International audienceMOST modern transport aircraft wings exhibit high aspect ratios (typically nine), and consequently undergo large deformations between ground and cruise, and beyond. The most noticeable effect is bending.Alarge bendingmodificationwill strongly contribute to the twist law alteration, and twist is amajor aerodynamic parameter.Wind-tunnelmodels undergo smaller deformations than flying aircraft, but these are often by no means negligible. Their aerodynamic effects can be quantified in pressurized wind tunnels by changing dynamic pressure. They can also be modeled by aeroelastic computational simulations.A puzzling thing is that, often in wind-tunnel tests, the effect is obvious on CL(α), Cm(α), and CL(Cm) curves but almost indiscernible on CL(CD) drag polars. The same phenomenon can happen with numerical simulations comparing a rigid-wing polar and a flexible-wing polar.It is the purpose of this Note to explain under which conditions this phenomenon may take place

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The design and performance analysis of a wing tip device proposed within the M-DAW project by ONERA is presented. A proto-design process is described and the device was thoroughly assessed (mainly with Reynolds-Averaged Navier-Stokes simulations). The process was further explained through wind-tunnel tests at both low speed and high speed in the pressurised and cryogenic European transonic wind tunnel in Cologne. The device is a downward pointing winglet designed for a retrofit scenario (the wing could be modified only within the 96% – 100% bounds of the span). It was designed to keep the wing root bending moment of the clean wing at cruise unchanged so that the aerodynamic gains are the net gains provided by the device that can be directly installed without structural modifications of the wing.

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