Can this RV-6 ASI be recalibrated ?

Bernie RV7 · #1 07-04-2016, 11:33 PM

https://www.dropbox.com/s/a72niddt76...6ASI.jpeg?dl=0

I believe my ASI is over reading by about 8kt, is this model able to be recalibrated or do I get another one.
Cheers Bernie

Ironflight · #2 07-05-2016, 08:51 AM

Are you sure it's the ASI? A static leak will cause just about that amount of error in that direction in many people's experience.

Bernie RV7 · #3 07-05-2016, 04:38 PM

Thanks Paul
I was assuming that the static system was ok because the discrepancy is between my new Gemini AP airspeed and my original ASI and both use the same static system.... but I will check the static system out for leaks before I do anything else.

Cheers

Mark Albery · #4 07-05-2016, 05:01 PM

The easiest way to check ASI calibration is to make a water manometer connected to the pitot head.
A suitable long length of poly tubing that's a tight fit on the pitot should work.

There are several online descriptions and tables for converting head of water to airspeed such as this.

If it's a heated pitot, you may have to break into the line to connect up your manometer.

It will also detect a leak in the pitot system if you see the airspeed slowly decaying.

catmandu · #5 07-05-2016, 05:52 PM

Yes, it can.

Someone I may or may not resemble might have let one like that slip off the wing during a recent EFIS screen size upgrade. After getting back into the E6B books and with the help of a couple apps airborne, I confirmed the TAS of the EFIS was correct, the IAS on the EFIS matched the IAS on my Gemini AP, so I concluded the ASI (which is now a backup to a backup) was reading incorrectly.

Decided to experiment, opened it up and quickly figured out there is a toothed cam driven by pressure change that rotates a gear attached to the needle on the face display. Said cam was barely engaging said gear, and obviously could have jumped a tooth or two with a sudden deceleration. Made an educated guess as to how many teeth to move the cam on the gear, bent it ever so slightly into a better engagement position and did a test flight.

I guessed well, ASI IAS was +\- 2 kts compared to the EFIS IAS, good enough for backup for me. Sorry, did not take pictures, hope the description helps.