RCU Review: Greg Covey's Amp'd Issue 20: Building a Giant

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    Contributed by: Greg Covey | Published: April 2011 | Views: 34114 | email icon Email this Article | PDFpdf icon




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    Issue 20
    Article By Greg Covey

    Print Issue 20 "Building a Giant"

    The World Models 42% Ultimate
    The World Models 42% Ultimate Biplane is made from high quality balsa and plywood construction. It is available in two different color schemes and is light weight yet strong for aerobatic maneuvers. The model offers hand-painted fiberglass cowling and wheel pants. It comes with strong 1/4" thick aluminum landing gear and all the hardware needed to complete the arf.

    I had done many electric conversions on other World Models planes so the time was right to start building a giant scale Ultimate biplane.

    • Wing Span: 98 in / 2489 mm
    • Wing Area: 3300 sq in / 213 sq dm
    • Fuselage Length: 104 in / 2640 mm
    • Flying Weight: 38lbs / 1720g
    • Engine Required: 150 cc gasoline engine
    • Radio Required: 6-channel radio w/ 17 servos

    The World Models 42% Ultimate is the same airplane as Chip Hyde''s 2002 TOC airplane that was designed and built for him and then produced by Aeroworks for several years starting in 2003. After Aeroworks started their QB line of ARFs, made by a different manufacturer, World Models continued to produce the old Aeroworks Ultimate line (150, 100, 50cc sizes) under the Airborne Models distributor name.

    Jason Noll flew the new Aeroworks 150cc 20-300 ARF-QB Ultimate on electric power last summer at Joe Nall so big biplanes have been a crowd favorite for many years!.

    In the Boxes

    The 42% Ultimate comes in three big boxes, two via Fed Ex, and the biggest box (containing the fuselage) via Greyhound Express (aka Trailways).

    The wing box contains four wing halves. One wing set, shown right, is slightly shorter than the other because it attaches to the fuselage. The ailerons are taped in place and the covering scheme is different on the top and bottom sides.

    Two large decal sheets and a 14-page manual are also included in the wing box.


    In box 2 of 3, we have the cowl and hardware. Again, everything was well protected and arrived in perfect condition.

    The flawless cowl was beautifully painted and trimmed. The clear plastic canopy was also ready to install. The painted pilot was very well done and a nice added touch to the kit! Although air-filled tires are also included, I have had problems in the past with these tires from World Models so we'll see if I decide to use them or obtain others.

    The spinner looked to be very good quality with an aluminum backplate. The wheel pants were reinforced on both sides with fiberglass-covered plywood so they can be used on either side.

    As in my 1/4-scale and 1/3-scale Cub reviews for World Models, the tailwheel assembly looked top notch and the hardware bags were all numbered to match the steps in the manual. It's little extras like these that make The World Models ARFs a great value!


    Box 3 of 3 travels via Greyhound Express (aka Trailways) so you need to pick it up yourself from the local terminal. My Ford Expedition came in very useful for this big box!

    In this box, we have the fuselage, gear mains, and tail sections. The yard stick gives you some perspective on the size of each part. The aluminum gear mains is 1/4" thick and very strong.

    When you need to use a step ladder for photos and your 5-month old granddaughter can fit in the cockpit, you start to wonder if you have gone too far!

    Note: Granddaughter not included.

    Receiver Safety

    For ULTIMATE safety, I planned to use the following components.

    • Spektrum AR9100 DSM2 9-Channel PowerSafe Receiver
    • Two Spektrum VR6010 Voltage Regulators 6v, 10A
    • Two Spektrum LiPo Receiver Packs 2000mAh

    The Spektrum system provides true redundancy in receiver and power to the servos. There are three receivers and two separate receiver power supplies that are ORed together. If any one receiver or power supply fails, the others take over. You can also add an optional fourth remote receiver (sold separately). A fail-safe switch operation is also provided. If the On-Off switch fails, the receiver and servo power stay on. In the Off position, the AR9100 draws less than 1mA.

    When I was at the 2010 NEAT Fair, I was presented with some evidence by Rick Vaughn that using A123/LiFe cells without a regulator provided a superior power system without glitches. He used this device from XPS called a TattleTale. It showed that his receiver power supply glitched when under certain conditions like multiple servos reversing direction at the same time. After he switched to using 2-cell A123/LiFe packs directly, the TattleTale reported no glitches.

    Armed with this new information from Rick, I decided my Spektrum AR9100 Power Safe receivers will be fed by two Hobbico LiFe 6.6v 3200mAh packs. The LiFe packs can be charged up to 1,000 times with no loss in performance. Further, no regulators are required, reducing cost and parts count. Both packs can be recharged at the same time using a single FMA CellPro 10s charger. The combination of using the AR9100 Power Safe receivers with dual LiFe packs provides an extreme level of safe redundancy.

    I made a short adapter to temporarily allow me to use the system until I figured out where things will reside in the Ultimate.

    A New Power System

    I decided to try the new Turnigy C120-70 outrunner. This motor appeared to be similar to other designs on the market but only 1/3 the price! The C120-70 is not made to order but rather stocked so that it can be purchased quickly. This type of affordability and off-the-shelf solution was right in line with my goals for converting the Ultimate to a high-power electric plane.

    Although information on the motor was sparse, data had already been posted using the ICE HV 160 ESC on a 12s LiPo and a 27x10 prop. At 7000 watts, 169 amps, 7200 RPMs, this setup will run all day. My plan was to prop it for a peak of around 225 amps which the ICE HV 160 ESC should easily handle for 5 second bursts. I planned to start with a 30" prop and see what the CC ESC data logging reported.

