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Starter Contactor location on a Long-EZ

 
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Airdog77



Joined: 24 Nov 2013
Posts: 76
Location: Northern Virginia

PostPosted: Fri Jan 26, 2018 10:12 am    Post subject: Starter Contactor location on a Long-EZ Reply with quote

Bob, et al.

BACKGROUND: I was doing some research on Brian DeFord's Cozy that burned up on the ramp some years back due to an electrical issue with the starting/charging system (i.e. electrical wires through the firewall). That led me to some info where a number of canard builders are mounting their STARTER contactors on the cold/forward side of the firewall (again, these are pushers).

After assessing it, I like the idea of not having my big power cable --coming from the BATTERY contactor up front-- traversing the firewall. The net result of moving the starter contactor to the cold/forward side of the firewall would be that only 2 wires/cables (6 AWG starter wire & 8 AWG ALT B lead) would then require traversing the firewall versus 5 wire/cables if I leave the starter contactor on the hot/aft side of the firewall... the big bubba cable from the battery contactor of course being one of those 5 traversing wires/cables.

The physical location change would require about 1-2" longer runs for the starter cable and B-lead wire, which to me seems minimal and non-issue. I do however want to ask for a crosscheck on this plan to ensure I'm not missing any possible critical issue(s).

Thanks,
Wade


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PostPosted: Fri Jan 26, 2018 2:52 pm    Post subject: Starter Contactor location on a Long-EZ Reply with quote

At 12:12 PM 1/26/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: "Airdog77" <Airdog77(at)gmail.com>

Bob, et al.

BACKGROUND: I was doing some research on Brian DeFord's Cozy that burned up on the ramp some years back due to an electrical issue with the starting/charging system (i.e. electrical wires through the firewall). That led me to some info where a number of canard builders are mounting their STARTER contactors on the cold/forward side of the fireall (again, these are pushers).

After assessing it, I like the idea of not having my big power cable --coming from the BATTERY contactor up front-- traversing the firewall. The net result of moving the starter contactor to the cold/forward side of the firewall would be that only 2 wires/cables (6 AWG starter wire & 18 AWG ALT B lead) would then require traversing the firewall versus 5 wire/cables if I leave the starter contactor on the hot/aft side of the firewall... the big bubba cable from the battery contactor of course being one of those 5 traversing wires/cables.

The physical location change would require about 1-2" longer runs for the starter cable and B-lead wire, which to me seems minimal and non-issue. I do however want to ask for a crosscheck on this plan to ensure I'm not missing any possible critical issue(s).


The battery side of the starter contactor is the
power node for starter, alternator b-lead, and any
other hi-current accessory that might find its
way under the cowl . . . so in any case, there
is potential for always hot wires to cross the
firewall irrespective of contactor location.

The more fundamental questions would investigate
techniques for bringing any power/fluid/control
line through the firewall. There's over a century
of lessons-learned and documented design
practices that should have kept this conversation
from happening in the first place.

If it were my airplane, the contactor would be on
the engine side of the firewall.



Bob . . .


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Airdog77



Joined: 24 Nov 2013
Posts: 76
Location: Northern Virginia

PostPosted: Fri Jan 26, 2018 3:08 pm    Post subject: Re: Starter Contactor location on a Long-EZ Reply with quote

Bob,

Roger... I'll go back and take a deeper look at all this.

Thanks!
Wade


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PostPosted: Sat Jan 27, 2018 8:32 am    Post subject: Starter Contactor location on a Long-EZ Reply with quote

On 1/27/2018 10:57 AM, Airdog77 wrote:
Quote:
2. "Standard" Pusher: Battery >> Battery Contactor >> longer big wire >> FIREWALL >> Starter Contactor >> Starter

3. "New" Cozy style: Battery >> Battery Contactor >> longer big wire >> Starter Contactor >> FIREWALL >> Starter

Hi Wade,
FWIW, with my battery in the tail, the system in my tractor config
Glastar is the same as #2.

I don't see any immediate reason why #3 should not work.

In either case, the protections of the big wire going through the
firewall should be the same.

I also agree with the other folks that if the installation is done
properly, #2 should also be fine. My Glastar has been flying with this
configuration for 18 years, and other aircraft far longer. From an
electrical perspective, I do not see any differences between a pusher
versus a tractor.

It is your airplane, and you need to do what will make you feel
comfortable, IMHO.

