At high speeds the centre of lift on the wings moves progressively rearwards, so greater control forces are needed to keep the aircraft flying straight and level. If the centre of lift moves sufficiently rearwards and exceeds the ability of the control surfaces to keep the nose up, then the aircraft will suffer a high speed buffet and enter a dive. The use of delta shaped and swept wings helps to keep the centre of lift within the trim capabilities of the aircraft, but it is possible for straight winged aircraft to fly at supersonic speeds if they have an all moveable surface tailplane.