The Black Horse Model's Decathlon ARF is a semi-scale plane that delivers strong aerobatic performance with an AXI Outrunner Brushless motor. It is a quick build ARF that comes with all the major parts pre-built and pre-covered with quality hand iron-on Oracover®. The factory painted fiberglass cowl and wheel pants are pre-finished. Construction is conventional built-up balsa and ply, which is both lightweight and strong. A well written 16-page manual was accompanied by a small sheet of finishing decals.

The airplane was designed as a glow plane but easily converts to clean and quiet electric power. The conversion is simple, as I will show in this review, and, the entire build will only take a couple of evenings. Flight performance is excellent; the wing airfoil is semi-symmetrical, the long ailerons give the airplane a fast roll rate. The airplane’s overall light weight makes this a good aerobatic trainer with a predictable stall, solid handling and slow landing speed. The red and white star burst pattern provides excellent flying orientation, even at long distances.

The kit includes pre-bent aluminum landing gear, foam wheels, steerable tail wheel, all control surfaces pre-installed and pinned, spinner, and hardware. The airplane is for 4 channels; Ailerons (2 servos), Elevator, Rudder and Throttle. All the control surfaces are pre-mounted and pinned.

Specifications:

• 65" wingspan
• 49-1/2" long
• 680 sq. in. wing area
• 6-1/4 lbs. flying weight
• 4-6 Channel
• 5 Servos
• .40-.50 2-Stroke

Power System Setup:

• AXI 2826/10
• Jeti 70-amp Advance PLUS Opto ESC
• APC 11x8.5 e-prop
• Cellpro 4-cell 3200mAh LiPo pack (FMA Direct)
• 6v UBEC
• S3K On/Off Switch Assy (Tower Hobbies)

The motor installation on the Decathlon ARF was quite simple. The Nylon Tube Spacers in the Hobby Lobby Motor Mounting Hardware provided an elegant yet sturdy technique to mount the motor. It also resulted in a low cost and low weight mount that has great strength!

I measured that a 4" distance was needed from the firewall to the spinner backplate. This meant that in addition to the 1" nylon spacers, I also needed an additional 1/2" spacer. Hobby Lobby has corrected the BH026AP Accessory Pack for the Decathlon ARF accordingly.

After soldering the Jeti ESC mating connectors onto the AXI motor and installing the Radial Mount set, I positioned the motor over the hole in the firewall and traced the holes onto the firewall. I then drilled four 7/32" holes in the firewall and opened the holes in the AXI Radial mount to 11/64" to accept the 8-32 machine screws.

The T-nuts were installed next using a small metal rod to guide them into position from behind the firewall. Once held by my fingers from inside the firewall, I used one of the 8-32 machine screws and two 1" nylon spacers to anchor them hard into place.

The final step was to mount the motor using a machine screw, a 1" spacer, and a 1/2" spacer into the T-nut.

ESC Mounting:

Before mounting the cowl and spinner, I mounted the ESC in the direct airflow in the box meant for the glow engine muffler.

I like to keep the final battery connection external when possible so I can recharge during the day without having to remove the wing. The ESC control line and UBEC input lines were fed through a hole into the fuselage. The hole was drilled large enough to fit the Dean's Ultra plug from the 4-cell Lithium pack, once installed.

I used a combination of servo tape and PFM Adhesive-Sealant from Hobby Lobby to secure the ESC onto the painted plywood making sure that the Jeti label was showing for maximum cooling effectiveness.

To hold the wires away from the rotating motor, I used a scrap piece of plywood in the shape of a "U" channel. Before the plywood was epoxied to the firewall, I drilled shallow holes for the legs to sit in to create a better hold.

 

Aileron Servos:

Since the ailerons are already installed, I only needed to install the servos and linkage into the two wing halves. I used Hitec HS-322 standard servos.

Aileron Linkage:

All the linkage components were supplied with the Decathlon kit so I first mounted the control horns and then bent a right angle into the control at the proper distance to insert in the servo arm. The supplied keepers hold everything in place.

Wing Joiner:

The two wing halves are joined together with an aluminum bar and pre-mounted wooded dowel in the back. I used a "Y" adapter to connect the two aileron servos together. The wing assembly is held in the fuselage by two pre-mounted dowels up front and two nylon screws in the back.