    The main issue here was that the motor performance was really an unknown. Would the quality be good enough for my giant scale Ultimate? Should I mount it in the plane without testing it first?


    My Turnigy CA120-70 motor arrived on a Sunday from China. The EMS shipping is very quick!

    I took it out of the double boxes where it was surrounded by cooler foam and sealed in a plastic bag. So far, it seems as advertised and the quality looks good. The magnets are somehow sealed into channels in the outer case. I'm not sure how this was machined but it should help them stay in place.

    At the time I purchased my motor, the only available information was the specifications seen below and the one Castle Creations Data Logging report using a 27" prop. Many questions remained about the quality and performance of this new Turnigy motor. Noone had used it yet in a real application so I decided that it must be checked out to my satisfaction before going into my Ultimate.

    Turnigy CA120-70 8600W Brushless Outrunner Specifications

    • Model: 120-70-15
    • Resistance: 4.8ohm
    • ESC Required: 250A
    • Input Voltage : 30~70V
    • Kv : 150 rpm/V
    • Weight: 2550g
    • Shaft: 10mm
    • 20v Non Load Current: 11A
    • Dimensions: 168x140x118mm (Including Mount)
    • Equivalent: 110cc Twin Gas Engine (20hp+)

    Designed as a 100cc gas engine replacement, this motor is a great alternative for 3D and sport planes up to 35lbs! The motor is very well built with strong mounts, end bell and a concentric double bearings at the rear to support large propellers and rotating can, especially during hard 3D flight. This motor is very well engineered and of the highest quality. The factory can produce only a limited number of these motors per month due to the increased time in balancing and machining such a large object.

    If the motor received 70V and 250A that would be 17.5 kW input. Typically, motors and ESCs are not rated for both max voltage and max current at the same time. This is all part of the specsmanship. The total power level (voltage times current) is what really limits these components. Further, there are constant ratings and peak ratings so in applications like R/C, you can often obtain a sizable increase of power for short periods (5-10 seconds) which can be used for certain maneuvers (knife edge, hovering, pull out, verticals, etc).

    As for the manufacturer's "110cc equivalent" suggestion, their "20 h.p." is closer to a DA-200 power level so you have to take these suggestions with a grain of salt and perform some of your own tests.

    I ordered 8mm bullet connectors from both XPS and Hobby King. To my surprise, the ones from HK were much larger. Further, you get a whole bag of 12 sets for $15. I plan to use these on all ESC connections. For battery pack connections, I plan to use the Castle Creations 6.5mm connectors which can handle 200amps. These 6.5mm connections will be paralleled (12s3p) going to the 8mm bullets.

    I made some measurements on the Turnigy CA120-70 motor and they did not match up to the DA-150.

    I measured the prop adapter to be 29 mm across from the holes which would make the mounting the same as the DA-100 and 3W 4-cylinder (112iB4) engines.


    Building the Motor Test Box

    For about $10 at Home Depot, I picked up some #6 x 1" screws and a 1/2"x6"x4' piece of Poplar. After a few hand cuts, I was ready to make my test box. Poplar isn't a hard wood but it is fun to work with and becomes plenty strong if you put enough screws in it.

    The idea here is to clamp and tie the box to my portable Work Bench and then move the portable station outside for testing. My prop had not arrived yet so my next step will be to finish the setup on the Work Bench and do a quick test on 6s at low RPMs without a prop. The CC ICE HV 160 ESC will mount on the side of the test box. I still needed to solder the 8mm bullet connectors onto the ESC.

    I picked up a Heavy Duty Battery Cutoff Switch (66789) for $10 at Harbor Freight Tools to use as my safety arming switch outside the plane. The low-cost switch locks in both the On and Off positions and is rated for 500 amps at 24v which should be good for around 250 amps at 48v. The switch weighs 7.7oz but I consider it a requirement for safety and convenience on a giant-scale electric conversion that approaches 10KW of power. I'll detail use of this switch along with a momentary push button anti-spark setup later in the column.


    The motor passed its first test. Not only does it run but it appears to be vibration-free. I tested it on my work table using a 6s LiPo pack and was very happy that it appeared to run flawlessly at a range of throttle settings. The Spektrum AR9100 DSM2 9-Channel PowerSafe Receiver and Hobbico LiFe 6.6v 3200mAh pack are inside the box.

    I started assembling my portable Work Bench to be used in the outdoor prop testing. You can see my technique of clamping and strapping the motor test box. The 12s3p LiPo packs will sit on the left side.

    I mounted the HD Battery Disconnect Switch and the momentary push button to my test box. In this setup, the operator presses the button first, then pulls and twists the battery switch for a spark-free arming of the power system. The momentary push button connects a 100 ohm 1w resistor across the battery switch to charge up the capacitors on the ESC within a second.

    Castle Creations ICE ESCs

    The Castle Creations ICE ESCs are rated for a continuous current draw with a 5mph air flow. The short term peak ratings are not published. For normal flight, how often do you fly at full throttle? Typically, we hit full throttle for 5-10 second bursts when going vertical or doing a knife edge or a fast fly-by (especially in jets). With a little experience, and a few tips from others using the same controller, you can make use of this extra capability.

