Post on 13-Jul-2020
Staging, Clustering, and Complexity
Why add complexity?
• Improve the performance of your rocket • Meet design specifications • Fly to greater altitudes (or space) • Prove your engineering capabilities • It looks cool • Impress that special someone
Why avoid complexity?
• Complexity usually leads to higher costs • Risk of failure • Difficulty of design or construction
Staging low-power rockets
Ejection delay timer
Staging
Direct staging of low-power rockets
• Black powder ignites very easily
• Motors can be staged using the ejection charge of the booster motor
• Upper stage motors must be reasonably close to the booster motor to prevent cooling of ejection gases
• Can also be staged using electronic timers or switches
Gap staging of low-power rockets
• Very similar to direct staging
• Add vent holes to allow hot gas to reach the staged motor
• Vent holes should be no larger than 0.25” in diameter
• Avoid spacing stages too far apart (>10 inches)
Staging with composite motors
• Composite motors take a long time to ignite, and thus cannot be directly staged
• Use electronic staging timer or pre-programmed flight computer
• Most staging timers work by sending a charge some number of seconds after an acceleration event
• Remote staging is possible and can prevent unwanted staging events
General staging tips
• Be sure to couple the stages together, but do not use glue
• Shear pins are not recommended, either • Allow components to vent to prevent
premature separation (pinside>poutside)
Staging “Do” and “Don’t”
Do • Watch your CP/stability
for each stage • Check all staging timers
and delay timers for the correct values
• Add vents where necessary
Don’t • Forget to arm any electric
arming systems • Use plugged motors for
hot gas method • Seal off motor mounts
when using direct and gap staging
• Forget about motor retention
• Forget about recovery
Why stage?
• Fly higher (remember Newton’s Second Law) by reducing the mass flown in a given stage
• Staging is difficult, and thus a good engineering challenge
• Start small (low power) and work your way up for optimal success
• Finally put those C6-0 motors to use
Clustering
Clustering
• Group multiple motors together on the same stage
• Cluster only BP motors with other BP motors or only composite motors with other composite motors – Allows all motors in a cluster
to ignite • BP motors can be clustered
using a clip whip • Because of high current
draw, composite motors may require ignition by electronics
Clustering “Do” and “Don’t”
Do • Be mindful of the CG
when adding motors to a cluster (stability)
• Carefully align all motors to prevent unbalanced moments
• Carefully install all igniters, plugs, and leads
• Pay attention to the polarity of a given lead
Don’t • Cluster black powder
motors with composite motors*
• Asymmetrically cluster motors
• Add enough motors to allow the thrust-to-weight ratio to fall below 5
Why cluster?
• Add more thrust to a single stage • Boost the altitude capabilities of a rocket • Induce a spin (flying saucers)
Thrust Vectoring
• Angling a motor any direction other than directly up the longitudinal axis of your rocket
• In commercial rockets, useful for stability and control without using fins
• NAR/TRA frown upon active guidance, so use in a cluster to cancel out unbalanced moments
Experimental Motors
• Restricted to research launches for Tripoli Level 2 and up, or non-sanctioned launches
• Requires knowledge of chemistry, thermodynamics, heat transfer, and compressible flow
• Dangerous to make, but can produce powerful and/or visually interesting propellants
• Significantly cheaper than commercial motors despite a high start-up cost
• Significant probability of failure
Experimental Motors