13.6 Power Supply

This entry is part 43 of 67 in the series 13 - Electrical / Instruments

I went with a 24v electrical system. There are a couple of reasons behind this.

1) All new production aircraft being built today are 24v. 2) A 24v system is more efficient, uses lower current and requires a smaller diameter wire.
3) The engine came with a 24v starter and alternator.

Maybe not the best reasons, but they’re mine and that’s the way it is.

Once I started doing the electrical system, I learned of a drawback to 24v systems; In the experimental aircraft market, many of the suppliers are either 12v only or charge extra for 24v.  So for things like the EFIS screens, I had to pay a little more to get the 24v version.

But the area that really bit me was in batteries. The 12v guys have tons of small, lightwieght batteries to choose from. 24v batteries are pretty much unchanged. Frustrating, but I can live with that. Where it really stings is in battery backups. The EFIS supplier (Grand Rapids Avionics) have a backup battery that will keep the EFIS and AHRS screens alive for at least an hour if there’s an electrical system failure.  But it’s only available in a 12v version. That’s not a huge problem as I’ve got two alternators.

However, the EFIS screens also show engine information. And that’s nice to see when you start the engine. But when you start the engine, the battery voltage can drop low enough (under 20v) that the EFIS reboots.  So how to keep the primary screen glowing while starting the engine?  I looked at getting a couple of small 12v scooter batteries and wiring them in series. But then I would have to find a place for them. Possible, but that would add more work and I’m not looking for new work.

I thought about building a “de-slumpifier” from some plans I got from Eric Jones and Perihelion Design. Basically, it’s  a bunch of capacitors that discharge when the voltage drops to maintain 24v for a short period of time. But remember, I’m not looking for new things to do.

So then I got an email from Tim at TCW Tech. He provided my trim controllers. They also have an Intelligent Power Stabilizer (IPS). This is like the “de-slumpifier” in that it will continue to provide 24v if the input power drops down, but the IPS will continue to put out 24v all continuously as long as the input voltage is above 10v. Now it can only supply about 5amps but since the EFIS only draws about 1amp, that’s fine.

The next problem was where to put it.  My Avionics Sub-Shelf wouldn’t have enough room. So I have to expand it.

Here’s the original sub-shelf which sits over the VPX. The TCW Tech Trim Controller is on top. The empty area behind the trim controller is for the GPS.

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And here’s the expanded sub-shelf with a penthouse suite. The IPS is on the lower shelf where the GPS was going to go. Now the GPS will go on the upper shelf.

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Then I just added a pair of fuses to the fuse panel for the output to the primary EFIS and AHRS.

13.8.2 Annunciator Panel Problem

This entry is part 41 of 67 in the series 13 - Electrical / Instruments

On the annunciator panel, there are eight indicators:

Fuel Pump On
Pitot Heat On
Low Oil Pressure
Low Voltage
Starter Engaged
Pilot Door Unsafe
CoPilot Door Unsafe
Parking Brake Set

Most of these are activated by a wire going to ground which completes the circuit and turns the indicator on.  The Low Oil Pressure indicator wire goes to the Grand Rapids Engine Information System (EIS) alarm.

When I powered up the EIS and annunciator panel I noticed a minor problem.

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The indicators don’t photograph too well, but you can see the Low Oil Pressure is lit. Just not very bright. The problem is that I haven’t programmed the EIS to alarm on anything. Which means that the indicator is not on.  This occurs because EIS was designed to illuminate an incandescent light bulb. This results in some power leaking through the circuit that wouldn’t illuminate a incandescent bulb but does cause an LED to come on partially.

The standard fix for this is to put a 1k resistor across the LED to drain off the leaking voltage. But when I did this on the oil pressure LED, in addition to stopping the partially lit LED when it was supposed to be off, it also made it dimmer than the rest when it was supposed to be on.

Now this wouldn’t be a huge problem if it weren’t for being able to adjust the brightness of the annunciator panel. When I turn the brightness down, the Low Oil Pressure LED actually goes out while the other LEDs are still on. This could lead to not seeing a low oil pressure warning.

