Design and Performance Analysis of a Hybrid-Motor Powered Model Rocket

Ted Kapustka15 Mar 2011

Photographs from http://www.libertylaunchsystems.com/Gallery/2009-10-BALLS18/Full/_LLS7884.jpg

2

Introduction

• In recent years, high-power model rockets routinely reach altitudes of 10,000 feet (3048 m) with some rockets reaching altitudes in excess of 45,000 feet (13,716 m).

• The use of hybrid motors is becoming increasingly popular.

• In a hybrid motor the fuel and oxidizer are different phases, e.g. gaseous N20 as an oxidizer and solid ABS plastic as a fuel. The fuel and oxidizer are kept separate until they are mixed in the combustion chamber.

• Record altitudes for the solid-propelled rockets far exceed the altitudes for hybrid-powered rockets.

• Goal – design a K-class (less than 2560 Ns total impulse) hybrid motor and rocket that can achieve an altitude of 29,266 feet (8920.3 m).

Tripoli Model Rocket Altitude Records

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5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

45,000

50,000

H I J K L M N

Class

Alti

tude

- ft

All Motor TypesHybrid Motors

3

Approach

• By maintaining a maximum Mach no. of 0.8 drag can be minimized---this requires an optimized thrust curve

• Develop tool to predict rocket performance– Drag prediction– Ability to input thrust curves for various

certified motors• High thrust/short burn more likely to encounter

high drag conditions

• Determine rocket configuration and thrust curve to maximize altitude

• Design hybrid motor with optimized thrust curve

– Determine oxidizer (N20)quantity– Select fuel type, quantity and shape of grain– Design nozzle optimal performance over

required altitude and thrust ranges

Thrust Comparison for K-motors

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0 2 4 6 8 10 12

Time - sec

Thru

st -

N

K1050K660K475K458K250

130 mm Sounding Rocket

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0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Mach No,

Cd

Burn

Coast

Data

Prediction

4

Status – Drag PredictionCompleted drag prediction program using

Visual Basic in ExcelJon Champion’s methods used (converted to S.I. units)

Program performs three functionsCd vs. Mach number – for comparison to wind tunnel dataCd components vs. Mach number – for rocket optimizationDrag vs. Altitude and Velocity function - for rocket performance simulation

130 mm Sounding Rocket

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0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Mach No,

Cd

Burn

Coast

Data

Prediction

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0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8

T/S

Base

Exc

Pro

Fin

Body

5

Status – Drag PredictionCompleted four calibrations

130 mm sounding rocketGood overall agreement with data

Drag increase for coasting condition predictedNACA L65931 rocket

Good overall agreement with dataAerobee 150A rocket wind-tunnel dataGood agreement subsonicOverpredicts transonic dragRASAero model rocket simulationSubsonic trend does not matchOverpredicts transonic drag

130 mm Sounding Rocket

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0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Mach No,

Cd

Burn

Coast

Data

Prediction

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0.1

0.2

0.3

0.4

0.5

0.6

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

Cd

Mach No.

L65931 Aerobee 150A Stage 2

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6

Mach No,

Cd

Burn

Coast

Predicted

Data

LOC/Precision Caliber IspProject Simulation vs. RASAero

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0.10

0.20

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0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

Mach No,

Cd

Burn

Coast

My Prediction

RASAero

6

Status – Performance Simulation

• Completed– Program to integrate motor performance, Drag Prediction, and

altitude conditions into performance prediction – Includes motor mass loss function– Good agreement with I-class model record (LOC/Precision ISP)

• Data provided by RASAero– Good agreement with K-class record altitude

• Actual motor used for record • Rocket optimized for 54mm diameter solid motor

Altitude vs. Time

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1400

0 2 4 6 8 10 12 14 16 18 20

Time - sec

Altit

ude

- M

SimulationBarometric Altimiter Data

Altitude

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Time - sec

Altit

ude

- M

Simulation of LOC/Precision Caliber ISP Simulation of K-class record rocket

7

Status – Performance Simulation for Ideal Thrust Curve

• Simulation with K300 solid motor shows large portion of flight with Mach no. greater than 0.8 and peak Mach no. ~2.1

• Alteration of thrust curve resulted in a 5400 m (45%) increase in peak altitude– Minimum thrust = 1/6 Maximum thrust – Further improvement possible with larger thrust reduction

Altitude

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0 5 10 15 20 25 30 35 40 45

Time - sec

Altit

ude

- M

Mach

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0.5

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1.5

2

2.5

0 5 10 15 20 25 30 35 40 45

Time - sec

Mac

h Nu

mbe

r

Thrust

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0 10 20 30 40 50Time - sec

Thru

st -

N

Thrust

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0 10 20 30 40 50Time - sec

Thru

st -

N

Mach

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0 20 40 60 80Time - sec

Mac

h N

umbe

r

Altitude

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16000

0 20 40 60 80 100Time - sec

Alti

tude

- M

Simulation with K300 Solid Motor

Simulation with 6:1 Thrust Reduction