Experiment Design for Complex VTOL Aircraft with Distributed Propulsion and Tilt Wing

Abstract

Selected experimental results from a wind tunnel study of a subscale VTOL concept with distributed propulsion and tilt lifting surfaces are presented. The vehicle complexity and automated test facility were ideal for use with a randomized designed experiment. Design of Experiments and Response Surface Methods were invoked to produce run efficient, statistically rigorous regression models with minimized prediction error. Static tests were conducted at the NASA Langley 12-Foot Low-Speed Tunnel to model all six aerodynamic coefficients over a large flight envelope. This work supports investigations at NASA Langley in developing advanced configurations, simulations, and advanced control systems. Bi = regression coefficients CN = normal force coefficient Cm = pitching-moment coefficient = mean aerodynamic chord, ft R 2 = multiple correlation coefficent xi = regressors α = angle-of-attack, deg β = sideslip angle, deg σ = standard error Abbreviations ANOVA = Analysis of Variance BWB = Blended Wing Body CCD = Central Composite Design DEP = Distributed Electric Propulsion DOE = Design of Experiments FCD = Face-Centered Design ME = Main Effects OFAT = One Factor At a Time RSM = Response Surface Modeling VIF = Variance Inflation Factor VTOL = Vertical Takeoff & Landing 2FI = Two-factor Interaction Aircraft Factors aoa = aircraft angle of attack, deg beta = aircraft sideslip, deg LWS1 = left wing outboard surface, deg LWS2 = left wing middle surface, deg LWS3 = left wing inboard surface, deg RWS4 = right wing inboard surface, deg RWS5 = right wing middle surface, deg RWS6 = right wing outboard surface, deg LTS1 = left tail elevator, deg RTS2 = right tail elevator, deg Ttilt = horizontal tail position, deg Wtilt = wing position, deg Rud = rudder position, deg LWEi = left wing engine i=1-4, rpm RWEj = right wing engine j=5-8, rpm LTE1 = left tail engine, rpm RTE2 = right tail engine, rpm American Institute of Aeronautics and Astronautics 1 Downloaded by UNIVERSITY OF IOWA on July 30, 2015 | http://arc.aiaa.org |

A Review of Distributed Electric Propulsion Concepts for Air Vehicle Technology

“…The GL-10 aircraft is another DEP configuration developed by NASA, which is outfitted with 10 propellers, 8 of which are located across the leading edge of a tilting wing and two on the horizontal stabilizer. Work has been performed to demonstrate how a flight controller can be developed for such a complicated system with a total of 21 control actuators and applicability to hover, transition, and forward flight modes [32].…”

An Investigation into the Potential Benefits of Distributed Electric Propulsion on Small UAV’s at Low Reynolds Numbers

“…Figure 10. Load cell assembly (Stoll, 2015) In a study by Murphy and Landman (2015), wind tunnel tests were conducted for the GL- Transonic propulsive wing application of a distributed exhaust system underwent wind tunnel experiments at the University of Illinois in the 5x5 Supersonic Tunnel facility (Perry et al, 2016). The aim of the research was to design a new propulsive wing concept to meet the efficiency goals of the NASA generation N+3 aircraft.…”

Nonlinear Unsteady Aerodynamic Modeling Using Wind-Tunnel and Computational Data

“…Unique modeling requirements also exist for both large and small UAV designs. UAV challenges stem from small UAVs that operate at very low Reynolds numbers [20], or larger complex designs, such as the NASA GL-10, with VTOL capability obtained through distributed electric propulsion (DEP) and tilt-wing features [21][22][23]. A common aerodynamic feature in all applications is the presence of nonlinear unsteady aerodynamic behaviors in some portions When these behaviors are present conventional modeling approaches are limited and more general aerodynamic models are required.…”

“…DOE has been developed over many decades and is used in many engineering and science applications. It can be used in conjunction with aircraft SID techniques and is especially effective for complex aircraft studies [21].…”

“…In [65] the sensitivities of systematic errors on stability derivatives using a high fidelity simulation of a forced-oscillation test was done using both DOE and Monte Carlo methods. In [21] modeling of a complex aircraft with 23 factors required DOE to allow an efficient and statistically rigorous experiment to be designed. In [66] the impact of a flexible test rig, sting, and balance was investigated.…”