Hybrid Parabolic Rocket Nozzle

Contribution & Results

The final nozzle cut mass 73% relative to my initial design and increased predicted thrust 5%. Calculated thrust was 7.86 lbf at the 45,000 ft design condition and 2.65 lbf at sea level; mechanical analysis gave a 7.8 FOS under modeled loads.

The ABS-like resin nozzle survived an approximately two-second hotfire. A load-cell malfunction prevented usable thrust-data collection, so the thrust improvement remains a prediction rather than a measured result.

Role & Technical Scope

I led a five-person team through three design reviews, coordinating nozzle geometry, FEA, engineering drawings, and the launch computer.

• Nozzle Design & CAD: Modeled an 80%-length Rao parabolic de Laval nozzle in SolidWorks using isentropic-flow equations, G.V.R. Rao’s contour method, Rocket Propulsion Elements.
• SolidWorks FEA: Assessed mechanical pressure stresses using sourced ABS-like resin yield strength, density, Poisson’s ratio, and elastic modulus; revised the outer contour for handling and assembly robustness.
• Manufacturing: Prepared the single-use nozzle for Formlabs SLA printing in ABS-like resin.

Contour Development

I selected an 80%-length Rao parabolic contour to shorten the nozzle while targeting the performance of a longer conical contour. That performance comparison remains a design intent, not a measured result.

I calculated the area ratio and candidate nozzle lengths, then constructed the diverging contour from a three-point Bézier curve using G.V.R. Rao’s geometric method. Circular arcs define the converging and throat regions.

Structural Analysis

I initially reduced wall thickness until the modeled geometry retained a 2.0 yield FOS. A design review identified fragility risks during print removal, handling, and assembly, so I strengthened the outer contour. The final SolidWorks analysis calculated a 7.8 yield FOS under the modeled mechanical pressure loads.

The model applied pressure to the chamber, throat, diverging surface, and external faces, with bolt fixtures representing the mounting adapter. Material properties were sourced for the selected ABS-like resin. The 7.8 FOS excludes thermal softening, erosion, and coupled thermal stresses during firing; hotfire survival does not verify that mechanical-only margin.

Testing & Data Acquisition

Hotfire: The printed nozzle remained intact through an approximately two-second firing. The test did not measure thrust or verify the calculated structural margin.

Launch Computer: I led the team responsible for designing, soldering, and programming the launch computer used to actuate the test. The measurement architecture used LabJack acquisition and a load cell, but a load-cell malfunction on the day of the test prevented usable thrust data.