China is increasing its purchases of military equipment and services from Ukraine. This trade is huge for Ukraine. Last year 43 percent of Ukrainian exports went to China, and that will increase with new deals that increase the components and services Ukraine sells to China for the many Russian designed aircraft China uses. China also builds many of these aircraft, some of them illegal copies whose manufacture by the Chinese was made possible by cooperation from Ukraine.
China has become a major customer for Cold War era Ukrainian plants that lost most of their business when the Soviet Union broke up in 1991, and military spending in the successor states (especially Russia and Ukraine) dried up. At first, China favored Russian firms with contracts, but in the last decade Russia realized that China often bought Russian weapons with the express intention of learning how to build illegal copies. In the last five years China has had a more difficult time buying Russian. The Ukrainians have no such hang-ups (as most of the Soviet era weapons development was within what is now Russia, the stuff was only built in Ukraine) and in the last decade has become an enthusiastic exporter to China.
For example, last year China bought 250 AI-222 jet engines, for its JL-15 trainer, from Ukrainian firm Motor Sich. This was an extension of an earlier program that had Motor Sich supplying AI-25 engines for the older K-8 trainer. The new, 9.5 ton, twin engine JL-15 can achieve supersonic speeds and has the kind of high-tech cockpit found in modern fighters. The JL-15 was designed to be produced in two versions: advanced trainer and initial fighter trainer. This would smooth the transition to high end aircraft like the J-10 (similar to the F-16) and J-11 (a Su-27 clone).
Also known as the JL-8, the K-8 uses the 350 kg (770 pound), 3.1 meter (9.5 foot) long AI-25TLK (3,300 pounds of thrust) jet engines to power the 4.3 ton, two seat aircraft. Originally, China was going to use 3,600 pound thrust American engines but after the brutal 1989 Chinese crackdown on pro-democracy groups, the United States cut off the supply of engines. The AI-222 is a 5,500 pound thrust engine that is more compact and somewhat heavier than the AI-25.
Ukraine is supplying components and services that Russia is holding back (in protest against Chinese technology thefts). Ukrainians have no fondness for Russia, having been forcibly incorporated into Russia in the 18th century. That long period of domination only ended in 1991, and Ukraine sees the Chinese as a useful ally in helping to keep the Russians out.