Originally Posted by bjnginge
Look mate I know how deltas work , I have three of them. If you took the time to look at the photo you would see inboard flaps and outboard elevons.
I assume when flaps are deployed that the elevons are used in a crow more like air brakes.
Just assuming, they could be used as separate elevator/aileron controls unless they are big trim tabs
Those are not inboard flaps, just split controls. Many full size do that, and mix so that if the pilot applies both elevator and aileron the bias shifts to moving the inboard ones as elevator and the outboard ones ailerons - the Avro Vulcan for example does that.
You can certainly move one pair down and one pair up but you don't get flap effect because the ones going up to compensate for the ones going down reduce the lift as much as the ones going down increase it, all you get is drag, so it doesn't allow the plane to land any slower because there is no additional lift.
There are ways for tailless aircraft to have lift increasing flaps and but they do not apply to standard deltas like the Mirage. One way is to have a controllable foreplane which can act to produce an upwards force to compensate for the nose down force created by lowering the trailing edge. Another is to have a highly swept trailing edge so that the inboard surfaces acting as flaps are close to the CG and have little pitch leverage whereas the outboard surfaces which are much further behind the CG can deflect just a little to compensate for the pitch change and thus not reduce the lift by as much as the inboard surfaces are increasing it.