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HobbyKing Soar 40 Electric Conversion




A New Project

As wannabe R/C pilot, I have been flying high-wing trainers for some time. Some club members suggested it was time to move to a low–wing aircraft in order to advance my flying skills: a low–wing aircraft would force me to "fly" the aircraft without depending on the forgiving characteristics of the typical high–wing trainer. So, I began searching for a low–wing aircraft that would be flyable by a relative novice. A club member noticed the low–cost Soar 40 on the HobbyKing web site and I decided to order one, convert it to electric power, and continue my flight training, including aerobatics, using the new aircraft. Because the Soar 40's size and long tail–moment, the Soar 40 promised to be flyable—even by me.

The Power System

The power system for the Soar consists of the following:

  1. eRC .46 Size Brushless Outrunner, 600Kv motor,
  2. eRC 65A Brushless Programmable ESC w/SBEC,
  3. POWERWING 4-Cell 14.8V 4500mAh 20C LiPo Pack,
  4. 13X8 prop.

Installing the Motor

After receiving the ARF, I began the conversion project by cutting out a new 1/4" firewall. I used 1/4" triangle stock behind the new firewall and installed blind nuts for the motor mount. I used epoxy to glue the new firewall in front of and parallel to the existing firewall. I shaped the lower side of the new firewall to make access to the nose–wheel mount easier and to provide a route for the motor wiring. A temporary mounting of the motor showed plenty of prop clearance.



Installing a New Firewall
Installing a New Firewall

Motor Mounted
Motor Mounted

Nose Gear Modifications

I was not satisfied with the stock nose gear mounting. The bearing had been drilled out too much so that there was excessive slop when the nose gear was installed. Furthermore, I discovered that instead of using blind nuts to hold the bearing in place, nuts were used on the rear of the firewall. I cut a small hole in the bottom of the fuselage and removed the existing nuts and nose mount. I installed blind nuts and attached a new nylon nose gear bearing. Also, because I knew that I was going to lengthen the landing gear to achieve adequate prop ground clearance, I used a DuBro 5/32" bent nose gear and nylon steering arm. I also used a 1/4" plywood spacer between the nose bearing and the old firewall. The guide tube for the servo wire needed to be repositioned. After repositioning the guide tube, the linkage between the steering arm and the nose servo worked with very little friction—without having to bend the servo wire at either end. I attached the servo wire to the steering arm with a z-bend. I used a separate servo for the nose steering. I mixed the servo with the rudder servo. The nose servo can be trimmed independently for ground handling.



Blind Nuts for Nose Bearing
Blind Nuts for Nose Bearing

Nose Gear Assembly
Nose Gear Assembly

The Hatch

There are many ways the battery and ESC could be installed. I decided to build a removable hatch in the cockpit. This was pretty easy to do. I removed the balsa cockpit floor and replaced it with a 1/8" piece of plywood. The rear of the hatch is held in place with magnets; the front of the hatch is held in place by the lip of the instrument panel and with a dowel glued to the underside of the hatch. Pilots and an additional instrument panel for the copilot were mounted to the topside of the hatch. I decided not to use the thin canopy but to leave the cockpit open. The stock canopy has been replaced with a spiffy windshield.

Old Cockpit Floor Removed
Old Cockpit Floor Removed

Cockpit Hatch in Place
Cockpit Hatch in Place

Pilots and Instrument Panels
Pilots and Instrument Panels

Hatch Dowel
Hatch Dowel

Battery and ESC Installation

The next part of the project was the hardest. First, I built a battery holder out of balsa. The battery is held in the holder with Velcro. Next, I constructed a battery cradle within the fuselage into which which the battery holder slides. The battery holder slides forward against the original firewall. Once inserted, the battery and holder are prevented from moving either forward or up and down by the cradle. A short length of Velcro is fixed to the battery holder and a matching piece is fixed to the fuselage. With the battery holder inserted all the way into the cradle, and with the Velcro meshed, the battery holder is prevented from moving to the rear. After both raising the nose and shaking the fuselage and after actual flight with loops and rolls, the battery remained fixed in place. The ESC is routed below the battery cradle. I had a 6" battery extension built at my local hobby shop in order to match the Dean's connection on the ESC with the EC3 battery connection. The extension makes for an easy battery connection. I had to cut away some of the wood from the servo-mounting plate in order to be able to slide the battery and holder in and out. The Velcro "tab" fixed to the holder serves as a pull tab for removing the battery and holder.

Battery in Holder
Battery in Holder

Test Fit of Battery and Holder
Test Fit of Battery and Holder

Velcro Fixed to Fuselage
Velcro Fixed to Fuselage

Battery Holder Secured
Battery Holder Secured

Main Landing Gear

Using the stock, wing–mounted landing gear as a template, new gear was bent to fit the wing mounts. The length of the new gear was increased to provide the desired prop ground clearance. Also, the gear was bent 1—1/2" to the rear; the nose gear was bent somewhat forward. Bending the gear in this way made the ground handling much more stable. I used Dave Brown 3–1/4" Treaded Lite Flite Wheels for both the mains and nose.



Main Landing Gear
Main Landing Gear

Balancing

The plane was balanced at around 83-85mm. Weight was added to the motor firewall and fixed into place with servo screws.

Final Notes

Finishing the project included covering the top of the fuselage between the old and new firewalls. The bottom access hole was also repaired. Space is tight under the cockpit. I finally velcro mounted the receiver aft of the servos and accessible from beneath the wing. On the field, and as expected, the ground handling was very good and only a small amount of trim was needed for level flight at half throttle.



Receiver Mounting
Receiver Mounting

Finished Nose View
Finished Nose View

Finished Side View
Finished Side View

Special thanks is due to two members of the Sanderson Field RC Flyers(SFRCF), Shelton, Washington, who helped me finish this project. D.R. Phillips bent the new landing gear, applied new finishing materials to the fuselage, fashioned the new windshield, and helped me balance the Soar. He also kept me away from some pretty goofy building mistakes—and patiently corrected others. Dick Robb helped with attaching and aligning the flying surfaces and offered good advice throughout the project—and provided me with the pilots and instrument panels. Dick also piloted the maiden flight and insured that the aircraft would fly reliably and predictably during my future training sessions.

References




I hope you enjoyed this article.

Royce Tivel

Royce Tivel

Royce Tivel

rtivel@selectdigitals.com