I typically jump out of the manual's building sequence to my favorite part of electric power system design and motor mounting. The power level on a high-performance biplane like the Ultimate must be able to overcome the large drag of having so much combined wingspan and provide awesome aerobatics. To achieve this, I recommend using a 150w/lb to 200w/lb power system. Assuming an all up weight of 5lbs, this puts us in the 1000w motor class as 1000w/5lbs = 200w/lb.

Although the manual recommends a distance of 4-1/2" from the firewall to the spinner backplate, this provides what most people would consider an excessive gap. My motor mount provided a perfect 4-3/8" distance and a perfect gap for the supplied spinner.

Cooling System:

These .40-size bipes are a tight fit so it was important to create a good cooling system for proper air flow in flight. My air cooling system has two sections, one for motor cooling and the other for battery and ESC cooling. This was relatively easy to do with a drill, dremel tool, and razor knife for tools.

The inside framework already has many holes in it to allow the air to flow through the fuselage out of the holes I cut in the bottom. In the diagram, the dashed lines are inside air flow and the solid lines are outside airflow.

Alternate Power System:

An alternate power system in the 1000 watt motor class was my Kontronik 600 geared motor. I have used this motor successfully in 9-10lb conversions like the Great Planes Lancair ES and Lil Toni Pylon racer.

To mount the motor, you will need to order the Type 8 front and back plates from Esprit Model. Instead of using the expensive extension rods and spacers from Esprit, I connected my plates using four standard #8 standoffs (7/8" long) and #8-32 hardware from Home Depot. The Kontronik 600 gearbox connects to the front mounting plate using four M3 screws about 10mm long. This motor assembly will be the proper length to bolt onto the Ultimate 40S firewall for 1/8" spinner backplate clearance.

Mounting the motor assembly was as easy as moving the four stock T-nuts in the firewall. Since the top T-nuts were close to the upper wall, I used a Dremel tool to flatten them on one side for easier mounting.

The motor assembly mounted using the stock hardware. I used a MJ4705 collet prop adapter for 5mm shaft from Hobby Lobby. Alternatively, you could also use the Great Planes 5mm Prop Drive.

I was initially using the new Phoenix HV 45 ESC from Castle Creations to control my Kontronik 600 brushless motor. The ESC is rated at over 2000 watts so it will easily handle my 1000 watt application with minimal cooling. When my used Kontronik motor was determined to be defective after testing, I swapped the motor for an AXI 4120 and the ESC for a Jeti 77-amp Opto controller. Any combination of these components should work fine together.

A 6v UBEC from Hobby Lobby provides the receiver and servo power from the main battery so you never need to charge a second Rx. pack. I like using the Tower Hobbies System 3000 On/Off Switch Harness to keep the power system disabled until I'm ready to fly. It is a plug-n-play solution for an On/Off switch.

The UBEC's 6v output is simply plugged into the S3K On/Off switch harness, which in turn, is plugged into any free receiver channel. The receiver, servos, and Opto ESC remain off until the switch is turned on. In this manner, you can plug in the battery and attach the wing without the plane being "on". For safety, always keep clear of the prop when the battery is plugged in, even if the switch is set to Off.

The Jeti 3.5mm Gold Connectors and Jeti 77-amp ESC are also from Hobby Lobby.

Servos and Linkages:

For the lower wing servo, the Hobbico CS-35 Mini BB Servo was a perfect fit. All the linkage was supplied including the keepers. The ailerons are glued to the wing by soaking the fiber hinges with thin CA. Remember not to use any CA kicker accelerator on the hinges as we want the CA to soak into the balsa for added strength.

I was very happy with the linkage assembly because most of the work was already done for you. The control rod tubing is pre-installed and the little bags of parts are numbered to match the step in the manual. Pin holes were already drilled into position for the control horns so I simply opened them a bit larger with a drill bit.

The control horn screws fit nicely into the anchors on the other side. Everything seemed to fit perfectly!

I finished up the tail linkage and installed two FMA DS300BB Digital servos for smooth, repeatable control.

The elevator halves are controlled by a joiner that connects the two rods together at the servo end. All the hardware is supplied including the snap keepers. I rearrainged some components to improve the routing of wires.

Gear Mains:

When installing the gear mains, I needed to drill two holes where the cowl covered the t-nut openings in the covering. The wheel and pant assembly installed without issue. I could now stand my Ultimate 40S Bipe on its own three wheels.

Although the stock foam wheels worked ok on my first flights for the video, they seemed a bit small and soft for the job. After sitting in my trailer for days, the foam would retain a flat spot that made for an uneven roll.

I decided to replace the stock wheels with bigger 2-1/2" Dubro Treaded Lightweight Wheels (250TL). The 5/32" (4mm) axle diameter was perfect for the stock hardware and I only needed to round the outer ends of the pant opening. The firmer rubber wheel should provide for better ground handling.

CG Correction:

A note of warning was posted from an RCU member about a problem with the CG location given in the instructions. The published CG is at 36% of mean aerodynamic chord and he found the aircraft was unmanageable. If 36% corresponds to the 3-3/4" back from the top wing LE center line, as per the manual, then we wanted to investigate what went wrong.

