Here is an asymmetrical variable capacitor suitable for working with a Colpitts Oscillator
Note the symmetry seen with most variable air capacitors here:
In the first section of this unit, we’ll be exploring LC type oscillators, and in particular the Colpitts Oscillator. First though, we’ll look at the need for positive feedback in an amplifier to create a free running LC oscillator.
Electronics_ Introduction to LC Oscillators ~ 1974 US Air Force Training Film TVK 30-536.mp4
A re-examination of the phasor diagram for AC parallel RCL circuit will help to understand how the feedback frequency determining network sits in relation to the overall oscillator circuit. For some circuits, a series RCL approach would be more appropriate, but this is the only video I have at the moment
Electronics_ Parallel RCL Circuits 1972 US Air Force Training Film TV2013EK.mp4