VTOL A vertical take-off and landing (VTOL) aircraft is one that can take off and land vertically without relying on a runway. This classification can include a variety of types of aircraft including helicopters as well as thrust-vectoring fixed-win ...

aircraft An aircraft is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines ...

tail The tail is the section at the rear end of certain kinds of animals’ bodies; in general, the term refers to a distinct, flexible appendage to the torso. It is the part of the body that corresponds roughly to the sacrum and coccyx in mammals, r ...

Nikola Tesla Nikola Tesla ( ; ,"Tesla"
''

Nazi Germany Nazi Germany (lit. "National Socialist State"), ' (lit. "Nazi State") for short; also ' (lit. "National Socialist Germany") (officially known as the German Reich from 1933 until 1943, and the Greater German Reich from 1943 to 1945) was ...

during the

Second World War World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...

. Development of such aircraft spiked during the late 1940s and 1950s, as aircraft designers and defence planners alike recognised the potential value of fixed-wing aircraft that could perform both a vertical take-off and vertical landing while also transitioning into and out of conventional flight. Inherent problems with tail-sitter aircraft were poor pilot visibility and control difficulties, especially during vertical descent and landing. Programmes to develop manned tail-sitters were typically terminated in the form of the more practical

thrust vectoring Thrust vectoring, also known as thrust vector control (TVC), is the ability of an aircraft, rocket, or other vehicle to manipulate the direction of the thrust from its engine(s) or motor(s) to control the attitude or angular velocity of the v ...

approach, as used by aircraft such as the

Hawker Siddeley Harrier The Hawker Siddeley Harrier is a British military aircraft. It was the first of the Harrier series of aircraft and was developed in the 1960s as the first operational ground attack and reconnaissance aircraft with vertical/short takeoff an ...

and

Yakovlev Yak-38 The Yakovlev Yak-38 (russian: Яковлев Як-38; NATO reporting name: "Forger") was the Soviet Naval Aviation's only operational VTOL strike fighter aircraft in addition to being its first operational carrier-based fixed-wing aircraft. It w ...

.

Description

A tail-sitter sits vertically on its tail for takeoff and landing, then tilts the whole aircraft forward for horizontal flight. This is very different from the many other kinds of

VTOL A vertical take-off and landing (VTOL) aircraft is one that can take off and land vertically without relying on a runway. This classification can include a variety of types of aircraft including helicopters as well as thrust-vectoring fixed-win ...

technologies, which have horizontally-oriented fuselages. Tail-sitters change fuselage orientation after take-off. They start off with the back of the aircraft to the ground (...a vertical orientation), and then reorient to a horizontal orientation in flight. Some tail-sitters then landed conventionally in horizontally-oriented configuration, while others had a much more ambitious goal of landing vertically with the aircraft's back to the ground, a highly hazardous procedure for many reasons, prime of which was increased fuel consumption and limited pilot visibility.

History

Early work

The concept of a tail-sitting aircraft can be attributed to originate with the inventor

Nikola Tesla Nikola Tesla ( ; ,"Tesla"
''

patent A patent is a type of intellectual property that gives its owner the legal right to exclude others from making, using, or selling an invention for a limited period of time in exchange for publishing an enabling disclosure of the invention."A p ...

during 1928. However, no immediate attempt to implement this concept into a functional aircraft would emerge for almost two decades. During the

Second World War World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...

,

Nazi Germany Nazi Germany (lit. "National Socialist State"), ' (lit. "Nazi State") for short; also ' (lit. "National Socialist Germany") (officially known as the German Reich from 1933 until 1943, and the Greater German Reich from 1943 to 1945) was ...

worked on the Focke-Wulf ''Triebflügel'' (wing-driven) fighter that incorporated the tail-sitter concept into its design. It featured three wings that were mounted radially as a rotor on a rotating section of the fuselage, these were driven by small

jet engine A jet engine is a type of reaction engine discharging a fast-moving jet of heated gas (usually air) that generates thrust by jet propulsion. While this broad definition can include rocket, Pump-jet, water jet, and hybrid propulsion, the term ...

s positioned on the wingtips to propel the aircraft via this wing rotation. For takeoff and landing, it would fly vertically (akin to a

helicopter A helicopter is a type of rotorcraft in which lift and thrust are supplied by horizontally spinning rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forward, backward and laterally. These attributes ...

