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Starter Contactor location on a Long-EZ

 
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nuckolls.bob(at)aeroelect
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PostPosted: Fri Jan 26, 2018 4:57 pm    Post subject: Starter Contactor location on a Long-EZ Reply with quote

At 05:08 PM 1/26/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: "Airdog77" <Airdog77(at)gmail.com>

Bob,

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

Is there a published failure analysis of
what transpired in the unhappy event?

A significant proportion of my career in aviation
focused on what-went-wrong-and-why. In hind-sight,
I wish I had kept a journal on the various inquiries,
facts found and resolution of root causes. I
can state with confidence that a majority of
failure events had root cause in 'somebody
didn't read/understand some bit of history in
design or application.

A few instances, like the sticking trim relays on the
Beechjet, involved new discoveries. But most unhappy
events were founded on inattention to rudimentary
details. I've worked some exceedingly expensive
problems ($millions$) that had roots in $100
decisions . . .

Whatever you decide to do with your airplane,
it NEVER hurts to take some pictures, post to
the List and ask questions. The most elegant
solutions are invariably a team effort by
competent observers. You'll have a hard time
finding a more capable group than right here . . .


Bob . . .


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michaelagarmon(at)gmail.c
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PostPosted: Sat Jan 27, 2018 3:44 am    Post subject: Starter Contactor location on a Long-EZ Reply with quote

Bob,There is an account of the incident on Brian Deford’s website located at http://deford.com/cozy/fire.html.
I am also considering installing the starter solenoid on the inside (cabin side) of the firewall. I also plan on protecting alternator B leads with fusible links sized to protect the wire ( larger than the alternator capacity). In this way, any wire crossing the firewall will be protected.

Michael Garmon
Cozy Mk IV
Houston, TX
Sent from my iPad

On Jan 26, 2018, at 6:56 PM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
Quote:
At 05:08 PM 1/26/2018, you wrote:
Quote:
--> AeroElectric-List message posted by: "Airdog77" <Airdog77(at)gmail.com (Airdog77(at)gmail.com)>

Bob,

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

Is there a published failure analysis of
what transpired in the unhappy event?

A significant proportion of my career in aviation
focused on what-went-wrong-and-why. In hind-sight,
I wish I had kept a journal on the various inquiries,
facts found and resolution of root causes. I
can state with confidence that a majority of
failure events had root cause in 'somebody
didn't read/understand some bit of history in
design or application.

A few instances, like the sticking trim relays on the
Beechjet, involved new discoveries. But most unhappy
events were founded on inattention to rudimentary
details. I've worked some exceedingly expensive
problems ($millions$) that had roots in $100
decisions . . .

Whatever you decide to do with your airplane,
it NEVER hurts to take some pictures, post to
the List and ask questions. The most elegant
solutions are invariably a team effort by
competent observers. You'll have a hard time
finding a more capable group than right here . . .


Bob . . .


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Airdog77



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

PostPosted: Sat Jan 27, 2018 7:57 am    Post subject: Re: Starter Contactor location on a Long-EZ Reply with quote

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


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Wade Parton
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www.longezpush.com
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nuckolls.bob(at)aeroelect
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PostPosted: Sun Jan 28, 2018 10:46 am    Post subject: Starter Contactor location on a Long-EZ Reply with quote

Quote:

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).

But has there been any forensic analysis of
cause/effect in any of these incidents?
If wires 'smoked', were they small wires
improperly protected or fat wires improperly
installed? Did quantitative analysis
show that the 'incidents' were more prevalent
in pushers as opposed to tractor airframes?

I think the problem is being over-worried . . .
concerns which are certainly understandable
but for reasons based more on lack of information
than from rational actions to reduce risk.

To be sure, fire wall penetrations of all stripe
have figured in failures. I recall one incident
on a tractor airplane where a bulkhead fitting
on a fuel line did not receive the benefit of
safety-wired flare-nuts. The line leaked and
an in-flight, fuel-fed fire ensued.

I can recall dozens of articles in the aviation
mags and publications by Tony B et. als. where
reliable fire wall penetration is discuesed
in detail. The air framers I've worked for had
books of process and practice specifications
for such things . . . books that have seen
only minor revision over decades . . .

As a class of incident, these are way
down the charts in frequency of occurrence.
Virtually all such events have root cause in
failure to observe legacy design rules that
have served well on hundreds of millions of vehicles
of all kind for over a century . . . not the
least of which are airplanes.



Bob . . .


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nuckolls.bob(at)aeroelect
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PostPosted: Mon Jan 29, 2018 3:48 pm    Post subject: Starter Contactor location on a Long-EZ Reply with quote

Quote:


I will say --and not that this is my reasoning for a go/no-go decision-- that I've learned over these past few days that placing the starter contactor on the cold side of the firewall is a VERY common practice in the canard community --again, for whatever reasons individual builders' have. Actually, surprisingly common in fact.

Perhaps some of that has to do with the inherent design of canards, wiring and space logistics (my overarching reason for going this route), tribal culture, or just individual preference.

As you have alluded to many times, this flexibility is one of the outstanding characteristics of the OBAM world... to adjust when necessary to optimize one's build.

. . . a well reasoned decision. My only concern about
this thread (and similar threads in the past) was
that some readers perceive value in moving their
contactor as a prophylactic against having
their airplane catch fire.

My sense is that you've got a handle on the
need/value/processes for risk management. A quality
that has very little to do with architecture.

May The Force be with you sir . . .



Bob . . .


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Airdog77



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

PostPosted: Sat Feb 03, 2018 5:14 pm    Post subject: Re: Starter Contactor location on a Long-EZ Reply with quote

Thanks Bob!

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Wade Parton
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