Of all the light piston twin airplanes that saw light in the 1950s and 1960s, the Cessna 310 is by many considered as the most elegant one, in particular the versions with a short nose and swept vertical fin. Over the years, Model 310 received quite some updates, also changing its appearance. Common on all versions are the straight, low placed wings with horizontally opposed piston engines in quite boxy nacelles on top of the wings. Also, all versions have tip tanks (with different shapes though) and a single wheel main landing gear that retracts sideways in the wings. The single wheel nose gear retracts rearward. On many version it is located near the tip of the nose and tilted forward, a typical recognitions point. The underside of the fuselage is fairly straight; the top of the fuselage tapers down much more towards the tail.

The different versions of the Cessna 310 and 320 can be distinguished by:

• the shape of the vertical stabiliser
• the length of the fuselage
• the number and shape of the cabin windows
• the shape and length of the engine nacelles
• the location of the exhaust(s)
• the presence of cowl valves at the side of the nacelle
• the shape of the nose
• the shape of the nose gear
• the presence of a ventral fin
• the shape of the main gear doors
• the number of propeller blades
• the shape of the cockpit front window(s)

When the first Cessna 310 was developed in the 1950s it had a straight vertical stabiliser, that is nearly rectangular, but with a slight trapezoidal shape. In front is a small dorsal fin. The piston engines are in nacelles on top of the wings and have double exhausts near the trailing edge of the wings. They drive two blade propellers. The front cockpit windows are separated by a frame in the middle. There are two side (cabin) windows. The nose gear is attached to the tip of the short rounded nose and tilted forward: the nose wheel is on front of the nose. At the wing tips are large tip tanks, with a 'tuna' shape. Fi­nal­ly, the original Cessna 310 has rectangular main landing gear doors.

Cessna 310A was the model number given to the USAF ver­sion, designated L-27A and later U-3A Blue Canoe. The Cessna 310B was a slightly upgraded versions, without any external changes.

To recognise the Cessna 310C from the earlier models, you will have to look at the nacelles and exhausts. While the exhausts are still above the wings, they are longer than on the 310 and 310B and extend until the trailing edge. Moreover, the nacelle has five long, narrow slots in front of the leading edge of the wings.

The 1960 model year version, called Cessna 310D, is the first to have a swept vertical stabiliser. For the rest it is externally the same as the Cessna 310C and earlier variants.

The Cessna 310F has a third, small side window, but is otherwise externally the same as the 310D. So a swept tail, 'tuna' tip tanks and exhausts above the wings, although some aircraft may have been converted with underwing exhausts.

Cessna 310E (also known as Cessna 310M) is model number of the US military version, designation L-27B and U-3B.

The main upgrade on the Cessna 310G compared to the 310F is in the tip tanks. These are slimmer than the 'tuna' type ones, and canted. The Cessna 310H has a large interior, but that is hardly visible from the outside. The model E310H is the same except for a lower maximum take-off weight.

From this angle, the canted slimmer tip tanks of the Cessna 310H are easily visible. Note the exhausts are still above the wings. (photo (modified): ZidaneHartono/WikiMedia))

The two long exhausts above the wings had their problems, so from the model 310I on they are moved to the underside of the nacelles, under the wings. They still have long tubes though, unlike the Riley 65 conversions (see below). At the same time, the nacelles have been lengthened, and they now been extended to beyond the trailing edge of the wings. Given the problems with the original nacelles, some older models have been converted with the new nacelles and exhaust. Then the Cessna 310G and H become externally the same.

The Cessna 310J is quite similar, at least on the outside. The 310J-1 variant is certified with a lower maximum take-off weight and four seats only. Also the Cessna E310J has different certified weights.

Given the three side windows and long nacelles with exhausts under the wings, this is a Cessna 310I or 310J. And indeed it is the latter one. Beware however that older models can be converted with the same nacelles! (photo: ZLEA/WikiMedia)

The 1966 model Cessna 310 is the first to combine the second and third side window in a single, long 'vista' side window. That is the main external difference between the Cessna 310K and previous variants. It also has a three blade propeller as an option, but that is not really a distinguishing feature as later models have the same option.

The new item on the Cessna 310L compared to the 310K is the redesigned main gear. The most obvious difference is in the shape of the main gear doors along the gear leg. At the bottom they become wider. Also new is a single piece front windshield as standard, but as this is available as a retrofit for older model (see photo at the top), it is not really suitable for recognition.

