The Short-Mayo Composite Aircraft - The Trans-Atlantic Piggyback Experiment

The Antique Airshow
Nov 12
4 min read

The Short Mayo Composite Aircraft - Weird and Wacky!

The story of the Short Mayo Composite aircraft begins in the 1930s. By this time, it was well understood that aircraft could maintain flight carrying greater loads than they could take off with. An aircraft’s take-off weight was the limiting factor in how much fuel and cargo it could carry. For Major R.H. Mayo, the Technical General Manager of Imperial Airways, this presented a challenge — and an opportunity.

What if an overloaded aircraft, unable to take off under its own weight, could instead be lifted into the air by another aircraft? In essence, a smaller aircraft could be piggybacked on a larger one, released at altitude, and then continue under its own power. Such a system would allow the upper aircraft to carry heavier loads and achieve greater range.

The Air Ministry seemingly accepted the idea, as Specification 13/33 was drawn up to cover the design of such an aircraft. It was agreed that the cost of development would be shared equally between Imperial Airways and the Ministry, with Short Brothers contracted to undertake the design work. The result was the Short Mayo Composite, an aircraft made up of two components: a large four-engined seaplane on the bottom and a smaller four-engined floatplane mounted on top.

The lower component, the Short S.21 Maia, acted as the carrier aircraft, tasked with lifting the smaller aircraft—known as Mercury—into the air.

The Carrier – Short S.21 Maia:

Although Maia was derived from the Short Empire flying boats, it featured several key differences. Its wing area was 250 square feet larger than that of the Empires, and the sides of its hull had tumblehome (a slight inward curve toward the top), whereas the Empires’ hulls were straight. The four Bristol Pegasus X engines of the Maia were moved further away from the wing root to avoid the upper planes floats, and the rear of the fuselage was swept up, raising the tailplane in relation to the wing. Finally, Ontop of the Maia a pylon structure was added to allow the ability to carry another aircraft. Maia could carry up to 18 passengers and made its maiden flight on July 27, 1937 - initially without its pylon, which was added shortly afterwards.

The Upper Aircraft – Short S.20 Mercury:

The upper component was the Short S.20 Mercury, an all-metal floatplane designed by Arthur Gouge, Short Brothers’ chief designer, and R.H Mayo It was powered by four Napier Rapier H engines and measured 51 feet in length with a wingspan of 73 feet. Desgined to operate at 10,000ft, the Mercury had a maximum cruising speed of around 190mph, could carry a payload of 1,000lbs and was operated by a crew of two. With Captain John Lankester Parker at the controls, the aircraft made its first flight on September 5, 1937, lasting 15 minutes. Early testing indicated that the Mercury’s performance was better than expected.

The Mercury was secured to the Maia using three locks: two manually controlled and one automatic. The pilot of the Maia and the pilot of the Mercury each had control over one release lock respectively. The third lock was an automatic spring-loaded lock which would automatically unlock once a force of 13,000 Newtons was reached. When released the Maia would naturally drop away and the Mercury would lift up, allowing the aircraft to safely separate and stay out of each other's way.

The first successful flight of the combined aircraft occurred on January 20, 1938, followed by the first successful in-flight separation on February 6, 1938. After a series of test flights, the pair were ready for their first long-distance mission.

The Transatlantic Flight:

On July 21, 1938, the Short Mayo Composite departed Southampton. Mercury was loaded with 600lbs of cargo — newspapers, press photographs, and newsreel film — while Maia carried 10 passengers and their luggage. After take-off, the two aircraft separated over Foynes, Ireland. The Maia would land at Foynes, while the Mercury continued westward alone on its transatlantic journey.

After 20 hours and 21 minutes, the Mercury made it to Montreal, Canda where it landed with 80 gallons of fuel onboard. This marked the first commercial non-stop east-to-west transatlantic flight by a heavier-than-air aircraft

The Short Mercury detaches from the Short Maia.

Record-Breaking Flight to South Africa:

The Short Composite aircraft made a number of other flights including a routine Imperial Airways mail flight to Alexandria. In late 1938 it would attempt a record-breaking flight from Britain to South Africa.

To undertake this flight, the Mercury had its floats strengthened and sealed, allowing it to carry extra fuel. On October 6, 1938, the pair took off from Britain, separating over Dundee, Scotland.

Battling strong headwinds and thunderstorms, the Mercury flew for just over 42 hours, covering a distance of 9,652 km (6,000 miles) before landing on the Orange River near Alexander Bay, South Africa. This feat set a new world distance record for seaplanes, a record that still stands today.

The Short Mayo Composite Aircraft during take-off.

Conclusion:

The outbreak of the Second World War brought an end to further experiments with the Composite. Mercury was transferred to Felixstowe, where it was used by No. 320 (Netherlands) Squadron RAF. In August 1940 it was registered to BOAC, before returning to Short Brothers in August 1941, where it was eventually dismantled for scrap.

For the Maia, it lasted until May 1941 being destroyed by a German bombing raid while residing in Poole Harbour.

Only one Short Mayo Composite was ever built. Although its operational life was brief, the concept represented a remarkable and forward-thinking experiment in aviation engineering. NASA would utilize the concept some several decades later to transport their Space Shuttles on the back of a Boeing 747.

While the age of the flying boat soon gave way to larger land-based airliners capable of crossing the Atlantic unassisted, the Short Mayo Composite remains a fascinating and daring chapter in the history of flight.