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  #21  
Old 01-23-2020, 10:01 AM
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GalinHdz GalinHdz is offline
 
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Originally Posted by rvbuilder2002 View Post
Us caution with the adjusting method you are using. It is very possible to have a non linear indication as a result of you making the high speed end accurate. Doing so may make the low speed end even further off. A very bad thing if it makes the low speed end read high.......
If it is a dynamic static source error, which his appears to be, then it is very improbable for that to happen. Yes, these errors are non linear but the error becomes larger as airspeed increases and smaller as airspeed decreases. At low airspeeds it is very possible the airspeed is dead on and it is only affecting the displayed altitude, a real bad situation especially in actual IMC conditions. That is why people wind up thinking they have a fast airplane.

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Last edited by GalinHdz : 01-23-2020 at 10:13 AM.
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  #22  
Old 01-23-2020, 10:41 AM
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rvbuilder2002 rvbuilder2002 is offline
 
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Originally Posted by GalinHdz View Post
If it is a dynamic static source error, which his appears to be, then it is very improbable for that to happen. Yes, these errors are non linear but the error becomes larger as airspeed increases and smaller as airspeed decreases. At low airspeeds it is very possible the airspeed is dead on and it is only affecting the displayed altitude, a real bad situation especially in actual IMC conditions. That is why people wind up thinking they have a fast airplane.

From what I have seen in the past, being involved with this issue with lots of different RV's, either one of us could be right.

Only flight testing will prove who is.
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  #23  
Old 01-23-2020, 11:05 AM
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GalinHdz GalinHdz is offline
 
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Only flight testing will prove who is.
Exactly.
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  #24  
Old 01-23-2020, 03:55 PM
sailvi767 sailvi767 is offline
 
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Location: Charlotte NC
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I had flush static ports on my Rocket. Today I added rivet heads over the ports in a attempt to correct a 10-12 knot airspeed error. Airspeed at stall remained the same. Airspeed at cruise went up about 15 knots. Ground the heads down just a bit and Airspeed is now very close.
G
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  #25  
Old 01-23-2020, 04:42 PM
JackZ JackZ is offline
 
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Location: neustadt ontario
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I flew again today after measuring the thickness of my tape stack. It was only a few thousands thinner than a 960 10 washer. I cut a washer in half and glued it on. Speeds are right on, same as yesterday. Today I also flew a 3 way at low speed (65 kias) and it was right on. I went up high and the altimeter and the gps derived altitude were also within a 150 feet or so. On my plane all is now well.

Thanks to all.

Jack

C-FEES RV9A
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  #26  
Old 01-23-2020, 07:00 PM
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GalinHdz GalinHdz is offline
 
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Originally Posted by JackZ View Post
I flew again today after measuring the thickness of my tape stack. It was only a few thousands thinner than a 960 10 washer. I cut a washer in half and glued it on. Speeds are right on, same as yesterday. Today I also flew a 3 way at low speed (65 kias) and it was right on. I went up high and the altimeter and the gps derived altitude were also within a 150 feet or so. On my plane all is now well.

Thanks to all.

Jack

C-FEES RV9A
Glad to hear the good results. FWIW, I would still do the ILS altitude check just to be sure your displayed altitude is accurate and reliable.

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  #27  
Old 01-23-2020, 09:07 PM
Bcone1381 Bcone1381 is offline
 
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On days when the temp is colder than standard, an altimeter will read ....hummmmm....high I think....so your lower than you think you are. So if it reads 10000 feet you'll run into a 10000' mountain because your really at like 9700'. Crunch.

When you miss the mountain, its usually No big deal. Everyone flying around will be at the same temp and have the same error when they run into each other.....unless they fly at the proper altitudes according to direction flight and they'll miss each other because everyone has the same cold temp error.

The further you are from sea level, the worse the temp induced error gets. Its not uncommon that RNAV RNP approach procedures to have a cold temp limitation. I'm looking at the RNAV RNP Y runway 29 at Newark and its not authorized when its colder than 11F. At LAX the RNAV RNP rwy 24R is not authorized colder than 41F unless a compensated BARO-VNAV system is used. (I don't know what that is.) (I wonder if a cold temp compensated Baro will screw up cruise altitude separation on a really cold day?)

I wrote this about approaches because if your GPS says your at 10,150, and your altimeter says your at 10,000 its more than just inaccurate altimeter settings. It would seem logical to me to ask if the atmosphere is at a standard temperature before declaring things not quite right. You might also ask what the GPS accuracy. The other day I saw 11M. So I think that means its 95% sure the number its gives me is within 11M or what....35 feet.

I really like the idea of flying fast down the runway and just checking that way. I even think shooting the ILS and checking the altitude over the marker to be exposing oneself to temperature related errors.

Don't forget to tap the altimeter too. Knock on it like your checking to see if anyone is in the bathroom. That knock will release some of the resistance of movement of the gears and effect the reading slightly.
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