was 590g (20.8 oz) before assembly.

Additional components required are:

• a suitable motor,
• folding propellor with spinner and yoke suitable for your motor shaft,
• a speed control with adequate current rating & BEC,
• a 7-cell sub-C or similarly sized battery,
• three Hitec HS-81 or similar servos, and
• receiver with at least 4 channels.

No other accesories are required - all pushrods and linkages, control horns, and hardware are provided.

A brief note on radio selection should be included. You must be able to operate the spoilers in a proportional fashion,this is usually assigned to the traditional "throttle" channel. It is recommended that the motor be operated by a switch, you will only need one power setting - full on! Consult your transmitter's documentation to ensure you will be able to accomplish this. Many transmitters allow you to assign channel 5 to a landing gear function. This would be a good choice if you have no other way to program the throttle onto a switch - but you will need to purchase a 5-channel receiver or better to accomodate this.

Assembly

Wing

The instructions provide detailed information on how to configure the servo arms in order to accommodate the included hardware. With this task performed, installation of the spoiler servo was quick and simple - I deviated slightly from their recommendation to attach this servo with double-sided tape, choosing instead to wrap this servo with tape, securing small blocks to each side of the servo, then using epoxy to hold everything in place. An exit hole for the servo lead was also provided.

Small blocks help retain the spoiler servo Installation of the spoiler complete

The spoiler was then attached to the wing at the leading edge with the provided tape. I found that in the closed position, the outer trailing edges of the spoiler were raised slightly above the surface of the wing. This was remedied by careful removal of a small amount of exposed rib material in the servo opening. The spoiler is somewhat oversized, and should suffice to get the model down from altitude quickly, as well as nailing a spot landing!

Wing panels may be glued together. A good fit allows tape alone to be used to secure the panels.

The next step was to glue the wing tip panels in place, if so desired. I chose to simply tape them in place at the field, to ease transportation as well as test the durability of the model assembled in this fashion. As luck would have it, I accomplished my goal, and the model survived with no damage!

Fuselage

Assembly of the tail section was quick and simple. The provided, pre-bent control horns were installed into the ruddervator surfaces, which had holes drilled and slots cut in the leading edge.

The provided pre-bent control horns work well. I taped the ruddervators to the surfaces.

The ruddervators had to be taped to the tail surfaces, which themselves simply slid onto the preinstalled mounting pins. Again, these may be permanently glued in place, or taped to allow easy transport. I chose the latter, and placed them aside while I continued working on the fuselage.

The tail surfaces slot onto pre-installed alignment pins. The completed tail surfaces may be taped in place.

Motor mount and motor

Installation of the motor mount was once again well documented, and is worthy of further explanation as it utilized a method I had not previously seen. There was a small jig provided, which allowed the mount to be accurately recessed behind the front edge of the fuselage. After ensuring the mount was able to fit into the correct location (sanding the edges at a slight taper), I simply applied a just couple of drops of thick CA (to provide working time), then pressed the jig up against the nose of the fuselage, pressing the mount into place from behind. Once the CA has cured, the jig may be removed, and the mount will remain in place, ready to be permanently secured with epoxy. They recommend adding some chopped fiberglass to the epoxy for additional strength, which I did, and then ran a bead of the mix to both the front and rear edges of the mount.

The motor mount and alignment jig. Motor mount installed.

Note that an additional mount was provided to allow different sized spinners to be used. As provided, the nose matched a 40mm (1.5") spinner, but if a larger (40 or 42mm) spinner was desired, the nose could be sanded back (taking care to ensure the correct thrust angles are maintained), and the large mount installed.

The motor is retained with appropriate hardware.

The motor was installed with the appropriate mounting hardware. To simplify routing of the wiring between the ESC and motor, I would strongly recommend planning the motor mount installation such that the wires from the motor follow a natural path down the bottom of the fuselage through the pre-cut opening underneath the battery tray. I did not consider this, and it took a fair amount of effort working in a confined space to get my wiring routed to my satisfaction. I installed a Phoenix 60 ESC in the space beneath the battery tray.

The battery and servo tray is installed at the factory. Preinstalled pushrod guides and an exit path for the antenna were provided.

Radio Installation

As detailed information on how to configure the servo arms had been provided before starting assembly, installation of the servos for tail control was quick and simple. With the servos centered, the arms were installed, and the provided clamp-style EZ connectors mounted to the arms. The servos were screwed into the ply mounting plate using the hardware provided with the servos. The ball sockets were screwed onto the provided pushrods, which then slid down the preinstalled pushrod guide tubes and through the EZ connectors. With the tail surfaces taped in place and the control horn ball links connected, the EZ connectors were tightened and the installation of the servos was complete!

Installation of the servos couldn't be simpler. In no time at all, the fuselage was complete!

The receiver was mounted to the floor of the fuselage behind the servos, providing adequate room to allow the spoiler servo to be plugged in before flight without using a servo extension lead.

Completion

Ready to fly!

Assembly of this model, not including time for the epoxy to cure, was two hours. I literally finished it in a single morning, including time spent waiting for the epoxy joints (I just worked on other sections while I waited). A quick calculation showed that a 14x8 prop would give adequate performance on 7 cells, and as luck would have it, the model balanced on the recommended 3" mark with a 7-cell CP1700 pack installed at the front edge of the battery tray. A quick test produced 50A current draw (330W) at 5300RPM - more than enough to haul the (46oz finished weight) model around the sky - I would tune the power system once the model had a few flights on it.