) before tilting over horizontally to fly as a self-propelled wing generating both lift and thrust. The contemporary

Heinkel Lerche The Heinkel Lerche ( en, Lark) was the name of a set of project studies made by German aircraft designer Heinkel in 1944 and 1945 for a revolutionary VTOL fighter and ground-attack aircraft. The ''Lerche'' was an early coleopter design. It would ...

project had an annular wing forming a duct around a conventional propeller, and in the transition from vertical to forward flight the lift would have transferred to the wing.Sharp, Dan. ''Luftwaffe: Secret Weapons of the Third Reich.'' Mortons, 2015. pp. 98-101.

Cold War era

During the 1950s, aircraft designers around the world engaged in programmes to develop fixed-wing aircraft that could not only perform both a vertical take-off and vertical landing, but transition into and out of conventional flight as well. As observed by the aviation author Francis K. Mason, a combat aircraft that possessed such qualities would have effectively eliminate the traditional reliance on relatively vulnerable runways by taking off and landing vertically as opposed to the conventional horizontal approach.Mason 1967, p. 3. Accordingly, the development of viable

vertical take-off and landing A vertical take-off and landing (VTOL) aircraft is one that can take off and land vertically without relying on a runway. This classification can include a variety of types of aircraft including helicopters as well as thrust-vectoring fixed-win ...

(VTOL) aircraft was particularly attractive to military planners of the early

postwar In Western usage, the phrase post-war era (or postwar era) usually refers to the time since the end of World War II. More broadly, a post-war period (or postwar period) is the interval immediately following the end of a war. A post-war period ...

era. As the

thrust-to-weight ratio Thrust-to-weight ratio is a dimensionless ratio of thrust to weight of a rocket, jet engine, propeller engine, or a vehicle propelled by such an engine that is an indicator of the performance of the engine or vehicle. The instantaneous thrust-to- ...

of

turbojet The turbojet is an airbreathing jet engine which is typically used in aircraft. It consists of a gas turbine with a propelling nozzle. The gas turbine has an air inlet which includes inlet guide vanes, a compressor, a combustion chamber, and ...

engines increased sufficiently for a single engine be able to lift an aircraft, designers began to investigate ways of maintaining stability while an aircraft was flying in the VTOL stage of flight. One company that opted to engage in VTOL research was the French engine manufacturer

SNECMA Safran Aircraft Engines, previously Snecma (''Société nationale d'études et de construction de moteurs d'aviation'') or Snecma Moteurs, is a French aerospace engine manufacturer headquartered in Courcouronnes and a subsidiary of Safran. It ...

who, beginning in 1956, built a series of wingless test rigs called the Atar Volant. Only the first of these was unpiloted and the second flew freely, both stabilized by gas jets on outrigger pipes The third had a tilting seat to allow the pilot to sit upright when 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 ...

was level and had the lateral air intakes planned for the free flying aircraft, though it always operated attached to a movable cradle. The pilot for these experiments was Auguste Morel. However, the Atar Volant was not an end onto itself; its long term purpose was to serve as precursors to a larger fixed-wing aircraft. Independently of this work, substantial influence on the direction of development came from the Austrian design engineer Helmut von Zborowski, who had designed an innovative doughnut-shaped

annular wing A closed wing is a wing that effectively has two main planes which merge at their ends so that there are no conventional wing tips. Closed wing designs include the annular wing (commonly known as the cylindrical or ring wing), the joined wing, ...

that could function "as power plant, airframe of a flying wing aircraft and drag-reducing housing". It was theorised that such a wing could function as a

ramjet A ramjet, or athodyd (aero thermodynamic duct), is a form of airbreathing jet engine that uses the forward motion of the engine to produce thrust. Since it produces no thrust when stationary (no ram air) ramjet-powered vehicles require an ass ...

engine and propel an aircraft at

supersonic Supersonic speed is the speed of an object that exceeds the speed of sound ( Mach 1). For objects traveling in dry air of a temperature of 20 °C (68 °F) at sea level, this speed is approximately . Speeds greater than five times ...

speeds, suitable for an

interceptor aircraft An interceptor aircraft, or simply interceptor, is a type of fighter aircraft designed specifically for the defensive interception role against an attacking enemy aircraft, particularly bombers and reconnaissance aircraft. Aircraft that are cap ...

