Astounding Aerospace

Methods of Propulsion

The Propeller

An aircraft propeller, or airscrew, converts rotary motion from an engine or another power source, into a swirling slipstream which pushes the propeller forwards or backward. It comprises a rotating power-driven hub, to which are attached several radial airfoil-section blades such that the whole assembly rotates about a longitudinal axis.

1200px-Hercules.propeller.arp — Propellers of an RAF Hercules C.4

Three types of aviation engines used to power propellors include reciprocating engines (or piston engines), gas turbine engines, and electric motors.

The amount of thrust a propeller creates is determined by its disk area—the area in which the blades rotate. If the area is too small, efficiency is poor, and if the area is large, the propeller must rotate at very low speeds to avoid going supersonic and creating a lot of noise, and not much thrust. Because of this limitation, propellers are favored for planes that travel at below Mach 0.6, while jets are a better choice above that speed.

Reciprocating Engine

Reciprocating engines in aircraft have three main variants, radial, in-line and flat or horizontally opposed engine. The radial engine is a reciprocating type internal combustion engine configuration in which the cylinders “radiate” outward from a central crankcase like the spokes of a wheel and was commonly used for aircraft engines before gas turbine engines became predominant.

An inline engine is a reciprocating engine with banks of cylinders, one behind another, rather than rows of cylinders, with each bank having any number of cylinders, but rarely more than six, and maybe water-cooled.

A flat engine is an internal combustion engine with horizontally-opposed cylinders.

Gas Turbine

A turboprop gas turbine engine consists of an intake, compressor, combustor, turbine, and a propelling nozzle, which provide power from a shaft through a reduction gearing to the propeller. The propelling nozzle provides a relatively small proportion of the thrust generated by a turboprop.

Electric Motor

An electric aircraft runs on electric motors rather than internal combustion engines, with electricity coming from fuel cells, solar cells, ultracapacitors, power beaming, or batteries. Currently, flying electric aircraft are mostly experimental prototypes, including manned and unmanned aerial vehicles, but there are some production models on the market already.

Solar Impulse 2 (Solar-powered Aircraft)

Jet Engine

Jet aircraft are propelled by jet engines, which are used because the aerodynamic limitations of propellers do not apply to jet propulsion. These engines are much more powerful than a reciprocating engine for a given size or weight and are comparatively quiet and work well at higher altitude.

Variants of the jet engine include the ramjet and the scramjet, which rely on high airspeed and intake geometry to compress the combustion air, prior to the introduction and ignition of the fuel. Rocket motors provide thrust by burning a fuel with an oxidizer and expelling gas through a nozzle.

Turbofan

Most modern jet planes use turbofan jet engines, which balance the advantages of a propeller while retaining the exhaust speed and power of a jet.

This is essentially a ducted propeller attached to a jet engine, much like a turboprop, but with a smaller diameter. When installed on an airliner, it is efficient so long as it remains below the speed of sound (or subsonic). Jet fighters and other supersonic aircraft that do not spend a great deal of time supersonic also often use turbofans, but to function, air intake ducting is needed to slow the air down so that when it arrives at the front of the turbofan, it is subsonic.

Ramjet

A ramjet is a form of jet engine that contains no major moving parts and can be particularly useful in applications requiring a small and simple engine for high-speed use, such as with missiles. Ramjets require forward motion before they can generate thrust and so are often used in conjunction with other forms of propulsion, or with an external means of achieving sufficient speed.

Scramjet

A scramjet is a supersonic ramjet and aside from differences with dealing with internal supersonic airflow works like a conventional ramjet. This type of engine requires a very high initial speed in order to work.

Wingtip Vorticies

Wingtip vortices are circular patterns of rotating air left behind a wing as it generates lift. One wingtip vortex trails from the tip of each wing. Wingtip vortices are sometimes named trailing or lift-induced vortices because they also occur at points other than at the wing tips.

Wingtip vortices are associated with induced drag, the imparting of downwash, and are a fundamental consequence of three-dimensional lift generation.

Careful selection of wing geometry (in particular, aspect ratio), as well as of cruise conditions, are design and operational methods to minimize induced drag.

Effects and Mitigation

Wingtip vortices are associated with induced drag, an unavoidable consequence of three-dimensional lift generation.

The rotary motion of the air within the shed wingtip vortices (sometimes described as a “leakage”) reduces the effective angle of attack of the air on the wing.

