ASI mismatch/calibration

[uk_figs]

When I built my panel back in 2007/8 with the Dynon D100/D120 system I decided to add a backup ASI and Altimeter but rarely looked at them as I was comfortable with the glass. As a part of getting my instrument rating recently I had the IFR pitot static checks done which included my backup steam gauge altimeter and everything checked out fine.
During the partial panel element of the rating I decided to cross check the backup ASI against the EFIS display and noticed that my steam gauge ASI is consistently reading about 10 MPH higher than the EFIS indicated airspeed. All of the stall AoA tests were done with the EFIS and generally were very close to the vans published numbers so I believe the EFIS is correct. Is there a way to cross check the numbers and calibrate the steam gauge ASI?
Figs

 

[azrv6]

Kevin Horton leads the way. I have used this method with success.

https://vansairforce.net/community/showthread.php?t=326

 

[Carl Froehlich]

SNIPIs there a way to cross check the numbers and calibrate the steam gauge ASI?
Figs

The short answer is yes. The longer answer is you will need to make a rig to calibrate the analog airspeed instrument.

I made a simple (but amazingly accurate) manometer. I still have the scale to translate manometer height to airspeed - PM me your email address and I’ll send. I’ve fixed a few of the standard Van’s instruments to read right.

Note - there are several calibration set screws that need to be adjusted, some for low speed some for high. You’ll figure it out.

Carl

 

[planenutz]

If you wouldn't mind sharing that manometer information it would be appreciated.

My back-up ASI reads spot-on in cruise but seems to have an error at the lower end that annoys me. At approach speeds the ASI reads about 5 knots faster than the EFIS and after checking a number of times it seems the EFIS is correct.

 

[koupster]

A good starting point would be a check to make sure that the round dial ASI is hooked up to the same pitot and static sources as the EFIS without any kinks/restrictions or leaks in the systems.
An ASI with the static port reading cabin pressure rather pressure from a properly placed static port will not be accurate.

 

[Dan 57]

Using an avionics test set would be the quickest way for sure… a good relationship with your local provider sure helps

 

[uk_figs]

The short answer is yes. The longer answer is you will need to make a rig to calibrate the analog airspeed instrument.

I made a simple (but amazingly accurate) manometer. I still have the scale to translate manometer height to airspeed - PM me your email address and I’ll send. I’ve fixed a few of the standard Van’s instruments to read right.

Note - there are several calibration set screws that need to be adjusted, some for low speed some for high. You’ll figure it out.

Carl

Carl
PM sent
Figs

 

[uk_figs]

A good starting point would be a check to make sure that the round dial ASI is hooked up to the same pitot and static sources as the EFIS without any kinks/restrictions or leaks in the systems.
An ASI with the static port reading cabin pressure rather pressure from a properly placed static port will not be accurate.

Yes it is, tee'd off the fittings for the D100 and right next to it with short runs. The pitot static system passed all the IFR and leak down tests with flying colors just a month ago and the static ports are in the standard RV-7 location. I do have the static system bypass switch on the panel and I might try that this weekend just to see what the impact is
Figs

 

[Carl Froehlich]

If you wouldn't mind sharing that manometer information it would be appreciated.

My back-up ASI reads spot-on in cruise but seems to have an error at the lower end that annoys me. At approach speeds the ASI reads about 5 knots faster than the EFIS and after checking a number of times it seems the EFIS is correct.

Happy to Mike, but need you to PM me your email address.

Carl