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Ongoing ASI errors

I tend to rely on my AOA more than ASI anytime I'm below 70 knots anyway, I think I would prefer the accurate reading in cruise. YMMV.
 
lr172 said:
I ended up making the air dams out of .063" AL and my ASI at cruise seems to be about dead on. However, since adding the air dam, I have felt that my approaches have been fast, with floating. I did some stalls and my stall speed is about 7-8 MPH faster than during my Phase I. I did some GPS boxes and at 80 MPH, My Indicated is about 4 MPH high. I suspect it is even more at 60 MPH, but haven't tested there yet.

For those of you that have added these dams to increase static pressure, have you found similar results? Maybe the shape of my dam is part of the cause. Here is a picture of mine. It is just taped on until I complete testing.
Larry
Click to expand...

Not in my case. My ASI is within 2Kts from just above stall to top speed. I don't know but maybe making it too accurate on one end of the spectrum can make it a bit inaccurate at the other end.

:confused:
 
ASI reading too low

My ASI is reading about 5-10kts too low, depending on speed. I have the standard Van's static ports, and a simple stainless steel tube for pitot, in the same shape and size as the plans specify. Both were checked by an A&P to ensure that the instruments are reading correctly, so it is probably due to "installation error".

I have not yet flown with my wheel pants as I have been breaking in the engine, but will install them shortly.

Seems that reading too high is common, reading too low not so much. What's the currently accepted way of correcting this? Thanks!
 
rv8ch said:
My ASI is reading about 5-10kts too low, depending on speed. I have the standard Van's static ports, and a simple stainless steel tube for pitot, in the same shape and size as the plans specify. Both were checked by an A&P to ensure that the instruments are reading correctly, so it is probably due to "installation error".

I have not yet flown with my wheel pants as I have been breaking in the engine, but will install them shortly.

Seems that reading too high is common, reading too low not so much. What's the currently accepted way of correcting this? Thanks!
Click to expand...
The same method, but backwards. The small "air dam" goes in front of the static port hole instead of behind it. This is fairly common in some Cirrus airplanes.

 
Correct rivet for static port?

I did several 4 course speed runs to confirm my airspeed calibration and found it to be 7 kts lower than the GPS calculations.

I used a standard pulled rivet for the static port and am wondering if I this is correct, can someone please post a photo of the correct style rivet.

Thank you
 
dpansier said:
I did several 4 course speed runs to confirm my airspeed calibration and found it to be 7 kts lower than the GPS calculations.

I used a standard pulled rivet for the static port and am wondering if I this is correct, can someone please post a photo of the correct style rivet.

Thank you
Click to expand...

You want a broad-head rivet Don - something like this:

https://www.aircraftspruce.com/pages/ha/rivets/cowlsealhardware6.php

Used for baffle seals, you can also get them in aluminum - Van’s has them, but it was faster for me to find them at ACS.

Paul
 
Thanks Paul,
Looks like I have the wrong rivets and my punishment will be a trip into the
long and narrow.:eek:
 
Pitot and static leak test

rvbuilder2002 said:
Test pitot and static system for a leak.
Click to expand...
I had both tested by an A&P along with my transponder - they "passed".

IMG_0502-1024x1024.jpeg


I also used the type of rivet that Paul linked to - the broad head type that is also used on the baffles.

So an air dam in front of the rivet is the trick?
 
rv8ch said:
I had both tested by an A&P along with my transponder - they "passed".

IMG_0502-1024x1024.jpeg


I also used the type of rivet that Paul linked to - the broad head type that is also used on the baffles.

So an air dam in front of the rivet is the trick?
Click to expand...

Did the inspector also check the pilot circuit for leaks?
Your photo shows a static system test for a transponder certification. Here in the USA, having a transponder certification check done doesn't automatically mean that a pitot leak check is done also.

A leaking pitot circuit will cause a low IAS indication.

If you know for sure that it is leak free then a static pressure adjustment may be needed.


Edit: I just looked up the tester shown in your photo and the specs say nothing about it being able to pressurize and test pitot systems.
 
Last edited:
Pitot and static leak test

rvbuilder2002 said:
Did the inspector also check the pilot circuit for leaks?
Your photo shows a static system test for a transponder certification. Here in the USA, having a transponder certification check done doesn't automatically mean that a pitot leak check is done also.

A leaking pitot circuit will cause a low IAS indication.

If you know for sure that it is leak free then a static pressure adjustment may be needed.


Edit: I just looked up the tester shown in your photo and the specs say nothing about it being able to pressurize and test pitot systems.
Click to expand...
Yes, you are right - he had a different calibrated box for the ASI and Altimeter test - this is required as part of our "certification" process here.

IMG_0634-1024x768.jpeg


IMG_0624-1024x1024.jpeg


Just curious - wouldn't the leak have to be pretty big to cause a significant ASI error?

Thanks again for your help in debugging this.
 
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