All my small warbirds were originally
designed to fly well with stock direct drive Speed 400 powerplants
NiCad or NiMH cells. Obviously, electric power systems have
advanced a great deal in the years since the Hellcat prototype
took to the skies. While the humble Speed 400 works as well
as it ever did, affordable brushless systems and lightweight
polymer cells have largely taken over the electric flight
Today there are simply too many
power systems to cover them all in this or any other single
document. So what follows here is a general overview and
tips for selecting a suitable power system for your model.
bear in mind these comments are one man's opinion, and I know some
modelers may prefer systems very different from what I'm outlining
Guidelines: In my opinion, the "optimum" power system for
warbirds turns an APC 7 X 5E (my preferred prop) at about 11,000
RPM. I know some builders have installed far higher power,
certainly it's possible to fly these models with far less power as
(the original Hellcat flew on a 6V motor and 6 X 600AE
But with an APC 7 X 5E, I think 11,000 RPM is just about perfect -
of the flight can be at 1/2 to 2/3 throttle, and you have a
power reserve for launching, vertical maneuvers and high-speed
While some modelers have used larger
props than the 7 X 5E, this can raise the issue of torque effects
during the hand launch, and since these models generally don't
rudder control, that can make for some interesting moments at the
of a flight.
Given these guidelines, your task is
select a motor that will turn an APC 7 X 5E at 11,000 RPM
your chosen battery pack. This is accomplished by selecting
motor with the correct Kv (voltage constant) for your
application. A performance prediction program like ElectriCalc
can come in very handy here, but here are some approximate
three different battery options:
2200-2S LiPo Battery: 2000 Kv
(range from 1800 to 2200).
2200-3S LiPo: 1250 Kv (range
1100 to 1400).
8 X 1400 NiMH: 1500 Kv (range
1300 to 1800).
Nearly any 400 class brushless motor
will handle the current for these three systems, but I would
motor and controller rated for at least 20 amps continuous (head
is cheap insurance).
Simple enough? So what are some
good motor choices? There's a bewildering and ever-growing variety
small brushless motors on the market, and there's no way one man
hope to test them all. But here are some thoughts to keep in
Outrunner: This is practically heresy in some
I prefer inrunners over outrunners for these particular
The most important reason is that these warbirds position the
very close to (in some cases touching) the motor case, and with a
whirling outrunner case, that's a recipe for disaster. If
insist on an outrunner, you'll want to make provision to install
that it can't contact the battery pack. But even aside of
concern, many of the small outrunners on the market are
not very well-designed and are generally much less efficient than
equivalent inrunner. A good many outrunners have
the 60% range, and some are even lower. Certainly there are
exceptions, like the excellent Hacker motors, but most of the
basement outrunners being sold have no better efficiency than an
Speed 400. All you're really gaining is higher torque and
ability to turn a larger prop.
Examples: While there are dozens of inrunners with
requsite Kv and power rating, here are some examples that I have
personally tested and found to work very well:
16/15/X Series: The Mega 16/15/X series were the
widely available brushless motors with a Kv suited to running a 7
prop. They're available in a wide range of winds, so that
a motor for nearly any choice of battery pack.
Series: Much like the Mega motors, the E-Flite Six
Series are available in a range of winds. In my experience
have proved to be very high quality motors, with excellent
and durable construction.
Series: While primarily known for ducted fan
applications, the HET-RC Typhoon series includes some motors that
well for small warbirds. In particular the HET-EDF5W (Kv
1800) and the HET-EDF4W (Kv 2250) bracket the range for a 2-cell
pack. The 5W will be your best choice for sport power, and
is better if you want higher performance.
MR-028-032-XX00 Series: The Medusa research
motors are also available in a range of winds, with Kv options of
1500, 1900, 2400 and 2800. These are very high quality
with excellent efficiency.
AstroFlight 020: This was the first brushless motor to see widespread use in 400-size aircraft. The Kv is too high for a 7 X 5E prop, but it flies great with a 2-cell LiPo pack and 6 X 4 prop.
Brushless Speed Controls: As with motors, today we have a bewildering variety of brushless speed controls. I know some of you are getting good results with inexpensive Asian ESCs, but my airplanes are too valuable to me to cut corners with something as important as the ESC, which it must be remembered supplies power not only to the motor but also to the radio. The Castle Creations Phoenix series is my first choice for controllers. I've used quite a number of other brands, but the Phoenix controllers are my clear favorite. For these warbirds, I use the Phoenix 25, which is very compact but offers plenty of head room. It's one less thing to worry about.
E-mail to Jim Ryan