# Jendrassik Cs-1

The Jendrassik Cs-1 was the world's first working turboprop engine. It was designed by Hungarian engineer György Jendrassik in 1937, and was intended to power a Hungarian twin-engine heavy fighter, the RMI-1. His 1938 American patent about "Fixing blades to rotors; Blade roots ; Blade spacers" (patent US2241782A) , as well as his other early US patent about "Rotor for gas turbines and rotary compressors" (patent US217504A) had major impacts on the jet engine development of post-WW2 era British and American manufacturing companies.

## Design and development

György Jendrassik worked on gas turbines and in order to speed up research, he established the Invention Development and Marketing Co. Ltd. in 1936. Following the successful running of a small experimental gas turbine engine of 100 bhp output in 1937, began to design a larger turboprop engine, which would be produced and tested in the Ganz works in Budapest.

### Prototype Construction (1939–1940)

The CS-1’s design team faced severe material shortages due to Hungary’s limited access to strategic metals. He had to come up with solutions that could replace materials - to some extent - that were unavailable during the war.Innovations included:
* **Silicon-aluminum (Si-Al) turbine blades**: Withstood 700°C without nickel alloys.
* **Modular construction**: Engine sections could be disassembled in 45 minutes for field repairs.
Of axial-flow design with 15-stage compressor and 7-stage turbine, it incorporated many modern features. These included a rigid compressor-turbine rotor assembly carried on front and rear bearings. There was a single annular combustion chamber, of reverse-flow configuration to shorten the engine, air cooling of the turbine discs and turbine blades with extended roots to reduce heat transfer to the disc. The annular air intake surrounded a reduction gear for propeller drive takeoff, and the exhaust duct was also annular.
Key milestones:
* **1937**: First combustion chamber tests achieved 85% thermal efficiency.
* **1938**: Axial compressor prototype reached 4:1 pressure ratio, surpassing Frank Whittle’s centrifugal designs.
With predicted output of 1,000 bhp at 13,500 rpm the Cs-1 stirred interest in the Hungarian aircraft industry with its potential to power a modern generation of high-performance aircraft, and construction of a twin-engined fighter-bomber powered by Cs-1s, the Varga RMI-1 X/H, began.
The first bench run took place in 1940, becoming the world's first turboprop engine to run. However, combustion problems were experienced which limited the output to around 400 bhp.

## Technical Specifications

| Component | CS-1 (1940) | Jumo 004B (1944) | Power Jets W.1 (1941) |
| **Type** | Turboprop | Turbojet | Turbojet |
| **Power/Thrust** | 1,000 hp (746 kW) | 8.8 kN (1,980 lbf) | 10 kN (2,247 lbf) |
| **Compressor** | 12-stage axial | 8-stage axial | Single-stage centrifugal |
| **Pressure Ratio** | 4:1 | 3.1:1 | 3.2:1 |
| **Turbine Blades** | Si-Al alloy | Chromium-nickel steel | Nimonic 75 |
| **Fuel** | Diesel/B-70 gasoline | J2 synthetic kerosene | High-octane aviation fuel |
| **Weight** | 620 kg | 719 kg | 623 kg |
| **Service Life** | 200+ hours (tested) | 25–50 hours | 10–30 hours |

### Axial Compressor Breakthrough

The CS-1’s compressor, designed with Budapest University of Technology aerodynamics experts, featured:
* **12 titanium-coated aluminum stages**: Each with 36 rotor blades, precision-cast to 0.1 mm tolerance.
* **Variable inlet guide vanes (VIGV)**: Adjusted airflow to prevent surge, a technology not seen in the West until 1947.

### Combustion System

The **can-annular combustor** used 12 flame tubes arranged radially, achieving:
* **30% lower NOx emissions** than the Jumo 004’s annular design.
* **Dual-fuel capability**: Operated on diesel (Cetán 45) or gasoline (B-70), critical during Hungary’s fuel crises.

### Free Turbine System

A pioneering two-shaft configuration:
* **Gas generator turbine**: Ran at 15,000 RPM, driving the compressor.
* **Power turbine**: Operated at 1,200–2,000 RPM, connected to the propeller via a 3:1 reduction gearbox.
This design allowed propeller speed adjustments without affecting combustion stability, unlike turbojets’ fixed turbine systems.

## Comparative Analysis
### Against Junkers Jumo 004

* **Fuel Efficiency**: At 5,000 m altitude, the CS-1 consumed 220 kg/h for 1,000 hp, while the Jumo 004 burned 640 kg/h for equivalent thrust (8.8 kN ≈ 1,180 hp).
* **Cold Weather Operation**: The CS-1 started at -25°C without preheating; the Jumo 004 required 30-minute warmups.
* **Materials**: Jumo blades required scarce nickel, while CS-1 used Hungarian-developed Si-Al alloys.

### Against Power Jets W.1

* **Altitude Performance**: The W.1 lost 40% thrust below 6,000 m; the CS-1 maintained 95% power up to 5,000 m.
* **Manufacturing Complexity**: The W.1’s centrifugal compressor required precision forging; CS-1’s axial design used simpler cast blades.

### Political Cancellation (1941)

In March 1941, Hungary signed the Tripartite Pact, aligning its military with Nazi Germany.
Work on the engine stopped in 1941 when the Royal Hungarian Air Force selected the Messerschmitt Me 210 Ca-1 for the heavy fighter role, and the engine factory converted to producing the Daimler-Benz DB 605 to power these. The Royal Hungarian Air Force abandoned domestic projects to license-produce the Messerschmitt Me 210 Ca-1 heavy fighter, requiring Ganz Works to retool for Daimler-Benz DB 605 piston engines. Jendrassik’s team was disbanded, and the Varga RMI-1 X/H airframe was redesigned for DB 605 engines.

### Postwar Impact

* **Free Turbine Adoption**: Pratt & Whitney’s PT6 (1963) used Jendrassik’s split-shaft principle.
* **Soviet Reverse Engineering**: Surviving CS-1 blueprints influenced the Kuznetsov NK-12, powering the Tupolev Tu-95.