    Let's look at some of the CastleLink screens I took snapshots of when downloading my data logging. These are the actual settings of my ICE HV 160 ESC for the CA120-70 motor. I went along the tabs and took a snapshot of each one.

    The Data Logging is my favorite feature of the CC ICE ESCs. I no longer need to stick my face and fingers close to the power system running at full throttle to get a measurement. The data is saved even after the ESC has been turned off! Once downloaded from the ESC, with the motor disabled, a separate application (CastleLink Graph Viewer) allows you to view the downloaded data. The graph can get very "busy" with all the parameters so even if you logged all the data, the viewer allows you to remove it from the displayed graph. I usually disable a bunch of the less important parameters before I save a graph as a .jpg image for posting. The data logging is saved in sessions (or ESC power-ups) and acts as a FIFO (First In First Out) buffer that continuously wraps around. As you can see from the screen image, a 5 sample/second rate can log all the paramters for over 15 minutes without wrapping around.

    The Software tab reveals another one of the great features of the Castle ESCs in that they can be reprogrammed for new firmware right from the Web! I don't always upgrade to the latest beta version because the changes are often for helis, not planes. Further, if you have a problem with a newer version of beta firmware, you can always revert back to an older version.

    The last help screen below shows the various ways to trip a low-voltage cutoff. I often disable this on larger models because it has been my experience that the planes will no longer fly before you get to the "danger zone" on the LiPo cell voltage. 3.0v/cell reduces longevity, 3.2v/cell is fair, 3.4v/cell is what I typically strive for as a minimum after a full flight. During a full throttle pass, it is ok for the LiPo cell to dip below 3v momentarily and then recover once throttled back. You typically don't want your motor to cut out during this period. With the voltage cutoff disabled, a performance plane becomes noticeably wimpy when the voltage drops to 3.4v/cell. The sensitivity of the voltage dip depends on many parameters like pack capacity, C-rating, aggressiveness of setup, and how long into the flight you perform the maneuver. In my Ultimate setup, I don't think the 15AH capacity at 30C will have much of a voltage dip so I initially used the default settings of Auto-cutoff at 3.0v/cell.

    The help screens are seen from pressing the question mark in the blue circle. For Current Limiting, you have 5 choices. I typically leave mine at normal which is the default setting. Competitors and demo pilots sometimes disable the current limit, after they are comfortable with their setup parameters, so that the ESC cannot shut down unexpectedly.

    The CastleLink application also detects when a new version of PC software is available. It directs you to the Castle Creations downloading page and upgrades the application seamlessly. Castle currently has only a version for PCs but they are also working on a version for the MAC.

    Assembling a "Super Pack"

    When you assemble a super battery pack like this 12s3p 15AH configuration, you must keep safety your first priority. I use safety goggles when soldering and sanding with the Dremel tool. I also have several fire extinguishers nearby.

    The test packs I used here for testing are similar but not matched cells. I will likely purchase six 6s packs of the same type before flying the plane.

    I soldered Castle Creations 6.5mm bullet connectors to all the 6s packs. These connectors are rated to 200 amps. The red wire gets the male connector so that when using a single pack, the last connection to the ESC can easily touch the anti-spark resistor (soldered to the ESC female bullet) just before being inserted. On this application, I am using a separate arming switch and resistor so the male/female orientation is meant for other smaller applications.

    Each set of 6s packs are first balanced charged separately and then connected in series to make a 12s pack. The resultant three 12s packs are then connected in parallel to create the super battery pack.


    I made my own 3:1 adapters using #10 Castle Creations "wet noodle" silver wire. I don't know what the rating of the HK 8mm bullet connectors is but they are more like 10mm connectors so I expect them to be sufficient.

    On my test box, I have one #10 gauge wire coming from the arming switch to the battery packs that I will eventually replace with a #8 wire. For testing purposes, the #10 wire should be sufficient. The Robot MarketPlace sells high quality wire by the foot in many gauges including #8.

    I charged the packs last week. No matter when they are charged, you should measure each 12s configuration before connecting them in parallel. I measured 49.8v, 50.0v and 49.9v so I knew that I would have no issues when connecting them in parallel. The resultant super pack voltage was 49.9v. The super pack sits on a piece of 1/4" aircraft grade lite plywood and is held by two Velcro (p/n 90700) One-Wrap straps. A similar configuration will be used in the plane once I assemble the motor box.


    Each connection of the bullet connectors is covered with a 1.5" piece of masking tape. This is done for safety since there is often a small ring of metal showing that the shrink tubing doesn't cover. I also found a piece of EPS foam with the perfect density to make some end caps for both the battery leads (when separated) and the final two 8mm connectors. The red cap has the EPS foam inside. The advantage of using the EPS foam is that it will not press the male connector pins during storage and has no memory for being slightly forced onto the connector. They are inexpensive and can be made in seconds with a razor knife and ruler. The EPS foam caps will not fall off or be shaken off.

    Testing the Power System

    As stated before, the reason I was testing the motor outside the plane is because the Turnigy CA120-70 had no track record. Once satisfied with its performance, we'll build the motor box in the Ultimate and mount the motor. Assuming all works well, it will be a relatively low-cost giant scale power system.

    • Turnigy CA120-70 motor - $300
    • Castle Creations ICE HV 160 ESC - $272
    • Xoar 30x10 Beachwood Prop - $61

    A Xoar 30x10 PJA Series Beechwood prop was purchased from Tower Hobbies. These props are constructed of top-grade German beechwood and balanced during every stage of production. I also bought the Xoar Prop Covers that work up to 34" props.

