RCU Review: World Models Ultimate 40S Glow and Electric

More On This Product

  • Research Airplanes
  • Research Boats
  • Research Cars
  • Research Helicopters
  • Research Engines & Motors
  • Research Radio Equipment
    Contributed by: Greg Covey | Published: July 2006 | Views: 74153 | email icon Email this Article | PDFpdf icon
    Ultimate 40S ARF

    Review by: Greg Covey
    Flying Photos: Papa Jeff Ring
    Video Pilot: Lynn Bowerman


    World Models Ultimate 40S
    Distributed exclusively by:

    Airborne Models

    2403 Research Drive,
    Livermore, CA 94550

    Ease of Assembly

    Wing Incidence Guides
    Great ARF value and looks
    Superb Flying Performance

    Small stock wheels

    Ultimate 40S ARF

    The World Models Ultimate 40S Biplane ARF from Airborne Models comes in two color schemes with the following specifications and key features. Spare parts are also available on-line at Airborne Models.


    • Wing Span: 42.0 in / 1060 mm
    • Wing Area: 578 sq in / 37.3 sq dm
    • Flying Weight: 4.5lbs / 2025 g
    • Fuselage Length: 39.5 in / 1000 mm
    • Engine Required: 2C 0.40 cu in / 4C 0.48 cu in
    • Radio Required: 4 channels, 4 servos

    Key Features:

    • Top quality balsa and plywood construction
    • Light weight but strong for aerobatics maneuvers
    • Hand painted fiber glass cowling and wheel pants
    • Built-up wings with symmetrical airfoil
    • All necessary hardware included

    ARF Contents

    The Ultimate 40S ARF comes very well protected in its box and every part is sealed in plastic. The plane is beautifully covered and detailed.

    The fiberglass cowl is painted and comes with a plastic guide for cutting sections away when a glow engine is used. The wheels, fiberglass pants, and a pre-painted pilot figure are also included.

    A quick peek at a page from the manual reveals detailed linkage assembly and instructions to properly set incidences. Another page clearly states the proper throws and CG settings.

    The kit includes a wing guide set for checking the alignment between the two wings. This is a nice feature from World Models!

    A few closeups of the fuselage show the solid but light contruction techniques. The firewall has pre-mounted T-nuts for the supplied glow engine mount.

    Electric Conversion

    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.

    My plan is to use the Hobby Lobby AXI 4120/14 motor on an FMA Direct 6s BalancePro HD Lithium pack for a safe conversion to clean and quiet electric power. On a higher voltage 6s Lithium supply, I can spin a smaller prop very fast. The cowl is held by the 4 stock screws and rubber grommets to keep the paint from chipping. I used the nylon spacers and hardware from Hobby Lobby to mount my AXI motor.

    AXI Power Setup:

            • AXI 4120/14 motor
            • Jeti 77-amp Opto Advance PLUS ESC
            • BalancePro HD 1p6s 3200mAh pack
            • APC 11x7 e-prop
            • HLH8855 1" Long Spacers (8 for 2" length)
            • HLH8876 4", 8-32 Phillips Roundhead Machine Screws (4)
            • HLH8860 8-32 Blind Nuts (4)

    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.

    ESC Wiring

    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.


    Strut Supports:
    The wing strut supports were installed with white glue after first cutting away the two slots in each wing.

    The tail cutouts were supported by two balsa wedges. The elevator was installed first using thin CA drops as before. I used thick white glue (that dries clear) to install the stabilizers. The Aileen's Origial Tacky Glue won't yellow over time like 5-minute epoxy does. A thin plastic wedge was needed to correct the horizontal stab incidence.

    The vertical stabilizer was glued in place and checked for a right angle incidence with the horizontal stabilizer. My Ultimate 40S bipe starts to take shape.

    Remember to add some Locktite to the set screws before you tighten them.

    Tail Wheel:
    The tailwheel assembly came in its own bag and installed easily. The rudder bottom needs to be drilled and a channel cut for the control bar of the tailwheel. I roughed up the control bar with sandpaper and epoxied the assembly in place. The black plastic base is secured to the fuselage bottom with two screws.

    Pilot and Canopy:

    The pilot and canopy installed without issue. The pilot has many details and the kit also includes an instrument panel for the dash. The canopy has pre-drilled holes and can use either the supplied double-sided tape or the four sets of screws and rubber washers.

    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.


    My Ultimate 40S is RTF at 90oz (5.6lbs) including the 20oz Lithium pack. I measured 53amps static current (or 1100 watts) with my AXI 4120/14 using an APC 11x7 e-prop. My 6-cell BalanceProHD Kokam 3200mAh pack can deliver 64amps continuous so nothing is getting stressed. My power to weight ratio is 1100w/5.5lbs = 200w/lb.


    Test Flying

    We had a successful maiden flight with the Ultimate 40S. The bipe flew great and I shot some video at a local electric event in the Finger Lakes of NY. The AXI 4120 provides awesome power and the BalancePro HD 6s1p 3200mAh pack provides about 7 minute flights. We saw no bad tendencies in flight and landings were relatively easy.

    The video of the Ultimate is in some pretty brisk 10-15mph wind. It had plenty of power and didn't really affect the flight. The combination smaller prop on a 6s Lithium pack really makes it nice and fast. Although it was rather windy, my Ultimate 40S still tore up the sky!!