As a result of this consequence, aircraft with a high lift-to-drag ratio is desirable, such as gliders or long-range airliners. Such wings, however, have disadvantages with respect to structural constraints and maneuverability, as evidenced by combat and aerobatic planes which usually feature short, stubby wings despite the efficiency losses.

images — The High Lift-to-Drag Ratio of a Glider

Another method of reducing induced drag is the use of winglets, as seen on most modern airliners. Winglets increase the effective aspect ratio of the wing, changing the pattern and magnitude of the vorticity in the vortex pattern.

Visible Vorticies

The cores of the vortices are sometimes visible because water present in them condenses from gas (vapor) to liquid, and sometimes even freezes, forming ice particles.

Condensation of water vapor in wingtip vortices is most common on aircraft flying at high angles of attack, such as fighter aircraft in high g maneuvers, or airliners taking off and landing on humid days.

Vorticy Hazards

Wingtip vortices can pose a hazard to aircraft, especially during the landing and takeoff phases of flight. The intensity or strength of the vortex is a function of aircraft size, speed, and configuration. The strongest vortices are produced by heavy aircraft, flying slowly, with wing flaps and landing gear retracted. Large jet aircraft can generate vortices that can persist for many minutes, drifting with the wind.

The hazardous aspects of wingtip vortices are most often discussed in the context of wake turbulence. If a light aircraft immediately follows a heavy aircraft, wake turbulence from the heavy aircraft can roll the light aircraft faster than can be resisted by use of ailerons. At low altitudes, during takeoff and landing, this can lead to an upset from which recovery is not possible. Air traffic controllers attempt to ensure adequate separation between departing and arriving aircraft by issuing wake turbulence warnings to pilots.

In general, to avoid vortices an aircraft is safer if its takeoff is before the rotation point of the airplane that took off before it. However, care must be taken to stay upwind from any vortices that were generated by the previous aircraft. On landing behind an airplane the aircraft should stay above the earlier one’s flight path and touch down further along the runway.

Seating Maps

An aircraft seat map or seating chart, is a diagram of the seat layout inside a passenger airliner. They are often published by airlines for informational purposes, and are of use to passengers for selection of their seat at booking or check-in.

Elements included in these seating maps include the basic seating layout, numbering and lettering of the seats, emergency exits, lavatories, galleys, bulkheads and wings of the aircraft.

Seat Designation

On most aircraft, the rightmost seats have letter designations HJK, skipping the letter I. This is because each seat has a row number followed by a letter; letters that confuse with numbers (I, O, Q, S, or Z) must be avoided.

Occasionally, aircraft with a seating structure of 2+2 may letter the seats as “ACDF” to keep with the standard of A/F being the window and C/D being aisle on short-haul aircraft (which generally have 3+3 seats).

Some airlines omit the row number 13, reputedly because of a widespread superstition that the number is unlucky.

Seating Arrangement

In very small aircraft Beechcraft 1900 there are only individual seats on each side of the aisle (1+1 seating).

download — 1+1 Seating on the Beechcraft 1900D

The widest narrow body aircraft such as the Airbus A320 family and Boeing 737 aircraft have six abreast seating in a 3+3 layout.

Asymmetrical layouts also exist, examples including the Embraer Regional Jet which has 1+2 seating while the Douglas DC-9 and Sukhoi Superjet 100 aircraft typically feature 2+3 seating.

On wide body-aircraft, the center block of seats between the aisles can have as many as 5 seats on planes like the layout on most McDonnell Douglas DC-10 and some Boeing 777 aircraft, although Boeing recommends the 3+3+3 over the 2+5+2 layout.

Very wide planes such as the Boeing 747 or the Airbus A380 have ten seats abreast, typically in a 3+4+3 layout.

A Look Into Stabilizers

Horizontal Stabilizers

A horizontal stabilizer is used to maintain the aircraft in longitudinal balance. It exerts a vertical force at a distance so the summation of pitch moments about the center of gravity is zero. This force exerted by the stabilizer changes according to the center of pressure, which is dependent on the aircraft’s lift coefficient and wing flaps deflection.

Another role of a horizontal stabilizer is to provide longitudinal static stability. Stability can be defined only when the vehicle is in trim; it refers to the tendency of the aircraft to return to the trimmed condition if it is disturbed.

