Aerodynamics

CDR 14 October 2023

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Overview

Fin Can

Aeroshells

Bill of Materials

Simulations

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Fins

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Fin Requirements

Maximize apogee

• > 150kft desired

Ensure the stability of the rocket

• Static and dynamic stability margin always > 2

Withstand in-flight forces

1.5 safety factor, 5° (Booster) and 15° (Sustainer) angle of attack margins

• Booster loads: 3505N drag, 4135N lift
• Sustainer loads: 1275N drag, 2515N lift
• Must remain below flutter velocity and divergence velocity at all times

Withstand in-flight temperatures

• Max temp 250°C (stage 1), 500°C (stage 2)

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Flutter Speed

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Flutter and divergence speed calculated with FinSim

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Booster must not exceed 2,967.81 ft/s

Booster max velocity 2,285 ft/s

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Sustainer must not exceed 13,000 ft/s

Sustainer max velocity 3,431 ft/s

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Flutter not a risk on second stage due to high altitude

Drag Force (0 AoA)

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ρ from online table

v, C_D from flight simulations

A from fin geometry

Drag Force (5° AoA)

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ρ from online table

v, C_D from flight simulations

A from fin geometry

Lift Force - 0° AoA

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*Negative force indicates force in the opposite direction. The rocket is oscillating with an AoA << 1°

ρ from online table

v, C_L from flight simulations

A from fin geometry

Lift Force - AoA Comparison

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ρ from online table

v from flight simulations

A from fin geometry

Coefficient of lift at subsonic speeds

Coefficient of lift at supersonic speeds

Overview

Carbon fiber tube

Four fins on each stage

Each fin consists of a core and leading/trailing edge pieces

Components are epoxied together

Joined to tube with epoxy fillets*

Reinforced with tip-to-tip carbon fiber layers*

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*Not pictured

Fins

⅛” thick quasi-orthotropic Dragonplate carbon fiber core

Ablative CE phenolic leading and trailing edges with slot for attachment

Core reinforced with 5 plies of 3K 2x2 twill carbon fiber on each side between lips of leading and trailing edges for a full thickness of ¼”

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Fin Dimensions

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Sustainer fins 10” tall, 3.75” wide

Booster fins 16” tall, 6.5” wide

Dimensions optimized through flight simulation

Boundary condition: stability margin >2

Minimized span for high altitude and resistance to flutter

Minimized sweep angle to keep fins within Mach cone as much as possible

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Fin Attachment

Fillets made of epoxy mixed with 20% carbon fiber powder

Will conduct load tests to determine necessary fillet size

Join fins to ⅛” thick carbon fiber tube

3 layers of carbon fiber tip-to-tip goes over the assembly to reinforce the joint

Since the fillets were the point of failure on our past Hermes II rocket, we intend to make them much more robust.

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Manufacturing Steps

• Lay up 10 plies of carbon fiber over mandrill to create tube
• Cut, bevel, and slot leading and trailing edges on mill
• Epoxy to ⅛” Dragonplate core
• Add 5 plies of carbon fiber to each side
• Epoxy fins to tube using assembly jig
• Add fillets
• Add 3 layers of tip-to-tip to finish

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Quality Control

Create test fin can� Use instron to verify fins can withstand defined loads

Heat fin can and repeat to verify thermal robustness

Apply load to leading edges to check strength of attachment

Create T-joint samples with varying fillet thicknesses

Use instron to determine which thickness can withstand necessary

loads

Empirically measure properties of finished composite for more accurate predictions

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Questions?

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Aeroshells

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Aeroshell Requirements

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Keeps external cameras below their maximum operating temperature of 50°C

Shape creates minimal drag

Mounts securely to airframe

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Overview

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• 2 ply carbon fiber layup over 3D printed nylon 66 frame
• ½”x ½” cross section
• Heat resistant paint applied over surface
• Has slots in bottom to slide over screw heads protruding from MPT*

*Not pictured

Simulation and Testing

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• Thermal simulation in progress
• Aerodynamics of shape will be evaluated through CFD
• Set camera and aeroshell in sun for an hour to ensure the heat emitted from the camera dissipates to not cause overheating
• Set aeroshell in front of heat gun (400°-500°C) for 30 seconds. Measure internal temperature with thermocouple.

Bill of Materials

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Bill of Materials

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Bill of Materials

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Questions?

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Flight Simulations

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Run on RASAero II

Altitude

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156,797 ft apogee, 101 second flight �Separation begins at 6,117 ft, 4 seconds into the flight

Mach Number

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3.5

2.1 (max q)

4s booster burn | 10s separation delay | 9s sustainer burn | 78s sustainer coast

Max q at separation: 2,285 ft/s (Mach 2.1) at an altitude of 5,890 ft

Separation delay is chosen to be the maximum length of time before the rocket drops below Mach 1.

This minimizes drag on the sustainer by allowing its speed to lower before igniting in a region of less

dense air.

Stability Margin

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Static Stability Margin: 2.5 calibers

Stability must stay above 2 calibers at all times.

2.09

(Max speed)

2.1 (Separation)

CG Location (in) = 50, 113

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Questions?

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