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Recovery Systems
Tripoli Minnesota
Gary Stroick
December 2012
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Copyright © 2012 by Off We Go Rocketry, LLC 2
Agenda
• Overview
• Dual Deployment Designs
• Avionics Bays
• Electronics & Ejection
• Attachment Points
• Parachutes & Packing
• Summary
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3
Overview
• Why use Dual Deployment?
1. To stay out of mosquito infested
swamps.
2. To reduce the drift distance
ensuring that the vehicle remains
in the recovery area as specified
by the Tripoli Safety Code.
3. So those with bad hips don’t have
to walk so far.
Unless …
You’re
Bill
You’re
Verno
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Overview
• Two Stage Recovery Philosophy
• Initial Rapid Controlled Descent
• Descent Rate 100 ft/sec
• Techniques: Flat Spin, Body
Separation, Streamer, Parachute
• Slow Final Descent
• Descent Rate 20 ft/sec
• Techniques: Parachute
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Failure Modes
Attachment Points
• Quick Links not
Connected or Left Open
• Poor Knot Selection
• Inadequate Hardware
Deployment
• Too Small/Not Tested
• Incorrect Altimeter Setup
• Loss of Power
• Electrical Wire Disconnects
Parachute, Bridle, etc.
• Improperly Folded
• Improperly Sized
• Inadequately Protected
• Fatigue Considerations
Related Failures
• Drag Separation
• Zippers
• In Flight Self Impact
• Shear Pin Failure
5
#1 Cause of Failure is Recovery!
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6
Dual Deployment Designs
• Design Approaches
1. Split Airframe Deployment
2. Inline Deployment
3. Rear Deployment
4. Hatch Deployment
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Split Airframe
Typical & Most Popular Design
7
Booster Section
Drogue Chute
Airframe Splits
AV Bay Main Chute
Top of Airframe
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Split Airframe
8
Ejection Charges
Ejection Charges
Avionics Bay
Rivets
Attachment
Points
Attachment
Points
(Bad!) Main
Bridle
Drogue
Bridle
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Inline
Typical Design
9
Airframe Drogue
Ejection
Charge
Piston
Retainer
Line
Main
Chute
ARRD
Wiring
AV Bay
Coupler
Main
Bridle
Piston
Support
Ring
Piston
Bridle ARRD Eye Bolt
Drogue
Chute
Drogue
Bridle Piston
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Rear
10
Parachute
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Hatch
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Avionics (AV) Bays
• Design Philosophies
• Redundant Systems (if possible)
• Complete System Independence
• Power
• Switches
• Separate Power Sources
• Altimeter
• Pyro Channels
• Ease of Use!
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AV Bay
Internal Components
• Avionics Mount
• Usually a Sled
• Z-Axis Alignment
• Internal Sled Support
• Rods & Tube/Eyes
• Slotted Bulkheads
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AV Bay
Power Systems
• Batteries
• 9V Duracell or Werker (Soldered)
• LiPo recommended for some systems
• Battery Mounts
• Connections always at Aft
• Immovable on all 3 axis
− Zip Tie/Velcro/Mechanical Fasteners
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AV Bay
Switches
• Mount Internally
• More Aerodynamic
• Avoids Shearing
• Wiring
• Solder
• Terminal Blocks
• Must be Vibration/Bounce Resistant
• Mount with “On” in the Down Position
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AV Bay
Static Ports
• Required for Barometric Sensors
• Recommend 3 or more ports
• Port Sizing
• DP=Diameter of Port
• VAB
=Volume of AV Bay
• NP=Number of Ports
16
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Electronics
• Dual Deployment Altimeters
• Always have a Barometric Sensor
• May have Accelerometers, GPS, or
Timers
• Ex. Co-Pilot, Marsa54, XTRA, …
• Timers, etc may be used but are
not recommended.
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Electronics
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Electronics
Altimeter Configuration
• Altimeter Dependent but …
• 1st
Deployment (Drogue) at Apogee
• 2nd
Deployment (Main) at ??? ft AGL
• Parachute Opening Time
− Parachute Size
− Bridle Length
• Wind Conditions
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Ejection Charges
• Under 25,000 feet
• Solutions include Canisters or
Surgical Tubing
• Typically on AV Bay Bulkhead
• Over 25,000 feet or CO2
• Requires Airtight Chamber
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Ejection Charges
• Sizing Based on Parameters
• Deployment Volume
• Shear Pin Size & Number
• No Shear Pins - Coefficient of Friction
• Mass of Ejected Components
• Desired Ejection Velocity
• Contingency Factor
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Ejection Charges
• Ejection Pressure (PE)
• Nose Cone Force (FNC
)
• Requisite Black Powder using
Ideal Gas Law (mBP
)
22
WNC
= Weight of Nose Cone
NC
= Velocity of Nose Cone
NSP
= Number of Shear Pins
SP
= Pin Shear Strength
FNC
= Nose Cone Force
C = Contingency Factor
ANC
= Area of Nose Cone Base
VRB
= Volume of Recovery Bay
RBP
= BP Specific Gas Constant
TBP
= BP Combustion Temperature
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Ejection Charges
• Online Calculators Inadequate
• Don’t Handle Shear Pins
• Don’t Handle Nose Cone Mass
• Don’t Handle Desired Exit Velocity
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Attachment Points
• Use Appropriate Hardware
• Don’t Use
24
Plastic Loops - Recipe for Disaster
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Attachment Points
• Apogee deployments typically
experience 20 to 25g’s
• Validate Strength of Materials
• Hardware Working Load Limit (WLL)
• WLL/Weight = X g’s (Maximum)
• Evaluate Bulk Plates and Joints
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Attachment Points
• Install Correctly
• Use Washers to Distribute Load
• Fabricate needed Parts
• Secure Nuts
• Loctite
• Nylon Inserts
• Cotter Pins
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Attachment Points
Bridle (Shock Cord)
• Knots
• Bowline
• Follow Thru Figure 8
• Others significantly weaken cord
• Sewn Loops (Stronger than Knots)
• Thread Material same as Bridle
• Use Rectangle with Cross Pattern
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Attachment Points
Bridle (Shock Cord)
• Provide Thermal Protection
• Don’t Ignore Material Fatigue &
Thermal Shock
• Replace Periodically (every 10
flights or less)
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Parachutes & Packing
• Drogue Chute
• High Velocity Deployment Implies Higher
Strength Requirements
• Main Chute
• Shock Forces Controllable based on
Drogue Chute Selection
• Provide Thermal Protection
• Heat Shield, Deployment Bag, Cellulose,
Piston, Baffles or use Kevlar Materials
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Parachutes & Packing
• Parachute Sizing
• where:
• W = Total Weight
• ve = Desired Descent Velocity
• CD = Parachute Drag Coefficient
• = Air Density
• S = Surface Area of Parachute
• Diameter determined by Shape
30
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Parachutes & Packing
Folding Instructions
1. Fold with shroud lines as
shown
2. Make one last fold over
shroud lines
3. Fold top end over end until
you reach the bottom edge
4. Connect to bridle
5. Insert thermal protection
6. Insert into airframe
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Summary
• Success Factors
• Physical Design & Construction
• Proper Sizing & Testing
• Charges, Parachutes, Bridles, Hardware
• Avionics Configuration
• Use of Appropriate Materials
• Thermal Protection, Fatigue Assessment
• Checklist, Checklist, Checklist
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What can happen?
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References
• Modern High Power Rocketry 2;
Canepa, Mark; Trafford
Publishing, 2005
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Selected Websites
• http://www.offwegorocketry.com/
• http://www.tripolimn.org/links
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