Stinson Fixed Wing Slots
As you look at the forward part (called the “leading edge”) of each wing you will notice that toward the wing tips there is an opening through the bottom of the wing that leads up to the top of the wing.
Stinson 10 wing slot (right wing leading edge)
This feature is called a “fixed leading edge slot. When a wing is moving through the air at an angle to the incoming air of about 15 degrees (varies with some airplanes) the airflow over the top of the wing does not flow smoothly and the amount of lift it is generating decreases rapidly. This event is known as a “wing stall” and the wing will no longer support the weight of the aircraft in flight.
By placing this design into the wing structure the angle of the wing may now be increased to about 22 degrees or more before it stalls.This allows the airplane to fly at a much lower speed than it would if it did not have this device built into the wing.
You might also take note that on this airplane the slots are not the entire length of the wing and in particular are in front of, or in line with, the ailerons on the wing (along the back edge [trailing edge] of the wing). This means that the ailerons will maintain their effectiveness at a higher angle while the part of the wing closest to the cabin of the airplane is starting to stall. This action promotes good low speed handling characteristics of the airplane (no loss of control) when the airplane is approaching a stall. A slotted wing does have some disadvantages one of the greatest being that slots increase drag on the airplane resulting in an increase in fuel consumption per unit of distance flown. ”
Stinson 10 Cockpit Instrument Panel