---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Tue 06/13/23: 1 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 01:25 PM - Re: Re: Z101 switch state question: engine and main bus shutdown (Robert L. Nuckolls, III) ________________________________ Message 1 _____________________________________ Time: 01:25:51 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: Z101 switch state question: engine and main bus shutdown >Bob, >For me, the critical factor here is not independent control of the >battery; it's that the aux alternator is effectively playing the >role of the internal generation system of a magneto; supplying >electrical energy to the engine, even when the entirety of the >airframe is made electrically 'cold'. As drawn in Z101: What accessories will be fed from your proposed aux bus loads that you would not want to power in combination with keeping the engine running? The fundamental premise for the aux bus is to power accessories most useful for continuation of flight with minimal energy demands. Primarily of concern where battery-only ops are part of the plan-b, i.e. no aux alternator. When an aux alternator is present, then battery-only ops are so statistically remote that battery selection can be minimized for weight and volume . . . assuming that plan-b load analysis (and perhaps even flight testing) demonstrates that aux alternator will support necessary loads. >the aux alt cannot be working unless the aux bus is 'hot'. So, >if we make the airframe 'cold', we're left with the battery running >the high current-required engine control/injection system. Electrically induced smoke in cockpit is an exceedingly tiny risk. So aside from finding yourself on short-final-to-the-rocks, when would you expect to want the electrical system completely 'cold'? This condition would call for the engine to be shut down as well. So what's your FEMA/Plan-B analysis show? Will your anticipated aux alternator not carry the engine plus minimal flight accessory loads? >My choice on my project was to have both the output >and the control source tied to the *engine* bus, so >if muscle memory causes me to shut down the airframe >in an emergency, I can react in the same way that I >trained in old mag/carb aircraft. This leaves the aux alt >supplying current to the engine bus. Muscle memory? When did this replace a well conceived and practiced check list? When faced with a need to reduce energy consumption in a Z101 architecture, I would think that line item 1 would be to switch ENGINE BUS ALTERNATE source feeder ON. Item 2 would be to switch AUX BUS ALT FEEDER and AUX ALTERNATOR to ON. 3. Set master switch to OFF to kill any potential main alternator field drain and eliminate battery contactor drain. These steps carried out on the very compact DC POWER management panel will assure smooth transition to the Plan-B condition with no interruption of power to either engine or aux bus loads. >Running an automotive style high pressure fuel injection >system/computer/ignition places significantly higher demands on the >electrical system, making battery-only operation a poor choice if >there's any way to avoid it. Real world in-flight tests using a >good-condition PC680 has demonstrated a max endurance of about 40 >minutes of battery-only operation, even if the rest of the airframe >loads are minimal. Reading the PC680 capacity specs aligns with >real-world experience. Not acceptable, when it's so easy to work around it. If you plan an aux alternator then without a doubt, due diligence is required to confirm that it meets DESIGN GOALS for continued flight sans main alternator. Unlike the legacy considerations for sizing the main alternator, one doesn't have to consider excess capacity for battery recharging. You can PLAN for 100% utilization of alternator capacity for flight ops. Ideally, the aux alternator would happily carry those loads. I.e. battery energy is not a factor for planning. I'm not seeing any value for plan-b ops sans AUX BUS. Energy to Comm, primary nav, panel lights and transponder should not represent a terrible concern for aux alternator energy management. Been out of pocket for a few days. Sons came to trim some trees around the house and yours truly spent a few hours dragging bush and trucking loads to the dump. Feel like I went too many rounds in bar-room brawl! Bob . . . //// (o o) ===========o00o=(_)=o00o======== < Go ahead, make my day . . . > < show me where I'm wrong. > ================================ In the interest of creative evolution of the-best-we-know-how-to-do based on physics and good practice. ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message aeroelectric-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/AeroElectric-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/aeroelectric-list Browse Digests http://www.matronics.com/digest/aeroelectric-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.