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bakerocb
Joined: 15 Jan 2006
Posts: 727
Location: FAIRFAX VA
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 Posted: Thu Mar 27, 2008 3:30 am Post subject: Using NC Switches |
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3/27/2008
Hello Again Tom, I am disappointed that nobody on the aeroelectric list
responded
to your request that I forwarded to them for help on using NC switches .
(See copy below)
Let me take a stab at your request and if I provide bum information maybe
one of the experts on the list (even Bob Nuckolls) may step in and provide
correct, or better, information.
There are small electrical relays, commonly called "ice cube relays" because
of their size, that can be used for the purpose that you want -- providing
an electrical signal when all you have available for control is a NC
(normally closed) switch in your aircraft's control grip.
Here is one such relay available from B&C -- I am sure that there are many
others:
http://www.bandc.biz/S704-1_tips.html
It has a 12 volt activated coil and two contacts activated by the slug that
is moved when electricity is applied to the relay coil. One of the contacts
is labeled NC (normally closed) and the other is labeled NO (normally open).
Status A) If there is no electricity flowing through the relay coil the
relay NC contact is connected to the relay common contact and the relay NO
contact is not connected to the relay common contact.
Status B) When there is electricty flowing through the relay coil the relay
NC contact is disconnected from the relay common contact and the relay NO
contact is connected to the relay common contact.
You can wire one side of the NC switch in your control grip with a wire
leading to one of the relay coil contacts. Then you can wire the other relay
coil contact on to aircraft ground. Then you can wire the other side of the
NC switch in the control grip to a live electrical source in the aircraft.
You will have created a continuous electric flow through the coil and the
relay and its contacts will be in status B above.
Now you determine whatever electrical signal is to be sent to the
transponder in order to have it ident and wire a continuous source of that
signal to the transponder through the relay common and the relay NC
contacts. Because you are in status B there is no connection between the
relay common connection and the relay NC contact and the transponder will
not ident.
When you depress the button for the NC switch in your control grip the relay
will go into status A and an ident signal will be sent to the transponder as
long you keep the button for the NC switch on the control grip depressed.
Realize that there are some downsides to this arrangement:
1) There will be a continuous drain on your electrical system to keep the
relay coil activated at all times except for the brief moments when you
depress the NC switch button on the control grip.
2) If you have a wiring disconnect beween the NC switch on the control grip
and the relay the transponder will receive a continuous signal to ident.
There are probably more elegant electrical solutions to solving this problem
and one could eliminate the two downsides listed above by using two relays
to accomplish the ident (or other actions desired), but that is left as an
exercise for the reader.
'OC' Says: "The best investment we can make is the effort to gather and
understand knowledge."
PS: I realize that HOTAS (Hands On Trottle And Stick) is appealing to some
homebuilders as a high tech form of snobbery, but it ain't my cup of tea. I
fly in a pretty intense radar coverage environment (the Washington DC ADIZ)
and I bet that in the past several years that it has been in effect that I
haven't been asked to ident more than 4 or 5 times. Not a big deal to just
reach over and push the button on my transponder.
-----------------------------------------
3/12/2008
Hello Tom, You wrote:
1) "For clarification, the NC switch means that I press the button to
actually cut the power. Why would this be used on an old military
helicopter stick? What is the reason for cutting the power on a switch?"
We used to say that having helicopter time in your pilot's logbook was like
having an STD entry (it was called venereal disease back then) in your
health
record.
So I will reluctantly admit that I did fly a helicopter (CH-46) for a year
in Viet Nam. The cyclic grip had a button on it that when pressed would
disconnect the electronic flight stability / attitude positioning system so
that one could manually reposition the stick and the helicopter's attitude
then releasing the button would reengage the electronic attitude positioning
system.
Maybe you have a control stick grip that does something similar.
2) "Again, is there any way I can wire it to work with my remote ident
operation?"
I am not the right guy to answer that question, but I am sure that by using
two of the small "ice cube" type relays that ident operation could be
accomplished. It might be a pretty awkward way of doing it though from an
electrical viewpoint.
I'll forward your question to the Matronic's aeroelectric-list and maybe one
of the electrical experts there (even the great guru Bob Nuckolls) would
take a shot at it.
'OC' Says: "The best investment we can make is the effort to gather and
understand knowledge."
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nuckolls.bob(at)cox.net
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| Posted: Thu Mar 27, 2008 5:35 pm Post subject: Using NC Switches |
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