Although many factors determine if an aircraft will fly or not, one principle of flight is crucial: lift. Airplane wings are the key to developing lift, and they do so by creating a difference in air pressure.
Most airplane wings are built with a curved upper surface and a flatter lower surface, creating a cross-sectional airfoil shape. When air, generated by the aircraft’s engines, rushes over the curved upper wing surface, it must travel a longer distance than the air that passes underneath. To cover the longer distance in the same time, it must travel faster.
According to Bernoulli's law, pressure is inverse proportional to the air velocity, so the fast-moving air on top of the wing is at a lower pressure than the slow-moving air under the wing. The imbalance in air pressure results in lift and powers the plane upward.
During the history of aviation, many bizarre aircraft have been designed and built. Some designs followed the basic principles of flight, and others did not. Many never had a chance to fly while others were successful.
Here are twenty of the strangest planes people actually flew.
20 Goodyear Inflatoplane Experimental Project
The all-fabric inflatable Goodyear airplane was wheeled out to the runway like a wheelbarrow. Using less air pressure than required to inflate a car tire, it could be blown up in about 5 minutes. The Inflatoplane was powered by the two-cycle 40-hp Nelson engine that held 20 gallons of fuel and required hand-starting.
The army canceled the project when they couldn’t find "valid military use for an aircraft that could be brought down by a well-aimed bow and arrow."
19 Convair F2Y Sea Dart Supersonic Seaplane
The Convair F2Y Sea Dart Supersonic is the only seaplane capable of traveling at supersonic speeds.
Created in the 1950s, the plane was designed to take off and land on water, addressing the problems supersonic jets had landing on aircraft carriers. However, the F2Y’s underpowered engines and violent vibrations during takeoff spelled the end for this prototype.
18 Vought V-173 "Flying Pancake"
Charles Lindberg test flew the Vought V-173 and praised its handling. The "Flying Pancake" was designed during World War II to meet the need for U.S. ship-borne aircraft that could take off from short runways.
The proof-of-concept vehicle had a circular wing just over twenty-three feet in diameter and a symmetrical NACA airfoil section. The design demonstrated unusual flight and control responses but effective handling characteristics during tests. The aircraft could almost hover.
17 Caproni Ca.60 Flying Boat
Gianni Caproni designed the prototype Ca.60 (Noviplano) boat with nine wings, and eight engines to carry 100 passengers on transAtlantic flights. He believed that such an aircraft would facilitate travel to remote areas more quickly than ground or water transport. The flying boat once flew to an altitude of 60 feet, but it promptly crashed into the water.
16 Lockheed XFV Helicopter and Airplane
The Lockheed XFV was a design inspired by the need for an aircraft that could take off and land in a small space. The unique aircraft used huge turboprop engines during a period when the Navy was struggling with the development of turbine engine technology.
The XFV succeeded in transitioning from conventional to vertical flight, but aircraft was slow and challenging to fly, requiring highly experienced pilots. The Navy canceled the program.
15 Hiller X-18 Tiltwing
The first, and only, prototype of the Hiller X-18 was completed in 1958, and the first flight test took place in November 1959. It was the first test vehicle for tiltwing and vertical short takeoff and landing (VSTOL) technology.
The Allison T40-A-14 turboprops engines and huge counter-rotating props generated significant lift thrust, providing the X-18 with excellent performance through the transition from vertical to horizontal flight.
14 1949’s Aerocar, World’s First Flying Car
American designer, Moulton Taylor, built the first-ever Aerocar in 1949 proving that a roadster with foldable wings towed behind on a trailer could travel on city streets and fly. In its airplane configuration, the four-wheel, side-by-side seating Aerocar has a 30ft wingspan, and a single Lycoming 0-320 engine mounted over the rear wheels. Only five Aerocars were ever built, and of the four surviving models one is in the EAA museum, one in the Smithsonian, and two are owned privately.
13 German Luftwaffe Blohm und Voss Bv 141
During the late 1930s, the German Nazi military needed an observation plane that had superior visibility to conventional aircraft for scouting out targets.
Dr.-Ing. Richard Vogt's proposed the unorthodox, asymmetrical BV 141 short-range reconnaissance airplane representing a novel approach to the problem of endowing a single-engine aircraft with outstanding all-round vision. The asymmetrical layout featured a tail boom with a radial engine on one side, and a shorter crew compartment made almost entirely of windscreens on the other.
12 McDonnell XF-85 Goblin
The egg-shaped XF-85 Goblin jet had no landing gear and only a retractable steel skid for emergencies. The “parasite fighter” was not designed for land takeoffs but instead carried aloft by a large nuclear bomber and air dropped when needed to defend the mothership from approaching enemy fighters. Once its mission was accomplished, the Goblin reattached to the mothership for the ride back to home base.
Difficulties hooking up to the mothership and the development of long-range fighters like the P-47 and P-51 spelled the end for parasite fighters.
