Even disregarding the possible aerodynamic issues, I don't think opening the canopy in preparation for a crash is such a good idea.
I think an unlatched canopy has a much greater possibility of being torn from the fuselage. If it *IS* torn from the fuselage, I would think there's a good chance it will strike the occupant(s). Additionally, a closed and latched canopy can provide the occupants protection from debris, fuel and fire postcrash.
If you are concerned the canopy might jam closed, consider this: I recall a warning in the USAF KC-135 Dash-1 (operating manual) that states (in so many words) any crash violent enough to jam a hatch closed will likely provide a fuselage break for egress.
Regards,
Mark Sletten
Steve Reeves [sreeves@sc.rr.com] said:
> I tend to agree. I know my instructor, when we were doing instrument
> training in a Cheetah, would tell > me to slide the canopy back, stick
> your shoe in it (or something similar) and slide it back onto
> whatever you were cramming into it.
> Steve