There are actually a few facts available to support the contention that tailwheel aircraft are more difficult to operate in the take-off, landing and ground-handling phases.
1) Position of the main wheels relative to the centre of gravity.
If the aircraft heading is slightly different from the aircraft's direction of motion, a side force is exerted on the wheels. If this force is in front of the center of gravity, the resulting moment rotates the aircraft's heading even further from its direction of motion. This increases the force and the process reinforces itself. This is a divergent condition. To avoid a ground loop, the pilot must respond to any turning tendency quickly, while sufficient control authority is available to counteract it. Once the aircraft rotates beyond this point, there is nothing the pilot can do to stop it from rotating further - et voila, the groundloop!
This is simply not the case with a tricycle gear, as the moment tends to correct the deviation, not reinforce it.
Someone said that groundloops can only happen on landing - well crap! The aircraft doesn't care whether it's coming or going - if the deviation starts (for whatever reason) it will tend to increase, whether on take-off, landing or taxying.
2) Angle of attack of the wing when on the ground.
In a tail-wheel aircraft, the wing is at a high angle of attack when on the ground, leading to handling problems in windy conditions.
Again, this is simply not the case with a nose-gear aeroplane.
3) Poor forward visibility.
Due to the poor forward visibility, landing approach alignment, judgement of flare and taxying are all more difficult than in a tricycle aircraft.
4) Gyro effect
Associated more (and rightly so) with high-power engines, there is an additional gyro effect (swing) with tail-wheel aircraft that is not present in nose-wheel types - i.e. when the tail-wheel lifts off. Combine this effect with the others above to increase further the difficulty of a tail-wheel take-off compared to a tricycle.
Note that the points above simply show why a tail-wheel aircraft is more difficult to fly than a nose-wheel type. It would only be more dangerous if the operator was unable to master the difficulty.
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