Although the official designation has remained BK117 throughout the years, the external appearance of this helicopter has changed a lot in the course of three generations. It started as a joint-venture between MBB of Germany, known for the Bo105, and Kawasaki of Japan. They made the original BK117. The BK117 is characterised by a rather high fuselage, that slopes up after the cabin. Clamshell doors proved access to the rear of the cabin. Above is a short tail boom holding a vertical stabiliser with the tail rotor on top. Just in front are the horizontal stabilisers with hugh swept vertical fins at the end, pointing up and down. The sweep angle of the upper part is the same as that of the central vertical fin. The two turboshaft engines are placed on top of the cabin. There is only a single engine/gear box hub.

Later MBB became Eurocopter Deutschland and without the help of Kawasaki developed a variant with a shrouded tail rotor (marketed as EC145). This evolved into the Airbus Helicopters H145. These variants have a different fuselage and/or don't have the typical tail of the BK117, but are still officially variants of the BK117. Details are described below.

The different versions of the BK117, EC145 and H145 family can be recognised by looking at:

• the type of tail rotor
• the size of the tail rotor
• the shape of the fuselage
• the presence and shape of end plates at the horizontal stabilisers

Originally, the BK117 has a four blade main rotor and two blade tail rotor, placed on the left top of the vertical stabiliser. It has large vertical fins at the ends of the horizontal stabilisers, bigger than the central vertical fin. The cabin has a straight frame between the front and side cockpit windows. The length of the constant chord part of the tail rotor is about three times the chord width.

All are improved versions of the original BK117. Apart from changes that are not visible on the outside, they have a wider diameter tail rotor. It is difficult to see though that the length of a blade is about four times the chord width.

The dedicated military version of the BK117A-3 has outrigger pylons behind the cabin doors for storage of missiles, a gun mounted underneath the fuselage and taller skids.

When Eurocopter had taken over the activities of MBB (and Kawasaki), it made a significant make-over of the BK117 helicopter. The largest visible change is the replacement of the front fuselage with that of the EC135. As you can see from the photos the EC145 has a more rounded fuselage, with also a curved frame between the front cockpit window and the first side window. For the rest the EC145 is externally nearly the same as the BK117C-1, including the tail with large vertical fins and a two blade tail rotor. These fins at the ends of the horizontal stabilisers now have a swept back instead of swept forward lower part. The official designation is BK117C-2.

EC145e is the marketing name used for a 'simple' EC145 with less sophisticated systems and standardised interior. Its official designation is BK117-C2e.

A militarised version of the EC145 is used by the United States Army under designation UH-72A Lakota.  

To bring the EC145 more in line with other Eurocopter models, the conventional tail rotor was replaced by a shrouded fan rotor, or fenestron. Gone are the characteristic large swept outer vertical fins. The horizontal stabilisers now have no endplates at all, although the protoype had EC135 style endplates.

This version is marketed as Airbus H145 (originally EC145T2), but officially known as BK117D‑2. The five blade main rotor version is known as BK117D-3, but the marketing name remained H145. The dedicated VIP version is marketed as ACH145.

In British military service the H145 is known as Jupiter HT1. The US Army has a version that is called UH-72B Lakota.

The militarised version of the H145, with the capability of adding armor and retractable machine guns, amongst others. It has optionally pylons attached to the side of the fuselage to carry weapons like rockets. Like the H145 it comes in a version with four or five main rotor blades, designated BK117D-2m and BK117D-3m respectively. 

This is an example of a four blade H145M fully outfitted, including a structure attached to the side of the fuselage. (photo: Srđan Popović/WikiMedia)