The Antonov An-225 was the largest aircraft in the world and came with six engines. The United States designed the Boeing B-52 Stratofortress in the 1950s with a whopping eight engines. But the 1950s were a time when jet engines were still in their infancy and were underpowered and unreliable. By the 1960s, Boeing and Lockheed designed the Boeing 747 and C-5 Galaxy, respectively, with just four engines. Now, all subsonic passenger jets are designed with just two engines.
The An-225 is (by some measures) the largest aircraft to fly and was one of the last major projects of the Soviet Union. Built by Antonov in the Ukrainian SSR, only one An-225 was built by the time the Soviet Union collapsed. That aircraft continued to fly until it was destroyed in 2022, while a second aircraft remains unfinished in Ukraine. Here is what to know about why the Soviets built the An-225 with six engines.
The Soviet Stagnation Amid Competition With The West
Soviet aviation engineering was a mixed bag. In some respects, the country produced interesting, advanced new designs and pioneered in some areas. For example, the Soviet Union pioneered ekranoplan development and vertical thrust needed for V/STOVL operations. In many other areas, the Soviet Union copied and trailed Western technology. This became increasingly true as time went on in the 1970s and 1980s as the USSR entered a prolonged period of stagnation.
The supersonic Tupolev Tu-144 was built to compete with the European Concorde and be the first to take flight. Its engineers did not prioritize comfort and practicality as a commercial passenger jet. The Antonov An-225’s design reflected the dynamics of the time. The Soviet Union boasted a massive aviation industry, building thousands of new aircraft. It was a country striving to keep up with the West, especially the United States.
The US put the first man on the moon in 1969, and in 1981, the first Space Shuttle took flight. The US ferried the Space Shuttles around with specially modified Boeing 747s. The Soviets built their own analog, the Buran spacecraft. To ferry these around, it built a special, massively up-scaled variant of its massive Antonov An-124 Ruslan military cargo transport.
The Massive Thrust Needed To Carry Buran
The An-225’s task was immense and required an aircraft larger than had been created before. To achieve the maximum takeoff weight of around 1.4 million pounds, including a payload of up to 550,000 pounds, the aircraft needed a lot of thrust. The engine that the Soviets had available was the Progress D-18T turbofan, providing 51,500 lbf. Six provided around 309,000 lbf.
The smaller An-124 Ruslan is powered by four D-18T engines providing around 206,000 lbf. This is sufficient for its requirements of carrying payloads of up to 330,000 pounds and sporting a MTOW of around 892,000 pounds. But the An-225 needed to carry the Buran orbiter and other oversized cargo. In a publicity stunt, the Soviet Union even carried a 109-ton diesel locomotive engine with the Mriya. On another occasion, it carried a 146-ton locomotive from Melbourne to Zurich for refurbishment.
Design work began in the late 1970s for the aircraft to haul the 100-ton Buran space shuttle piggyback. It also needed to carry its Energia rocket boosters and other heavy equipment required for the program. Simply, limited by the engines available, six engines were needed to provide the redundancy, stability for low-speed and high-lift requirements for the aircraft.
Limited By The Engine Available
Boeing had managed to design the massive Boeing 747 Jumbo, and Lockheed had built the Lockheed C-5 Galaxy with four first-generation turbofan engines two decades earlier. But, as stated, those aircraft did not have the same thrust requirements. The An-225 had to be built with the Progress D-18T engine, as that was the engine available and was the Soviet Union’s most powerful turbofan.
These engines were also inferior to their Western counterparts of the era. Progress D-18T engines had higher fuel consumption and shorter lifespans compared to contemporary Western counterparts. The Soviets did not have an engine that exceeded 55,000 lbf. At the time, the West had several engines in the 50,000-60,000 lbf range, including the General Electric CF6-50, Pratt & Whitney PW4000-94, and the Rolls-Royce RB211.
The Progress D-18T emphasized high thrust, simplicity for mass production, and was built to operate in harsh conditions. As Russia seeks to russify its domestic MC-21, Superjet, and other airliners today, it continues to face similar problems. Domestic Russian engines are heavier, less powerful, need more maintenance, and are more expensive than Western counterparts.
