Erratic Arspeed indicator

bertibub · Post by **bertibub** » Sat Sep 20, 2003 8:48 pm

We've been enjoying our newly restored 170A immensely but have come across an ASI that reads erratically. Speeds on same climb attitude, same load and same conditions vary from 40 to 80 mph. The static is clear and the system seems to hold pressure with no obvious leaks. The ASI was overhauled and calibrated prior to installation. The Pitot tube is not smoothly curved being slightly bent at the base but is aligned with the wing chord. The stall clean reads at 45 and full flap 40 mph
Any ideas???
Bert

spiro · Post by **spiro** » Sat Sep 20, 2003 10:34 pm

1.) make sure you've tested both static and pitot systems for leaks.

2.) check the pitot tube profile (drawing in service manual?).

n3439d · Post by **n3439d** » Sun Sep 21, 2003 3:41 am

water in the pitot tube/lines is a common cause of airspeed problems.

ken

wa4jr · Post by **wa4jr** » Thu Sep 25, 2003 2:46 am

I'd suspect water first and a break in the metal pitot line second. I've had the water problem, and while taking out the nasty A-30 encoder for a Sandia replacement, the shop found a crack/split in the metal pitot line in the area of the left front pillar. The aircraft had had two other pitot/static checks in the last year, but this leak was not detected. The third shop was more careful to find the leak. My static system had numerous leaks as well, again not detected by the two other shops.