Case Study – Aptera 2e Composite Structural Analysis
Will the Aptera 2e redefine the urban automobile? With three wheels, a battery/electric powertrain, and an aircraft-inspired design, the Aptera 2e makes a dramatic statement about the future of transportation. The Aptera 2e is the first in a series of innovative vehicles to be produced by Aptera Motors, a Californiabased startup. One of the key elements of Aptera Motors’ vision is the use of lightweight yet strong composite materials to reduce mass while enhancing safety and enabling aerodynamically efficient shapes. Aptera (Greek for “wingless flight”) enlisted Pratt & Miller to optimize the 2e’s innovative composite body structure. The objectives of the project were to minimize weight while meeting all performance requirements. Since the composite material properties are unique for each application, Pratt & Miller utilized its experience to define, run, and interpret the results of a composite material property testing program.

DESIGN:
The first phase of the project included finite element modeling of the complete body structure to determine stresses under various loads and a modal analysis of the body structure. Using CAD data provided by Aptera, Pratt & Miller created a mesh model, and evaluated its performance under different conditions.

DEVELOP:
An initial lay-up schedule matching the construction of the composite structure was defined, with consideration for the thickness of the composite cloth, locations of the core material, and the glue seams used to join the individual body components. Several design iterations were then performed to manage the stresses on the body.

The results of the Pratt & Miller defined material property test program were then used in the finite element analysis model to match the planned cloth and resin system properties. A modal analysis was performed to determine the frequency and shape of each of the body structure modes, and several design iterations were performed to adjust the modal frequencies and shapes.

BUILD:
This project was executed digitally, without any physical builds. Several design iterations were “constructed” virtually and included in the finite element model to improve the body structure performance.

RACE:
Advanced finite element analysis was used to perform strength and safety testing in a digital environment without the time and expense of physical testing. By utilizing these powerful computer-aided engineering (CAE) tools, many design improvements were incorporated quickly and efficiently.

WIN:
The result of the Aptera 2e composite structural analysis was a shortened product development cycle with increased confidence in passing the physical test that will be performed for verification. Pratt & Miller’s expertise in composite material modeling and testing eliminated the need to construct and test expensive prototypes during the development phase of the ground-breaking Aptera 2e vehicle.

Aptera Motors highlighted the benefits of composite construction in its marketing by explaining to customers, “When you can let an elephant sit on your car with no problems, you’re doing something right.”

Pratt & Miller used computers instead of elephants to test the Aptera 2e’s body structure, but the results were equally impressive.

UPDATE – X Prize Finalist:
Pratt & Miller’s continuing work with Aptera Motors includes refining the body structure, modeling and testing. In 2010, Pratt & Miller supported Aptera’s entry in the Progressive Insurance Automotive X Prize competition to achieve over 100 MPGe (equivalent miles per gallon) in a production-capable vehicle. This support included competition strategy, logistics and transport, and a full-time race engineer, who was assigned to the team to assist with vehicle development, data acquisition and telemetry. Preparation work involved analyzing problems and creating solutions, operating just like a race team. It included manufacturing removable composite body panels, suspension and handling optimization, weight reduction, wind tunnel testing, and an engine oiling system redesign.

More than 111 teams entered the competition, and preliminary events reduced the field to 12 finalists, including the Aptera, which was arguably the most production-representative vehicle in the group.