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jpx(at)qenesis.com
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 Posted: Tue Oct 09, 2007 7:54 pm Post subject: 14V verus 28V |
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Bob, I just read your comments on Greg Richter's "Aircraft Wiring For
Smart People". I found it very enlightening, since I had originally
accepted most of it at face value. I really like your style of
including the references for your facts. I am eagerly awaiting my
copy of your book to eventually be delivered by Canada Post that I
ordered a week ago.
One part of your comments that most interested me was characteristics
of the choice of a 14V versus 28V system. Prior to any thought at
all, I had assumed I would build a 14V airplane. Greg's article
originally prompted me to consider a 28V one.
Most equipment will work happily with any voltage. A few parts are a
little harder to get, or slightly more expensive. Many aircraft
manufacturers now produce 28V products. Cessna has built many more
aircraft than I have, so holding them up as an example seems
practical. So I have been planning a 28V airplane.
The only hitches I have found so far, is that the company I might buy
an inexpensive autopilot from sells only 14V servos and Dynon sells
only a 14V heated pitot tube. This can be solved with a DC-DC
converter, but that adds a nice heat source under the instrument panel
and another part to fail (although not a critical one for a VFR only
airplane).
So after reading your comments, and realizing that Dynon expects that
virtually all of their market to build 14V aircraft, I am back to
thinking I should build a 14V system. This certainly simplifies a few
things.
Before I make the final decision for 14V, do you know of any important
reasons in favor of a 28V system ? Most reasons, such as slightly
lighter weight are insignificant really.
Thanks,
Jeff Page
Dream Aircraft Tundra #10
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rtitsworth
Joined: 16 Jan 2006
Posts: 76
Location: Detroit, Mi
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| Posted: Tue Oct 09, 2007 8:31 pm Post subject: 14V verus 28V |
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Jeff,
Lots of emotion on 24v vs 28v - features and compromises on both sides.
One advantage of 28v is often overlooked is that: essentially twice the
power is available from the alternator for essentially the same alternator
weight. This comes into play if you're building an all electric, dual
alternator bird. The backup alternator is typically smaller than he main
one. With a 28v system the smaller backup alternator (say 20 amps = 480
watts) will power more stuff, than a similar 14v Alternator (20 amps = only
280 watts). That may or may-not be significant depending on the bird you're
building and/or it's mission profile.
Rick
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nuckolls.bob(at)cox.net
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| Posted: Wed Oct 10, 2007 5:10 am Post subject: 14V verus 28V |
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At 11:52 PM 10/9/2007 -0400, you wrote:
| Quote: |
Bob, I just read your comments on Greg Richter's "Aircraft Wiring For
Smart People". I found it very enlightening, since I had originally
accepted most of it at face value. I really like your style of
including the references for your facts. I am eagerly awaiting my
copy of your book to eventually be delivered by Canada Post that I
ordered a week ago.
One part of your comments that most interested me was characteristics
of the choice of a 14V versus 28V system. Prior to any thought at
all, I had assumed I would build a 14V airplane. Greg's article
originally prompted me to consider a 28V one.
Most equipment will work happily with any voltage. A few parts are a
little harder to get, or slightly more expensive. Many aircraft
manufacturers now produce 28V products. Cessna has built many more
aircraft than I have, so holding them up as an example seems
practical. So I have been planning a 28V airplane.
The only hitches I have found so far, is that the company I might buy
an inexpensive autopilot from sells only 14V servos and Dynon sells
only a 14V heated pitot tube. This can be solved with a DC-DC
converter, but that adds a nice heat source under the instrument panel
and another part to fail (although not a critical one for a VFR only
airplane).
So after reading your comments, and realizing that Dynon expects that
virtually all of their market to build 14V aircraft, I am back to
thinking I should build a 14V system. This certainly simplifies a few
things.
