It takes a licking and keeps on ticking...

The Phoenix Altimeter

by Lynn Kissel, LUNAR #009

I seem to have bad luck with altimeters. They're not cheap, and it kind of hurts when I destroy one -- I've done that twice already.

My first altimeter, an Adept RA2A recording altimeter, was purchased in June, 1993. For those who are unfamiliar with this particular device, the RA2A uses the change in air pressure to determine altitude above its launch point. It records altitude readings every 1/10 of a second for up to 48 seconds onto a nonvolatile RAM that can be downloaded to a PC. On recovery, the RA2A also "beeps" out the maximum altitude that it recorded.

The first flight that I recorded with the RA2A was on June 27, 1993, when LUNAR was launching out of Gardella Greens in Livermore. My Aerotech Arreaux reached a peak altitude of 405 feet on an E15-7. On flight #4 of my RA2A, I set my current personal altitude record of 2304' on July 25, 1993, at the Wings for Charity air show at the Livermore airport.

It kind of makes you dizzy, doesn't it! The newer LUNAR members have been jaded with all the big stuff that the club flys now. In 1993, an Arreaux was fairly big stuff for us. We all stopped and paid close attention in those early days when Eric Kleinschmidt lit off an "F" motor.

That September, my RA2A altimeter, Midnight Oil (a PML Ariel), my family, and other LUNAR members traveled to Black Rock for Fireballs 003. The burning of Midnight Oil on September 4, in a launch pad fire is something of a legend at LUNAR. Club president Mark Weiss captured that moment on video tape -- we'll have to show that tape again sometime for the newer members along with my video of that incident that has never been aired in public.

But, no, my RA2A altimeter was NOT destroyed with Midnight Oil in that famous fire; it survived! But picture this, here I am at Black Rock, my beloved Midnight Oil and my ego in ashes, my fancy altimeter in my pocket, when Frank Kosden asks the crowd for someone to let him "borrow" an altimeter for an experimental flight. I didn't know who Frank Kosden was, and I certainly didn't know that he has a reputation of NEVER recovering his experimental flights. So, sure, he can use my RA2A with his Alienator II, a four-inch diameter, 78" long, 40 pound aluminum rocket powered by a nasty N4150 motor.

I guess that you can anticipate the outcome. Ole Alienator never released its parachute (but probably no one there who knew Frank expected it to). Instead, it came back ballisticly from about 25,000 feet and made a very impressive one-point landing about 1/2 mile from the spectator line. I've never been in a battle-field situation, but I imagine that the return of Alienator II to good mother earth sounded a lot like an incoming artillery round. The rocket buried its entire length, plus some, into terra firma. The accompanying photos show two stages in the extraction of the rocket from the dry lake bed.

Photo 1. Frank Kosden, the owner/builder of Alienator II, takes a turn at recovering his rocket, and my altimeter, at Fireballs 003. (photo by Lynn Kissel - 26 KB)

Photo 2. The butt end of Alienator II is finally uncovered about a foot below the surface of the Black Rock Desert. (photo by Lynn Kissel - 29 KB)

Photo 3. At a later stage in the extraction process, a makeshift frame and "come along" are used with a chain wrapped around the exposed end of Alienator II in an attempt to pull the rocket to the surface. The boards break instead, and more digging is needed before the rocket can be pried from the desert soil. At one point, a motor home is attached to the rocket, but this also fails to pull Alienator II free. (photo by Lynn Kissel - 27 KB)

The next day, Frank returned my altimeter in a baggie. He didn't offer any compensation, but did bug me for about 6 months to try reading the memories to see if there was recoverable information. (There was data there, Frank, but that's another story.) If Frank Kosden ever asks to "borrow" anything from you for one of his experimental flights, offer to sell it to him. If you want, you can agree to buy it back if it's returned in working order.

