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Proposed Z-14 implementation

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nuckolls.bob(at)aeroelect
Guest

Posted: Fri Jan 24, 2020 4:07 pm Post subject: Proposed Z-14 implementation

At 02:33 PM 1/23/2020, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "johnbright" <john_s_bright(at)yahoo.com>



 Thanks Bob,



 I do understand, as importantly shown in the N811HB accident investigation, that failures that have no effect on the current flight should be detected before the next flight! Those unfamiliar with N811HB may well learn more than one lesson at  http://www.aeroelectric.com/Reference_Docs/Accidents/N811HB_Feb2008_LA-IVp/ 

 	


  This is an example of a system that was DESIGNED

  to fail. The builder attended one of my seminars

  out in Eugene OR some years earlier. Had the book.

  Was assisted by a degreed engineer neighbor.



  The same neighbor adapted Z-14 as a recommended

  architecture for a high performance airplane

  carrying a full-up compliment of Garmin glass . . .

  but then ignored the advice offered by his

  own recommendations by bringing BOTH ignitions

  to a common bus with a poorly crafted constellation

  of protective devices.



  The whole point of the Z14 philosophy is

  independent redundancy . . . but lost in

  this airplane by adding a feature that negated

  that philosophy in a catastrophic way. The

  feature?  A dual diode feed common bus for

  both ignitions.



  If they had simply subscribed to this List

  and run the ideas past the members, the error

  would have most certainly been avoided with advice

  from numerous members.



  	  Quote: 	
		  I am planning an O-360 with dual SDS ignition and injection. Part of my approach is to develop a detailed schematic of what it takes to keep the engine running, have a radio, and have a "six pack" of instruments long enough to make an alternate airport with the main contactors open (Z-14 derivative). I plan an engine bus with dual feeds, one from each battery via Schottky diodes; loss of one feed is preflight detectable using EFIS voltmeters. 	


   Why dual feed bus? Run half the engine

   goodies from one battery bus, the rest

   from the opposite battery bus.



   These busses are already QUAD feed.

   either bus has the opportunity to power

   up from a total of 4 sources. No single

   failure will deprive BOTH busses of

   a robust energy source.



 

  	  Quote: 	
		  I do a wire by wire failure analysis that informs the preflight checklist:

 Assume only one failure per flight.

 What are the effects of a wire shorted or open? 	


   Wires, bus bars and most power distribution

   components are considered to be exceedingly

   low failure rate . . . those kinds of things

   are generally never a part of the system

   reliability study.



  	  Quote: 	
		  Does the failure affect safety? If so, can the safety effect be designed out?How will the failure be discovered before the next flight? 	


   This is important for failures that may not be

   obvious in flight . . . for example a light

   bulb in a warning system, exterior lamps,

   back up pumps for the engine driven mechanical

   pump, etc. One might suffer a failure that

   would go unnoticed unless explored as part

   of a pre-flight process.



  	  Quote: 	
		  If the failure affects flight safety, can something be done about it? 	


   Have an alternative  . . . i.e. plan-B . . .

   a way to do without that accessory.



  	  Quote: 	
		  How will the crew know what to do? Can they do it immediately by simple predetermined actions? 	


   You betcha . . . that's what the FEMA and architecture

   refinement is all about. The design goal is to be able

   to tolerate failure of any LRU (line replaceable unit)

   with the least possible work load on crew. Z-14, for all

   it's robustness, only has three switches to fiddle with.

   They have NO potential for pilot-induced hazard. I.e.

   no mis-positioning of switches creates immediate

   hazard. 



  	  Quote: 	
		  In case of electrical fire can the battery contactor(s) be opened without affecting flight safety? 	


   Generally yes . . . I've initiated and/or completed

   numerous flights in the "J-3" mode . . . ZERO

   electrics. With engine feeds as recommended

   above, you can shut down all DC power

   management switches without affecting

   engine ops.



 

  	  Quote: 	
		  Some failures not detectable by preflight checks are added to annual inspection: 	


   There should be no useful/critical accessory that is not

   at least pre-flight testable . . . otherwise,

   why carry it around?



  	  Quote: 	
		  A fat wire short to sheetmetal that clears itself.

 Redundant grounds for both the computer and the injector driver sections of the ECUs. (Loss of computer ground sends injectors and coils 100% duty cycle.)

 Redundant grounds to voltage regulators.



 Some check done twice yearly:

 Ship's batteries and EFIS backup batteries capacity checks.