    Ultimate 40S Electric-powered video.
    CLICK HERE (7meg)

    I took a video of another Ultimate 40S on its maiden flight that uses a .51 Super Tiger glow engine. It also flew great!

    Ultimate 40S Glow-powered video.
    CLICK HERE (6meg)




    The Ultimate design is known as a "Muscle Bipe" because of its extreme aerobatic capability. They fly fast and land hot. The smaller span models under a 40" wingspan are the most difficult to handle usually due to high wingloading. In recent years, lighter construction techniques have allowed the 40" span and up bipes to become less of a handful to fly and land. The World Models Ultimate 40S design is in this new category.

    Only intermediate flying skills are needed to handle this bipe as it is designed to fly very well and land slower with some low power required until touchdown. The key to a good flying aerobatic bipe is to have proper incidences and sufficient power. The World Models light ARF design and incidence guides make the task a whole lot easier.

    Although a .40-size glow engine will provide sufficient power, a .50-size engine makes the Ultimate 40S very spirited! For a glow-to-electric conversion, having around 200 watts per pound provides great performance that is both clean and quiet. A motor in the 1000 watt power class is recommended.

    Ultimate 40S ARF


    Manufacturer and Distributor Info

    Airborne Models
    2403 Research Drive,
    Livermore, CA 94550

    FMA Direct
    5716A Industry Lane
    Frederick, MD 21704
    Website: www.fmadirect.com
    Sales: 800-343-2934 or 301-668-7614

    Hobby Lobby
    5614 Franklin Pike Cr.
    Brentwood, TN 37027

    Esprit Model
    1240 Clearmont St. NE
    Unit 4
    Palm Bay, FL
    32905, USA

    Comments on RCU Review: World Models Ultimate 40S Glow and Electric

    There are no comments

    The comments, observations and conclusions made in this review are solely with respect to the particular item the editor reviewed and may not apply generally to similar products by the manufacturer. We cannot be responsible for any manufacturer defects in workmanship or other deficiencies in products like the one featured in the review.

    Tower HobbiesJ-3 CubWith its distinctive looks, it is probably safe to say that the J-3 Cub is one of the most recognized and known airplanes in ...11/23/2015
    RCGF21cc Twin Cylinder Gasoline EngineRCGF, a Chinese manufacturer of gasoline engines, designs and manufactures engines specifically for 'the RC aircraft market. ...11/23/2015
    RCGF120cc Twin Cylinder Gasoline EngineRCGF, a Chinese manufacturer of gasoline engines, designs and manufactures engines specifically for the RC aircraft market. T...11/23/2015
    Seagull ModelsMaule Super Rocket 10-15cc ARFWhen Seagull Models announced that they were going to produce not just a model, but an ARF of the Super Rocket, I just had to...11/22/2015
    HobbicoEstes Proto-ZThe Proto-Z is a Blast of micro-sized fun! It's the ultimate user-friendly drone- The fastest, easiset and most economical wa...11/22/2015
    FliteworkEdge 540The Flitework Edge 540 is an electric only ARF airframe with a generous wing span of 66.9" and also beautifully dressed up in...11/21/2015
    Seagull ModelsSteen Super Skybolt 15cc ARFSeagull Models introduced this biplane early on in 2015, and SIG mfg. had a pre-production sample at the Toledo Expo. That pr...11/20/2015
    ST ModelSaltoST model brings us a fun aerobatic glider with the H101 Salto. The self-launch electric glider has no bad tendency and will b...11/19/2015
    RCGF10cc Gasoline EngineRCGF, a Chinese manufacturer of gasoline engines, designs and manufactures engines specifically for 'the RC aircraft market. ...11/17/2015
    Seagull ModelsFunky Cub 10-15cc ARFThe new Funky Cub has some really cool attributes, borrowed from scale aircraft, that should add up to make it a great flying...11/16/2015
    RCGF20cc Gasoline EngineRCGF, a Chinese manufacturer of gasoline engines, designs and manufactures engines specifically for 'the RC aircraft market. ...11/15/2015
    ST ModelASW28ST Model chose to reproduce the Schleicher ASW28, a single seater standard class glider capable of glide ratio up to 45. The ...11/10/2015
    The World Models30% PT-17 Stearman ARF (U.S. ARMY) Some may call me lucky. I would agree! One of the reasons that the PT-17 is so close to my heart is that I have a personal co...10/03/2015
    Bomberfield USA 201527th Annual B-17 GatheringEvery year, the end of the summer brings the big birds back to Monaville, TX, for a festive fly-in weekend at the local RC si...10/03/2015
    HeliMaxVoltage 500 3DThis quad is absolutely not for the faint of heart, but if you·re an established heli pilot with some experience under your b...10/03/2015

      Return to Magazine Homepage

    Copyright MH Sub I, LLC dba Internet Brands Copyright © 2001-2019.
    Terms of Service | Privacy Policy

    Search | Marketplace | Event Central | Local Clubs | Magazine | Product Ratings | New Products | Discussion Forums

    Photo Gallery | Instructor Search | Field|Track|Marina Search | RCU Youtube Channel | | RCU Twitter!

    Member Locator | Advertisers | Hobby Vendor Resources | Rate Manufacturers | Sign In/Sign Up

    Products Videos WattFlyer.com RC Classifieds

    RCU2 | | 0 | 1 | 10:49:05 AM EST | NC