Autonomy & Software Senior Simulation Engineer Remote

Architect and build the simulation capability — from nonlinear 6-DOF models and SIL through real-time execution and flight-test support — that lets us design and test clean-sheet autonomous aircraft.

Grex Defense builds autonomous systems for air dominance. The character of conflict is changing, with autonomy, mass, and software now deciding outcomes. The advantage goes to whoever can field new capability first, and Grex Defense exists to provide rapid capability solutions for hard defense problems.

Grex Defense is seeking a hands-on Senior Simulation Engineer to architect, develop, and deploy the simulation capabilities required to design and test clean-sheet autonomous aircraft. You will connect aerodynamic data, vehicle dynamics, controls, actuation, environmental models, and visualization within an integrated simulation environment — designing software-in-the-loop (SIL) systems, establishing simulation workflows and standards, and building models that progress from conceptual analysis to real-time execution and flight-test support.

As an early member of a growing aerospace startup, you will work across traditional engineering boundaries, make practical decisions with incomplete information, and help determine which technologies to build internally versus acquire or integrate. You will also help define key hires, evaluate technical partners, mentor engineers, and build a simulation organization capable of supporting multiple vehicle programs.

This is a highly collaborative role requiring equal comfort with first-principles physics, production-quality software, controls, data analysis, and integrated system debugging.

What we look for:

• Significant professional experience developing flight-vehicle, robotics, automotive, marine, or other complex dynamic-system simulations.
• Expert proficiency with MATLAB and Simulink.
• Strong software development in C and C++, including integrating compiled code with MATLAB and Simulink.
• Experience architecting and developing nonlinear six-degree-of-freedom vehicle simulations.
• Strong understanding of rigid-body and multi-body dynamics, equations of motion, numerical integration, coordinate transformations, and reference-frame management.
• Experience designing and implementing SIL environments for control, autonomy, or embedded software development.
• Expert knowledge of model linearization, state-space analysis, PID control architectures, gain scheduling, controller tuning, and stability analysis.
• Strong understanding of actuator dynamics, sensor behavior, nonlinearities, delay, latency, bandwidth, sampling rates, and real-time execution constraints.
• Experience building automated test harnesses, regression tests, Monte Carlo simulations, and model-verification frameworks.
• Experience developing aerodynamic databases from CFD, wind-tunnel, lower-order analysis, or flight-test data.
• Experience creating surrogate surfaces, response surfaces, reduced-order models, or ML-based representations of complex datasets.
• Ability to move between high-fidelity CFD data and computationally efficient real-time simulation models.
• Working knowledge of lower-order aerodynamic methods: lifting-line theory, vortex-lattice, panel methods, or comparable physics-based approaches.
• Understanding of atmospheric, wind, turbulence, gust, and other environmental disturbance models.
• Experience modeling actuator and control-system behavior: saturation, rate limits, deadband, backlash, compliance, delay, and bandwidth.
• Ability to investigate complex simulation behavior, isolate root causes, and communicate model assumptions, limitations, and findings.
• Ability to develop tools and processes from a clean sheet in a fast-paced startup environment.
• Ability to work collaboratively across aerodynamics, GNC, autonomy, propulsion, systems, software, and flight-test disciplines.
• U.S. person status under U.S. export-control law (ITAR/EAR).