Kate, who is royal patron and Honorary Air Commandant of the RAF Air Cadets, looked radiant in red as she joined the air cadets at RAF Wittering near Peterborough.
Wearing black jeans and a burgundy jacket, the Duchess met some cadets and climbed into the cockpit of a Tutor aircraft.
She was then spotted trying her hand at the controls of the simulator.
Kate reached a speed of 60 knots at an altitude of 4000ft as she took the controls of a flight simulator.
The simulator mimics the performance of a Vigilant motor glider that the air cadets use.
After about five minutes of trying the controls, she gradually took over after instruction from Fl Lt Michael Salter.
He said: "She was gentle on the controls. Very often people are too rough but she had it exactly right.
"The controls are extremely sensitive and she was extremely sensitive.
The Duchess of Cambridge took to the controls of a flight simulator as she spent her Valentine's Day
Kate is royal patron and Honorary Air Commandant of the RAF Air Cadets
"She now realises how the controls alter the sensation in the air. She was a natural."
Kate told Flt Lt Salter that she felt the movement in her feet on the pedals.
He said: "It flies exactly like the real aeroplane. She said 'sometimes it sways'."
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Flt Lt Michael Salter explained before Kate arrived: "It's exactly like it feels in the air.
The Duchess met some cadets and climbed into the cockpit of a Tutor aircraft
"At the end of a day I have to manage the stress levels of the cadets because they get so enthusiastic."
The air cadets, who are in the first months of their membership, were taking part in a personal development training lesson.
The Duchess was introduced to air cadets from the Bedfordshire and Cambridgeshire Wing Air Training Corps, who are taking part in a half-term skills development camp.
The last time she visited cadets was at an air show in Gloucestershire last summer when she and Prince William memorably brought their son Prince George along.
Kate took up her role with the RAF Air Cadets in December 2015, taking on the post from the Duke of Edinburgh who had been involved with the organisation for more than 60 years.
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The Duchess now represents 42,000 air cadets aged from 12 to 19, and 15,000 adult volunteers at more than 1,200 units across the UK and abroad.
The RAF Air Cadets comprises both the Air Training Corps (ATC) and the Combined Cadet Force (RAF).
The ATC was first established in 1941 during the Second World War, with the aim of training young men in aviation skills before they joined the RAF.