In straight and level flight (a) let’s assume the stall speed of a given model to be 25MPH. As the angle of attach of the wings increases, turbulance occurs (b). When too much turbulance exist (c), the wing looses lift.
25MPH would be the ideal airspeed for the model to stall and flare to land on the runway. The same aircraft in a bank with the wings at say 30º, the stalling speed goes up to about 30MPH. In a bank of 45º the stalling speed increases to around 45MPH. Now increase the angle of bank to 60º and the stalling speed could be 50 to 55MPH. The stalling speed increase dramatically with the angle of bank and if you incorporate elevator as well to initiate a turn the airspeed now starts to reduce because of the induced drag. If the pilot is not aware the model will rapidly loose height and crash if measures are not taken to rectify the situation.
The above situation is even more relevant with a Jet (or an EDF) because there is reduced airflow over the flying surfaces. With a propeller driven model there is airflow over the control surfaces from the propeller. However, please note the airflow will only be over the elevator and rudder. The ailerons will have little or no authority out towards the tip of the wing.
Now, consider a landing circuit the model is on the downwind leg of the pattern, you have reduced power and loosing height. At a given point you make a 90º turn onto a base leg all the while reducing the power slightly to reduce the height. The last turn on to the final for the approach is the most likely place the model will stall and crash if the pilot is unaware. As you make the turn you roll the aircraft into a bank and at the same time you start to apply up elevator and perhaps the rudder as well. These are the same control inputs for a spin. The final turn onto the landing approach should always be a very shallow gentle turn.
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