Before I make the final decision for 14V, do you know of any important
reasons in favor of a 28V system ? Most reasons, such as slightly
lighter weight are insignificant really.
|
Weight differences are minuscule to non-existent and very
few aircraft really need the 2x power capability for alternator
sizing . . . so the big driver for me is that when you go
28v you lock yourself out of all current automotive offerings
for devices (quite suitable for use on our airplanes) and you
have to build your own battery from 2x 12v devices or purchase
a "real" 24v battery - invariably more expensive and heavier
for the same contained energy.
There's just no compelling reason for considering 28v in
the first place unless you're planning on exploiting
the used/refurbished hardware from tens of thousands
of Cessnas . . . and that's a step backwards.
Bob . . .
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n395v
Joined: 10 Jan 2006
Posts: 450
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| Posted: Wed Oct 10, 2007 8:35 am Post subject: Re: 14V verus 28V |
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I built with a 28V system for what I thought were some good reasons and then had to deal with the nightmare of much of what I needed not being available in 28V so I had to add a converter (more weight and expense)
Then I had to add a 14v bus and wiring (more complexity)
Net result
More weight
More cost
More expense
Net benefit... I'll let you know if I ever realize any.
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Milt |
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dstroud(at)storm.ca
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| Posted: Wed Oct 10, 2007 10:18 am Post subject: 14V verus 28V |
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I'm in a similar boat, Milt. I muckled onto a real nice Huosai engine,
prop and ss exhaust, then only to find a sweet deal on a Jasco 28v
alt. All dirt cheap so, for me, a good enough reason for 28v. I already
had a 14v King radio though and foolishly thought I'd go thru the 2 x 14v
battery combo and pull off 14v halfway with a battery equalizer, allowing
me to pick and choose the rest of the components 28 or 14 v only to learn
that the battery equalizer costs about $750 which is about what a new alt
would cost. So..my solution is to go mostly 28v with a drop converter to 14v
for one or two items. With a payload of 1,800 + lbs I don't need to watch
every ounce but I am mindful of it.
David Stroud Ottawa, Canada
C-FDWS Christavia
Fairchild 51 under construction
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Bruce(at)glasair.org
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| Posted: Wed Oct 10, 2007 10:52 am Post subject: 14V verus 28V |
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The main reason Cessna, Piper, and Beech all went 28v is commonality of
production. There's nothing wrong with 28v, you just have to shop for your
electro whizzies at the local truck stop rather then at NAPA.
Bruce
www.Glasair.org
Glasair III, 28v
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mlas(at)cox.net
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| Posted: Wed Oct 10, 2007 7:24 pm Post subject: 14V verus 28V |
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Jeff,
When I was building my ALL electric Lancair I went round and round on
this issue. I couldn't find any more than three reasons for a 28v
system. 1 Anti-ice/de-ice systems, 2 the need to have a Christmas tree
amount of lights, and 3 air conditioning. Most of us are not building
airplanes with ice systems, or air conditioning and lighting now comes
in low use systems. My airplane has all the bells and whistles as far
as EFIS, Auto pilot, In-flight Entertainment, Electron ignition,
electronic engine monitor, back up EFIS, ect. With the navigation and
landing lights off my nominal use of power is about 15~20 amps (at) 14vdc.
Mike
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rtitsworth
Joined: 16 Jan 2006
Posts: 76
Location: Detroit, Mi
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| Posted: Wed Oct 10, 2007 9:12 pm Post subject: 14V verus 28V |
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The only components that I could not find readily available in 28v (vs 14v)
were the Ray Allen trim servos (and they sell small converters). Most all
28V aircraft components are now essentially the same price as 14v. I do
have a 28-14V converter, but it only drives the cigarette style power ports.
Rick
All electric, Dual Alt, Lancair ES
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jpx(at)qenesis.com
Guest
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| Posted: Thu Oct 11, 2007 7:44 pm Post subject: 14V verus 28V |
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I appreciate everyone's opinions and the consensus is clear. I will
be building a 12V aircraft, without worrying that I had missed
something important.
Thanks !
Jeff Page
Dream Aircraft Tundra #10
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