Russia Still Can’t Produce Powerful Engines
Both Ukraine and Russia belong to an exclusive club of countries capable of designing and producing engines. Progress D-18T engines were originally built in Ukraine, and at the time of independence, Ukraine boasted a large aerospace industry. However, this industry atrophied in the 1990s and 2000s. Ukraine continues to supply engines for advanced Turkish drones and has supplied engines for Chinese advanced trainers (specifically the Chinese Hongdu JL-10). However, while Ukraine’s jet engines are limited, Russia can produce a larger range of engines.
Even so, the most powerful Russian engine in serial production today is the Kuznetsov NK-32 found in the Tupolev Tu-160 “Blackjack” strategic bomber. Those engines provide 55,000 lbf. Limited to the criteria of Russian turbofan suitable for transport/civilian aircraft, the most powerful engine in production is the Aviadvigatel PS-90A1 that provides up to 39,000 lbf. That family of engines powers Russia’s Il-76 military transport and Il-96 airliners.
The Progress D-18T remained in production from the late 1980s through to the early 2000s, by which time up to 400 engines had been produced. Less than 200 are believed to be in operation today. These engines primarily sustain the world’s existing fleet of Antonov An-124 military transport aircraft. According to RuAviation, Russia is currently working to put the D-18T back into serial production by late 2027. Russia has most of the world’s operational fleet of An-124s, and it wants to keep them operating well into the future.
Possible With Four Engines Today
While the United Kingdom and the United States boasted more powerful engines than the Soviet Union in the 1980s, no engine was available that would have met the 77,000 lbf needed for a four-engined An-225. But this has now changed. Today, four engines would be needed if those were the GE9X or Rolls-Royce Trent XWB. These would meet or exceed the thrust of the original six engines while improving the aircraft’s range and payload, even taking into account the differences in engine weight.
The RR Trent XWB-97 rated thrust is 97,000 lbf or almost double that of the D-18T’s 51,300 lbf, while the GE GE9X’s max rated thrust is 105,000 lbfs (although it has been run at 134,300 lbf). The GE9X is the engine set to exclusively power the upcoming Boeing 777X and has been developed from the GEnX, which powers the Boeing 787 Dreamliner. Ukraine has spoken about its desire to rebuild the An-225 once the current conflict is over. It is unclear if it plans to utilize the unfinished airframe and use components from the destroyed An-225 or build a completely new airframe.
|
Select leading engines today |
Thrust |
|---|---|
|
CF6-80E1 |
65,800–69,800 lbf |
|
Rolls-Royce Trent 7000 |
65,005 lbf |
|
Rolls-Royce Trent 900 |
84,098 lbf |
|
Engine Alliance GP7000 |
81,500 lbf |
|
Rolls-Royce Trent XWB-97 |
97,000 lbf |
|
General Electric GE9X |
103,500 lbf |
A new airframe could be designed with four engines. These modern engines would also add the benefits of being far more efficient and reliable than their original Soviet engines. It is probably infeasible to build the aircraft with just two engines. The GE9X is the most powerful engine on the market today, and even its max test thrust would still provide about 13% less thrust than the aircraft’s original six engines. The thrust deficit widens more when noting its rated thrust is 105,000 lbfs, not 134,300 lbfs.
Could Be Made With Four Western Engines Or Six Ukrainian/Russian Engines
The Antonov An-225 was a product of its time. It broke world records and was, in many ways, a marvel of engineering. It was also built to demonstrate the might of the Soviet Union and its ability to compete with the United States’ space program. While the USSR was able to develop the An-225 and complete the first aircraft, it collapsed before it could complete the second aircraft.
At the time, there was no engine powerful enough to meet the An-225 thrust requirements with just two engines. But if the aircraft were to be redesigned now, it could be powered by four GE Aerospace or Rolls-Royce engines. Those four engines would offer significant improvements over the original six Progress D-18T engines. Those improvements are not only because they are Western engines, but also because they represent another four to five decades of innovation and improvement.
If the An-225 were to be remade in Ukraine, Ukraine would lack new-build engines powerful enough to power it, short of repurposing existing engines from the original An-225, spares, or An-124 engines. The same is true of Russia. However, this may change in 2027, as Russia plans to restart D-18T production to sustain its An-124. This means a hypothetical new An-225 made today using Soviet/Ukrainian/Russian engines available would still require six engines.
