Title: Towards a New Approach for Shipboard Recovery Wind Envelope Determination for Small UAS Applications
Author(s): Susan Polsky, Joshua Butler, and Theresa Shafer
Abstract: Ship-based flight operating envelopes for small Naval Unmanned Aircraft Systems (UAS) are currently developed using similar flight testing procedures to their larger manned counterparts. This process entails executing flight test events for each ship class from which the UAS may operate. Often times, ship availability for flight testing of UAS systems is minimal due to competing ship priorities. As a result, UAS flight envelope testing are either delayed due to ship availability or restricted to benign wind conditions. ONR investment has allowed NAVAIR to develop a modeling and simulation (M&S) analysis tool (the SAFEDI Tool) that enables assessment of ship airwake effects on aircraft launch and recovery. The approach employs computational fluid dynamics (CFD) to create time accurate ship airwake models specific to ship topside configuration and wind-over-deck angle and speed. The ship airwake data is injected as the wind environment model into high fidelity six degree-of-freedom (6DOF) aircraft performance simulation models which are then used to model approach and landing scenarios. Results are compared to recovery simulations to a known ship to assess risk of recovery performance degradation. To date, this approach has been used as a risk reduction tool for ship design and flight test planning, but has not been applied to flight test reduction for manned systems due to lack of validation data. For small UAS systems, however, risk associated with application of an M&S approach for flight test reduction/elimination is more palatable. Unfortunately, high fidelity 6DOF models that include flight control systems models and autonomous controller software often are not available to the government for small UAS systems. This work examines the feasibility of using fundamental aerodynamic characteristics (Cl, Cd, Cm, etc.) of a UAS in conjunction with CFD generated ship airwake data to assess general controllability of a small UAS system for shipboard recovery operations. The approach is similar to the SAFEDI tool approach described above in that assessments will be made relative to a existing flight tested wind envelope from a ship of similar configuration to determine the level of “similarity” between the know ship and desired ship. Ship “similarity” has long been a quality used by NAVAIR to, for example, approve flight envelopes for an entire ship class despite differences in topside configuration of specific ships. The approach explored here is an attempt to refine the existing similarity process to include characteristics specific to ship induced wind environments and fundamental aircraft characteristics. The end goal of this effort is to provide an inexpensive, quick turnaround analysis process to enable on-going clearance of launch and recovery (L&R) envelopes through an M&S process in place of flight testing for small UAS systems.