Next to Douglas Lockheed was the second aircraft manufacturer to develop a three engined wide body aircraft, the L-1011 TriStar (basic model 93). On the TriStar two hang on pylons under the wings, while the third is located in the tail cone. It is fed by a S-shaped duct, with the air intake placed on top of the fuselage, in front of the vertical fin. The L-1011 has two main gears with a four wheel bogey each, and a double wheel nose gear. 

The different versions of the L-1011 can be distinguished by:

• the length of the fuselage
• the wing span
• the presence of a dorsal fin
• the presence of refuelling hoses under the rear fuselage
• the presence of a large cargo door
• the presence of a refuelling probe above the cockpit 

These are all long fuselage versions of the TriStar, and externally not different. They differ only in fuel capacity, engine thrust and maximum weights. Also, all long body versions have three large cabin doors slash emgergency exits, and a smaller one in front of the horizontal stabilisers.

The -1, -100 and -200 were production models, with official FAA designation L‑1011‑385‑1, L‑1011‑385‑14 and L‑1011‑385‑15 respectively. The L‑1011‑50, -150 and -250 were conversions of the production models. In case of the L-1011-250 it concerns a significant strengthening of the centre wing boxes and gear, but without any external visibility of that.

One external feature of the L-1011-500 later became available as a retrofit for older, long body model. This is the small dorsal fin underneath the middle air intake. 

Several passenger TriStars were converted to cargo airplane by the addition of a large cargo door in the left front fuselage, and the replacement of cabin windows by metal plugs. These aircraft received an 'F' behind the original designation as marketing name.

To better compete with the DC-10-30 Lock­heed developed the short body L-1011-500, officially known as L-1011-385-3. While this shorter body is normally quite easy to see, this version also has only three large cabin doors/emergency exits, two in front of the wings and one at the end of the cabin. Additionally, the -500 has a three metre wider wing span with more curved wing tips and a small curved dorsal fin in front of the centre engine air intake.

In the wake of the Falkland war the Royal Air Force obviously needed other tanker and troop transport aircraft. Six TriStar 500s were acquired from British Airways and three from PanAm. The latter were conver­ted to pure military passenger aircraft, and designated TriStar C2 or C2A, depending on the avionics package. They are only recognised by their paint scheme and serials.

The pure tanker versions of the Royal Air Force TriStars are designated TriStar K1. On the outside they look like regular L-1011s, except for two bumps under the rear fuselage. From these bumps hoses can be extended to refuel other aircraft. Originally, they could also be refuelled themselves through a probe above the cockpit, but this was later removed. 

This TriStar K1 has refuelling equipment under the rear fuselage, but no large cargo door. Here it still has the own refuelling probe above the cockpit (photo: Felix Goetting/WikiMedia)

Four former British Airways were configured to be used as aerial tanker and cargo/pas­senger transport. These TriStar KC1s have the same bumps under the rear fuselage as the TriStar K1, but additionally a large cargo door in the left forward fuselage. There are no cabin windows in this door.

The TriStar KC1 is the only version with a large cargo door and refuelling equipment. The latter is not visible here, but the cargo door is recognised by the door hinge and lack of cabin windows. (photo: Steve Lynes/WikiMedia)