Great Model Planes and an Any-Battery Charger/Monitor

The peak charger w/ ammeter, voltmeter and plugs. 
   Several ready-to-fly electric airplanes fly very well, can be flown almost
anywhere and are very affordable.  They're great for long-time modellers,
but especially for their youngsters and new flyers.  So it's not unusual to
find modellers with many different battery packs with different capacities and
chemistries for various planes, radio gear and accessories.
   We added a battery diagnostic box to a peak charger. It lets you know the
current going into any battery pack and the voltage. The ammeter can easily be
read in the brightest sunlight, unlike the peak charger's LED.  We use an
adaptor cable that clips to the car battery terminals and has a cigarette
lighter socket. This was so the car's ignition switch does not have to be in
the Accessory position and the keys left inside.
  The diagnostic box consists of a 5A ammeter which is installed in a 2" x 3"
x 6" plastic project box, along with a 6A DPDT switch and a solid-state
voltmeter module.  We can see the charge current and keep track of all our
battery pack peak voltages.  The proper charging current and the peak voltage
are marked on each battery pack.
   The voltmeter module needed calibrating, which was set by adjusting its
readings to match the average of two different digital multimeter's readings.
However, actual accuracy is not important as long as it is the only meter
used for your batteries.
   The DPDT switch powers up the voltmeter and also connects power to all the
charging plug's positive terminals. We did not incorporate a discharging
capability, since electric motors and transmitters discharge their packs
fully if left on.  NiCad & NiMH packs should be discharged before recharging.
   Battery packs are rated by milliamp-hours.  A one-amp-hour pack delivers
one amp for one hour. And so it must be charged at one amp for one hour or
the equivalent.
   NiCad packs can be recharged at 3C, or 3 times capacity.  For example,
a 600 mAh pack can be recharged at 3 x 600 = 1800 mA (1.8 A).  So they
require one-third of an hour, 20 minutes, at this rate to fully charge.
   NiMH packs can be recharged at 2C, or 2 x 600 = 1200 mA (1.2 A) for
one-half hour.
   We do not use any LiPoly cells.
   Eight AA NiCads can be field-charged in a holder that has a 9-volt-battery
type terminal on it.  The charger has the matching 9-volt battery clip for
this purpose with reversed polarity to mate properly with the cell holder.
   There is an 8.4-volt, 900 mAh NiMH pack and two 600 mAh NiMH packs for the
Gypsy. And a 1000 mAh pack for the BeginAir. All take the white plug. The 600
mAh battery is lightest and lets the planes fly better.  But the flight will
not last as long.  Keep another pack charging while flying.
   There are two 7.2-volt, 600 mAh packs for the Skyseeker.
   There is a 9.6-volt NiCad pack in our Futaba transmitter.  But it is not
supposed to be fast-charged, so we use the AC wall charger the day before.
Special part:
     Voltmeter module:  7537-ME (no longer available)
     Available now:     6929-ME (requires 12073-RS resistors)
                       12305-ME (built-in resistors)
     Marlin P. Jones, Inc.,  1-800-652-6733
The Gypsy balsa plane with 380 electric motor. 
  This ARF balsa old-timer style model is precision made using laser cut ply
and balsa. We put a spare 380 can motor in it instead of the geared 370, as
well as micro, not sub-micro, servos which we had on hand.  Two holes needed
to be drilled to mount the 380 motor and the servo area had to be enlarged.
   We use a Ventura folding prop and two others direct-drive, so the landing
gear was shortened, the axles were moved far forward and bigger wheels put
on. The total weight is 1 lb.  It flies very well with the light 600 mAh, 8.4
volt NiMH battery pack.
Three good props for the 380 can motor.
  The 380 motor with the 8.4-volt pack turns a Ventura 6D x 4P folding prop
at 10,500 RPM (32 watts) and throws air back at 27 MPH.  The prop center was
drilled 13/64" and also cut back to fit onto the 380 motor shaft prop hub.
  The 380 motor turns a red Hobby Zone (HCAQ 3492) 6.4D x 3P prop at 10,000
RPM and throws the air back at 26 MPH.
  A gray Park Zone (PKZ 1002) 6D x 3P prop spins at 10,000 RPM and throws air
back at 28 MPH.  These last two props were also modified to fit onto the 380
motor shaft prop hub.  The spinner part was cut off and the centers were
drilled 13/64".  These are pusher props, so they are turned around.
  All the props give about 7 oz. of static thrust.  The aluminum prop hubs
for the 380 motor shaft were slightly drilled out, to 3/32", to fit the shaft
without having to force them on.
  We use E-Flite 10-Amp ESCs (EFLA104) and have had no trouble with them. We
soldered both types of battery connectors to them for either the 600 mAh or
900 mAh packs.
The SkySeeker RTF with direct-drive 370 motor.
  This is a very light (13 oz.) RTF plane that is about as good a model as
possible for beginners who want to learn to fly on their own.  There are two
wings, two tail assemblies and three props.  Everything comes pre-assembled.