-Dj

--
Dj Merrill - N1JOV - EAA Chapter 87
Currently Flying: Glastar
Previously: Cessna 150 - Glasair 1 FT - Grumman AA1B


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PostPosted: Sat Jan 27, 2018 11:23 am    Post subject: Starter Contactor location on a Long-EZ Reply with quote

Wade, are you forgetting the two alternator "b" leads? In the contactor on the cold side they both have to pass through the firewall. In the std setup they connect to the hot side of the starter contactor.
Don

On Saturday, January 27, 2018, Airdog77 <Airdog77(at)gmail.com (Airdog77(at)gmail.com)> wrote:
Quote:
--> AeroElectric-List message posted by: "Airdog77" <Airdog77(at)gmail.com (Airdog77(at)gmail.com)>

Bob,

I have to admit I'm puzzled on what appears to be sticking to the standard convention of mounting the starter contactor/solenoid on the firewall of a pusher aircraft when the A-to-Z of the power distribution configuration is different than a traditional tractor airplane.

If we look at the different configurations, which I spelled out in asking advice on this from some canard builder/fliers, it looks like this:

1.  Tractor:  FIREWALL >> Battery >> Battery Contactor >> shorter big wire >> Starter Contactor >> Starter

2.  "Standard" Pusher:  Battery >> Battery Contactor >> longer big wire >> FIREWALL >> Starter Contactor >> Starter

3.  "New" Cozy style: Battery >> Battery Contactor >> longer big wire >> Starter Contactor  >> FIREWALL >> Starter

Not to be critical of Brian in any way, and in the discussion I discovered in support of placing the starter solenoid on the cold side of the firewall, was a point made that he "didn't turn off the master" which controls the power flow through the big power cable, as is a prominent feature of #2 above.  I understand doing analysis on past events, and looking at standard practices in an attempt to mitigate potential issues (which is exactly what I'm attempting here), but Brian's scenario isn't the only reported instance of smoking wires in a pusher, it's simply the most tragic (that I know of).

The second point in this discussion is that if control of the electron flow through the big cable ends at the cold side of the firewall (as is proposed), and the only (initial) action that results in electrons flowing across the firewall boundary is when the starter button is depressed... then very most likely only one action is required if there is any malcontent going on "back there" and that is simply to STOP pressing the starter button.  Then Step 2: TURN OFF THE MASTER is moved from the critical column to the probably a good idea column.

Moreover, the ancillary logistical benefits of moving the starter contactor to the cold/forward side of the firewall in routing wires is quite significant.  It simply makes for running less wires through the firewall, wire runs to the Hall Effect sensor for both the primary and SD-8 backup alternators are optimized, and it places more items in the rather empty Hell Hole area and gets them off a very crowded firewall.  In short, it just really appears on the face of it to make for an easier install and a safer operational setup.

And again, going back to my original statement, I'm not really sure why the starter contactor/solenoid should be on the hot side of the firewall in a pusher airplane.  Moreover, in looking at the pros/cons for moving the starter solenoid to the cold side, the pros vastly outweigh any cons that I could find.  Not that I am in any way the most knowledgeable on this stuff, but from what I know, have researched and discussed it appears to be the best option thus far.

Regards,
Wade

--------
Airdog
Wade Parton
Building Long-EZ N916WP
www.longezpush.com


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Airdog77



Joined: 24 Nov 2013
Posts: 76
Location: Northern Virginia

PostPosted: Sat Jan 27, 2018 1:04 pm    Post subject: Re: Starter Contactor location on a Long-EZ Reply with quote

Hi Don,

As for big wires coming off the Starter Contactor I have an 8 AWG B lead from the alternator that connects to the same lug on the hot side of the starter contactor. On the other side of the starter contactor I have a 6 AWG lead going to the starter.

Yes, I do have an 18 AWG F-lead that also comes off the alternator that transitions through the firewall back to the Voltage Regulator, but I was looking primarily at the heavy gauge wires through the firewall. I understand the 8 AWG wire traversing the firewall is still on the hot side of the contactor, connected to the same post as my mega cable coming from the nose, but it is a lot more manageable.

