The flying tourbillon distinguishes itself from the classical tourbillon through one precise constructive detail: the cage is anchored on only one side, without the upper bridge closure. The technique was perfected in 1920 by German watchmaker Alfred Helwig, and since then it has remained one of the most copied and most misunderstood solutions in haute horlogerie.
In the traditional tourbillon, the cage is held between two bridges, one lower and one upper: a solid structure, geometrically stable, but one that obscures the view of the mechanism. Removing the upper bridge completely frees the sight line, but introduces a genuine engineering challenge: the upper pivot of the cage must support alone the stresses that in a balanced system are distributed across two points. The solution lies through tighter tolerances, lighter materials and, often, cages in titanium or exotic alloys that reduce the rotating mass.
From the bench I have seen how this construction has two immediate effects: on the aesthetic side, the cage appears suspended in void, an effect that works best on open or skeletal dials; on the technical side, reducing the cage mass lowers the moment of inertia and can favor subtler movements. The Bianchet Rotondo UltraFino reaches 3.85 mm in height also thanks to this choice. Piaget, which I know well from my years working on those ultra-thin calibers in the seventies, used this logic systematically.
The flying tourbillon can be fixed in position, as in the Audemars Piguet Code 11.59 at 6 o'clock, or orbiting: in the Jaeger-LeCoultre Master Grande Tradition caliber 948 it travels the entire dial in 24 hours, becoming itself a time indicator. There is also the inclined variant, as in the David Candaux DC7, where the cage is tilted 30° relative to the dial plane to compensate for gravity effects in multiple positions of wear.
A related but distinct concept is the flying governor, the speed regulator of minute repeaters: similar name, completely different function. It controls the rhythm of the chimes, not the precision of the balance. Ulysse Nardin's flying carousel in the Freak similarly borrows the idea of the structure without upper bridge, applying it however to an entire segment of the movement that acts as a hand.
Beware of terminology in catalogs: «flying tourbillon» and «tourbillon volant» always indicate the same thing; «orbital tourbillon» adds the rotatory motion around the dial, which is a further separate complication.