Our client came to us with a proposition. He wanted to know if we could develop with him an idea he had to fit an air extractor to his glider's access panel aperture on the upper side of the fuselage. This was based on the rationale of depressurising the cabin which as well as diminishing drag by reducing leakage, also reduces noise which is desirable when you are trying to keep your boundary layers laminar. Traditionally gliders rely on an exit in the tail of the fuselage to exit cockpit flow but this involves a tortuous route for the air with the associated pressure rise making it difficult for the air entering the cockpit (for cooling purposes) to escape.
This presented an interesting challenge as it is critical that the air exiting from the louvred air extractor does not trip the laminar boundary layer on the fuselage creating turbulence or even worse separation. We worked together and developed a set of laminar aerofoil sections that assertively turn the cabin bleed air to the same direction as the free-stream flow. While some increase in the boundary layer momentum thickness on the fuselage due to the lower energy air emerging from the cockpit is inevitable we can see that this is minimal and that the freestream air successfully entrains the cabin flow increasing its momentum and delivering a smooth flow on the fuselage downstream of the air extractor.
Flight tests are now successfully completed and the final installation signed off. You can now buy the product at the customer website LJ Panels.