I've decided to remove my BE-LOVED Loran...my KLN-88....
...and replace it with a look-alike.... a KLN-90B GPS unit I've bought from a local avionics shop. This will likely take a week or two to complete as I've got other honey-do's scheduled in-parallel, ....and it's not as simple a swap as might appear at first-glance.... but thought I might as well bring it up in discussion.
Firstly, things the two units actually have in common besides mfr'r is their size, appearance, and many features of operation. They also have a mutal requirement for cooling of their CRT displays, and I will re-use the existing set-up of the KLN-88 installation, a small air-scoop on the left side, just aft of the static-port, similar to later C-172's of the mid '70's vintage.
The installation manual of both units state that ram-air cooling does not meet the requirements of warranty, that their KA-33 cooling fan or similar must be used. But I did/do not wish to make unnecessarily-complicated additions to this class of airplane and the cooling scoop is so nicely in the prop-blast, and with no plans to operate the unit more than a few minutes without the engine running, I had no concerns regarding adequacy of cooling air. (4 cu.ft/min are recommended, and the 10 years of operation of the KLN-88 has never given any indication of lack of cooling adequacy.)
I installed a small piece of screen material between the scoop and the scat hose to prevent the entry of insects, and I routed the scat forward/upward from the scoop to prevent water ingress, even in rain. There is no evidence of water ever entering the system despite numerous washings and countless flights thru moderate and heavier rainshowers.
The things that will require changes are:
1. The rack. They do not actually utilize the same rack despite their other similarities. The 88 used a 37-pin connector and the 90B uses a 50 pin connector, so their racks have different sized cut-outs for their connectors.
2, The antenna. This is an obvious matter, especially since the 88's antenna was mounted on the belly in order to avoid making holes in the cabin roof of my airplane, as during it's previous restoration that cabin-roof skin was completely replaced to get rid of numerous patches from previous years of avioncs/antenna changeouts. I also am in favor of as few holes as necessary in any roof, but directly overhead appears to be the best location for a GPS antenna.
I'd like to place the antenna along the centerline, but I am thinking about the possibility of the occasional avgas that might exit the gooseneck and flow back over the antenna, and also the fact that my comm antenna is already on the centerline and above the baggage compartment. The GPS antenna should ideally not be closer than 3 feet from any comm antenna and the centerline over the cabin will violate that by about a foot or so. (The KLN 90B does make claims to be more tolerant of comm-interferance than most other units, however I'd hate to cut a hole and then find out I've got a problem. This antenna-placement consideration is my most prevalent concern at the moment. Any/all input from others is solicited on this matter.)
3. Altitude input data. The KLN 90B requires altitude data, usually from an encoder, in order to provide accuracy for approaches. Although I do not plan to IFR-certify this installation, I would like to preserve the unit's capability in that regard. No other peripheral equipment such as OBS/CDI indicator, annunciators, or external switching is planned. This will be a stand-alone unit, but it will require patching the 90B harness into the existing harness between my Narco AT-150A and my Narco AR-850 encoder. The KLN-88 had no such input requirements.
I will begin removal of the KLN-88 this afternoon and will post updates as this changeout advances. Please post any comments/advice/laughter as you may feel inclined.
![Laughing :lol:](./images/smilies/icon_lol.gif)
PS: I have three KLN-88 units available for purchase by any interested parties. This includes the one pictured, as well as the two "spares" I'd purchased in anticipation of the future high-desireability of these model units. This includes the one John Hess unloade... errr... sold me at the Tehachapi Convention-auction,... doubtless contributing significantly to the assets of the Assoc'n. Anyone wishing to make a similar donation to our wonderful Assoc'n may purchase any/all of these units at a remarkable discount from their original $5,000.00 sales-prices. All proceeds will go to TIC170A.
![Very Happy :D](./images/smilies/icon_biggrin.gif)
PSS: The CRT in the 88's are very expensive should it have failed, I figured I might as well have cheap spares, another reason I wanted the extra units. This CRT should also be a swap with the same CRT in any 89/90A/90B series GPS, so I'll keep my 4th KLN-88 as a spare.)
![Wink :wink:](./images/smilies/icon_wink.gif)
![Laughing :lol:](./images/smilies/icon_lol.gif)