Sunday, December 28, 2008

Electrical system work

I had hoped to spend the weekend working on finalizing the electrical system for N614EF. I've tried; I really have. I put together the load analysis spreadsheet for the Vertical Power system, and I realize the instructions need to be "dummified" more. Why? Because I'm a dummy, not an electrical engineer.

I'm a writer and if you could design and install an electrical system by turning a phrase or two, I'd have it done by now. To people well-schooled in electronics, a schematic is much easier to implement than subject-verb tense agreement. Everybody's different.

It's still not clear to me, for example, how I supply always-on power to the Dynon unit (which keeps the clock updated etc.). As near as I can tell, the wiring would require a line from the battery, which tells me that there should be some sort of battery buss somewhere under the subpanel somewhere, in a fashion that avoids the Vertical Power control unit altogether.

Vertical Power's Marc Ausman -- a really good guy -- said on VP's support forum, "...anything else will will be powered from the VP-50 or the aux bus (like starter contactor power) which is wired downstream of the battery contactor." I get that, I guess. But it's still not clear to me what that looks like when I lean over and look at someone's RV subpanel.

And therein lies the problem for people like me. We learn by actually SEEING things. I can ruminate for hours over what a schematic tells me about what to do with shielded cable, but it's a lot easier for me to look at that schematic, then go downstairs and pull out the Dynon harness and see what SteinAir did. Voila! Now the schematic makes sense because I saw what it looks like in real life.

This is a typical electrical system schematic:

After spending weeks looking at that, it finally made sense what the philosophy of it was. But what does it look like in an RV airplane? I couldn't tell you, but because this is one of the most common installations, there are enough builder Web sites out there to give me a clue.

And this is also why Van's electrical system instructions are so good for people like me. It approaches building the system this way:

1. Start here.
2. Mount this thing there.
3. Mount the other thing here.
4. Run a wire from this location, to that location and back to this location.

See what I mean? It doesn't give me philosophy, it gives me instructions. And because Van's is helping you build an airplane, they don't just concentrate on their own product and give you only the information pertaining to its product, they tell you the whole shootin' match.

In other words, they're focused on the whole, not on the parts.

Here's an example. Dan Checkoway's excellent Web site carries pictures of the firewall and such things as the ANL limiter. Now, I've read the AeroElectric Connection -- about 13 times. And it sort of makes sense in its philosophical ways, but a site, like Dan's, which says "put this here, put that there, the hambone is connected to the leg bone" is the way instructions should be put together for airplane builders like me.

Unfortunately, that's not possible with a product so new as Vertical Power. Don't get me wrong, it's a great product and the instructions are well written, but because it's such a new product, there aren't any Web sites out there that do for it what sites like Dan's, or Walter Tondu's do for the traditional electric system.

I was out at the hangar yesterday trying to figure out where to mount the Vertical Power-50 control unit. With a traditional unit, you enter your search terms in Google, check however many of the 1,000 RV builder Web sites you want, and do what they did. You can't do that with the Vertical Power system. There's only one RV-7 builder site. Bernie Daenzer and Alex Lichtensteiger's , and they're using the VP-200. Also, it's not a step-by-step Web site.

So, I never really came up with a good solution, partly because I don't know what else I need to fit under the subpanel because there aren't any Web sites with pictures and step-by-steps of installing a complete electrical system.

So what to do now? I have to think some more about whether I'm the right guy to be one of the first builders to install a VP-50. If I am, I'd put together a Web site on how to do it. Or do I want to punt and just go back to the tried-and-true traditional electrical system, and take advantage of the online resources that, as I indicated, are available? A lot depends on the answer to that. I can't send the instrument panel out to be cut until I know whether it will have circuit breakers, for example.

One thing that's great about the VP boys, however, is when you send them your load planning worksheet, they send you back suggestions for how to improve your plan. You gotta love that!

Here's what changes Marc made to mine (including catching my mistakes):

-Swap the EFIS and 296. The loads were not correct, and Dynon recommends a 3A breaker.
- The flaps draw 4.4 amps under load. So I put them on a 10A circuit. Usually a 5A CB is fine, but sometimes you need more.
- The flaps need to have their own external flap switch, the VP just provides power (unlike the VP-100 and 200 which actually drive the flap motor directly). See VP-50 wiring diagram.
- What trim systems are you installing? The trim is not filled in (some blacked out).
- Do you have a 296 or 496? It is unclear. In either case, it is on its own pin
- I put the aux bus items each on their own pin. You have extra pins.
- I assume the ext warning light is for something else and you just need power? It is now on J8-23

Odd, I don't remember adding an exterior warning light. I don't need it, though.

Here's what my spreadsheet looks like:

Once I fully understand the Vertical Power system, then I have to figure out how to set up a backup system in case it goes south. With the schematic above (the traditional system), you can flip a switch and voila! You're on a backup electrical system. Simple? No, but as I said, enough people have put this system in that you can just look at where they put what and do the same thing.

Vertical Power has drawn out a schematic for a "get home" system here. As near as I can tell, it takes the main battery power, runs it through a fuseblock, and then out to the Vertical Power unit. And then has several switches to bypass the VP-50 if you need to. Philosophically, I get it. I also get that it adds expense back to a system that I'd hoped the VP-50 would cut. What it looks like behind the panel? I haven't a clue.

It's times like this I really appreciate the homebuilders of yesteryear. They had no Internet to compare their projects with. Of course, they didn't have the electrical systems homebuilt aircraft do today.

Meantime, if you have also purchased a Vertical Power 50 system for an RV-7A and you've designed your electric system and have some pictures of your installation (maybe even a step by step guide), by all means, contact me.

One thing I did accomplish yesterday was finalizing the location of the main instrument on the panel -- the Dynon 100.

This will require moving the left rib closer to the center. I also moved the backup airspeed and altimeter to just left of the Dynon (instead of below it) and moved the TruTrak autopilot selector to below the Dynon. I also eliminated one switch. Now I've got to figure out how to get this into some sort of CAD design to take to place that can cut the panel.

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