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  #11  
Old 11-26-2010, 07:34 PM
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dmaib dmaib is offline
 
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Originally Posted by jsharkey View Post
Suitably inspired I ran some tests today and input the data into the NTPS spreadsheet.

TAS as indicated by my temperature and pressure corrected Dynon D100 is consistently reading 5 or 6 kts higher than that calculated from the GPS496 ground speeds.

Anyone know what this means? It implies that the pressure difference between the pitot and static ports is higher than it should be. It's unlikely that the pitot is high so could the static read low if it has a leak?

Jim Sharkey
RV6 - Phase 1


PS - std dev was more like 1 kt instead of the 0.1 kt shown above. Guess I need to fly more accurately
Kevin Horton had an article in Kitplanes a few months ago that answered your questions. There are some mods to try with your static port, but I don't remember all of the details.
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  #12  
Old 11-26-2010, 08:22 PM
elippse elippse is offline
 
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Location: Arroyo Grande, CA
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[quote=jsharkey;375083]Suitably inspired I ran some tests today and input the data into the NTPS spreadsheet.

TAS as indicated by my temperature and pressure corrected Dynon D100 is consistently reading 5 or 6 kts higher than that calculated from the GPS496 ground speeds.

Anyone know what this means? It implies that the pressure difference between the pitot and static ports is higher than it should be. It's unlikely that the pitot is high so could the static read low if it has a leak? QUOTE]

It most likely means that the staic port is located in a place where the pressure is below static. Do you know that you have a leak, or were you just thinking that might be a possible cause? If you have a leak in the cabin the cabin pressure is usually lower than static which will make your IAS read high. You can compensate for a bad location by putting tape ahead of, reading low, or behind, reading high, the static port. What you are seeing is typical for most homebuilts! Two Q-200s that I know of had 15 kt errors, and three RVs had 9-12 mph errors.
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  #13  
Old 11-27-2010, 06:08 AM
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plehrke plehrke is offline
 
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Location: Defiance, MO
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Quote:
Originally Posted by elippse View Post
It most likely means that the staic port is located in a place where the pressure is below static. Do you know that you have a leak, or were you just thinking that might be a possible cause? If you have a leak in the cabin the cabin pressure is usually lower than static which will make your IAS read high. You can compensate for a bad location by putting tape ahead of, reading low, or behind, reading high, the static port. What you are seeing is typical for most homebuilts! Two Q-200s that I know of had 15 kt errors, and three RVs had 9-12 mph errors.
I did some calibration flights a few weeks ago and found my static to read low. This makes my calibrated airspeed about 8-9 kts low at cruise. Here is my calibration curve. (FYI, I used the Van's recomended location and the Van's static kit with the pop rivet port)

Either my static leaks or I have position error. Since I just had a transponder check I assume position error. I read some where to fly down the runway just few feet high at several different airspeed and see if you get different altitude readings. I did this and got a 50 ft higher reading at 80 kts then when sitting on the runway. At 190 kts IAS (remember Vne is CAS) I got a 150 ft increase in altitude. Not sure if that 150 ft reduction in static pressure results is the entire 10 kts of IAS to CAS correction. I have been reading a lot on Kevin Horton's website lately. Since my flight computer shows Calibrated airspeed readout by inputting the data in the graph above, I have decided to not fuss with the static port location until I get the urge to experiment more. One thing I really learned this year trying to get accurate speed data, is that your accuracy starts with the accuracy of OAT probe and pitot/static system.
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Last edited by plehrke : 11-27-2010 at 06:53 AM. Reason: added satement on static port I used
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  #14  
Old 11-28-2010, 12:23 PM
elippse elippse is offline
 
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Try about 5-6 layers of Scotch tape right behind your two static ports and do your runway thingy again. 50' is 0.05"Hg and 150' is 0.15"Hg, so you definitely need to increase the static pressure by putting some tape immediately behind it, about 1/2"H X 1"L. On my friend's RV-6 he ended up with a thicky washer cut in half and surrounding the rivet to get rid of his 11mph, 9.6Kt TAS error.
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  #15  
Old 01-07-2012, 06:26 PM
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petehowell petehowell is offline
 
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Default Year 5 Speed Data

Finished the annual over Christmas and just now had the chance get out for some testing. 875 hr on the plane. RV-9A, O-320, Carb, Dual P-Mags, Hartzell

Conditions: Temp -9C, Altimeter 30.11, 8000ft, MP 22.1 in, 2260 RPM,
1/4 Carb Heat

She is holding right in there - about 151 KTAS on 6GPH, and still a hoot to fly.

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Amateur Plane - RV-9A N789PH - 2050+ Hrs
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  #16  
Old 01-07-2012, 09:27 PM
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islandmonkey islandmonkey is offline
 
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The link to the spreadsheet your using is now broken Pete. I know that post was a few years ago but is there any way of getting another copy of the spreadsheet your using? I could help out here and include a link on my website to make this sheet available to VAF if you send me a blank copy of the sheet.

Tony
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  #17  
Old 01-07-2012, 09:49 PM
campi campi is offline
 
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Default Link for Download

Tony,

Take a look at the site: http://www.ntps.edu/ . Once there, look at the "information" tab, and select downloads. You will find both the word document explaining the procedure, and the excel spreadsheet.
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  #18  
Old 01-07-2012, 10:07 PM
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islandmonkey islandmonkey is offline
 
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Quote:
Originally Posted by campi View Post
Tony,

Take a look at the site: http://www.ntps.edu/ . Once there, look at the "information" tab, and select downloads. You will find both the word document explaining the procedure, and the excel spreadsheet.
Thanks Fernando that was just what I wanted.
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Anthony Johnston
Brit working in Zurich, Switzerland.
1500 hour pilot and ex instructor and examiner.
RV-4 s/n 4572 Emp Kit.
RV-3B s/n 11460 Emp Kit. (In storage).
Anthony's RV-4
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  #19  
Old 01-08-2012, 09:59 PM
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petehowell petehowell is offline
 
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Default New Link to GPS Speed SS

Here is: http://www.ntps.edu/images/stories/d...ts/gps-pec.XLS
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Amateur Plane - RV-9A N789PH - 2050+ Hrs
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Doggies Delivered - 25+
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  #20  
Old 01-18-2013, 06:20 PM
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petehowell petehowell is offline
 
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Default Year 6 Performance Data

Hi Guys,

Here is the annual update - the old girl has a 1000 HRS and 6 yrs under her belt.

She has not lost a step according the PEC 4way GPS Spreadsheet - actually picked up a knot!!. We tested at 8000ft/8370ft Density, 0degC, with Otto the pilot holding altitude and GPS ground track. Engine was set to LOP at 6.0 GPH and 2270 RPM. Here are the stats:



29 statute MPG at 175 mph. I still love this plane!

Nice high clouds above and frozen lakes below.....


Almost got her to hover in the wind!

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Pete

Amateur Plane - RV-9A N789PH - 2050+ Hrs
Amateur Radio - KD0CVN
Doggies Delivered - 25+
St. Paul, MN

Last edited by petehowell : 01-18-2013 at 07:34 PM. Reason: Pete kan't spel
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