Chuck and Ryan's Build Tips

[ceslaw]

Auto pilot, Part I

Auto pilot in a Carbon Cub? Purists would say ‘that’s just wrong.’ But in the broad scheme of things the additional cost is not that great and the G3X has the means of controlling it without any external controls, so no one need know our plane is so equipped. Unless they read this post.

Pitch. The bracket and hardware for the pitch control is straightforward. The positioning is pretty well defined by the bracket. Here are some tips:

1. Temporarily set the drive pulley in place when installing the bracket. The pulley should be centered below, and the bracket parallel to, the torque tube.

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2. Five of the AN960-416 washers provide about the right spacing between the bracket and the support clamps. Friction tape was used under each of the clamps.

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3. Use AN3-7 bolts to fasten the servo motors to the brackets.

4. A bit of filing was needed to fit the short perpendicular support that bolts to the servo.

5. The cable that goes around the pulley and connects to the control cable was not installed. It will not be added until after the plane is complete and all control surfaces adjusted.

Roll. The bracket and the hardware for the roll servo is from Tru Trak. Here are more tips:

1. There is a diagram on Drop Box under the Tru Track caption that references the location. We deviated slightly from those measurements so that the control arms on the servo and the torque tube would be on the same plane. (No pun intended). Note that the servo shaft will be parallel to the adjacent cockpit floor in this location. The backing plate on the outside of the seat base looks better positioned this way, in my humble opinion.

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2. The Garmin stop that came with the servo was used rather than the Tru Trak stop. A tiny corner of the Garmin stop was trimmed to fit. The arm does not reach the stop, but it will prevent the servo from going beyond its intended arc and locking the stick in a full left or right position. (This issue is detailed in the G3X manual).

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3. The control arm that bolts to the torque tube is secured with a single rivet on the bottom. We will not rivet it until the plane is complete and all adjustments are made.

4. The wire harness for the two servos was carefully routed and tied in place. Note that there are two extra green wires; GSA03A22 and GSA04B22. The former is grounded and the other connects to the Normally Open (NO) kill switch that needs to be mounted on the control stick. The second wire from that switch is also grounded with a builder supplied wire. All the wiring was routed to assure no interference with the control cable below the torque tube.

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5. Careful attention needs to be paid to possible mechanical interference between the battery cables and the servos. The roll servo linkage was very close to the positive lead, so an Adel clamp was added to an existing bolt on the front of the seat support. Another clamp was added to the side to neatly secure the wire harness.

[ceslaw]

Auto Pilot, Part II, Kill Switch

Adding the kill switch was expected to be a real challenge. How does one install a tiny switch inside a long tube and then tighten it once it is positioned? It turned out to be much easier than we expected taking only about 20 minutes.

The location was marked. It is directly below the PTT for the COM, just past where the padded hand grip will end which will keep it out of the way but easily reached. A quarter inch hole was carefully drilled, using a step drill to assured it stayed centered without damaging the trim and PTT wires.

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Next a length of stiff TIG welding wire (any stiff thin wire will do) was inserted through the bottom of the tube exiting out the quarter inch hole. The switch was then guided up the welding wire in the opening created by the two wires soldered to the bottom of the switch. With a minimal effort the switch popped right in the hole just as the welding wire was backed out and was easily pulled through so the nut and lock washer could be screwed on. It was tightened with a small wrench without turning the switch. This was a pleasant surprise!

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The grommet for the trim / PTT was popped out and the kill switch wire fed through. A separate matching Monel connector was added for the two switch wires and the shield wire. The position of the male and female connectors was reversed from the PTT plug so they would not inadvertently get misconnected

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The two conductors are connected, one to ground and the other to GSA04B22 coming from the autopilot harness. The shield was connected to one of the ground wires on the roll servo plug.

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[ceslaw]

ADS B Out, Part I

The FAA relaxed the standards for experimental aircraft with its announcement of a “performance based standard” for ADS B out in July, 2015, just before Air Adventure. Immediately thereafter Garmin announced the coming GPS 20A which would provide ADS B out with a Garmin ES equipped transponder. This opened the door to affordable ADS-B out. Several other manufacturers have since jumped on the band wagon as well.

The G3X system as packaged by Cub Crafters has all the primary parts needed for the GPS 20A to function including the GDL 39 (for ADS B in) and the GTX 23ES transponder, with the required extended squitter. So before putting the boot cowl in place the time was right to go ahead and get it installed.