 Primary and aux alternator crowbar test.

 	


   You've got an excellent start on the

   task . . . let's keep talking.



 

 

   Bob . . .

johnbright

Joined: 14 Dec 2011
Posts: 166
Location: Newport News, VA

Posted: Mon Jan 27, 2020 12:29 pm Post subject: Re: Proposed Z-14 implementation

Thanks Bob,



I'm planning dual ECU SDS electronic fuel injection and ignition for an O-360.



The reason for a dual feed bus is that there is only one set of injectors. At present I am showing all engine related items on an engine bus. I don't know how to decide if this is the way to go or if it would be better to have an injector bus and put main and aux pumps, coils, and ECUs on main and aux battery buses. In the case of SDS the check engine light would go on the main battery bus and the injector relays on the aux battery bus.



I plan voltmeters on main, aux, and battery buses in order to detect open or shorted engine bus feed diodes during preflight. These voltmeters are built into the dual EFIS screens and the backup EFIS.



I also plan one radio on the engine bus so in event of electrical fire, master contactors open, the crew will have a running engine and a radio until main and aux batteries are depleted. (EFIS screens have backup batteries from their manufacturers.)



The ECUs do not power the injectors. The ECU box has a computer section and an injector driver section. The injector driver section is transistor switches that ground the injector minus lead; injector power comes from ships power. Double-throw relays are used to switch injectors from primary to backup ECU in case of ECU failure.



If we were looking for a universal solution that would work with EFII (brand) six cylinder applications as well as SDS applications the coils would logically go on an engine bus because EFII uses three four-cylinder coils and one of them fires top and bottom of cylinders 5 and 6 so loss of that coil is loss of two cylinders. This is not the case for SDS who use two six-cylinder coils; one for top and one for bottom. By the way, four-cylinder coils have integral drivers and six-cylinder coils have external drivers mounted next to them.



It's interesting that power distribution components are not generally part of a reliability study. This saves me a lot of (wasted) work.



I attached a snip of my electrical schematic. For those interested the full schematic and related documents are at https://drive.google.com/drive/folders/1u6GeZo6pmBWsKykLNVQMvu4o1VEVyP4K

snip of Electrical Schematic RV-6A with SDS dual EM-5-F rev F.jpg

Description:

Filesize:

243.21 KB

Viewed:

13402 Time(s)

snip of Electrical Schematic RV-6A with SDS dual EM-5-F rev F.jpg

_________________
John Bright, RV-6A, at FWF, O-360
Z-101 single batt dual alt SDS EM-5-F.
john_s_bright@yahoo.com, Newport News, Va
N1921R links

Last edited by johnbright on Tue Jan 28, 2020 5:03 pm; edited 1 time in total

user9253

Joined: 28 Mar 2008
Posts: 1944
Location: Riley TWP Michigan

Posted: Mon Jan 27, 2020 4:12 pm Post subject: Re: Proposed Z-14 implementation

What if the smoke in the cockpit is coming from Com 1?

I suggest removing Com 1 from the engine bus.

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Jan 27, 2020 5:35 pm Post subject: Proposed Z-14 implementation

At 06:12 PM 1/27/2020, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com>



 What if the smoke in the cockpit is coming from Com 1?

 I suggest removing Com 1 from the engine bus. 	


   or turning it off



 

   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Jan 27, 2020 5:36 pm Post subject: Proposed Z-14 implementation

At 02:29 PM 1/27/2020, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "johnbright" <john_s_bright(at)yahoo.com>



 Thanks Bob,



 I'm planning dual ECU SDS electronic fuel injection and ignition for an O-360.



 The reason for a dual feed bus is that there is only one set of injectors. At present I am showing all engine related items on an engine bus. I don't know how to decide if this is the way to go or if it would be better to have an injector bus and put main and aux pumps, coils, and ECUs on main and aux battery buses. In the case of SDS the check engine light would go on the main battery bus and the injector relays on the aux battery bus. 	


  Okay, riddle me this . . . suppose all injectors were

  powered from the aux bus of Z14. Deduced and cite the

  failure that would bring the aux bus down . . . and

  what would be the mitigating action?



 

   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Jan 27, 2020 5:53 pm Post subject: Proposed Z-14 implementation

At 02:29 PM 1/27/2020, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "johnbright" <john_s_bright(at)yahoo.com>



 Thanks Bob,



 I'm planning dual ECU SDS electronic fuel injection and ignition for an O-360.



