View Full Version : OAT gauge - static or moving air?
criticalmass
9th Mar 2001, 01:00
Should an Outside Air Temperature gauge for a light aircraft be mounted in static air or in moving air? (Max speed of aircraft is 85kts).
Thanks in advance.
Shouldn't make any difference really, ram rise due to speed isn't a factor at such low speeds.
Only thought I have is if its in static air it may not react as quickly to changes in OAT.
Aircraft I've flown in have them mounted in the airflow.
CaptainSquelch
9th Mar 2001, 14:56
On the other end HP, if it gets wet (rain) in the open airflow the probe cools due to evaporation and thus the temp indication can be considerably lower.
We had this problem on the CF6 engines where flying through rain fouled up the Compressor Inlet Temperature sensor which in turn fouled up the Main Engine Control causing loud bangs and lots of flames. Great way to make people wet in a closed cockpit.
Sq
criticalmass
10th Mar 2001, 01:19
The potential for cooling of the probe due to evaporation of water droplets was pretty much uppermost in my mind when I posted the question as I figured temperature rise due to compressibility would be practically negligable at 85kts IAS.
Looks like I need to have dynamic air-flow with some sort of water-trap to minimise accretion of liquid water on the probe. Actually, since the aircraft has an open cockpit, rain avoidance is a high priority anyway, meaning a reduced chance of liquid water gaining access to the probe in the first place.
I'll see if I can design/make a shroud to trap water but permit a resonably dynamic flow of air.
Appreciate all the help from fellow Ppruners.
Regards
HPSOV
10th Mar 2001, 06:12
Point taken,
Well, I just flew a Duchess this morning, and its temp probe sticks straight into the airflow into the rain (and yes it was raining!). So maybe it doesn't make enough difference in a lighty for it to matter? In a CF6 on the other hand I'm sure its quite a consideration!
CaptainSquelch
10th Mar 2001, 21:09
wind and rain :::
Miniature umbrella <
probe o
with the wind coming in from the left this it what the CF6 solution basically looks like:
:::<o
Keeps the worst of the rain away from the probe.
Hope you got the picture. Hope it works
Sq
criticalmass
11th Mar 2001, 02:21
Ahah! Looks like I should get my little lathe out and machine an open-ended tube,put an umbrella/deflector at the front, mount it facing straight into the relative airflow, place the probe inside it and add some side-holes. Should work just fine.
Again many thanks to all for the help.