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was RV- 14, now electrical redundancy

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fly4grins(at)gmail.com
Guest

Posted: Sat Oct 25, 2014 5:04 am Post subject: was RV- 14, now electrical redundancy

 	  Quote: 	
		  Peter and Jeff-

	




I wrestled with the same issues, and although I've not yet flown my night / ifr capable RV yet, I like what I've come up with.Â  The short version is that I've a primary efis w/ engine instruments and a backup efis six pack.Â  Given that cranking and avoiding brown out pretty well required two batteries, I ultimately adopted Bob's two identical battery, swap one out per year concept.Â  The starter, main alternator, main bus (including the switched stby efis), and main battery comprise one branch of my system.Â  The essential Â battery (Sorry folks; Â I'm not interested in any semantic arguments... Â call it a kumquat if you like!) carries the essential bus, which powers the primary efis un-switched and is supported by an SD-8 on the vacuum pad.Â  The two batteries are tied together with a Schotkey diode, and the SD-8 regulator is set between battery and main alternator voltage. Â 

Operation is dirt simple.Â  Starting with the main alt off tests the stby.Â  In flight, the main alt carries the whole electrical system.Â  Should the main alt fail, the main bus is carried by the main battery and the SD-8 picks up the essential bus with precisely zero switch flipping by the pilot.Â  The efis will annunciate the drop in main bus voltage.Â  Load shedding at one's leisure will prolong the life of the main bus, but the SD-8 will ensure all the most important goodies have power for probably two hours after the prop stops windmilling, even with battery contactors on line. Â Â 

I use fuses, with the only breakers on power sources.Â  Failure of ANY one component can't hurt me.Â  YMMV, but I like it, a lot.





  [quote][b]

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Kellym

Joined: 10 Jan 2006
Posts: 1705
Location: Sun Lakes AZ

Posted: Sat Oct 25, 2014 6:24 am Post subject: was RV- 14, now electrical redundancy

This discussion, as good as it is, has focused on hardware installed and 

its capabilities, not mission "need".

Need varies from a military requirement to complete the mission 

regardless of circumstances to if something fails I will land at nearest 

suitable airport and deal with it. Night IFR by itself only has certain 

minimum requirements, and if you "assume" that your missions will keep 

you within XX minutes of a suitable airport, your needs are different 

than if you assume you will need to fly to destination and thus need 

electron capacity equal to the aircraft fuel range. Having electron 

capacity greater than fuel range just adds unnecessary wt.

Then there is the consideration of how much effort the backups need to 

allow pilot with minimum effort to safely reach his pre-determined goal.

I like the system described below, IF you assume your mission is over 

hostile terrain, at night in IFR and need to go a considerable distance 

to a suitable landing spot after a failure. Most of us don't really have 

that mission requirement, but may want the capability.

Personally, having managed to escape a night time partial panel episode 

in a non-radar mountainous region will no longer consider combining 

night, IFR and mountains on the same flight in a single engine normally 

aspirated aircraft. My preference would be to limit risk to one of those 

challenges, but will consider a flight that combines two of them. 

However, I really don't want mountains at night in anything with only 

one engine and no turbo regardless of VFR or IFR. I already have enough 

experience there to not want to do it again.

That is why I consider suitable IFR backup to be enough electrons to 

function for 1 hour, maybe 1+30 to be adequate, and easily achievable 

with batteries only backup rather than a second alternator. Each builder 

will have to assess their mission goals and risk tolerance to decide how 

much redundancy they need and how much they want. How much complexity 

that does or does not add is a minor factor in the equation. I believe 

Bob has always pushed us to most carefully evaluate what our goals and 

mission needs were to decide on what architecture is appropriate.



