L3 Countdown

[Bruce R. Schaefer]

Ken, I have two mini’s and plan to use one on my next “big” rocket and one for J’s-K’s. Just kinda hang in there. Mike’s av-bay environment was unique, and he will explain as soon as possible.

JW has a good thread on static ports in another area… can’t remember where… hold on… oh, yeah, in Construction. 😉

[Conway StevensParticipant]

Having said all that, what really troubles me is that both altimeters were in the exact same bay, under the exact same conditions yet only one of them fired prematurely – twice. This suggests rather strongly to me that, rather than there being a problem with the ports, there is something wrong with that particular altimeter.
You said the root cause of the failure had been determined. I, too am quite interested to know what the cause was, but I don’t think it was the ports.

Your right as I and others have stated. It is NOT an issue with the ports. Its also not an issue of it being a defective altimeter or anything anyone should worry about or get concerned with. Mike is working with his TAP’s and has spoken with the manufacture and discussed the issue and its special circumstances creating the problem… As Bruce has stated its not an issue for anyone to get worried that they have an altimeter that has issues or anything like that as this situation is quite unique and could have happened to almost any manufacture.

Conway

[Bruce R. Schaefer]

Plus, Conway, didn’t you use a mini on your L3, if not for the certification flight, definitely right after? Ken, that’s not the issue. Hang in there…

[Conway StevensParticipant]

Plus, Conway, didn’t you use a mini on your L3, if not for the certification flight, definitely right after? Ken, that’s not the issue. Hang in there…

No, I didnt use a mini. Ive used RRC2x,2 differnt ARTS, and an RMCS, in my L3 flights. BUT I have had some experience with the mini. I helped Jim with testing on a unit at OF last year with several flights and have seen it used by several flyers now even at LDRS and not one issue yet. There is a learning curve. I highly recommend to get it down and learn it. Even set it up with the instructions every time. ( I do that with all my altimeters, saves me every time)

Also let me mention I have no issues running a Mini if I had one. Been to busy to get one yet.. But I will.

[MikeSModerator]

I only have two duel deploy.
One 3″ and One 5.5″.
Both use the RRC2X.

Used Conway’s calculations on both. Both have worked perfect.

My third duel will be launched at MHM 08. I feel 100% confident
in the Missile Works RRC2X, Missile Works Pet 2 Timer, and
using Conway’s calculations.

[slipstick]

Here’s the root cause

Here’s the short version: I’ve been playing with a GPS that transmits its locations on the MURS band around 150 Mhz. I inadvertantly had wires within the 5″ dia x 12″ long L3 avbay that were of a length conducive to being an antenna receptive to the transmitter frequency and subsequently induced a spurious RF signal into one of my altimeters. The altimeter detected a launch because of it (it looks for a 300 foot variation in barometric pressure before looking for an apogee event and evidently found it prematurely). Once the launch was determined, even though the rocket was happily resting on the rail, the altimeter saw neither a positive nor negative change in elevation, and determined that it was at apogee, and fired off the drogue charge. One second later, as 2/3 of the rocket was in the air above the rail, the altimeter discovered that it was below 1000 feet AGL and fired off the main, as it was designed to do.

In my 3″ dia x 8″ long L2 avbay which also contained a GPS/TX, the length of the wires were much shorter and was never affected.

After three days of late night testing, I have determined that I needed to reduce the length and number of wires in my L3 avbay and to move the GPS transmitter into the nose cone. All is well again. If I didn’t have the tracking gear on board everything would have flown without a hitch. I love failures, its one less thing I have to learn.

I hope I didn’t keep you guys on pins and needles too long.

Mike.

[Anonymous]

Mike. that is a great analysis and a lesson well-learned. Sounds like a positive ID of the problem – Thanks for the update—

[Tim Thomas]

8) No harm, no foul! A very cheap lesson. One that many members of our club, picked up for free. Once again a failure, and in this case, a non-failure to launch, taught the biggest leasons. So, under the month of February, mark DUES PAID, Mike. Looking foward to next month! 😀

[James Russell]

My very first dual deploy bird had only a single altitude bleed hole into the avbay and it fired its charge on the pad when a gust of wind hit. Since then I’ve generally gone to 2 or 3 holes equally spaced around the avbay and have never had that kind of problem again. However, it was a specific altimeter that was known to have this problem – not a Missileworks.

I was told years ago by a manufacturer that you should always use 1 or 3 holes, not sure why but that is what I have always done. when using 1 hole I have the electronics on the opposite side of the board away from vent hole to help baffle against any abnormal air flow. I have never had a problem with wind causing an altimeter to go off.

[Warren B. MusselmanModerator]

Since that bird, I always use 3 holes and I try to make sure that the baro-sensor is somehow baffled from any direct airflow through those holes.

Warren

[Author]

Posts