Accounting for the Propeller and Airframe Interference in Computed Propeller Thrust Validation by the Flight-Test Data

Aeronautical and Space-Rocket Engineering


Аuthors

Voronich I. V.1*, Kashour I. 1**, Silkin A. A.2***

1. Moscow Institute of Physics and Technology (National Research University), Dolgoprudny, Moscow region, Russia
2. Scientific center of applied electrodynamics», 26, Rizhsky ave., Saint-Petersburg, 190103, Russia

*e-mail: voronich.iv@mipt.ru
**e-mail: kashur@phystech.edu
***e-mail: silkin-a-a@yandex.ru

Abstract

The article presents a procedure for the computed propeller thrust validating of a small airplane-type unmanned aerial vehicle by the flight-test data. The task being considered is an important one since the propeller thrust is often determined by the CFD-modeling of the rotating propeller in the uniform incoming flow, whereas, while the real flight,  propeller operates in the presence of the airframe elements. Thus, while comparing computed propeller thrust with the aircraft required thrust it is necessary to account not only for the accuracy of the propeller computational model itself, but the balancing losses and aerodynamic interference between the propeller and the airframe as well. The proposed procedure combines the telemetry data, the airframe wind-tunnel aerodynamic characteristics and the CFD calculations performed with the CADFLO software package. The required thrust is being determined for steady level-flight segments selected from flight-test records. The calculation employs the airframe aerodynamic characteristics previously obtained in the TsAGI T-102 wind tunnel on a 1 : 2 scale model. Besides, actual deflections of the control surfaces recorded during flight are being accounted for, which allows estimating the increase in the required thrust caused by the trim losses. The propeller thrust is being computed in two CFD formulations. The first formulation considers the isolated tractor propeller in the uniform incoming flow. In the second formulation the rotating propeller is being modelled as a part of the complete “airframe-propeller” configuration at the same flight conditions. This allows estimating the change in axial propeller thrust caused by the propeller installing on the airframe. Computation were fulfilled for the two level-flight modes at speeds of 46 and 62 m/s and propeller rotational speeds of 5280 and 6900 rpm. Accounting for balancing increased the required thrust by 14.6% in the first mode and by 2.8% in the second mode. The CFD simulation of the installed configuration demonstrated a propeller thrust decrease by 4.3–4.5% relative to the isolated-propeller case. After accounting for both trim and interference effects, the discrepancy between the calculated and required thrust was of −2.6% and −0.7%, respectively. The obtained results confirm the applicability of the proposed validation procedure and demonstrate the need to account for aerodynamic interference between the propeller and the airframe when validating computed propeller thrust characteristics.

Keywords:

propeller, small unmanned aerial vehicle, aerodynamic characteristics, flight tests, CFD-simulation, aerodynamic interference, CADFLO

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