    I was surprised with the quality of this prop. It was perfectly manufactured and painted with a clear coat enamel making it an excellent value.

    The DA100 (PDG-DA3W) Drill Jig was ordered from PSP Manufacturing and arrived in only a few days. I compared it with my Turnigy motor holes and it was a perfect match. This drill jig comes with a bit, washer, and holding screw. It can also be used for other DA and 3W patterns as well.



    My friend, Paul Weigand, mounted the Xoar prop to the Turnigy CA120-70 motor. He used the DA-100 drill guide (29mm centers) but still needed to open the holes by .020" (0.5mm) for a proper fit. This is typically required to properly align the screws through the prop and washer.

    We won't bother with the spinner and backplate mounting until I determine the prop size I want to use. The 42% Ultimate comes with a nice aluminum backplate and white locking nylon spinner.

    The weather initially prevented me from doing a full power test outside in my driveway but I decided to perform a low-RPM test inside in my gym room. The test was very successful and I was excited to try it again soon.

    The video below shows how easy it is to arm and disarm the power system without a spark. The portable work bench is weighed down in the back with a 75lb E-Z curl bar. My Spektrum transmitter was turned on just prior to filming and I removed the Xoar prop covers. In one of the low power checks, a framed photo blew off the wall and hit the video camera stand on its way down. The rubber flooring helped keep the glass from breaking. Even at low RPMs, the thrust from the 30" prop was apparent.

    Download and Watch in Windows Media Player here

    Turnigy Motor Test 1 (6 meg)


    It wasn't much warmer on the following Sunday but at least the sun was out. I thought it was 20 degrees but it was really 15 degrees with a single digit wind chill. It didn't stop us as we proceeded to have the second motor test. My buddy, Jeff, made a LiPo pack warmer from insulation bags used on tropical fish. It kept the super pack from directly feeling the single digit wind chill.

    The video below is both impressive for the power that this setup can deliver and humorous as I kept having to put more weights on the bench to keep it from tipping. I throttled up slowly and kept an alert eye on the bench from a safe distance inside the garage. We were amazed at the prop blast that was blowing 25 feet into the garage.

    The result summary is that while I obtained a 10.8KW power level, I reached the limit of the Castle ICE HV 160 ESC as it tripped the current limit at 260 amps. This is what it is designed to do when set to "Normal" current limit. My goal using this ESC is to obtain a power level closer to 9KW with a current peak around 200-225 amps.

    In the video, I mentioned that I would try using a low timing setting but after checking the current level on the data logging, I realized that I needed to drop to an 11s3p configuration if I still want to use my 30x10 prop. So this would be my next test for the following weekend; stay with normal timing and use an 11s3p setup.

    I also planned to beef up my motor test box and work bench as the power level at 10,000 watts was impressive! In all my electric conversions, I had never encountered this much power.

    Download and Watch in Windows Media Player here

    Turnigy Motor Test 2 (16 meg)


    The next testing session with an 11s3p 15AH LiPo was much better and did not trip the current limit. Using the Xoar 30x10 prop, the system produced runs of 7400 watts at 203 amps. The RPMs went down to about 6050 at full throttle. I was running all the default settings as shipped from the factory for the ICE HV 160 ESC.

    I was prepared to change the timing, if needed, by bringing the Castle Field Link Portable Programmer. It turned out that we didn't need it as the ICE HV 160 can sustain 200 amp peak draws without issue. It was a cold 10 degrees out which didn't seem that bad without wind but the prop blast into the garage was not fun. I added four metal brackets to the front corners of the test box to help improve its integrity. We also tied the top of the work bench to the garage door supports with some Nylon rope. This kept the work bench from pulling forward and eliminated the tipping. The weights were still used to keep the test bench relatively heavy.

    We had no issues this time but my tachometer reading was incorrect. The 7000 RPMs mentioned in the video was really from full throttle on the 12s LiPo and not partial throttle on the 11s testing. I am not sure why the reading was incorrect but the pole count is indeed 24 poles.

    At this point I am happy with the motor performance so we will move forward with building the motor box and finishing up the cowl and spinner.

    The 7400 watts will provide a 180w/lb power level on a 40lb plane. My power system limitation right now is the ICE HV 160 ESC. The Turnigy CA120-70 motor may be able to handle a higher power level but we will not be sure until we see some flight testing, measure the temperature, and test its longevity.

    Download and Watch in Windows Media Player here

    Turnigy Motor Test 3 (11 meg)


    Motor Test Conclusion:

    Overall, this setup makes for a relatively low-cost giant scale power system. Since the peak current is only 200amps for 7400 watts, when using a 30" prop on an 11s LiPo supply, a lighter 2p configuration could be used on smaller giant-scale models in the 27% to 33% range. Alternatively, you can use a 12s setup with a 27" prop for about 7000 watts at 169 amps.

    • Turnigy CA120-70 motor - $300
    • Castle Creations ICE HV 160 ESC - $272
    • Xoar 30x10 Beachwood Prop - $61

    Building a Giant - Ailerons

    The World Models 42% Ultimate assembly begins with installing the ailerons on all four wing halves.

    The manual says to replace the CA hinges with the supplied metal ones. I didn't see any metal hinges in the kit, so I decided to use Robart Super Hinges. I have used these in the past on giant scale projects as they come highly recommended.

