Outside air temp. probe

[N13BN]

If anyone has suggestions where to install an outside air temp sensor, I would be most interested. I'm trying not to re-invent the wheel.

Bill Newkirk
N283RV

[Webb]

Where ever you can reach the back of it, out of the sun, and out of the exhaust trail.

Mine is on the bottle of the wing, near the tank drain and I can reach the back through the inspection plate.

[Brambo]

I mounted mine ON the inspection plate under the wing. Easy to remove and replace if needed.

[L.Adamson]

Mine is also on the lower wing, and a lot more accurate than those that are stuck in NACA inlets on the side of these planes. The inlet mounted probes usually show higher temps.

L.Adamson --- RV6A

[randylervold]

If you mount it anywhere on the fuselage it will not read accurately... heat from the engine will bleed out and effect it. I recommend in one of the wing bays on either side of an inspection cover, easily reached that way. You could put it in the inspection cover also but then you need to disconnect it to get the cover out of the way.

[RV7AV8R]

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?

[Andy Hill]

Dynon Manual for 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.

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.

On our 8 we have the probe under the HS, and have no reason to believe it is anything other than accurate for it's needs - i.e. very occasionally look at it out of interest

[randylervold]

Originally Posted by RV7AV8R

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?

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.

[Kevin Horton]

Originally Posted by randylervold

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'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).

Any probe that sees the blast of moving air flow will read a bit high, no matter if it is in a FAB, on the bottom of a wing or in a NACA scoop, etc. But, the amount it reads too high should be fairly predictable, and you can take it into account when you look at the OAT. The probe will read too high by an amount:

ram temp rise = K * (TAS^2)/7592

where K = the recovery factor of the OAT probe - probably between 0.8 and 0.9.
TAS is true airspeed in knots
the temperature rise is in degrees C

So, at 180 kt TAS, the OAT indication would probably read about 3 deg C too high.

If the probe is mounted somewhere where it is not subjected to an air blast, it may not see a ram temp rise, but it probably is affected by a large delay when responding to changes in actual air temperature.

[RV10Rob]

On or near an inspection plate on the wing is perfect, assuming you're either still building or can run the wires easily.