Emil's flap

[Charge]

It can be assumed of their design that they work well in low speeds but I was thinking that at higher speeds they may have adverse effect on handling and the gap in ailerons seems to be one factor which may make the aileron control stiffer unless sufficient counter balancing is used.  IIRC the 109E has external counter balances and according to some sources it was inferior to Spit 1 in rolling maneuvers in higher speeds (even to fabric covered one?). So I guess the design change was well called for as the experiences pointed that the engagement speeds were constantly increasing.

So maybe it can be concluded that in a fighter it is generally better if the aileron is not vented to upper surface through the gap or any other means, where as in flap designs it can be a desired feature.

-C+

[gripen]

Well, the RAE report claims the ailerons of the Bf 109E about as bad as in the Spitfire I (fabric covered) at high speed. The Curtiss H75 (as well as the P-40) featured slotted ailerons (and these were generally praised by pilots even at high speeds so I don't think that slotted aileron means allways higher control forces at high speeds .

The ailerons changed to the frise type in the Bf 109F and the flaps to the plain type. Interestingly the F series prototypes (at least in the V24) featured slotted flaps outside the radiator part, these being some sort of frise/fowler hybrids (probably with rather complicated mechanism).

[Charge]

I'm not sure if the naming convention with flaps was very precise. If you look at the NACA808 doc and the picture of fowler and slotted flap they look almost the same. The main difference is that Fowler extends outside the "lip" where as slotted flap stays inside the lip at all deflections. Also the slotted flap in that document is quite different from the slotted flap in 109E which does not really "extend" but merely provides only the pressure vent to upper surface provided by hinge geometry. Maybe that qualifies it as a slotted flap, dunno.

It seems that Frise is generally hinged form upper part of aileron and wing and slotted is hinged from lower part to create the flow gap upon deflection but it is probably not slotted despite the hinge arrangement if the flow has been cut with a deflector vane at lower part of wing next to aileron. The slotted aileron can function satisfactorily too if the hinge point and counter balancing is done properly along with aileron control geometry to prevent it from being too light at slow speeds.

-C+