    Each of the 8 CA hinges was replaced with a Robart Super Hinge. After first checking the fit and swing, I glued them in place using BVM V-poxy for a strong hold that won't weaken or yellow over time. Note that each hinge was lightly sanded to help the glue hold and then coated in the center area with Vasoline to prevent glue from getting in the hinge.

    Before installing the aileron servo and linkage, I covered the gap on the bottom side with a strip of clear Monokote. In this manner, the dust and dirt won't stick to the center and the strip can't be seen from the top side.

    The hardware set that comes with the World Models 42% Ultimate is pretty good. I have used this hardware on their other giant scale models with great success and it adds to the value of the ARF.

    The servo arm extension attached to the stock wheel of the Spektrum A6030 servo without any modifications.

    After cutting away the covering over the inner servo bay (I'm using a single servo per aileron), the servo mounted in place without issue. I attached a 24" HD extension on the servo wire which easily routed through the wing due to the pre-installed strings.

    A hardwood block exists in the aileron where you need to drill the hole for the horn. Each end of the control rod is threaded for a clevis which is then attached to the bearings with a screw and locknut. The horn covers are a nice added touch giving the linkage a cleaner look.

    Three more wings to go so repeat ad nauseam.

    All four wing halves were completed. Each wing was built like the first one and had the aileron sealed on the bottom side with clear Monokote. The supplied linkage hardware worked well here.

    Since I am using only 8 servos total for the entire plane, instead of 16, I realize about a pound in weight savings.

    Building a Giant - Cockpit

    After completing the second wing half, I needed a diversion so I assembled the cockpit. Although the World Models 42% Ultimate comes with a closed cockpit (which is much better than many other giant scale open cockpits) the dash is left blank without any decals. Further, the supplied pilot was actually only a quarter-scale sized figure so it needed to be replaced.

    I detailed my Ultimate cockpit using the Aeroworks 150cc Ultimate Instrument Panel and the Great Planes (GPMQ9006) 1/3 scale sport pilot. It isn't a perfectly scale size but it was reasonable and well priced.

    The new Aeroworks Ultimate has a very different fuselage width than the original World Models design so I needed to cut down the instrument panel and then make a backing from black felt. The result was a better detailed cockpit with little effort.

    Building a Giant - Gear Mains

    The Ultimate was brought from my plane storage room to the back room where I can complete the assembly. The gear mains came next. After the metal brackets (for the flying wires) are installed into recessed slots, the main gear bar is screwed into place with the supplied cap head screws. Notice that the t-nuts are offset so that you cannot install the mains backwards.

    I replaced the stock air-filled wheels with Dubro 5" Treaded Lightweight (500TL) solid rubber wheels. The World Model air-filled wheels tend to leak. The wheels are held in position on the axle with a collar on each side.

    I discarded the supplied hardware for the pants and used my own small cap head screws and t-nuts. After checking the alignment of the pant, I drilled two holes through the metal gear mains and through the pants. The pants are well designed and have an indentation on both sides to mark where to drill the axle hole. Since both of the inner sides have plywood plates fiber-glassed into place, either pant can be used as either a left or right pant. I used a Dremel tool to sand a Dime-sized recess on the outer side where the pant meets the welded nut on the axle.

    All the parts seemed solid when finished. I plan to add some extra V-poxy to the hardwood mounts inside the plane that secure the gear mains. This should help hold things together in the event of a rough landing.

    Once finished, I held the cowl in place with a single piece of tape. The Ultimate was starting to shape up!

    Building a Giant - Tail Section

    I installed the elevators in the two halves using the same techniques used for the wings. The CA hinges were replaced with Robart Super Hinges and the gap was sealed on the bottom with clear Monokote. The stock hardware was used for the linkage. The servo arm extension attached to the stock wheel of the Spektrum A6030 servo without any modifications.

    Since the two halves operate in opposite directions, I will connect one to the elevator channel and mix in the AUX4 channel for the other elevator. This also allows for easier electronic trimming of the two surfaces.

    I prepared the tail for mounting the horizontal stabilizers by trimming the covering on both sides. When you cut away the rudder servo bay opening, it allows access to the control line tubes. This is a nice feature on the World Models 42% Ultimate to keep the long servo extensions secure. Now was a good time to run the four long 48" servo extensions through the tubes into the cockpit area. I'm using two servos for the rudder for a dual push-pull configuration and two servos for the elevator halves, one on each half.

    The stabs are held by a thick aluminum tube that is filled in the center with wood. The center hole is for the servo control lead and the front hole is for the alignment rod. It took me a moment to figure out what the instructions meant. The Ultimate has two set screws already mounted in the stabs, one on top and one on the bottom of each stab. Using these set screws, you can tighten them with a 1.5mm Allen wrench and obtain a perfect alignment between the two stabs. They are also used to adjust the incidence, up or down, as needed.

    To hold the stabilizers in place, one sheet metal screw and one machine screw are used on the bottom side. Since there were no holes pre-drilled, you can drill and tab where desired.

    The rudder was first glued to the vertical stabilizer using five of the Robart Super Hinges. I drilled some holes in the tail to allow the bottom two hinges to be glued in place without cutting them shorter. The assembly was then glued to the fuselage tail with V-poxy after first checking the fit and incidence.

    Now that's an Ultimate rudder!

    The original 42% Ultimate was designed to use 4 servos in the aft end of the fuselage for the rudder or a pull-pull configuration to the center of the fuselage. For some reason, my model only had three servo bays in the tail instead of four so I used the two that were equal distance on both sides. Since the servos were now mounted in the forward bays, the supplied control rods were too short.



