The increasing interest in Small Air Transportation (SAT), to enhance global connectivity, is highlighting the need for reducing take-off distance: lift coefficient has to be increased without penalizing the configuration drag, weight and complexity.
The objective of the MOTHIF project was to quantify the efficiency of a jet blowing technique at the trailing edge of an wing to improve lift.
Inside the AIR ITD (Airframe Integrated Technology Demonstrator), within the EU ( European Union) CleanSky 2 research project, a blown flap configuration has been developed to allow STOL (Short Take Off and Landing) capabilities of a future affordable and green hybrid/electric small commuter, up to 19 seats, belonging to EASA CS 23 (European Union Aviation Safety Agency Certification Specification) regulatory base. The developed blown flap has been tested in a wind tunnel facility through the collaboration between Piaggio Aerospace and the MOTHIF consortium, composed by VKI (Von Karman Institute) and SONACA.
The blowing system design choice is aimed at keeping the inevitable associated increase in pitching moment very low, and not penalizing performance when blowing fails. In collaboration between Piaggio Aerospace and the MOTHIF consortium, a wing model was designed, built and tested in the VKI’s large subsonic L1-A wind tunnel, reproducing bi-dimensional preliminary results obtained during the design phase. In order to reduce and predict three dimensional and blockage effects, CFD has been used extensively to obtain a proper test chamber configuration and to reproduce some wind tunnel test results, so that both the accuracy of wind tunnel and design methodology can be assessed.
During the wind tunnel measurements, the pressure distribution across the main wing and flap and the total forces generated by the model have been recorded. The jet blowing influences positively the pressure distribution on the main wing. An increase of the jet blowing pressure ratio has resulted in a gain in lift force.
The measurements have been supplemented by PIV measurements for flow field visualization and detailed flow characterization. The analysis of the jet behavior indicates that as the incoming wind speed increases, the trailing edge blowing deviates away from the flap and the jet becomes wider. When the pressure ratio increases, the jet impacts further downstream the flap and increasing the flap angle leads to a deviation from the jet away from the flap; with the situation at a flap angle of 30° where the core of the jet is not at all impacting on the flap.
