HB Helicopter Engines
1972
Originally brought out in 1971 and marketed under the label of (Veco Europe Series). In 1972 the engine was redesigned with new internals and brought out as the HB61 after the owner/designer Helmut Bernhart being then distributed by Graupner. HB was only a small manufacturer not particularly well known outside of Germany and only produced two sizes of engine, 20 size for cars and 61 size in aero and marine versions.
HB 20 and 61 engine - 73 booklet with specifications of pre 73 engines
Helmut being interested in helicopters took the opportunity to help develop the helicopter of H Demuth and provided his 61 size engine specifically adapter to suit. The modification replaced the aero engine back plate with a larger mounting that incorporated a through shaft driven from the crankshaft 'big-end' pin. Fitted to this shaft was a radial fan with a duct housing fitted to the back plate that directed the air over the engines cylinder head.
HB 61 Stamo (Red head) 1973-1977 (Graupner Bell 212)
HB Stamo (red head) - Oct 74 review with helicopter modifications - noted power output being 1.1 BHP at 13500 Rpm (5% nitro).
Dec 73 advert 
Oct 74 advert
1975
HB25 fitted to the Graupner Bell 47G
Again in conjunction with Graupner, Helmut developed the HB25H engine (long stroke HB20) specifically for use in the Bell 47G incorporated a built in flywheel mounted cooling fan and also a large rectangular cylinder head to additionally aid cooling; this type of head was to become synonymous with future versions of model engines from any manufacturer developed for specific helicopter use.
Aug 75 advert 
Dec 75 Advert
Because of the involvement with the Graupner helicopters Helmut decided to increase his model range and as noted in the advert, soon to be released in additional sizes of 12, 15, 40 and 50.
1976
Jan 76
It was decided to offer replacement helicopter heads for both the smaller 20/25 engines and the 61 size engine as these types of heads were finding use in cars and also scale aeroplanes; both types could suffer from inadequate cooling and in these circumstances the heat sink heads prevented the engines from overheating.
HB 40 & 50 - Engine reviews - may 1976
1977
New PDP (Perry Directional Porting) in both 40 and 61 size.
Note - PDP was not Schnuerle porting but a revision of the cross-flow principle which improved power but not quite to the extent of a full Schnuerle ported engines. Both engines fitted with Perry carb's and power output of the standard 40 was 0.67 Bhp @ 14500 rpm (5% nitro); unfortunately the PDP 40 was only tested un-silenced however with a similar reduction taken into account it should have put out around 0.75 Bhp @ 15000 Rpm (5% nitro).
additionally, the Graupner Bell 212 was also updated in 1977 with the new HB 61 PDP Stamo fitted with the rectangular helicopter head.
HB 61 PDP - Review of aero version May 1977.
HB 40 - Engine review both normal and PDP versions - Dec 1977
1978
Apr 78 advert
1979
Mar 79 advert
79 and the newly released Graupner Bell_222 was fitted with the HB61 PDP Stamo but this time with the Round heat sink head
1980
Jun 80 advert but no helicopter versions?