Greg Covey

The Hobby Lobby [link=http://www.hobby-lobby.com/decathlon.htm]Decathlon ARF[/link] 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.

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.

Specifications:
[ul][*] 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
[/ul]

Greg Covey

Although the parts were not packaged as carefully as I have seen on other models, there was no damage on any of the parts and they were individually wrapped in plastic. I was immediately drawn to the brilliant colors and large size of this Decathlon ARF. The covering was simply suburb! All the control surfaces were pre-mounted and pinned.

A well written 16-page manual was accompanied by a small sheet of finishing decals.

Greg Covey

A look around the fuselage reveals the solid firewall and muffler outlet, quality construction, pre-mounted control rods, pre-installed wing and gear mounts, and, pre-installed windows.

Greg Covey

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. 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.

StephenT

Greg


Nice plane! I see it is now on sale at HL. How does it fly with the recomended set up?

Greg Covey

Stephen,

I'll let you know with a video here in this thread after I first finish building it. I was waiting for additional 1/2" motor mount spacers to arrive that were apparently left off the original BH026AP Accessory Pack.

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.

Greg Covey

The Nylon Tube Spacers in the Hobby Lobby [link=http://www.hobby-lobby.com/motormt.htm]Motor Mounting Hardware[/link] is an elegant yet sturdy technique to mount the motor. It result is 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.

Greg Covey

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 [link=http://www.hobby-lobby.com/adhesive.htm]PFM Adhesive-Sealant[/link] 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.

Greg Covey

The cowl mounted easily with 4 supplied machine screws. I left a 1/4" gap between the spinner backplate and the cowl.

The spinner and prop fit on the adapter without any drilling. I needed to cut the spinner cone slightly deeper for the APC prop to fit.

The power connectors are easily accessed behind the cowl. The AXI motor and Jeti ESC will have excellent air flow for cooling.

gouda

My Feedback: (69)

Greg;

Which AXI is it?

algutkin

My Feedback: (1)

The motor is a 2826/10 Axi. However, it looks like Greg used a 70 Amp. Jeti Controller which was a smart move. The recomended 40 amp Jeti controllers, that are listed by Hobby Lobby and combined with the 2826 motors, don't seem to work that well, they constantly shut my motors down at 33 amps. I returned all five that I had. Lesson to be learned, overkill works.

Check the wires to the motor. I did the same thing, the plane wanted to run backward because the motor ran backward. LOL

Al

Greg Covey

Al,

The newer [link=http://www.hobby-lobby.com/jetiblue.htm]Jeti Advance PLUS[/link] ESCs may work better than the older Jeti Advance ESCs because they allow for programming a Lithium Low Cutoff Voltage. The older ESCs only allowed for motor timing and brake programming. All that being said, it is usually a good idea to overkill on the ESC selection on a glow conversion because the extra fraction of an ounce weight is neglegable. It does, however, raise the cost about $30.

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.

Greg Covey

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.

Greg Covey

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.

algutkin

My Feedback: (1)

Greg:

Glad to see that you are working inside. Strong winds and below zero weather tend to keep us inside. I am trying not to read this thread, because........as my wife says, enough is enough. And your project really looks inviting.

Good idea, keeping the wheels centered. A rubbing wheel might cause the craft to veer one direction or another on take off. Before it can be straightened out, well, we all know what can happen. LOL That would certainly screw up the video.

Take care

Al G.

Greg Covey

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.

Greg Covey

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, Kokam 3200mAh pack weighs 13.6oz and the power cable is conveniently run through the hole in frame to the ESC.

Greg Covey

My Decathlon was Ready-To-Fly (RTF) at 100oz (or 6-1/4lbs) using the 14oz 4-cell Kokam 3.2AH pack.

The power system measured 700 watts at 50amps which provides 112w/lb for strong aerobatic performance. Recall that full throttle is only used for 15 second bursts using throttle management and there is a 10%-15% offloading in the air.

I can't wait to test fly it!

Power System Setup
[ul][*] AXI 2826/10[*] Jeti 70-amp Advance PLUS Opto ESC[*] APC 11x8.5 e-prop[*] Kokam 4-cell 3200mAh LiPo pack[*] 6v UBEC[*] S3K On/Off Switch Assy (Tower Hobbies)
[/ul]

Greg Covey

My [link=http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXJC15&P=ML]S3K On/Off Switch assembly[/link] arrived from Tower Hobbies so I installed it 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.

gouda

My Feedback: (69)

Greg; Is there something unique about that switch?

Greg Covey

The uniqueness is that it never gets added into the list of parts needed for glow conversions and it is a plug-in-play solution. The higher power Opto-isolated ESCs do not come with On/Off switches. Hobby Lobby does not sell one that I am aware of.

Unless you just purchased your radio system, you will need an On/Off switch to keep the power system disarmed until you go from the pits to the flying station. This allows you to safely connect the battery power if you need to invert the plane on a cradle or grass.

Keep in mind that although the motor should be disabled, always stay clear of the prop when the battery power is connected.

fixnit2day

any body flown the hl decath yet? ive got one coming in the mail. cant wait! going with axi 2826/10 and jetti 70 opto pull. unless some vet says theres a better set up? also any battery ideas like 2 smaller 3s packs paraleled instead of the monster 4s 3300? any help apreciated! thanks....

Greg Covey

fixnit2day,

The 3-cell Cellpro Kokam 3200mAh pack for $120 at [link=http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXLPD5&P=7]Tower Hobbies[/link] powers an AXI 2826/10 nicely.

fixnit2day

thanks! have you flown the decathlon with the setup described? if so any changes made? thanks..... still waiting for mine, ups to slooooowwwwww. is there a cheaper alternative to the recomended ultramat 12 charger from hl?

Greg Covey

I'm still waiting to fly my Decathlon.

There are many less expensive Lithium chargers at Hobby Lobby [link=http://www.hobby-lobby.com/chargers_lipoly.htm]here[/link].