e-power - some operational parameters to consider.

[Mike McConville]

That was very insightful. Thanks! As one who has a lot to learn about ep, I
really appreciate that info.

-----Original Message-----
From: Keith Black [mailto:tkeithb at comcast.net]
Sent: Thursday, August 07, 2003 4:32 PM
To: discussion at nsrca.org
Subject: Re: e-power - some operational parameters to consider.


Here are some comments on a few of Eric's points.
 
2. No real idle or purr for stall turns and spin entry control.
This could easily be handled with a throttle up switch or flight profile.
 
3. Twitched in the air when gunned.
Should be easy to deal with with throttle curve/expo. The bigger planes I've
seen fly were smooth as silk.
 
5. No RX pack required
Actually some of the serious electric flyers with bigger power plants do us
a separate RX pack.
 
8. Lots of wires - battery connector a weak point  -got hot
True, but if separate pack is used for RX worst case is a dead stick.
 
11. When the battery "dumped" it was LAND NOW!
Again, with separate RC pack this is no worse than a dead stick. Even when
using a BEC without a separate RX pack electrics give you an indication of
when the battery is fading. Furthermore, when the BEC kicks in if you
throttle down you almost always can throttle back up and get a short run
before it stops again, this certainly isn't the case for an IC engine when
it goes dead stick.
 
12. Needed spare 12 V battery - one or two charges and your car will not
start after the inverter was finished producing 30v DC from your car
battery. 
Carrying a spare 12 V battery is normally done by serious electric guys, but
in lieu of doing this you can just start your car and charge off of the
alternator rather than running your battery down. Carrying the spare 12 V
battery is a hassle since they are heavy, but with electrics you don't need
to carry a starter, a starter battery, chicken stick or glow starter. You do
however end up with more chargers. FYI, most guys just leave the big 12 V in
their trunk and never need to lug it to the field. To charge you just take
your battery pack to the car, not the entire plane.
 
14. The packs did not really cool down enough to charge at the field - even
using blower tube.
I share your concern here, but there electric guys I know never have an
issue here, especially with three batteries.
 
16. Extreme care of TX required when motor armed - lose a finger at any time
without warning if throttle just nudged 
Very good point, this is dangerous and difficult for IC guys to get used to.
I've seen many people retrieve electric planes after landing and grab the
prop, or near the prop. VERY DANGEROUS!. On the big engines it's a common
practiced to use an arming plug so the radio can be activated but the engine
will not be armed until the moment just before taking off. Likewise the
FIRST thing you do when retrieving the plane is remove the arming plug, then
pick up the plane. 
 
17. Ran low-throttle failsafe from bench installation onwards.
I would disagree with this because if you did loose radio contact and the
plane crashed the electric engine would keep running until it tore itself
up. One thing that IC engine guys don't consider is that after a crash, flip
over, etc. that electric engine will keep running until the throttle stick
is brought down, even after the prop hits the ground. Newbies to electric
are used to the engine stopping when the prop hits the ground, not so with
electric. 
 
18. Test "burp" in workshop to show wife, blew pliers and squares and
wrenches clear off the bench. - Big dust cloud in shop...
Clearly an indication of not realizing how powerful these engines are ;-)
Keep in mind that with a flip of a circuit inside the speed control electric
motors can go from cold to power that exceeds the top end of a DZ in an
instant!
 
Another interesting point about electric motors that differs from IC motors.
With IC motors you have to find the "right" prop that pulls enough but
doesn't bog down the motor. With electric you can keep adding more prop and
it will just draw more power. Your only limitations are how much battery you
have (i.e. flight time) and how many amps your speed control and motor will
tolerate. 
 
Something that no one has mentioned, with electric you don't need a throttle
servo.
 
Having spent time around electrics there's no question in my mind that
electrics are far preferable assuming the following: 
1) Cost of batteries is reasonable, (remember you have to have multiple
batteries), 
2) Flight durations are equal to IC flight times (15+ minutes), and 
3) Power is consistent throughout the flight (in other words as the battery
drains the engine will be less powerful). This is actually related to #2
flight duration.
 
Last observation, the best way to convince most people of the potential of
electrics is to see one fly in person.
 
Keith

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