On 10/25/2014 6:03 AM, GLEN MATEJCEK wrote:

 	  Quote: 	
		  

     Peter and Jeff-

 I wrestled with the same issues, and although I've not yet flown my 

 night / ifr capable RV yet, I like what I've come up with.  The short 

 version is that I've a primary efis w/ engine instruments and a backup 

 efis six pack. Given that cranking and avoiding brown out pretty well 

 required two batteries, I ultimately adopted Bob's two identical 

 battery, swap one out per year concept.  The starter, main alternator, 

 main bus (including the switched stby efis), and main battery comprise 

 one branch of my system.  The essential  battery (Sorry folks;  I'm 

 not interested in any semantic arguments...  call it a kumquat if you 

 like!) carries the essential bus, which powers the primary efis 

 un-switched and is supported by an SD-8 on the vacuum pad.  The two 

 batteries are tied together with a Schotkey diode, and the SD-8 

 regulator is set between battery and main alternator voltage.



 Operation is dirt simple.  Starting with the main alt off tests the 

 stby.  In flight, the main alt carries the whole electrical system.  

 Should the main alt fail, the main bus is carried by the main battery 

 and the SD-8 picks up the essential bus with precisely zero switch 

 flipping by the pilot.  The efis will annunciate the drop in main bus 

 voltage.  Load shedding at one's leisure will prolong the life of the 

 main bus, but the SD-8 will ensure all the most important goodies have 

 power for probably two hours after the prop stops windmilling, even 

 with battery contactors on line.



 I use fuses, with the only breakers on power sources. Failure of ANY 

 one component can't hurt me.  YMMV, but I like it, a lot.



 *

 *

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_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor # 5286
KCHD

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Oct 25, 2014 7:49 am Post subject: was RV- 14, now electrical redundancy

 	  Quote: 	
		  

That is why I consider suitable IFR backup to be enough electrons to 

function for 1 hour, maybe 1+30 to be adequate, and easily 

achievable with batteries only backup rather than a second alternator.


	


   But why limit your horizon to 90 minutes if there's

   simple, light, low cost of ownership combination of

   hardware and planing that keeps the panel lit until

   the engine runs out of fuel?



   This is a mode of thinking not generally offered to

   C-172 owners.  I had a conversation with a company

   pilot at Beech who had just delivered a new A-36

   to a proud customer. He was extolling the virtues

   of all the electro-whizzies on the panel to the

   customer.



   Later, I asked, "Did you check the guy out in flying

   this airplane in the J-3 mode"?



   "Say what? Why would I do that? He just paid a half

   million for an airplane with air conditioning and the

   kitchen sink . . . why would I even suggest that

   he might want to acquire such skills about?"



   Why indeed. The point is, I respectfully suggest that

   there is no reason any OBAM aviation pilot should

   experience an electrical 'emergency'. No single failure

   should be cause to seek the nearest airport in boonies

   because risks for continued flight to airport of

   intended destination have driven up your pucker-factor.

 	  Quote: 	
		    Each builder will have to assess their mission goals and risk 

 tolerance . . .


	




   Right ON! Let's not 'tolerate' risk, let's drive

   it so close to zero that throwing a prop-bolt becomes

   the more likely event to ruin your day.

   Bob . . .

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ralphmariafinch(at)gmail.
Guest

Posted: Sat Oct 25, 2014 8:56 am Post subject: was RV- 14, now electrical redundancy

On Sat, Oct 25, 2014 at 7:22 AM, Kelly McMullen <kellym(at)aviating.com (kellym(at)aviating.com)> wrote:

 	  Quote: 	
		  --> AeroElectric-List message posted by: Kelly McMullen <kellym(at)aviating.com (kellym(at)aviating.com)>

 

 This discussion, as good as it is, has focused on hardware installed and its capabilities, not mission "need".

	




Not true. I speculated on the OP's mission: IFR as stated, possibly at night, probably single-pilot, certainly single engine.

 



 	  Quote: 	
		   Need varies from a military requirement to complete the mission regardless of circumstances to if something fails I will land at nearest suitable airport and deal with it. Night IFR by itself only has certain minimum requirements, and if you "assume" that your missions will keep you within XX minutes of a suitable airport, 	




An optimistic assumption...dangerous to make. Better to make pessimistic assumptions.



