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APC 17 x 8E propeller powered by a 5,000mAh 6S battery
draws about 80A, 1,750 Watts @ 7,500rpm (these are the
initial, static/non-fl ying readings using a fully charged battery).
And in-fl ight data from the ELogger shows that the average
current draw throughout a normal fl ight is about 40A with the
maximum current draw during full-throttle events about 72A.
Once you run your motor on the ground you can compare
your numbers to these as well as the current specifi cations
for the motor. The specifi ed limits for the RimFire 1.20 are
50A constant current and 80A surge current. Because the
setup we are using draws a maximum of 72A in the air, this
is within the specifi ed 50A constant/80A surge limit and is an
acceptable combination as long as full throttle is used only in
short bursts (say, during up-lines or on takeoff).
So, if you are using a RimFire 1.20 and your Watts-Up meter
tells you it is pulling around 80A on the ground, you will know
everything is working normally. However, if for some reason
you are not getting close to those numbers, you will know
something is wrong. It could be a greatly imbalanced propeller,
too large of a propeller, a damaged motor, defective wiring,
etc. Find and correct the problem before fl ying your Sequence.
CAUTION: Never run the motor on the ground for more
than a few seconds. Otherwise, you may overload the
motor, battery or ESC.
Another smart thing you can do is record the fl ight time and
capacity used from the battery for each fl ight in a log book.
Record the fl ight time (from the timer on your transmitter or
other timer) immediately after each fl ight and record how
much mAh (capacity) went back into the battery read from
the display on your charger. (Number your fl ight packs so you
will be able to correlate each battery to each fl ight.) When
you know the fl ight time and recharge capacity (capacity
used for the fl ight) you can calculate valuable data indicating
how your motor is performing and whether or not your fl ight
time is too long or too short.
For the Sequence 1.20 for example, say we record a 6
minute fl ight. And back in the shop we record that the battery
took 4,000mAh to recharge. With these numbers we can
calculate the average, in-fl ight current draw:
4,000mAh (used in fl ight) / 1,000 = 4 Ah / 6 minutes =
.67Amps/minute x 60 minutes = 40A.
The average, in-fl ight current draw was 40 Amps. Even
though we know the motor is drawing 72A during brief, full
throttle bursts, the average current draw over the duration of
the fl ight was only 40A so the motor and ESC are operating
comfortably within their limits.
Another calculation we can make is the percentage of charge
remaining in the battery. If 4,000mAh was used from a 5,000mAh
battery, 20% was remaining. This is generally accepted as a
safe reserve. Flying your LiPos down to no further than 20%
capacity is a good way to extend its life and performance.
Based on this information, you may want to start out setting
your fl ight timer to a conservative four or fi ve minutes. After
the fl ight note the exact fl ight time and the recharge capacity
in your log book. Calculate the percentage of charge that
was left in your battery and adjust your fl ight time accordingly.
Keep in mind that many variables can determine your in-
fl ight current consumption such as how much you used full-
throttle, weather conditions, battery condition, etc. Due to
these variables it is always a good idea to calculate your
maximum fl ight time conservatively.
Range Check
Don't forget to perform your usual ground range checks as
written in the instruction manual that came with your radio
system to be certain it is operating correctly.
ENGINE / MOTOR
SAFETY PRECAUTIONS
Failure to follow these safety precautions may result
in severe injury to yourself and others.
Keep all engine fuel in a safe place, away from high heat,
sparks or fl ames, as fuel is very fl ammable. Do not smoke
near the engine or fuel; and remember that engine exhaust
gives off a great deal of deadly carbon monoxide. Therefore
do not run the engine in a closed room or garage.
Get help from an experienced pilot when learning to operate
engines.
Use safety glasses when starting or running engines.
Do not run the engine in an area of loose gravel or sand; the
propeller may throw such material in your face or eyes.
Keep your face and body as well as all spectators away from the
plane of rotation of the propeller as you start and run the engine.
Keep these items away from the prop: loose clothing, shirt
sleeves, ties, scarfs, long hair or loose objects such as
pencils or screwdrivers that may fall out of shirt or jacket
pockets into the prop.
Use a "chicken stick" or electric starter to start the engine.
Do not use your fi ngers to fl ip the propeller. Make certain the
glow plug clip or connector is secure so that it will not pop off
or otherwise get into the running propeller.
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