|
|
Finn, you are quite right in suggesting the "cross talk" between two wires.
Out of 26 A-7s at Des Moines, there was one suffering from this phenomenon.
When I'd be descending back at home base the controller's standard
instruction was to clear us down to 5,000. I'd descend with autopilot's
"heading and attitude hold" engaged, then approaching 5000, I'd apply slight
back pressue to the stick to level. At that moment, the Radar Warning
Receiver's "Launch" warning would go off with full aural and scope and
"launch light" indications. When we finally isolated this to a single
aircraft, the avionics guys started digging - found a 5v digital signal wire
(to Radar Warning sys) in a pin right next to a 28v wire to the autopilot
pitch actuator system. Thus, every time I'd apply back pressure to the
stick grip, a "force transducer" in the stick grip would sense the pressure
and send a 28v signal to de-activate or override the "attitude hold" (Pitch
attitude in this case). That 28v signal was feeding into the 5v digital
"launch" system. Didn't fry any chips, but demonstrates the thing you are
suggesting. They moved the 5v wire to the opposite side of this big
connector and we never had the problem again.
David
----- Original Message ----- From: "Finn Lassen" <finn.lassen@verizon.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Monday, February 14, 2005 10:41 AM
Subject: [FlyRotary] Re: Bernie update on N19VX (blowing chips)
Ok, there just *might* be a 4th possibility. If the cable bundle
containing the with to pin 30 includes a wire that sees a very high
current spike, in theory, that may introduce a voltage spike in the wire
to pin 30. I guess the wires in the bundle may have to be twisted for
this to occur. If your pin 30 wire wraps around the starter cable a
couple of times, it may even be likely.
Finn
jbker@juno.com wrote:
>Ed A wrote:
>
>
>Bernie,
>
>A faulty switch could certainly be the problem - just a chip of metal in
the
>casing that could short a couple of pins in the switch just for a tiny
>fraction of second would do it. Also some of the "Make-before-Break"
>are
>"spring" loaded such that the "Make and Break" happen in 10s
>of
>milliseconds, so it might not register on anything less than an
oscilloscope
>type instrument. The fact that you are apparently not frying any more
chips
>with your single switch would to me strongly indicate:
>
>1. Wiring error (which I would consider highly unlikely the number of
times
>you have been over the wiring)
>2. A defective switch (which might account why the EC2 survived for at
>least some amount of time before blowing)
>3. A "Make - before-Break" switch(es) in the batch of three
>
>Ed A
>
> ----------------------------------------
>
>Ed,
>
>Tracy pretty much ruled out item 3 since they would not transfer 12 volts
from one side of the switch to the other, only to the open position on the
same side of the switch.
>
>I ruled out #1 :>)
>
>Bernie, sucessful cold start yesterday
>
>
>
>>> Homepage: http://www.flyrotary.com/
>>> Archive: http://lancaironline.net/lists/flyrotary/List.html
>>>
>>>
>
>
>
|
|