    I created some longer controls rods using Du-bro (#802) 4-40 by 12" Threaded Rods and then strengthened them using some thick-walled carbon tubing that I had on hand. Since the other end of the rod was not threaded, I replaced the stock servo arms supplied in the kit with some Du-bro (#671) Super Strength Servo Arms and used a Du-bro (#885) E/Z Link. The threaded end of the rod used the stock clevis and connected to the stock hardware on the rudder. I'll cover the E/Z Link with some shrink tubing or a rubber keeper before flying.

    The tailwheel assembly (below) installed easily. It has a built-in spring to absorb shock when landing. The spring links to the rudder which allows the tailwheel to twist if it encounters a rough surface.

    I wasn't happy with the supplied hardware for the tail wires except for the anchors that mounted through the stabilizers. I replaced the supplied steel cable, crimps, and wheel collars with some Dubro and Great Planes 4-40 rigging hardware.

    • Dubro (#518) 4-40 Pull-Pull system
    • Du-bro (#618) 4-40 Rigging Couplers
    • Du-bro (#896) Crimps
    • Great Planes (GPMQ3795) 4-40 Threaded Steel Clevis

    We decided to make both ends adjustable for a symmetrical look. In the photos, I have not yet added the rubber keepers to the clevis. We used a crimp tool and triple feed through for maximum hold.

    Building a Giant - Motor Box

    I temporarily taped the motor box together to see if my 12s3p 15AH pack would fit inside. I then measured the distance needed to extend the Turnigy motor so that the the spinner backplate mounted 1/8" from the cowl. It turned out to be about 4". However, we decided not to extend the motor on stand-offs but rather extend the motor box to meet the motor and allow more room for the packs to adjust the CG, if needed.

    The fuselage was then delivered to my friend, Paul Weigand, for installing and modifying the motor box. Paul is an excellent craftsman and had several good ideas on accessing the battery pack from the cowl.

    The first step was to mount the cowl in position so that all the decals lined up. Paul used the stock screws and rubber washers for this step.

    The supplied backplate and spinner were mounted next. The backplate came with a nice 10mm brass fitting that fit the Turnigy motor shaft perfectly. The spinner cone needed to be cut for the thick prop blades.

    One issue here is that the long spinner screw was meant for a gas engine threaded hole on the shaft and there was nothing to hold it on the Turnigy motor. Paul needed to make a new prop washer that has a center hole tapped for the spinner screw.

    After making the motor box extension, Paul needed to test the position of the motor and backplate to the cowl before starting to glue the box together. The only place he could stand it upright, center the motor in the cowl, and, be able to work from above it was in the stairway to his second floor. Now that is dedication to precision work!

    Note that the motor mount spacers are used to extend the CA120-70 motor to allow extra room for possible substitution in the future.

    The stock motor box has 1/16? aircraft ply doublers on each side so it will be plenty strong. Paul also planed on fiber-glassing the front corners of the box even though, it is drilled and pegged. This will create a strong motor box that you can be confident will stay together.


    The next step was to install the mounts for the cabane struts because you can?t get to them once the bottom of the motor box is in place.

    The slots for the cabane strut mounts were 1/8? closer together than the motor box sides so Paul made up shims for each side. He then tapped the motor box for 6-32 screws because they now needed to be longer and then finally V-poxyied it all together.

    Paul also added some flooring to the motor box about 6? behind the firewall in case all the batteries don?t need to be far forward for the CG. The result is an 18? long battery compartment to move them around in for the proper CG.

    The 4 holes drilled in the front of the cowl, behind the spinner give access to the motor mounting bolts, with the cowl in place. This allows you to check the mount on occasion and tighten it, if needed.

    Paul's alignment efforts can be seen with the spinner gap resulting in a mere 3/32 of an inch!

    The completed motor box uses nylon tabs (old servo arms) to secure the top. Paul's goal was to allow a battery change without using any tools. The removable top and reinforcements accomplishes this while keeping the box strong enough for 10000+ watts of power!

    The six 5s 5AH packs and three 2s 5AH packs demonstrate that they can reside all the way forward or all the way back. Once we balance it, and decide where the packs should go, we'll make foam inserts and use Velcro to keep them in place inside the box.

    Paul did a great job on creating a removable hatch on the cowl. In this manner, the batteries can be easily accessed without using any tools. Although you can barely see the lines in the cowl, my plan was to add a large RCU globe vinyl-transfer decal over the area. We'll see if I dare cover up this work of art!

    Some detail photos of the cowl above help show the hatch construction. The foam blocks are used to aid in positioning the cowl when mounting it. They keep the cowl from sliding further back on the fuselage than wanted. Paul says that he did not glue anything to the cowl before cutting the hatch opening and added the framework afterward. The goal here is to retain the slight curve of the hatch after it has been cut away, so when gluing in the framework, be sure to not flatten the hatch area.

    The holes in the front of the cowl allow you to make fine adjustments to the motor position and then tighten it in place. This provides a perfect alignment between the spinner backplate and the cowl molding. Once the motor has been tightened, additional nuts are placed on the ends of the screws behind the T-nuts for double locking.

    Building a Giant - Wired for Usability

    The ESC and arming switch mounted nice and easy on the new motor box. I needed to only add an additional 8" piece of red #8 Castle Creations wire to my existing test box setup. Note the fiberglass on the pegged front corners on the motor box. An added touch by Paul for reinforcement.