The Cessna 310N is externally not different from the 310L, except that it optionally has a cargo door.

The first external change on the Cessna 310P is the long ventral fin under the rear fuselage. Additionally, the bottom of the trailing edge of the vertical stabiliser is curved towards the tail cone. Finally, the nose gear is shorter and more or less straight, i.e. not tilted foreward.

Initially, the Cessna 310R was only a 310P with minor changes, at least not visible from the outside. However, during the production run the top of the rear fuselage was raised and given a sky light window. Only these 310Qs can be distinguished from other variants.

The final version of the Cessna 310, the 310R, received the most visible external change since the swept vertical stabiliser was introduced. The Cessna 310R has a longer, pointed nose, in which the nose gear is not at the tip anymore. In addition, this non-turbo version has nacelles with short exhausts and no cowl flaps at the side (unlike the Cessna T310R described below). Finally, three blade props come as standard.

Based on the model 310F Cessna made the Cessna 320 Skyknight, a stretched version with turbocharged engines. The longer fuse­lage translates in an additional, rectangular cabin window, making four side windows in total. The nacelles are short and do not extend beyond the wing's trailing edge. The have three cooling exhausts on the under­side. For the rest it has the Cessna 310F characteristics like the 'tuna' tip tanks and rectangular main gear doors.

Cessna 320-1 is the designation for a Cessna 320 with higher operating weights.

Simultenously with updates to the Cessna 310, the Cessna 320 was upgraded. Hence the Cessna 320A has the same canted tip tanks as the Cessna 310G. For the rest it is externally the same as the Cessna 320.

Like the Cessna 310I the engine nacelles of the Cessna 320B are stretched and extend beyond the trailing edge of the wings.

The 320C model only differs in details from the 320B

The Cessna 320B has long nacelles, although that is not easily visible on this photo. (photo: Tomás Del Coro/WikiMedia)

Externally, you can distinguish the Cessna 320D from a 320B or C best by the shape of the last cabin window. The widest point is in the top half of the window instead of at the bottom. Also, the 320D can be fitted with two or three blade propellers.

It is a bit difficult to see on this photo but the Cessna 320D has a different last cabin window, but still the rectangular main gear doors. (photo: Alec Wilson/WikiMedia)

The last versions of the model 320 differ from the 320D mainly by the shape of the main gear doors. These widen significantly at the bottom, like on the Cessna 310L. Also, a single piece front windshield is standard and the nose is more pointed.

Cessna stopped producing the model 320 when it started offering normal and turbocharged versions of the 310, starting with the T310P. This is thus a Cessna 310P with turbocharged piston engines. They can be recognisied from the regular 310P by the short, vertical exhausts and cowl flaps at the side of the nacelle.

Like above the Cessna T310Q is a 310Q with turbocharged engines, with short vertical exhausts and cowl flaps.

The Cessna 310R with turbocharged engines is called T310R. It has the long, pointed nose of the 310R, but slightly different engine nacelles. The latter have cowl flaps in the lower sides, on the outside of the nacelle. Finally, the exhausts are straight down, instead of slightly tilted aft.

Colemill Entreprises replaced the engines of the Cessna 310G until 310Q with more powerfull ones, driving three blade propellers. On the outside, there seem to be no difference though between these Executive 600s and the original aircraft.

The same applies to the Bearcat I & II, which are conversions of the T310P, T310Q, 310R and T310R and the Century 600, the marketing name for the same conversion of the Cessna 320.

Since Colemill went out of business, the same conversions are offered by Mike Jones Aircraft Sales.

The most externally visible change for these Riley converisons was to replace Cessna's over-wing augmentor exhaust system of the 310 until 310H with a system fitted below each engine nacelle. The exhaust pipes are along the bottom of the nacelle, but not as long as on the Cessna 310I and later. Also, a third cabin window was added, with a slightly different shape than the factory original of the 310F. While the engines of these conversions differ, but all power a three blade prop, they seems to be the same on the outside.

The Riley Super 310 has the same engines as the Riley Super 340. Likely it has the same nacelle shape as well, with narrower cooling intakes at the front and a short, nearly vertical exhaust.

This modification involves the replacement of the original Continental engines of the Cessna 310Is and later and 320Bs and later by Lycoming ones. In this case the complete engine installation of the Piper PA-31 Navajo, including the nacelle, is placed on the Cessna. They can best be recognised by the cooling intake at the front, which are in the lower part of the nacelle instead of the upper part.