RCU Review: Greg Covey's Amp'd Issue 22: Giant Scale Electrics

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    Contributed by: Greg Covey | Published: October 2011 | Views: 24246 | email icon Email this Article | PDFpdf icon




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    Issue 22
    Article By Greg Covey

    Print Issue 22 "Giant Scale Electrics"

    In the past, many R/Cers just didn't have the budget for giant scale projects. If you enjoyed the benefits of electric flight, the cost was even greater than a gas power system. A cost comparison of the power system used in this column with a few existing gas-powered alternatives reveals an interesting paradigm shift.

    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. In this month's column, my 42% Ultimate takes flight for only half the cost of its gas engine equivalent!

    Finishing the 42% Ultimate

    There were still a few loose ends remaining when I submitted the "Building a Giant" column, back in April, before I considered my 42% Ultimate finished. I also needed to test the CG before attempting to remove it from my house. It was an exciting time last spring and I could feel the maiden flight was getting close.

    To connect the top wing aileron servo wires, I used some cable tubing to route the top aileron lines into the fuselage through an opening made with a plastic piece I found in the electrical section of Ace Hardware for $0.55. A second one sits next to the installed one. I simply traced it with a marker and then cut through the sheeted foam with a razor knife.

    The 1/2" cable tubing fits snugly through the plastic piece. The top aileron servos are then connected inside the cockpit.

    I mounted the flying wires on one side of the plane using the supplied hardware. The steel wire was wrapped three times around the fuselage anchor and then secured with a cable tie to keep the wire in place when disconnected from the cabanes.

    In order to make the twin anti-vibration dowels more scale, I made some brass tube joiners that I eventually spray painted black.

    I wanted to keep the split for easier storage of the flying wires when the plane was in the trailer so the brass tubing solved both issues.

    The supplied flying wire was just a few feet short which required me to find a replacement. After some considerable searching, both local and on-line, I found a thread on the RCU giant-scale forum with the key words I needed to describe the wire; down rigging cable. Armed with this description, it was easy to point to the fishing/marine industry and find some nylon coated stainless steel down rigger cable. I bought some AFW Surlon 150lb test nylon coated IX7 stainless steel leader wire from Fish307. The thinner black-coated leader wire should blend into the background better than the supplied white wire.

    Checking the CG

    I started to look at the CG by marking the center metal brace at the recommended 175mm from the leading edge. I then ran a string from wing tip to wing tip and you can see that the Ultimate wings are so swept back that I cannot use the wing tips to test the balance.

    The manual recommends hanging the plane from a wire around the front wing bar by slightly pulling the top wing apart. The top wing bar is centered on the 175mm mark.

    I was still hoping to test the CG in the back family room so I thought about it further. It just seemed too difficult to grab the leading edge, with two people, near the end of the wing.

    I then discovered an advantage of having a drop ceiling in the backroom as there is a perfectly located stud right above the wing center.


    When we tested the CG by hanging the Ultimate from the top wing bar, we discovered that the plane was tail heavy even with the 8lb 11s3p super pack all the way forward. The plane required 5lbs of weight at the front of the motor box to balance. When I put the weights on the top of the battery box, as shown in the photo, it required 7.5lbs.

    The flying weight when balanced at the recommended CG is 48.4lbs including the 8lb battery pack and 5lb lead weight.

    While it was a bit disappointing, adding 10% of the plane weight for balance is not unreasonable on a biplane.

    We also used a weighing procedure used on full-scale aircraft. By measuring the distance from the recommended CG to the gear mains and the tail wheel (or nose wheel), you can determine if your plane is balanced using the ratio on the weight at these two points.

    As shown in the diagram, I had about a 10:1 length ratio from the gear mains and the tail wheel to the CG. When we measured the weight at the tail wheel, it was indeed 1/10th the weight under the gear mains. In this manner, you can see how it makes checking the CG on larger models or full scale aircraft much easier.

    The same technique can be used to determine the CG if you change the weight. By removing the 5lb of lead, my gear mains weighed 40lbs, which changed the ratio from 10:1 to 9.1:1. When you divide the new ratio by the total length from the mains to the tail wheel, you get 8.2" back instead of the original 6.7" so my CG without adding weight is about 1.5" behind the recommended setting.

