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I have many errors (just ask my wife) but not in referring to every Lancair
and in every case, as you do. Many have the bulbs grounded with the gear
switches providing 12 v when closed to illuminate said bulbs (down and locked),
substantiating my earlier post. Early builder's manuals (back when they
were in monthly flux and the illustrations were hand-drawn) had a
suggested circuit diagram showing it this way and I'll bet most builders back
then wired the system just that way - I know I did, and for a couple of reasons.
One, so my indicator lights (all of them, not just the gear lights) could use a
simple "press to test" circuit from a single button, and two, simple failure
analysis said that it is slightly safer to run the bus voltage to the switches
so the rest of the wiring, during flight, was effectively at ground via the
bulbs.
If you didn't know this, I'll see your' snide comment and raise you
ten.
Dan Schaefer
Early LNC-2
----- Original Message -----
Sent: Saturday, November 28, 2009 9:54 AM
Subject: Gear warning indicator
Hmmm . . . The gear position switches provide a GROUND to the bulbs.
If one or more of the lights are lit by a gear position switch, the voltage at
that side (my diodes) of the bulb is GROUND which can not feed any voltage back
to the circuit.
Look again and hopefully you will see the error of your ways.
Wolfgang
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Excuse me!! This looks to have at least two
design faults.
Problem 1: If the airspeed switch is closed and any
one (or more) of the green "down and locked" lights are energized via the
gear position switches, 12 volts will be applied thru one or more of the
diodes to this "blinker" and it will try to operate - e.g., the 1000 mike
capacitor will charge thru the 100 ohm resistor until the voltage reaches
the relay pull-in voltage.
Problem 2: Unfortunately, as soon as the
capacitor charges sufficiently to pull in the relay, the relay contacts
close and the 12 volts is shorted directly to ground. Hopefully, only
blowing a fuse or popping a breaker, but effectively taking at least the
gear light circuit down.
Neat!
Dan Schaefer
PS: Stick
the resistor on the other side of the relay contacts to at least solve the
shorting - not sure what to do to keep this thing from blinking the lights
when at least one gear leg is down and locked. But what do I know? I'm
just a retired EE and things have a way of getting fuzzy in 10
years!
DS -- |
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