13.9.2 Auto Pilot Pitch Servo Mounting

This entry is part 35 of 67 in the series 13 - Electrical / Instruments

I’ve already installed the autopilot roll servo in the back of the cabin. Now it’s time to install the pitch servo.

First, I have to figure out the best location. After talking with Malcolm, I decided to put it on the right side of the canard.

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I made a mock bellcrank out of cardboard to determine how long the bellcrank              needs to be. My goal was to try and keep it from infringing on the avionics shelf area.

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After playing around with this bellcrank, the linkage, and some basic math, I determined that it wasn’t going to be a very big bellcrank.

I talked with Malcolm and he recommended cutting a notch in the canard so the bellcrank doesn’t have to move so far aft.

I contacted my friend Robert who fabricated the parts for my nose gear door mechanism and sent him the drawings for the bellcrank.  As usual, he came up with some really good changes.  While we were talking, I mentioned my frustration about drilling holes through the center of a shaft. He said “I can fix that”.  I figured that he would tell me some secret about how to drill holes.

About a week later, he called and I went to pick the bellcrank. Not only did he make me a bellcrank, but also a fixture to clamp it in place  and align the drill bit!  Sweet!!!

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Here’s a dry fit in about the location I think the servo will end up.

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Here’s the bellcrank clamped in place with the drill fixture.  I miscalculated the length of the bellcrank arm and had to drill another hole in the bellcrank arm. Once I was happy with the location, I drilled out the holes. And they were perfectly through the center of the torque tube.
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I made a pair of hardpoints out of aluminum and used structural adhesive to bond them in place.
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To make sure that I’m not going to go over-center on the servo, I made a protractor that allows me to measure the rotation of the bellcrank. With this, I was able to determine that I was about 10 degrees under the maximum rotation without going over-center.

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Next, I trimmed off the excess metal of the bellcrank and painted the parts.
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Another dry fit checking the motion.
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Covering the hardpoints with 2xBID
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Final installation (I still have to replace the phillips head screws and replace them with drilled head AN3 bolts and safety wire them).
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13.3.5 Avionics Wiring

This entry is part 34 of 67 in the series 13 - Electrical / Instruments

As I mentioned before, I have elected to go with the FastStack wiring Hub for the avionics. While the wiring and termination of the all the connectors is something I’m very familiar (and comfortable) with, the volume of it was a bit daunting.

This is the wiring for a Beech Duke.

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The Approach FastStack box arrived today.

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I’ve got to say this is some of the best documentation I’ve run across in a long time. Each cable is labeled and comes in its own bag with QC documents and configuration.

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The manual is also very clear and well laid out.

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In short, this should make the avionics wiring significantly easier.

13.2 Instrument Panel Layout

This entry is part 33 of 67 in the series 13 - Electrical / Instruments

One of the huge pitfalls that can ensnare a builder is what I call “panelitis”.  That’s when you start building the airplane and at the same time you begin designing and purchasing the components for the panel.

The problem with purchasing your radios and GPS, audio panel, instrumentation, etc., is that 1) the warranty will expire WAY before you get close actually putting it in the airplane and 2) technology will make the stuff you’re already bought obsolete.

Which is why I avoided anything to do with equipment purchases for the panel.

A few years ago I bought the EIS (Engine Information System) because I was installing the engine.  Then 8 months ago, I bought the Vertical Power VPX-Pro power distribution system because it was time to actually start pulling wires. So you see, I’ve been doing good. 🙂

From the beginning, I was planning on a “glass panel”. This is where the traditional “six pack” of gauges are replaced by an electronic display.  Just about every aircraft made today has this type of display.

Cessna-172-Instrument-Panel  vs.  c-172-g-1000-glass-cockpit

The vendor I was going to use is Grand Rapids Technologies. They’ve been making EFIS’s (Electronic Flight Information Systems) for a while and they have an excellent reputation. At the time, they had a couple different sizes of displays and I made a couple different layouts.

Panel4b

This is what I would call “rev 1”. The vertical dashed line indicates the center of sight from the pilot’s seat. Here I’m using two screens (one for flight information and one for engine data), a traditional radio stack, a circuit breaker panel and a trio of old school gauges as backup.

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This layout is similar to rev 1 but uses slightly larger screens in a side by side configuration. Another builder, Terry Miles, told me that reaching across with your left hand to work your primary radio can be really annoying. He suggested positioning it for easy left hand access.

I had actually purchased the backup instruments from my good friend Albert about 4 years ago. But then… technology advances. Companies started coming out with miniature EFIS that had built in batteries. This would eliminate the three gauges. So I sold the backup gauges (and even made a couple dollars). Over time, the backup EFIS units have gotten smaller and cheaper.

 

Panel4a

This is rev 3. Just like rev 2 except the backup gauges are replaced with the small, backup EFIS.

Then about a year and a half ago, I heard that GRT was coming out with some really new equipment. You’ll notice that all the designs that I’ve done have two screens. That’s because one of them is for flight information and the other is for engine information. I’ve always felt this is kind of wasteful. Well the new EFIS allows you to use an Android tablet as the second display. And… here’s the best part:  remote avionics. Which means that the radios, GPS, transponder and audio panel will no longer be taking up panel space. They will be mounted behind the panel and controlled from the EFIS.

So I made another panel layout.

Panel5

The new HXr screen is much bigger and I eliminated the circuit breaker panel because the VPX is controlled by the EFIS (or the tablet). This makes for a much “cleaner” looking panel. As soon as heard about the new EFIS, I got a quote. Huge savings over what I was planning. Then every time I stopped by at Sun-n-Fun or Oshkosh, I would have the quote updated.