I tried numerous fixes and none worked. I eventually got a tip to use a MOSFET to control the circuit. This required quite a bit of hacking on the original PCB but it worked.

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It ain’t pretty, but it gets the job done. If/when I ever make a version 2 of the PCB, I’ll integrate the MOSFET circuit into the low oil pressure line.

Here’s the current annunciator circuit for anyone interested.

2014-06-20 Annunciator

15.2.7 Rear Vanity Panel

This entry is part 3 of 9 in the series 15 - Interior

At the back of the cabin (behind the rear seats), a horizontal baggage shelf and vertical vanity panel have to be fabricated. For the baggage shelf I used 3/8″ divinycell foam and two layers of BID on each side. For the other parts, a single layer of BID is all that’s needed.

First I used cardboard to determine the basic shape. At first, I wasn’t sure how I was going to deal with the transverse bulkhead and aileron cables. In the end, I decided to create small “boxes” cover that.

Here you can see the shelf, vanity panel and the front-to-rear parts of the boxes made from cardboard.

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Then I used the cardboard templates to cut the shelf and main vanity panel. I cut them a little big and sanded them down to fit.

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In this picture, I have the two sides of the boxes bonded together. I decided to angle the sides because… why not?

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And finally with the boxes finished. The green tape was just a g   uide to let me locate them in the same place while testing the fit.

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I bonded aluminum angle to the sides and bolted a piece across the back of the gear bulkhead to make the mounting brackets for the shelf. This is the only part that will be screwed down. All the other pieces will be velcroed. in place.

There’s a philosophy which says to make the vanity panel easily removable so that if the main landing gear doesn’t come down that I could go back and gain access to the gear mechanism. I just don’t know about climbing back there (in flight) to fix a landing gear problem. The risk management part of me says that rarely (if ever) has anyone been injured landing gear up.  But there are many instances where people have died messing around with landing gear.

So I haven’t decided about hinging the top of the vanity panel to access the gear mechanism. The vanity panel won’t be installed until I have many hours on the plane anyway.

 

12.3.5 Minor setback on Avionics wiring

This entry is part 40 of 67 in the series 13 - Electrical / Instruments

Tim at Approach FastStack saved me a ton of frustration when he discovered that I would have to have two displays. So here’s how the all the avionics will connect to the displays:

HXr-1Serial 1: Nav-1
Serial 2: AHRS-1
Serial 3: AHRS-2
Serial 4: EIS
Serial 5: Audio Panel
Serial 6: Com-1
Serial 7: Transponder
Serial 8: AutoPilot

HXr-2
Serial 1: Unused
Serial 2: AHRS-2
Serial 3: AHRS-1
Serial 4: EIS
Serial 5: GPS
Serial 6: Com 2
Serial 7: VPX
Serial 8: AutoPilot

But once I started getting everything connected, I discovered that the VPX should be connected to the number 1 display. That display will be on prior to engine start and the only way to see if there are any electrical problems is if the display that the VPX is connected to is powered on.

So a quick call to Tim and he said “no problem”. He’ll send me a new configuration plug that will put the VPX on EFIS-1, Serial 7 and the transponder on EFIS-2, Serial 1. Excellent! Two days later, I get the new config plug, and start getting the HXr’s setup. But the transponder isn’t talking to the EFIS-2!

Now here’s the big problem with remote avionics: You don’t even know if it’s on! With panel mount stuff, there are all sorts of lights and such that tell you if it’s on. So when the transponder isn’t talking, there’s no way to know if it’s dead, or on and not talking. I check power and I can see 24v to the connector that connects to the transponder. And the ground is good. So I can assume that the box is getting power. But I still can’t verify that it’s actually on.

What to do?

I connected the old config plug and powered everything up. Transponder is talking away. New config plug and the transponder is quiet.

Hmmmm.

