“But now, what about them canopies?? Why did the Brits and the Portuguese not use the bubble canopy in their production??”
Twochai, this is a very good question indeed. I’ve checked all my references, as well as asking two “Chipmunk history gurus” and it seems that there’s no documentation to indicate that the MoD or RAF ever asked for blown canopies!
When the DHC-1A was evaluated at Boscombe Down the existing canopy was extensively criticized. While the canopy adopted for the T.10/Mk.20 series looks similar it’s actually quite different. The thicker framing and blown rear side panels are readily apparent, but the canopy is also of a much broader cross-section (it’s wider at the top) in order to improve head room.
The T.10/Mk20 specification seems to have been settled in 1948. The DHC-1B-S3, the first Canadian-built version to sport the blown canopy, didn’t appear until a year later by which time UK production was getting underway. Perhaps they didn’t want to interrupt production to accommodate a new canopy?
Installing a DHC-1B blown canopy on a T.10/Mk.20/21/22 is not as straight-forward as it appears initially, in that both the rails and windscreen cross-section are different. However there have been subsequent blown canopies designed privately (both in the UK and Australia) to “fit” the T.10/Mk.20/21/22 so perhaps the desire to do so wasn’t there at the time anyway.
I can see two possible reasons why the RAF weren’t interested. Firstly, if the Chipmunk has an accident involving coming to rest inverted, it’s not possible to slide the canopy aft. However, egress from the UK-built aircraft is still possible as the LHS canopy panels can be jettisoned. This is obviously not possible with the blown canopy, which is perhaps why my DHC-1B Flight Manual (undated) contains a requirement to take off and land with the hood open – now this must have been fun in a Canadian winter! This issue has been addressed subsequently by the mandatory carriage of a canopy axe. Also the RAF initially used two-colour blind-flying screens on the forward side panels which required a flat surface for mounting, again not possible with the curved blown canopy. This scheme seems to have fallen into dis-use by the 1960’s.
None of the above really explains the apparent disinterest in the blown canopy; can anyone expand further on this subject?
As a devoted T.10 owner, I would be the first to acknowledge that the DHC-1B has a superior cockpit in virtually every aspect. My one reservation would be the lack of a baggage compartment on the Canadian-built version – even a ludicrously small compartment is better than none at all.