  Leaving the transmitter trims zeroed and the servos neutral, the pushrod
clevises at the control surface horns were adjusted so that the surfaces were
zeroed. The clevises should be left in the outer holes (least throw) because
this plane is squirrely.  The pushrods also needed to be bent so that there
was minimum rubbing against the fuselage exit holes.
  The props are 5D x 3P pushers.  The 7.2 volt 600 mAh NiMH battery, which
has the old standard white plug, spins the prop at 15,000 RPM with a prop wash
of 34 MPH. We took out almost all the motor shaft angle, which was VERY high.
  The charger light goes from blinking (charging) to on (charged) prematurely.
You should pull the power plug from the wall transformer out and put it back
in once or twice to fully charge the batteries.
  After one hard landing, both servos had their gears stripped.  We replaced
them with E-Flite sub-micros.
The BeginAir aileron-trainer, 480-motor plane.
   This plane has a light plastic body, styrofoam wing, covered-foam tail and
a stick boom back the tail. We got the basic plane and put in our radio gear.
The plane weighs 1 & 1/2 lbs. It comes with a 9.6V, 1,000 mAh NiMH pack.  The
plane electronics are turned on with a pushbutton.
IMPORTANT NOTE: The motor does not shut off fully with the factory ESC, even
with the transmitter trim as low as possible!
   An electric motor is a different animal from a combustion engine. The
only thing that they have in common is that a propeller is used to change
shaft power (torque and RPM) into propulsive force (reaction). In both cases,
prop selection is critical for the best performance and highest efficiency.
   Fuel engines are confined by their displacement and having the right
fuel-air ratio (needle valve setting).  So they can only produce more power
with higher RPMs, which can be done by using exotic fuel additives such as
nitromethane. The amount of fuel burned determines the total work available.
   Electric motors produce more power by using a higher voltage battery pack.
The batteries are marked in volts and milliamp-hours. Total work available is
the milliamps times volts times hours (milliwatt-hours).  In a similar way,
for a steam engine, the work is done by the fire in the boiler.  The boiler,
not the engine, is rated in horsepower.  The total work depends on how much
fuel is burned in the boiler's furnace.
   Electric power (watts) is the product of volts times amps. But when using
a battery for electrical power, raising the current that is drawn out drops
the pack's voltage.  So the power drawn out is about the same, while
propulsive force can vary greatly!
   "Too much" prop will drop the RPM, raise the current, drop the voltage
and waste power by generating heat in the motor and in the battery, reducing
the propulsion work done.
   "Not enough" prop will raise the RPM, drop the current, raise the voltage
and waste power by not accelerating air backwards as much as otherwise
possible, reducing the propulsion work done.
   You need to find the right prop, the "Goldilocks prop", for each battery,
motor, airplane and flight regime.
   New-chemistry battery packs either put the same power into the prop for
a longer time (more work). Or they produce the same work with less weight.
Both of which are plusses for flightcraft.  Of course, if the new batteries
store more work inside, it takes more work to fully charge them.
  The transfer of one source of power into an absorber of power is called
impedance matching. It is very noticeable when the impedance match is wrong
if you try to pedal a bike that is in the wrong "gear" (chain-and-sprocket).
  Three impedance matches occur when an audio amplifier (electronic) puts
power into a speaker (electromechanical) which in turn puts power into moving
the air (mass) which is heard as sound.  A different kind of "speaker" must be
used to put sound power into water for sonar, and it is called a hydrophone
or sonic transducer.
   With boats and aircraft, power transfer is done by propellers. Boat props
move denser water and so are smaller than air props.  But any given fuel
engine or electric motor can impart the same propulsive (reaction) force to
either medium.
   Any electric motor acts like a generator when it turns.  But the generated
current is opposite to the battery current coming in.  So if you over-prop,
this reverse current is too low, the battery current is too high and the
pack is drained inefficiently.  An extreme example is to hold the prop.
   If the motor is under-propped and thus over-revs, the reverse current is
too high.  Not enough current goes into the motor from the battery and not
enough torque/thrust is produced. An extreme example is no prop on the shaft.

   In a similar manner, generators act like motors when operating under a
load. This counter-torque reacts by fighting the driving engine's torque.
The more power you take out, the harder the engine must work to put power
in against this counter-torque, and so more fuel must be used. (The governor
on a construction-site generator maintains constant RPM automatically.)
 Any fuel model plane can be electrified if certain ratios are maintained:
 The aircraft-plus-radio-gear weight should never be more than the electric-
 motor-plus-battery weight if you expect good flying.
 Slow flying requires wing loadings of about 10 oz. per square foot or less.
 Fast flying (and thus fast landing!) can have double that wing loading.
  NOTE: There seems to be some disagreements on how NiMH battery packs
        should best be charged. The info given here is from articles in
        several model plane and car magazines by the guys who use them.
        See also:
Spread-Eagle with Cox .049 Venom glow engine. 
  This was an early glow-engine plane we used for "guided-missile" testing
of flight using binoculars.  There was a pyrotechnic flare in the back that
was visible for a long distance.