Depending on the "system" you install might affect the location e.g. on the Dynon it can be wired into the Remote Compass... so wherever you choose the remote compass to go might affect the OAT probe.Mount Location
It is important that the OAT probe be mounted somewhere on the skin of the aircraft where it will not be affected by heat sources (sun, engine, aircraft interior, etc). It is acceptable to extend the length of the included wiring for the OAT. The ideal location would receive no heat from the aircraft engine or any other source in the aircraft body. While this may be impractical, it is a good idea to mount the probe as far away from heat sources as possible. On the RV series, common locations include the wingtip and under the horizontal stabilizer.
Roger on the NACA inlet not working, heard from dozens of builders on that. Locating it in the FAB is an interesting idea, never heard of it before. Might just work since it should be getting clean air before anything has a chance to warm it. I would think locating it as close to the inlet as possible would be the way to go just to reduce the chance of it picking up any heat. Regarding picking up heat due to the (slight) compression or speed of the, I'll leave that to the engineer types, but it should be considered.The NACA inlet doesn't work, I tried that and it reads high. I am in the process of trying a new place in the FAB intake. Maybe some one else has tried this but my first attempt is to put it just down stream of the Carb heat door inside the FAB. My theory is normally it will read inlet air temp and when I pull Carb heat I should be able to see a difference. The best choice perhaps will be two probes, one before the carb heat flap hinge and one down stream, that way you would always have an OAT. The compression of inlet air may raise the temp a tad but it has to be more accurate than the NACA inlet. Coments?
I'm not familiar with FABs, as I have fuel injection with the snorkel horizontal induction system. Would the back side of the probe be heated by air warmed by the engine? If so, it would almost certainly read too high, just as ones mounted in NACA scoops on fuselage sides read too high (they are warmed by cockpit air on the back side of the probe).Roger on the NACA inlet not working, heard from dozens of builders on that. Locating it in the FAB is an interesting idea, never heard of it before. Might just work since it should be getting clean air before anything has a chance to warm it. I would think locating it as close to the inlet as possible would be the way to go just to reduce the chance of it picking up any heat. Regarding picking up heat due to the (slight) compression or speed of the, I'll leave that to the engineer types, but it should be considered.
I would hope that a high quality OAT sensor would be relatively insensitive to the temperature of the back side of the probe. But, many builders are quite interested in low price when purchasing engine monitors, OAT systems, etc. So it is possible that some vendors are purchasing lower cost OAT probes that might not be so well insulated on the back side, so they can quote lower prices.From Kevin's post "I'm not familiar with FABs, as I have fuel injection with the snorkel horizontal induction system. Would the back side of the probe be heated by air warmed by the engine? If so, it would almost certainly read too high, just as ones mounted in NACA scoops on fuselage sides read too high (they are warmed by cockpit air on the back side of the probe)."
I aways assumed the NACA read high due to blowby at the cowl attach point. If the temp of the base affects the reading, the the FAB may not work so good because the base will be in Warm engine heated air. Are you saying the probe tip will be at a temp affected by incoming air on one end and a hot base on the other and therefore the net has to be warmer than incoming air alone? Reasonable and interesting, I think I need to do some tests with my solder gun tip!!