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 designed to operate at night between

New York City New York, often called New York City (NYC), is the most populous city in the United States, located at the southern tip of New York State on one of the world's largest natural harbors. The city comprises five boroughs, each coextensive w ...

and

Chicago Chicago is the List of municipalities in Illinois, most populous city in the U.S. state of Illinois and in the Midwestern United States. With a population of 2,746,388, as of the 2020 United States census, 2020 census, it is the List of Unite ...

. 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, established in 1792. From 1872 to 1971, it was officially in the form of a Cabinet of the Un ...

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 40 species of coniferous evergreen trees in the family Pinaceae, found in the northern temperate and boreal ecosystem, boreal (taiga) regions of the Northern hemisphere. ''Picea'' ...

and

plywood Plywood is a composite material manufactured from thin layers, or "plies", of wood veneer that have been stacked and glued together. It is an engineered wood from the family of manufactured boards, which include plywood, medium-density fibreboa ...

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

fuselage The fuselage (; from the French language, French ''fuselé'' "spindle-shaped") is an aircraft's main body section. It holds Aircrew, crew, passengers, or cargo. In single-engine aircraft, it will usually contain an Aircraft engine, engine as wel ...

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 struts, 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 struts, 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 roll (or movement around ...

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 weight of an aircraft or flying animal divided by the area of its wing. The stalling speed, takeoff speed and landing speed of an aircraft are partly determined by its wing loading. The faster an airc ...

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_cooling#Internal_combustion_engines, water-cooled 45° V12 engine, V-12 engine, displacing and making , designed for a high power-to-weight ratio and ease of mass production. It was designed principally as ...

water-cooled

V12 engine A V12 engine is a twelve-Cylinder (engine), cylinder Internal combustion engine#Reciprocating engines, piston engine where two banks of six cylinders are arranged in a V engine, V configuration around a common crankshaft. V12 engines are more c ...

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

radiator A radiator is a heat exchanger 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, on the front part of an aircraft, spacecraft, or submersible, from which a pilot controls the vehicle. The cockpit of an aircraft contains flight instruments on an instrument panel, and the controls th ...

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 stabilizer, is a small lift (force), 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 ...

mounted on top of the fuselage carrying

elevator An elevator (American English) or lift (Commonwealth English) is a machine that vertically transports people or freight between levels. They are typically powered by electric motors that drive traction cables and counterweight systems suc ...

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. F ...

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 taxiing, takeoff or landing. For aircraft, it is generally needed for all three of these. It was also formerly called ''alighting gear'' by some manufacturers, s ...

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