Outside Air Tempeture Instrument in Glider

I plan on installing a tempeture guage inside the cockpit of my
glider. I think it's a good thing to have that can add to safety.
For instance, it's nice to know just how hot it is during those summer
days on a short runway. Also, to know if your in potential icing
conditions at altitudes. I've hit some bad icing before in the
spring, at 15,000 feet that iced over my windshield so bad I couldn't
see out even with the windshield heat on (in an aircraft).

Most of all, I'm real interested to find out if anyone has installed
one and noticed a tempeture change when entering a thermal?

Can it be used, in anyway, to help center a thermal? Seek out a
thermal?

Some flight computers have temperature gauges built in or that can be
retrofitted. You can buy one made for a car at Radio Shack; they have a
probe that can be pushed into your fresh air inlet. Reaction time on any
of them is much too slow for identifying thermals; stick to your vario for
that.

At 13:26 28 October 2008, wrote:
I plan on installing a tempeture guage inside the cockpit of my
glider. I think it's a good thing to have that can add to safety.
For instance, it's nice to know just how hot it is during those summer
days on a short runway. Also, to know if your in potential icing
conditions at altitudes. I've hit some bad icing before in the
spring, at 15,000 feet that iced over my windshield so bad I couldn't
see out even with the windshield heat on (in an aircraft).

Most of all, I'm real interested to find out if anyone has installed
one and noticed a tempeture change when entering a thermal?

Can it be used, in anyway, to help center a thermal? Seek out a
thermal?

On Tue, 28 Oct 2008 06:26:14 -0700, scottandrewalexander wrote:

Most of all, I'm real interested to find out if anyone has installed one
and noticed a tempeture change when entering a thermal?

Its normal to use a sensitive thermistor-based temperature sensor to find
thermals when flying Free Flight duration models in a contest. The usual
temperature swing when a thermal blows through is about 1 degree
Centigrade though it can vary from 0.5 to 2 degrees depending on weather
etc. with the measurement made at around 5m. Secondly, you need a fast
response, which means a very small thermistor bead (no bigger than 0.8mm
diameter and under 0.5 mm is preferable) and it must be a naked bead -
common units which enclose the bead in plastic or metal probes are
useless because their response lags the actual temperature change by
anything up to 30 seconds.

I've never made or heard about comparable measurements at flying heights
and would be interested to hear if anybody else has measurements above
ground level. For the moment lets assume the same temperature range is
found at flying height.

Can it be used, in anyway, to help center a thermal? Seek out a
thermal?

You'd need a read-out with a resolution of at least 0.1C to be able to
reliably see the shape and position of a thermal so if your read-out
isn't that accurate you're on a hiding to nothing: my SDI C4 only reads
in whole degrees. Last but not least, its thermistor is buried in a 3mm
diameter plastic housing, so while its fine for monitoring the average
air temp or spotting icing conditions, its response is far too slow to
find thermals: a good vario has a 2-4 sec response, so it follows that
the thermistor-based thermal detector must have a similar response rate.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

Its my understanding that the thermal reaches the ambient air temp
pretty quickly due to nearby air being entrained. Its the water vapor,
being less dense than dry air, that makes the parcel of air bouyant
and inertia contributes as well. Could be wrong, though.

Mike

On Tue, 28 Oct 2008 06:26:14 -0700 (PDT),
wrote:

I plan on installing a tempeture guage inside the cockpit of my
glider. I think it's a good thing to have that can add to safety.
For instance, it's nice to know just how hot it is during those summer
days on a short runway.

Others have commented here on thermaling, but I'd like to add that I
wouldn't set much stock by an OAT for predicting density altitude.
Without airflow to stabilize its own temperature, it will just tell
you the temperature of whatever cockpit part it's attached to. Or
more, if it's exposed to sunlight.

In order to get the air temperature on the ground, you need a
thermometer in a well-ventilated and fully shaded spot, insulated from
its support.

rj