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Bill,
This is really a long shot, but I can remember some reference to a discrepancy in different versions of the plans on which bulkhead to measure from to install the port. Have you called Van's to confirm the location?
FWIW, my 1st -4 with flush ports was 10kts slow & 100ft low at cruise speeds until I glued the pop rivet heads over the ports. (Thanks to Kevin Horton on the RV-list.) After the pop installation, it read correctly.
Charlie
Michael McGee wrote:
At 13:12 2004-06-26, you wrote:
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This version reduced the altimeter error to 50-70 ft high and the indicated to around 7 KTs too high.
Not sure what to try for the next version.
Bill Eslick
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I'm surprised your ASI is that far off Bill. I'm using the same pop rivet static ports (one each side) and the ASI has been accurate to within 2 mph or less at all speeds I've checked. Tracy
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Tracy,
I am very sure the problem is static, since the altimeter reads high and two ASIs read exactly the same (Dynon and round-dial).
Since I have already plumbed in a static probe (removable), I will continue to investigate probe shapes until I get a winner.
Bill
You guys are comparing an RV-4 with an RV-6 (I know, you knew that). The -6 is known to have some flow separation aft of the bulkhead where the angle changes along the side. Bill, throw some yarn tufts in a grid on the side around the static port and forward past the bulkhead where the angle changes and go get some air to air pics. You should see a difference in the air flow patterns. This may help you pick a better location for the static port.
Mike McGee, RV-4 N996RV, O320-E2G, Hillsboro, OR
13B in gestation mode, RD-1C, EC-2
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