PDA

View Full Version : Indicated Airspeed at idle on the ground



Wicked Stick
12-01-2010, 09:05 AM
Just wondering about an adjustment to the airspeed indicator at the very low end of the scale.
When on the ground with engine running at idle, I typically see about 14 to 18 kts.

My pitot tube is further outboard than Van's standard location so I don't believe it's coming from the prop wash. Granted there may be some wind from the outside environment.

I will check to see what it indicates inside the hangar next time I am there and see if it is closer to zero. If not, whats the recommended procedure to adjust it ? And more importantly, will adjusting it throw off the curve/numbers at the stall speed range ? (don't want to mess with that as it seems to be right on at that speed)

Trevor Conroy
12-01-2010, 12:13 PM
Adjusting it will throw off the numbers across the board. We cut off airspeed below 30 knots as the sensors are not accurate that low. If you are running the latest software, you shouldn't see any speed below 30 kts.

Wicked Stick
12-03-2010, 09:19 PM
We cut off airspeed below 30 knots as the sensors are not accurate that low. If you are running the latest software, you shouldn't see any speed below 30 kts.

Thanks Trevor,
I did notice that on the display it starts showing around 30 kts as I was taxiing into the wind. When I download the data log though it records and shows up as low as 14 kts.

Trevor Conroy
12-06-2010, 09:15 AM
That is an acceptable reading. The air-data sensors are not accurate at very low speeds, which is why we clamp them off until 30kts on the airspeed tape. However in Instrument Calibration and in the data logs you may see a small indication of speed.