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Cambridge 302 Gear/Airbrake Warning - How to Test?
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 |
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Cambridge 302 Gear/Airbrake Warning - How to Test?
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 Connect a large syringe (ideally with a ballast volume) to the pitot tube system and use this to carefully increase pressure. This feature of the C302 is very nice. Darryl |
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Cambridge 302 Gear/Airbrake Warning - How to Test?
Darryl,
Thanks for the response. Yes, this does seem like a nice system. Alerts no matter what the volume is set to, brakes on tow warning, etc. Questions/comments... 1) While the syringe approach to mimic moving at 25+ knots would logically work, it isn't optimal as something easily done during each day's pre-flight. 2) What is a "ballast volume"? 3) Do you know how the 302 determines the difference between a warning for "brakes deployed while gear down and on tow" and the warning for "brakes deployed while gear up and landing"? The two states seem a contradiction. My only thought is that it determines the glider is descending versus assending. Thanks again. |
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Cambridge 302 Gear/Airbrake Warning - How to Test?
On 9/8/11 1:29 PM, ContestID67 wrote:
1) While the syringe approach to mimic moving at 25+ knots would logically work, it isn't optimal as something easily done during each day's pre-flight. How about using the spoilers to help aileron control during takeoff and leave them open until 30 KIAS? ;-) Actually, mine stopped working a few years ago... Tests just fine on the bench, and the syringe on the pitot works too. But leaving the spoilers unlocked to well over 30 KIAS doesn't set off the alarm. Had Gary, when he was at CAI, check it out during the last calibration and it worked just fine. Very odd indeed. -Tom |
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Cambridge 302 Gear/Airbrake Warning - How to Test?
On 9/8/11 9:29 PM, Tom Serkowski wrote:
On 9/8/11 1:29 PM, ContestID67 wrote: 1) While the syringe approach to mimic moving at 25+ knots would logically work, it isn't optimal as something easily done during each day's pre-flight. How about using the spoilers to help aileron control during takeoff and leave them open until 30 KIAS? ;-) Actually, mine stopped working a few years ago... Tests just fine on the bench, and the syringe on the pitot works too. But leaving the spoilers unlocked to well over 30 KIAS doesn't set off the alarm. Had Gary, when he was at CAI, check it out during the last calibration and it worked just fine. Very odd indeed. -Tom Tom well then obviously you need to order a new ClearNav vario... I expect/hope they are U/C and spoiler switch pinout compatible with the C302. Darryl |
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Cambridge 302 Gear/Airbrake Warning - How to Test?
On 9/8/11 1:29 PM, ContestID67 wrote:
Darryl, Thanks for the response. Yes, this does seem like a nice system. Alerts no matter what the volume is set to, brakes on tow warning, etc. Questions/comments... 1) While the syringe approach to mimic moving at 25+ knots would logically work, it isn't optimal as something easily done during each day's pre-flight. It is possible to worry too much - You don't pre-flight test your ASI and that is likely more critical than these warning buzzers. And you can certainly test behavior of say the gear warning while in the air. 2) What is a "ballast volume"? A bottle/flask connected in series with the syringe so that moving the syringe plunger has less of an effect on the pressure than if used directly. You really don't want to blow out instruments connected to the system. You can disconnect the instruments but then the futzing with connections itself may introduce problems. And it may just be easier to just slide a tube over the pitot for these kind of tests. And remember the manual says to connect the ASI and static ports on the C302 to the ships pitot and static not that of the TE/triple probe - one reason is to have these alarms etc. to work properly if the TE/triple probe is left off 3) Do you know how the 302 determines the difference between a warning for "brakes deployed while gear down and on tow" and the warning for "brakes deployed while gear up and landing"? The two states seem a contradiction. My only thought is that it determines the glider is descending versus assending. I believe it is simply state based. If the gear has been raised and the airspeed is high then it knows its "gone flying" and is ready to detect subsequent spoiler deployed before the gears is locked down. For example I've pulled gear up while on tow and later cracked spoilers to handle a little bit 'o rotor while on tow and had the undercarriage alarm go off as expected. There is no way altitude or climb rate affects this. The developers are too smart to do that. Darryl |
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Cambridge 302 Gear/Airbrake Warning - How to Test?
If your airbrakes "suck open" after you are going faster than 25 knots
it will not warn you, just FYI... It would work a tad better if the "spoiler open on tow" worked until the first "gear up" condition before it reverted to the "spoiler open / gear not down" mode. |
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Cambridge 302 Gear/Airbrake Warning - How to Test?
On 9/8/2011 1:03 PM, Mark wrote:
If your airbrakes "suck open" after you are going faster than 25 knots it will not warn you, just FYI... It would work a tad better if the "spoiler open on tow" worked until the first "gear up" condition before it reverted to the "spoiler open / gear not down" mode. If you install the airbrake switch correctly, the Cambridge 302 will warn you even before the airbrakes "suck open". The Cambridge system is designed to work with a switch that detects when the spoilers are _unlocked_, not after they are extended. It's an important difference, but it's usually easy to install a switch that does that. On the gliders I've had, there is at least 0.5" of movement of the spoiler handle and connecting linkage to unlock the spoilers. So, it's more accurate to refer to it as "spoiler's unlocked on tow", instead of "spoilers open on tow". -- Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me) |
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Cambridge 302 Gear/Airbrake Warning - How to Test?
If your spoilers "suck open" and you don't recognize it, you shouldn't be
flying. "Mark" wrote in message ... If your airbrakes "suck open" after you are going faster than 25 knots it will not warn you, just FYI... It would work a tad better if the "spoiler open on tow" worked until the first "gear up" condition before it reverted to the "spoiler open / gear not down" mode. |
#10
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Cambridge 302 Gear/Airbrake Warning - How to Test?
"Dan Marotta" wrote:
If your spoilers "suck open" and you don't recognize it, you shouldn't be flying. But those pilots clearly are flying. And are killing themselves and hurting passengers etc.in depressingly familiar accidents. In the case of the C302 (and hopefully ClearNav vario) this feature works very well and I would connect in any glider I owned. The limit with these things is does having a lots of these alarms just end up confusing/distractions and can the pilot handle and respond to the alarm (and given how far behind the aircraft some seem this may be a problem). But a "it's there problem" attitude and just sitting by while pilots kill themselves is not going to help this sport or those pilots. And yes if somebody is clearly having problems with safe spoiler operation/handling emergencies/distractions etc. my first call would be time with a good instructor not add a gadget but those gadgets may have a place as well. Darryl |
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