Powerplant Options:

All my small warbirds were originally designed to fly well with stock direct drive Speed 400 powerplants on NiCad or NiMH cells.  Obviously, electric power systems have advanced a great deal in the years since the Hellcat prototype first took to the skies.  While the humble Speed 400 works as well now as it ever did, affordable brushless systems and lightweight lithium polymer cells have largely taken over the electric flight world. 

Today there are simply too many possible power systems to cover them all in this or any other single document.  So what follows here is a general overview and some tips for selecting a suitable power system for your model.  Please 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 here. 

General Guidelines: In my opinion, the "optimum" power system for my warbirds turns an APC 7 X 5E (my preferred prop) at about 11,000 RPM.  I know some builders have installed far higher power, and certainly it's possible to fly these models with far less power as well (the original Hellcat flew on a 6V motor and 6 X 600AE cells!).  But with an APC 7 X 5E, I think 11,000 RPM is just about perfect - most of the flight can be at 1/2 to 2/3 throttle, and you have a generous power reserve for launching, vertical maneuvers and high-speed passes.

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 have rudder control, that can make for some interesting moments at the start of a flight. 

Given these guidelines, your task is to select a motor that will turn an APC 7 X 5E at 11,000 RPM using  your chosen battery pack.  This is accomplished by selecting a 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 numbers for three different battery options:

2200-2S LiPo Battery:  2000 Kv (range from 1800 to 2200). 

2200-3S LiPo:  1250 Kv (range from 1100 to 1400).

8 X 1400 NiMH:  1500 Kv (range from 1300 to 1800). 

Nearly any 400 class brushless motor will handle the current for these three systems, but I would select a motor and controller rated for at least 20 amps continuous (head room is cheap insurance). 

Simple enough?  So what are some good motor choices? There's a bewildering and ever-growing variety of small brushless motors on the market, and there's no way one man can hope to test them all.  But here are some thoughts to keep in mind: 

Inrunner versus Outrunner:  This is practically heresy in some circles, but I prefer inrunners over outrunners for these particular models.  The most important reason is that these warbirds position the battery very close to (in some cases touching) the motor case, and with a whirling outrunner case, that's a recipe for disaster.  If you insist on an outrunner, you'll want to make provision to install it so that it can't contact the battery pack.  But even aside of that concern, many of the small outrunners on the market are not very well-designed and are generally much less efficient than an equivalent inrunner.  A good many outrunners have efficiencies in the 60% range, and some are even lower.  Certainly there are exceptions, like the excellent Hacker motors, but most of the bargain basement outrunners being sold have no better efficiency than an old Speed 400.  All you're really gaining is higher torque and the ability to turn a larger prop. 

Inrunner Examples:  While there are dozens of inrunners with the requsite Kv and power rating, here are some examples that I have personally tested and found to work very well:

Mega 16/15/X Series:  The Mega 16/15/X series were the first widely available brushless motors with a Kv suited to running a 7 X 5 prop.  They're available in a wide range of winds, so that there's a motor for nearly any choice of battery pack. 

E-Flite Six Series:  Much like the Mega motors, the E-Flite Six Series are available in a range of winds.  In my experience these have proved to be very high quality motors, with excellent efficiency and durable construction. 

Typhoon EDF4 Series:  While primarily known for ducted fan applications, the HET-RC Typhoon series includes some motors that work well for small warbirds.  In particular the HET-EDF5W (Kv 1800) and the HET-EDF4W (Kv 2250) bracket the range for a 2-cell LiPo pack.  The 5W will be your best choice for sport power, and the 4W is better if you want higher performance. 

Medusa Research MR-028-032-XX00 Series:   The Medusa research motors are also available in a range of winds, with Kv options of 1200, 1500, 1900, 2400 and 2800.  These are very high quality motors, 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.  

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