    On a swept wing like the Ultimate, CG changes have less effect. At this point, I will likely start with the added weight in five 1-lb sizes and see if the pilots feel the CG can be moved aft...eliminating 1lb at a time.

    Another alternative is to move the two rudder servos from the tail to the cockpit area. While this isn't exactly under the CG, you can make a rough estimate by using the 10:1 ratio. (e.g. 4.4lbs - 0.25lbs = 4.15lbs for our new tail weight) This would mean that the gear mains only need to weigh 41.5 lbs instead of 44lbs. for a minimum savings of 2.5lbs of lead. Where the lead resides on the front of the motor box, it may eliminate the entire 5lbs.

    For those projects where you don't have a scale or a rafter to hang the plane, Southwest System's EZ Balancer II is designed to balance giant scale planes from 8lbs on up to all legal AMA and IMAA limits.

    Reducing the Tail Weight

    For about $100, I was able to reduce the tail weight by 2.5lbs by purchasing the 2U offset tray and 4-40 cable fittings from AirWild.

    I removed the rudder servos and cables. The weight to balance the plane dropped in half from 5lbs to 2.5lbs. It was a good start and I really liked the AirWild tray and combo sets. The three in-line servo bays in the Ultimate are too far back so I mounted the tray where the receiver packs used to be.

    My pull-pull rudder modification was almost complete. I was very happy with the quality of the AirWild servo tray and of all the parts in the hardware kit, which were made from Dubro and Hangar 9 products. The Spektrum A6030 servos also fit perfectly.

    I first mounted the servos in the tray and set up the JR X9503 transmitter for a dual-rudder mode. This allows me to use the trim tab for both servos and a separate sub-trim for the back servo. After the arms were aligned electronically, I mounted all the Pro-links and tested it again with the receiver. After a few clicks on the back servo sub-trim, all the "singing" was gone from the digital servos. The tray was then mounted in the fuselage across areas that I reinforced with some hardwood slats under the floor.

    Next, I laid out the 60lb test cable and found a good area to make some exit holes in the tail. By "good area", I mean an area that gives almost no deflection in the cable and allows it to pass through a balsa wall for support on its way to the rudder control horn. In order for the cable knot in the 4-40 fitting to fit in the Dubro HD ball link, I needed to strip away the nylon coating to get the knot small enough. The installation was solid and clean, so I connected the cables to the rudder.

    I relocated my two receiver packs just aft of the super pack. This change not only moved some weight forward but allowed me to access them via the cowl hatch so I no longer needed to remove the canopy between flights. I like the changes that help both balance and usability!

    I also ended up adding only 16oz in weight using the Great Planes 1/4oz self adhesive lead weights. I placed them on the back of the front panel of the motor box. They are covered by the yellow floor foam and easy to get at (without removing the cowl) if I decide I can eliminate them after a few flights.

    The guys that e-mailed me about the WM 42% Ultimate CG all said it is a very stable design and the CG location is not critical. My goal was to dump the pound of lead after seeing how it flies. As it turned out, this weight was entirely removed by the third flight.


    High Capacity Charging

    One of the interesting finds at the 2011 Toledo Show was this Doc Brown's 47 Amp 12V Power Supply from Radical RC. Priced at only $49, it costs about $1 an amp which beats most of the other power supply prices on the market! They can also easily be ordered on-line from Radical RC. I initially bought two of them and had those shipped Priority Mail for only $6.

    We tested them out, even though they are tested before shipping, and they easily provide the advertised current. They are surplus H.P. Power Supplies that have been modified for easy use and double standard 4mm banana inputs.

    The concept for my Field Charging Station utilized the Stanley FatMax 4-in-1 Mobile Work Station. I bought mine at Home Depot for $70.

    The main goal was to create a self-contained, pre-connected, charging station that could be wheeled around a grass field to an available generator. By using the AC output of a Honda 1000 or 2000 generator, you can supply power to many chargers. I will likely have a direct DC connect option for my trailer batteries in case a generator is not available. We do not have any electric service at our flying fields but you could plug the extension cord into that as well.

    A long extension cord, not shown, will connect the Field Charging Station (FCS) to the generator. Each of the Doc Brown's DC Power Supplies will provide full power needs to two Cellpro 10s chargers. There is room for three of these supplies in the FCS connected to a multi-strip outlet. All the components can stay in place when the FCS is folded up and ready to wheel away. A few added holes were drilled to allow the charger to connect to the battery and DC supply. The upper tray even sits into the open top for storing optional adapters for various brand packs. The idea is to share the FCS when you are not using it.