. SNECMA's design team decided to integrate this radical annual wing design into their VTOL efforts. Accordingly, from this decision emerged the basic configuration of the C.450 Coléoptère. In December 1958, the Coléoptère first left the ground under its own power, albeit while attached to a gantry. Several challenging flight characteristics were observed, such as the tendency for the aircraft to slowly spin on its axis while in a vertical hover; its pilot also noted that the vertical speed indicator was unrealistic and that the controls were incapable of steering the aircraft with precision while performing the critical landing phase. Dead-stick landings were deemed to be an impossibility. One of aircraft's flights involved a public display of its hover performance before an assembled audience. The eye-catching design of the Coléoptère rapidly made waves in the public conscious, even intentionally; author Jeremy Davis observed that the aircraft had even influenced intentional efforts, having allegedly motived the

United States Navy The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage ...

to contract American helicopter manufacturer

Kaman Aircraft Kaman Corporation is an American aerospace company, with headquarters in Bloomfield, Connecticut. It was founded in 1945 by Charles Kaman. During the first ten years the company operated exclusively as a designer and manufacturer of several h ...

to design its own annular-wing vehicle, nicknamed the Flying Barrel. Accordingly, the United States experimented with its own tail-sitters, typically involving

propeller A propeller (colloquially often called a screw if on a ship or an airscrew if on an aircraft) is a device with a rotating hub and radiating blades that are set at a pitch to form a helical spiral which, when rotated, exerts linear thrust upon ...

-driven design configurations with relatively conventional fixed wings. The

Convair XFY Pogo The Convair XFY Pogo was an experiment in vertical takeoff and landing (VTOL) tail-sitter. The Pogo had delta wings and three-bladed contra-rotating propellers powered by a turboprop engine. It was intended to be a high-performance fighter aircr ...

was one such aircraft, featuring a

delta wing A delta wing is a wing shaped in the form of a triangle. It is named for its similarity in shape to the Greek uppercase letter delta (Δ). Although long studied, it did not find significant applications until the Jet Age, when it proved suitabl ...

with

cruciform tail __NOTOC__ The cruciform tail is an aircraft empennage configuration which, when viewed from the aircraft's front or rear, looks much like a cross. The usual arrangement is to have the horizontal stabilizer intersect the vertical tail somewhere ...

configuration; initial test flights were conducted inside of a naval

airship hangar Airship hangars (also known as airship sheds) are large specialized buildings that are used for sheltering airships during construction, maintenance and storage. Rigid airships always needed to be based in airship hangars because weathering was a s ...

at Moffett Field in Mountain View, California. The XFY successfully demonstrated the full transition between flight modes on 5 November 1954. A somewhat similar aircraft was the

Lockheed XFV The Lockheed XFV (sometimes referred to as the "Salmon") was an American experimental tailsitter prototype aircraft built by Lockheed in the early 1950s to demonstrate the operation of a vertical takeoff and landing (VTOL) fighter for protect ...

''Salmon'', which paired a straight wing with an

X tail The empennage ( or ), also known as the tail or tail assembly, is a structure at the rear of an aircraft that provides stability during flight, in a way similar to the feathers on an arrow.Crane, Dale: ''Dictionary of Aeronautical Terms, third e ...

; however, the XFV never achieved the crucial flight transition. However, it became evident during flight testing that such VTOL aircraft would be flown only by the most experienced pilots, even if all technical problems were disregarded; thus, it was not feasible to place VTOL fighters—as previously hoped for—on every ship. Also, whereas jet-engined fighters had top speeds that approached Mach 2, the turboprop VTOL fighter was at a disadvantage due to its maximum speed being below Mach 1. As a result of these circumstances, work on the XFY was halted. During 1955, the United States commenced flight testing of a jet-powered design, the Ryan X-13 Vertijet. Two prototypes were constructed, both of which flew, made successful transitions to and from horizontal flight, and landed. The X-13's final test flight was conducted near

Washington DC ) , image_skyline = , image_caption = Clockwise from top left: the Washington Monument and Lincoln Memorial on the National Mall, United States Capitol, Logan Circle, Jefferson Memorial, White House, Adams Morgan, ...

during 1957. An inherent problem with all these tail-sitter designs was poor pilot visibility, especially of the ground, during vertical descent and landing. Ultimately, most work on applying the concept towards manned aircraft were abandoned upon the arrival of more practical form of VTOL appeared, in the form of

thrust vectoring Thrust vectoring, also known as thrust vector control (TVC), is the ability of an aircraft, rocket, or other vehicle to manipulate the direction of the thrust from its engine(s) or motor(s) to control the attitude or angular velocity of the v ...