 

 	  Quote: 	
		   your needs are different than if you assume you will need to fly to destination and thus need electron capacity equal to the aircraft fuel range. Having electron capacity greater than fuel range just adds unnecessary wt.

	




No. Aircraft batteries add more weight than standby alternators and provide much less endurance. At any rate, a bit of extra weight for an RV-14 is hardly the critical factor.

 

 	  Quote: 	
		   Then there is the consideration of how much effort the backups need to allow pilot with minimum effort to safely reach his pre-determined goal.

 I like the system described below, IF you assume your mission is over hostile terrain, at night in IFR and need to go a considerable distance to a suitable landing spot after a failure. Most of us don't really have that mission requirement, but may want the capability.

	




Most of the inter-mountain West (USA) would be considered hostile terrain as is the Appalachian Range; we don't know where the OP lives, but at some point he might cross them. Airports in the mountains are not close together.  And what if a nearby airport is under minimums and he needs to travel a distance to reach an acceptable airport? He may not plan on night IFR, but could easily find himself with a choice: late departure, arriving at destination at night, OR stay overnight in Podunk Airport and leave in the morning. 



So plan for a system with at least, say, a 2- or 3-hour e-buss capacity. But as Bob points out, it's easy--not more effort--to add indefinite endurance, so why not do it? 



I don't understand the notion that a 2nd alternator is greatly increased complexity and effort, therefore all backup must be battery. Once you are trapped in that thinking, poor trade-offs result.



  [quote][b]

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nuckolls.bob(at)aeroelect
Guest

Posted: Sat Oct 25, 2014 9:40 am Post subject: was RV- 14, now electrical redundancy

 	  Quote: 	
		  I don't understand the notion that a 2nd alternator is greatly increased complexity and effort, therefore all backup must be battery. Once you are trapped in that thinking, poor trade-offs result. 	


    Precisely. "greatly increased" is non-quantified. To quote from

    one of my heros . . .



 "When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge of it is of a meager and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely, in your thoughts, advanced it to the stage of science."



 Sir William Thompson, Lord Kelvin (1824-1907) 



    and one other . . .



 "A number cited without knowing its degree of uncertainty is meaningless"



 Walter Lewin (PhD Physics and professor at MIT)



    These two gentlemen laid foundation for my suggestion to our

    newest member to the List who was starting to plan his

    electrical system, buy parts and start drilling holes.



    I suggested that he first make a list of every electrical

    load in the airplane and assign its duties in the conduct

    of various phases of flight. Those numbers combined with

    an assessment of criticality to comfortable continuation

    of flight to airport of intended destination is where

    one might begin to size the task and make measured

    decisions of known significance.



    Task I: Measure and tabulate it . . .



 

   Bob . . .    [quote][b]

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jluckey(at)pacbell.net
Guest

Posted: Sat Oct 25, 2014 10:42 am Post subject: was RV- 14, now electrical redundancy

".. I don't understand the notion that a 2nd alternator is greatly increased  complexity and effort, therefore all backup must be battery.  Once you are trapped in that thinking, poor trade-offs result."



Ralph, it is unclear from the context; are you promoting a single battery, dual alternator system?  I don't see any problem with that, given a particular set of design criteria.



If one of your goals is to maximize endurance after an alternator failure, then the second alternator makes sense.  However, a system with a single battery does not solve the brown-out at start-up problem.



So  it comes down to what's important to you.  There is no right or wrong answer - there can be different designs based upon different sets of constraints & criteria that result in different, but equally legitimate, designs.

-Jeff

 

     On Saturday, October 25, 2014 10:49 AM, "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com> wrote:  

      	  Quote: 	
		  I don't understand the notion that a 2nd alternator is greatly increased complexity and effort, therefore all backup must be battery. Once you are trapped in that thinking, poor trade-offs result. 	
    Precisely. "greatly increased" is non-quantified. To quote from    one of my heros . . . "When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge of it is of a meager and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely, in your thoughts, advanced it to the stage of science." Sir William Thompson, Lord Kelvin (1824-1907)     and one other . . . "A number cited without knowing its degree of uncertainty is meaningless" Walter Lewin (PhD Physics and professor at MIT)    These two gentlemen laid foundation for my suggestion to our    newest member to the List who was starting to plan his    electrical system, buy parts and start drilling holes.    I suggested that he first make a list of every electrical    load in the airplane and assign its duties in the conduct    of various phases of flight. Those numbers combined with    an assessment of criticality to comfortable continuation    of flight to airport of intended destination is where    one might begin to size the task and make measured    decisions of known significance.    Task I: Measure and tabulate it . . .     Bob . . .    

