What does a proper Birmingham Roller need to do to be worth watching?
The roller should roll over backwards holding its wings up to a parallel point at the top of its axis and on the wings on the down stroke should also finish when parallel. This gives the illusion, if fast enough, of a smooth spinning ball. When seen from below it may present as a spinning ‘H’ or if the wings go slightly the parallel position it may look like an ‘A’. When the wings do not reach a full parallel point before commencing the downward stroke it may appear like an ‘X’ from below. For most novices the most important thing to note is that when the bird is rolling and viewed from the side at a right angle, it should give the impression of either a solid ball or a ball with a hole through the middle.
Pensom’s ‘considerable distance’ should be long enough for the viewer to see it start, notice its shape, speed, and style, and whether the bird stops correctly. If the roll is too short the viewer will not have enough time to do all this.
The proper Birmingham Roller should start cleanly and sharply in the roll, roll in a straight line, show no change in speed or style throughout the duration of the roll, and stop cleanly, facing the same direction the kit is flying.
The bird should be capable of rolling frequently as least once a minute or more often. More important it should roll with the kit and as often as it rolls and should be able to roll throughout the duration of the fly. – Graham Dexter (edited)