DECA II

Introduction

Diameter: 58mm payload / 54mm rocket body

Length: 2200mm

Weight fully loaded: 6000gr (of which aproximately 1100gr ballast)

Motor: DECA 8 grain KNDX

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Rocket was sucessfully launched during the NERO Launch Day 07-05-2010

Goals

  • Prove of concept: modular built with stand alone payload.
  • Achieve a peak altitude of approximately 2km
  • Determine the usefulness of an on-board GPS tracker for rocket re-location
  • Determine the usefulness of an on-board Turnigy True 30 fps camera

Design & Construction

Motor:

Motor is the DECA 8 grain. A 54mm motor with 8 bates grains and a total impuls of  approximately 1400Ns. The nozzle has a 16mm throat and is optimised for the 20mm core Bates grains (core-to-throat ratio of about 1,5:1 to avoid erosive burning). Ae/At ratio is 6,0:1. The nozzle is held in place with 2 rows of 6x – M3 countersunk hex socket bolts. Forward bulkhead is retained by the coupler which is secured the same way as the nozzle.

27.03.10 – 2nd Static test DECA 14 motor – full data recording and suitable for launch at NLD 2010.

13.03.10 – Static test DECA 14 motor – no data.

20.02.10 – Static pressure tested the casing to 150% op MEOP – 90bar.

Fin can:

Same as used with the first DECA rocket in 2009

Fin can mass: 152gr. CoG @ 76mm from short end

Body tube:

Similar to the first DECA rocket, this rocket will break up above the motor for first stage tumble recovery. This rocket has a revised design that the coupler has been incorperated into the forward bulkhead retention design of the motor.  This will simplify the rocket lay out with less tube butt-to-butt connections. The 850mm long aluminium body tube cointains (motor-to-nose cone shoulder):

  1. 5 meters of 3,2mm tubular kevlar shock cord for the first stage tumble recovery. In the middle of the shock cord a swivel is mounted to reduce spinning caused by the motor and fin section.
  2. Recovery electronics bay which is positioned 100mm into the tube and the lower bulkhead is retained by 6x M3 countersunk hex socket bolts. Upper bulkhead is of floating type. Both bulkheads seal the recovery electronics bay by means of a 50x46mm O-ring.
  3. 5 meters of tubular kevlar
  4. Gps tracker
  5. Main parachute (800mm diameter) with kevlar cloth burito style wrap
  6. Nose cone or payload with nose cone

Second stage recovery will either eject a nose cone or a stand alone payload made out of HPR materials.

Recovery

Main parachute 800mm diameter + 1m tubular kevlar with end pliced for connection to d-shackle. 5m  tubular kevlar with both ends spliced for d-shackle. Payload with M6 eyebolt for connection to d-shackle.

Burrito style parachute bag. Kevlar cloth 350 x 235mm. Length = spare (60mm) + length parachute (150mm) +GPS tracker (70mm) + overlap (70mm) = 350mm. Width = 1,5 · π · ID tube = 235mm.

18.04.10 – Main parachute ejection test with 1,0gr BP in a latex finger. No confident separation: 54mm, DECA II rocket, main parachute test – 19.04.10. Next test will use the proven 1,0gr BP straw igniter.

Payload

02.05.10 – Assembled rocket & payload. Determined Cp & Cg. Added 1100gr of ballast to keep under the 2km limit and now has a static margin of 1,25 cal.  

Notes

Length:

  • Parachute in tube: 200mm
  • First stage kevlar shock cord: 100mm
  • GPS tracker: 65mm

Glass Body tube

  • OD = 57.8mm
  • ID = 54.6mm

Glass Coupler tube

  • OD  54.5mm
  • ID = 50.9mm

Machining the glass tube to length: While cutting square on lathe don’t go all the way and leave 0,4mm wallthichness remaining. Final cut by hand with sharp hobby knife. This to prevent glass fiber weave to catch up with cutting tool thereby causing delamination of inner layer.

>>>Motor mass full: 2624 – 2633gr (2572 SolidWorks). CoG @ 385mm from top casing / 338 from nozzle (340 SW).  Length motor (top casing to nozzle end) = 723mm.<<<

>>>Recovery electronics & body tube mass: 1402gr (1399 SW). CoG @ 465 from top / 385mm from end.  CoG from nozzle = 1108mm (1110 SW). Length body tube = 850gr.<<<

Conclusion

  1. Stand alone payload worked like a charm. Continue with same concept without any changes.
  2. Peak altitude was pefectly matched although pre-flight estimate of Cd was too high which resulted in a slightly higher peak altitude.
  3. GPS tracker worked giving landing coordinates. Next flight a tape should be wrapped around te unit to secure battery to GPS tracker (H13A lost its battery dou to a violent recovery).
  4. Camera worked OK although it should be removed from the flight control electronics bay. Activating the camera was difficult from the outside due to many buttons and switches. Therefore entire recovery electronics bay was needs to be removed from its body tube prior to launch. Preperations were therefore  not ideal. If removed from the recovery electronics bay the entire recovery section can be prepared in the shop or hotel rather than on-site in a tent. Fin misalignment caused a severa spinning of the rocket. New fin can to be made.
  5. Due to the use of vaseline with the o-rings the aluminium tape strips to secure the separate section did not tear upon firing of the main charge but failed on the sticky bond.

Post flight analysis of Flight I – 07-05-2010 – by BO

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