Construction
To build the flying buttress, it was first necessary to construct temporary wooden frames which are called centering. The centering would support the weight of the stones and help maintain the shape of the arch until the mortar was dry. The centering was first built on the ground by the carpenters. Once that was done, they would be hoisted into place and fastened to the piers at the end of one buttress and at the other. These acted as temporary flying buttresses until the actual stone arch was complete.Because the majority of the load is transmitted from the ceiling through the upper part of the walls, making the buttress as a semi-arch extending far from the wall provides almost the same load-bearing capacity as a traditional buttress engaged with the wall from top to bottom, yet in a much lighter and cheaper structure. And because the flying buttress relieves the load-bearing walls with a much smaller area of contact, much larger voids are able to be built into those walls, such as for windows, than would otherwise be possible.
Often on Gothic churches, two arched 'flyers' were used one above the other. In such cases the lower flyer (positioned a little below the springing point of the vault) is designed to take the lateral force of the vault while the upper one resists the effect of wind-loading on the roof.
The vertical buttresses at the outer end of the flyers were often capped with pinnacles that provide additional vertical loading to help resist the lateral thrust transmitted by the flyer.
Read more about this topic: Flying Buttress
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