List the possible causes of altimeter blowing the main under boost.
Altimeter failure
- Thread starter David Schwantz
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What altimeter was it that failed? Did it have accelerometer?
Was this flight the first time you used it?
Was this flight the first time you used it?
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Don't want to knock any brand. Have checked anything I could think of. Vent holes are 3 in the switch band. Charges wired correctly, did not put drogue on the main. But even so, should not have gone off under boost. Both charges fired. Shear pin in NC to payload joint. Put a 20" zipper in a 54MD carbon fiber payload section, and even after that bent the welded SS eyebolt flat on top of the bulkhead. It was a 2000 lb kevlar braided cord that went through it. Gotta love that kevlar stuff
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Did you have pressure vent holes in the recovery sections (not the altimeter vent holes)?
Did you or were you expecting to get close to or break mach?
We really needs a lot more data to help
Did you or were you expecting to get close to or break mach?
We really needs a lot more data to help
rfjustin
Well-Known Member
David,Don't want to knock any brand. Have checked anything I could think of. Vent holes are 3 in the switch band. Charges wired correctly, did not put drogue on the main. But even so, should not have gone off under boost. Both charges fired. Shear pin in NC to payload joint. Put a 20" zipper in a 54MD carbon fiber payload section, and even after that bent the welded SS eyebolt flat on top of the bulkhead. It was a 2000 lb kevlar braided cord that went through it. Gotta love that kevlar stuff
Our experience was (2) Missile Works RRC2+ units, both had flown before, yet on a recent voyage, a main charge was activated about 2-3 seconds after motor burnout occurred. I LOVE MW units and have never encountered this issue before, so just chalking this off to a one-off situation. Our our project, the avionics bay collided with a fin, so no real way to address root cause with everything getting so heavily banged up. Shear pins, vent holes, other details were spot on, so no cause for concern there... video of our SNAFU, and no it did not shred:
Vent holes in payload and booster section. Flew on AT J250W. Aeropack MD retainer, non vented. Madcow CF Tomach. Battery charged night before. All wiring was intact after flight. Double checked that main and drogue were not labeled wrong on alt board.
Hey Justin, vid not work
rfjustin
Well-Known Member
Click the "Watch on Youtube" link within the video please.Hey Justin, vid not work
rfjustin
Well-Known Member
Duplicated
The most common one in the past for this scenario would be lack of a programmed mach delay or a pressure spike inside the av-bay that the altimeter mistakes for apogee.
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Sounds like you may have a micro crack on your board. I threw a RRC2 away years ago , as it popped the main 1second after everytime it blew the drogue.
We had some steady winds from the south, south west that day (North Branch MN Tripoli). I think winds at 3000' were around 29mph and sunny.
I am sorry to hear about the flight David, beautiful rocket as always.
I am sorry to hear about the flight David, beautiful rocket as always.
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Witness! I have several datasets from a MW RRC3 where the baro trace is up and down on the descent, trending downward, but with a clear period that seemed to correspond with the rocket spinning on the recovery. The rocket was unpainted 'regular' green/clear fiberglass, and as soon as I painted the rocket, the strangeness in the data sets went away in subsequent flights.
It was posited here on TRF that sunlight was causing the issue, and since it went away completely AFTER I painted it, I'm a believer.
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somebody better tell cwbullet about this, he flies all his rockets naked.
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Never had an issue. I wonder if it happened in certain climates.
rharshberger
Well-Known Member
Could be...the Southeast is typically somewhat cloudy, where I fly is typically very clear skies and bright sun.
It was sunny and windy as John said. Rocket it natural black carbon fiber and very glossy.
Charles_McG
Ciderwright
@David Schwantz - if you've said, I missed it: was it a logging altimeter, and what did the altimeter think happened?
Guessing, I'd agree with Steve above. Maybe the chute bundle sliding forward after burnout, like a piston, and pressurizing the avbay so it looked like altitude flattened out. A false reading below the programmed main alt, so both fired.
Guessing, I'd agree with Steve above. Maybe the chute bundle sliding forward after burnout, like a piston, and pressurizing the avbay so it looked like altitude flattened out. A false reading below the programmed main alt, so both fired.
rfjustin
Well-Known Member
Interesting...VERY sunny in our case, good input here, thanks all!
I’ve seen it on descent graphs also as a rocket turns under chute. It’s much less apt to happen during ascent (though not impossible) though because the av-bay is inside of another layer of G10.
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The single most common is user error and we’ve probably all done it. That’s how we learn.
Probably the least common is a problem with the altimeter as it ships, but sometimes having more programmability can make life interesting. Back about fifteen years ago I seem to remember that someone programmed a very programmable altimeter to pop the main at some very reasonable number feet.
Unfortunately he programmed the event to occuron ascent rather than descent.
Was the flight vertical?
Any shimmy leaving the rail?
Did you have a Mach delay or some kind of algorithm that is immune to Mach effects?
What time of day was it?
What were the setting?
What model of altimeter was it? I know you want to be fair. My question isn’t intended to slam the manufacturer but rather to understand how that model’s features may have affected the operation.
Eggtimer Quantum. Flight was perfect other than main too soon. Morning flight. Sim said under Mach 1. Main was to deploy at 500 agl
Mach effects can start at a lower velocity but I think Cris has some kind of algorithm to protect against high speed pressure anomalies. I think we can rule that out.
Is it possible that it was simple drag separation? It can happen before complete engine cutoff. When it happens the altimeter would blow its charges.
As a morning flight there is a possibility that sunlight entered through the vent hole. It’s less apt at noon and increases in possibility late in the day.
And sometimes we just don’t know and that’s particularly frustrating.
Did anyone get video? I assumed not or otherwise you would have posted it.
One other thing to look at would be an intermittent power problem.
No matter what, don’t beat yourself up.
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Did both charges fire? If so, my bet would be on drag separation. That would slow down the rocket real quick, and the Drogue and Main charges would fire shortly afterwards in succession if you were below the selected Main altitude.
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I saw the flight and the rocket was above the Main deploy altitude... I estimate about 4K+ AGL when the event happened
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Did you send an email on this? I don't see one from you in the [email protected] account...
I'd like to see the flight data, and preferably also a memory dump. That usually tells the tale, at least the "what" side of things.
I'd like to see the flight data, and preferably also a memory dump. That usually tells the tale, at least the "what" side of things.
When a rocket comes apart at high velocity, buffeting can cause all kinds of pressure spikes that could be seen as a descent to the main deployment altitude. I don’t know if Cris filters those.
Or the rocket’s violent motions cause the BP charges to spill. Then the altimeter burns the matches at the main deployment altitude and later inspections conclude that the charges fired.
I’ll be very interested in what Cris sees in the data.
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