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Attitude gyro problem.

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Greg.Puckett(at)united.co
Guest

Posted: Tue May 22, 2007 2:15 pm Post subject: Attitude gyro problem.

Help!! My attitude indicator is driving me nuts!  

   

The attitude indicator is a RC Allen RCA26AK2 (14v electric) with 8deg tilt installed in my RV-8.  

   

From the first flight, the indicator showed signs of what I thought was precession. During constant altitude standard rate turns, when rolling out to wings level the indicator would show up to 10deg bank in the opposite direction. While turning at standard rate level altitude, after 90 deg of hdg change in one direction the indicator would show up to 5deg of false climb and 5deg of false descent when in the other direction. BTW, the indicator does not show any bank during turns on the ground.  

   

I thought, well this thing has been sitting for some time, the bearings must be bad. I sent the indicator back to Kelly Mfg for repair, they replaced the bearings and recalibrated. After reinstalling, I still had the same problem. I suspected that the repair was not sufficient and sent it back again with no fault found. I still had the same problem in the airplane after reinstalling.   

   

I checked some things with the A/C such as actual panel tilt, voltage at the instrument with respect to the instrument ground, noise on the power in. The only thing I found was that my actual panel tilt was more like 5.5 deg and not 8. I shimmed the instrument so that it was exactly 8 deg and it did not help the problem at all. I thought for sure, something must be wrong with the instrument. Kelly mfg agreed to exchange it for a new manufacture instrument. I still have the same problem with the new instrument.  

   

I then thought, even though it’s a spinning hunk of mass, something must be interfering with it. I wrapped the case in mu-metal, turned off all electrical equipment in the panel including both alternators and you guessed it, I still have the problem. WTF….  

   

What else could possibly be causing this????  

   

   

Thanks in advance,  

   

   

Greg  

   

   

   

         [quote][b]

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simon(at)synchronousdesig
Guest

Posted: Tue May 22, 2007 3:28 pm Post subject: Attitude gyro problem.

Greg,

  

 Measure the voltage at the unit, not  at the battery, and report back.

  

 Simon Ramirez, Aerocanard  Builder

 <?xml:namespace prefix = ns0 ns =  "urn:schemas-microsoft-com:office:smarttags"  /><?xml:namespace prefix = st1 ns =  "urn:schemas-microsoft-com:office:smarttags" />LEZ  N-44LZ

 Oviedo, FL  32765   USA

  

 Copyright © 2007

  

  



   From:  owner-aeroelectric-list-server(at)matronics.com  [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of  Puckett, Gregory [DENTK]

Sent: Tuesday, May 22, 2007 6:13  PM

To: AeroElectric-List(at)matronics.com

Subject:  Attitude gyro problem.

 

  

  

Help!! My attitude indicator is  driving me nuts! 

  

The attitude indicator is a RC Allen  RCA26AK2 (14v electric) with 8deg tilt installed in my  RV-8. 

  

From the first flight, the indicator  showed signs of what I thought was precession. During constant altitude standard  rate turns, when rolling out to wings level the indicator would show up to 10deg  bank in the opposite direction. While turning at standard rate level altitude,  after 90 deg of hdg change in one direction the indicator would show up to 5deg  of false climb and 5deg of false descent when in the other direction. BTW, the  indicator does not show any bank during turns on the  ground. 

  

I thought, well this thing has been  sitting for some time, the bearings must be bad. I sent the indicator back to  Kelly Mfg for repair, they replaced the bearings and recalibrated. After  reinstalling, I still had the same problem. I suspected that the repair was not  sufficient and sent it back again with no fault found. I still had the same  problem in the airplane after reinstalling.  

  

I checked some things with the A/C  such as actual panel tilt, voltage at the instrument with respect to the  instrument ground, noise on the power in. The only thing I found was that my  actual panel tilt was more like 5.5 deg and not 8. I shimmed the instrument so  that it was exactly 8 deg and it did not help the problem at all. I thought for  sure, something must be wrong with the instrument. Kelly mfg agreed to exchange  it for a new manufacture instrument. I still have the same problem with the new  instrument. 

  

I then thought, even though it’s a  spinning hunk of mass, something must be interfering with it. I wrapped the case  in mu-metal, turned off all electrical equipment in the panel including both  alternators and you guessed it, I still have the problem.  WTF…. 

  

What else could possibly be causing  this???? 

  

  

Thanks in  advance, 

  

  

Greg 

  

  

 

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No virus found in this incoming message.  Checked by AVG. Version: 7.5.467 / Virus  Database: 269.7.6/814 - Release Date: 5/21/2007 2:01 PM    [quote][b]

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Greg.Puckett(at)united.co
Guest

Posted: Tue May 22, 2007 4:49 pm Post subject: Attitude gyro problem.

Hey Simon,

 

Thanks for the response.

 

When I say

 

 	  Quote: 	
		   voltage at the instrument with respect to the instrument ground. 

 
	


I meant what you said, at the backshell of the indicator, while in flight. It was reading .2 volts less that the buss voltage with 5 mv of ripple with the alternator online. To me, that seemed in the reasonable range.

 

Greg

 

p.s. I did notice today that the panel cutout had almost a 1 deg error in roll with respect to the main spar that I corrected by elongating the holes in the panel. I can't believe something like that could be the answer and unfortunately, the weather was too crappy to fly and see. Let me know if you can think of anything else to try.

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hmanvel(at)manvel.com
Guest

Posted: Thu May 24, 2007 8:58 am Post subject: Attitude gyro problem.

Greg,

 In case the other suggestions don't do the trick; I  had trouble with my vacuum horizon for many hours early in the testing phase of  my airplane.  It would show a bank when wings were level, usually after a  long climb or descent. Nothing I did solved the problem, until I isolated the  gauge with a rubber tube used as a gasket.  This cured it, proving that the  problem was vibration.  I then installed one of those "Nu-Lite" lighted  circles in place of the gasket, and it still works perfectly.  I guess it  did enough to either dampen the vibrations, or it changed the frequency at which  the gauge would get attacked by it .

 Harry Manvel

 Defiant N2HM

 PTK / Pontiac, MI

 [quote]   ---

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Nick1

Joined: 05 Jul 2007
Posts: 2
Location: Canada

Posted: Thu Jul 05, 2007 9:09 pm Post subject: Re: Attitude gyro problem.

Greg,

Just curious what was the problem?

Do you need any more suggestions?

Nick

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