I’m not sure what I was thinking about earlier this morning, must have been too early for me. Of course the flap systems are separate. There is a jack on each wing to blow the flaps down and spring pressure to raise them. On the ground they extend in less than a second, although retraction can take up to 15 seconds. With air loads, at the flap limiting speed, extension can take up to 1 second and is normally symmetrical. Retraction takes up to about 8 seconds and is normally asummetric to some extent. On MJ730 the asymmetry was more pronounced than on other Spits I have flown.

Further, as it takes up to 8 seconds for the flaps to retract in the air, the positions can be seen from the cockpit and any asymmetry can be verified visually.

Now, I’m certainly not going to get into an argument about it, but I can assure you that it is possible to hold the Spitfire level at flap limiting speed with one flap down and one flap up with about half aileron and no significant rudder pressure – and before you start on about asymmetric drag from the flaps, the torque from the engine is far more significant and any rudder required for the flap drag is not noticeable.

A

PS – I like the logo Mark V

I don’t know the official answer, but here’s another possibility – I suspect that up and full down were all that was required on the prototype, both practically and in the design spec. After that, there was minimum change due to war. The act of putting blocks in the Seafire flaps was an elegant solution to the take-off problem, and probably a lot cheaper than a design and manufacturing change.

From experience, on the Mk IX at least, full asymmetric flap, i.e. one up and one down, can be held easily with about half aileron up to the flap limiting speed of 140 kts.