Configurations of Horizontal Stabilizers

Conventional Tailplane:

In the conventional configuration, the horizontal stabilizer is a small horizontal tail or tailplane located to the rear of the aircraft. On many aircraft, the tailplane assembly consists of a fixed surface fitted with a hinged aft elevator surface.

Most airliners and transport aircraft feature a large, slow-moving trimmable tailplane which is combined with independently-moving elevators. The elevators are controlled by the pilot or autopilot and primarily serve to change the aircraft’s attitude, while the whole assembly is used to trim and stabilize the aircraft in the pitch axis.

Three-Surface Aircraft:

The tailplane is a stabilizer as in conventional aircraft; called the foreplane or canard, provides lift and serves as a balancing surface.

Some earlier three-surface aircraft, such as the Curtiss AEA June Bug or the Voisin 1907 biplane, were of the conventional layout with an additional front pitch control surface which was called “elevator” or sometimes “stabilization”.

Canard Aircraft:

In the canard configuration, a small wing, or foreplane, is located in front of the main wing.

In naturally unstable aircraft, the canard surfaces may be used as an active part of the artificial stability system, and are sometimes named horizontal stabilizers.

Tailless Aircraft:

Tailless aircraft lack a separate horizontal stabilizer. In a tailless aircraft, the horizontal stabilizing surface is part of the main wing.

Longitudinal stability in tailless aircraft is achieved by designing the aircraft so that its aerodynamic center is behind the center of gravity. This is generally done by modifying the wing design.

THE LAST BRITISH AIRWAYS CONCORDE FLIGHT TO TAKE OFF FROM HEATHROWLEAVES THE AIRPORT IN LONDON. — British Airways’ Concorde

Vertical Stabilizers

A vertical stabilizer provides directional (or yaw) stability and usually comprises a fixed fin and movable control rudder hinged to its rear edge. Sometimes there is no hinge and the whole fin surface is pivoted for both stability and control.

When an aircraft flies into a horizontal gust of wind, yaw stability causes the aircraft to turn into the wind rather than in the same direction.

If an aircraft does not have a vertical stabilizer than that aircraft is almost unmaneuverable.

A Very Canadian Airline

Timeline:

Trans-Canada Air Lines (1930s to 1960s):

The predecessor of Air Canada, Trans-Canada Air Lines (TCA), was created by federal legislation as a subsidiary of the Canadian National Railway (CNR) on April 11th, 1937.

Using $5 million in Crown seed money, two Lockheed Model 10 Electrasand one Boeing Stearman biplane was purchased from Canadian Airways and experienced airline executives from United Airlines and Delta Airlines were brought in.

Passenger flights began on 1 September 1937, with an Electra carrying two passengers and mail from Vancouver to Seattle, a $14.20 round trip. Transcontinental routes from Montreal to Vancouver began on 1 April 1939, and by January 1940, the airline had grown to about 579 employees.

By 1964, TCA had grown to become Canada’s national airline and on January 1st 1965, its name was officially changed to Air Camada.

Early Years (1970s to 1980s):

During the 1970s government regulations ensured Air Canada’s dominance over domestic regional carriers and rival CP Air. Air Canada’s fares were subject to regulation by the government.

In 1976, with reorganization at CNR, Air Canada became an independent Crown corporation. The Air Canada Act of 1978 ensured that the carrier would compete on a more equal footing with rival regional airlines and CP Air, and ended the government’s direct regulatory control over the Airline.

The airline would later have a fleet expansion with the acquisition of Boeing 727, Boeing 747, and Lockheed Tristar jetliners.

In 1988 Air Canada was privatized, and 43% of shares were sold on the public market. Around the same time, CP Air had become Canadian Airlines International following its acquisition by Pacific Western Airlines.

On 7 December 1987, Air Canada became the first airline in the world with a fleet-wide non-smoking policy, and in 1989 became completely privatized.

Strategic Changes (1990s):

In the early 1990s, Air Canada encountered financial difficulties as the airline industry slumped in the aftermath of the Persian Gulf War. After hiring Delta Air Lines executive Hollis L. Harris as its CEO, Air Canada was able to recover and acquire new international flight routes. These routes included one from Canada to Osaka and 30 new flights between Canada and the US.

In May 1997, Air Canada became a founding member of the Star Alliance, with the airline launching codeshares with several of the alliance’s members.

On 2 September 1998, pilots for Air Canada launched the company’s first pilots’ strike, demanding higher wages. At the end of 1999, the Canadian government relaxed some of the aviation regulations, aimed at creating a consolidation of the Canadian airline industry.