Here is a list of parts ordered from Aircraft Spruce:

1. Comant antenna, CI-2480-201 11-05489 @ $573.00

2. Green 22 G hook up wire. 11-07796 @ .27/foot. [6 feet]

3. RG 142, M17/60. MIL-DTL-17 11-00043 @ 3.95/foot [10 feet]

4. 90^ RG 142 TNC connector 11-04450 @ $56.75 [1 each]

5. Straight RG 142 BNC connector 11-01802 @ $3.60 [1 each]

6. GPS 20A 011-03913-00 @ $845.00

7. Garmin Connector kit 011-03914-00 @ $25.00

Only specific antennas will work with the GPS 20A. (The antenna must have an internal amplifier). The Comant antenna is an expensive dual band VHF / GPS, but is what Cub Crafters will be using, so we expect it to work properly. It is specifically identified as an acceptable option in the G3X manual.

The aluminum turtle deck came pre drilled for the VHF antenna supplied by Cub Crafters. Unfortunately the Comant antenna has a different hole pattern with two antenna feeds: A BNC for the VHF line and a TNC for the GPS line. By placing the VHF BNC in the existing hole, the remaining holes can be drilled and all the pre drilled holes will be covered.

A pattern was made per the supplied dimensions and the forward pattern hole centered over the existing hole.

Once the five additional holes are drilled it looks a bit nasty, but everything will get covered up.

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Four 10-32 1 inch long SS bolts were used with small SS fender washers on the bottom side. This is, of course, temporary, since the turtle deck will have to be primed and painted.

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[ceslaw]

ADS-B Out. Part II.

The GPS 20A was mounted on the bottom of the transponder tray directly in front of the GDL-39. Two pieces of aluminum, 6” x ¾” x 1/16” were cut and drilled and installed using counter sunk screws, in the same manner as the GDL-39. Here is the hardware list:

1. AN507C632R8 Countersunk screw (8 each)
2. AN365-632A Nyloc nut (8 each)
3. MS35649-265B Brass nut (4 each)
4. AN936-A6 Lock washer (4 each)
5. AN960-6L Flat washer (4 each)
6. Aluminum, 6 x 1/16 x ¾ inch (2 each)

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Note that the way the hardware is used, the two units can be removed by simply unscrewing the nyloc nuts holding the brackets in place without removing the transponder from the tray. Torque seal was placed on the nuts that should not be removed, leaving the remaining clean, so that any would be future service person would be able to see which nuts should be unscrewed to remove the units.

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This location for the GPS 20A has several advantages. First, it is a logical location, keeping the two ADS-B units together. Second, it is easily accessible. Third, the LED indicator lights can be seen under the panel. Finally it does not interfere with the pilots legs and is barely noticeable.

[ceslaw]

ADS-B Out, Part III.

The RG-142 antenna cable for the GPS-20A was routed on the left side, opposite the VHF cable, to minimize the risk of interference. The cable is ten feet long. The power connection was routed to the avionics bus with an inline 3 amp fuse.

Although both the GDL-39 and the GPS 20A have in line fuses, we opted to wire them to a circuit breaker on the Avionics bus as well. Since we deleted the autopilot control head and replaced it with the two steam gauges, the circuit breaker marked GMC was not being used. It came with a 2 amp breaker, which we replaced with a 5 amp breaker. This gives us the option of manually disabling the two ADS B units by simply pulling the breaker. The “GMC” will be relabeled “ADSB.”

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The wire harness is a simple affair, as detailed in the G3X manual. The RS 232 Channel was used. Figure 23-2.3 from the G3X manual.

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The plug pins were soldered. Silicone self-adhesive tape was wrapped around the crimp point. I had not used this tape before; it is pretty neat stuff.

A #5 cushioned clamp was used to secure the wire to the side of the transponder tray.

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That green LED was a reassuring sight!

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Finally, a special thanks to Matt at Cub Crafters for posting the detailed information needed to get this GPS 20A installed. Without Matt's timely post this project would probably have been pushed back until New Years Eve, 2019, if ever.

[Dickey]

Great job with this guys! Looks great. I'm glad I could help.


Sent from my iPad using Tapatalk

[ceslaw]

Wiring, Part VI, Testing

Once the wiring was complete, we went back over every connection to make sure there were no errors. Before turning on the power, an antenna was connected to every device that would need one; a total of seven: GPS, XM, Transponder, Com, ELT, GDL 39, and GPS 20A.

The battery was temporarily placed in its location under the seat and the connections made. The MAIN switch was turned on. In a few moments the panel came to life with the ADHARS on the left and a map on the right. The map pinpointed our location. In the garage the GPS was picking up seven satellites! That made our day.

