Model aircraft have gotten very big. Big enough that they have to be powered by miniature jet engines.
A major development is the use of small jet turbine engines in hobbyist models, both surface and air. Model-scale turbines resemble simplified versions of turbojet engines found on commercial aircraft, but are in fact new designs (not based upon scaled-down commercial jet engines.)
The first hobbyist-developed turbine was developed and flown in the 1980s by Gerald Jackman in England, but only recently has commercial production (from companies such as Evojet in Germany) made turbines readily available for purchase. Turbines require specialized design and precision-manufacturing techniques (some designs for model aircraft have been built from recycled turbocharger units from car engines), and consume a mixture of A1 jet fuel and synthetic turbine engine or motorcycle-engine oil.
These qualities, and the turbine’s high-thrust output, makes owning and operating a turbine-powered aircraft prohibitively expensive for most hobbyists, as well as many nations’ national aeromodeling clubs (as with the USA’s AMA) requiring their users to be certified to know how to safely and properly operate the engines they intend to use for such a model. Jet-powered models attract large crowds at organized events; their authentic sound and high speed make for excellent crowd pleasers.
U.S. Coast Guard C-130J Hercules, this monster does get airborne.
B-52 Stratofortress bomber