 The reason for a dual feed bus is that there is only one set of injectors. At present I am showing all engine related items on an engine bus. I don't know how to decide if this is the way to go or if it would be better to have an injector bus and put main and aux pumps, coils, and ECUs on main and aux battery buses. In the case of SDS the check engine light would go on the main battery bus and the injector relays on the aux battery bus. 	


  Okay, riddle me this . . . suppose all injectors were

  powered from the aux bus of Z14. Deduced and cite the

  failure that would bring the aux bus down . . . and

  what would be the mitigating action?



 

   Bob . . .

kenryan

Joined: 20 Oct 2009
Posts: 429

Posted: Mon Jan 27, 2020 6:11 pm Post subject: Proposed Z-14 implementation

Turning it off? Really? Is turning it off with a knob considered the same as cutting the power coming to the device?



On Mon, Jan 27, 2020 at 4:41 PM Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:



 	  Quote: 	
		    At 06:12 PM 1/27/2020, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>



 What if the smoke in the cockpit is coming from Com 1?

 I suggest removing Com 1 from the engine bus. 	


   or turning it off



 

   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Jan 27, 2020 7:09 pm Post subject: Proposed Z-14 implementation

At 08:07 PM 1/27/2020, you wrote:

  	  Quote: 	
		  Turning it off? Really? Is turning it off with a knob considered the same as cutting the power coming to the device? 	


  Probably . . . it's the first thing

  to try if you KNOW the smoke is coming

  from that appliance. 



  Panel mounted devices are not a

  potential source for much smoke.

  they might smell bad but don't

  represent much of a hazard.



 

 

   Bob . . .

johnbright

Joined: 14 Dec 2011
Posts: 166
Location: Newport News, VA

Posted: Tue Jan 28, 2020 5:25 pm Post subject: Re: Proposed Z-14 implementation

 	  nuckolls.bob(at)aeroelect wrote: 	
		  At 02:29 PM 1/27/2020, you wrote:



  Okay, riddle me this . . . suppose all injectors were

  powered from the aux bus of Z14. Deduced and cite the

  failure that would bring the aux bus down . . . and

  what would be the mitigating action?



 

  Bob . . . 	




Thanks Bob,



The feed to the bus itself could be interrupted resulting in engine stoppage. It is unlikely to lose a bus feed but not impossible; probably due to poor craftsmanship which in my anecdotal experience occurs too often. Also in an electrical fire in the cockpit scenario the crew would take the main and aux power buses down.



Attahced is a bus config pros and cons table I put together for EFI+I; attached as a gif and in my filespace linked from my signature.

bus config pros and cons for EFI+I rev 02.08.2020.jpg

Description:

Filesize:

535.85 KB

Viewed:

13116 Time(s)

bus config pros and cons for EFI+I rev 02.08.2020.jpg

johnbright

Joined: 14 Dec 2011
Posts: 166
Location: Newport News, VA

Posted: Wed Jan 29, 2020 5:22 pm Post subject: Re: Proposed Z-14 implementation

 	  user9253 wrote: 	
		  What if the smoke in the cockpit is coming from Com 1?

I suggest removing Com 1 from the engine bus. 	




Thanks Joe,



FWIW the engine bus in my post from Jan 27, 2020 above seems to meet FAR 23.1361. Nothing is ideal but I lean toward keeping com 1 on the engine bus.



Com 1 is 3 A max, Dynon D6 0.9A max.



Sec. 23.1361 — Master switch arrangement:



(a) There must be a master switch arrangement to allow ready disconnection of each electric power source from power distribution systems, except as provided in paragraph (b) of this section. The point of disconnection must be adjacent to the sources controlled by the switch arrangement. If separate switches are incorporated into the master switch arrangement, a means must be provided for the switch arrangement to be operated by one hand with a single movement.



(b) Load circuits may be connected so that they remain energized when the master switch is open, if the circuits are isolated, or physically shielded, to prevent their igniting flammable fluids or vapors that might be liberated by the leakage or rupture of any flammable fluid system; and



(1) The circuits are required for continued operation of the engine; or



(2) The circuits are protected by circuit protective devices with a rating of five amperes or less adjacent to the electric power source.



(3) In addition, two or more circuits installed in accordance with the requirements of paragraph (b)(2) of this section must not be used to supply a load of more than five amperes.



(c) The master switch or its controls must be so installed the  switch is easily discernible and accessible to a crew member.