Tail and Linkages:

The stabilizers installed easy in the tail of the fuselage. I only needed to cut away the covering before gluing. I used thick white glue that dries clear although the instructions call for using 30 minute epoxy. My Hobbico builder's triangle helped to insure a right angle between the stabilizers.

The linkage installation was next. The control rods already come inserted into the pre-installed tubes for rudder and elevator control. I use a staged assembly technique that helps to insure minimal binding in the linkage. First, I install the clevis onto the threaded rod end and then attach the control horn. The horn is then positioned onto the control surface so that the holes are directly over the hinge gap. After checking the swing for binding, I adjust the hole height that the clevis is connected to the control horn. In this model, since less swing is needed as it is not a 3D plane, I used the second hole from the top of the control horn. This helps with stronger torque and increases the resolution of control from the servo. Once satisfied with the position and swing, I mark the holes with a felt tip pen on the control surface.

The servos were positioned to allow room for the Hitec Electron 6 receiver since no throttle servo is needed. I ran the antenna wire out a hole in the bottom of the fuselage and taped it back to an extra hole I drilled in the tailwheel assembly. Since the tailwheel guide is already mounted on the rudder bottom, the whole assembly installed easy using just two screws. Note that the most aft screw has a smaller head size.

Wheel Pants:

There are many ways to mount the wheel pants and we sometimes have our own preferences. I deviated slightly from the recommended approach in the manual to hold the wheel in the center of the pant.

Wing Assembly:

The wing mounted easily using on two nylon thumb screws. The front of the wing is held by two dowel rods. Note the perfect wing saddle fit on the underside.

Strut Mounting:

The struts are anchored to an aluminum bar that is secured to the fuselage plywood frame using two screws. The other end is connected via a clevis to anchors that are screwed into hidden metal plates in the wing frame.

Although the strut length is adjustable, I found them a bit short to use the pre-drilled holes under the covering on the wing bottom so I needed to drill my own holes about 1/4" closer. The strut is connected to the metal bar near the fuselage using a screw and several washers.

The end of the strut that connects to the metal brace on the fuselage was also re-drilled closer to the end of the rod so that they would fit onto the metal brace without digging into the fuselage.

Battery Placement:

Using the battery placement shown, my CG was about 10mm forward of the recommended 100mm. This was a very good starting point for initial testing. The Lithium pack is secured using Industrial Strength Velcro. I used CA on the piece connected to the plywood base for extra hold.

Note that the 4-cell, Cellpro 3200mAh pack weighs 13.6oz and the power cable is conveniently run through the hole in frame to the ESC.

On/Off Switch:

I installed my S3K On/Off Switch from Tower Hobbies before the test flight. The assembly mounts easily and is very secure. It plugs in between the UBEC output and the receiver power input or any unused channel.

 

Watch the Decathlon in Action!
CLICK HERE (9meg)

The Decathlon flew like a dream! Plenty of power and very aerobatic. It flew light and was easy to take-off and land. The symetrical airfoil allows it to fly inverted and roll very well.

Summary

The Black Horse Model Decathlon ARF proved to be a great value as it was easy to assemble and flew extremely well. The wing struts needed some work to fit properly. (since this article was originally written, this issue has been corrected) The only change I made after the initial test flights was to add a small amount of right thrust in the motor mount by adding two small washers to the left side standoff spacers. Flight times were about 7 minutes with many spirited aerobatic maneuvers. The Decathlon ARF looks great in the air and will stay clean with the electric power system.

The BalancePro HD 6s charger can safely recharge and balance the 4-cell Cellpro 3200mAh pack at a 3C rate or about 20 minutes. Adapters are available for many other popular brand Lithium packs. The safe balancing 10amp charger allows you to recharge the pack right in the plane! Plug 'n Play and Walk Away.

Black Horse Model Decathlon ARF
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5614 Franklin Pike Cr.
Brentwood, TN 37027
615.373.1444
www.hobby-lobby.com

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Frederick, MD 21704
Website: www.fmadirect.com
Sales: 800-343-2934 or 301-668-7614