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.
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.
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)
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.
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.