Today's Message Index:
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1. 12:07 AM - Re: RV10 primary elec sys wiring (airknot)
2. 06:39 AM - Re: Re: RV10 primary elec sys wiring (Robert L. Nuckolls, III)
3. 06:52 AM - Re: RV10 primary elec sys wiring (airknot)
4. 06:57 AM - Re: Re: RV10 primary elec sys wiring (Charlie England)
5. 07:17 AM - Re: Re: RV10 primary elec sys wiring (Charlie England)
6. 10:17 AM - Re: RV10 primary elec sys wiring (user9253)
7. 01:50 PM - Re: thermocouple calibration (Gerald Cruz)
8. 07:54 PM - Re: Re: RV10 primary elec sys wiring (Robert L. Nuckolls, III)
Message 1
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| Subject: | Re: RV10 primary elec sys wiring |
OK, got it. 1st thing I noticed is that you didn't totalize current for
[/quote]
the various phases of flight. Even without looking there, your 'typical'
consumption for everything is only 36 A. I'd look at cruise, with pitot
heat and boost pump included for worst case numbers. Re-examine what
you've included for each phase of flight. ex: Looks like you show 1 A
for the flap motor, for all phases of flight. Also, look carefully at
recommended circuit protection values for each device. ex: Even though
the flap motor may only consume 5 A, IIRC, the docs for it recommend
closer to 15 A for circuit protection due to startup surge.
I suspect that the number for the boost pump number is a bit low. The
automotive injection pumps typically used in a/c boost pumps typically
draw a *minimum* of around 4.5A; most will draw closer to 6A. That draw
doesn't really change with engine power, since they pump the same
quantity of fuel at the same pressure, regardless of flow to the engine
(excess is bypassed back to the inlet). The Walbro pumps (not the one
used by AFP) recommend a 20A circuit protection, due to startup surge
current.
I didn't do a line-by-line analysis, so you can probably find more power
savings.
Charlie
[/quote]
thank you, Charlie. will try!
...without experience in Experimental Aviation field, especially systems design,
this task seems to be unrealistic. i can't aloow myself to rely just on my assumptions.
thinking how to figure out...
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=497836#497836
Message 2
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| Subject: | Re: RV10 primary elec sys wiring |
>
>I didn't do a line-by-line analysis, so you can probably find more power
>savings.
>
>Charlie
>[/quote]
>
>thank you, Charlie. will try!
>...without experience in Experimental Aviation field, especially
>systems design, this task seems to be unrealistic. i can't aloow
>myself to rely just on my assumptions. thinking how to figure out...
Value to be secured in conducting detailed
load analysis is 2-fold.
(1) legacy design goals for TC aircraft dictate
that under worst case running loads, the ship's
alternator is loaded to only 75 or 80% of nameplate
rating.
This design point makes sure that there is
ample headroom in available energy not just
to run the ship's electro-whizzies . . . but
with energy left over to RECHARGE the battery
within a reasonable interval after takeoff.
This goal correctly assumes that the battery
will be capable of supporting design goals
for battery only endurance within some
acceptable time after takeoff. Of course, this
dovetails with another design goal that
calculates/demonstrates battery only endurance
with a battery that is nearing end-of-life
at 80% of new capacity.
The second goal for doing a load analysis
is to establish loads for the various phases
of flight to be compared with a hopefully
KNOWN battery condition. This exercise is
analogous to KNOWING how much fuel is aboard
to reduce the risk of mission failure for
having exceeded what should have been
easily predictable limits.
Your customer has stacked a lot of hardware
on the project . . . big engine, fat alternator,
big battery, backup battery and perhaps
things like heated pitot tubes. Assuming
all things are working as installed, this
project has energy to burn.
But some of this stuff is for backup . . .
to save the day in the 'event
of failure'. But all the backup in the
world may be of poor or no value if it
is not SIZED AND MAINTAINED to step up
to certain calculated/demonstrated
tasks.
This is good practice for any aircraft . . .
TC or OBAM.
Given the cited selection of hardware
for this project, I'm exceedingly
disappointed that a second engine
driven power source was not included
even if it's just a 4-pound, SD-8
spline driven alternator.
I'd trade a dozen stand-by batteries
for a single second-source of engine
driven power. Batteries are like house
plants . . . they demand consistent
attention. Alternators are more like
hammers . . . they'll be there when you
need them.
But of course, all this is academic
and un-quantified until the homework
is done.
"Knowing is not understanding . . . you
can KNOW a great deal and still UNDERSTAND
nothing." --C.F. Kettering--
"Until you have measured something and can
talk about it in numbers, your understanding
has barely scratched the surface of science."
