Reconciling Vent Size and Number for Different (Redundant) Altimeters

Discussion in 'Rocketry Electronics and Software' started by gary7, Nov 3, 2019.

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  1. Nov 3, 2019 #1

    gary7

    gary7

    gary7

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    How do you reconcile the number and size of electronic bay vents when two different altimeters are used with different requirements? Can you get too big or too many for one of them? Or can you go too small and too few for the other? Etc.

    Altimeters planned:
    RRC2
    StrattologgerCF

    Thanks
     
  2. Nov 3, 2019 #2

    Cameron Anderson

    Cameron Anderson

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    I have used both those altimeters interchangibly in the same av bay with the same holes. Always better to go too big as opposed to too small.
     
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  3. Nov 3, 2019 #3

    rharshberger

    rharshberger

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    +1, use the larger recommended size for whichever alt requires the larger static ports.
     
  4. Nov 15, 2019 #4

    Handeman

    Handeman

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    From my understanding, hole sizes is designed to allow pressure equalization at desired rates. If the rate is too slow, the rocket will arch over apogee and start back down before the pressures equalize and starts going up in the av-bay, indicating apogee.
    I believe larger holes are better. I generally use much larger holes than any of the calculators say.

    From previous posts, the only issue with oversized holes is if wind gusts are able to make significantly large pressure spikes inside the av-bay while the rocket is on the pad. Four holes are supposed to prevent this. The pressure spikes would have to be large enough to cause a launch detect to be an issue. Once the rocket is in flight, the air flow over the vents becomes so large that wind gusts become insignificant.

    I have no data, but would be very comfortable using vent holes 3 or 4 times the diameter that the calculators indicate.
     
  5. Nov 16, 2019 #5

    SammyD

    SammyD

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    +1 on all these posts. I fly Missileworks and PerfectFlite altimeters in redundant configurations in the same 3" and 4" AV Bays (4 vent holes at 1/8" each) - no problems in dozens of flights. I recently used the same two altimeters in a 5.15" rocket with 1/4" vent holes, and no problems there either :)
     
  6. Nov 16, 2019 #6

    blackjack2564

    blackjack2564

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    Years of testing with Missleworks and Perfectflite units, along with scientific calculations, determined they will function correctly by using either guidelines shown in both their manuals. I was part of the beta testing, and helped write the manual for Missleworks.
    Follow the guidelines provided and all will be happy in altimeter land.:)

    2 major points: if in doubt SLIGHTLY larger holes function better than smaller ones.
    Remember both units do not arm till reaching 160-300 ft altitude, though sampling.
    They both can be set by user to various arming altitude. Lower the setting results in being more prone to "spoofing" on the pad to higher wind gusts.
     
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  7. Nov 17, 2019 #7

    gary7

    gary7

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    Thank you, Jim!
     
  8. Nov 17, 2019 #8

    Dave A

    Dave A

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    I have several , identical, universal av bays that fit every rocket from 3" to my 9" rockets.
    It has a single 3/4" hole so I reach through it to arm 2 miniature slide switches for dual altimeters.
    Never had an issue, ever.
     

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