Altimeters/Accelerometers Commercial Altimeters or Altimeter/Accelerometers are probably the most widely flown pieces of avionics on High Power and Amateur rockets. They range in complexity from those which just beep or flash out the peak altitude reached by a rocket, to more advanced units which record the entire flight altitude and acceleration, fire a second stage, deploy a drogue parachute and deploy a main parachute at a lower altitude, and can then be connected to computers such as PCs and PalmPilots. Generally, altimeters and altimeter/accelerometer combinations are sized to fit in standard High Power Rocketry airframe tube diameters. Most fit in 38mm diameter tubes, some only fit in 54mm diameter tubes, and others are capable of fitting in tubes as small as 29mm and even 24mm diameter. There are 2 brands of rocketry altitude recording devices currently available for sale in the UK, namely (1) The R-DAS, by AED, and (2) The ALTACC, by Black Sky Research. Personally, I currently use an R-DAS flight computer in my rockets which are 54mm diameter or larger, and a G-Whiz LC Deluxe altimeter/accelerometer for my rockets which are less than 54mm diameter. I also sometimes fit both of them in rockets for redundancy. I used to use a commercial altimeter/accelerometer called the ALTACC, manufactured by Black Sky Research of California. It records data for the full flight, and interfaces to both my laptop PC and my Palm V. The latest version of the ALTACC fits in a 38mm diameter tube, although the previous one didn't - hence the fact that I broke it when I tried to modify it to fit in a 38mm diameter tube (an expensive mistake). Another popular choice of altimeter/accelerometer (well at least amongst members of MARS) is the Cambridge Instruments IAX-96. This provides even more functionality than the ALTACC that I use. The reason I don't have one is (a) it is more expensive than the ALTACC and the G-Whiz LC Deluxe, and (b) I have seen a fair few of them experience problems with their complicated wiring harnesses (something the ALTACC or G-Whiz LC Deluxe don't suffer from). A comparison chart of the commercially available altimeters, shows the various features of the altimeters and altimeter/accelerometers. Additional pages are available on both the R-DAS and the G-Whiz LC Altimeter/Accelerometer.