Most aeroplanes are shaped by aerodynamics. The Short Skyvan was shaped by what would fit inside it.

Short Brothers started from the cargo and worked outwards: a square-section fuselage of constant cross-section, running straight back to a full-width rear ramp, with the wing braced above it on a single strut per side so nothing intruded on the floor. Wikipedia describes the result as resembling a railroad boxcar, which is exactly right and exactly the point.

Sixty years later they are still working, because nothing else does the job quite as well.

It began with somebody else’s wing

In 1958 F. G. Miles Ltd approached Short Brothers looking for backing on a design called the HDM.106 Caravan. That aircraft descended from the HDM.105, which was a Miles Aerovan fuselage fitted with an enormous high-aspect-ratio wing developed by the French firm Hurel-Dubois.

Short turned the Caravan down, bought the design work and the flight-test data, and used what they had learned to build their own aircraft. So the Skyvan’s lineage runs back to the Aerovan, but by inheritance rather than descent.

The prototype flew from Belfast in January 1963 on piston engines. Turboprops arrived later that year, and the aircraft went through two of them — the Astazou turned out to lose performance at altitude in hot conditions — before settling in 1968 on the Garrett TPE331, which is what almost every surviving Skyvan flies behind today.

The mountains of Dhofar

Oman became the largest military operator, taking sixteen. During the Dhofar War the Sultan of Oman’s Air Force used Skyvans to resupply positions on mountain tops that nothing else could reach — the first landing on the newly cleared airstrip at Simba came on 19 April 1972.

That is the Skyvan’s natural habitat: short, rough, high, hot, and a long way from a paved runway. Civil operators used it the same way, from Loganair in the Scottish islands to Wien Consolidated in Alaska.

Not everyone found it a refined experience.

Why skydivers will not let it die

The Skyvan has one feature that almost no other aircraft in its class offers: a full-width ramp at the back, with twin fins set outboard so the airflow behind it is clean. Twenty jumpers can walk out of it together, standing upright, in formation, without threading themselves through a door one at a time.

That is why drop zones from California to Poland to Israel still run them, alongside freight operators, mosquito-control flying in Florida, and camera work. Two air forces — Oman and Guyana — still fly them as well.

What it turned into

Short stretched the concept. The Short 330 took the same square section, added span and length and thirty seats, and first flew in August 1974; 141 were built. Stretch that again, swap the twin fins for a single swept one, and you get the Short 360.

Give the 330 a full-width rear ramp back and you get the C-23 Sherpa, which flew for the US Army and Air Force. The whole family descends from a decision to design around a rectangular hole.

Skyvan start-up and departure, which conveys the noise better than any description:

Flying one in Alberta, from the cockpit:

And a short-field departure:

Sources: Barnes and James, Shorts Aircraft since 1900; Jane’s Civil and Military Aircraft Upgrades 1994-95; Vintage Aviation News; BBC Northern Ireland, "Your Place and Mine".