Avionics Cooling Fan

[Nathan Miller]

I'm ditching the Ram Air avionics cooling system to avoid the possibility of moisture infiltration while flying IFR. Unconfirmed, since I have yet to fly IFR in this aircraft, but I have (yet-to-be founded) concerns.

Question - in my stack, I have all new Garmin toys with integral cooling. No external cooling is required, as it states in the install manuals. However, I've retained 3 legacy boxes. 2 Collins VIR-350 Nav Receivers and a Collins VHF-250 Com which is used to monitor ATIS/AWOS and 121.5 while en route.

I can't see much heat being generated. Would it be a mistake to let these boxes passively cool?

Discuss

 

[Bell206]

Would it be a mistake to let these boxes passively cool?

Depends. Most avionics equipment has environmental temp operating ranges. In my experience, we've always preferred to run the radios in the lower range of eviron temps. Perhaps once you close off the ram air system put in a temporary temperature sensor behind the stack and see how hot it gets. You might be surprised how hot it can get.

 

[Nathan Miller]

Depends. Most avionics equipment has environmental temp operating ranges. In my experience, we've always preferred to run the radios in the lower range of eviron temps. Perhaps once you close off the ram air system put in a temporary temperature sensor behind the stack and see how hot it gets. You might be surprised how hot it can get.

Good point. And I had to check the manuals - surprisingly, the units can put up with 131°F (with intermittent temps up to 159°F for up to 30 mins).

 

[Bell206]

the units can put up with 131°F (with intermittent temps up to 159°F for up to 30 mins).

But you don't want to run that hot. Have always been told temps above 110-120 deg F start you on a slippery slope toward failure with any electronic item. While your garmins have fans, they'll be pushing that hot air where? On your Collins stuff?

 

[NordicDave]

Nearly all Garmin installation manuals specifically state additional cooling is OK, but if the source of the cooling is external ship air sources the warranty is void.

 

[kshaw]

I had a Sandia 3-port avionics fan installed in my Warrior a few years ago. https://sandia.aero/product/acf-328/ One port was piped into my Garmin 430w and another port was piped behind my avionics stack and blows toward remaining avionics. I had one port capped.

 

[Nathan Miller]

Nearly all Garmin installation manuals specifically state additional cooling is OK, but if the source of the cooling is external ship air sources the warranty is void.

I heard that rumor too. I've reviewed all of my installation manuals (GNX 375, GMA 345, GTR 225, GSB 15) and haven't found any language to support the rumor. However, given that I've spent more in my little stack of avionics than I did to buy my entire airplane last year, I think a lil' fan is cheap insurance

375 language: The display head has a cooling fan that draws air in through the side of the bezel and exhausts the air at the bottom of the chassis near the display head. No other forced air cooling is provided or needed.
345 language: 2.7 Cooling Air - The GMA 342/345 does not have provisions for attaching cooling air, however the thermal characteristics of the installation should always be assessed. An undesirable thermal condition could be created due to the unit's own internal power dissipation combined with restricted ventilation, or due to heat generated by adjacent equipment. Limiting thermal build up, by means of fan or natural convection is always a good practice and recommended to increase the product life.
225 language: 3.5 Air Circulation and Cooling - The GTR/GNC unit meets all requirements without external cooling. However, as with all electronic equipment, lower operating temperatures extend equipment life. Units packed tightly in the avionics stack heat each other through radiation, convection, and sometimes by direct conduction. Even a single unit operates at a much higher temperature in still air than in moving air. The GTR/GNC has a cooling fan integrated into the chassis to draw forced-air cooling through the unit. There are inlets along the right side of the GTR/GNC chassis that allow air to flow through the unit. Ensure that there are no obstructions to the air inlets or fan exhausts. Air should be able to freely flow from the chassis inlets to the fan outlet on the rear of the unit.

Each manual gives a URL for warranty information. No mention of ram air or external cooling air sources.

Again - fan = cheap insurance. Water and electronics rarely mix well to produce desirable results.