The Skyward Electronics Altimeter available from Space Modeling Solutions, (480) 497-1960, is a full featured, extremely well designed unit at a very attractive price. For $95 (+ shipping) you will receive a very easy to use altimeter that is more flexible in use than other comparable units. I am fortunate to have the distributor of these altimeters present at my launches so getting one was almost too easy. The first thing you notice when you view the construction is how durable it is. Surface mount technology eliminates all soldered on resistors and capacitors that could move under pressure or worse, break. Every thing on this thing is solid state and very small, making for an altimeter that is compact and light weight (Fig. 1). Measuring in at 4" X 1-1/8" and only weighing 2.7oz with battery. The battery holder has proven itself under extreme impulse without tape or zip ties to hold the battery down for added measure. The screw terminals are very high quality. Using a standard small screwdriver, your power and ejection leads are held firmly in place.

Programming the altimeter for flight is simple and straight forward. Using the two supplied 220 ohm resistors, you can program either main only, main and drogue at apogee, or dual deploy. With no resistors, you can program for recorded altitude only. Mach delay of 4, 8, 12, or 16 seconds is achieved by switching dip switches 23. Main deploy altitudes of 500, 800, 1100, or 1400' is achieved by switching dip switches 45.The altimeter communicates to you what it's doing to you via a series of different tones (high and low) during programming and pre-flight continuity checks. Prepping for flight is easy with the quick reference chart stuck to the altimeter itself (Fig. 2) enabling you to double check your pre-programmed mode, mach lockout, and main deploy altitude. 

At the pad, once armed, the unit will do a continuity check of the ejection charges. If everything passes you will hear 3 ascending tones. Then it will confirm what mode you have programmed it for using 2 tones. It will then be looking for launch detect. While waiting, you will hear a short high tone every three seconds letting you know it's ready to go. If the main or drogue circuit doesn't pass the test, you will hear a very offending low tone beeping out that something is not right. 1 low tone, your main is open, 2 low tones, your drogue is open. Error tones are very distinguishable as I found out myself when I didn't get one of the ejection charge screw terminals tightened all the way down. The use of different tones makes communicating with the unit a snap as they are very distinguishable and hard to misinterpret.

For testing, I built a 2.56" dia rocket of basic design with a traditional dual deploy design. Using the supplied 1/4" X 1/2" stand-offs I was unable to mount the unit on a tray inside of the payload compartment. Instead I fastened the unit directly to the payload compartment side using 1/4" plywood pieces, sanded to contour to fit the payload bay (Fig. 4) Bolting the unit down from the outside with counter-sunk 4-40 screws. This positioned the weight of the unit directly down the centerline of the rocket not making one side heavier then the other. For venting I used (2) 1/4" holes.

Three flights have been made with perfect results from the altimeter each time. The first flight was launched on an H-238, deploying the main at apogee and popping off the nose cone at 500' with it's own small chute, recording an altitude of 1852'. Now that I was comfortable that it was all working, I swapped the chutes and launched with an H-180. The drogue ejected right at apogee and the main deployed right on time at 500' albeit a little tangled (operator error) recording an altitude of 2618', no harm done. The third flight with an H220 wasn't so perfect with operator error once again. The drogue didn't eject at apogee, getting a "uh-oh" from the crowd as it arched over and started to come straight down, but the back up motor ejection saved the day. The jolt caused the main to yank out, saving the rocket and it's payload. Arriving at the rocket it was beeping out an altitude of 1991'. Upon investigation it was concluded that my drogue ejection charge fell apart on take-off as the flash bulb had gone off but there were no powder burns anywhere. The main ejection charge had gone off just fine though as was evident by the powder burns.

For review purposes I wanted to exploit the fit of this unit in other size applications. Fig. 4 shows the fit in 2.56" coupling. With a 3" coupling (not shown) you can mount the altimeter on a board for easier in/out. The best part of this unit is it's fit in smaller applications making for "no brainer" installs. Fig. 3 shows the altimeter in a 38mm motor mount 'coupling'. Removing the stand-offs provides the perfect fit. Not too tight, not too loose, while keeping itself perfectly centered. Some foam padding on each end is all that's required here. And for those that are comfortable with soldering, by cutting through the double sided tape that holds the battery holder and soldering on 9V power leads for remote battery location, you will achieve again a perfect, slide right in fit with 29mm motor mount tube (Fig. 5) The Skywards Electronics Altimeter has proven itself worthy with myself and the few others in my club that are using it. Ease of use and it's given size for convenient installation make this one a winner. At the time of this writing version 1.5 has just been released. Resulting in fewer parts, this altimeter is now 1" shorter than tested and even more reliable. Distribution and customer service is handled through Space Modeling Solutions. Quality and reliability make the $95 price tag almost a steal. WildRocket.com Editors Note: The FCS also happens to be the altimeter of choice here at WildRocketry. It has flown in numerous projects and continues to work as promised.