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  #1  
Old 03-26-2021, 03:25 AM
KayS KayS is offline
 
Join Date: Jul 2009
Location: lake constance
Posts: 358
Default how far off was your 7's air speed?

Hi All,

i think most have done a GPS speed box run to determine their pitot/static error. let's omit the the instrument error, as this is different for every instrument. but for a standard RV7 with the static ports and pitot tube in the locations the manual tells you... how far off was your calibrated ASI over the speed range? was it indicating more or less than actual TAS?

Kay
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  #2  
Old 03-27-2021, 09:53 PM
Bob Redman Bob Redman is offline
 
Join Date: May 2006
Location: Newcastle NSW Australia
Posts: 91
Default STATIC ERROR

G'day Kay,

KIAS was within 1Kt of Van's published stall speeds for 1400 & 1800lb.

GPS box indicated (best fit) linear difference from stall to 4KIAS slow at 140 KIAS cruise.

Heated Dynon pitot. Standard Vans rivet static ports as per plans.

Cruise performance at WOT, 2400RPM, LOP, seems consistent with flight plan, Dynon TAS/winds/groundspeeds, and other RV-7 data posted here.

RV-7, IO-360M1, 2 x Pmag, Hartzell CS blended.

Regards,

Bob
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  #3  
Old 03-28-2021, 04:18 AM
penguin penguin is offline
 
Join Date: Jan 2005
Location: England
Posts: 1,103
Default

Using the Van's recommended static ports will give quite accurate airspeed reading, within 1 to 2kt through out the speed range. Flush static ports will give around a 10kt error. Inaccurate airspeed reading are usually caused by leaks in the pitot piping or static ports not accurately measuring the free stream pressure. Indicted airspeed will usually be lower than TAS, look up how to calculate TAS from IAS/CAS. The difference depends on your altitude and the OAT (difference in local air density compared to the standard atmosphere).

Pete
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  #4  
Old 03-28-2021, 05:47 AM
BH1166 BH1166 is offline
 
Join Date: Nov 2017
Location: Eatonton Georgia
Posts: 411
Default TAS Calculation

http://www.edwilliams.org/avform.htm. Was shared by Grands Rapid Technology support staff. I wanted to know how TAS was calculated with EIS4000 and Sport SX EFIS.

You can get real close by subtracting MSL from cruise altitude, multiply IAS by 2% for each 1000

EXAMPLE 6750 cruise altitude, surface below 750MSL ..... 6000 above surface MSL. 146 KTS IAS X 1.12 =163KTS
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  #5  
Old 03-28-2021, 12:47 PM
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rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,301
Default

Quote:
Originally Posted by KayS View Post
Hi All,

i think most have done a GPS speed box run to determine their pitot/static error. let's omit the the instrument error, as this is different for every instrument. but for a standard RV7 with the static ports and pitot tube in the locations the manual tells you... how far off was your calibrated ASI over the speed range? was it indicating more or less than actual TAS?

Kay
One key detail required to accurately answer your question is what actual static ports were installed in the standard location.

This one point has had major error induction in many RV's over the years when static ports other than the kit recommended ones were used.
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  #6  
Old 03-28-2021, 01:52 PM
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 5,889
Default

I plotted from 110/120/140/160 KTAS against GPS - multiple triangles and although it wandered a little with speed, was 1.4 kts low relative to GPS.

Vans rivet port, late 7 plan location.

It is sensitive though. My ports when viewed with a head magnifier had little burrs around the center. The rivet puller anvil hole was a little larger than the center hole in the pull rivet. I sanded lightly with #1000 sandpaper and it changed reduced the curve about .5 kts to it's current value. The paint shop masked the port rivet and I rechecked the calibration curve after paint to find it virtually identical.
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  #7  
Old 04-14-2021, 03:23 PM
BoydBirchler BoydBirchler is offline
 
Join Date: Jul 2020
Location: Indianapolis
Posts: 74
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My RV7 seems to be off about 5 kts slow. It was off about 15kts slow until I replumbed the static system.
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  #8  
Old 04-14-2021, 07:36 PM
rightrudder rightrudder is offline
 
Join Date: Mar 2014
Location: Laguna Hills, CA
Posts: 1,846
Default

My airspeed indication is slightly pessimistic, by about 1-2 kts, but that's within experimental error. Standard Van's setup with the rivet static ports.
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  #9  
Old 04-15-2021, 04:53 AM
KayS KayS is offline
 
Join Date: Jul 2009
Location: lake constance
Posts: 358
Default

my first try GPS speed run resulted in around minus 5 kt. that means my air speed indicator is a little bit pessimistic.

i have some fancy static ports installed that protrude 2 or 3/32. i don't recall the supplier.

when looking at your pop rivet reports, it seems to me that the standard super-simple el cheapo Van's solution is the best one. as so often, looks like Van's engineering did in fact invest more thinking into something than i did.

Last edited by KayS : 04-15-2021 at 04:57 AM.
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  #10  
Old 05-01-2021, 08:39 PM
BoydBirchler BoydBirchler is offline
 
Join Date: Jul 2020
Location: Indianapolis
Posts: 74
Default

Still 6 or 8 knots slow, after replumbing all static and pitot lines and drawing a vacuum on all lines to assure "NO LEAKS". Using Vans screw on static ports.
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