A Review of Current Research in Subscale Flight Testing and Analysis of Its Main Practical Challenges

Alejandro Sobron,David Lundström,Petter Krus

doi:10.3390/aerospace8030074

Abstract

Testing of untethered subscale models, often referred to as subscale flight testing, has traditionally had a relatively minor, yet relevant use in aeronautical research and development. As recent advances in electronics, rapid prototyping and unmanned-vehicle technologies expand its capabilities and lower its cost, this experimental method is seeing growing interest across academia and the industry. However, subscale models cannot meet all similarity conditions required for simulating full-scale flight. This leads to a variety of approaches to scaling and to other alternative applications. Through a literature review and analysis of different scaling strategies, this study presents an overall picture of how subscale flight testing has been used in recent years and synthesises its main issues and practical limitations. Results show that, while the estimation of full-scale characteristics is still an interesting application within certain flight conditions, subscale models are progressively taking a broader role as low-cost technology-testing platforms with relaxed similarity constraints. Different approaches to tackle the identified practical challenges, implemented both by the authors and by other organisations, are discussed and evaluated through flight experiments.

Highlights

Downscaled physical models, referred to as subscale models, have played an essential role in aerospace
This paper aims to present an overall, up-to-date picture of subscale flight testing (SFT) focusing on its main practical applications in contemporary aircraft research and development
Similarity of the flow field, disregarding similarity of the aircraft self-motion Similarity of the rigid aircraft motion as well as the aerodynamic loads that cause it Builds on dynamic scaling and includes similarity for vehicle deformations Scaled demonstration of a particular technology, system, or capability; partially or fully disregarding the vehicle’s similarity conditions

Summary

Introduction

Downscaled physical models, referred to as subscale models, have played an essential role in aerospace. Computational methods are slowly pushing experimental techniques towards a secondary role as verification or calibration tools, but physical models are still undoubtedly effective at revealing unexpected issues and providing confidence in estimations and assumptions. Wind-tunnel testing is probably one of the most established experimental methods in this field, but it sometimes fails to satisfy the requirements of modern aeronautical research and development: modern wind tunnel facilities are a scarce and costly resource, and are not efficient for quick or iterative explorations of the design space during the initial stages of aircraft development. Flight testing of full-scale, manned vehicles is, at this stage, often prohibitive in terms of both cost and risk. Testing of untethered subscale models, often referred to as subscale flight testing (SFT), could offer an affordable and low-risk alternative for gathering both qualitative and quantitative information

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Conclusion