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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: 167
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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Ivan Luke
Hope Valley, RI
RV-7 SB
Flying as of 9/13/21 (9 1/2 years!)
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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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Kurt Lohmueller A&P, DAR
Powder Springs, Ga
RV6A "Kurt's Toy" - Flying
RV12 - Flying - Sold
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  #3  
Old 10-14-2021, 06:47 AM
sailvi767 sailvi767 is offline
 
Join Date: Sep 2010
Location: Charlotte NC
Posts: 1,361
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 online now
 
Join Date: Sep 2007
Location: Central IL
Posts: 6,220
Default

Please post a picture of your static port as installed. This will help.
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RV-7
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  #5  
Old 10-14-2021, 08:19 AM
cdeggz cdeggz is offline
 
Join Date: Jun 2021
Location: Campbell, CA
Posts: 33
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: 167
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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Ivan Luke
Hope Valley, RI
RV-7 SB
Flying as of 9/13/21 (9 1/2 years!)
2021 dues paid
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  #7  
Old 10-14-2021, 12:21 PM
sailvi767 sailvi767 is offline
 
Join Date: Sep 2010
Location: Charlotte NC
Posts: 1,361
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: 105
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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