nuckolls.bob(at)cox.net
Guest
|
 Posted: Sat Jul 05, 2008 2:54 pm Post subject: AeroElectric-List Digest: 29 Msgs - 07/03/08 |
 |
|
At 08:23 PM 7/4/2008 -0400, you wrote:
| Quote: | Bob, you made a point yesterday, that I had not thought through. I do not
have an electrical/charging/output performance card in my flight test
deck. I do of course, have operational performance checks planned on all
my avionics, but I don't have a specifice plan for checking out the
performance of my "as designed" electrical system (not flying yet).
Wonder if you or anyone else can recommend specific flight test procedures
to accomplish a reasonable system test in a sequenced and logical
form? My system is all electric with a Plane Power 60 amp, internally
regulated main alternator, an SD-8 backup, all wired a la Z-13/8 with
"auto excitement" of the SD-8. I have an EDM-900C engine monitor with
voltage and amperage readings and the B&C BC207-1 over/under voltage
sensor (not yet wired up). Any recommendations as to wiring changes that
might facilitate the above would also be appreciated.
|
You wouldn't want to know what we go through to prove
the concept for a fresh system design on a TC aircraft.
Those-who-know-more-about-airplanes-than-we-do can
ask a LOT of questions for which only an approved test
plan with lots of data gathering followed by a test
report weighing at least 5 pounds is indicated.
The key questions for your as-installed equipment
are pretty simple.
What RPM on the engine will produce rated output
of the main alternator? I would test this on the
ground with a snap-on DC ammeter around or (shunt in
series with) the alternator b-lead. Perhaps you have
altenrator load-meters already installed that can
serve this purpose? Hook a battery tester . . .
http://aeroelectric.com/Pictures/Battery_Testers/HF_Carbon_Pile_Load.jpg
across the ship's battery. Use the battery tester
to add load until the alternator produces full
output at say 2200 rpm and then reduce rpm until
alternator output begins to fall off. The reading
on the battery tester is irrelevant. You're only
using it as a load bank to ADD to ship's loads
until the alternator output is maxed out. The
bus voltage should not fall below 14.0 volts
until the rpms are too low to support full output
from the alternator.
The SD-8 has to be tested in cruising flight.
Turn the SD-8 on, turn main alternator OFF,
adjust ships loads until to show that you can
maintain 13.0 volts or more at 10.0 amps
of SD-8 output.
Now, if I were putting this system into a TC
aircraft, I would have to demonstrated cooling
under hot-day, Vx climb conditions. Of course,
heating is a slowly changing condition that
is almost never demonstrable in a hot-day
environment. So we do a lot of testing. Average
a lot of data and then correct that data to
expected hot-day performance 'cause today just
wasn't that hot.
When you're testing 600A generators, it can get
pretty warm in the cabin when those load banks
are tossing out the heat produced by those big
honk'n generators!
| Quote: |
BTW , I don't see over/under voltage detection or indications on
schematics for the SD-8 typically. Is the expectation that the BC207-1
will provide adequate early warning of main alternator failure and that
then battery and SD-8 power will be adequate for any reasonable endurance
bus/fuel remaining scenario---such that further warning that the SD-8 has
failed too is considered an unnecessary complication?
|
Some form of low voltage indication on the e-bus
is a good thing. Not low voltage warning, only a
readout. You won't be concerned about e-bus voltage
EXCEPT after a main alternator failure. Further, you
MIGHT just choose to load the SD-8 down to the level
where a low voltage warning might come on (13.0 volts)
so just a meter is fine.
| Quote: |
If the SD-8 failed after the main alternator had already failed on my
aircraft, my battery (Odyssey 925) is the final arrow in the quiver.
|
Yes . . . but dual failures of any kind in the electrical
system on any one tank of fuel is exceedingly rare. So rare
in fact that we don't even consider probability rates for
loss of both alternators in Part 23 airplanes and only
in Part 25 aircraft used in flight-for-hire in IMC. Even
then, failure rates for dual loss are always comfortably
small.
| Quote: | The 925 is a monster though and personally, I would already be headed for
good weather/divert/home base/whatever if the SD-8 let go. I don't think
I need another warning system, but thought I'd ask the group. What's the
consensus thinking on this one?
|
Exactly. Z-13/8 with a properly maintained SVLA battery
has better overall system reliability than that which flies
in any Part 23 aircraft and most Part 25 aircraft. LV warning
for the main bus, voltmeter for the e-bus and good preventative
maintenance for the battery will let you launch with zero
concerns for electrical energy sufficient to the task.
Keep in mind that there are thousands of OBAM aircraft
flying where the SD-8 is the only engine driven power
source. I would not attempt to dissuade you from unplanned
termination of flight should you have only the SD-8 working.
But for my airplane, I'd KNOW that I can do it battery only.
The three-layer energy development system embodied in Z-13/8
offers an opportunity to enjoy 100.0% reliability of the
electrical system for the purpose of completing the intended
mission . . . IN SPITE OF INEVITABLE FAILURES. That's what
failure tolerance is all about.
Bob . . .
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
|
|
|
Get Email Distribution Too!
FAQ
Search
Memberlist
Usergroups
Register
Profile
Log in to check your private messages
Log in
