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  #1  
Old 10-14-2021, 06:15 AM
Iluke Iluke is offline
 
Join Date: Jun 2011
Location: Hope Valley, Rhode Island
Posts: 170
Default IAS error 7 MPH a lot?

Hi everyone,

I'm doing my test cards as part of phase 1 and have determined my IAS is reading about 7 MPH low at cruise. Haven't finished all the tests yet, but it seems more accurate at lower speeds.

It's an RV-7 with a Dynon Skyview system including their pitot tube and stock Vans static ports.

7 MPH error at cruise sounds like a lot to me- Is it?

I previously tested my pitot system for leaks and found none. Any suggestions for where else to start looking fora problem?

thanks
Ivan
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Hope Valley, RI
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  #2  
Old 10-14-2021, 06:33 AM
664781 664781 is offline
 
Join Date: Jan 2005
Location: Powder Springs, Ga
Posts: 333
Default Manometer

Search the post for building a Manometer. It will tell you if your indication is good or not. If good then it is probably your static port.
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RV6A "Kurt's Toy" - Flying
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  #3  
Old 10-14-2021, 06:47 AM
sailvi767 sailvi767 is offline
 
Join Date: Sep 2010
Location: Charlotte NC
Posts: 1,364
Default

A 7 MPH error will make the Dynon wind indications unusable. As mentioned itís probably the static ports. A jewelers file and several test flights fixed my issue.
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  #4  
Old 10-14-2021, 07:22 AM
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 6,237
Default

Please post a picture of your static port as installed. This will help.
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  #5  
Old 10-14-2021, 08:19 AM
cdeggz cdeggz is offline
 
Join Date: Jun 2021
Location: Campbell, CA
Posts: 41
Default

Is it indicating faster than reality or slower?
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  #6  
Old 10-14-2021, 10:22 AM
Iluke Iluke is offline
 
Join Date: Jun 2011
Location: Hope Valley, Rhode Island
Posts: 170
Default

Thanks everyone-

Sailvi767- What did you do with the jewelers file that helped?

BillL- I will shoot and post some pictures as soon as I can get back to the airport.

Cdeggz- It is reading slower that actual. IAS indicating 150 mph when calculations based on GOS ground speed, density altitude and flying a three leg route to average out wind says it should have been 157 MPH.


-Ivan
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  #7  
Old 10-14-2021, 12:21 PM
sailvi767 sailvi767 is offline
 
Join Date: Sep 2010
Location: Charlotte NC
Posts: 1,364
Default

Quote:
Originally Posted by Iluke View Post
Thanks everyone-

Sailvi767- What did you do with the jewelers file that helped?

BillL- I will shoot and post some pictures as soon as I can get back to the airport.

Cdeggz- It is reading slower that actual. IAS indicating 150 mph when calculations based on GOS ground speed, density altitude and flying a three leg route to average out wind says it should have been 157 MPH.



-Ivan
I have the rivet head style static ports. They needed to be filed down to provide the best airspeed reading. I would test fly using the below TAS calculator, land and file then repeat. Took 3 flights to get it right.
http://www.csgnetwork.com/tasgpscalc.html
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Last edited by sailvi767 : 10-14-2021 at 12:23 PM.
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  #8  
Old 10-14-2021, 01:01 PM
BoydBirchler BoydBirchler is offline
 
Join Date: Jul 2020
Location: Indianapolis
Posts: 108
Default

Adjust the indicated airspeed for temperature and altitude to determine "true airspeed": you may very well find it is indicating closer to what it should than you would first think.
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  #9  
Old 10-19-2021, 08:34 AM
Iluke Iluke is offline
 
Join Date: Jun 2011
Location: Hope Valley, Rhode Island
Posts: 170
Default Static port problem?

Quote:
Originally Posted by BillL View Post
Please post a picture of your static port as installed. This will help.
Thanks all for the replies. I collected and analyzed more data and confirmed that my IAS is reading low across the speed range, suggesting high pressure in the static system.

I am posting pictures of my static ports and would welcome any thoughts.

How do I know IAS is low? I ran the three-leg test recording GPS ground speed, averaging it to adjust for wind, corrected to TAS using an electronic E6B for temperature, altitude and altimeter setting. I consistently found IAS 4-5 MPH low at pattern and approach speeds and 7-9 MPH low at cruise.

This suggests that the pressure differential between the pitot and static lines is less than it ought to be, meaning either the pitot side is too low or the static side is too high. I did a leak-test on the pitot side and found no significant leak-down. So my suspicion is that the static ports are somehow resulting in high pressure.

Is my logic sound?

Thanks, -Ivan
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  #10  
Old 10-19-2021, 09:35 AM
mountainride mountainride is offline
 
Join Date: Jan 2018
Location: Golden, Colorado
Posts: 58
Default

I had the opposite happen where an incorrectly installed static port caused a low pressure burble and a higher than actual airspeed. This magnified at higher speed.

Also skydivers when positioned just right on the rear step of a king air, sometimes caused altitude to jump a few hundred feet.
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