_________________
John Bright, RV-6A, at FWF, O-360
Z-101 single batt dual alt SDS EM-5-F.
john_s_bright@yahoo.com, Newport News, Va
N1921R links

Randy C-GRPY

Joined: 21 Apr 2018
Posts: 26

Posted: Fri Jan 31, 2020 10:56 am Post subject: Re: Proposed Z-14 implementation

 	  nuckolls.bob(at)aeroelect wrote: 	
		  At 02:33 PM 1/23/2020, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "johnbright" <john_s_bright>



 Thanks Bob,



 I do understand, as importantly shown in the N811HB accident investigation, that failures that have no effect on the current flight should be detected before the next flight! Those unfamiliar with N811HB may well learn more than one lesson at  http://www.aeroelectric.com/Reference_Docs/Accidents/N811HB_Feb2008_LA-IVp/ 

 	


  This is an example of a system that was DESIGNED

  to fail. The builder attended one of my seminars

  out in Eugene OR some years earlier. Had the book.

  Was assisted by a degreed engineer neighbor.



  The same neighbor adapted Z-14 as a recommended

  architecture for a high performance airplane

  carrying a full-up compliment of Garmin glass . . .

  but then ignored the advice offered by his

  own recommendations by bringing BOTH ignitions

  to a common bus with a poorly crafted constellation

  of protective devices.



  The whole point of the Z14 philosophy is

  independent redundancy . . . but lost in

  this airplane by adding a feature that negated

  that philosophy in a catastrophic way. The

  feature?  A dual diode feed common bus for

  both ignitions.



  If they had simply subscribed to this List

  and run the ideas past the members, the error

  would have most certainly been avoided with advice

  from numerous members.



  	  Quote: 	
		  I am planning an O-360 with dual SDS ignition and injection. Part of my approach is to develop a detailed schematic of what it takes to keep the engine running, have a radio, and have a "six pack" of instruments long enough to make an alternate airport with the main contactors open (Z-14 derivative). I plan an engine bus with dual feeds, one from each battery via Schottky diodes; loss of one feed is preflight detectable using EFIS voltmeters. 	


   Why dual feed bus? Run half the engine

   goodies from one battery bus, the rest

   from the opposite battery bus.



   These busses are already QUAD feed.

   either bus has the opportunity to power

   up from a total of 4 sources. No single

   failure will deprive BOTH busses of

   a robust energy source.



 

  	  Quote: 	
		  I do a wire by wire failure analysis that informs the preflight checklist:

 Assume only one failure per flight.

 What are the effects of a wire shorted or open? 	


   Wires, bus bars and most power distribution

   components are considered to be exceedingly

   low failure rate . . . those kinds of things

   are generally never a part of the system

   reliability study.



  	  Quote: 	
		  Does the failure affect safety? If so, can the safety effect be designed out?How will the failure be discovered before the next flight? 	


   This is important for failures that may not be

   obvious in flight . . . for example a light

   bulb in a warning system, exterior lamps,

   back up pumps for the engine driven mechanical

   pump, etc. One might suffer a failure that

   would go unnoticed unless explored as part

   of a pre-flight process.



  	  Quote: 	
		  If the failure affects flight safety, can something be done about it? 	


   Have an alternative  . . . i.e. plan-B . . .

   a way to do without that accessory.



  	  Quote: 	
		  How will the crew know what to do? Can they do it immediately by simple predetermined actions? 	


   You betcha . . . that's what the FEMA and architecture

   refinement is all about. The design goal is to be able

   to tolerate failure of any LRU (line replaceable unit)

   with the least possible work load on crew. Z-14, for all

   it's robustness, only has three switches to fiddle with.

   They have NO potential for pilot-induced hazard. I.e.

   no mis-positioning of switches creates immediate

   hazard. 



  	  Quote: 	
		  In case of electrical fire can the battery contactor(s) be opened without affecting flight safety? 	


   Generally yes . . . I've initiated and/or completed

   numerous flights in the "J-3" mode . . . ZERO

   electrics. With engine feeds as recommended

   above, you can shut down all DC power

   management switches without affecting

   engine ops.



 

  	  Quote: 	
		  Some failures not detectable by preflight checks are added to annual inspection: 	


   There should be no useful/critical accessory that is not

   at least pre-flight testable . . . otherwise,

   why carry it around?



  	  Quote: 	
		  A fat wire short to sheetmetal that clears itself.

