Aerodynamic Design of a New Affordable Main Rotor for the Apache Helicopter

An affordable, five-bladed composite rotor for a growth Apache aircraft, and a low cost four-bladed variant with essentially the same blade design for the current AH-64D aircraft, were developed. The goals and design constraints of this rotor development program known as AARP (Affordable Apache Rotor Program) are discussed, along with the design approach used. A discussion on the rationale and selection of blade conceptual aerodynamic design parameters, which relied heavily on the Boeing corporate design database and practices, is presented. Trade studies conducted during the preliminary design that significantly modified the conceptual aerodynamic design in terms of blade number, blade twist, airfoil distribution and tip shape to satisfy the program goals of low cost and producibility, and low technical risk to meet low vibratory loads, are presented. The aerodynamic performance of a five-bladed AARP rotor design that satisfied the program goals is presented. A four-bladed variant of this design with an extended blade trailing edge tab, which is compatible with the AH-64D hub, is discussed. Airfoil wind tunnel tests conducted in the Ohio State University wind tunnel for the modified VR-22E airfoil section used in this new rotor, along with the original VR-22 airfoil used in the five-bladed rotor design and the HH-02 airfoil used on the AH-64D rotor are briefly discussed. It is shown that the new four-bladed AARP rotor with a blade design consisting of a 21-inch chord VR-22E airfoil inboard blade section, a moderate linear twist and a swept tapered tip will increase the predicted vertical rate of climb of the AH-64D by 46% or payload for hover out-of-ground-effect by 49%, and increase its predicted maximum level flight forward speed by 2% and combat mission radius by 5%.