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Factory Certified but is this safe?

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Michael Wynn

Joined: 10 Jan 2006
Posts: 148
Location: San Ramon, CA

Posted: Tue Jun 18, 2019 5:17 pm Post subject: Factory Certified but is this safe?

Hi all,

 

 

  I am rebuilding and restoring a 1977 factory certified S1-S Pitts.  The electrical system is pretty basic but there is one aspect that I am trying to understand.  The battery is located behind the pilot's seat.  There is a contactor directly adjacent that energizes the starter.  There is a large wire, #8 or so, that goes from the battery that goes down the frame to the console between the pilot's legs where the circuit breakers and switches reside.  That wire goes into an ammeter and from there to the main bus, on which the various circuit breakers reside.  There is no fuse, contactor or other circuit interruption device between the battery and the console.  If that main feed wire were to erode through or otherwise short, there would be nothing to stop the welding action until the battery died.

  

 

  I wired my RV8 per the excellent instructions in the Aeroelectric Connection.  I feel quite safe about it.  There is a very short run between the batter and the main contactor but all other wires are protected.  Not so with the factory Pitts wiring.  Should I be adding a fuse or contactor or something near the battery to protect this circuit?

  

 

  Regards,

  

 

  Michael Wynn

  RV8

  Pitts S1-S

  Livermore, CA

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Michael Wynn
RV 8
San Ramon, CA

user9253

Joined: 28 Mar 2008
Posts: 1908
Location: Riley TWP Michigan

Posted: Tue Jun 18, 2019 6:04 pm Post subject: Re: Factory Certified but is this safe?

A pilot should have the ability to shut off electrical power near each source.  A 40 amp automotive relay will work for this situation.  I would NOT install a fuse or circuit breaker at the battery.

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Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Jun 20, 2019 4:55 pm Post subject: Factory Certified but is this safe?

At 08:16 PM 6/18/2019, you wrote:

  	  Quote: 	
		  Hi all,



 

 I am rebuilding and restoring a 1977 factory certified S1-S Pitts.  The electrical system is pretty basic but there is one aspect that I am trying to understand.  The battery is located behind the pilot's seat.  There is a contactor directly adjacent that energizes the starter.  There is a large wire, #8 or so, that goes from the battery that goes down the frame to the console between the pilot's legs where the circuit breakers and switches reside.  That wire goes into an ammeter and from there to the main bus, on which the various circuit breakers reside.  There is no fuse, contactor or other circuit interruption device between the battery and the console.  If that main feed wire were to erode through or otherwise short, there would be nothing to stop the welding action until the battery died.



 I wired my RV8 per the excellent instructions in the Aeroelectric Connection.  I feel quite safe about it.  There is a very short run between the batter and the main contactor but all other wires are protected.  Not so with the factory Pitts wiring.  Should I be adding a fuse or contactor or something near the battery to protect this circuit? 	


   Do you have a schematic of the system?

   How big is the alternator/generator?



   I am surprised that a type certificated

   airplane would be configured as you've

   described because it does not comply

   with Part 23 rules for crew management

   of power sources.



   You could add a battery contactor for

   just that feeder . . .but if you're

   going to add ANY contactor, why

   not wire per 99.9% of other TC

   aircraft?



   Add a legacy battery contactor

   upstream of the starter contactor

   then move the 8AWG feeder to

   the junction between those

   contactors. Of course, you'll

   need to add a battery master

   to the panel.



   What's your situation with respect

   to 'mods'? Do you need to execute

   a Form 337 Field Approval?



 

    



 

 

   Bob . . .

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Michael Wynn

Joined: 10 Jan 2006
Posts: 148
Location: San Ramon, CA

Posted: Sun Jun 23, 2019 6:16 am Post subject: Factory Certified but is this safe?

In looking at the original published plans, the starter contactor next to the battery and no master is what is published.  I am working with my A&P to sort out the legalities of the situation but my decision is to rewire using the Z11 basic form.  I changed out the alternator for the TSO'd version of the B&C 40 amp alternator and LRC-3 regulator.  In my view, safety trumps legality.  I cannot explain how the type certificate was approved this way but the original design was from the 1940's and I'm not sure when the type certificate was given.  It certainly wouldn't pass at present. 

 

  I have a call in to Aviat to see if there is a service bulletin or something that allows me to legally make the changes.  Beyond that, safety first is the byline.  If I need the 337, then we will get that done.  I cannot believe I am the first Pitts owner to encounter this situation.  Thanks for the feedback.

  

 

  Regards,

  

 

  Michael Wynn

  RV8

  Pitts S1-S

  Livermore, CA

 

 

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Michael Wynn
RV 8
San Ramon, CA

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Jun 23, 2019 6:01 pm Post subject: Factory Certified but is this safe?

At 09:15 AM 6/23/2019, you wrote:

  	  Quote: 	
		  In looking at the original published plans, the starter contactor next to the battery and no master is what is published.  I am working with my A&P to sort out the legalities of the situation but my decision is to rewire using the Z11 basic form.  I changed out the alternator for the TSO'd version of the B&C 40 amp alternator and LRC-3 regulator.  In my view, safety trumps legality.  I cannot explain how the type certificate was approved this way but the original design was from the 1940's and I'm not sure when the type certificate was given.  It certainly wouldn't pass at present. 	




   Yeah . . . that would have been a CAR3

   rules. I'll have to see if I still have

   a copy of the light-plane rules in

   my archives. I would be interesting

   to see what was required back then.



 

  	  Quote: 	
		  I have a call in to Aviat to see if there is a service bulletin or something that allows me to legally make the changes.  Beyond that, safety first is the byline.  If I need the 337, then we will get that done.  I cannot believe I am the first Pitts owner to encounter this situation.  Thanks for the feedback.

 	


   Is there a type-club that might

   have exemplar 337 submissions

   that were successful upgrades?



   Barring that, consider a

   337 that cites an 'upgrade

   to the original system with:



   (1) architecture patterned after 1968 C172



   (2) fully compliant with FAR23 paragraphs

       23.1351 thru 23.1367



   (3) installed per practices described

       in AC43-13 and all applicable

       manufacturer's recommendations.



   Then attach a drawing of the system (should

   be pretty simple). Break it up in page

   per system format like that found in the

   back of the various Cessna service manuals

   available from my website.



   I know a DAR type that could help

   you craft the document.

       



 

 

   Bob . . .

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Michael Wynn

Joined: 10 Jan 2006
Posts: 148
Location: San Ramon, CA

Posted: Tue Jun 25, 2019 8:49 am Post subject: Factory Certified but is this safe?

Very good.  Thank you for the input.  I will keep everyone posted on this. 

 

  Regards,

  

 

  Michael Wynn, 

  RV8

  Pitts S1-S

  Livermore, CA

  

 

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Michael Wynn
RV 8
San Ramon, CA

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