 Redundant grounds for both the computer and the injector driver sections of the ECUs. (Loss of computer ground sends injectors and coils 100% duty cycle.)

 Redundant grounds to voltage regulators.



 Some check done twice yearly:

 Ship's batteries and EFIS backup batteries capacity checks.

 Primary and aux alternator crowbar test.

 	


   You've got an excellent start on the

   task . . . let's keep talking.



 

 

   Bob . . . 	




Good day Bob.



I watched your videos with great interest related to that accident report.  It was my understanding that the diode on the the feed between the two sides was what led to the current hogging that happened and which ultimately caused the whole thing to come crashing down.   With Z-14, if I am understanding correctly, should not be an issue since the two sides are also isolated.  Is this correct?



Also, assuming proper fusing and wires, if you had two batteries powering one bus, it would be, and should be, easy to check each power feed during the preflight.  



I too am using Z-14 to power my SDS ignition. As John pointed out, the difference with the accident case is that that plane only had the ignition system to deal with. With the SDS, its fuel system as well as the ignitions system. It is the injectors specifically that make it difficult from the layman's perspective.  If they all have to be on a single bus then is there a point to two buses at all? 



I posted a separate thread on how to properly choose protection for the bigger wires.  I will try and post my schematic there.



Thanks for being such a good resource.



Regards

Randy

user9253

Joined: 28 Mar 2008
Posts: 1944
Location: Riley TWP Michigan

Posted: Fri Jan 31, 2020 12:49 pm Post subject: Re: Proposed Z-14 implementation

The diodes did not cause the failure.  The 5 amp fuses did.  If 20 amp circuit breakers

had been used instead of 5 amp fuses, the whole bus would not have lost power.

_________________
Joe Gores

Randy C-GRPY

Joined: 21 Apr 2018
Posts: 26

Posted: Fri Jan 31, 2020 3:42 pm Post subject: Re: Proposed Z-14 implementation

 	  user9253 wrote: 	
		  The diodes did not cause the failure.  The 5 amp fuses did.  If 20 amp circuit breakers

had been used instead of 5 amp fuses, the whole bus would not have lost power. 	




Yes, I understand that it wasn't fused with a big enough breaker/fuse.  Bob did another video in that series though that poo pooed that design even with properly sized fuses.  I didn't understand why he felt it was a bad design since it is easy to check both feeds to the bus during the run up.  He championed having the ignitions on two completely independent busses for which I appreciate the reasons.  His design doesn't  completely transfer over from what I can tell to combined ignition/fuel injection systems like SDS.  So I guess the question that I would have is: Is that diode protected double fed single bus still a design waiting to fail if one does his due diligence including checking redundant power to the busses during run up and properly sizing and fusing the wires?



Randy

johnbright

Joined: 14 Dec 2011
Posts: 166
Location: Newport News, VA

Posted: Fri Jan 31, 2020 6:40 pm Post subject: Re: Proposed Z-14 implementation

 	  Randy C-GRPY wrote: 	
		  I didn't understand why he felt it was a bad design since it is easy to check both feeds to the bus during the run up...



Randy 	




I don't understand how this can be done. Ref attached bus schematic of N811HB.

N811HB bus schematic.png

Description:

Filesize:

1.75 MB

Viewed:

13272 Time(s)

_________________
John Bright, RV-6A, at FWF, O-360
Z-101 single batt dual alt SDS EM-5-F.
john_s_bright@yahoo.com, Newport News, Va
N1921R links

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Jan 31, 2020 8:40 pm Post subject: Proposed Z-14 implementation

 	  Quote: 	
		  Good day Bob.



 I watched your videos with great interest related to that accident report.  It was my understanding that the diode on the the feed between the two sides was what led to the current hogging that happened and which ultimately caused the whole thing to come crashing down.   With Z-14, if I am understanding correctly, should not be an issue since the two sides are also isolated.  Is this correct? 	


  Z-14 (and all other z-figures depicting dc power

  feeds to ignition, fuel, injectors, etc.) show

  INDEPENDENT feeds to all such devices. In other

  words, redundant accessories never share hardware

  once the electrons leave the source through

  single feeder protection.



  Indeed, the guest-engineer on the project

  used Z-14 as a basis for a 'recommended'

  power distribution system that powered

  a full-up compliment of Garmin glass

  on the panel. In his published architecture,

  he replaced the cross-feed contator with

  a fat diode and ran one ignition from the

  main battery . . . the second ignition from

  the aux battery.  But he failed to describe

  a recommended operating protocol for the

  two alternators.