 	  Quote: 	
		  

	


  

 

  

 

 [quote][b]

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jmjones2000(at)mindspring
Guest

Posted: Sat Oct 25, 2014 1:49 pm Post subject: was RV- 14, now electrical redundancy

Glen,

What Schotkey diode part number are you using?

Thanks!

Justin



 



On Oct 25, 2014, at 07:03, GLEN MATEJCEK <fly4grins(at)gmail.com (fly4grins(at)gmail.com)> wrote:

[quote] 	  Quote: 	
		  Peter and Jeff-

	




I wrestled with the same issues, and although I've not yet flown my night / ifr capable RV yet, I like what I've come up with.  The short version is that I've a primary efis w/ engine instruments and a backup efis six pack.  Given that cranking and avoiding brown out pretty well required two batteries, I ultimately adopted Bob's two identical battery, swap one out per year concept.  The starter, main alternator, main bus (including the switched stby efis), and main battery comprise one branch of my system.  The essential  battery (Sorry folks;  I'm not interested in any semantic arguments...  call it a kumquat if you like!) carries the essential bus, which powers the primary efis un-switched and is supported by an SD-8 on the vacuum pad.  The two batteries are tied together with a Schotkey diode, and the SD-8 regulator is set between battery and main alternator voltage.  

Operation is dirt simple.  Starting with the main alt off tests the stby.  In flight, the main alt carries the whole electrical system.  Should the main alt fail, the main bus is carried by the main battery and the SD-8 picks up the essential bus with precisely zero switch flipping by the pilot.  The efis will annunciate the drop in main bus voltage.  Load shedding at one's leisure will prolong the life of the main bus, but the SD-8 will ensure all the most important goodies have power for probably two hours after the prop stops windmilling, even with battery contactors on line.   

I use fuses, with the only breakers on power sources.  Failure of ANY one component can't hurt me.  YMMV, but I like it, a lot.





   	  Quote: 	
		  



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lectric-List"">http://www.matronics.com/Navigator?AeroElectric-List

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[b]

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ralphmariafinch(at)gmail.
Guest

Posted: Sat Oct 25, 2014 3:37 pm Post subject: was RV- 14, now electrical redundancy

On Sat, Oct 25, 2014 at 11:41 AM, Jeff Luckey <jluckey(at)pacbell.net (jluckey(at)pacbell.net)> wrote:

 	  Quote: 	
		  ".. I don't understand the notion that a 2nd alternator is greatly increased  complexity and effort, therefore all backup must be battery.  Once you are trapped in that thinking, poor trade-offs result."





Ralph, it is unclear from the context; are you promoting a single battery, dual alternator system? 



	




Not necessarily, two aircraft batteries may be preferable for the OP's mission and tolerance of risk. I AM arguing against the apparent insistence by at least one here that a 2nd alternator adds such complexity it should not be considered.

 



 	  Quote: 	
		  

If one of your goals is to maximize endurance after an alternator failure, then the second alternator makes sense.  However, a system with a single battery does not solve the brown-out at start-up problem.

	




Don't know what that is precisely...if it's important, then put in a 2nd battery. Sounds like someone is turning on all the avionics, then starting the engine...if so, couldn't the engine be started, then turn on the glass panels?

 	  Quote: 	
		  So  it comes down to what's important to you.  There is no right or wrong answer



	




There are multiple solutions or answers to the OP's question, with different levels of satisfying his requirements. But forgoing a 2nd alternator because it's "complicated" is not true and is unhelpful. 



  [quote][b]

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