Do NOT use only one. Use three or four smaller holes.
https://www.vernk.com/AltimeterPortSizing.htm
Also, search the archives. This topic has come up even after the RF crash so posts are available that discuss this.
"Do NOT use one..."
Why do you think one is NOT a good idea???
Justin
I'm going with 4 1/4" holes. Sound good ?
Simple. That one vent is going to control all the air flowing into your ebay and its pressure. If there is some type of turbulence around that hole or it is in some way blocked, you can have a problem because the pressure inside the ebay will actually be different than what the outside (altitude) pressure actually is. Your altimeter will, therefore, use anomalous sensing data with which to determine proper deployments. With multiple smaller holes (which together have the same hole area as the one large hole), if one is blocked or is disturbed by unusual turbulence around THAT hole, the other holes can compensate and the ebay will properly pressurize and eliminate the anomalous sensing problem.
A single hole is more sensitive to the wind blowing across the rocket while sitting on the pad. The pressure coefficient on the surface of a cylinder varies from -3 to +1 around the cylinder. The +1 occurs on the side facing the wind and -3 occurs at the points 90 degrees away from the wind. With one hole, the sensed pressure will depend on the direction the hole faces. With either 3 or 4 holes, the average pressure coefficient is -1 no matter which way the wind blows. If the altimeter uses a rapid change in pressure to sense launch, a single hole will be more prone to false triggering, but it would have to be a really strong gust to do it.
Well, I didn't want to come off sounding judgemental, but I agree. In case you haven't figured it out, I'm an engineer, an aerospace engineer to be precise, and anything worth doing is worth over-doing.![]()
...... and if the wind is blowing that hard, you shouldn't be flying rockets anyway. I've flown countless rockets with one hole, never had a problem.
Lesson learned-- use 'remove before flight' shunts to isolate BP ejection charges until the rocket is ready for liftoff...
Agreed!Program altimeters and electronics BEFORE loading/hooking up ejection charges in the rocket...
Not necessary if you don't powr up the altimeter until it's on the pad.Perhaps cover altimeter ports with tape or something in gusty conditions
Absolutely.Safety is the word! OL JR![]()
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