  However, in the accident aircraft, fuse

  protected feeders from each battery was

  brought through diodes to a common bus

  whereupon power was distributed out through

  breakers to the two ignition systems.



  Bad deal.



  First, there was no way that loss of one

  battery bus fuse could be detected in

  pre-flight . . . which was the case leading

  up to this accident. Having the aux alternator

  off line caused the aux battery ignition feeder

  voltage to be LOWER than the main battery

  by approx .7 volts. This caused the main battery

  ignition fuse to carry the load for BOTH

  ignitions causing failure of the main fuse

  followed by the aux fuse hours later.



  Further, a fault in one system would have

  taken out BOTH fuses and killed both

  systems.



  If he had left out the diodes, common bus

  and the do-nothing breakers . . . that ship

  would probably be flying okay today.



  Lessons learned . . . diodes are handy

  critters for lots of applications but

  are SELDOM warranted in power distribution

  systems. I've used them in the normal feed

  path to an endurance bus in several figures

  and in Z-19 where a SINGLE ECU and FUEL

  PUMP configuration are provided two power

  sources through independent switches.



  Fiddle the architecture with caution . . .



  The latest Figure Z-12 . . .



  http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z12NP1.pdf

 

  artfully crafted is as robust as anyone

  should need in an OBAM aircraft . . .

  if you really gotta have dual batteries,

  add Z-30.   



 

 

   Bob . . .

Randy C-GRPY

Joined: 21 Apr 2018
Posts: 26

Posted: Sat Feb 01, 2020 9:07 am Post subject: Re: Proposed Z-14 implementation

 	  nuckolls.bob(at)aeroelect wrote: 	
		   	  Quote: 	
		  Good day Bob.



 I watched your videos with great interest related to that accident report.  It was my understanding that the diode on the the feed between the two sides was what led to the current hogging that happened and which ultimately caused the whole thing to come crashing down.   With Z-14, if I am understanding correctly, should not be an issue since the two sides are also isolated.  Is this correct? 	


  Z-14 (and all other z-figures depicting dc power

  feeds to ignition, fuel, injectors, etc.) show

  INDEPENDENT feeds to all such devices. In other

  words, redundant accessories never share hardware

  once the electrons leave the source through

  single feeder protection.



  Indeed, the guest-engineer on the project

  used Z-14 as a basis for a 'recommended'

  power distribution system that powered

  a full-up compliment of Garmin glass

  on the panel. In his published architecture,

  he replaced the cross-feed contator with

  a fat diode and ran one ignition from the

  main battery . . . the second ignition from

  the aux battery.  But he failed to describe

  a recommended operating protocol for the

  two alternators.



  However, in the accident aircraft, fuse

  protected feeders from each battery was

  brought through diodes to a common bus

  whereupon power was distributed out through

  breakers to the two ignition systems.



  Bad deal.



  First, there was no way that loss of one

  battery bus fuse could be detected in

  pre-flight . . . which was the case leading

  up to this accident. Having the aux alternator

  off line caused the aux battery ignition feeder

  voltage to be LOWER than the main battery

  by approx .7 volts. This caused the main battery

  ignition fuse to carry the load for BOTH

  ignitions causing failure of the main fuse

  followed by the aux fuse hours later.



  Further, a fault in one system would have

  taken out BOTH fuses and killed both

  systems.



  If he had left out the diodes, common bus

  and the do-nothing breakers . . . that ship

  would probably be flying okay today.



  Lessons learned . . . diodes are handy

  critters for lots of applications but

  are SELDOM warranted in power distribution

  systems. I've used them in the normal feed

  path to an endurance bus in several figures

  and in Z-19 where a SINGLE ECU and FUEL

  PUMP configuration are provided two power

  sources through independent switches.



  Fiddle the architecture with caution . . .



  The latest Figure Z-12 . . .



  http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z12NP1.pdf

 

  artfully crafted is as robust as anyone

  should need in an OBAM aircraft . . .

  if you really gotta have dual batteries,

  add Z-30.   



 

 

   Bob . . . 	




Thanks for the detailed explanation Bob.



Most builders powering the SDS system are doing it off of a single bus from two independent batteries as per manufacturers recommendation.  From what you say above, this is similar to Z-19 and diodes are justified in this scenario.



In my plane I do have a cross-tie and not a diode.  The normal flight configuration will have X-tie open, thus effectively having two independent systems, each with an alternator to keep the batteries charged.  I hope this accomplishes what you suggest as being imperative.



