Static port question

[RktSledhead]

Looking for some feedback on static port placement for my altimeter. I am working on a Blackhawk 38 and it would work very nicely for me to put the ports in the lower third of the 6" coupler. Meaning the ports would be drilled thru the lower section of the airframe and thru the coupler, and yes, this is going to be a separation point.(meaning the ejection charge will be pushing the coupler out of the lower section of the airframe) Aside from always needing to make sure the holes are lined up prior to launch, is there any reason this is a bad design? I'm sure this has been done before, but I can't seem to find any reference to it. I hope I explained that well enough to understand. Thanks in advance for your feedback!

 

[John Beans]

Usually what I consider are:
1. Safety first (will deployment work well)
2. Accuracy (will the payload see anomalous high/low pressure, or time lags)
Seems like you're okay with both, assuming you have, say, 3 sets and they're sized well. I'd suggest over sizing either the inner OR outer set of holes so that alignment isn't as critical, and the section can rotate a little without choking the ports.

 

[Handeman]

What John says about over sizing holes is pretty good advice. You might want to consider oversizing the inner holes instead of the outer. You'll get some turbulence from the BT joint above the ports. I don't know how much over sized holes on the outside will add to that and if it would even be an issue.

I would also try to make sure you have a snug fit between the lower part of the coupler and the BT. Help prevent as much blow by from the ejection charge as possible, although I don't think it will really matter since it will only happen after the apogee charge goes off and and should have no effect at all on when the main deploy event occurs.

Seems like a good design to me.

 

[fyrwrxz]

Do it all the time- even CJ does it-so it's gotta be good to go. Clear skies, buddy!

 

[Salvage-1]

I usually put mine in the upper section of the alt bay, drilling through the payload tube and the coupler, but, I recently saw a few rockets that did it the way you are saying, through the lower body tube and the coupler. I was a little concerned that as the separation occured, the static holes get covered for a microsecond. It was explained to me that the altimeter would have no problem with this if it had an automatic Mach lock built in. Dont know if this is correct, but it does make sense. Most altimeters now can easily handle a microsecond of 'spurious data' if it happens.

 

[Disaster_Guy]

Are you using shear pins for the lower section? If so, drill for them first, insert your pins, and then drill your static ports. This will help to ensure that they remain lined up nicely.