Baro unit for main deployment

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War Bird

Well-Known Member
Aug 13, 2003
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I know there has been a lot of discussion here about altimeter and port hole location. I have a project that I want to put a barometric altimeter (MAWD) in the nose cone shoulder. The main parachute will reside above the shoulder in a two piece nose cone. If I'm just using the MAWD for main chute deployment at 500', can I get away with putting the vent hole in the shoulder only? The MAWD will sample the pressure at ground level when armed and the nose cone will be ejected at appogee with another unit. Has anyone done this or have a unique venting idea? What am I not thinking about here? This will not be a supersonic speed demon.


Kevin Trueblood
Maybe this was a dumb question or simply nobody knew the answer. However, here is the answer from PerfectFlight for those who want to know.

"As the rocket picks up speed the air surrounding the nosecone will
get more dense and the pressure fed into the sampling hole will
increase. The increase in pressure will appear to the altimeter as a
reduction in altitude, which will subtract from the actual
(increasing) altitude. Usually the true altitude will be increasing
more rapidly than the pressure-induced reduction, so it will not
interfere with the operation of the altimeter. Near apogee the
rocket will be moving slowly so it is essentially a non-issue. But
it will "warp" the altitude/time curve so if you're counting on the
downloaded curve to be accurate the sampling port(s) should be
several airframe diameters back from the nosecone shoulder."

-- Peter
I fall in the "didn't know the answer" category.
Thanks for sharing the info from PerfectFlight!:)