Thanks,
Wade


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PostPosted: Sun Jan 28, 2018 1:33 pm    Post subject: Starter Contactor location on a Long-EZ Reply with quote

Hi Wade,

I've got O235 Longeze N45FC.  It's coming up on 1400 hrs or so but only 400 hrs of that is after I purchased it and completely rewired it (along with quite a bit of other work).
I thought long and hard about the battery, alternator, starter and associated contactors issue before I made my decisions.  This included reviewing the Bob N. wiring architecture diagrams, searching forum archives and posting my own questions.
From this work I concluded that Bob's preference (IIRC) was to run a fat wire from master contactor (up front) to starter contactor (in back) and then have the alternator B+ "piggy back" on the same wire (i.e. it goes from alternator to starter contactor).  This eliminates the weight of one wire of sufficient gauge for the alternator current (in my case #8 for a 40A alternator) but, in trade, you have a fat wire that is hot whenever the master contactor is enabled running the full length of the fuselage.  Bob provided referenced as to why this was considered acceptable. 
My own cost/benefit analysis led me to buck the aeroelectric conventional wisdom and do it different.
In my bird the B+ gets its own #8 wire from the alternator in back to a 40A ANL in front and from there to the master contactor.  I've reserved room for a starter contactor up front, next to the master contactor for the starter contactors.  I will pull a new + fat wire for the starter should I reinstall it (I took it out when I overhauled everything and haven't seen it worth reinstalling).  I will also have to replace my existing #8 ground wire from the front to the back with a fat wire should I want the starter.  (Truth be told, I will also have to install a new flywheel as I removed the ring gear and supporting metal to reduce weight).
In my mind, the advantage of eliminating a single #8 wire in trade for a hot-whenever-the-master-is-on and otherwise totally unprotected fat wire running the full length of my aircraft just wasn't worth it.
It was well after that conclusion that I also concluded that the convenience of a starter wasn't worth the weight and additional failure modes.  If I was running a high-compression O320 or O360, I might have come to a different conclusion on this point, but not the previous one.
I encourage you to gather all the input you can and consider all your own tradeoffs, which it appears is exactly what you are doing.
Best of luck!  And I look forward to meeting you at a canard fly-in one of these days!
Steve Stearns
O235 Longeze N45FC
Boulder/Longmont CO


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PostPosted: Mon Jan 29, 2018 8:51 am    Post subject: Starter Contactor location on a Long-EZ Reply with quote

At 03:26 PM 1/28/2018, you wrote:

Quote:
My own cost/benefit analysis led me to buck the aeroelectric conventional wisdom and do it different.

Keep in mind that we're talking several issues
only slightly intertwined . . .

One is selection of parts and ARCHITECTURE.
I'd be surprised if more than a couple percent
of OBAM aircraft flying were heavily influenced
by the AeroElectric Connection. Yet, they are
all flying and perform to builder's expectations
else they would get FIXED. That's one of the big
reasons for going the OBAM aviation route . . . if
you don't like it, fix it.

The second issue is failure mode effects . . .
irrespective of the architecture floats your boat
. . . or flies your airplane . . . the project
benefits greatly from FAILURE TOLERANT design.
I.e. loss of no single PROPERLY INSTALLED COMPONENT
should put the outcome of the flight at risk.

The last, and perhaps the most important focuses on
that word "PROPERLY" . . . we've read waaayyy too many
stories about bad days in the cockpit wherein the
installation and sometimes the selection of components
fabricated an ACCIDENT WAITING TO HAPPEN.

All the worrying in the world about architecture
and even parts selection produces no benefit unless
the two most important of those issues are skillfully
resolved. FAILURE TOLERANCE and PROPER INSTALLATION.

Some really 'nice' airplanes have gone down, some
with loss of life, for IGNORANT reasons implemented
by individuals who were not stupid . . . just inadequately
prepared to the task. Those root causes are invariably
unrelated to anything discussed outside of Chapter 17
in the 'Connection.

The place to start your educational endeavors is
in study of the history of the art. A study of
how-they-did-it in a C172 or PA28 may not be very
exciting, but there is confidence to be gained
in knowledge of successfully repeated experiments.
An advantage we have in OBAM aviation is the freedom
to explore new ideas. But the slickest new idea is
of little value if its failure modes or lack of
attention to process raises risk to unacceptable
levels.

Be wary of decisions driven by unsubstantiated
worries. We don't KNOW root cause in the
loss of Brian's airplane. If the loss personal to
Brian wasn't enough, loss to the community for not
knowing root cause was far worse. Worries that
prompt deviation from perhaps a century of successfully
repeated experiments do not add value to the
art and science of building low risk aircraft.
Further, they dilute the value of our $time$ expended
on seeking solutions for problems that can
only be imagined because we have no data.


Bob . . .


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