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Fly Navy - 1

By Joe Ladwig

Madcow Rocketry Super DX3

   This Super DX3 is my first HP rocket as I reenter rocketry after a long hiatus.  I built it in concert with my son's first HP kit, a LOC Precision Zephyr.  He and I intend to certify at L-1 and L-2 in the years ahead.  Our certifications will bump start our local NAR Section the Count Down Cardinals (NAR Sect #887) and get the community launching some larger rockets locally.   

   As I built the DX3 I sought insight from John Coker (YouTube) and Tim van Milligan at Apogee (via YouTube).  I purchased additional components from Apogee, AeroTech, and LOC Precision.  I am buying my motors from BuyRocketMotors.com.  Each of these resources and vendors have been helpful.  LOC Precision was pretty dismissive as I expressed my newbie concerns over the use of their vented LP-36 to recover my +2 kg rocket.  They replied, "It will be fine if you don't come down on a hard surface."  That’s not a forecast I’d pay for.

Internet instructors made a case to make some upgrades from the start. 

A) External MMA Construction.  John Coker recommended that I construct the MMA externally with an additional centering ring at the top of the fin set.  I slipped the MMA in whole, gluing the aft centering ring in place after mounting the fins per Coker's recommendation.  This process improvement allowed for higher quality epoxy filets on the fin/MMA joints and the fin/tube slit filets internally.  The additional rigidity provided gives me consolation as I press larger and larger motors into service. 

B) Nosecone E-Bay.  I followed John Coker's instructions to install an E-bay in the voluminous 16" ogive nosecone, just inside the 4" shoulder.  Making use of that ballasting space would make for a more stable rocket.  I opted to construct a variable mass ballasting system (VMBS) there instead of inserting electronics.  I may add electronics as I grow into my process with this concept.  By mounting a PVC ballast housing filled with an appropriate number of 3/8" BBs (~3.6 g each) I can optimize my CoM to provide a consistent 1.34 cal stability ratio AND minimize rocket mass for improved flight performance.  My Jolly Logic Altimeter-2 is attached to the nosecone U-bolt in the vented cargo bay. 

   

C) Parachute Upgrade. The DX3 came down quickly (~8.5 m/s according to my OpenRocket simulation) in a soft field on the LP-36 chute using a H283-14 motor and appropriate ballast.  Apogee's Tim van Milligan recommends about a 4 m/s descent rate in Peak of Flight #149,  (https://www.apogeerockets.com/education/downloads/Newsletter149).  I have since upgraded the chute to an LP-58 main with a gentle 5 m/s descent rate. 

    The main is deployed at 400’ by a Jolly Logic Chute Release (JLCR).  I have employed the LP-36 as a drogue at apogee but am considering employing an even smaller, rectangular, 20" x 28", sonobuoy drogue chute from my olden days. 

   I have hand-sewn quick links into the shock cord, one at each end and a third for the main chute, attached 5’ down the cord from the sustainer attachment point.  The drogue chute is attached at the sustainer end.  

   I have constructed a parachute sled that neatly organizes all of the recovery gear.  It is attached to the cord just below the center quick link and the JLCR reefs the main until 400'AGL.  I have chosen to slow main chute deployment with a 1.25" reefing ring to minimize highspeed opening snapback. 

 

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