Jan 13, 2025
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Ukrainian volunteers are assembling a small cruise missile with a pulsating Trembita engine. Its task is to destroy objects and exhaust the enemy’s anti-aircraft defense at a depth of up to 140 km.
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Ukraine has grown its defense industrial base to ensure that it can continue equipping its warfighters amidst increasing uncertainty with foreign military aid. Given the dynamic and intense nature of the Russia-Ukraine War, Ukrainian defense companies have had to innovate novel solutions to field these weapon systems faster and in large quantities, as seen with their domestically produced drones and howitzers. PARS, a bureau consisting of Ukrainian volunteers, is developing a domestically produced cruise missile, the Trembita. While, the current design has a range of 140 km, the Economist recently reported that a future iteration of this cruise missile will have a range of 600 km allowing Ukraine to strike targets deep in Russia. In order to quickly and cheaply develop the Trembita, PARS chose to use a pulse jet engine—a technology that stands out for its simplicity and cost-efficiency.
Pulse Jet Engine Technology
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A pulse jet engine operates by generating thrust through a series of rapid combustion pulses. The process begins when air and fuel are drawn into the combustion chamber. In a valved pulse jet engine, mechanical valves control the air intake. The fuel-air mixture is then ignited, causing a rapid expansion of gases. This expansion pushes hot gases out of the exhaust tube, creating thrust. The vacuum created by the escaping gases draws fresh air and fuel to enter the chamber, restarting the cycle. In a valveless design, the mechanical valves are replaced by aerodynamic effects to facilitate this self-sustaining process.
Pulse jet engines differ fundamentally from conventional jet engines. In conventional designs, air is compressed by an axial compressor, mixed with fuel, and combusted continuously. The exhaust gases then pass through a turbine that drives the compressor, producing smooth and controlled thrust. This process results in higher efficiency and smoother thrust output compared to pulse jets. However, pulse jet engines require fewer components and are mechanically simpler, making them lighter and more cost-effective.
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Pulse jet engines are not a new technology. Indeed, the earliest cruise missile design, the V-1 flying bomb used during World War II, was powered by a pulse jet. Known as the “buzz bomb” for its distinctive sound, the Germans used the V-1 to attempt to strike targets in the United Kingdom. Although most modern subsonic missiles use jet engines because of their smoother operation, pulse jets remain attractive due to their simplicity and low cost.
Regardless, their usage has been limited. The United States Navy used a pulse jet in its XKDSG-1 target drone, which was discontinued in the 1950s. More recently, the BBC reported in 2020 that the Islamic State was attempting to develop pulse jet drones modeled after the V-1 missile. Additionally, Wave Engine Corp, a Baltimore-based startup, is currently developing a pulse-jet powered drone for the United States Air Force. Research efforts in academia and industry continue to focus on advancing pulse jet technology by enhancing thrust, improving fuel efficiency, and reducing noise.
Benefits of Using Pulse Jet Engine in the Trembita
The decision to use a pulse jet in the Trembita is driven by its simplicity, enabling large-scale production at a low cost. The total cost of the Trembita is $10,000, with more than half of this cost associated with the navigation system. By comparison, an American ATACMS missile costs around $1.5 million. Propulsion systems are among the key cost drivers in missiles. Pulse jets, being much simpler than jet engines, eliminate the need for complex components like turbines and compressors, making them ideal for rapid, large-scale manufacturing under resource constraints. Additionally, the Trembita’s pulse jet runs on gasoline, a readily available fuel.
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While the primary advantage of the pulse jet is its low cost and ease of manufacturing, there are also secondary benefits. The inefficiencies of a pulse jet engine generate significant heat, giving the Trembita an increased heat signature. Combined with its substantial acoustic signature, the missile is easily detectable by most modern air-defense systems. While this could be perceived as a flaw in its design, the Ukrainians can exploit these characteristics by including Trembita missiles in strike packages alongside other missiles. In doing so, the Trembita missiles would effectively mask the signatures of the other missiles. Even when used independently, the Trembita’s low cost enables the Ukrainians to deploy large numbers, overwhelming Russian air-defense systems through sheer quantity.
As the Russia-Ukraine war rages on the battlefield, both countries are attempting to innovate new technology that will provide their warfighters with an advantage. While the goal is often to deploy cutting-edge technology, in attrition-based warfare, the ability to rapidly field large quantities of weapons often takes precedence, even if they are not the most advanced. In the case of the new Ukrainian cruise missile, the pulse jet engine is not new or advanced. However, its low cost and simplicity will allow Ukraine to quickly produce these in large quantities, providing them the capability to continue striking Russian strategic targets without the need for foreign aid.
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Amazing in what directions the Ukrainians are going to defend themselves … even back to WWII. But, whatever makes mafia land burn is always a good thing.