THE MIGHTY BIPLANE FLIES AGAIN!
Two sets of wings and a 4-in-1 rocket engine accelerates a Chinese plane to up to seven times the speed of sound. The design kick-starts a new era of hypersonic aircraft.
Olde-timey flight was all about biplanes, then we abandoned that idea. But maybe we need to revisit it, to go even faster...
Three planes leave Beijing for New York at the same time. An ordinary Airbus A320 airliner, the pensioned-off supersonic Concorde, and the new Chinese I-plane design, which is a biplane with two sets of wings. In the imagined scenario, the Airbus A320 and the Concorde will land in New York 14 and six hours after take-off, respectively. A businessman, who travelled on the I-plane, is in a meeting in New York after only two hours, and he can get back to Beijing again and get a good night’s sleep, before the Airbus A320 ever reaches New York. The trick behind the I-plane ’s hypothetical feat is a new engine type combination, which can accelerate the plane to hypersonic speeds, i.e. seven times the speed of sound: Mach 7.
The stability of the I- plane at such extremely high speeds is due to the two sets of wings, which also increase the load capacity and seems to minimize the supersonic booms caused by speeds of Mach 1+. The combination of innovative design and the TRRE engine makes the Chinese aircraft quite a sensation. If the I-plane takes off as planned in 2025, it will be at a speed of 8,600+ km/h.
Plane surfs on shock wave
Hypersonic aircraft are planes that can fly at speeds of Mach 5+ or what corresponds to about 6,200 km/h at sea level. Normally, the speed will be reached in thinner air layers, where the speed of sound varies slightly depending on temperatures, etc. At such high speeds, flying is hazardous, and so, the speeds have primarily been confined to drones and rockets. However, the I-plane design allows for a hypersonic passenger plane race.
The most successful aircraft design for hypersonic flight is the waverider design, which functions according to the same principle as a surfboard. Any craft travelling through the air pushes air in front of it. At supersonic speeds, the air drag turns into a wave that causes a boom of up to 200 decibels, as the plane passes through it. The higher the speed, the more powerful the pressure wave and the drag that it makes up. In other words, a waverider plane surfs on the drag by pointing its nose upwards at a specific angle and maintaining the pressure under the craft on a carefully developed, flat, or slightly inwardly curved subsurface.
The I-plane also takes advantage of the waverider principle, but the Chinese scientists behind the concept concluded that the design involves a number of weaknesses. Intense shock waves make aerodynamics at hypersonic speeds too unpredictable to make a stable waverider design, and wave-rider planes are very thin and fragile and leave too little space for passengers and other cargo. So, the Chinese scientists added two extra wings, which tackled many of the major challenges of hypersonic flight in recent wind tunnel tests.
Double wing balances air flow
The I-plane still needs to pass a long series of tests, before the craft can take off, but if the two extra wings perform just as efficiently in real life as in the first tests, the plane will be stable, able to carry more load, and is seemingly less noisy than other supersonic aircraft.
The wings were added, when the scientists noticed that at hypersonic speeds, compressed air flowed up along the top side of the plane. They concluded that the flow could be used, so they placed another set of wings at the top of the plane, and subsequent tests showed that the design was much more stable and generated more lift than the clean- cut waverider design.
The powerful lift allows the plane to bulge on the top side, leaving space for the craft to one day being able to load up to five tonnes of goods or some 50 passengers. So far, waverider planes have only been able to carry one single person.
Moreover, the I-plane’s extra wings will alter the pressure, splitting up and minimizing the sound of the supersonic boom. So, supersonic and hypersonic aircraft may one day be allowed to fly above land, which is now illegal in China, the US, and major parts of the world. The ban was vital for the Concorde never becoming a major success.
Hardly any biplanes have been made since the 1930s due to increased weight, air drag, and poor fuel economy, but plane designers' experiments will now apparently allow biplanes a comeback in the shape of the I-plane.
Aerodynamics and plane design are notoriously hard to calculate, particularly at hypersonic speeds, as countless factors affect the plane’s lift and resistance. At ordinary speeds of less than that of sound, an object such as a car, a plane, or a wing will split the air into flows around the object. In the case of a plane, successful aerodynamic design will accelerate the air across the craft, forcing it in a downward, backward direction. The motion causes underpressure above the plane, allowing the air flow passing the subsurface to push the object upwards.
As a plane accelerates to supersonic speeds, the rules of lift and aerodynamics become unpredictable, and hypersonic speeds are even more complicated. At around Mach 5, the laws of aerodynamics hardly apply anymore. At almost 6,200 km/h, the resistance does not come from the air, but rather from the waves that the plane produces.
As the I-plane’s extra wings seem to counteract supersonic booms and reduce the extent of waves that could cause turbulence, etc., scientists have found a design that can manage the extremely high speeds.
Supersonic aerospace activities
The future existence of the I-plane also requires that its TRRE engine passes a series of tests in 2025. The engine is the first of its kind to combine four engine types in the same system, and it could pave the way for hypersonic aircraft. So, the I-plane design might be interesting in several ways.
Much of the hypersonic race is aimed at space. Taking off from a runway, carrying goods, astronauts, or tourists into space, and landing safely on the ground again is a challenge that hypersonic planes hope to handle in the future. If the I-plane can function as a reusable lifting module, the plane will reduce the costs of aerospace activities considerably, perhaps allowing more and more frequent space missions.
However, the Chinese and American militaries also closely observe the development of hypersonic planes, whose high speed reduces the distance between the great powers, i.e. the technology constitutes a threat that they must be prepared for.
In relation to the general public, the I-plane and its competitors could kick-start a new era, in which air traffic makes the world even smaller than today. The demand for supersonic passenger flight is rising in an increasingly globalized world. The Concorde flew at Mach 2.2, but was scrapped in 2003 after a tragic crash and subsequently years of losses. The I-plane promises to be successful, so the dream of travelling to remote corners of the world in only three hours is more realistic than ever.