Reorganization, Merges, and Modernization (2000s):

In January 2001, Air Canada acquired Canada’s second largest air carrier, Canadian Airlines, merging the latter’s operations, becoming the world’s twelfth-largest airline in the first decade of the 21st century.

To combat its deteriorating financial shape, Air Canada pursued an expedited merger strategy, but in summer 2000 integration efforts led to flight delays, luggage problems, and other frustrations. However, service improved following Air Canada officials’ pledge to do so by January 2001.

On 31 October 2004, the last Air Canada Boeing 747 flight landed in Toronto from Frankfurt as AC873, ending 33 years of 747 service with the airline. The Boeing 747-400 fleet was replaced by the Airbus A340 fleet.

On 19 October 2004, Air Canada unveiled a new aircraft color scheme and uniforms.

b787-8_2467 — Air Canada’s Livery (2004-2016)

On 9 November 2005, Air Canada agreed to renew its widebody fleet by purchasing 16 Boeing 777s, and 14 Boeing 787-8s. It placed options on 18 Boeing 777s and 46 Boeing 787-8s and -9s.

Deliveries of the 777s began in March 2007 and deliveries of the 787s began in May 2014. As the 777s and the 787s are delivered, the airline will gradually retire all Boeing 767s and Airbus A330s.

Air Canada has also taken delivery of 15 Embraer 175s and 45 Embraer 190s. These aircraft are being used to expand intra-Canada and Canada/USA routes.

Further Re-Branding and Fleet Modernizations (2010s):

On 9 February 2017, a new retro red and black aircraft livery was launched, to coincide with Air Canada’s 80th anniversary and Canada’s 150th anniversary of Confederation.

air canada new livery — Air Canada’s Livery (2017-)

Air Canada signed an agreement with Bombardier Aerospace to replace the E190s with Airbus A220/CSeries aircraft in 2019.

bombardier_airbus_cseries.jpg_large — Airbus A220-300

In July 2017, Air Canada reintroduced Premium Economy on its North American wide-body flights.

On 17 April 2018, Air Canada rebranded its international business class cabin as Air Canada Signature Class.

Slats

Slats are aerodynamic surfaces on the leading edge of the wings of fixed-wing aircraft which allow the wing to operate at a higher angle of attack when it is deployed. A higher coefficient of lift is produced as a result of angle of attack and speed, so by deploying slats an aircraft can fly at slower speeds, or take off and land in shorter distances. They are usually used while landing or performing maneuvers which take the aircraft close to the stall, but are usually retracted in normal flight to minimize drag.

Slats are one of several high-lift devices used on airliners, such as flap systems running along the trailing edge of the wing.

Types of Slats

Automatic

The spring-loaded slat lies flush with the wing leading edge, held in place by the force of the air acting on them. As the aircraft slows down, the aerodynamic force is reduced and the springs extend the slats.

Fixed

The slat is permanently extended. This is sometimes used on specialist low-speed aircraft or when simplicity takes precedence over speed.

Powered

The slat extension can be controlled by the pilot. This is commonly used on airliners.

Operation



The slat effect


The velocities at the leading edge of the downstream element are reduced due to the circulation of the upstream element thus reducing the pressure peaks of the downstream element.



The circulation effect


The circulation of the downstream element increases the circulation of the upstream element thus improving its aerodynamic performance.



The dumping effect


The discharge velocity at the trailing edge of the slat is increased due to the circulation of the main airfoil thus alleviating separation problems or increasing lift.



Off the surface pressure recovery



The deceleration of the slat wake occurs in an efficient manner, out of contact with a wall.



Fresh boundary layer effect


Each new element starts out with a fresh boundary layer at its leading edge. Thin boundary layers can withstand stronger adverse gradients than thick ones.

The slat has a counterpart found in the wings of some birds, the alula, a feather or group of feathers which the bird can extend under control of its “thumb”.

Cargo Aircraft

A cargo aircraft, also known as freight aircraft, freighter, airlifteror cargo jet, is a fixed-wing aircraft that is designed or converted for the carriage of cargo rather than passengers. Such aircraft usually do not incorporate passenger amenities and generally feature one or more large doors for loading cargo.

Aircraft designed for cargo flight usually have features that distinguish them from conventional passenger aircraft. These include a wide/tall fuselage cross-section, a high-wing to allow the cargo area to sit near the ground, a large number of wheels to allow it to land at unprepared locations, and a high-mounted tail to allow cargo to be driven directly into and off the aircraft.