Oh yeah, they also came out with their own autopilot. Which was a fraction of the cost of the S-Tec 55x that I had bought which was going to be a freakin’ nightmare to install.

See how waiting is a good idea?

So about 6 months ago I ordered the EFIS and auto pilot servos. I didn’t really need the EFIS yet, but it’s the only way to see what’s happening with the VPX power system.

So now it’s present time.

I’ve been trying to decide on whether or not to wire everything myself or use the Approach FastStack Hub. Normally, some of the wires from one device may go one, two, three, or more other pieces of equipment. So you have 25 wires coming out of one box with 10 going to box A, 5 going to box B, and 15 going to box C. With the FastStack Hub, everything connects to the hub. And the hub takes care to sending what to where. I asked around and everyone that’s done it both ways all said that would use the hub in the future.

I called Tim at Approach FastStack, told him what I was doing and he got to work.  A day later, I got “the call”.

So here’s the deal: All the radios, GPS, transponder, autopilot… EVERYTHING communicates with the EFIS. I’ve got about 11 devices in total that talk to the EFIS using serial ports. And the EFIS has eight serial ports. Don’t ask me how, over the last 18 months, I’ve gotten multiple quotes from GRT for a configuration that simply won’t work.

I called GRT and they confirmed what Tim had discovered. The only way to “fix) this is by adding another EFIS screen (8 more serial ports). The guys at GRT felt pretty bad that nobody ever noticed this so they gave me a pretty decent discount on the second screen. It still stings. And I’m going to lose some of the panel space that I would have been able to play with… and for a screen that I really don’t need… I just need the serial ports that come with it.

But at the end of the day, I’m still better off than I was 2 or 3 years ago.  (yeah, I’m trying to be positive)

Back to the drawing board for a new layout.

Electrical System - New

 

 

6.2.2 Safety Harness Hardpoints

This entry is part 14 of 42 in the series 06 - Fuselage

So far, the only safety harness hardpoints that I’ve installed are in the overhead beam for the front seat shoulder harness. I held off on the lap belt hardpoints until I had the harnesses so I could more accurately determine their location.

Well, the harnesses are in. I’m going with a 3/4-point harness in the front (3 attach points but 4 connections at the buckle) with an inertia reel for the shoulder harnesses.  The back will be the standard 3-point with a diagonal shoulder harness (just like in your car).

Here’s the front seat shoulder harness with inertia reel installed.

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I decided to embed the outboard lap belt hardpoint in the sill just in front of the B-pillar.

This the sill cutout

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Since the sill is about 3/4″ thick, I decided to use 3/4″ 2×2 aluminum for the hardpoint.

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Bonded in position with structural adhesive.

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And covered with two layers of Triax (to bring it flush with the sill and 3 layers of BID.

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Once it cures, I’ll drill a hole through the BID/Triax.

 

 

 

12.4.2 Exhaust Fairing

This entry is part 39 of 50 in the series 12 - Engine / Propeller

A while back I installed the custom 3 to 1 exhaust and made the cowling cutouts.

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The manual says a 1/4″ clearance but Malcolm says that close and the glass starts showing signs of charring. He recommends 1/2″.

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It’s a minor thing, but I think it will look and function better with some fairings forward of the exhaust. Not only will it be more aerodynamic, but it should be another path for air to exit the lower cowling.

My initial plan was to make the fairing out of blue foam and simply cover it with some BID. But Malcolm advised against that. He said that method would result in unneeded weight (doesn’t sound like much, but I guess every little bit counts), be a pain to cover and wouldn’t be as effective in being an efficient exit for air. He suggested in making a form, covering it on the outside, cutting away the cowling from the inside, removing the form and then adding fiberglass layups on the inside.

My first attempt at the forms was to use a mailing tube of the same diameter at the exhaust pipe.

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But that didn’t work very well so I used some blue foam, formed it to the correct shape and used 5-minute epoxy to attach it to the bottom of the cowling.

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Then to aid in making a consistent radius, I whipped up some sacrificial micro. I call it “sacrificial” because it will be removed from the inside once I cut away the cowling on the inside.

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Then I covered the forms and radius with duct tape.

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I applied 2xBID over the forms. That’s really not enough for a rigid structure but it’s only to get the shape defined.

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Once the layups cured, I removed the cowling and then began working from the inside to carefully cut away the cowling under (above?) the foam. This took a while because I didn’t want to cut through the fairings. So what I did was to make very shallow cuts well inside of the fairings and removed the cowling which exposed the blue foam.

Then it was time for another Hangar 18 trick… Acetone. Pour a small amount on the blue foam and it dissolves. Then just work and the remaining cowling with carbide burrs and some 24 grit on the grinder.

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Now it’s time for the reinforcement. One layer of Triax and two more BID gets applied to the inside. The result is a fairing that’s roughly the same thickness and strength as the cowling itself.

Here’s the cowling back on with some rough cuts for the opening.

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I fussed about what the final cut should look like. If I made it to have a consistent 1/2″ clearance to the pipe, it would have a funny shape. If I cut it to have a nice, symmetrical, pleasing shape, it would be too close in some places and too far in others. I spent about two days worrying that issue.

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In the end, I split the difference. If the places that it’s too close start to show charring, I’ll trim it back.

Once I made the cuts, I started filling process.

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All filled, sanded and ready for primer.

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A comparison (Before & After)

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