Tuesday, April 28, 2009

Layup... FAIL!! Then success!

Alright so I completed my layup as planned below.  Again the Mylar stuck preferentially to roughly 50% of the cured surface.  It took me 3+ hours (no exaggeration) to peel/cut/scrape/wedge the film off the part.  Note the voids, scrapes, and residue:Having failed to release the film cleanly with all three methods to date I contacted Dave Triano and here's his reply:
"Are you oven curing this laminate right off the bat? If you have 'pre-heated' the oven (not good, you should plug it in when you insert the part), and leave it in too long (over 1 hour, or too hot), the laminate will stick as you describe. Try just allowing the laminate to cure at room temp overnight, then remove the mylar, then post cure the laminate."
I was confused by this reply since it seemingly contradicts the advice in Dave's videos and instructions.  Perhaps I'd missed something.  In any event I laid up another test part last night with only a single layer of Teflon release on the Mylar and... it worked perfectly!  While I'm elated to now fully understand the recipe I'm a bit bummed that I can no longer cure parts in an hour.  :(  I wanted to share his feedback in case others were frustrated as I was.  On a side note that's a single wrap of Carbon/Kevlar hybrid fabric on a 38mm cardboard tube with the glassine layer peeled off and...  it's insanely strong!  I'll reiterate: 1 wrap over cardboard tube!! It would likely survive aJ570.  Composites frickin' rock.

Sunday, April 19, 2009

M750 payload section layup

I had purchased two 48" lengths of 98mm cardboard tubing for the M750 rocket below. However design stuff nags me in my sleep and lucid dreams so, instead, I purchased much stronger phenolic tubing from Public Missiles Ltd. just to be sure.  The added weight will probably cost me margin for the 20,000' goal but I eventually plan to fly it on much more punchy motors so... oh well.
Today I cut the payload tube to 26" and laid up three wraps of 5.6 oz. carbon fiber cloth with excess resin.  This time I mostly painted the epoxy on axially rather than radially so the fibers should be much straighter than my first two attempts.  I also applied two coats/buffs of carnauba wax to the Mylar™ film this time to lower its surface energy and mitigate/prevent stickage to the cured Aeropoxy.  My curing oven has been cooling down since about 1PM so I'm gonna pull the part soon (nice asymptotic cooling!).  I'm hoping that it's light, smooth, and devoid of voids.

Sunday, April 5, 2009

April launch report

Yesterday was the April Plaster City Launch.  Again the weather was almost perfect so that makes three months in a row for San Diego now!  Coincidentally both the March and April launches were preceded with excessive wind gusting to 35+ MPH the Friday before.  Then as of Saturday morning calm to mild gusts all day.  Great success!
This month I only had three flights due to setup complexity and the fact that our FAA waiver closed between 1:30-2:30PM for local flight maneuvers:
  • Minimum-diameter, carbon fiber "Fity-Fo" on a brutal J800 -
    this was the first flight for my custom design and it was just supposed to a) verify the strength of the carbon exterior and b) test the radio tracking system mentioned below.  After the incredibly fast and straight ascent we could see that the 36" green 'chute had ejected at apogee.  This means that dual-deploy hadn't worked and I'm guessing that the nose cone popped off during drogue ejection.  I'll need to friction-fit that better next time.  The rocket touched down very close to the launch site so the radio tracker wasn't necessary but it was good to practice with that system anyway.  When my buddy Doug's son Brandon picked up the rocket the ARTS2 altimeter beeped out 12,235'!!  I later downloaded the data and the exact barometric altitude was 12,012' (2.23 miles) and max speed was 1162.7 ft/sec (mach 1.02).  I had just smoked my personal altitude record of 8,079' so I was happy.  Having just read this unofficial compendium of altitude records (Word format here) by motor type I recalled that the J800 motor checked in at ~8,100' so I might have a record here. In any event I plan to register this as my 10K altitude flight with Extreme Rocketry magazine. [Update: Rick Saunders accepted this as a record on that site. I also checked it in as my 10K+ flight with Extreme Rocketry.]

  • Then I flew my primed yet not yet painted 4" V2 on a 54mm I229 Blue Thunder motor.  Very punchy and cool.  I synthesized this FAKE composite image from two separate frames (one of the boys reacting and a second of liftoff) because it amuses me to do so:

  • Finally I'd planned to fly a K270 in the carbon fiber Fity-Fo above.  However as I assembled everything I realized that there wasn't enough room to fit the recovery system because the motor was too long!!  I'm convinced that combination would have topped 16,000' but I had to move to plan B.  I prepped the 3" Vertical Assault for the K270 and included the radio tracker since the previous flight on a K185 hit 7,076' (below) and this motor is roughly 33% bigger.  The ascent was rapid and impressive but nobody saw anything after burnout.   I could tell that the transmitter had ejected because the signal pulse jumped in intensity.  I audibly tracked that which I could not see for roughly 3 mins and then then the signal seemed to cut off.  I experienced some panic here until I fiddled with the controls and again the pulse resumed.  I meandered out into the desert for a mile or so and found the rocket between two bushes.  Unfortunately the main parachute had not ejected so the exterior was a total write off.  I did recover the motor casing, altimeter, radio tracker, and some internal parts however.  I should also note that I NEVER would have found this rocket without the tracker.  Those transmitters are a bargain at $95 and the club offers the free use of a receiver.  Highly recommended equipment! The altimeter was beeping an error tone having collided with the ground so hard.  I was able to download the data and was astonished at both the altitude of 11,485' and speed of 978 fps (mach 0.86).  That's a slower burn motor in a 12 pound rocket so those stats are impressive:

    Here's the state of the remnants (note the car paint job on the top portion):
I just ordered a replacement Vertical Assault but without the pre-fiberglassing this time and I requested that they not cut the slots for the fin can.  I plan to carbon fiber the exterior myself in the hope that this second version will last much longer.

Belated March launch updates

The March Plaster City launch featured amazing, wind-free flying.  I must say that this is the first year of many when the stars have aligned to allow confident flying so I'm going as often as I can.  I had four flights that day:
  • Vertical Assault 3" on a K185 - 7,076' with successful dual-deployment recovery using the ARTS2 altimeter.
  • Talon 2" on a Redline H210 - altitude unknown with higher altitude direction shift and successful recovery.
  • Bullet 4" on Redline I285 - altitude known with early ejection causing zipper.  Nosecone lawn-darted but, surprisingly, remained intact.
  • Jayhawk 5.5" on a J415 - perfect and impressive flight with ejection exactly at apogee (10 second delay is ideal in this warmer weather).  I also swapped out the 7' parachute for a 10' so there was no canard fin damage unlike the first flight.
I was busy flying all day so I didn't shoot any photos of my stuff. However, as I was about to leave at dusk, Ken Sparks flew an M1850 motor in an 18' tall rocket.  Both flight and recovery were perfect.  You can see most of my photos in this album.

Electronics inventory update

Dok and Kurt encouraged me to build experience with varied electronics packages.  As such I've been stocking up.  At the time of my L3 cert I was using:
Since then I've added:
And plan to rev them up this flying season.  Also, while not electronic, I purchased a Defy Gravity tether to enable dual deploy recovery from a single internal volume. Very cool.  I'll keep you posted on my progress with these new devices.