History

Aircraft were put to use carrying cargo in the form of “air mail” as early as 1911. Although the earliest aircraft were not designed primarily as cargo carriers, by the mid-1920s aircraft manufacturers were designing and building dedicated cargo aircraft.

The World War II German design, the Arado Ar 232 was the first purpose built cargo aircraft. The Ar 232 was intended to supplant the earlier Junkers Ju 52 freighter conversions, but only a few were built.

Postwar Europe also served to play a major role in the development of the modern air cargo and air freight industry. It is during the Berlin Airlift at the height of the Cold War, when a massive mobilization of aircraft was undertaken by the West to supply West Berlin with food and supplies. To rapidly supply the needed numbers of aircraft, many older types, especially the Douglas C-47 Skytrain, were pressed into service.

Types of Cargo Aircraft

Derivatives of non-cargo aircraft

These types of cargo planes are transformations of passenger aircraft. They can be converted by installing a main deck cargo door with its control systems; upgrading floor beams for cargo loads, replacing passenger equipment and furnishings with new linings, ceilings, lighting, floors and drains.

Dedicated civilian cargo aircraft

A dedicated commercial air freighter is an airplane which has been designed from the beginning as a freighter, with no restrictions caused by either passenger or military requirements.

Interior view of the Bombardier Dash 8 series 100 cargo conversion

The main advantage of the dedicated air freighter is that it can be designed specifically for air freight demand, providing the type of loading and unloading, flooring, fuselage configuration, and pressurization which are optimized for its mission.

Joint civil-military cargo aircraft

One benefit of a combined development is that the development costs would be shared by the civil and military sectors, and the number of airplanes required by the military could be decreased by the number of civil reserve airplanes purchased by air carriers and available to the military in case of emergency.

There are some possible drawbacks, as the restrictions executed by joint development, the punishments that would be suffered by both civil and military airplanes, and the difficulty in discovering an organizational structure that authorizes their compromise.

V-Speeds

In aviation, V-Speeds are standard terms used to define airspeeds important or useful to the operation of all aircraft. These speeds are derived from data obtained by aircraft designers and manufacturers during flight testing for aircraft type-certification testing. Using them is considered a best practice to maximize aviation safety and aircraft performance.

The actual speeds represented are specific for a particular model of aircraft. These are expressed by the aircraft’s indicated airspeed and not the ground speed, as this will allow pilots to use them directly, without having to apply correction factors.

In general aviation aircraft, the safety-critical airspeeds are displayed as color-coded arcs and lines located on the face of an aircraft’s airspeed indicator. The lower ends of the green arc and the white arc are the stalling speed with wing flaps retracted, and stalling speed with wing flaps fully extended, respectively. The yellow range is the range in which the aircraft may be operated in smooth air, and then only with caution to avoid abrupt control movement, and the red line is the V_NE, the never exceed speed.

Common V-Speeds

V₁:

V1 is the speed beyond which the take-off should no longer be aborted. If a abortion of take-off is attempted beyond this speed, it will lead to a runway overrun and could seriously damage the plane.

V₂:

V₂is the speed at which the airplane can maintain a safe climb with the failure of one engine. At this speed the aircraft with one engine inoperative, can leave the runway with 35 feet of clearance and maintain a 200ft/min climb rate thereafter.

V₃:

V₃ is the speed at which flaps are retracted.

V_r:

V_ror the rotation speed is the speed at which the pilots make the nose of the airplane pitch up.

V_LOF:

V_LOFis the speed at which the main gears leaves the ground. This is also known as the lift-off speed for a given aircraft.

Aircraft Cabins

An aircraft cabin is the section of an aircraft in which passengers travel. At cruising altitudes of modern commercial aircraft, the surrounding atmosphere is too thin for passengers and crew to breathe without an oxygen mask, so cabins have to be pressurized.

In commercial air travel, particularly in airliners, cabins may be divided into several parts. These can include travel class sections in medium and large aircraft, areas for flight attendants, the galley and storage for in-flight service. Seatsare mostly arranged in rows and alleys. The higher the travel class, the more space is provided.

Cabin Pressurization

Cabin pressurization is the active pumping of compressed air into the cabin of an aircraft in order to ensure the safety and comfort of the occupants. It becomes necessary whenever the aircraft reaches a certain altitude, since the natural atmospheric pressure would be too low to supply sufficient oxygen to the passengers. Without pressurization, one could suffer from altitude sickness including hypoxia.

