Well I wasn't going to do a flight report but I got enough questions
so I put this together.
On July 10th in Millican Oregon I launched my "Community
Four" airframe for my Tripoli Level 3 certification. It was
a successful flight and achieved all my goals - Tripoli level
3 certification being one of them.
Here are some useful, I think, technical details.
- Overview
- 6" diameter airframe, 10.5 feet length, 37 lbs. pad weight.
- Construction:
- Airframe tubing, internal centering rings and fins made by
Giant Leap. The tubing was kevlar and fiberglass reinforced. The
motor mount and nose are from PML. Fins are .125 G10. All very
good quality parts. Giant Leap and PML both get a big thumbs up.
The electronics bay was constructed using a design by Stu Barrett.
This was published in HPR June 1994. I also used Stu's anti-zipper
design.
- Electronics:
- On board was an ALTS25 and a Cambridge IA-X96 with barometric
option. Each was connected to its own apogee and main charges.
Each charge was capable of separating the airframe. This was confirmed
in a ground test. Why both pieces of electronics? I wanted a redundancy.
I was not too concerned that if both charges went simultaneous
that I would damage the airframe as the IA-X96 detects apogee
by accelerometer and the ALTS25 by barometer so I figured that
they would go off at slightly different times. The main was set
at 1200 feet for the ALTS25 and at 1000 for the IA-X96 - again
a good chance that simultaneous firing would not happen. Didn't
that double the chance of false apogee detection - that is, firing
charges during boost? Yes, but in my experience that happens much
less that no deployment at all. Couldn't I use one apogee and
one main charge each with two igniters? Yes, but I hoped that
if the first charge didn't fully deploy the chute - why that would
happen I don't know - I had hope that the 2nd charge would complete
the job.
- Motor:
- AeroTech M1315. I used a single FireStar igniter for ignition.
I've read so many things in the past about the Byzantine methods
some folks use to ignite big motors and I can't understand why.
Last year I saw a M1939 (98mm) ignite on a single FireStar. These
things work. Thumbs up to them too.
- Recovery:
- The drogue chute was a RocketMan R7C and the main a R14C The
drogue recovery harness is 44 feet of 1" tubular nylon. The
main harness of 20 feet 1" tubular nylon. No bungee or kevlar
was used - they are not necessary and are often inappropriate
technology. Nomex heat shields were used to protect the chutes.
1/16 styrene rod was used as shear pins in both the motor-to-drogue
section and main-to-nose section joints.
- Flight:
- Launch was from a BlackSky ProRail. The altitude as recorded
by the ALTS25 was 9894 feet AGL. The altitude as reported by the
IAX-96 accelerometer was 10,090 feet AGL. Max velocity was 902
feet/sec and max acceleration was 10.3g
The flight worked absolutely as expected.
TAP members were Stu Barrett and Dennis Winningstad. To both,
I offer my gratitude.
Why did the flight work? I tested. Everything. I've been flying
with altimeters since my level 1 certification flight (ALTS25
just along for the ride). Dual deployment on my level 2 certification
flight. I carefully simulated the flight so I could set all the
IA-X96 backup timers as appropriate. I ground tested the deployment
charges. Charges too small? Too big? Shear pins too big? Too small?
I knew they were correct. I also had a seven page checklist and
it got followed. Finally, the same airframe flew on two testing
flights - once with a K700 and again on an L850.
I should have pictures by the end of the week and will get them
posted on www.NorthwestRocketry.com
I plan on flying it again at LDRS on a L1120.
Kimberly Harms TRA 6206 L3