Altimeters

[denverdoc]

Warren,

Interesting commentary, but irrespective of the resolution, I have recently learned that baro based units are inherently inaccurate for a number of reasons, not the least of which are local and temporary departures from the 1976 model. My understanding is that the higher rez models offer more precision and if downloaded to a good program the data can then be massaged into more accurate readings. But that aint gonna happen–“gee guys wait til my ACME atmosphric integrator ver 2.31 comes up with the real altitude!”
The other reason is that the altimeter algorithms are all different and offer a best guess, but its only that so while you might put them into a hypobaric chamber and get significant correlation, the reported altitudes will vary by a significant margin. For LDRS I plan on flying four different brands plus GPS to see whats up with this.

So we seems weez stuck until GPS is good enough to nail the Z coord, currently need 4 sats in the sky, pretty well spread out to get the theoretical WAAS error times a factor of 1.5. Theoretically within 10M or so.

Con, given your interests the Loki/Ozark ARTS might be your best bet for now. (the picoalt I mentioned was for other uses). It attempts to solve a set of simultaneous eqns from acc data and baro to spit out thrust, impulse, Cd etc. Obviously a best guess as well as there are too many variables, but John Bixler loves his and uses it to characterize his research motors. If you like dinking with math/sims a no brainer.
JS

[Warren B. MusselmanModerator]

I’m within a couple shop hours of having my GPS downlink system functional. The GPS works AND the serial RF data link works… just have to get the RS232 integration down…

Then its just a packaging issue.

Warren

[denverdoc]

Warren,

Way 8) ! Hopefully in time for a blast at LDRS! I’m still waiting for the darn mini phono jack connector to take the audio out to the PC soundcard, so LDRS will be the first time for the Bee Line.
J

[CJ Jones]

Hey Guys

I just found this interesting, at ROC Stock last weekend, one guy put a H999 in a minimum diameter unweighted rocket.
Flew it with a Perfectflite for deployment, that was completely unmodified, and everything whet fine. Oh man did it shoot up into the sky. We estimate the gees at 127. The Perfectflite was undamaged, but when he down loaded the data it looked really weird.

CJ Jones

[denverdoc]

sounds like he was a lucky man. You gotta figure and hope really that the alt decisions are based on sound data, from the report u gave data was corrupted, survived to tell about it, Guess my point is you gotta take these high gees flights seriously, certainly not a testimonial for MAWD.
j

[Conway StevensParticipant]

So I am looking further into the ARTS Altimeter as a Back up and Data recorder for my RRC2X 40k for my L3 Flight. Curious how well if anyone knows that this ARTS does with dealing with High G forces and what about MAch delay issues? I just need some final questions figured out before I jump and purchase.

[Warren B. MusselmanModerator]

With that kind of acceleration, I’m surprised the unit survived. The big electrolytic capacitor on Perfectflight and also on Missileworks altimeters (the only brands I own) are poorly supported against acceleration and I’ve had them rip off of the PC board on one project due to acceleration (or rather rapid deceleration when it hit the ground – estimated only 80 g’s rather than 127 as in the case described.)

Just a few weeks ago I potted one of my Missileworks altimeters and it wasn’t difficult. I made a wall of masking tape around the board as a whole, then dammed off the terminals, the switch and the baro sensor, and then poured in about 3/8″ of West Systems epoxy to cover the components. Of course this makes the unit completely unrepairable and voids the warranty, but it should make the unit proof up to well over a 100 g’s if mounted long-ways in axis with the rocket. Flat on, I’d be concerned that the membrane in the barosensor would tear from it’s own mass at significant G loads.

[Conway StevensParticipant]

Well I went and Did it. I ordered the ARTS. I played with the software and read the manual and spoke to a few owners. looks pretty good.

[Warren B. MusselmanModerator]

They’re a nice unit and I like the add-on GPS module. My biggest issue with it is price, but then again, I’m a cheapskate.

Warren

[denverdoc]

con,

I think you’ll be very happy with the arts, John Bixler sent me some data he obtained with his, and it did everything but wrote an article about the flight. Very impressive attempt at using some math wizardry to compute too many unknowns at once. Course the CD on the Nike came in at 0.1, but the thrust data compared reasonably against his static tests IIRC.

As to the MAWD, short of a full potting, one can strip the film of the electrolytic can, lean it over, and epoxy it to the board. Warren is absolutely right that this is the achilles heel of the unit. I’ve sheared two off and I’m sorry to say both times it was from rapid D’celeration. Good news is PF fixed it for free both times, bad news is now I’m afraid its sitting at the bottom of the reservior at Bear Creek. 😥

John S

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