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Some thoughts on 'standby' batteries

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nuckolls.bob(at)aeroelect
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Posted: Wed Apr 01, 2020 8:00 am Post subject: Some thoughts on 'standby' batteries

Batteries have been an essential component

of aircraft electrical systems from day-one.

The first airborne electrics were battery powered

by devices recharged after every flight given

that engine driven power sources were not

yet prominent fixtures. Indeed, wind-driven

generators were more prevalent (read low power

and DRAG!).



Batteries were 'wet', produced fumes when

charged. dribbled acid over themselves and

the airplane and had relatively short service

lives. I.e. they were a commodity like tires,

oil and gasoline. Their reliability as a

power source depended on constant monitoring

of condition.



While secondary (rechargeable) batteries have

become much more efficient, environmentally

friendly, more per pound and cubic foot, they

are still a commodity. You cannot install

a battery into any function expecting it to

perform as needed for more than a tiny fraction

of the airframe service life. Further, if loss

of a battery-supported system adversely impacts

probability for comfortable termination of

flight like fuel and oil . . . the battery's

condition demands reliable monitoring of

condition for continued airworthiness.



This is a burden on cost of ownership. It

expands the operator's work load for periodic

and capable preventative maintenance peppered

with the expense of replacement on condition.



Design goals for elegant electrical systems

architecture includes minimizing the need

for batteries in both number, size and expense.

The ultimate achievement for reduction of

batteries might be (1) a battery capable

of but one start cycle and (2) sufficient

capacity to operate landing lights during

the last 60 seconds of a dead-stick landing

at night.



THAT battery might indeed be quite small and

its cost of ownership very nominal. It might

even be cheap enough to simply replace it at

every annual . . . or perhaps every 100 hours

just as you might change the oil. Thus you've

eliminate the need for time, effort and test

equipment necessary to conduct preventative

maintenance on ship's battery(ies).



This line of reasoning sets the design goals

for an electrical system tailored to a project's

engine, airframe, capabilities and planned

missions. One goal is to minimize singling

out any particular set of loads as critical

but to consider the machine, pilot and

flight environment as a system.



Over the past 30 years, a family of architectures

have been proposed, refined, published and

applied to projects in the OBAM aviation

community. Some have served the builder's

design goals well . . . others not so well.

It's an iterative evolutionary process that

strives for demonstrable success.



The proposed Z01 architecture takes into account

the pronounced shift in aircraft designs that

incorporate multiple engine driven power sources,

electrically dependent engines and yes . . .

a desire to shed as much of the battery weight

and cost of ownership as practical.



Discussions here on the List and elsewhere

are needed to ferret out any failure to meet

a design goal . . . not as SUPPLIERS of any

particular electro-whizzy but as USERS

of those devices as components of the whole

FLIGHT SYSTEM.





   Bob . . .

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Peter(at)sportingaero.com
Guest

Posted: Wed Apr 01, 2020 2:01 pm Post subject: Some thoughts on 'standby' batteries

Hi Bob,



My last job working for a large blue chip company was part of the design

team for a nuclear submarine. As you can imagine some of the failure

scenarios in the risk register had some fairly catastrophic consequences. As

a result many sub-system owners sought to increase the reliability of their

functions by designing in back-up power supplies. As there was no overall

systems engineering lead (a failure of engineering management as much as

anything else) no-one had the required oversight to spot what was happening.

Before very long there were batteries for everything, with a huge

maintenance overhead (and their own failure scenarios). What was really

required was an electrical power policy at the ship level flowed down to

each sub-system, rather than the sub-systems driving what the ship was

doing. Eventually the high paid help realised what was happening and set in

place a painful (expensive, $$ and time) re-design that ended up having

quite far reaching impacts.



This has a direct parallel to OBAM aircraft. Many of the electro-whizzes on

offer include a back-up battery of some description. As the system design

authority for our own aircraft we have to be sufficiently smart to engineer

in power sources that meet our reliability goals, and not to be dictated to

by sub-system suppliers. That doesn't say back-up batteries in sub-systems

are necessarily bad, just that they have to earn they way onto the aircraft.

As ever the operational goals of the aircraft should dictate the systems

design and equipment selection.



Regards, Peter



--

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nuckolls.bob(at)aeroelect
Guest

Posted: Thu Apr 02, 2020 8:03 am Post subject: Some thoughts on 'standby' batteries

At 04:55 PM 4/1/2020, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "Peter Pengilly" <Peter(at)sportingaero.com>



 Hi Bob,



 	


   <snip>



  	  Quote: 	
		  Before very long there were batteries for everything, with a huge

 maintenance overhead (and their own failure scenarios). What was really

 required was an electrical power policy at the ship level flowed down to

 each sub-system, rather than the sub-systems driving what the ship was

 doing. Eventually the high paid help realised what was happening and set in

 place a painful (expensive, $$ and time) re-design that ended up having

 quite far reaching impacts. 	


    Yup . . . a story repeated countless times

    when legacy systems are burdened with new

    requirements for reliability. I try to avoid

    that condition for our readers by striving

    for architectures that are unlikely to come

    up short in the future.

    



   <snip>



  	  Quote: 	
		  As ever the operational goals of the aircraft should dictate the systems

 design and equipment selection. 	


    Absolutely . . .



    Which is why I encourage attention (1) making

    every bus 'reliable' and/or (2) not driving

    an 'essential' accessory from a minimally

    reliable source.



    The OBAM aviation supplier cannot

    know the technical acumen of every customer

    which no doubt drives their decisions/suggestions for

    adding batteries. Klaus advocated for

    an auxiliary battery to support his LightSpeed

    ignition products. The N811HB accident

    carried LightSpeed ignition installed contrary

    to both Klaus's -AND- AeroElectric recommendations.

    He was a defendant in the original filing

    of lawsuits but ultimately joined my client

    as plaintiff as the technical details of

    the case unfolded.



    I've often recommended that builders 'follow

    the manufacturer's instructions' when the

    conversation ponders departure from the

    printed instructions. So I'll have to

    be mindful of that 'rule' when encouraging

    our readers to do their homework such that

    departures from instruction are supported

    by good science and tribal knowledge.



    Thank you for your enduring participation

    on the List!



 

   Bob . . .

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