Hello,
I am finishing up on my Level 3, and need some input from the veteran Level 1, 2 and 3 flyers.
I have calculated out the proper sizes for my three altimeter vent holes on my Electronics Bay, and the proper sizes for my BP charges.
I plan on setting the altimeters ( 2 seperate units ) to fire the drogue at apogee ( both altimeters ), then the first main charge at 1000 AGL, and the second ( slightly larger charge ) at 800 feet AGL.
I am using 4 of the 4-40 nylon screws to hold the sections together ( four of the 4-40 screws in both the upper and lower sections. )
What I need to find out from those who are " In the Know " is this:
Should I still drill a small ( .125 or so ) hole in the airframe sections to prevent overpressure seperation of the Ebay from the lower and upper sections ?'
I know the 4-40 screws will shear as they should, from ground testing, but I never had the overpressure vents drilled in the lower and upper sections of the airframe.
Any Thoughts ???
I would appreciate any input regarding the over pressure vent ports ( one for the upper section and one for the lower section ).
My body tube is 5.54 inches O.D. and the length of the sections ( for the chutes is 24" long )
Planned Altitude of the flight is to 11780 Feet from the North Site.
Thanks
I typically drill a 1/16" or 3/32" hole in each section that will be pressurized. Make sure this hole is not subject to blockage by anything -- say a piston or a parachute that shifts.
For my part, I use pistons, shear pins, and vents. I've often been told that the vents are not needed if I'm using shear pins. I use them anyway.
Part of the equation is also how fast you will ascend. A slower, deliberate ascent will allow some of the overpressurized section to "bleed" off. In a 38mm rocket that you might put a J570 into, you need bigger and/or more vent holes.
Always ground test AFTER you have installed the vents, and always ground test with the rocket loaded, i.e. with the chutes and cords and such.
Hope that helps. Good luck. When are you flying this?
JW
The best vents are those that close as soon as the charge blows. Usually this is done with a 1/16" hole through both airframe and coupler. When the charge blows and the airframe starts moving, the hole closes and the pressure stays high until separation.
Warren
Sounds like it should be a nice flight.
I would use a small vent hole at least, as you will be going quite high. As Warren said, one good way is to drill it through the coupler, as this will seal it when the rocket starts to separate.
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