Landing speed too low and so too near the stall air speed.

Pilot Error.

Although not readily intuitive, optimised air speed for landing can be adjusted by the model pilot via elevator trim. By increasing up elevator trim gradually, the tailplane, (stabiliser), is forced to sit lower in the air flow, thus raising the nose and increasing the mainplane's, (wing's),  angle of attack. When this is done the engine's speed must also be reduced to stop the climb. Following this procedure in small steps allows the model pilot to investigate at what level of up elevator trim the stall occurs. When this value is found during flight testing, the model pilot then dials in a moderate amount of down trim so that the stall is avoided on the landing approach. Once this value is correctly set, a stall becomes impossible provided the model pilot uses engine only to control height. Put another way the pilot has set the elevator trim to give an engine off, stall free optimised glide, i.e. the minimum glide angle. This approach is often further developed by the the use of flight modes where the pilot can grab the setting at the flick of a switch, while listening to a audio message from his transmitter which announces "Landing Mode" Once this is set the pilot avoids all use of up elevator until the flair. Should he forget and pull up, he will stall and likely damage the aeroplane due to lack of height. To be absolutely sure the pilot has achieved the needed 10% air speed margin above the stall, the model pilot will typically fly circuits at this setting at good height to confirm the setting is not too severe.

There are other ways of achieving the needed flight speed:

i.) Use telemetry to set engine revs. that give the desired air speed.

ii.)  Use a pitot tube, and calibrate to announce the desired air speed when set.

With all this set up, how the aeroplane is flown is very important, e.g. aileron and/or rudder turns must be gentle. If your approach circuit is not what you need and you feel the need to add elevator in one of your turns then more power must be given first. If your positioning over the strip is incorrect then more power will allow the aeroplane to climb safely away. It is recommended that anybody new to this should practice in the simulator. We use the Phoenix flight sim. which covers our needs.

The following article link with videos shows this approach working:

landing-problems-with-rc-model-aircraft