, as used by production aircraft such as the

Hawker Siddeley Harrier The Hawker Siddeley Harrier is a British military aircraft. It was the first of the Harrier series of aircraft and was developed in the 1960s as the first operational ground attack and reconnaissance aircraft with vertical/short takeoff an ...

and

Yakovlev Yak-38 The Yakovlev Yak-38 (russian: Яковлев Як-38; NATO reporting name: "Forger") was the Soviet Naval Aviation's only operational VTOL strike fighter aircraft in addition to being its first operational carrier-based fixed-wing aircraft. It w ...

.Brown 1970, p. 81. An

unmanned aerial vehicle An unmanned aerial vehicle (UAV), commonly known as a drone, is an aircraft without any human pilot, crew, or passengers on board. UAVs are a component of an unmanned aircraft system (UAS), which includes adding a ground-based controller ...

(UAV) does not suffer the problem of pilot attitude. The

Dornier Aerodyne The Dornier Aerodyne (also referred to as "Lippisch-Dornier Aerodyne"KRISTINA KIRKLIAUSKAITE,Lippisch-Dornier Aerodyne: Wingless and tailless aircraft, ''Aerotime,'' retrieved 19 March 2021.) was a wingless VTOL unmanned aircraft. Conceived by Al ...

is of ducted-fan configuration similar to a

coleopter A coleopter is a type of VTOL aircraft design that uses a ducted fan as the primary fuselage of the entire aircraft. Generally they appear to be a large barrel-like extension at the rear, with a small cockpit area suspended above it. Coleopters ...

, and a test UAV flew successfully in hover mode in 1972, before development was discontinued. Another contemporary UAV project was the NSRDC BQM-108 that was developed by the

United States Navy The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage ...

; although work was discontinued almost immediately after its single successful test flight.Eilertson 1977. During the 1970s, several studies and

wind tunnel Wind tunnels are large tubes with air blowing through them which are used to replicate the interaction between air and an object flying through the air or moving along the ground. Researchers use wind tunnels to learn more about how an aircraft ...

models were made of a tail-sitting version of the

General Dynamics F-16 Fighting Falcon The General Dynamics F-16 Fighting Falcon is a single-engine Multirole combat aircraft, multirole fighter aircraft originally developed by General Dynamics for the United States Air Force (USAF). Designed as an air superiority day fighter, it ...

that was intended for use onboard ships; however, it was decided not to pursue further development of the concept due to the large thrust requirement involved, as well as the need for extensive apparatus to handle take-off and landing.

In the present

At present, most of the tail sitter projects or proposals fall under the category of

unmanned aircraft An unmanned aerial vehicle (UAV), commonly known as a drone, is an aircraft without any human pilot, crew, or passengers on board. UAVs are a component of an unmanned aircraft system (UAS), which includes adding a ground-based controller ...

such as Bell Apt or

Northrop Grumman Tern Tactically Exploited Reconnaissance Node (TERN), a joint program between DARPA and the U.S. Navy's Office of Naval Research (ONR), seeks to greatly increase the effectiveness of forward-deployed small-deck ships such as destroyers and frigates by ...

.

List of tail-sitters

References

Citations

Bibliography

* Allen, Francis J. "Bolt Upright: Convair's and Lockheed's VTOL fighters". ''Air Enthusiast'' (Key Publishing) Volume 127, January/February 2007, pp. 13–20. ISSN 0143-5450. * Brown, Kevin
"The Plane That Makes Airfields Obsolete."
''Popular Mechanics'', 133(6), June 1970, pp. 80–83. * * * Taylor, John W. R. & Michael J. H. ''Jane's Pocket Book of Research and Experimental Aircraft''. Collier Books: New York, 1977 . * Wilson, Stewart. ''Combat Aircraft since 1945''. Fyshwick, Australia: Aerospace Publications, 2000. . * Winchester, Jim. "Lockheed XFV-1 Salmon." ''Concept Aircraft: Prototypes, X-Planes and Experimental Aircraft''. Kent, UK: Grange Books plc., 2005. . {{Refend Tailsitter aircraft Aircraft configurations