Well, back in my early years, I used to spend a fair amount of time troubleshooting computer peripherals that communicated using RS-232. Which, coincidentally, is how the transponder talking to the EFIS. So I dug around in my old tools and luckily enough, I still my old breakout box. So I connected this in-line between the transponder and the EFIS and here’s what I saw using the old config plug:

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You can’t see it in the picture but the transmit and receive lights are flashing away.

With the new plug, those lights are out.

I do some tracing and it seems to me that the config plug is wrong. I email Tim and within an hour he responds that they made a mistake (and apologizes all over the place). I get a new config plug within a two days and all is well.

I just goes to show: it’s always something.

13.2 Panel installation

This entry is part 39 of 67 in the series 13 - Electrical / Instruments

I finished up the wiring and installed the pitot static lines. Mounting the speed switch for the two-speed trim controller required a building a mounting bracket. The speed sensor adjusts how fast the pitch trim motor runs (faster at slow airspeed and slower at higher airspeeds). But there’s an adjustment on the back (or bottom) of the sensor.

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When the panel was installed, I discovered that some of the wiring was interfering with the parking brake linkage and had to reroute a wiring bundle.

Here’s the installed panel with the landing gear control, master warning panel,  lighting sub-panel, left lower-panel, right lower-panel and backup EFIS mounted.

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Then I installed the two EFIS displays.

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Then I threw the master switch.

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12.3.6 Cabin Heat Damper Control

This entry is part 40 of 50 in the series 12 - Engine / Propeller

Like the Oil Cooler inlet damper, I was going to control the damper (or diverter) for the outlet to allow the heated air to dump overboard or into the cabin.  I had the servo and servo controller all set. But I couldn’t get a good mount for the servo and the damper.

I tried different size gears but the location and orientation of the damper prevented me from finding the correct position for the servo.

In the end, I had to fall back to the old standby of using a cable from the cabin.

I took the arm that I had originally made and put a cable stop on it.

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The I ran the cable from the copilot side of the keel just under the instrument panel, through the canard bulkhead, up, over and down to the outlet damper.

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I oriented the cable so that when the control is pushed in, it will direct the heated air overboard. When you pull it, the air will be directed into the cabin.

Here’s the control end of the cable.

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Now that I’m looking at this, I think that I’ll remove and paint it with the interior paint that I’ve been using.

 

 

15.1.4 Seats

This entry is part 2 of 9 in the series 15 - Interior

I had Oregon Areo make the foam for the front seats. They make seat cushions for military and high-end corporate aircraft. Their cushions are considered to be the best you can get. But they’re a bit pricey. So that’s why they’re only doing the front seats. And their job was even more interesting since I had to… modify the left seat to accommodate my longer than average stature. 🙂

For the back seats. I made my own by purchasing raw foam from Jim and Janet Fix of Hi-Tech Foams. In the 15 years we’ve been flying our 182-RG, we’ve put over 1,200 hours on the plane. In that time, the back seat has been occupied for about 100 hours. That said, the foam cushions I made for the back seats are way better than what’s in the Cessna.

For now, when I’ve needed to sit in the seats to determine a position for the glareshield, switches, etc., I would cover the seat with plastic and install the seat. But that’s an inexact science since an upholstered seat will be a bit wider and result in a slightly higher seating position. Which means it’s long past the time for getting the seats covered. I was going to use Dave Spano. He did Brett Ferrell’s interior and the glareshield for our Cessna. But he’s not in the upholstery business anymore.

I know the owner of a local body shop and he sent me to his interior guy.  Wicked expensive!  I called around, asked other builders, googled and found Flightline Interiors. I called and spoke with Abby. They specialize in RV’s but Abby said that they’ve done a couple Velocity’s. So Ann and I drove up with a front and rear seat (in the middle of snowstorm) and looked at some of their previous work. They really know airplane interiors!

One of my biggest concerns is that the pilot and co-pilot seats are obviously different sizes. I was worried that it would look funny after they were upholstered. Abby said that she had an idea on how to minimize the difference in appearance. She and Ann talked about colors, patterns, etc. while I watched the snow.

