Specifics of Aircraft Screw Propulsion Unit Thrust Computing by the Airscrew Aerodynamic Characteristics

Aeronautical and Space-Rocket Engineering


Аuthors

Zinenkov Y. V.1*, Fedotov M. M.1**, Raznoschikov V. V.2***, Lukovnikov A. V.2****

1. Air force academy named after professor N.E. Zhukovskii and Y.A. Gagarin, Voronezh, Russia
2. Central Institute of Aviation Motors named after P.I. Baranov, Moscow, Russia

*e-mail: yura2105@mail.ru
**e-mail: m38@mail.ru
***e-mail: raznoschikov@mail.ru
****e-mail: avlukovnikov@ciam.ru

Abstract

The entire range of the propeller power unit altitude-velocity characteristics of the aircraft, on which the propeller is installed, may be obtained employing airscrew aerodynamic characteristics in the form of dependencies of power factors and thrust on the blade pitch angle and advance ratio. However, a research engineer, preoccupied with efficiency assessment of various power plants by the aircraft criteria, may not always have at his disposal experimentally obtained characteristics of the propeller applied as a part of the power unit under study. He does not as well always have the opportunity to conduct intensive research on obtaining the airscrew characteristics with numerical methods, which require extra means and qualification. Thus, he should preferably have in this subject area a technique for mathematical modeling of a wide set of aircraft propellers employing propeller experimental characteristics at his disposal.
For the said problem solving, the authors developed a technique for the thrust computing of the propulsion units with airscrew of arbitrary parameters employing available airscrew characteristics.
Different air propellers operate in the same environment, but they are being differentiated by a number of characteristic parameters that form different flow-around patterns around of their blades. On assuming that various propellers are of geometric similarity, then it is necessary to make sure that they are operating under the similar aerodynamic conditions when computing their aerodynamic characteristics.
The requirements for such conditions are set by the theory of similarity, according to which states the flows can be considered similar if the flow around two geometrically similar bodies with identical physical properties satisfies the equality of two or more similarity criteria determining the flow conditions around these bodies.
The similarity criteria determining the flow-around conditions for the propellers are Strouhal number, the Mach number, and the Reynolds number. The article presents the operation rationale of the two air propellers in aerodynamically similar conditions by the said criteria on the example of the AV-68 and AV-72 air propellers.
The results of computations demonstrate that the flow-around conditions generated by the operation of the AV-68 and AV-72 air propellers are aerodynamically similar with respect to the Strouhal and Mach numbers, while for the Reynolds number, they fall within the region of aeroelastic similitude. Thus, the aerodynamic characteristics obtained from testing the AV-68 air propeller in a wind tunnel can be utilized for the of the AV-72 airscrew thrust obtaining.
On this basis, the altitude-velocity characteristics of the of the AN-24 aircraft power plant with the AI-24VT turboprop engine and AV-72 air propeller have been computed. The obtained characteristics comparison for various modes of the engine operation with characteristics from the AN-24 Aircraft Technical Description revealed that the error in the propulsion unit thrust determining is within the acceptable for engineering computations value of 5% for the Mach numbers up to 0.4.
The practical value of this study, which consists in the fact that its results may be employed by scientific and design institutions preoccupied with the prospective propulsion units development, as well as ordering organizations and industry when substantiating requirements to new aviation technology samples, is worth mentioning.

Keywords:

thrust coefficient, power factor, velocity factor, turboprop engine, AN 24, AI-24VT, AV-72, flight trajectory computing, air screws similarity criteria

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