A High Efficiency Fuselage Propeller (”Fusefan”) for Subsonic Aircraft 1999-01-5569
This report proposes a new high efficiency “fuselage fan” concept of aircraft propulsion for subsonic airplanes also noted as “fusefan” (FF). The fusefan concept consists of one or two rings of swept blades rotating around the fuselage. This variable pitch fan has an important advantage in comparison with currently used turbofan engines: it dramatically increases the cross-sectional bypass area of the propulsion system by 3-5 times. As shown in the paper this propeller has an efficiency in cruise flight of 9-16% more than the current turbofan propulsion system. It also provides a large increase in static thrust (40-75%), which in turn decreases takeoff distance about 30-45%, and has a clean wing aerodynamically due to the absence of nacelles.
An analysis of the benefits of the fuselage fan compared with the Advanced Turboprop Propeller (ATP) and propfan “Unducted Fan” (UDF) shows that for equal disk loading the “fuselage fan” has the following advantages:
The most efficient section of the blade is near the tip, from 0.7R to R (where R is radius of propeller). The fusefan has only this section and a constant load in this ring area. This in turn increases the propeller efficiency 4-6%.
A short blade design is required using very small blade thickness (1.5-2%), high blade sweeping, supercritical profiles, all of which combine to increase the propeller efficiency up 5% and critical propeller Mach number up to M =0.84.
The wing can benefit with a laminar flow system (since no wing engines are on them) which can also reduce wing drag 5-19% (total aircraft drag 2-4%).
The fusefan draws in air flow over the root part of the wing, thereby increasing the area of the wing and fuselage where laminar flow occurs and decreasing total drag.
The fusefan decreases noise.
The horizontal and vertical tail is located in the fusefan flow, and as such is more efficient and can be decreased in size and weight.
Wing engine-out propulsion and safety issues are not a factor.