Adept Rocketry - Installing and Using

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The most serious installation and usage problems discovered so far are caused by the user who has failed to do something absolutely necessary:

at least once

Most of the devices are installed lengthwise in a rocket tube. The ALTS25, PST440, and ES236 will fit lengthwise in a 38 mm ID tube. Also, they may be mounted lengthwise on either side of a center plate inside a 54 mm tube. In larger tubes the ALTS25 may be mounted flat against a bulkhead, but the PST440 and ES236 must be mounted lengthwise in a rocket—they have an Integral Acceleration Sensing System™ that must be oriented properly.

When installing devices that have a vertically oriented battery holder for a 12-volt lighter battery, be sure to install the device with the spring portion of the battery holder facing upward. This would be when installing an ALT05, ALTIM1, ALTS1, ALTS2, ALTS20, ST1205, or an ST210. It is possible, in cases where a rocket launches with several tens of Gs acceleration, for the spring to be compressed if mounted incorrectly toward the bottom. Battery connection could be interrupted.

The mounting holes in devices are .090 inch diameter for #2 hardware. Use #2 screws, standoffs, and hexnuts when mounting an instrument to a plate or bulkhead. Do not enlarge the mounting holes (voids warranty), and do not use Velcro. The recommended mounting hardware (#2 size) is more than sufficient to support the smaller devices, even during a high-G liftoff. But for the larger devices, especially the ones that use a heavy 9-volt size battery, the aft end of the device should be supported against a bulkhead or some sort of supporting block. In this case, the mounting screws only serve to hold the device in place. The bulkhead or block supports the device during strong acceleration forces.

An altimeter must be installed in a “sealed” chamber with a vent or vents to the outside. A sealed bulkhead below the altimeter chamber is necessary to avoid the vacuum caused by the aft end of a rocket during flight. A sealed bulkhead above the altimeter chamber is necessary to avoid any pressure fluctuations that may be created at the nose end of the rocket.

The vent (also known as a static port) to the outside of the rocket must be in an area where there are no obstacles above it that can cause turbulent air flow over the vent hole. Do not allow screws, ornamental objects, or anything that protrudes out from the rocket body to be directly in line with and forward of a vent hole. The vent must be neat and burr free and on an outside surface that is smooth and vertical where airflow is smooth without turbulence.

Some rocketeers use multiple static ports (vent holes) instead of just one. Very strong wind blowing directly on a single static port could affect the altimeter. Multiple ports evenly spaced around the rocket tube may help cancel the effects of strong wind, the pressure effects of a non-stable liftoff, or the pressure effects that occur due to flipping and spinning after deployment. If you wish to use multiple ports, then use three or four. Never use two. Ports must be the same size and evenly spaced in line around the tube.

The general guideline for choosing static port size is to use one 1/4 inch diameter vent hole (or equivalent area, if multiple holes are used) per 100 cubic inches of volume in the altimeter chamber. For instance, An eight-inch long four-inch diameter tube has a volume of about 100 cubic inches. Use one 1/4 inch port, or three or four 1/8 inch ports evenly spaced around the tube. An altimeter chamber two inches in diameter and eight inches long (25 cubic inches) needs one 1/8 inch vent hole or three or four 1/16 inch vent holes. Keep hole sizes within -50% or +100% of the general guideline. Do not make the holes too small, and especially do not make them too large. A vent or vents in a small rocket tube, such as an Estes BT-20 (18 mm) body tube, will be quite small.

Vent holes should be a minimum of four body diameters below the junction of the nosecone with the rocket body. This is necessary with high performance (high speed) rockets. The tremendous pressure on the nosecone leeches down the rocket body as much as four diameters before it dissipates.

www.adeptrocketry.com 2-27-06