    I currently have three CellPro 10s chargers, three BalancePro 6s chargers, and four CellPro 4s chargers so we'll see what I decided to put in the FCS. I will likely buy a third DC Power supply for about 150 amps of 12v power to the chargers. Since the unit seals up in just seconds, it makes for convenient water-proof storage in the event of a storm or just packing up for the day.

    Here are some of the features of the Stanley FatMax:

    • 4 storage solutions in one includes toolbox, part bins, portable tray and oversized lower bin for larger items
    • Patented tiered cantilever multi-level rolling system allows easy access to all 4 storage areas at the same time
    • Durable Structural Foam construction
    • Telescopic handle for easy maneuvering
    • Easy latch system includes a quick push to close feature
    • Large front latch that locks the entire unit
    • Ball bearing slides for smooth operation even under heavy load
    • V-groove on top of lid holds materials such as lumber and pipes in place for cutting
    • Extra large, heavy duty metal latches with pad lockable eye lets
    • Extra heavy duty rubber-coated 7” wheels – for maximum stability

    I added some components to finish up my charging station. The two 47-amp supplies are plugged into a multi-strip that will connect to a generator using the 50' heavy duty extension cord.

    All the heavy current chargers are connected to the DC supply directly and the smaller chargers via the Integy 6-channel power strip. My Hobbico Quick Field charger is for recharging transmitters and receiver packs.

    I did a power up test of all seven chargers and programmed the presets on the FMA Cellpro 10s chargers. The free 10s charger software (shown below) makes it easy to program the presets and update the charger firmware. After a few flights, I'll check out the individual packs to see if there are any balance issues.

    Sometimes when using packs in parallel, or dissimilar packs, with unequal wire lengths, it can create a "favorite path" for the current to drain one set of batteries more than another.

    Battery Case

    My battery case was made from a Pelican travel case. It is tough and meant to protect heavy items so it will travel well in my trailer.

    My goal was to have two completely assembled 9lb, 11s3p super packs ready to drop into the Ultimate for each event day. The cart-like case can be pulled on its wheels or carried. It makes the heavy packs easier to tote around and will keep them from getting banged up.

    The case also carries my two LiFe receiver packs, support parts, and repair kits for the flying wires and pull-pull wires. The contents inside weighed about 25lbs.

    Elvis Has Left the Building

    After applying the last RCU globe decal to the top wing and replacing the flying wires with my new 150lb test down rigger cable, the Ultimate was finally finished and ready to load into the trailer.

    The photo of my now empty backroom shows proof that "Elvis has left the building".

    It was a bit tricky to get out of the house but we managed to get it out the front door which was the widest opening without having to remove hinges.

    Due to the unusually wet spring, I decided to cancel my backyard checkout and do it right at the field over Memorial Day weekend.


    Field Assembly

    It helps to have lots of friends when it comes time to assemble the Ultimate. Lynn, Paul, and Dave all chipped in to make the task much easier. Notice my $10 outdoor tables from Harbor Freight to hoist the plane to a coffee table height. Most of the assembly can be done standing up, which saves your back and knees from abuse.

    The stock wing incidence guides make a nice support for the top wing until the cabanes are installed.

    Paul cut an opening in the cowl bottom for cooling. I also planned to add an opening in the fuselage bottom and add a deflector fin to direct the air coming in the cowl onto the motor.

    Time to Fly!

    The first two flights of the Ultimate were very successful in some pretty poor conditions. The field was wet and soggy with thick grass that squished under your feet. The weather was hot and the air was super-humid!

    On the first few flights, we lost some of the trim covering and one side of the cabane covering as it flew off during the flight. Other than that, the Ultimate flew like a dream! Lynn Bowerman was at the sticks and put the Ultimate through a well-planned series of tests.

    On the second day, we removed half of the lead weight as the Ultimate performed a dead stick drop very well. I still planned to improve the air cooling as the motor got a bit hot since I had no air exit in the fuselage.

    On the first two flights, we flew for 5 minutes and depleted the packs about 50%. On the next two flights, we flew it much harder for 6 minutes and used about 75% of the capacity. The 11s3p "super pack" temperature was just warm.