11 Airbus Flying Beluga Whale
Everyone knows that whales can’t fly, and this Airbus Beluga XL doesn’t look like it can fly either. The transporter aircraft is a modification of the Airbus A330-200 jetliner and one of the largest planes in the world. The huge plane uses two Rolls-Royce Trent 700 Turbofan engines for power, costing about $40 million each.
The aircraft is so big the North Wales airport had to widen their runway to accommodate the whale.
10 Italian Stipa-Caproni Barrel-Shaped Plane
Although the experimental Italian airplane designed in the 1930s flew just a few brief test flights and was demolished in 1933, the Stipa-Caproni was a forerunner of jet airplanes. The “barrel-shaped” aircraft built with a large cylindrical fuselage that enclosed the engine and propeller, made the air thrust propelling system more efficient.
However, the airplane’s bulging shape produced excessive drag and counteracted the benefits gained by the engine’s efficiency.
9 Avro Project 1794 Flying Saucer
Declassified after 64 years, a U.S. government memo claimed the Avro Project 1794, developed by the USAF and Avro Canada in the 1950s, could fly. The flying saucer boasted some impressive performance numbers: capable of flying between Mach 3 and Mach 4 (2,300-3,000 mph) achieve an altitude exceeding 100,000 feet (30,500m), and a range of around 1,000 nautical miles.
However, little proof exists to verify the claims, and it remains uncertain (classified) if the aircraft ever flew.
8 NASA AD-1 Pivot Wing Airplane
Although this aircraft appears to have a broken part, it was intentionally built to test the aerodynamic characteristics of a pivoting wing.
While mathematical analysis and wind-tunnel experiments are obligatory for any new aircraft design, flight testing confirms the theoretical analysis. The NASA AD-1, first built in 1979, is an example. Flight tests demonstrated that the straight and rigid wing of an aircraft is capable of pivoting up to 60 degrees during flight while maintaining stability.
7 Nemuth Parasol Circular Wing Aircraft
This aircraft appears to have a parasol (umbrella) mounted over the pilot cockpit, perhaps to provide some shade on a sunny day?
However, the Nemuth Parasol, built in 1934 by students at Miami University, demonstrated that a conventional wing shape is not required to fly a plane reliably, but even a circular wing can provide enough lift.
6 Grumman X-29 Reverse Wing Aircraft
The Grumman X-29, developed in 1984, was an American experimental aircraft built with canard control surfaces, a forward-swept wing, and other state-of-the-art aircraft technologies. The X-29's inherent airframe aerodynamic instability required the use of computerized fly-by-wire control for its success.
The test program proved that the underlying lifting properties of a jet wing are not compromised even when the wings are angled in reverse.
5 Scaled Composites White Knight Two
The Scaled Composites White Knight Two, first flown in 2008, is designed to carry a sub-orbital spacecraft between its twin fuselages. Steering the aircraft from the right fuselage, a pilot can ascend to a maximum height of 70,000 feet.
In April 2018, the White Knight Two carried the Virgin Galactic SpaceShipTwo VSS Unity to 46,000 feet above the Mojave Desert, where it detached and continued to climb to 84,000 feet before gliding to a safe landing. White Knight Two touched down on the desert floor 30 minutes later.
4 H-4 Hercules 2 "Spruce Goose"
Billionaire business mogul and aviator, Howard Hughes was famous for his eccentric behavior both in his business and private life. He was no different with his H-4 Hercules 2 project. The 200-ton monstrosity is the largest seaplane with a fixed wing ever built. The heavy transport aircraft was nicknamed the “Spruce Goose” because its frame was made of wood, (although it was mostly birch).
The seaplane made only a one-mile test flight at 70ft. Only one aircraft was built, and it currently resides in an Oregon museum.
3 The Lippisch Aerodyne
A vertical take-off and landing (VTOL) aircraft, the Aerodyne fits into the same classification as helicopters and rotor-powered aircraft. Just one of the many inventions of master German aircraft designer Alexander Lippisch, the bizarrely shaped aircraft doesn’t look like it can fly. However, its design was sound and well ahead of its time.
Despite the success of the Aerodyne’s first test flight in 1972, development for the project officially ended on November 30 of the same year.
2 Tandem-Wing Scaled Composites Model 281 Proteus
Burt Rutan, famous for his design of Voyager, the first aircraft to fly around the world without refueling, designed the thin, tandem-winged Scaled Composites Model 281 Proteus.
The aircraft’s design is so efficient, it can fly at 65,000 feet for over 18 hours. However, the advent of unpiloted aircraft has eliminated the need for flying a piloted aircraft for such long-endurance missions.
1 Wingless M2-F1 Lifting Body
In 1962, NASA's Flight Research Center built a light-duty lifting body as a prototype to flight test the wingless concept. Designated the M2-F1, the “flying bathtub” featured a plywood shell placed over a tubular steel frame.
During the first flight tests, the M2-F1 was towed aloft by a performance-enhanced Pontiac convertible that reached speeds up to 120 mph across Rogers Dry Lake. The aircraft was later pulled aloft with a tow plane and released to fly back to a landing strip freely.
Sources: airandspace.si.edu, defensemedianetwork.com, popularmechanics.com, extremetech.com