Biplanes can get squirrelly if the CG is too far aft or if the incidences are wrong. It sounded like we should start out with a CG forward of the manufacturer's recommendation. It appeared that our calculations were correct, assuming the dimensions are correct, and, we wanted it balanced at 25% average mean cord. Many skilled pilots will fly a ship balanced at 33% to 35% AMC, but, it can be a real surprise at times, especially if the plane has a heavy wing loading. This CG is not recommended for initial test flights.

According to our findings, we now feel that the correct starting point for the CG for test flying is 2-7/8" (not 3-3/4) back from the LE of the top wing. The 3-3/4" CG in the manual appears to be for extreme performance once you are familiar with the bipe and have advanced flying skills. We brought this to the attention of the U.S. distributor for World Models, Airborne Models.

Fai Chan from AirBorne Models reported the following:

"I checked with the factory on their flying test record, they did have the prototype tested at 3 3/4 in. CG. Not sure if the test pilot had very skillful hands or they have added some off record nose weight. I went through the calculations and I agreed that the CG is too far back. I think 3 in. from leading edge of top wing is about right. Please try this and let me know if it works."

Lithium Battery and Safe Balanced Charging:

For the ultimate in Lithium safety and longevity, I'll be using a BalancePro HD Lithium system from FMA Direct. The BalancePro HD 3200mAh R/C Aircraft Pack and BalancePro HD 6s Discharge Protection Module provide discharge protection for each cell during flight. You simply cannot over-discharge the pack and the Discharge Protection Module provides an early warning by pulsing the motor so you have sufficient time to land without a dead stick.

For charging, the BalancePro HD 6s 10amp LiPo Charger not only balances each cell on every charge but can charge at a 3C rate for a quick 20 minute charge!

I will be recharging my Lithium pack in the plane. For these smaller glow conversions, especially Bipes, it is often easiest to install the battery at the beginning of the flying day, recharge it in the plane, and fly it several times during the day at the field or at an event.

In the past, this was a dangerous scenario when using a Lithium pack and I would not recommend it. The BalancePro HD system eliminates this danger because it cannot over-charge a pack and it cannot get the wrong cell count! The BalancePro HD product line completely protects every cell in the pack.

Above is a typical interconnect diagram of the BalancePro HD Lithium Power Solution. The ESC control line is routed through the DPM so it can pulse the motor for an early warning of pack depletion to aid in a proper landing before cutting off the motor power. Note that the On/Off switch assembly would go in-line with the UBEC output to the receiver.

Component Layout:

Here is a layout diagram in both block and picture form. It shows the component inter-connections except for the On/Off switch assembly that is inserted between the Rx. pack (or UBEC) and the spare receiver channel.

You can mount the components using either Velcro or servo tape. I typically mount my On/Off switch so that ON faces the front toward the motor. The left area where the UBEC resides will be covered by the servo tray. The flight pack will side by the receiver up front behind the firewall.

My M5 v2 receiver using a white antenna wire so I routed it through the bottom of the fuselage and taped it back to the tail. Sometimes, if the fuselage is sufficiently long, you can run the wire through a plastic tube and keep it inside the fuselage.

Battery Mounting:

I first rough tested the CG by laying the pack on the outside of the fuselage. It looked near perfect to where the 6-cell BalancePro HD pack would only fit inside without modifications. This was a good start. I removed the bottom wing which required unscrewing 3 screws.

After lining the top of the fuselage inside with IMPAD foam from FMA Direct, I was able to insert the BalancePro HD 6s 3200mAh pack into position. It was almost secure without any additional foam blocks to hold it.

I decided to move the BalancePro HD 6s DPM to the other side next to the ESC to make routing the wires easier. It also allowed me to create an access hatch so I can connect the BalancePro HD pack to the DPM from outside the plane when the lower wing is attached.

The pack can then be recharged inside the plane by disconnecting the DPM and using the 12" BalancePro HD Extension Cable to the charger.

I can also easily connect the Dean's Ultra plugs from the DPM to the ESC to arm the plane once I am at the flying station. This access may not be needed but I decided to try it. The optional LED/Spkr Module was mounted outside the plane so that I can hear the DPM warning for pack depletion in addition to feeling the motor pulsing. In other applications, I have been able to hear the audible alert from a considerable distance.

My hatch was created with scrap plywood and a toothpick. I sealed some of the cut covering with clear tape.

Wing Assembly:

Mounting the wings was even easier than I had expected it to be. The incidence templates and well fitting ARF parts made the assembly a snap. This is usually a time intensive task of measuring incidences.

The first step was to mount the bottom wing using a single screw and washer into a pre-mounted t-nut. Next, the upper wing braces are mounted and then the wing is positioned in place and held by the incidence templates. Since the proper position is revealed against the fuselage, it was an easy process to drill four holes and screw the upper wing braces to the fuselage sides. The last step is to attach the outer wing cabane on each side. I drilled the holes through both the cabane and wing holder while the incidence template was in place. I then removed the template to secure the cabane with the supplied screws, washers, and nuts. The other side was assembled in a similar fashion.

I had two spare metal braces left over that I couldn't figure out where they were needed. I saw no reference to them in the manual but I had the tiny screws and nuts in my kit to mount the braces. Another RCU member building the same ARF had a newer manual and showed me where to mount the braces. I'll have to assume that it was a modification and it took a while for the manual to catch up.

The upper to lower aileron linkages were supplied in the kit and the ailerons have pre-positioned pin holes for perfect alignment of the control horns.