Cambridge 302 Gear/Airbrake Warning - How to Test?

On Sep 8, 12:09*pm, ContestID67 wrote:
I am in the midst of a project to install a gear/airbrake warning
system on my glider based on the built-in capability of my Cambridge
302. *This system is better than the simple "airbrakes open, gear up"
warning system (http://www.wingsandwheels.com/pdf/gear%20warning.pdf)
as it also alerts the pilot to "airbrakes open on tow".

My "sensors" will be strategically placed reed switches and associated
magnets (and tefzel wire of course). * My primary question revolves
around how to do a pre-flight test of the system.

From the manual...

"Warnings depend on presence or absence of airspeed as well as the
switch contacts. Here
is the logic: Unlocking the airbrakes connects pin 7 to ground. When
airspeed rises above 25 knots, the
alarm sounds. The alarm is cancelled when the airbrakes are locked.
During flight with the
landing gear retracted, unlocking the airbrakes connects pin 7 to
ground and sounds the
alarm. Lowering the landing gear opens the connection between pin 8
and ground and
cancels the alarm."

Reading from the above it would seem that the alarm system is totally
inactive until the GPS indicates I am moving 25+ knots. *If so, how
can I test this system on the ground? *Anyone else install this system
and have any experience? * This weekend I will experiment to see if
the 302 programming is smart enough to allow testing while I am
standing still.

Thanks, John DeRosa

Launch, release from tow, open spoilers with gear up, listen for
warning horn.

On 9/9/2011 8:23 AM, glidergeek wrote:

Reading from the above it would seem that the alarm system is totally
inactive until the GPS indicates I am moving 25+ knots.

I believe the 302 uses airspeed, not GPS ground speed, to do the
measurement.

If so, how
can I test this system on the ground? Anyone else install this system
and have any experience? This weekend I will experiment to see if
the 302 programming is smart enough to allow testing while I am
standing still.

Thanks, John DeRosa

Launch, release from tow, open spoilers with gear up, listen for
warning horn.

That only tests the gear warning, which can also be done on the ground
with the fuselage in the trailer dolly and the gear up.

To test the "spoilers unlocked" warning, the airspeed must increase past
25 knots while the spoilers are unlocked, and once you have released
from tow, the airspeed won't do that.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "Transponders in Sailplanes - Feb/2010" also ADS-B, PCAS, Flarm
http://tinyurl.com/yb3xywl

On Sep 9, 2:50*pm, Eric Greenwell wrote:
On 9/9/2011 8:23 AM, glidergeek wrote:

Reading from the above it would seem that the alarm system is totally
inactive until the GPS indicates I am moving 25+ knots.

I believe the 302 uses airspeed, not GPS ground speed, to do the
measurement.

*If so, how
can I test this system on the ground? *Anyone else install this system
and have any experience? * This weekend I will experiment to see if
the 302 programming is smart enough to allow testing while I am
standing still.

Thanks, John DeRosa

Launch, release from tow, open spoilers with gear up, listen for
warning horn.

That only tests the gear warning, which can also be done on the ground
with the fuselage in the trailer dolly and the gear up.

To test the "spoilers unlocked" warning, the airspeed must increase past
25 knots while the spoilers are unlocked, and once you have released
from tow, the airspeed won't do that.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "Transponders in Sailplanes - Feb/2010" also ADS-B, PCAS, Flarmhttp://tinyurl.com/yb3xywl


Well, you could try the following at altitude. Theoretically it should
work. Lower gear, pull up hard enough to stall with no airspeed
showing, unlock brakes/spoilers at the stall break. Alarm should sound
when gaining speed during the stall recovery. Although the OP wants to
be able to test on the ground. That's the way I would test as well.

I have a method for testing my pnuematic lines (static, pitot, te). Go
to any pharmacy and get a syringe (without needle) in the smallest
diameter they have. My local pharmacy gives them to me for free. The
real small narrow ones allow for moderate plunger movement without
fear of damaging your instruments. That's not to say you shouldn't be
extremely careful. The point is the really small diameter syringes do
not move much volume. I keep one in my field box with a piece of
surgical tubing attached for testing. It would be perfect for
connecting to the pitot and applying a small amount of pressure to
test the 302 alarm. Not to mention the ease in which it allows one to
test for leaks throughout the rest of the ship.