High-Lift Propeller System Configuration Selection for NASA's SCEPTOR Distributed Electric Propulsion Flight Demonstrator

Abstract

Although the primary function of propellers is typically to produce thrust, aircraft equipped with distributed electric propulsion (DEP) may utilize propellers whose main purpose is to act as a form of high-lift device. These "high-lift propellers" can be placed upstream of wing such that, when the higher-velocity flow in the propellers' slipstreams interacts with the wing, the lift is increased. This technique is a main design feature of a new NASA advanced design project called Scalable Convergent Electric Propulsion Technology Operations Research (SCEPTOR). The goal of the SCEPTOR project is design, build, and fly a DEP aircraft to demonstrate that such an aircraft can be much more efficient than conventional designs. This paper provides details into the high-lift propeller system configuration selection for the SCEPTOR flight demonstrator. The methods used in the high-lift propeller system conceptual design and the tradeoffs considered in selecting the number of propellers are discussed. Nomenclaturec chord length C i coefficient row vector for β surrogate model c l section lift coefficient C D0 parasite drag coefficient c i,j scalar coefficient value for β surrogate model D drag i p propeller slipstream inclination angle K L lift multiplier (i.e., ratio of blown to unblown lift) L lift L lift per unit span R radius T thrust u distance of disk upstream of wing leading edge V velocity w induced velocity from point vortex X column vector for β surrogate model, 1 u/cT α angle of attack β velocity multiplier or twist angle of local blade element Γ circulation ρ density θ swirl swirl angle

Design and Performance of the NASA SCEPTOR Distributed Electric Propulsion Flight Demonstrator

“…Also note how some variables, such as propeller design lift coefficient, had little correlation -effectively, when conducting a MIL design of a propeller, it is possible to create an efficient on-design configuration for any manner of design lift coefficients. Instead, off-design behavior tends to push propeller design lift coefficient [7,15].…”

“…The scope of these discussions is far too broad for this single paper. Rather, the reader is referred to discussions by Borer et al [7], Stoll et al [35], and most recently the companion paper by Patterson et al [15]. Patterson's recent dissertation [36] provides an in-depth discussion of the multitude of effects and models necessary to select an appropriate highlift propeller system, using the SCEPTOR flight demonstrator as its example.…”

“…A future paper will detail the low-order integrated aerodynamic-propulsion modeling approach used for the "cruisesized" wing analysis, along with the subsequent validation of this approach to higher-order computational methods. A companion paper by Patterson et al [15] describes the design of the high-lift propeller system, which has been built up from previous work [6,7,16,17,18,19]. …”

Comparison of Aero-Propulsive Performance Predictions for Distributed Propulsion Configurations

“…Subsequently, a simple model of lift augmentation from high-lift propellers based on fundamental "first principles" was developed by Patterson and German [12], and was later updated by Patterson et al [26,27]. This model assumed the isolated propeller performance could be superimposed on the wing, and abstracted the propeller slipstream to a single, average axial velocity to determine lift augmentation.…”

Hybrid Regional Aircraft: A Comparative Review of New Potentials Enabled by Electric Power

“…These effects may not fully counterbalance the benefits mentioned previously but are to be considered in the trade study. One alternative solution, also implemented in the SCEPTOR project 8,9 , consists in folding the small leading edge-mounted propellers not required for cruise propulsion. The split ratio between nacelle-mounted and leading edge-mounted propulsive power can also be optimized (Fig.…”