For material, we would use an “Ultra Leather” product. I’ve sat in chairs that use this material and it’s really soft, breathes well and isn’t as expensive and natural leather. The pattern is based on the design that Bentley uses in their cars. Colors will be consistent with the carpet, trim and safety harnesses.

So we got on the schedule and on the appointed day I drove the seat frames and cushions up to Burlington, WI and dropped them off. It was almost lunchtime so Abby directed me to Freds. They claim to have the best burgers in Wisconsin… I can not dispute that claim.

About a month later Abby called to let me know the seats were done. So back in the Explorer and up to Wisconsin (and lunch at Fred’s!).

Here’s the pilot and co-pilot seats. They don’t look that different to me. 🙂

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Here’s all four.

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The color looks quite a bit… lighter than I expected. But Ann says it’s fine. And who am I to question anyone about colors?

13.2 Panel painting

This entry is part 38 of 67 in the series 13 - Electrical / Instruments

I’ve thought about different finishes for the panel. A couple of builders have gone with a carbon fiber finish. This looks nice but there are a couple of potential issues:  1) Getting the fabric to lay perfectly straight can be a challenge. 2) The finish would be glossy. I suppose that I could find a satin finish epoxy. 3) There is no chance for repair or modification. If a hole needs filled, it’s going to stick out like a sore thumb. With paint, you can either touch up or repaint the panel.

So then the question is, what color? On older aircraft, flat black was common. Newer panels when with gray in either flat or satin finish. I looked around and found a metallic dark iron gray.

Here’s the result (with the lower switch panels installed.

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13.7 Wiring

This entry is part 37 of 67 in the series 13 - Electrical / Instruments

Seems like a step backwards. It’s just a mess.

I’ve terminated some of the connections but trying to keep everything organized is a real challenge.  All the wires are in place, I just need to finish terminating them.

Here I’ve grouped the wires based on their destination.

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Next I’ll try to bundle them and finish this up.

13.7 Avionics and Wiring

This entry is part 36 of 67 in the series 13 - Electrical / Instruments

It’s time to start actually mounting avionics.  I’ve held off as long as I could because once the avionics shelf goes in, getting to things gets harder.

Prior to receiving all the various boxes that go on the shelf, I used blue foam cut into the correct size and shape to determine where everything would go.

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But now it’s time to start mounting things. Some builders will wire the components up on the bench first. But I couldn’t imagine running all the wiring for that temporarily.

Here’s the two comm radios and single nav radio. I made the brackets which combine the three radios into a single unit for mounting.

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Then I added the transponder (which actually attaches to a mounting tray.

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Next I put in the mounting tray for the FastStack wiring hub that all the boxes will connect to.

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And finally the Audio Panel. The AHRS, VPX, and trim controller sub-shelf had already been mounted.

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Then I installed the shelf into the plane to make sure everything still fit.

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Now it’s time to start pulling wires.

The largest of the wiring assemblies were for the EFIS screens and the Audio Panel. So I put those in first since they have the largest bend radius.

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One of the things I was worried about was the connectors for the EFIS screens. The extend towards the avionics shelf and I was worried about whether the installed avionics boxes would interfere with the connections. So I came up with a rather low-tech approach.

I cut a piece of card stock the size of the EFIS screens and cut out where the connectors would be. Then I taped some long stir sticks that ended on the panel mounting screws.

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Then I just put the ends of the stir sticks on the panel mounting holes and I could see where the connectors would end up.

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This confirmed that the connectors would not interfere with any of the existing equipment.

At this point it was time to start pulling the rest of the wires. The FastStack Hub greatly simplified the whole process. But even with that, there are still a bunch of wires.

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After a while, it starts getting a little better looking. But still a long way to go.

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I felt like I should make sure the panel cutouts for EFIS screens, switch panels and power ports were correct (I had checked them individually but not all at the same time). So I made a stand to hold the panel up and installed all the components.

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The only thing left to do is mount the Backup EFIS.