In the Shorts designation thread we had a discussion about the possible structure of the SBAC designation system.
http://www.secretprojects.co.uk/forum/index.php/topic,1878.30.html
It appears each manufacturer was allocated a main letter which reflected the first letter of the company's name, e.g. E = English Electric, S = Shorts etc. (Blackburn being Y is an exception).
Each manufacturer would then assign numbers sequentially in blocks of nine. Each block was identified by the letters of the alphabet, A, B,C etc., with a new letter whenever the next batch of nine was begun; e.g. S.A.1 to S.A.9, followed by S.B.1 to S.B.9, followed by S.C.1 etc.
This explains why variants of the same basic airframe often had different numbers through the series.
Why the SBAC chose to keep the designations to single digits is unknown, perhaps to avoid complications with errors with mis-numbered or in copying?
I am not sure to what extent the Ministry of Supply was the driver behind this system, but it seems only projects that were actually tendered or looked likely to be were assigned the next available number and all seem to have an official requirement or development contract associated with them. It is likely that the designation was meant to ease the MoS's admin headaches while keeping track of different variants and projects tendered. The fact that Short's being effectively majority-owned by the MoS persisted with this system the longest is perhaps an indication of the Ministry's desire for the system.
I have some additions to the list above by AM
Airspeed
X.A.8 - Ambassador airliner
Auster
Began using the system in 1947, but there are two odd features regarding Auster's use of the system. They seemingly only used the second alphabetic letter without a first letter to identify the company. It is possible these designations should actually be A.A.1 to A.E.1.
Also, they seem to have included all their projects from 1947 for new types unconnected with the pre-war and wartime types.
A.1 - Model M redesignated?
A.2 - Model N redesignated?
A.3 - 1947 light aircraft project
A.4 - 1948 AOP project
A.5 - 1948 AOP project
A.6 - 1948 touring trainer project
A.7- 1948 high-wing pusher project
A.8 - 1948 AOP project
A.9 - 1949 basic trainer project to T.16/48
B.1 - AOP project
B.2 - unknown
B.3 - 1951 pilotless target (production)
B.4 - 1951 prototype ambulance/freighter
B.5 - AOP.9 to A.20/49 (OR.270) and later 9M civil conversion
B.6 - 1953 agricultural aircraft project
B.7 - 1953 tourer project
B.8 - Agricola
B.9 - 1954 ultralight helicopter project to HR.144T (OR.319)
C.1 - 1955 light aircraft project
C.2 - 1955 light helicopter project
C.3 - 1955 light helicopter project
C.4 - Antarctic trainer
C.5 - 1955 ambulance/freighter project
C.6 - Atlantic light aircraft prototype
C.7 - 1956 light helicopter project
C.8 - 1956 light helicopter project
C.9 - 1956 light helicopter project based on B.9
D.1 - 1957 troop transport project
D.2 - 1958 AOP project
D.3 - 1958 light aircraft project
D.4 - D4/108 light aircraft
D.5 - Husky D5/160 light aircraft
D.6 - D6/160 and D6/180 light aircraft
D.7 - 1960 D.5 agricultural variant project
D.8 - 1960 D.6 with tricycle undercarriage project (led to Beagle A109 Airedale)
D.9 - 1960 D.4 with tricycle undercarriage project
E.1 - unknown
E.2 - unknown
E.3 - 1961 Auster 11 A.115
Boulton Paul
P.A.1 - Balliol prototype/T.1 with Dart
P.A.2 - Balliol prototype/T.1T.1 with Mamba
P.A.3 - Balliol, possibly prototype installation of Merlin
P.A.4 - Balliol T.2
P.A.5 - Sea Balliol T.21
P.B.1 - P.111
P.B.2 - P.120
Bristol (these to be confirmed)
R.A.4 - jet pathfinder/bomber project
R.A.6 - jet pathfinder/bomber project
Fairey
Vic Flintham in
Aircraft in British Military Service: British Service Aircraft Since 1945 states FA.1 Rotodyne, F.B.1 Gyrodyne and the F.D. series were SBAC designations, but these were actually Fairey's own designations, e.g. Fairey-Bennett No.1 and Fairey Delta No.1.
Heston Aircraft Company
The J.B. series was unused. There is some doubt whether these are SBAC designations, given many of them appear to be pre-war and so would pre-date the SBAC system, unless they were retrospectively assigned.
J.A.1 - Phoenix
J.A. 2 - Griffin project
J.A.3 - T.1/37 trainer
J.A.4 - T.1/37 project
J.A.5 - Type 5 racer
J.C.1 - T.23/43 project
J.C.2 - unknown
J.C.3 - unknown
J.C.4 - unknown
J.C.5 - A4/45 project
J.C.6 - AOP prototype to A.2/45
J.C.7 - unknown
J.C.8 - unknown
J.C.9 - scale Vickers Swallow VG wing research aircraft project (built but never assembled)
Marshall Flying Services
There is a possibility this was just Marshall's own company designation.
M.A.4 - BLC research aircraft converted from Auster AOP.6
Reid & Sigrist
Vic Flintham in
Aircraft in British Military Service: British Service Aircraft Since 1945 states the RS.3 and RS.4 were SBAC designations, but actually these follow on from the RS.1 in 1939 and there seems little doubt RS was simply the firm's own designation using the initials of the company.
Vickers
Vic Flintham in
Aircraft in British Military Service: British Service Aircraft Since 1945 states the VC series of airliners were SABC designations, but actually VC stood for Vickers Commercial and were not part of the SBAC system.
Westland
Only two W.A. numbers seem to be known, both licence-built Sikorksy helicopters and paralleling the better-known WS series Westland used publicly.
W.A.4 - S.51
W.A.8 - S.55