Later that year, I bought myself an early Christmas present, an Adept OBC2B on-board computer with recording altimeter. This baby is pretty sweet! In addition to the recording altimeter found on the RA2A, the OBC2B has two programmable output switches that can, for example, be used to fire a drogue 'chute at apogee (highest point in flight), and eject the main 'chute later at, say, 300 feet above the launch altitude. I've never used the output switches, but I've always planned to "when I got around to it."

After 8 successful flights of the OBC2B, it experienced a catastrophic failure from rapid deceleration syndrome when Scorpius (a PML Io, with an added payload section) hit an access road in Robertson Park, Livermore, on August 10 of this year. It really was own my fault. I launched Scorpius in moderately strong winds (18 mph, est.), with a low thrust motor (F22 "Black Jack") and pointed the launch rod into the wind. The PML Io is stable to start with, but stretch it with a payload section, then add the extra nose weight of the OBC2B payload, you get a rocket with all the characteristics of a weather vane. Immediately after leaving the launch rod, Scorpius turned its nose into the wind and flew at a sickeningly shallow angle with respect to the ground. The road met Scorpius about 2 seconds before the ejection charge was scheduled to go off. I stood there wishing that I had one of Pratt Hobbies ECS-2 radio-controlled ejection charge system. Of course, the OBC2B had those dual output switches and would have been happy to fire off an altitude-based eject charge if I had just "gotten around to it."

Under normal circumstances I wouldn't have sent Scorpius up -- I'm normally so cautious at LUNAR launches that Robert Taylor claims that I never fly at all -- but we were running the launches for the LARPD (Livermore Area Recreation and Parks Department) Science Camp program. We had been launching Estes Alphas all morning, and I wanted to show the kiddies what a real man's rocket looked like. "Pride goeth before a fall!" Within 8.4 seconds of liftoff, I had all the fixings for my 2nd "altimeter in a baggie." Sheesh!

At the September 23, 1995, LUNAR launch, I was talking with Chuck McConaghy, a new member of the club and an electrical engineer at Lawrence Livermore National Laboratory, a superior organization supplying much of the talent in LUNAR. I was telling him about my matching plastic-wrapped powdered altimeters. The OBC2B was not really that badly damaged (a couple of broken traces, broken battery holder, CPU leads badly bent as the chip had left its socket under protest, maybe a missing resister or two) and Chuck expressed an interest in trying to make it whole again. After a couple of nights, he'd gotten the OBC2B back up and running! Thanks, Chuck! I was so sick about my stupidity that I couldn't bring myself to try to fix it.

Using the repaired OBC2B Phoenix altimeter, I read the memory used with the LARPD Science Camp flight into my PC -- I wasn't sure what I would see. I was hoping for a good recording, maybe with "noise" after the rocket hit the road. But I was worried because I knew that the 1179' maximum altitude that the altimeter "beeped" out before I started the dump just couldn't be right. The resulting output from the 8/10/95 flight/crash is shown as the thicker points in Fig. 1. In fact, the maximum altitude for the first 8.4 seconds of the recording is 207', then the data jumps to a previous flight that was recorded into these memories on 4/23/95, which had a maximum altitude of 1179'. I had saved a recording of this earlier flight on my computer. The thin line representing the actual 4/23/95 data merges with the 8/10/95 read-out after the crash at 8.4 seconds. Apparently, the altimeter memory is only erased as new data is written into the memory. A third curve shown on the plot is the RASP (rocket altitude simulation program) output for Scorpius with the F22 motor. RASP predicts a maximum altitude of 373' if the rocket had flown vertically.

Figure 1. Altimeters readouts for two separate flights of Scoprius and RASP predictions for the ill-fated 8/10/95 flight are compared in this plot. (8 KB)

Chuck had several suggestions for my future flights of the Phoenix:

• use some cable ties to secure the battery, data memory and CPU chip to the board;

• wrap the board in some high-density foam to help protect it from future insults (but make sure that the pressure sensor can still "breath");

• test fire some flash bulbs with the output switches before I trust this board to handle the parachutes of a future model.

Copyright © 1995 by LUNAR, All rights reserved.

Information date: Oct. 13, 1995 lk