I can't document this, but what I've always believed is that the RAF release to service listed it at +6 and -3.
+6-3 were the limits marked on the accelerometer on the T.10 I had some experience of in the '80s (WZ868 / G-BCIW). I also believe, but can't prove, that the CAA required at least some Chipmunks to be restricted to +5-2.
The Chipmunk had a fairly difficult transition from military to civilian flying, with the CAA requiring a number of modifications which cost a lot of money. The absence of such mods never seeemd to make military Chipmunks fall out of the sky in unacceptable numbers, but that's government for you. The military Vne was a somewhat alarming 173 KIAS: in the civilian Mk.22 pilot's notes I have, Vne is listed as 155 KIAS.
However, in the real world +5-2 and 155 knots is more than enough to do anything with a Chipmunk that the reasonable pilot might wish, especially with no inverted fuel and oil and a distinctly "right way up" optimised wing section. The aeroplane does not really like negative G at all and anything more ambitious than a transient -1g slow roll or roll off the top of a loop might be regarded as rather unsympathetic handling of an aeroplane which has reached its half centenary.
Even transient negative G is not ideal for the engine. When I used to slow roll a Chipie using -1G in the middle, I was strongly encouraged to follow RAF practice in closing the throttle as the G went down past zero, and opening it smoothly only once positive G, and oil pressure, had been restored. The RAF in the Chipmunk's main service life, of course, had lots of money for engines. With a top-notch (meaning Vintech) Gipsy Major rebuild now costing as much as a small house in the North of England, and the engines only having a 1000 hour life on a transport category C of A anyway, I would be very much inclined these days not to go negative at all with any Gipsy Major I owned or might have to pay for. After all, that's what we have Yaks for (+7-5) nowadays!
Were you thinking of doing anything that requires a lot of negative G? I'm curious.
The worst thing I've ever seen done to a Chipmunk is in "the Great Waldo Pepper" where a modified Chippie is dolled up as a pre-war US stunt aircraft and subjected to a number of attempts at an outside loop from normal flight until it crashes, killing the pilot.
