A aviation & planes forum. AviationBanter

If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below.

Go Back   Home » AviationBanter forum » rec.aviation newsgroups » General Aviation
Site Map Home Register Authors List Search Today's Posts Mark Forums Read Web Partners

Honeywell KFC-225 autopilot - what could cause this failure?



 
 
Thread Tools Display Modes
  #1  
Old June 12th 04, 10:15 PM
Joerg
external usenet poster
 
Posts: n/a
Default

Hi Peter,

As far as I know the Socata TB20 is metal but has a composite cabin,
cowl and tail. Ground Radar is one source and when you fly through a
powerful long range beam that can really upset electronics. These are
hard to discern because it can happen tens of miles from the site and
their antennas turn slowly. But the software should recover. I don't
know about aerospace electronics but in medical we must demonstrate that
our systems come back to normal within seconds after a defibrillator
hit. If they remain in la la land instead of recovering we would not get
the agency blessing.

Anyway, there is another noise source but this one could only be
correlated if you'd record the NAV or GPS data the instant the AP quits.
There could be a high powered AM station on the ground. Also, some VHF
and UHF TV transmitters use highly directional antennas so you might get
hit with the full brunt well after passing a mast. They also concentrate
the beam to a very narrow vertical range of just a few degrees, mostly
to save energy costs. Therefore, the magnitude of the EMI effect depends
on the altitude when you fly through their antenna pattern. Last but not
least there are satellite feeder stations for TV and communications
which work with a beam width of just a few degrees and point upward. Due
to the narrow beam width the field strength can be tremendous. Again,
these can often be identified as a cause if the location where the AP
fails happens to correlate.

Then there is always the chance that a certain data pattern the AP sees
upsets the software. But that would be a very bad sign.

There is a way to test for at least some of the EMI behavior but it
would have to happen in a shielded environment and that can be expensive
or hard to find. You can blast the unit with variable frequencies. It is
a test that all system have to go through after completing a design.
What I do for pre-compliance is a trick that can pinpoint vulnerable
spots: I use an EMCO near field probe kit (little loop and point
antennas on a stick with a BNC at the end) or just a 2" loop soldered to
a coax if I don't have the kit with me. Then I send a few watts into the
probe and go over the unit under test in a dousing rod fashion. It is
tedious but usually finds the culprit.

The oil pressure EMI issue is a bit scary. Does Socata know about that?
They should really fix this. Protecting an input from EMI isn't rocket
science. If it is legal you could use ferrite toroids and have these
affixed on the cable bundle right before the gauge or its electronics
box if it has a separate one. 43 material (Amidon) works pretty good at
VHF. Even Radio Shack has some but in aircraft I'd stay away from the
snap-on cores because they can come off when you hit rough air.

Regards, Joerg

http://www.analogconsultants.com
 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Honeywell KFC-225 autopilot - what could cause this failure? Joerg Instrument Flight Rules 17 June 16th 04 10:05 AM
IMC without an autopilot Jon Kraus Instrument Flight Rules 101 April 18th 04 07:17 PM
KAP140 Autopilot Details News Instrument Flight Rules 27 October 22nd 03 02:01 AM
Looking for a home for C130 autopilot amplifier... tongaloa Home Built 0 August 18th 03 06:44 PM
Kinda OT but... Trying to flog a Sperry SP 20 autopilot servo ampfor C130... tongaloa Home Built 0 August 8th 03 07:45 PM


All times are GMT +1. The time now is 07:53 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
Copyright ©2004-2025 AviationBanter.
The comments are property of their posters.