    The arming switch and anti-spark button will stick out of the cowl bottom for easy and safe arming or disarming of the power system. A single large wood screw was used to hold the arming switch into the thick hard bottom wood of the fuselage. Since the whole plane could be moved around by the arming switch, I saw no need to make a mount for the other side. I secured the large nuts with a dab of V-poxy.

    After first lightly sanding the side metal, the anti-spark button is held in place with a little V-poxy.

    The main #8 red and black wires enter the motor box for easy connection to the 11s3p Super Pack that will be strapped into place, then further secured by Velcro and foam blocks.

    For an easy power upgrade from the $572 power system, only the ESC and battery pack need be changed.


    I prepared the battery box for loading by cutting a piece of light floor foam to form a barrier between the motor mount screws and the super pack. If you haven't used this type of foam before, I recommend buying some at a home improvement store like Home Depot. I used it to line the floor of my R/C trailer and it makes a great kneeling pad.

    The super pack is assembled outside the plane and then simply set into place in the battery/motor box. I'll start with it full forward when testing the CG. Once the desired location is found, I plan to lock the bottom plywood plate of the super pack in place much like Paul did with the hatches.

    After connecting the two disarmed super pack mains using the 8mm bullet connectors, the battery/motor box top is secured in place.

    In the lower right photo, you'll see the yellow cabane mount on the left which matches the Ultimate yellow quite well.


    Another nice service of Home Depot is that you can take any piece to them for instant color matching and buy a sample container (7.25 fl. oz.) for only $3.

    You usually end up with a lifetime amount of paint, but the price is right!

    Building a Giant - Receiver and Servo Power

    The receivers and batteries certainly had plenty of room to be spaced out properly. The receivers were oriented on different axis and opposite sides of the aircraft. The two 3200mAh LiFe packs weigh almost a pound and can be used to "fine tune" the balance by sliding up or down the tray to the main super pack.

    Note that no matchboxes were needed and no Y-harnesses used. The direct connection of each servo to the high-current fail-safe receiver provides maximum power when needed without additional cost.

    I used a mix for the rudder and elevator servos which allowed me to fine tune both the trim and reduce the opposite forces until the digital servos stopped "singing".

    Also note that the receiver satellite wires run on top of the tray and all the servo leads on the bottom. While this may not be necessary, it can't hurt to help distance the wires to reduce noise from the high-current servo leads.

    The On/Off switch is fail-safe and draws less than 1mA when in the OFF position. This means that I can leave the receiver batteries connected for over 6400 hours, which is plenty of time to remember to disconnect them after a weekend of flying. I'll mount the switch on the side of the fuselage.

    Building a Giant - Final Assembly and Details

    To properly mount the spinner, Paul made a custom washer that was tapped in the center for the cone screw. A washer like this may be available from Tru-Turn but the lack of photos on their Web site makes it difficult to tell without calling.

    I also purchased some slightly longer prop screws because the ones that came with the Turnigy CA120-70 motor were just a bit short when using the Xoar prop and aluminum backplate.

    After first mounting the cowl, the motor position was slightly adjusted so that the spinner backplate was perfectly centered. The holes in the cowl allowed us to slightly loosen the motor mount screws for the final adjustment. Once happy with the alignment, we tightened up the motor mount screws and added nuts behind the T-nuts to double lock the screws in place.

    The stock spinner for the World Models Ultimate is very good quality and matches the color scheme. Note how the nylon cone piece locks into the aluminum backplate so it cannot spin against the prop. I needed to cut the spinner cone screw threads about 1/4" shorter for a proper fit.

    The last step of my cowl, prop, and spinner installation is to put on the Xoar covers. The two covers are connected together using the supplied hook and loop straps. The covers help protect the prop and the people around it.

    The Ultimate is a fun plane to customize for your personal favorites, so when the first of my custom decals arrived from RCU's, Ken Isaac, I started adding some final details.

    The Flag Sticker Shop has left and right hand vinyl decals in various sizes with reasonable shipping rates.

    The canopy was lined with some (73305) silver 3M ScotchCal striping tape to give it a touch of a framework. The pilot name decals were compliments of RCU's Matt Kirsch and Ed Britton.


    By holding my super pack from the Velcro straps, it set right down in place. I'll start with the pack all the way forward when we do the initial CG check. There isn't much room for the pack to slide around so securing it will be easy. Only the two 8mm connections need to be joined and it is done while the power is disconnected from the ESC.

    After installing the top of the motor/battery box, it is secured in place with the four tabs made from servo arms.

    The cowl hatch is installed last. It gets secured by the two wooden dowels in the front and the 90 degree twist latch. It doesn't matter which way you turn the knob.

    For spark-free arming, the pushbutton and battery disconnect switch are easily accessed from the left side of the plane.

    The control surfaces are so heavy that they tend to droop when the power is not applied to the servos. Since I didn't want them to bounce around in my trailer, I found that two sizes of the plumber's pipe foam worked very well at keeping them secured. Note that I mounted my failsafe receiver On/Off switch just below the "A" in the AMP'D decal.

    The metal wing cabane and wooden cabin supports are installed before attaching the main wings. The cabin supports were glued in place to regain fuselage strength from the large removable cockpit hatch.

