Odd OAT readings.

[Karl Gosling]

My OAT reads spot on at ground level, matching what my car is showing and a standalone thermometer, it correctly shows a higher temp when I grasp the sensor with my hand and a lower temp if I cool it with a cup of cold water... But, once I take off and level out at say 2000agl it shows a HIGHER temperature by around 4 degrees than what it was on the ground?!
It's fitted to the rear underside of my CT2K's fuselage so no where near the exhaust, engine or any other source of heat and not in direct sunlight either.
As it seems to respond correctly to temperature change on the ground I am totally lost as to why it doesn't seem to be reading correctly once airborne, does anyone have any ideas please?!

Dynon Skyview HDX with OAT probe 100433-001

Thanks,
Karl

 

[jakej]

IMO - Underside of fuselage is not the place for it due airflow issues from the engine, I‘d install the OAT on the underside of a wing.

 

[airguy]

Agreed. You are getting engine heat under the belly of the plane. The ideal spot would be on the bottom of the wing, outside the propwash, like around the pitot tube area.

 

[Karl Gosling]

Ah this makes sense, I didn't think of prop wash, it's literally a hair dryer blowing hot air back towards the sensor isn't it... My installer obviously didn't think of it either.
Thanks chaps!

 

[Raymo]

My OAT reads spot on at ground level, matching what my car is showing and a standalone thermometer, it correctly shows a higher temp when I grasp the sensor with my hand and a lower temp if I cool it with a cup of cold water... But, once I take off and level out at say 2000agl it shows a HIGHER temperature by around 4 degrees than what it was on the ground?!
It's fitted to the rear underside of my CT2K's fuselage so no where near the exhaust, engine or any other source of heat and not in direct sunlight either.
As it seems to respond correctly to temperature change on the ground I am totally lost as to why it doesn't seem to be reading correctly once airborne, does anyone have any ideas please?!

Dynon Skyview HDX with OAT probe 100433-001

Thanks,
Karl

This is covered in the installation manual, page 5.15 in Revision AM

Sensor Location

The SV-OAT-340 is an outside air temperature sensor. In order for it work properly, it must be able to measure air temperature accurately. Avoid exposing the sensor to sources of heat that would interfere with outside air temperature readings such as:

• Direct sunlight
• Engine heat and exhaust
• Aircraft interior (back side of sensor)
• Heated air from the cabin exiting from an open window or cabin air exhaust port

 

[Jim8JD]

My OAT reads spot on at ground level, matching what my car is showing and a standalone thermometer, it correctly shows a higher temp when I grasp the sensor with my hand and a lower temp if I cool it with a cup of cold water... But, once I take off and level out at say 2000agl it shows a HIGHER temperature by around 4 degrees than what it was on the ground?!
It's fitted to the rear underside of my CT2K's fuselage so no where near the exhaust, engine or any other source of heat and not in direct sunlight either.
As it seems to respond correctly to temperature change on the ground I am totally lost as to why it doesn't seem to be reading correctly once airborne, does anyone have any ideas please?!

Dynon Skyview HDX with OAT probe 100433-001

Thanks,
Karl

This time of year here in Tucson I get higher temps when I climb a couple thousand feet from Thermal inversion affect, where cool air sinks so it is much cooler on the ground... high 60's and mid 80's when I climb up 2K. Nothing wrong with my OAT probe or placement. It only happens this time of year around here. If you keep climbing you will get through the inversion layer and the temp will go down like normal. Don't know if that is your problem but you might be seeing the same thing where you live.

 

[Karl Gosling]

This is covered in the installation manual, page 5.15 in Revision AM

Sensor Location

The SV-OAT-340 is an outside air temperature sensor. In order for it work properly, it must be able to measure air temperature accurately. Avoid exposing the sensor to sources of heat that would interfere with outside air temperature readings such as:

• Direct sunlight
• Engine heat and exhaust
• Aircraft interior (back side of sensor)
• Heated air from the cabin exiting from an open window or cabin air exhaust port

Yes we know, my installer thought it was more than far enough away from sources of heat and in fairness if asked I would probably have concurred... But it obviously isn't, we're moving it to one of the wings so that should be fine..

 

[Karl Gosling]

This time of year here in Tucson I get higher temps when I climb a couple thousand feet from Thermal inversion affect, where cool air sinks so it is much cooler on the ground... high 60's and mid 80's when I climb up 2K. Nothing wrong with my OAT probe or placement. It only happens this time of year around here. If you keep climbing you will get through the inversion layer and the temp will go down like normal. Don't know if that is your problem but you might be seeing the same thing where you live.

I actually wondered if this could be the case, I'm in the SE of the UK and it's only just Autumn here so I don't think thats what is, been the same for every flight since having my aircraft back on the 9th September and we've seen very varied weather over that period.