Motor

Design Review

CAD

Bates Propellant Grains

Nozzle Carrier

Forward Closure

Graphite Nozzle in

Phenolic Insulator

Boat Tail

Phenolic Liner

Finocyl Grain

CAD - Nozzle Carrier

Design - Nozzle Carrier

Nozzle Carrier

Aluminum replaced with Phenolic around Graphite Nozzle

• Lower Average Density - Overall Mass Savings (1.5 lb)
• Insulates Aluminum from Thermal Stresses
• Protects Aluminum from Erosion - Aluminum is Reusable

CAD - Case

79”

Bolted Aluminum Case with 5/16” Bolt Holes (attach to forward closure/nozzle carrier)

Bill of Materials - Reusable

Bill of Materials - Consumables

Summary of Changes from ‘17/’18

• Improved Propellent - better density, ISP, and burn characteristics
• Grain Geometry - Aft finocyl for high-force initial kick-off and lowered port mass flux
• Lighter and more thermally insulating nozzle carrier
• Bolt size reduction for cleaner assembly & reduced drag
• Revised Liner - Better thermal insulation, no spiral ‘weak points’, tighter tolerances

Design

New Propellant Formulation - Cherry Limeade

Changes from OW:

• Higher Solids Loading (82.5%)
• Removal of Burn Rate Catalyst
• Change from Trimodal to Bimodal AP

Results:

• Density increased 7% (0.057 -> 0.061 lb/in³)
• Viscosity increased slightly - still pourable
• Solids loading could increase to 83-84% in the future

Design

Formulation Specifics

Analysis

Characterization Fire - 6 motors with different KN tested

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Analysis

Characterization Results

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ISP ~= 200 s (without a divergent section)

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Design

Grain Geometry

Grain length increased - number of grains decreased�Aft grain replaced with a finocyl (demonstrated in January 2018)�Resultant burn profile split into two phases:

• More force early in the burn - easier to get off the launch pad while rocket is still heavy
• Gentler sustained second phase - reduced loads on the case when weakened by heat soak, better expansion ratio at lower atmospheric pressures

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Analysis

Burnsim Data - Grain Geometry

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Propellent Mass - 72 lb

Burn Time - 8.5 s

Impulse - 73000 Ns (P-8600)

ISP - 233 s

Max Pressure - 880 psi

Max Thrust - 2950 Lbf

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Pressure Thrust

Analysis

Static Analysis - Case Stress

Max Stress in Case: 96 MPa

Below Yield Stress of Al-6061-T6 up to 475 K - Use phenolic liner to insulate case

Potential to reduce wall thickness from 1/4” to 3/16”

• 9 lbs of predicted mass savings
• Stresses would increase by 1.33x (as σ ∝ 1/t)
• Requires thermal modelling to verify case temperature (data collection and simulation)

Analysis

Static Analysis - Notes on FEA Sim

• The model considers the loads on the aluminum case rigidly bonded to the forward closure and nozzle carrier (loads on connecting bolts analyzed elsewhere)
• 1400 psi pressure (~1.75x the expected maximum pressure) applied to inside of case
• A 2000 lbf load applied vertically downwards at top of case to model weight of mission package (~40 lb) at 25G and aerodynamic drag force of 950 lbf
• Effect of this found to be negligible compared to pressure loads

Analysis

Bolts & Fasteners

Bolts changed 3/8” -> 5/16”�Assuming max shear stress of 2.28 ✕10⁴ psi with a factor of safety of 1.8x

• Allows countersinks to be flush with�the wall of the case
• Mass Decrease (6 oz)

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Analysis

Propellent Mechanical Properties

Instron Test samples of CL to find elastic modulus, poisson ratio, and other mechanical properties

Use these to perform load analysis on propellant grains to ensure they won’t crack during flight under high acceleration

Manufacturing - Hardware

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• Axisymmetric parts (Nozzle, Carrier, Closures) machined on lathe
• Radial Holes drilled on Mill w/ Indexing Head
• Phenolic: waterjet from sheet, glued into round, then machined

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Manufacturing - Propellent

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• Ingredients mixed in a 30 quart mixer
• Propellent placed under vacuum to remove bubbles before casting
• Cast into grain-shaped casting tubes around taped mandrels
• Grains cured overnight
• Cured grains cut to length, ends are sanded

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Manufacturing - Mixing Procedure

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1. Add HTPB, IDP, and Castor Oil

2. Mix for 5 minutes

3. Add AL

4. Hand mix until wetted out, machine mix for 10 minutes

5. Add PDMS and Triton X-100

6. Mix for 30 minutes

7. Vacuum for 45 minutes

8. Repeat until all 200 AP is in:

a. Add a third of the original mass of AP

b. Mix for 1 minute

c. Scrape down

d. Mix for 10 minutes

9. Add the 90 AP

10. Mix for 1 minute

11. Scrape down

12. Mix for 45 minutes

13. Add curative

14. Mix for 20 minutes

15. Vacuum for 45 minutes

Link to Wiki

Manufacturing - Finocyl

Procedural Changes

Finocyl Grain uses modified process:

1. Fabricate Core Mandrel - Use foam wire cutter to cut profile of port out of foam
2. Waterjet End Caps - Matches port geometry
3. Cast Grain - uses standard process
4. De-mold grain - Dissolve core mandrel with acetone

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Process demonstrated in IAP/Spring 2018

Improvements:

• Core Stiffness
• Foam Cutter Reliability
• Removal of Splice Point

Manufacturing - Propellent

Pneumatic Sieve Shaker

• Uses pneumatic vibrator to shake AP 200μm and smaller through filter

Pneumatic vibrator

Rubber shock absorbers

Manufacturing - Motor Assembly

• Nozzle assembly:
• The three-piece nozzle assembly is fit-checked, then each sealing surface is coated in RTV. The pieces are then assembled
• Grains glued into liner with grain spacer O-rings
• 5-minute epoxy used for grain-bonding process
• Liner placed into case
• Other hardware bolted on

Testing

What do we need to do to make sure we can fly the rocket?

• Propellant Characterization - Completed
• Hydrostatic Testing - Up to 1400 psi
• P Motor Static Fire - Scheduled by End of Semester
• Propellent Mechanical Testing - January

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Risk Matrix

Risks and Mitigations for Flight

Open Issues

• Liner Splicing
• Thermal Modelling Capability
• Lab Space Change

Schedule to Completion

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Questions?