--Lord Kelvin--
Bob . . .
Message 3
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| Subject: | Re: RV10 primary elec sys wiring |
(1) legacy design goals for TC aircraft dictate
that under worst case running loads, the ship's
alternator is loaded to only 75 or 80% of nameplate
rating.
This design point makes sure that there is
ample headroom in available energy not just
to run the ship's electro-whizzies . . . but
with energy left over to RECHARGE the battery
within a reasonable interval after takeoff.
[/quote]
Bob, thank you
I have read about this and hence affraid we should replace 60 Amps alternator with
at least 70 Amps, or I understand this incorrectly?
but anyway such huge load is strange.
regaring secondary alternator - perheps we will do an upgrade later, as I am 100%
feel the same as you
Alex
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http://forums.matronics.com/viewtopic.php?p=497854#497854
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| Subject: | Re: RV10 primary elec sys wiring |
On Wed, Aug 19, 2020 at 2:11 AM airknot <airkbp@gmail.com> wrote:
>
> OK, got it. 1st thing I noticed is that you didn't totalize current for
> [/quote]
> the various phases of flight. Even without looking there, your 'typical'
> consumption for everything is only 36 A. I'd look at cruise, with pitot
> heat and boost pump included for worst case numbers. Re-examine what
> you've included for each phase of flight. ex: Looks like you show 1 A
> for the flap motor, for all phases of flight. Also, look carefully at
> recommended circuit protection values for each device. ex: Even though
> the flap motor may only consume 5 A, IIRC, the docs for it recommend
> closer to 15 A for circuit protection due to startup surge.
>
> I suspect that the number for the boost pump number is a bit low. The
> automotive injection pumps typically used in a/c boost pumps typically
> draw a *minimum* of around 4.5A; most will draw closer to 6A. That draw
> doesn't really change with engine power, since they pump the same
> quantity of fuel at the same pressure, regardless of flow to the engine
> (excess is bypassed back to the inlet). The Walbro pumps (not the one
> used by AFP) recommend a 20A circuit protection, due to startup surge
> current.
>
> I didn't do a line-by-line analysis, so you can probably find more power
> savings.
>
> Charlie
> [/quote]
>
> thank you, Charlie. will try!
> ...without experience in Experimental Aviation field, especially systems
> design, this task seems to be unrealistic. i can't aloow myself to rely
> just on my assumptions. thinking how to figure out...
>
> Naa... you can do it; you're just learning how right now. You've started
with the right techniques, and you're smart enough to ask if there's stuff
that you don't know that you don't know.
You have the basic analysis tool already, with the loads spreadsheet. Just
tweak it a line at a time. 'Fly' each component line, from startup to
shutdown, and update the spreadsheet to reflect that. Ex: Flaps would
(possibly) get activated for a few seconds prior to takeoff, and again for
a few seconds after liftoff. Negligible load on the alternator for those
actions, and then zero load until in the pattern for landing. And in most
light planes, not a requirement for landing, if conservation of electrical
energy was critical for other stuff, like landing lights at night. Plug
that into that line of the spreadsheet. Then move to the next line and go
through the same process. Slightly different for something like a Comm
radio; it will have very low but continuous energy demand, except when
transmitting. But transmit demand is 'reasonable' (unquantified, I know),
and will be in very short, infrequent 'blips'. So while you can't ignore
the demand when sizing circuit protection/wire size, you might be able to
ignore the peak transmission demand when looking at alternator capacity.
Those intermittent loads rarely all hit at the same time, so the alternator
would rarely (if ever) be tasked with supporting max consumption of every
device at the same time.
As I think I mentioned earlier, many mfgrs don't bother to give you
accurate current consumption numbers for their products in an 'idle' state
since they're focused on having you size circuits for worst case
consumption. I think you can already see that your 60A alternator has
plenty of capacity for your loads. If you're set on using a backup battery
for an 'E' bus, you could wait until you have all the hardware on hand to
measure each component's real world consumption, and size the battery to
handle total real world loads for your desired duration. (If you need help
with how to do that, just ask.)
But I must say that if I were planning on an IFR platform that's totally
dependent on electrons to keep the panel lit, I'd give serious thought to
Bob's recommendation of adding a 2nd alternator rather than a 2nd battery.