    The metal cabane parts were all labeled with stickers to match the diagrams in the manual, making this an easy task. It appears that the metal cabane cross-braces have been modified to improve strength. They are much thicker than the manual photos and required longer screws than supplied to hold them in place. I used three longer M3 screws of my own.

    Another nice feature of the World Models biplanes is the wing incidence guides that come in the kit. I have used them before but these are the biggest ones! The guides eliminate a good deal of the measuring work needed for straight wings.

    Unlike the hardware that I discarded for the tail wires, the hardware that comes in the kit for the main wing cabanes and flying wires is very nice. The posts snugly push through the cabanes and are easily secured with clips. The posts will also host the adjustable anchors for the flying wires.

    In the photos below, the lower wing was installed first. One side gets the machine screw for removal from the tapped tube and the other side is drilled for the sheet metal screw, once installed. When the upper wing was installed, I used the wing incidence guides to hold it in place so it didn't move around until the cabanes were installed. My "giant" was almost ready to fly! A future issue of AMP'D will cover giant-scale electric flying with considerations for high-capacity charging at the field.


    If you're an NCIS fan, you may have wondered how Gibbs got the boat out of his basement. Although my situation is similar, I have the advantage of removing the wings.

    By adapting positively to technology and globalization changes, the benefits can be used to attract more R/Cers into giant-scale electrics. We often find new choices in our hobby that simply didn't exist the year before and can suddenly be within our budget for exciting new projects.

    A lower-cost power system for giant-scale electrics that utilizes safe voltage levels can open up existing sectors of the market that were previously hampered by cost, complexity, or noise.

    A cost comparison of the power system used in this column with a few existing gas-powered alternatives reveals an interesting paradigm shift.

    • Turnigy CA120-70 motor - $300
    • Castle Creations ICE HV 160 ESC - $272
    • DA-100 Engine: $999.00
    • DA-100 Muffler Set: $145.00
    • DA-120 Engine: $$1199.00
    • DA-120 Stock Mufflers: $160.00
    • 3W-110iB2-F Classic Series $1195.00

    Fuel sources for electric power have also dropped in price dramatically in the past year. A typical 5-cell 5AH pack is about $50 with as little as 1 cent shipping from on-continent warehouses.

    In the past, many R/Cers just didn't have the budget for giant scale projects. Perhaps this will change soon...

    When you fly electric, fly clean, fly quiet, and fly safe!


    Special thanks for contributions by:
    "Papa Jeff" Ring and Paul Weigand


    This section of AMP'D covers some of the questions that our readers have sent in and I thought would be interesting for others.

    George B. asks:

    Greg, how is it possible that you draw so much current over a #12 wire gauge in R/C when it is not rated for this?

    Hi George,

    Most American standards are for house wiring that use 120v to 240v on 1000' length of copper wire to determine the gauge. Our R/C applications use much shorter lengths of silver wire which has even less resistance than copper wire. The length used is typically a short 12" or less.

    This Wire Size Calculator shows that you can use #12 wire for 120 volts at 800 amps if you keep the length to a foot. At 1000 amps, you need #10 wire for a 12" length. This Continuity Test Resistance Calculator shows a 0.001 ohm resistance for 12" length of copper wire, and silver wire would be even less resistance.

    The real capacity of a wire is actually best measured in watts, not amperage, because a watt is a unit of power that is a combination of amperage and voltage flowing through the wire. Watts measure the amount of power a wire can safely dissipate without getting too hot. In other words, the wire resistance has power loss which forms heat. Since most wire charts are done in amps, it is assumed to be at a single voltage level like 110v or 240v, which is fine because the chart has an assumed usage.

    For example, a chart for amperage ratings of various sized wires used on 110V AC house wiring is very different from a common 12v DC automotive usage. The chart like the one above represents a typical "max capacity" for an unknown length of wire. Although a 1000' length may be used in a home, it is much too long for automotive applications. Likewise, the lengths used in automobiles are too long for our R/C applications.

    So, the shorter lengths and lower voltages used in R/C make it possible to pass some heavy current. I hope this helps you see how we can draw such higher currents through very short #12, #10, and #8 wires.

    Ask questions by e-mailing me at greg@rcuniverse.com


    The World Models F4U Corsair

    eRC Rebel 70 Sport ARF from Hobby Lobby

    E-flite Habu 32 DF ARF

    TamJets Strut Upgrade Kit for E-flite 15-25 Electric Retracts


    Print Issue 20 "Building a Giant"

    Comments on RCU Review: Greg Covey's Amp'd Issue 20: Building a Giant

    Posted by: DominicM on 04/12/2011
    Really superb article Greg. Great to see a practical test of the Turnigy CA120-70. HobbyKing will probably sell more now you have done their work for them. Had been looking for a kill switch for my electric 40% Extreme Flight Extra so will get some of thos cut-offs shipped over to me in the UK. I'd feel much happier arming my 14 cell/16KW setup from the flight line rather than in the pits. Already looking forward to your next article on field charging such setups. We don't have mains power at most UK sites so please consider that scenario. Good luck with the maiden and subsequent flights... Dominic (aka Ditchit)
    Posted by: dvbr on 04/15/2011
    Hi Greg, Excellent article, following the rule of 3,7W/g this motor will stand with 9000W no problem. Unfortunately, the ESC for that level of power still the major cost. The Jeti Spin 200A is the logical choice for a 9000W setup but its the double price than CC. Regards
    Posted by: Moserkid on 04/20/2011
    sheesh that motor is huge!!
    Page: 1

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