Also, normal operation during flight would have both power feeds to the main bus hot.  Is this a bad idea?

Regards

Randy

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Feb 01, 2020 10:11 am Post subject: Proposed Z-14 implementation

 	  Quote: 	
		  Yes, I understand that it wasn't fused with a big enough breaker/fuse.  Bob did another video in that series though that poo pooed that design even with properly sized fuses.  I didn't understand why he felt it was a bad design since it is easy to check both feeds to the bus during the run up. 	


   How would that be done?  There were two fuses

   from always hot battery busses feeding a common

   bus . . . how does one independently verify

   existence of energy to for each feeder?



   Had they stayed with powering each ignition

   from it's own battery, the legacy 'mag check'

   would have verified independent functionality

   of each system.



  	  Quote: 	
		    He championed having the ignitions on two completely independent busses for which I appreciate the reasons.  His design doesn't  completely transfer over from what I can tell to combined ignition/fuel injection systems like SDS.  So I guess the question that I would have is: Is that diode protected double fed single bus still a design waiting to fail if one does his due diligence including checking redundant power to the busses during run up and properly sizing and fusing the wires? 	


    . . . but what event or combination of events

    will bring down power to the injectors if they

    were ALL driven from one bus?



    N811HB came down because the installed architecture:



    (1) failed to recognize that every bus in the

        system was ALREADY redundantly powered



    (2) failed to maintain independent power sources

        for EACH ignition system.

    

    (3) failed to exploit the fact that the engine

        would run well on EITHER ignition system.



    (4) added features not included in the original

        Z14 intended to ADD redundancy when in fact

        it NEGATED redundancy already in place.



    (5) placed undersized protective devices at

        risk for failure for lack of FMEA.



        NOTE: I've had builders bend over backwards

        to keep both ignition systems operating when

        in fact, a perfectly good plan-b for energy

        conservation would call for shutting one

        ignition system OFF during conditions of

        limited energy availability.



     So I'll repeat the question. Suppose all SDS

     injectors were powered from one bus . . . each

     protected by its own fuse. What failure condition

     would bring down power necessary to kill the

     engine?



 

   Bob . . .

Randy C-GRPY

Joined: 21 Apr 2018
Posts: 26

Posted: Sat Feb 01, 2020 12:35 pm Post subject: Re: Proposed Z-14 implementation

 	  nuckolls.bob(at)aeroelect wrote: 	
		   	  Quote: 	
		  Yes, I understand that it wasn't fused with a big enough breaker/fuse.  Bob did another video in that series though that poo pooed that design even with properly sized fuses.  I didn't understand why he felt it was a bad design since it is easy to check both feeds to the bus during the run up. 	


   How would that be done?  There were two fuses

   from always hot battery busses feeding a common

   bus . . . how does one independently verify

   existence of energy to for each feeder?



   Had they stayed with powering each ignition

   from it's own battery, the legacy 'mag check'

   would have verified independent functionality

   of each system.



  	  Quote: 	
		    He championed having the ignitions on two completely independent busses for which I appreciate the reasons.  His design doesn't  completely transfer over from what I can tell to combined ignition/fuel injection systems like SDS.  So I guess the question that I would have is: Is that diode protected double fed single bus still a design waiting to fail if one does his due diligence including checking redundant power to the busses during run up and properly sizing and fusing the wires? 	


    . . . but what event or combination of events

    will bring down power to the injectors if they

    were ALL driven from one bus?



    N811HB came down because the installed architecture:



    (1) failed to recognize that every bus in the

        system was ALREADY redundantly powered



    (2) failed to maintain independent power sources

        for EACH ignition system.

    

    (3) failed to exploit the fact that the engine

        would run well on EITHER ignition system.



    (4) added features not included in the original

        Z14 intended to ADD redundancy when in fact

        it NEGATED redundancy already in place.



    (5) placed undersized protective devices at

        risk for failure for lack of FMEA.



        NOTE: I've had builders bend over backwards

        to keep both ignition systems operating when

        in fact, a perfectly good plan-b for energy

        conservation would call for shutting one

        ignition system OFF during conditions of

        limited energy availability.



     So I'll repeat the question. Suppose all SDS

     injectors were powered from one bus . . . each

     protected by its own fuse. What failure condition

     would bring down power necessary to kill the

     engine?



 

   Bob . . . 	




