Electric power WAS : Diamond stab cross section - Dean Pappas

[Keith Black]

A few weeks ago I put together a list of questions directed to those already
flying electric pattern in hopes that their responses would help those
considering electric pattern. Unfortunately there were no responses to the
questionnaire on this mailing list and only two responses on RCU (thanks to
Steve K. and Tony F. for responding).

Based on the information I've been able to gather via these responses and
other extensive sleuthing I'm not convinced that the technology is at a
point that it will meet "my" objectives. This is not the result I wanted
from the research, but it's what I concluded.

My key concerns are 1) flight time, 2) reliability, and 3) life-span of
batteries.

1. Flight Time: From what I can tell the max reasonable flight time today
seems to be around 10 minutes. There are batteries with more capacity,
however this comes with a weight penalty. Also, I don't think the limited
time is purely a battery capacity factor, I think there are also concerns
about how log the batteries can supply the high amp load before being
damaged or getting too hot. If someone has some hard facts on this please
speak up.

For me 10 minutes per flight would be a big step backwards since I normally
fly 15 to 18 minutes per flight. Being a new Advanced pilot I have a LOT to
learn and just can't accomplish this without putting in a lot of stick time.
Also, since my practice time is limited I need to knock out three of four
15-18 min flights in a pretty short time. I can't just sit around the field
all day.

2. Reliability: I am 100% confident that a brushless motor operated as
designed will last longer than most pattern planes. Brushless motors are
extremely efficient and the ideal power plant. However, there are other
things to consider. 1) Will the motors hold up under the 60+ amp loads over
time, heat may be a problem. 2) How are the gear boxes holding up (where
applicable)? and 3) How will the ESC (Electronic Speed Controls) hold up? I
know from observation and experience in other electric applications that
ESC's get burned out, sometimes much more often than the electric guys want
to admit. Through all the research I did related to electric pattern I
wasn't unable to find anyone that has hundreds of flights on a single speed
control and motor combo. It may be possible, but no one out there is
admitting to such luck.

3. Life-span of batteries: This of course is the thing that everyone zeros
in on as the cost of operation. Assuming the motor and ESC don't need
frequent repair or replacement then we need to make sure we get enough
flights per battery pack to justify the $700 per flight pack. On a personal
note I'm not looking at electric as a cheaper alternative to glow. I would
go with electric even if it's incrementally more expensive because there are
many other benefits that to me justify a premium. However, the most flights
I've heard on a single pack is around 100 flights. I've also heard of many
failures long before 100 flights. In fairness much of this may be due to
early adopters of new technology. In most of these cases I think the mfgs
are replacing the batteries. With the new higher C rated batteries the most
I've heard of is around 50 flights. I'm not saying they die after 50, but
I've not found anyone that has exceeded that yet, possibly because they are
relatively new.

I'm not suggesting that my findings are all accurate. I'm just sharing what
I've been able to ascertain based on what others have been willing to share.
I'd love to learn that indeed the current state of electric is much further
along because I'm anxious to go electric when the technology is mature
enough to meet my needs. If I felt that were the case I would strongly
consider going with electric on my winter project.

Keith Black

----- Original Message ----- 
From: <JonLowe at aol.com>
To: <discussion at nsrca.org>
Sent: Monday, November 22, 2004 2:33 PM
Subject: Electric power WAS : Diamond stab cross section - Dean Pappas


> I hope Jason Shulman pops in here on the cost of electrics, but I
understand that the big electrics are getting nowhere close to 1000 cycles
out of their batteries.  What I hear is less than 100 cycles, in most cases
CONSIDERABLY less.  Why, I don't know.  At $600 a pack, the cycles you get
will change the cost effectiveness a lot!
>
> Jon Lowe
>

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