I have owned several airplanes over the years I have lived in the heat of the Texas Gulf Coast, but have never felt like I needed to have active cooling for my avionics. Partly, this is due to the advent of solid state avionics that use a lot less power (generating less waste heat), and partly because most avionics racks in panels allow a fair amount of natural ventilation. While the RV-3 we?re building is going to be sporting the latest in solid state boxes, the avionics stack - which is going to be mounted below the panel and between the pilot?s legs ? is going to be very compact and dense, allowing almost no air circulation through the units or the surrounding environment. For this reason, I?ve decided we should take advantage of the cooling air inlets on the back of the GNS 430 and GTX 330, forcing air through the boxes and thereby providing convective cooling for the equipment.
The problem, of course, comes when you see the price of an avionics cooling fan. Wow ? that?s a lot to spend for a computer fan with a duct and a couple of hose connectors! Fortunately, since we are homebuilders, tinkering and originality is encouraged?.we?re lucky to have a neighborhood store known as the Electronic Parts Outlet that specializes in having boxes and boxes of both new and surplus components. A few months ago, I was browsing the back shelve s and discovered some cooling fans that had been ?ganged? together for some unknown computer product ? four dual-disk 12 volt fans with a diameter of about two inches mounted on a common frame. Price for the assembly? $14.95! Although I had no project for it at the time, it called my name, and I couldn?t resist. It went in to the parts bin and into the back of my mind ? until I needed cooling for the RV-3.
The four fans came off the mount easily, and it didn?t take long to figure out the wiring for each one (no smoke escaped during the investigation). The problem was how to mount them and provide a reducer to attach a hose with an internal diameter of 5/8? that will interface with the Garmin radios. Fortunately, one set of shelves in our hangar is devoted to household repair items, and I happened to spy the PVC plumbing box. Sure enough, an inch and a half reducer was exactly the right diameter to sit on the end of the fan and direct the airflow into a piece of poly tubing with an outside diameter of ??, and an ID of 5/8? ? a little silicone would hold the tubing in place. OK, so how to attach the reducer to the fan?
Those who have done a Firewall Forward build have probably discovered the outrageous price of SCAT tubing. It is pretty much priced by the inch, so you do a pretty accurate job of estimating what you need before ordering, adding maybe a couple of inches ? just to make sure. Well, once you are done with the project, you generally have short little chunks four to 10 inches left over. I picked such a piece out of my box of scrap (never throw anything away, no matter what the spouse might suggest?), and what do you know, both the fan and the reducer fit inside the diameter like the proverbial glove. From there, it was a simple progression through sealant, cable ties, and judicious clipping of SCAT wire to make a complete fan, ready for installation. Just for fun, I built one with a lower-flow, short fan as well.
Unfortunately, when I went to flow test it with the clear tubing, I was seriously disappointed. I had reduced the diameter too far, and choked it. Without the tube, the PVC outlet roared ? with the tube ? nothin?. Once again, I am fortunate to have homebuilder neighbors, and one came up with some 1? CAT hose, and it fit snuggly inside the outlet of the fan package, and can be reduced at the radio end ? lots of flow too! A pair of these should be more than adequate for the two radios, and easy to mount with a large Adel clamp?
Paul
The problem, of course, comes when you see the price of an avionics cooling fan. Wow ? that?s a lot to spend for a computer fan with a duct and a couple of hose connectors! Fortunately, since we are homebuilders, tinkering and originality is encouraged?.we?re lucky to have a neighborhood store known as the Electronic Parts Outlet that specializes in having boxes and boxes of both new and surplus components. A few months ago, I was browsing the back shelve s and discovered some cooling fans that had been ?ganged? together for some unknown computer product ? four dual-disk 12 volt fans with a diameter of about two inches mounted on a common frame. Price for the assembly? $14.95! Although I had no project for it at the time, it called my name, and I couldn?t resist. It went in to the parts bin and into the back of my mind ? until I needed cooling for the RV-3.
The four fans came off the mount easily, and it didn?t take long to figure out the wiring for each one (no smoke escaped during the investigation). The problem was how to mount them and provide a reducer to attach a hose with an internal diameter of 5/8? that will interface with the Garmin radios. Fortunately, one set of shelves in our hangar is devoted to household repair items, and I happened to spy the PVC plumbing box. Sure enough, an inch and a half reducer was exactly the right diameter to sit on the end of the fan and direct the airflow into a piece of poly tubing with an outside diameter of ??, and an ID of 5/8? ? a little silicone would hold the tubing in place. OK, so how to attach the reducer to the fan?
Those who have done a Firewall Forward build have probably discovered the outrageous price of SCAT tubing. It is pretty much priced by the inch, so you do a pretty accurate job of estimating what you need before ordering, adding maybe a couple of inches ? just to make sure. Well, once you are done with the project, you generally have short little chunks four to 10 inches left over. I picked such a piece out of my box of scrap (never throw anything away, no matter what the spouse might suggest?), and what do you know, both the fan and the reducer fit inside the diameter like the proverbial glove. From there, it was a simple progression through sealant, cable ties, and judicious clipping of SCAT wire to make a complete fan, ready for installation. Just for fun, I built one with a lower-flow, short fan as well.
Unfortunately, when I went to flow test it with the clear tubing, I was seriously disappointed. I had reduced the diameter too far, and choked it. Without the tube, the PVC outlet roared ? with the tube ? nothin?. Once again, I am fortunate to have homebuilder neighbors, and one came up with some 1? CAT hose, and it fit snuggly inside the outlet of the fan package, and can be reduced at the radio end ? lots of flow too! A pair of these should be more than adequate for the two radios, and easy to mount with a large Adel clamp?
Paul
