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Basics of Electric Flight
I really enjoy getting together with clubs and speaking to
the group about the basics of electric power. However,
because there is so much information that needs to be
passed along, it would be difficult, if not impossible, for
those attending to remember much of the pertinent
information. For that reason, it's better to write up the
basic guidelines so that those who are interested in
getting into electrics would have the information available
for reference at a later date.
Here goes. I'll keep the numbers as simple as possible to
avoid unnecessary confusion.
OK, here's how it all shakes out. The basic power
required to fly an electric model is as follows:
Direct Drive Systems 60 watts/pound
Gear Drive Systems 50 watts/pound
Mild aerobatic performance 70-80 watts/pound
For all-out aerobatics 100-110 watts/pound
3-D performance 150 watts/pound or more
The above numbers are based on models with wing
loadings from 8-16 oz/square foot. As with gas models,
higher wing loadings require more power since they must
fly faster to support the added weight. By the same token,
a lightly-loaded model with a wing loading in the 3-5
oz/square foot range will fly very well at 25 -30
watts/pound.
What's a 'watt'; and where can I get some? Wattage is
the term used in electric flight to relate the level of power
that an electric drive system will produce. To relate it to
terms we're familiar with, 746 watts = 1 horsepower. To
calculate the wattage delivered by a given system looks
like this: amps x volts = watts. So where do these
numbers come from and how do I know how many volts
and amps are needed to fly a given model?
Okay, let's say you want a mildly aerobatic sport model
with a 14 oz/square foot wing loading that will weigh in at
2 pounds. We already know that the power requirement
for a model like this is about 70 watts/pound, so we're
going to need to generate about 140 watts. Let's assume
that you are going to use an eight-cell Ni-Cd battery. At
1.2 volts per cell, eight cells will deliver 9.6 volts. To
arrive at the necessary current draw to achieve 140
watts, simply divide 140 (watts) by 9.6 (volts) and you
arrive at 14.58 amps.
Now, let's assume that you have a three-cell Li-Poly
battery for the model, which is rated at 11.1 volts. The
formula is the same; 140 (watts) divided by 11.1 (volts) =
12.6 amps. As you can see, as the available voltage
increases, the lower the current draw needs to be to
deliver the necessary wattage.
Minutes
Meeting called to order around 2:30 pm. 7 members
present.
Rusty Selkow made a proposal to obtain a plaque for a
member of the year award to be handed from one
member to the next, something that could be engraved
yearly. Nothing has been finalized on this.
President Doug Goldman made a proposal/request that
our club’s Board Members continue with the finalization
of setting up membership participation award point
system. Details such as the number of prizes, and what
prizes will be awarded still need to be determined. These
details to be worked out by April 1st. A forum is available
on our club website for discussing suggestions/concerns
with the new point system. Our club officers came to a
mutual agreement that they WILL NOT be eligible for
participation in the membership point/prize award system.
This was decided in an attempt to make it fair to all
members.
Rusty Selkow is still checking into the possible
incorporation of our club and the details of the Aquafest
schedule.
Wayne Barta volunteered to organize and promote this
year’s Aquafest Float fly if we have one. This was
arranged via a phone conversation with Wayne by
president Doug Goldman during the meeting.
Kevin Kuehn to contact Ron Kopp and verify the date of
our Aquafest fun fly to be held in Moon Lake Park on
Sunday June 18th.
Event Committee Chairman Leon Olszewski. made a
proposal that our club give out two trophies this year:
possibly one for best of show and one other category.
Rusty made a motion for the club to allot $50 or less for
this purpose. Kevin seconded the motion. More details to
come in the future.
Leon Olszewski mentioned that he would be extending
his runway on the south end for better landing
approaches. Volunteers are requested to help with the
project when the weather permits.
Secretary Kevin Kuehn requested permission to renew
our club’s AMA charter/flying site insurance for 2006. All
members present agreed that both our Moon Lake Park
and our South Branch (Leon’s) field should be renewed
for 2006. Kevin also requested that Rusty confirm our
float fly date in the very near future so that we can also
insure Grampa’s Train Shop with the AMA for that one-
day event.
Treasurer’s Report given.
Kevin Kuehn made a motion to adjourn the meeting.
Motion seconded, meeting adjourned around 3:30pm.
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