Hi Guys

Thanks to all the people who commented and offered opinions and advice. Those of you, Like Dennis, who said that it was unlikely to be Pstatic were absolutely correct. It turns out that the problem was as simple as that I mounted the MGL GPS antennae in the left wing tip and had to have extension leads made to reach the EFIS. One of the gold-plated connections was not insulated and touched the inside surface of the carbon wing skin. Thus causing a double ground and all sorts of problems. Once I had insulated the connector the GPS held signal and in fact I have just returned from a weeks vacation in the aircraft where it was used every day and no further problems encountered.

BTW on a different note I can report favourable on the Legacy’s performance in and out of a gravel strip. My friends farm where we were vacationing has a 2750’ gravel strip well rolled and maintained. Field elevation is 1000’ and the Legacy took it in its stride. We also did some interesting canyon flying in the early mornings to avoid the heat.  Bit of a rush going down some of the wide canyons at 200kts. What a great machine.

Regards

Ross


On 2011/01/02 2:29 AM, "Dennis Johnson" <pinetownd@volcano.net> wrote:

Hi Ross,
 
P-static is a meteorological phenomenon that requires specific weather conditions.  I don't know about your typical weather in South Africa, but I wouldn't expect you'd have P-static issues on nearly every flight, beginning on takeoff.  Particularly on an airplane not known to have significant P-static problems.  If it were me, I'd look to other things before electrically bonding airframe parts.  
 
Have you tried swapping out the GPS antenna and the antenna cable?  Anybody near you with the same unit you could swap out for a test?  
 
If it's only the GPS part of the component, and only one GPS receiver, I'd look to the antenna and the coax.    
 
You might post this question on Bob Nuckolls' AeroElectric newsgroup at:
http://www.matronics.com/Navigator?AeroElectric-List
 
Someone there will likely give you a logical troubleshooting sequence that will minimize replacement of good parts while you're closing in on the problem.  
 
Dennis

 
 

 
Dennis

The loss of the GPS signal is as regular  as clockwork. Sometimes as the aircraft lifts off the ground it’s gone.  Initially I thought it was the gear pump but sometimes it goes well after gear  up. I have considered that I use a 28v system but MGL assures me that its  equipment can take the voltage. Nonetheless I tried a voltage converter to 14v  and still the GPS signal was lost. Then I smoothed out the input voltage using  a capacitor in an attempt to eliminate voltage spikes. Still lost the signal.  

Nothing else seems to be affected within the EFIS or the  other  avionics, which only adds to the mystery.

Thus, I am led to the idea of  P-STAT. Is there perhaps a momentary electrical discharge into the system that  disrupts the GPS. If so why only the one GPS and why none of the other  equipment? The Tru Trak AP is rock solid using the secondary GPS; the comms  are rock solid; as is the transponder.

BTW in answer to another list  member, all ground connections have been checked and are good.

All very  frustrating.

Ross


On 2010/12/30 4:21 AM, "Dennis Johnson"  <pinetownd@volcano.net>  wrote:

 

Hi  Ross,
 
There are many, many Legacies flying without P-static  problems disabling their avionics.  Before I went to a lot of trouble  electrically bonding parts of the airframe, I'd try to determine how your  Legacy is different from the others.  And I'd make sure all the  electrical grounds are solidly connected.  
 
Do you have  any indication that P-static is a frequent problem in your airplane?   Is anything except the GPS function of your MGL Voyager affected?   I once picked up enough static charge that what little hair I have on  my head stood straight up, towards the charged canopy.  It didn't cause  a problem with any of the avionics,  though.
 
Dennis