Assessment of Noncommercial Icing Prediction Capabilities for Army Applications

Ice prediction capabilities for Unmanned Aerial Systems (UAS) is of growing interest as UAS designs and applications become more diverse. This report summarizes the current state-of-the-art in modeling aircraft icing within a computational framework as well as a recent U.S. Army DEVCOM AvMC effort to evaluate ice prediction models for current use and future integration into the Computational Research and Engineering Acquisition Tools and Environments (CREATE) Air Vehicle (AV) framework.

December 1, 2023

U.S. Army Combat Capabilities Development Command, Redstone Arsenal, Alabama

Figure 1. The common research model in IRT was involved in this research project.

Historically, smaller Unmanned Aerial Systems (UAS), such as Class 2 RQ-1B Raven and Class 3 RQ-7Bv2 Shadow, have been restricted to not be approved to fly in icing conditions under the assumption that any ice accretion would cause an unacceptable risk of loss of the aircraft. However, interest exists in better understanding potential icing accretion on UAS to determine if less extreme icing conditions could result in only partial degradation and not total loss of the vehicle for the purpose of expanding approved flight envelopes. Icing accretion can be tested during a flight test, which is considered unacceptable due to lack of controlled conditions and risk to the UAS or in a controlled experiment, by using wind tunnel testing to evaluate a single icing condition. Cryogenic wind tunnel tests, such as those conducted at the National Aeronautical and Space Administration (NASA) Glenn Icing Research Tunnel (IRT), Cleveland, OH, as shown in figures 1 and 2, are prohibitively expensive and time consuming to evaluate a wide array of icing conditions on multiple UAS. The ability to simulate aircraft icing using computational methods permits evaluation across a number of vehicles and icing scenarios for a fraction of the cost and time.

Figure 2. Ice accretion on a powered force model rotor in IRT.

The aerospace scientific community has recently developed interest in ice prediction capabilities within a computational framework. In 2021, the first American Institute for Aeronautics and Astronautics (AIAA) Ice Prediction Workshop was held in conjunction with the AIAA Aviation Forum [2]. Twenty participants from academia, industry, and government evaluated ice accretion on Two-Dimensional (2-D) and Three-Dimensional (3-D) geometries where experimental ice shapes were publicly available by using a wide range of solvers to assess the state-of-the-art in icing prediction tools. Kestrel and Helios, the Computational Research and Engineering Acquisition Tools and Environments (CREATE) Air Vehicle (AV) simulation tools for fixed-wing and rotorcraft evaluation, do not have ice prediction capabilities.

DEVCOM AvMC conducted an assessment of NASA-developed icing prediction codes for potential application to Army UAS aerodynamic modeling predictions. Current capabilities are considered to be lacking for DEVCOM AvMC use due to 2-D formulation and a lack of CFD-based streamlined iterative solution methods. NASA is planning to address these issues with the public release of GlennICE. At this time, Commercial Off-The-Shelf (COTS) codes are considered to be the best path forward.

This work was performed by Amanda G. Kolpitcke, Kevin C. Losser, and Zachary M. Hall for the U.S. Army Combat Capabilities Development Command. For more information, download the Technical Support Package (free white paper) below. FCDDAMS-2301