The Aerial Service Mercury Senior, Aerial Mercury Senior or just Mercury Senior was a US

biplane A biplane is a fixed-wing aircraft with two main wings stacked one above the other. The first powered, controlled aeroplane to fly, the Wright Flyer, used a biplane wing arrangement, as did many aircraft in the early years of aviation. While ...

mailplane A mail plane is an aircraft used for carrying mail. Aircraft that were purely mail planes existed almost exclusively prior to World War II. Because early aircraft were too underpowered to carry cargoes, and too costly to run any "economy class" ...

designed to operate at night between

New York City New York, often called New York City or NYC, is the List of United States cities by population, most populous city in the United States. With a 2020 population of 8,804,190 distributed over , New York City is also the L ...

and

Chicago (''City in a Garden''); I Will , image_map = , map_caption = Interactive Map of Chicago , coordinates = , coordinates_footnotes = , subdivision_type = Country , subdivision_name ...

. A different, smaller, lower wing improved its performance for daytime flights. One was built and used by the

United States Post Office Department The United States Post Office Department (USPOD; also known as the Post Office or U.S. Mail) was the predecessor of the United States Postal Service, in the form of a Cabinet department, officially from 1872 to 1971. It was headed by the postmas ...

Design and development

The Mercury Senior was a single bay biplane without stagger and with dihedral only on the lower wing. Both wings were rectangular in plan out to blunted tips and had constant, thick sections; they were built around twin

spruce A spruce is a tree of the genus ''Picea'' (), a genus of about 35 species of coniferous evergreen trees in the family Pinaceae, found in the northern temperate and boreal (taiga) regions of the Earth. ''Picea'' is the sole genus in the subfami ...

and

plywood Plywood is a material manufactured from thin layers or "plies" of wood veneer that are glued together with adjacent layers having their wood grain rotated up to 90 degrees to one another. It is an engineered wood from the family of manufactured ...

spar SPAR, originally DESPAR, styled as DE SPAR, is a Dutch multinational that provides branding, supplies and support services for independently owned and operated food retail stores. It was founded in the Netherlands in 1932, by Adriaan van Well, ...

s and fabric covered. The upper wing was held over the

fuselage The fuselage (; from the French ''fuselé'' "spindle-shaped") is an aircraft's main body section. It holds crew, passengers, or cargo. In single-engine aircraft, it will usually contain an engine as well, although in some amphibious aircraft t ...

by a pair of N-form

cabane strut In aeronautics, bracing comprises additional structural members which stiffen the functional airframe to give it rigidity and strength under load. Bracing may be applied both internally and externally, and may take the form of strut, which act in ...

s. The

interplane strut In aeronautics, bracing comprises additional structural members which stiffen the functional airframe to give it rigidity and strength under load. Bracing may be applied both internally and externally, and may take the form of strut, which act in ...

s were in parallel pairs, assisted by the usual wire cross-bracing. There were externally interconnected

ailerons An aileron (French for "little wing" or "fin") is a hinged flight control surface usually forming part of the trailing edge of each wing of a fixed-wing aircraft. Ailerons are used in pairs to control the aircraft in Flight dynamics, roll (or ...

on both upper and lower wings. The novel feature of the Senior was the choice of lower wing: two were available, one with a shorter span than the upper wing and one with a longer span. The latter increased the total wing area by about 27% and decreased the

wing loading In aerodynamics, wing loading is the total mass of an aircraft or flying animal divided by the area of its wing. The stalling speed of an aircraft in straight, level flight is partly determined by its wing loading. An aircraft or animal with a ...

by 19%. Lower wing loadings decrease aircraft speeds, so the longer span set provided lower night landing speeds at the price of reduced cruising speed. The fuselage of the Senior was a welded steel tube frame, its forward part covered with light metal and the rear with plywood. Externally it was flat-sided with rounded upper decking. A

Liberty L-12 The Liberty L-12 is an American water-cooled 45° V-12 aircraft engine displacing and making designed for a high power-to-weight ratio and ease of mass production. It saw wide use in aero applications, and, once marinized Marinisation (also m ...

water-cooled

V12 engine A V12 engine is a twelve-cylinder piston engine where two banks of six cylinders are arranged in a V configuration around a common crankshaft. V12 engines are more common than V10 engines. However, they are less common than V8 engines. The fi ...

in the nose drove a two-bladed, steel Curtiss propeller. Its honeycomb

radiator Radiators are heat exchangers used to transfer thermal energy from one medium to another for the purpose of cooling and heating. The majority of radiators are constructed to function in cars, buildings, and electronics. A radiator is always a ...

was ahead of the engine, which had long exhaust pipes on both sides of the fuselage to take the emissions past the pilot. His open

cockpit A cockpit or flight deck is the area, usually near the front of an aircraft or spacecraft, from which a Pilot in command, pilot controls the aircraft. The cockpit of an aircraft contains flight instruments on an instrument panel, and the ...

was well behind the

trailing edge The trailing edge of an aerodynamic surface such as a wing is its rear edge, where the airflow separated by the leading edge meets.Crane, Dale: ''Dictionary of Aeronautical Terms, third edition'', page 521. Aviation Supplies & Academics, 1997. ...

of the wing. Up to of mail was stored in the space between engine and cockpit. The rear surfaces of the Senior were large, with a rectangular, strut-braced

tailplane A tailplane, also known as a horizontal stabiliser, is a small lifting surface located on the tail (empennage) behind the main lifting surfaces of a fixed-wing aircraft as well as other non-fixed-wing aircraft such as helicopters and gyroplane ...

mounted on top of the fuselage carrying

elevator An elevator or lift is a wire rope, cable-assisted, hydraulic cylinder-assisted, or roller-track assisted machine that vertically transports people or freight between floors, levels, or deck (building), decks of a building, watercraft, ...

s hinged at the end of it. Its wire-braced, tall, broad, rounded

fin A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foils that produce lift or thrust, or provide the ability to steer or stabilize motion while traveling in water, air, or other fluids. Fin ...

had a straight-edged unbalanced rudder which, like the elevators, overhung the extreme tail. The Senior's

landing gear Landing gear is the undercarriage of an aircraft or spacecraft that is used for takeoff or landing. For aircraft it is generally needed for both. It was also formerly called ''alighting gear'' by some manufacturers, such as the Glenn L. Martin ...

was fixed and conventional with wheels, well apart, on a single axle held on two V-struts; the forward struts of the Vs contained shock absorbers. An angled, flexible tailskid, with another small shock absorber between its ends, projected beyond the extreme tail. For night landings a pair of searchlights in streamlined housings were attached below the lower wings, under the feet of the interplane struts.

Operational history

The sole Senior flew for the first time in 1925 and was used by the Post Office until 1928.

Operators

* United States Post Office Department

Specifications (night flight configuration)

References

{{reflist, refs= {{cite journal , last=Serryer , first=J. , date=17 July 1925, title=L'avion postal "Aérial Mercury" , journal=Les Ailes, issue=213 , pages=2, url=http://gallica.bnf.fr/ark:/12148/bpt6k6568245t/f2 {{cite web , url=http://www.aerofiles.com/_ma.html, title=Aerofiles - Mercury , accessdate=28 April 2017 1920s United States mailplanes Biplanes Single-engined tractor aircraft Aircraft first flown in 1925