By: Steve Mahoney, submitted Dec. 2004
You can also download and print this page as Word document
The Pacific Northwest where I live and fly is well known for it’s overcast rainy weather and I have slowly started to get my feet wet with a little light IFR in the BD. The more I venture into the clouds, the more find myself wishing I had better equipment. I really liked the HSI (Horizontal Situation Indicator) that was installed in the Cessna 206 I got my instrument rating in. The HSI makes instrument flying so easy, compared with a conventional CDI, and gyro that’s it’s almost like cheating if you use it on the instrument test. I also wanted to add a second com radio and a GPS with approach capabilities. I would keep my good old reliable KX- 155 radio and it’s KI209 indicator. I decided to pull my old loran …it really served me well over the years and it was tough to take it out.
After many years of planning and accumulating all the parts… used audio panel, gyro, instruments, and installation manuals, etc. I finally had all the pieces I needed to build up a king KCS-55A HSI system. At the last minute I broke the bank and purchased a Garmin GNS430 to drive it.
This included adding the following equipment I purchased used.
- KMA-24 audio panel
- Ki 525 HSI
- KG 102A gyro
- KMT 112 Flux gate
- KA51A Slaving accessory
The first thing I did, was to install all the antennas that would be needed. I needed to add 5 new ones (that’s a lot of antennas) I didn’t want to use splitters (too much signal loss). I didn’t want to add drag to the airframe so I did my best to keep them internal when possible.
- Marker beacon (internal, inside the right wing tip)
- VOR #2 (internal, inside the right wing tip) (Bob Archer)
- Glide slope #2 (inside right wing root)
- Com #2 (blade type on top of the cabin)
- GPS (on top of cabin)
With the exception of the Com, I used smaller diameter RG-174 coaxial cable and fittings in place of the fat RG-58u that most avionics shops use. This saved a lot of weight and is much easier to run down the inside of the box side channels. The loss in signal gain is really not that significant over the larger cable.
The HSI wiring harness is quite complex and connects all the various parts together so they work as one system. I started by drawing a diagram on my cad system of every connection. (See attached PDF file). It took me many months to fabricate this cable. I now see why a friend of mine had to Pay $5K (labor only) to get this same system installed in his twin.
There’s a lot of wires! (note: the alt encoder which interfaces with the GPS)
I built up the whole rack system, wired, tested and debugged it at my desk at home, before taking it to the airport for installation in the aircraft.
I didn’t want to add a million circuit breakers, so I developed a “ load center” using auto resetting poly fuses. I found out that these fuses are used by Rockwell Collins in the Heads Up Displays they install in many airliners. I laid out a PC board with surface mount LEDs which indicate the status of each supply circuit. This is used for troubleshooting on the ground and is not visible from the front of the panel. Green led indicates an energized circuit and red one, if it gets tripped. Without the transmitters active this thing uses 7amps!
Note the cooling hoses, which supply bleed air from the engine cooling plumes.
Gyro sits in the way back under the baggage compartment.
You may have been wondering about the costs… I paid $400 for the KMA 24 audio panel and about $3100 HSI components (indicator, gyro with the flux gate and slaving accessory). Not bad, in comparison to some of the new CRT screens out there.
I was fairly surprised at the amount of weight this added, most of these type systems are intended for larger aircraft. I kept my old vacuum DG just because I had it. But I’m thinking that some day, I can replace my vacuum horizon with the new solid state electric LCD one from Dynon ….then good by vacuum pump, regulator and hoses! I can then reclaim some of the added weight.
SCHEMATICS TO DOWNLOAD:
And here are the custom schematics I made when I did the radio installation. These contain very useful information to anyone installing these kind of radios. It took me over a year to research (many manuals) and debug and draw these schematics (notice the one is at revision 21 and the other at rev 9).