Effect of Air Temperature on Wind and Reefing?

[Dockhead]

Originally Posted by a64pilot

Speed is not changed of course, but indicated speed is with any device that mechanically measures airspeed.
The anemometer cups will be affected just like a prop would.
Think how fast the airflow would have to be to windmill your prop like it does when you sail, the difference of course is due to the density difference in air and water.
A standard day is 59F at sea level with a barometer setting of 29.92 " of Mercury. Assuming an air speed indicator is calibrated for a standard day, temps higher and or anything that reduces air density will cause a lower than actual indicated airspeed, lower will read higher than actual.

Now my just installed WSO 1000 measures temp, barometric pressure and even humidity. All the things required to take indicated airspeed and correct it to true airspeed. Now if I built the thing and had all the necessary data to correct indicated to true, I would, but I would have it software selectable.

Now our sails, just like the airfoils on an aircraft only " know" indicated airspeed, so displaying indicated airspeed would give you the most repeatable results for sailing.

I don't understand why the WSO measures temp, humidity and air pressure if it doesn't use that data?

Everything is affected by temperature, but not necessarily linearly. A cup anemometer rotates at a percentage of the wind speed -- known as the "anemometer factor". It measures speed of the rotating cups. The anemometer factor does vary with temperature, but not in a direct or linear way, unlike a tube anemometer which is not measuring speed, but pressure.


As to your WSO 100 -- don't jump to conclusions about what the other data is used for. I remember how many people were so sure that the Airmar wind transducer was using accelerometers to compensate wind data just because accelerometers existed in the device, and this turned out to be false. Sonic anemometers also need some compensation for temperature, but I don't think we know how or if it's done in the WSO 100. Maretron make a big deal out of temperature compensation in their fuel flow meters, but don't say anything about doing it in the WSO 100, so I'm not sure whether it is done at all or not.

"Why" it measures temperature and humidity is simple -- the WSO 100 is sold as a weather station, and outputs this data separately from wind data.