    Although the power level is enough for aerobatic maneuvers it is not sufficient for 3D. Lynn Bowerman flew it very gracefully and he methodically tested it out from stalling to knife edge and hammer heads.

    By the forth flight, we had removed all the lead (16oz) from the motor box and Lynn was already requesting the pack be moved slightly back for the next flights. This confirmed that the manufacturers suggested CG typically favors stability. Perhaps I could have left the servos in the tail but it is best to play it safe and slowly change things after each flight. My flying weight was now close to 43lbs.


    42% Ultimate First Flights (35 meg)

    The video above is on the first four flights on the Ultimate. I took bits and pieces from each flight and gave some commentary along the way. After loosing some trim covering and half a cabane covering on the first two flights, we lined all the leading edges with 3M clear shipping tape. The conditions were oppressively humid with all the water rising from the ground. On the forth landing, the Ultimate took a victory bath along the runway. Overall, we had a fun and successful Memorial Day weekend!

    The graph on the left is the CC ICE HV ESC data logging from flight #4. I labeled several of the maneuvers on the chart and also included the temperature. The flight time was about 5 minutes in the air and another minute including taxi, take-off, and landing.

    There was a maximum temperature of 197F and it measured 186F during the hammer head. Castle wants to see the temperature less than 212F, so although I am still safe, I will likely improve the cooling by either moving the ESC or directing some air flow over it.

    More Test Flying

    The Ultimate was test flown next by Team Futaba's Devin McGrath. The conditions were windy and rainy but we wanted to get some flights in before an event demo on the following day. Devin put the plane through some new maneuvers and kept a safe height in the swirling winds. I was happy that the plane seems to be holding together and I didn't see any motor issues. Notice that I removed the remaining half of the yellow trim globe on the top wing. I ordered a black RCU globe that arrived later in the summer.

    The motor temperature measured around 120-125 degrees F and the windings measured about 160 degrees. You can see my cooling modifications on the underside of the plane. Although the motor temperature is not excessively hot, I still plan to create the plywood deflector which will force air across the motor.

    Devin's Ultimate Test Flights (28 meg)


    Our flight times were up to 6 minutes now with about 20% charge left in the packs. It seemed like a safe amount to have for various weather conditions and flying styles.


    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


    NEAT Fair Practice Flights (30 meg)



    After a summer of strange weather conditions, we had our final practice flights for the 2011 NEAT Fair over the Labor Day weekend. Our emphasis was on a scale flying demo for the fair. We tried some new maneuvers that the full scale biplanes demo, like a two-turn flat spin and tail slide, but my Ultimate was too nose heavy to perform them.

    The 42% Ultimate went on to have successful demos at the 2011 NEAT Fair. Scott from SKS Video even strapped an HD camera to the top wing for a rear view perspective so be sure to check out the event video when it becomes available.

    I felt that the Turnigy motor could easily handle more than 10,000 watts. My 7500 watt system, limited by the ESC, seems to not have any ill effects. I still love the sound of this plane and the way it flies so we'll see what changes are in store for it over the winter months. I added a vent for improved cooling that you can see on the right side as the plane comes toward the camera after the landings in the NEAT Fair practice video. The 42% Ultimate was a big hit at the 2011 NEAT Fair and can be seen on the SKS video for the event.

    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 revealed an interesting paradigm shift. Fuel sources for electric power have also dropped in price dramatically in the past year. A typical 5-cell 5AH pack costs about $50 today.

    • 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

    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, Paul Weigand, Lynn Bowerman, Devin McGrath, Ken Isaac, and Gary Jones


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

    Lee asks:

    Greg, how do you connect the anti-spark resistor into your system?

    Hi Lee,

    It's a very good question that I have been asked many times. This image and link to MGM-Compro should help out.

    Picture the momentary switch wired across the Aux connector and the Battery Disconnect Switch wired across the Power connector. By connecting the 100ohm resistor first, for a second, the spark is eliminated when turning the battery switch to On.

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


    Custom Vinyl Graphics, Stickers, Labels for your R/C Models - Callie Graphics

    Cellpro 10XP, 15A Multi Chemistry Charger

    E-flite F-4 Phantom 32 DF

    The World Models Piper PA-25 Pawnee


    Print Issue 22 "Giant Scale Electrics"

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