More Tales from the Crypt

by Geoff Canham, LUNAR #493

(JPEG, 69KB)
The original crash of the Crypt Ship.

Since my last article about the Crypt Ship (my NARTREK Gold rocket) it has completed its required six flights, and lived up to the comic-book story from which it originated. In the story it crashed at the end of its two flights, so you have some idea of how the flights went, if you didn't see them yourself.

The ship's fourth flight was at the August LUNAR launch, and the flight went fine (after two copper igniters failed), except that the parachute didn't fully open, and it came down rather hard on the bank on the far side of the road, breaking two fins.

But it was back for the September launch, which was originally going to be a Future/Fiction Scale Competition, but that got cancelled. That disappointed me, but it was handy as I had to get down south to Carlsbad for Open House at my stepson's (Matt's) school. So I arrived early to give the Crypt Ship one flight, then I would be off down the I-5. The ship was the second rocket of the day, in a slight drizzle (kind of heavy mist). It lifted off perfectly, veered away from the soccer field (where a game was going on), and started to descend. "Deploy, deploy, deploy, deploy, …" urged the LCO as I video'd a rather rapid descent. Deployment occurred about 10' from the ground, just in time to swing the delicate fins around so they hit the ground first in the animal pens. I'm sure most people who saw it thought it would never fly again, but a lot of glue and paint enabled it to be back a month later.

I arrived at the October launch just in time to get the ship up before the sun went down. The flight went well, the parachute deployed, it descended smoothly, … and landed right on top of the fence surrounding the pens, breaking two fins off. But it's back in one piece again, of course.

But what happened to it to cause the crash in September? On reviewing the videos of all the flights, the first thing that stands out is that it took 8.98 seconds from launch to deployment, while the other flights took from 5.08 seconds to 6.39 seconds. The normal variation was more than I would have guessed, but the one in September was about 50% more. But I also noted that the time to apogee on that flight was about a second less than the average for the other flights. Assuming that the thrust on each flight was similar, the normal drag coefficient works out about 0.80. To give the flight characteristics of the September launch, I have to use a drag coefficient of about 1.20 in the calculations (using the spreadsheet detailed in the last 'clips).

It is wrong to base a theory on one isolated event (and I have no intention of subjecting the ship deliberately to a similar flight) but it would appear that the light drizzle caused additional drag, and to take the effect into account means taking 150% of the normal drag coefficient. If anyone else has any similar flight information, I'd be interested in comparing notes.

Information date: November 14, 1998 lk