That 2nd battery is like a very heavy, very small tank of aux fuel, that
will have a relatively small capacity, and due to the aging process, a
shrinking capacity. An aux alternator, on the other hand, will cost a bit
more up front but will be lighter, and will supply energy until available
fuel is exhausted or the prop stops turning. If that happens, you're going
to be on the ground in less time than any decent primary battery will
last, anyway. With a primary alternator failure, it could be the difference
between knowing you have to be on the ground in 45 minutes (with everything
under you below minimums), to paying a bit more attention to bus voltage
while you continue your original flight plan to your destination.
Having fun yet?
Charlie
Message 5
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| Subject: | Re: RV10 primary elec sys wiring |
On Wed, Aug 19, 2020 at 8:58 AM airknot <airkbp@gmail.com> wrote:
>
> (1) legacy design goals for TC aircraft dictate
> that under worst case running loads, the ship's
> alternator is loaded to only 75 or 80% of nameplate
> rating.
>
> This design point makes sure that there is
> ample headroom in available energy not just
> to run the ship's electro-whizzies . . . but
> with energy left over to RECHARGE the battery
> within a reasonable interval after takeoff.
>
> [/quote]
>
> Bob, thank you
>
> I have read about this and hence affraid we should replace 60 Amps
> alternator with at least 70 Amps, or I understand this incorrectly?
> but anyway such huge load is strange.
>
> regaring secondary alternator - perheps we will do an upgrade later, as I
> am 100% feel the same as you
>
> Alex
>
Bob,
Should that 'worst case running loads' thing be a bit more... nuanced (for
lack of a more precise term), especially for new arrivals who are just
beginning to understand electrical loads? The current situation is a great
example. The literal worst case has flaps, landing lights, comm
transmitter(s), etc etc all running at the same time, and continuously.
This is obviously not going to happen. Hence the need for some..nuance...
in defining 'worst case'.
Or am I totally wrong?
Thanks,
Charlie
Message 6
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| Subject: | Re: RV10 primary elec sys wiring |
A 60 amp alternator will be more than enough for your plane unless you can
show that more is actually needed. One item needs to be removed from your
list: the alternator field current. A rating of 60 amps means that the alternator
will put put at least 60 amps in addition to the field current. In other words,
the alternator will put out 64 amps. The rating of an alternator is a nominal
value that depends on cooling and RPM. If kept cool and turned fast enough,
an alternator will put out much more than its nominal rating.
I would be surprised if your RV-10 electrical system will draw more 30 amps continuously.
Like Charlie suggested, measure the actual current. That can be done without
starting the engine by powering the system with a battery or power supply.
--------
Joe Gores
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| Subject: | Re: thermocouple calibration |
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| Subject: | Re: RV10 primary elec sys wiring |
>
>
>Bob, thank you
>
>I have read about this and hence affraid we should replace 60 Amps
>alternator with at least 70 Amps, or I understand this incorrectly?
>but anyway such huge load is strange.
>
>regaring secondary alternator - perheps we will do an upgrade later,
>as I am 100% feel the same as you
Like others on the List, I am skeptical of your
load figures. 60A is generally more than adequate
for a single engine airplane unless you have electric
cabin heater, heated seats, etc.
In all candor sir, we should beg your forgiveness for
loading such a task in the midst of pressing
demands from your 'clients'.
The 100% best way to get load values is go MEASURE
them. Easily done as you start lighting up the panel
with shore-power support. In fact, I just this minute
ordered another power supply like this
https://tinyurl.com/y42yceb4
0-16v, 0-10A, accurate digital displays. EXCEEDINGLY
handy for precision recharging of lithium cells in
a constant voltage, constant current mode. Would
be similarly handy for surveying your project's
accessory loads. Just pull the breaker/fuse for
an appliance. Apply 14.2 Volts to its feeder.
READ the running load from the face of the power supply.
I doubt you'll have many devices, if any, that
draw more than 10A each.
The critical feature of this exercise right
now is to segregate various loads into their
respective flight functions. There are few
airplanes that are operated with everything
up and running at the same time. Do not include
transient loads like landing lights and transmitter
current draws. You're attempting deduce the
ENERGY budget for various phases of flight.
Surprisingly enough, engine starters, flap
motors and transmitters are all but insignificant
in this study. ENERGY is measured in watt-seconds,
etc. A starter demands lots of WATTS but for
only a few seconds and then only once per flight
cycle. A suite of legacy incandescent navigation
lights (3 bulbs at 2A each) takes 3 x 2 x 14 x
10800 about 900,000 watt-seconds over the course
of a 3-hour night flight! Nav lights used to
be the most energy hungry system on most light
aircraft. You DID NOT include nav lights in
your battery-only endurance calculations.
That's what all those columns are for in the
load analysis . . . we can be 99% confident that your 60A
machine will be plenty.
Bob . . .
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