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gerry.vandyk(at)eastlink.
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 Posted: Fri Dec 29, 2023 11:57 am Post subject: Re[5]: Tailwind Electrical System Drawing and Power Analysi |
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It will be for mainly VFR touring and vacation, IFR Training and eventually IFR travel though VFR will be preferred over IFR. The VFR weekend breakfast flyins and hambergers will likely be the bulk of service. I want the personal rating and currency and the airplane's IFR capability to be there the 2 or 3 time per year when it's likely to be required. Like an annual pilgrimage to Osh. I don't want to be stranded for weather that's overcast but otherwise fairly benign.
Does that answer the question?
Gerry
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Peter(at)sportingaero.com
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| Posted: Sat Dec 30, 2023 2:36 pm Post subject: Re[5]: Tailwind Electrical System Drawing and Power Analysi |
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Gerry,
In your initial post you asked for “a good critique” of your system, please take these comments in the supportive way they are intended… You are building a lot of redundancy (along with complexity and cost) into your system that may not be required by the purpose for which you intend to use the airplane. If you just want the redundancy, and will tolerate the complexity and cost, then ignore what I have written below.
Certified installations are required to operate for no less than 30 minutes following loss of the alternator. There are various rules concerning how to calculate that endurance, but if your system can run for 45 minutes on around 50% of the name plate battery capacity then you are in about the right place. Your planned usage doesn’t really need two alternators and may not need 2 busbars. The things that will cause you the most problems are engine reliability, maintaining control of the airplane and then electrical reliability. We’re not really concerned with conventional engine reliability here. Fitting an attitude indicator like a Garmin G5 (or similar with on-board sensors and back-up battery) will provide *a lot* of redundancy. It may be you could tolerate one bus bar and a POH list of stuff to turn off if the alternator quits.
The assumption is if the electrical supply is lost you will always be within no less than 30 minutes flying time of an acceptable alternate. Actually, with aggressive load shedding, you will almost certainly be able to burn all the fuel you have on board before the battery runs out of juice, IMC, IFR or VMC. In a Tailwind you should be able to fly 50+ miles, and make an approach, in 30 minutes. In actuality you should be able to fly for an hour or two.
Take a step back and look at the design of the whole electrical system. Considering your intended usage do you really need all the complexity you have designed into it? Will a single main battery, single alternator, single busbar, battery backed-up AI system satisfy you needs? What hazard is the 2 alternator, 3 busbar system you have drawn intended to mitigate?
Peter
Battery capacity – many battery manufacturers are not entirely helpful with their nameplate battery capacities with the makers of the Odyssey series top of the list. The stated capacity is sometimes at the 10 or 20 hour rate, so the power provided if discharged over that time. For our purposes the one hour, or even the 30 minute rate is what is important. That number is usually less than the number quoted in the sales literature. For a PC680 (nominally a 17AH battery) the one hour rate is around 12Ah. Battery endurance calculations assume a battery with 80% capacity (so shortly before replacement) with 10% charge used on the ground, so take 72% of the one hour rate (8.6 Ah for a PC680). “Aircraft” battery makers are usually a little more helpful. There are also guidelines on how quickly to assume the pilot can carry out any loadshedding.
From: owner-aeroelectric-list-server(at)matronics.com <owner-aeroelectric-list-server(at)matronics.com> On Behalf Of Gerry van Dyk
Sent: Friday, December 29, 2023 7:57 PM
To: aeroelectric-list(at)matronics.com
Subject: Re[5]: Tailwind Electrical System Drawing and Power Analysis
It will be for mainly VFR touring and vacation, IFR Training and eventually IFR travel though VFR will be preferred over IFR. The VFR weekend breakfast flyins and hambergers will likely be the bulk of service. I want the personal rating and currency and the airplane's IFR capability to be there the 2 or 3 time per year when it's likely to be required. Like an annual pilgrimage to Osh. I don't want to be stranded for weather that's overcast but otherwise fairly benign.
Does that answer the question?
Gerry
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gerry.vandyk(at)eastlink.
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| Posted: Sat Dec 30, 2023 3:53 pm Post subject: Re[5]: Tailwind Electrical System Drawing and Power Analysi |
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Yeah, I'm obviously not above a little healthy hyperbole now and then. ;^)
Gerry
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