The Department of Defense, through DARPA, is seeking proposals for the development and flight testing of an Inertially Scaled Aircraft (ISaAc), specifically a small unmanned air vehicle (UAV) weighing between 55 to 300 lbs. The objective is to create a UAV that accurately mimics the dynamics of a tactically relevant target aircraft, enabling early identification of flight control challenges and reducing costs and risks associated with traditional aircraft development. This initiative is crucial for enhancing flight control design and software development, allowing for significant advancements in both military and commercial aircraft programs. Interested parties must submit their Direct to Phase II proposals by June 25, 2025, with further details available at the provided source link.

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Trusted AI and Autonomy OBJECTIVE: Develop and flight test a small (55 to 300 lbs.) unmanned air vehicle (UAV) that is inertially scaled to a tactically relevant target aircraft. The proposal must identify the target aircraft and if relevant data must be provided by the Government. The proposed approach to developing an inertially scaled UAV must show direct scaling and application to the target aircraft such that the flight control laws, and performance can be correlated to the target aircraft. DESCRIPTION: DARPA seeks proposals for an inertially scaled UAV for the purposes of demonstrating the utility of flight testing a subscale vehicle for high-risk flight controls development. Conventional aircraft development programs are forced to delay detailed flight control development until late in the program, requiring significant resources and adding risk to the overall execution of the program. Any challenges encountered during the flight controls development that require design updates are expensive and time consuming to accommodate. Learning flight control challenges early in the aircraft development cycle results in cheaper and less time-consuming solutions, which can be accomplished through development and testing of a small, inertially scaled UAV. Many modern aircraft designs have unique configurations (delta wings, tailless, high wing sweep, etc.) that demand more significant modeling efforts to predict full scale aircraft dynamics but continue to lack accurate full dynamic modeling throughout the flight envelope. A dynamically scaled sub-scale prototype is a risk reducing and cost-effective tool to provide significant flight data to accurately predict the full-scale aircraft behaviors. With an accurate full scale vehicle design to include the predicted mass distribution that defines the full-scale moments of inertia, an inertially scaled vehicle can be designed to execute open-air flight tests that accurately mimic the full-scale vehicle dynamics. The component and material selections for the UAV must consider the higher wing loading and takeoff/landing speeds expected to be encountered. Conventional hobby grade equipment may not be designed to these operating conditions so a plan to balance low-cost hardware and test processes with more expensive and traditional aircraft hardware and flight test processes must be proposed. Because the model’s angular motions will be much faster than those of the target aircraft, the models may be difficult to operate and control. Unique approaches to piloting and operating the aircraft are encouraged to maximize the utility of the UAV, which may require some degree of automation to simplify the workload of a remote pilot or include an autonomous flight control system. DARPA does not envision the proposed UAV leaving direct line of sight of the control station to simplify UAV flight control methodologies. PHASE I: This topic is soliciting Direct to Phase II (DP2) proposals only. Phase I feasibility must be demonstrated through evidence of completed fixed wing aircraft design and flight testing of similarly sized vehicles (55 to 300 lbs.). The aircraft designs must be of configuration types that are of interest to DoD and commercial use cases and must have recorded adequate flight test data to validate predicted design performance capabilities. Additionally, the proposal should describe the overall approach to inertial scaling such that the size and development time is appropriate to support a large aircraft program. Entities interested in submitting a DP2 proposal must provide documentation to substantiate that the scientific/technical merit and feasibility described above has been achieved and describe the potential commercial applications. DP2 Phase I feasibility documentation should include, at a minimum: • technical reports describing results and conclusions of existing work, particularly regarding the commercial opportunity or DoD insertion opportunity, risks/mitigations, and technology assessments • presentation materials and/or white papers/technical papers • test and measurement data • prototype designs/models • performance projections, goals, or results in various use cases The collection of Phase I feasibility material will verify mastery of the required content for DP2 consideration. PHASE II: DP2 proposals are expected to show a viable path to flight testing an inertially scaled aircraft with direct connection to a target fixed wing aircraft of relevance to DoD and/or commercial applications. Phase II fixed payable milestones for this program should include: • Month 1: Identification of relevant target aircraft to facilitate UAV design and performance assessments with achievable path to obtain necessary target aircraft data to evaluate utility of an inertially scaled aircraft. • Month 4: Preliminary design of inertially scaled aircraft (55 to 300 lbs) with a viable path to complete fabrication and flight test within the available program resources. • Month 9: Detailed design of inertially scaled aircraft as well as a flight simulation model for flight controller development and testing. • Month 12: Completed fabrication of inertially scaled aircraft including installation of major subsystem components. • Month 14: Completed ground test activities to verify functionality of the aircraft. • Month 16: Complete flight test campaign with sufficient flight test data to validate predicted performance and allow for application to target aircraft. Flight tests should assess controllability and overall vehicle performance throughout the flight envelope. • Month 18: Documentation of sub-scale vehicle performance with direct comparisons and assessment of relevance to target aircraft flight controls and maneuverability data to evaluate utility of the dynamically scaled testing approach. 6 Month Option fixed payable milestones for this program should include: • Month 21: Validation of models of vehicle performance using data collected in flight test and confirmation relative to those models. • Month 24; Prediction of flight maneuvers using validated models, and flight test validation of correlation between modelled and actual performance. PHASE III DUAL USE APPLICATIONS: Follow-on opportunities will include continued testing of the developed sub-scale aircraft as well as implementing the process for designing and testing an inertially scaled aircraft on future developmental efforts. It is anticipated that significant flight control design and software development can be accomplished sooner in aircraft development programs through the use of an inertially scaled testbed aircraft. Once proven, the approach developed under this effort can be applied to future large-scale military and commercial aircraft development programs. Trade space exploration of candidate configurations can be evaluated early in the design process with inertially scaled aircraft flight testing. Flight control laws and the associated software can be developed much earlier in the program when design changes can be made faster and cheaper than during large scale flight testing at the end of traditional aircraft programs. REFERENCES: 1. Chambers, Joseph R. Modeling Flight: The Role of Dynamically Scaled Free-Flight Models in Support of NASA’s Aerospace Programs. NASA SP 2009-575. 2. Turpak, John, Air and Space Forces Magazine, “Why USAF’s New T-7 Trainer Won’t Start Production for 2 More Years”, April 13, 2023. KEYWORDS: unmanned air vehicle (UAV), inertially scaled, tactically relevant, target aircraft

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