With their design I can't see how either.  However, could they have installed a switch or an appropriately sized relay for each of the main feeds so that each could be turned on and off in sequence?



As for the SDS, I think we are on the same page but maybe not.  You've said that the bus and the feeding wires properly installed are incredibly reliable. I think that it is therefore safe to run all of the injectors (each properly protected), as well as the other components (also properly protected) off of a single bus that has two useable power feeds as the manufacturer has designed.  No single battery or alternator failure will bring the house down. So to answer your last question in a different way, I don't think anything other than failure of the battery, the feeding wire, or the bus bar would kill the engine.



Boy I hope that I'm not being thick headed with this. Thanks for your patience.



Randy

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Feb 02, 2020 5:39 am Post subject: Proposed Z-14 implementation

 	  Quote: 	
		  

 >      So I'll repeat the question. Suppose all SDS

 >      injectors were powered from one bus . . . each

 >      protected by its own fuse. What failure condition

 >      would bring down power necessary to kill the

 >      engine?



 

 With their design I can't see how either.  However, could they have installed a switch or

 an appropriately sized relay for each of the main feeds so that each could be turned on

 and off in sequence? 	


  Sure . . . but consider that this increases parts

  count, some of which have moving parts and arcing

  contacts. All this fuss to raise confidence in

  a battery, alternator or bus structure?



  Would it not be more elegant to provide a

  redundantly robust source delivered from

  a single distribution point wherein no

  additional hardware (or pilot workload)

  is built into the system?



  	  Quote: 	
		  As for the SDS, I think we are on the same page but maybe not.  You've said that the

 bus and the feeding wires properly installed are incredibly reliable. I think

 that it is therefore safe to run all of the injectors (each properly protected),

 as well as the other components (also properly protected) off of a single bus

 that has two useable power feeds as the manufacturer has designed.

 No single battery or alternator failure will bring the house down. So to

 answer your last question in a different way, I don't think anything other

 than failure of the battery, the feeding wire, or the bus bar would kill the engine.



 Boy I hope that I'm not being thick headed with this. Thanks for your patience. 	


  No problem . . .that's what we do here. You are

  correct.



  Put yourself in the shoes of an accessory designer/

  manufacturer wherein the target market consists of

  end users . . . consumers. While more understanding

  of things technical, their range of skills covers

  a lot of ground most of which isn't herding electrons.

  So what's the best advice you can offer your customer with

  respect to keeping YOUR rather critical piece of

  hardware operating?



  It's this kind of worrying that gave birth to

  Lightspeed's main/aux battery recommendations

  which were duplicated in other products. It

  prompted some suppliers to incorporate standby

  batteries right into their product. It has

  encouraged the sales and incorporation of

  countless standby batteries in OBAM aircraft.



  The same philosophy drove sales of hundreds

  if not thousands of 'flight bag batteries'

  in the TC world.



  I recall a vendor at OSH hawking one of the

  earliest examples of an AGM battery along

  with a cable to plug it into the ship's

  cigar lighter. The idea was that when the

  panel goes dark, you can turn the generator/

  alternator and battery off then plug this

  device in to get some stuff running again.

  No STC required . . . not permanently

  installed.



  12 pounds of dead-weight carried around

  in the cockpit . . . for what? A

  hedge against failure in a CERTIFIED

  system that place the mission, hardware

  and people at risk. Ugh!



  Garmin stepped up to their worries by

  consideration of Z-14 as a recommended

  architecture for OBAM aircraft installations

  of their products . . . but stepped into

  the tar-pit with ill-considered 'adjustments'.



  While well meaning (and perhaps self serving

  for reducing liabilities) any attempt

  to keep ONE product energy independent

  doesn't account a real need to keep LOTS if

  not ALL products working.



  The obvious solution is to ditch all the

  electro-whizzy supplier's notions of back-up

  systems and concentrate on a failure-tolerant

  architecture that supports most if not

  all the electro-whizzies.



  Design goals should include minimized parts

  count which goes to increased reliability,

  reduced work load and decreased cost of

  ownership.



  If it's a good thing to worry about keeping sparks

  and pumps running . . . is it any less

  important to keep other things running too?

  Especially when boring holes in clouds,

  overflying mountains at night or hauling

  a cabin full of fellow travelers?



  I suggest it's far more elegant to ditch

  all back-up systems targeted to support one

  critical system in favor of one system

  designed with the greatest reverence

  for artful FMEA and craftsmanship.



 

   Bob . . .

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