A couple of strips of Velcro were sufficient to retain the battery. I normally use a strap of some kind, but the design of the tray prevented this, so I simply cut a small block of foam to help hold the battery against the Velcro - in case of "unexpected incidents". With the CG set, and the balance checked (there was no need to add any weight thanks to the tip panels having identical weights!), I set up some reasonable control throws on the surfaces and packed the model up ready for it's first trip to the field. I was excited at the prospect of being able to pack the model back into it's box for transport, but with a spinner installed, the fuselage doesn't fit! A small hole in one corner will solve that, however! I used a good quality white insulation tape to hold the tail surfaces and wing panels in place.

Flying

Although I often test fly models at the local church or school playgrounds, for a model of this size, I prefer to test fly at an official RC field. As it happened, a local club was holding a fly in and cook out for the Labor Day weekend, so the first flights took place just a couple of days after completion of the model.

Basics

A range check and a test glide are essential on any new model, and both were performed without incident. In fact, the test glide was very satisfactory - the model literally flew straight and level, and I did not touch the sticks at all. Then my trusty launcher gave the model another good heave as I applied power, and the Dust Devil climbed for the first time. Power was more than adequate, and I found that the chosen power system provided almost vertical climb capability, not needed for the kind of flying for which this model is intended, but sufficient for me not to worry about changing props for these first flights.

Taking Off and Landing

The model glides well from even a light throw, so launching is non-eventful, and power can be applied before or after release without incident. The spoilers were very effective, and although during the initial flights I spent some time fiddling with the amount of elevator compensation required, I was still able to utilize them to get the model down with some degree of precision. At first, I reduced the throw on the spoiler - even at 45 degrees, the model dropped out of the sky like a brick! With a few more test flights to tune the settings, however, I bumped it back up to 90 degrees, but with sufficient elevator compensation mixed in to maintain a reasonable rate of descent. On it's second trip to the field, we had some wonderful flying conditions - winds were gusty at first, but as the day warmed up and the winds died down, there was some strong thermal activity. I was able to thermal up to about 1400', at this altitude, the dark red covering makes it relatively easy to spot at altitude, yet it lights up nicely when you pass near to the sun.

The model can be trimmed to fly at different speeds depending on conditions, which makes it useful in different conditions. In gusty conditions, a couple of clicks of 'down' will bump the speed up, but in calmer skies, a few clicks of 'up' will turn it into a gentle floater. The tail area seems a little small in windy conditions, as the model does dance around quite a bit, but in calm air it's "just right". The control throws recommended work well as a starting point, they are quite high for the "average" pilot, so you might want to start with a 60% low rate setting. My final throws (measured at the root of the surfaces) were:

• Elevator each direction 5mm (3/16") from center
• Rudder each direction 10mm (3/8") from center
• Spoiler - 90 degrees with elevator compensation 4mm (5/32") "up" at 90 degrees

I did have high rates available which provided "significantly more" throw if needed, but after a lot of flying, never had to use them. In all conditions, during climb, thermal flying, or landing, the rates specified above are sufficient.

My best flight so far was just over 20 minutes on a 30 second motor run, and this was the second flight on that charge - the first was a 12 minute flight on a 26 second motor run, after landing, I just picked up the model and re-launched.

With the spoiler trim tuned, the model is easy to land with precision, which of course helps in competition, but also valuable to the sport modeler, to ensure he lands in a controlled fashion without risk of over-flying the field.

The one addition I've yet to try is some kind of landing skeg. The slick glass fuselage allows the model to slide significantly on landing, and this often also involves rotation of the airframe as one wingtip touches the ground. In most cases, this is not an issue, but a short skeg, to bring the model to a quick stop, would prevent this.

Is This For a Beginner?

One of my first landings resulted in the model performing a ground loop and almost a complete cartwheel in one elegant maneuver! Later, a friend was flying to allow me to take some in-flight pictures, and the gusty conditions resulted in another hard landing. These were unplanned, but did allow me to verify this models ability to survive rough handling, and the strength of the wing and tail assembly when secured only with tape. I am very happy to report that there was no sign of damage, although the pilots should check all controls and linkages before flying, as the ball-link connections can disconnect if the tail control surfaces receive an impact.

The Dust Devil is probably durable enough for a beginner - with the caveat that they enlist the help of an experienced modeler to ensure it is trimmed out and set up correctly for flight, and learn to land the model in a controlled manner. The instructions do caution against teaching yourself to fly, but with a little assistance from an experienced pilot, a durable sailplane can make an ideal trainer, and this one definitely fits the bill!

Flight Video and Photo Gallery

Downloads
Type Name Size The Cox Models Dust Devil review. 7.72 MB Same video, different codec file for windows pc users. 6.51 MB Same video, mpg format for those who cannot view the wmv files. 5.40 MB

The Dust Devil climbs out Turning to final   A low pass Final approach   Overhead Soaring off in the distance

Conclusion

The Cox Dust Devil is positioned as an electric sailplane designed to meet the needs of a wide range of electric flyers. The instructions are first-rate, and provide a great deal of detail on assembly and how radio and power system components should be installed. It's flight performance, ease of assembly, durability and price ($130 at time of writing) make it very attractive to both the beginner and more experienced pilot. As electric sailplane competition attracts more traditional "sport" pilots, this model is well positioned to allow those pilots a first taste of this type of flying. That said, the model is also capable of performing well enough to allow the experienced pilot to "take home some hardware"! With a low end brushed power system, this model would fly well, but with a powerful brushless motor, the Dust Devil will quickly reach altitude sufficient for extended thermal flights.