Travel Classes

First Class

The first class section of an airplane is the class with the best service, and it is typically the highest priced. The services offered are superior to those in business class, and they are available on only a small number of long flights.

First class is characterized by having a larger amount of space between seats, a personal TV set, high quality food and drink, personalized service, privacy, and providing travelers with complimentary items.

Due to its high cost, there are few airlines that offer this service.

104837326-First-Class-fully-flat-bed_preview.1910x1000 — Emirates’ First Class Cabin

Business Class

Business class is more expensive than the economy classes, but it also offers more amenities to travelers than the classes below it. These may include better food, wider entertainment options, more comfortable seats with more room to recline and more legroom, among others.

5ab52d73095b112b088b45a8-1334-667 — Emirates’ Business Class

Premium Economy Class

Premium Economy class is a travel class offered by some airlines in order to provide a better flying experience to the economy traveler, but for much less money than business class.

It is often limited to a few extras such as more legroom, as well as complimentary food and drinks.

China-airlines-a350-premium-business-class-review-9 — China Airlines’ Premium Economy Class

Economy Class

Economy class is the airline travel class with the lowest ticket price, as the level of comfort is lower than that of the other classes. This class is primarily characterized by the short distance between each seat, and a smaller variety of food and entertainment.

economy-ergonomical — Singapore Airlines’ Economy Class

Landing Gears

Definition

Landing Gear is the undercarriage of an aircraft and is used for takeoff or landing.

Landing gears support the aircraft when it is not flying, allowing it to take off, land, and taxi without damage. Faster aircraft usually have retractable undercarriages, which fold away to reduce air resistance or drag.

These landing gears are usually comprised of sets of wheels with simple shock absorbers, or more advanced air/oil oleo struts, for runway and rough terrain landing. Some aircraft are equipped with skis for snow or floats for water and/or skids

Gear Arrangements

Conventional or “taildragger” Undercarriage

The taildragger arrangement was common during the early propeller era, as it allows more room for propeller clearance. Taildraggers are considered harder to land and take off and usually requires special pilot training. Sometimes a small tail wheel or skid is added to aircraft with tricycle undercarriage, in case of tail strikes during take-off.

Concorde_-_Tail_bumper_wheel_G_BOAD — Concorde’s bumper wheel

The Concorde, for instance, had a retractable tail “bumper” wheel, as delta winged aircraft need a high angle when taking off.

Both Boeing’s largest WWII bomber, the B-29 Superfortress, and the 1960s-introduced Boeing 727 trijet airliner each have a retractable tail bumper.

Tricycle Undercarriage

This arrangement has a central main and nose gear with outriggers on the wings. This may be done where there is no convenient location on either side to attach the main undercarriage or to store it when retracted.

Examples include the Lockheed U-2 spy plane and the Harrier Jump Jet.

The B-52 bomber uses a similar arrangement, except that each end of the fuselage has two sets of wheels side by side.

Retractable Gear

To decrease drag in flight some undercarriages retract into the wings and/or fuselage with wheels flush against the surface or concealed behind doors; this is called retractable gear. If the wheels rest protruding and partially exposed to the airstream after being retracted, the system is called semi-retractable

Most retraction systems are hydraulically operated, though some are electrically operated or even manually operated.

Large Aircraft

As aircraft grow larger, they employ more wheels to cope with the increasing weights. The earliest “giant” aircraft ever placed in quantity production, the Zeppelin-Staaken R.VI German World War I long-range bomber of 1916, used a total of eighteen wheels for its undercarriage.

The Boeing 747 has five sets of wheels: a nosewheel assembly and four sets of four-wheel bogies, while the Airbus A380 also has a four-wheel bogie under each wing with two sets of six-wheel bogies under the fuselage.

The world’s largest jet cargo aircraft, the Ukrainian Antonov An-225 has 4 wheels on the twin-strut nose gear units and 28 main gear wheel/tire units, adding up to a total of 32 wheels and tires.

Nautical

Some aircraft have landing gear adapted to take off from and land on water.

A floatplane has landing gear comprising two or more streamlined floats.

A flying boat has a lower fuselage possessing the shape of a boat hull giving it buoyancy, usually with a “step” near the center of gravity to allow the aircraft to more easily break free of the water’s surface for takeoff.