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The AV switch was turned on next. The radio lit up. We tuned in the local airport and it displayed the frequency along with the call sign: KMWA. By tapping on the airport on the map a menu comes up for that airport from which one can select “frequency”. Up pop all the frequencies used at that airport. Tap on the frequency and it simultaneously appears in the standby position on the radio and the G3X. You can make it primary either on the panel or on the radio. We next checked the PTT buttons and they all worked; just briefly since I don’t like transmitting inside a garage.

Next we turned on the IDDS. The voltage for that device appeared on the screen.

We turned on the ignition switch. In the “Left” position the “Right” warning light came on. In the “Right” position the “Left” warning light came on. In “Both” neither light came on. In other words, the warning lights go on when that side is NOT working.

The configuration files were downloaded from the Cub Crafters drop box per the instructions and loaded on the SD card provided with the kit. Once loaded on the G3X per the directions the instrument ribbon appeared configured for the Cub. Nice!

Each light plug was checked with a voltmeter, flipping the switches to make sure they worked. After confirming each light circuit was functional, it was checked off on the wiring diagram for future reference.

The trim control on the stick was operated. The sound of the motor at the aft end made it obvious it was working. We temporarily configured the trim control indicator just to make sure the indicator circuit was working. (It will have to be ‘fine tuned’ once the elevator is installed.)

Headphones were plugged into the jack. Radio signals from the local airport came in clear. But there was annoying background music. It took a couple of moments to realize it was the XM radio free sample channel coming through. I was surprised to get XM reception inside the garage! (My car won’t do that).

The ground wire from the stall warning was grounded. No doubt that warning will be heard!

There was concern that the autopilot screen would not come up on the panel. It did show up on the ‘configuration’ screen per the Cubcrafters specs, but the control screen would not appear. Mitch informed us that it will not appear until the magnetometer is connected and the ADHARS configured, which of course cannot be done until the wings are in place.

[ceslaw]

Wiring, Part VII, Final Inspection

Before the boot cowl was installed we wanted to make sure there were no issues that would haunt us later. When the wiring was complete the interior panels were temporarily placed. This led to a bit of re-routing.

On the left sided the interior panel has a distinct opening that the harness passes through on its way to the A pillar. We waited until this location was confirmed before wraping and zip tying the harness.

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The right side kick panel is intended to be easily removed to access the two batteries. With the panel in place we noticed several things. First, the wire harness coming up the side came in contact with both the cup holder and the battery bracket. A 3/8” standoff was added, similar to what was used with the fuel lines, to assure there would be no interference.

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Second, the transponder antenna cable tied to the forward vertical tube interfered with the placement of the leading edge of the kick panel. Those wires were re-secured and a small stand-off added to assure they would not interfere. Make sure the standoff is no longer than about 3/16” or it will interfere with the ignition pick up wires firewall grommet. Note the leading edge of the interior panels goes on the outside of the frame to keep them in place.

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[the standoff was shortened after this picture was taken.]

Spiral wrap was added to all wires that were in contact with the frame or boot cowl which could be affected by vibration over time.

Finally, I took a bunch of pictures of the wiring at different angles for future reference.

[ceslaw]

Firewall, Gascolator

Something about putting a square peg into a round hole; that’s what was going through my mind as I struggled to insert a grommet with an inside diameter the same as the hole it was supposed to go into. A call to Mitch confirmed that this was indeed the right grommet, I just needed to try harder.

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With some effort it did indeed go in.

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Just for fun, the fuel line fitting was pushed in place. Really snug. But now the method behind the madness became clear: the purpose of the oversized grommet is to provide a very tight seal around the fuel line fitting. Sometimes knowing where you are supposed to end up makes it a lot easier to figure out how to get there.

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[ceslaw]

Control stick handle

We ordered the optional padded control stick covers. They are inexpensive (by Cub Crafter’s standards) and come in pairs: not because you need two but because you will likely destroy the first one when putting it on. So here is our little trick to make installation easy.

A strip of plastic was cut from a zip lock sandwich bag about an inch wide and as long as possible. This was placed over the PTT switch extending both above and below where the padded cover would end up.

A bit of dish soap was rubbed on the control stick.

The padded handle was slid into place. It goes on easily until you hit the PTT switch. At that point the plastic from the sandwich bag will help guide it over until the hole is centered. Once in place pull the plastic sandwich bag material from the top and bottom. It should rip about where the PTT switch is located and come out in two sections, top and bottom.

If I had done this the first time I would now have an extra padded handle without a rip.


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The PTT switch is barely visible. The lower switch is the autopilot override.