FXC Altitude Test Chamber

[markbaur 0]

I need an FXC altitude test chamber. The FXC Corporation list price is over $5500, but the company says that other versions can be used for the functional test as long as they're able to measure altitude and descent rate. Can anyone suggest a source for a used FXC test chamber, or another commercially produced test chamber, or a home-built version?

Please do not suggest using a plastic bag over the sensor. It's not a substitute for a functional test, and anyway, the only thing the plastic bag test shows is if the unit will fire if you're going fast enough at impact.

Mark

[flyboy62000 0]

I've seen a homemade one out of a 55gal drum with a vacuum pump. The lid has a rubber seal that the top ring seals to for an airtight seal. The lid has been cut out and a thick plexi window installed with sealing compound around it. Attached to the lid is a small shelf for setting altimeters on for testing, an aircraft altimeter and a vertical speed indicator from an aircraft. The problem is that the VSI maxes out at 6000fpm so if you want actual freefall speed you need two people, one activating the valve and one keeping track of the speed with a stopwatch, 5-6sec/1000ft. It's not the most accurate system, but you can fit an entire rig inside, it will read accurate altitude and provides a functional test for firing altitude and decent rate.

Blue Skies,
Adam

Blue Skies,
Adam
I fly because it releases my mind from the tyranny of petty things . . . — Antoine de Saint-Exupéry

[cobaltdan 0]

scientific supply companies , i.e. fischer scientific , sell vacuum decicators. i recommend an inexpensive plasic version. basically they are a plastic chamber for storing items under a vacuum. add to this item an inexpensive diaphram vacuum pump, i.e. gast, a certified altimeter (pref. not your altimaster), and a small needle valve to bleed the chamber back to atmosphere (simulate free fall) and you are good to go ! (there is a bleed valve on the desicator, but not all are finely adjustable)

you should be able to simply assemble a professional system for under $1500

sincerely,

dan<><>
atair aerodynamics
www.extremefly.com

Daniel Preston <><>
atairaerodynamics.com (sport)
atairaerospace.com (military)

[howardwhite 4]

I've seen homemade ones, and will ask tomorrow. Out of curiosity, how many FXCs are you still seeing in the field?

HW

[markbaur 0]

Quote

How many FXCs are you still seeing in the field?

Skydive Twin Cities has about 15, used on student rigs, and I saw a few on student rigs in East Troy last summer, but the other 10 or 15 DZs I've visited in the last couple years have all used Cypres on their student gear (some student models, some expert models). On the plus side, the FXC 12000 doesn't turn into a door stop after 12 years, and it can be turned on and off and on again in the aircraft. On the minus side, it requires a 2-year factory check instead of a 4-year, and there's that pesky requirement to chamber them at every repack. Action Air is advertising $37.50 for a chamber check, which seems like a lot until you figure out how many tests it takes to cover the $5500 price for an FXC chamber.

Mark

[markbaur 0]

Dan:

Is there a reason (besides comfort level and liability) why you'd use a certified altimeter instead of an uncertified one? Some of the newer uncertified digital ones are more accurate than certified analog ones, and are much cheaper, too. Also, I notice you didn't include a VSI. The last time I checked, many years ago, VSIs were TSO'd, but there were no calibration standards, even for IFR use. I think using an uncalibrated instrument (the VSI) in tandem with a calibrated one (the alti) gives an uncalibrated result. You'd be able to verify firing altitude, but not the 40 fps no-fire, or 65 fps always-fire.

Mark

[riggerrob 558]

Check with your local aircraft instrument shop. You should be able to get used, calibrated aircraft altimeters and vertical speed indicators for less than the cost of new.
Also consider the legal aspect. If your instruments have been calibrated recently by a certified aircraft instrument repair shop, then you have a legal leg to stand on the next time a student injures himself. Most of the time all you need is a stack of FAA-recognized documents when you tell a lawyer to f-off!

In answer to your second question, I have a genuine FXC test chamber and use it on a regular basis. A dozen of our student rigs have FXC Model 12000 AADs and most older Canadian DZs still use FXCs.

The main reason we bought a genuine FXC test chamber is because the boss figured that new aircraft instruments would cost about the same as a genuine test chamber.
I have used a few home-made test chambers. Aside from annoying problems with rubber seals, they worked as well as factory test chambers.

[cobaltdan 0]

if you are handy in this way, my recommendation would be to spend the money you would have spent on the calibrated vsi and put it towards a data acquisition card for a pc and a high accuracy pressure sensor.

the whole thing would be arround $500. in labview you can program a simple interface that would record and graph your altitude and vertical speed. i can not say for sure but my guess is that a .1% accuracy pressure sensor + a cheap 16bit daq would surpass the accuracy of a certified analog aircraft gauge. (we use a .1% sensor on our jump dataloggers and its accuracy without any kalman filtering is 33').

benefit to the pc/data acquisition set up is that you would have a printable record of the entire test and all variables.

sincerely,

dan<><>

Daniel Preston <><>
atairaerodynamics.com (sport)
atairaerospace.com (military)