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

1. Design and Performance Analysis of a Hybrid-Motor Powered Model Rocket Ted Kapustka 15 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).

3. Data Prediction 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

4. Data Prediction Status – Drag Prediction Completed drag prediction program using Visual Basic in Excel Jon Champion’s methods used (converted to S.I. units) Program performs three functions Cd vs. Mach number – for comparison to wind tunnel data Cd components vs. Mach number – for rocket optimization Drag vs. Altitude and Velocity function - for rocket performance simulation

5. Data Prediction Status – Drag Prediction Completed four calibrations 130 mm sounding rocket Good overall agreement with data Drag increase for coasting condition predicted NACA L65931 rocket Good overall agreement with data Aerobee 150A rocket wind-tunnel data Good agreement subsonic Overpredicts transonic drag RASAero model rocket simulation Subsonic trend does not match Overpredicts transonic drag

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 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 Simulation with K300 Solid Motor Simulation with 6:1 Thrust Reduction 7