Head End deployment: switches and vent holes

Discussion in 'Rocketry Electronics and Software' started by mad4hws, Apr 18, 2019.

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  1. Apr 18, 2019 #1

    mad4hws

    mad4hws

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    Hi everyone,
    I don't have much experience with altimeters in the nose cone.... My experience is limited to data recording altimeters only. So, now that I'm putting the altimeters in the nose cone that will control my ejection charges, I have a pretty basic question and want to know how others have handled it.

    The logical place for the vent hole would be to go through the shoulder of the nose cone and through the upper body tube where they meet. The nose cone would be secured to the upper body tube with shear pins, so that the vent hole does not become obstructed during flight. I am sensitive to the over-pressurization caused by the ejection getting through this vent hole and causing faulty readings. Is this something that I should be concerned about, or am i just being paranoid? The ejection canisters will be mounted to the base on the nose cone.

    I am planning on using the Missileworks screw switches to activate my altimeters. The hole to access these would serve a dual purpose as the vent hole. I appreciate any thoughts from those who have done this a few times before.
     
  2. Apr 18, 2019 #2

    Bat-mite

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    We may be confusing some terms, here. "Head end deployment" is dual deployment without a payload tube, with the main parachute in the nose cone. It seems like you are talking about single event deployment with the electronics in the nose cone.

    If the former, i.e., true HED, then the sampling ports go in the switch band. If the latter, then what you have proposed sounds reasonable. Just remember, however, that online port calculators assume you are filling a cylinder, not an ogive; so volume calculation is more complicated.
     
  3. Apr 18, 2019 #3

    mad4hws

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    Thanks Batmite.

    Sorry, terminology is probably wrong. I am installing a Strattologger and an RRC2 in the nose cone (RRC2 is the backup). This is for a madcow seawolf. there is no payload bay. The nosecone fits right into the booster. It will be dual deployment, both events controlled by the altimeters. The main will be deployed via cable cutters, but also controlled by the altimeters in the nose cone.

    Being totally dependent upon the altimeters in the nose cone for deployment events, I wanted to ensure that nothing would interfere with their operation.
     
  4. Apr 18, 2019 #4

    cerving

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    I've done plenty of head-end deployments, vent holes in the shoulder behind the break are fine. Just like any other AV bay, you'll want three vent holes, evenly spaced... you'll have to work your shear pins around them. Add the other two vent holes, even if one is larger because it's your screw switch access hole... they will help even out any uneven pressure distribution in the AV bay.
     
  5. Apr 18, 2019 #5

    mad4hws

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    Thanks. Excited to see how this turns out.
     
  6. Apr 19, 2019 #6

    Eric

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    I have added electronics to several nose cones. And Atterberry Performance Engineering makes a good sled for it. In several cases I added the static vent holes on the nose itself. I put them as low as possible. Even though there are some different air pressures around the nose cone. Deployments are still consistent at the top. But I believe any air speed calculations done by the altimeter would be flawed. But all I was looking for was deployment at the top. A magnetic switch makes activation very easy. As does an egg timer quantum that doesn't require a switch.
     
  7. Apr 23, 2019 #7

    mad4hws

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    thanks Eric,
    This is a perfect opportunity to try some magnetic switches. Thanks also for the advice on placement of the vent holes. I figured that the altitude readings might be a little bit off because of placement on the nose; however, I think (and it appears you are of like mind) that the baro sensors will be able to detect apogee (and therefore trigger deployment) without any issues.
     

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