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  #21  
Old 12-19-2010, 01:28 PM
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Alan Carroll Alan Carroll is offline
 
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Default CAFE testing

Quote:
Originally Posted by DanH View Post
Interesting thread, because I too seem to have a static error.

Back when, I fired up the lathe and made some billet static ports. The shape is a copy of the standard pop rivet head, but they have a barb fitting on the inside. They are installed in the standard location for an RV-8.

But....my airspeed indicates faster than true, per the NTPS method.

Hmmm. Did I miss on the head shape, or does the fastback and one-piece bubble reduce pressure at the static port location as compared to a stock fuselage? I dunno....any other Showplanes kit guys with the same experience?

Anyway, confirm please....making the port more flush tends to increase pressure/lower IAS, and a more protruding head tends to lower pressure/increase IAS?
Dan,

The CAFE performance reports for the RV-8A and RV-9A compared IAS obtained from the aircraft pitot tube and pop-rivet static port, to CAS measured with a test boom. At cruise speeds the reported IAS was as much as 5 mph faster than CAS for the 8A, and up to 7 mph for the 9A.

I have flush static ports, which I used because of the barb fitting inside. I did fairly extensive testing of the system, using 4-way gps and Kevin Horton's spreadsheet. I found that my IAS was between 1-2 kts slower than CAS in the cruise range.

At face value these tests don't seem to support the idea that the pop-rivet static ports produce more accurate IAS. I know Kevin has found otherwise however, so maybe its aircraft-dependent?
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  #22  
Old 12-19-2010, 01:40 PM
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Ironflight Ironflight is offline
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Quote:
Originally Posted by Alan Carroll View Post
At face value these tests don't seem to support the idea that the pop-rivet static ports produce more accurate IAS. I know Kevin has found otherwise however, so maybe its aircraft-dependent?
Ah, but lots of testing by individual builders with the pop rivets argues on the other side. I know that mine is within measurement tolerances (1-2 knots) with the pop rivets by the same 4-way GPS and spreadsheets, and so have many others. Interesting about the CAFE tests, as this really supports hat every airplane must be tested to see how well it works...which is why we fly Phase 1 as a test program.
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  #23  
Old 12-19-2010, 02:31 PM
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Does anyone have any experience with the Cleveland ports installed in the RV-10 standard location?

http://www.cleavelandtoolstore.com/p...p?number=SPF50

These are what I installed early in the project without having talked to others about their static port choices on the -10. I wish I had gone the SafeAir route, but I'm curious to know if anyone has experience with these.

Thanks,
Phil


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  #24  
Old 12-19-2010, 04:20 PM
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O.K. folks...so at what airspeeds do we really need to be accurate? I got it close at both 160kts and 100kts, but way off on the low end. Will it be possible to get it within say, 2 or 3 knots all along the whole range from 5 or 10 kts above stall all the way to Vne or should I call it good?

Jeremy
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  #25  
Old 12-19-2010, 04:51 PM
elippse elippse is offline
 
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Default pop rivet static port

As I've reported several times on the forum, the three RVs I've had the owners test, a -6, an -8A and a -9, all using the pop rivet, had errors from 9-12 mph. I think part of it is due to the curvature on the outside of the rivet which drops the pressure at the center. It's a simple job to fix it. Just add some tape in front, for low IAS or behind, for high IAS, and do the GPS comparison at cruise until it's right on. My druthers would be to have it correct around cruise and not worry about low speed..
I think what's making the difference on various planes of the same type that had their ports located the same but different results might be the fuselage flow from the different type of props that are used. Most CS props have really bad, aerodynamically speaking, root shapes which really turbulate the flow along the fuselage. A lot of FP props have really bad root shapes too, shown by a flat triangular area just outside of the spinner, and less than correct root pitch angle which, just as with the CS props, causes really turbulent flow along the fuselage. Just use the rivet and correct it!
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  #26  
Old 12-19-2010, 05:26 PM
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RV10inOz RV10inOz is offline
 
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Paul Dye is correct.

GPS altitude is only a guide as to whether you are close to the mark. Confirming your thoughts so to speak.

check your statics folks!
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  #27  
Old 12-19-2010, 06:17 PM
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rleffler rleffler is offline
 
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Quote:
Originally Posted by Phil View Post
Does anyone have any experience with the Cleveland ports installed in the RV-10 standard location?

http://www.cleavelandtoolstore.com/p...p?number=SPF50

These are what I installed early in the project without having talked to others about their static port choices on the -10. I wish I had gone the SafeAir route, but I'm curious to know if anyone has experience with these.

Thanks,
Phil

Phil,

I don't have the links handy, but Tim had several write ups on his site. If my memory is correct, I think he ended up with the Cleaveland product and was fundemental in Cleaveland coming up with their second iteration of the product.

bob

p.s. I have these installed too.
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  #28  
Old 12-19-2010, 06:38 PM
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Hey Bob,

Do yours have a dome or are they flat? Mine are dome shaped and the current photos are flat. I am wondering if I might have the first version?
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  #29  
Old 12-19-2010, 06:47 PM
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rleffler rleffler is offline
 
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Quote:
Originally Posted by Phil View Post
Hey Bob,

Do yours have a dome or are they flat? Mine are dome shaped and the current photos are flat. I am wondering if I might have the first version?

I believe the dome ones are the newer version. If I recall Tim's comments correctly, the original flat ones were generating inaccurate results. The newer ones I believe he was able to get it to less than one knot of error.

I'm sure Tim or Mike will chime in.....

bob
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  #30  
Old 12-19-2010, 07:28 PM
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Yep, thanks!
I just found it on his site with 1.8 knots error. Now I just have to hope my NACA vents don't mess with it.

Thanks,
Phil
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