The Shorts-Mayo Combination was an attempt to cross the Atlantic with a useful load.
A recent article on “Mother Ships” prompted recollection of a much earlier pairing of two aircraft—a Shorts Empire Class flying boat and a smaller Shorts four-engine float plane.
In the 1930s, the challenge was to design an airplane that could make the Atlantic Crossing carrying revenue generating passengers or mail. The Shorts Empire Class flying boats, with a crew of five, could carry up to 18 passengers and more than 4,000 pounds of cargo and mail, and it was a profitable aircraft on the European side of the Atlantic. To make the crossing from Great Britain to North America, however, passengers and cargo had to be replaced with fuel.
Aircraft engineers knew that an airplane could maintain flight at greater weights than it could take off with. Major Robert H. Mayo, Technical General Manager at Imperial Airways proposed the Shorts-Mayo Composite with a smaller float plane, that carried 1000 pounds of mail, mounted on top of a modified version Shorts Empire class flying boat. The larger flying boat would lift the float plane to its cruising altitude, they would separate, and Mercury would proceed to North America.
The pair of aircraft consisted of a Shorts S.21 Empire Class flying boat, the “Maia,” fitted with a structure that supported the smaller Shorts S.20 “Mercury” float plane on top. The bottom of the fuselage/hull of the redesigned flying boat had a flared bottom making it wider than the rest of the fuselage. This provided more planing surface under the hull, necessary for the greater takeoff weight. Other design changes included larger control surfaces, a larger wing with the engines mounted farther from the hull to make room for Mercury’s floats.
Mercury was a smaller aircraft, crewed by a single pilot and a navigator. During takeoff, Mercury’s flight controls were locked in a neutral position. Only the trim tabs were operational. Mercury was attached to Maia at three points. The attaching mechanism allowed some movement so that the pitch of the float plane could be adjusted in flight. Three lights in the cockpit indicated when Mercury was in fore-to-aft balance.
Upon reaching Mercury’s separation altitude, the pilots first released two of the three attachments. The third attachment released automatically at 3000 pounds of force. When released, Mercury automatically climbed up and away and Maia dropped, providing safe separation.
The first flight test was made in February 1938, completing a successful separation. Additional tests were conducted over the next several months. The first operational flight with passengers in Maia and mail in Mercury was flown in July 1938. After separation, Mercury continued west to North America—a flight that took more than 20 hours. Meanwhile, Maia turned east toward Europe with 10 passengers and luggage.
This, the only Shorts-Mayo Composite built, continued to operate into December 1938. During this time, the Mayo Composite also launched Mercury on flights to Alexandria, Egypt and South Africa. By the end of 1938 longer range flying boats had been developed with more powerful engines and higher payloads, making the combination unnecessary.
The fates of both aircraft were determined by World War two. Maia was destroyed 1941 in a German bombing raid at her mooring in Poole Harbour, while Mercury was used as a reconnaissance aircraft. It was soon replaced by newer aircraft, after which it returned to Shorts factory where it was broken up to recycle the aluminum needed for the war effort.
A Century of Flight, Ray Bonds, Salamander Books Ltd, 2003