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
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
were still a few loose ends remaining when I submitted the
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
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.
1/2" cable tubing fits snugly through the plastic piece.
The top aileron servos are then connected inside the cockpit.
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.
order to make the twin anti-vibration dowels more scale, I
made some brass tube joiners that I eventually spray painted
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.
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
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.
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.
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
then discovered an advantage of having a drop ceiling in the
backroom as there is a perfectly located stud right above
the wing center.
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.
flying weight when balanced at the recommended CG is 48.4lbs
including the 8lb battery pack and 5lb lead weight.
it was a bit disappointing, adding 10% of the plane weight
for balance is not unreasonable on a biplane.
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.
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
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.
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.
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.
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
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
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.
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
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.
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!
also ended up adding only 16oz in weight using the Great Planes
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.
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
of the interesting finds at the 2011 Toledo Show was this
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.
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.
concept for my Field Charging Station utilized the Stanley
4-in-1 Mobile Work Station. I bought mine at Home Depot for
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.
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
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.
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
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
Extra heavy duty rubber-coated 7” wheels – for
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
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.
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 was made from a Pelican travel case. It is tough
and meant to protect heavy items so it will travel well in
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.
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
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
photo of my now empty backroom shows proof that "Elvis
has left the building".
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.
to the unusually wet spring, I decided to cancel my backyard
checkout and do it right at the field over Memorial Day weekend.
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.
stock wing incidence guides make a nice support for the top
wing until the cabanes are installed.
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!
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!
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.
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.
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.
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.
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.
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!
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
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
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.
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
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.
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.
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.
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.
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
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,
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...
you fly electric, fly clean, fly quiet, and fly safe!
Special thanks for contributions
"Papa Jeff" Ring, Paul Weigand, Lynn Bowerman,
Devin McGrath, Ken Isaac, and Gary Jones
section of AMP'D covers some of the questions that our
readers have sent in and I thought would be interesting
how do you connect the anti-spark resistor into
a very good question that I have been asked many
times. This image and link
to MGM-Compro should help out.
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.