I know ! I Know !! Ooo! Ooo! I Know ! I Know !
Im not sure what you mean by Sticky out bits - but,
You must be referring to the protrusions on the engine nacelles - IE Strakes or Chines in US vernacular.
These have been used for several reasons - Douglas used two of them per nacelle on the DC-10 to increase lift ( Kerker was the Douglas Engineer that did the development ) - Im not sure of the aerodynamic theory as to how they work - because of the engine nacelle coupling - IE the DC-10 engines hang really low ( A300 has literally DC-10 engines, nacelles & struts ) - and therefore the nacellel vortexs do not interfer with the flow over the wings & spoil lift. Boeing & AIRBUS use the nacelle chines for a different purpose - to improve low speed stall characteristics- they physically improve the strength of the nacelle vortex so that it will not burst as it passes through the leading edge pressure gradient - these are vortex shed amplifiers - otherwise the characteristically week vortex would "burst" as it passes though the pressure differential when going from underside to topside of the wing. A bursting vortex will hose the flow over the top side of the inboard wing causing it to want to stall before the outside wing. Because of the fact that modern jets use a swept wing - this stalling unloads the inboard wing first - while the outbord reagion is still flying. This can cause a stall pitch down moment - that will limit your slowest approach speed - IE airplane will keep pitching over following stall & brealk - not allowing you to continue slowing down with AOA. If you make the damn thing too effective ( IE the size of the chine ) you will make the inboard wing hang on too long- IE NOT want to stall at all - making the aircraft divergent in pitch - IE Airplane wants to stay pitched up regardless of what the pilot wants - SSSoooooo - as St Augistine said - prudence is in the middle - IE there is a sweet spot in between too small & too Large. AIRBUS copied this use from Boeing - who did it on the 737, 767 & 777. The A320-100 delivered with out these & put them on later after they considered the cost & expense of trailing edge improvements. Now everybody uses them Embraer ERJ170 included. THe big question is WHY AIRBUS uses two of them instead of Boeing's use of one - & that is because they do not want to spare a left & right handed nacelle - IE they have a universal part. I believe Embraer is subscribing to that line of thinking ..
Correct ?