Propulsion as a key element for further development of the GA sector

The further development of general aviation (GA) and any forthcoming steps in this area are substantially limited by availability of modern certified propulsion units and reliable aircraft systems. Any kind of aircraft/rotorcraft configuration for future air taxi or regional transport will desire efficient and environmentally acceptable propulsion unit. As the development of new engine requires much more time than design of particular aircraft in this category, the aircraft are usually designed and built on existing engines. It is obvious that an adjustment and customization of engines to desired performance for particular aircraft is often necessary, but starting a new engine development from scratch is often impossible. According to the aircraft manufacturers a step-change in efficiency of air transport services provided by their small commercial aircraft cannot be made without new efficient systems and propulsion units.

Limited choice of gas turbine engines

There is a very limited choice of turboprop and turboshaft engines on the current market in the power range below 1000 kW. One sort of quite affordable engines is unfortunately technically very obsolete. The obsolescence is not connected only with engine itself but also with propulsion systems like engine control, diagnostics and health monitoring systems having an impact on pilot workload and higher operating costs. The second sort of engines are those, more modern ones, with appropriate electronics and other features, however their purchase price is too high for general aviation market to be employed in large scale for 5-19 passenger turboprop aircraft or for light helicopters. In small power ranges for 2-5 passenger aircraft affordable certified turbine propulsion practically does not exist.

Market opportunity for small turbine engines

Generally there is a worldwide growing need for efficient and environmentally friendly family of gas turbine engines with thermodynamic power range from 180 kW up to 1.0 MW. These categories of propulsion units are used to power small turboprop aircraft, light helicopters, transport utility aircraft and regional commuters. There is also a trend in the replacement of piston engines by turbines due to many reasons for example AVGAS 100 fuel unavailability, mass and weight reduction, longer TBO maintenance time, better passenger comfort or simply lack of spare parts for older types of piston engines. We should also mention the growing retrofit market where old types of turbine engines on currently operating aircraft are replaced by modern propulsion units. Last but not least the replacement of single piston engine on light helicopters by two light turbines can significantly increase their operational potential. Light helicopters with single engine are not allowed to land in the cities and therefore they cannot be used as an aero-taxi.

Lowering operation costs

Turboprop engines used in GA aircraft feature much longer service intervals (TBO) than reciprocating engines of similar power levels, especially as one gets into the higher power levels. Turboprops can typically go up to 5000 hours or more before their hot-sections become due for maintenance checks. Reciprocating (piston) engines used in GA aircraft typically have TBOs of 1000 to 2000 hours, with the higher horsepower models having the lower TBO numbers.
However, reciprocating engines are usually cheaper than turboprops and turboshafts – that is why they are used in smaller and lighter aircraft types. But one pays for the lower initial cost with mechanical and operational complexity that leads to much more frequent maintenance checks in case of piston engines. The currently available turboprop/turboshaft engines are not cheap, mostly due to the cost of the metal alloys used for their construction and manufacture techniques. On the other hand these engines are much simpler, easy to control and can produce large amounts of power while weighing much less than their reciprocating equivalents. Aircraft with GTE can fly higher, faster and farther than with piston engine and therefore they can be more efficient.

Increased safety and reliability for small aircraft

The safety and reliability of GA aircraft and its systems are also crucial conditions for their wider employment in the near future. Turboprops are more reliable than pistons because they have fewer moving parts. When operated and maintained properly, turbine engines are much more reliable than equivalent piston engines and they have a higher power output to weight ratio. Two small turbines instead of one piston engine for light helicopter is a significant contribution to the helicopter safety and its extended employment in urban areas. Nevertheless, the price reduction of gas turbine engines remains the constant challenge for engine manufacturers in order to make GTE more affordable for General Aviation.

Environmental aspects

According to the Report of the UN Intergovernmental Panel on Climate Change (IPCC), general aviation (including business aviation) represents about 2% of the CO2 emissions generated by all of aviation. And the whole sector of aviation represents about 2% of the total annual man-made CO2 emissions. In short, general aviation generates only about 0.04% of all man-made CO2 emissions, which means negligible environmental impact. Thanks to new turbine technologies and technological advancements such as full authority digital engine control (FADEC) a further gas emissions decreasing is envisaged. CO2 and NOx emission reduction belong to the ESPOSA objectives. The project will contribute to the better knowledge of emission pollution of small gas turbine engines and may contribute to the formation of the emissions standards in GA. Reduction of fuel consumption is a target of ESPOSA with regards to the air transport cost efficiency and with regards to rationale use of fossil fuels and will be accompanied also by CO2 and NOx emissions reduction. Replacement of reciprocating engines burning AVGAS with high lead content by a jet fuel has a factual positive effect for living environment.