Inlet Channel for a Ducted Fan Propulsion System of a Light Aircraft

Motor performance: 110kW The proposed aircraft will be certificated in the Very Light or Micro-light (Ultra-light) aircraft category. Hence, the maximum take-off weight must be less than 450 kg (including two pilots). The structure of the aircraft is made at composite materials. Previous unsuccessful attempts to utilize a “cold jet” power unit in an airplane structure showed the crucial lack of effective power output of such a propulsion unit. The problem of the Micro-light or Ultra-light Aircraft category is the strict restriction on maximum airplane weight. Usually, the utilization of a more powerful engine substantially increases the weight of the plane structure. Analysis of engines used nowadays for the Micro-light Aircraft category shows that their effective power output is insufficient for “cold jet” propulsion of a small aircraft. The problem of the necessary power output for our engine was solved by using a Yamaha YZF-R1 motorcycle piston engine. The engine of the Yamaha YZF-R1 is derived from a motorcycle racing engine and its performance to weight ratio is 2.5. The maximum performance of the Yamaha YZF-R1 engine is 110 kW. In addition, neither a reducer nor a built-in engine gearbox is necessary for propulsion of the ducted fan.


Introduction
The department of Aircraft Engineering at the Czech Technical University in Prague is developing a light aircraft powered by a ducted fan ("cold-jet") propulsion unit.The plane is a replica of the well-known Czech L-39 training jet plane.A drawing of the airplane is depicted in Fig. 1.

Main technical data
Two-tandem seated, low wing monoplane, all composite aircraft.Dimensions: Wing span : 7.2m Wing section MS 03XX Length: 7.34m Height: 3.0m Wing area: 8.5m Weight empty/take-off: 280kg/450kg Motor performance: 110kW The proposed aircraft will be certificated in the Very Light or Micro-light (Ultra-light) aircraft category.Hence, the maximum take-off weight must be less than 450 kg (including two pilots).The structure of the aircraft is made at composite materials.
Previous unsuccessful attempts to utilize a "cold jet" power unit in an airplane structure showed the crucial lack of effective power output of such a propulsion unit.The problem of the Micro-light or Ultra-light Aircraft category is the strict restriction on maximum airplane weight.Usually, the utilization of a more powerful engine substantially increases the weight of the plane structure.Analysis of engines used nowadays for the Micro-light Aircraft category shows that their effective power output is insufficient for "cold jet" propulsion of a small aircraft.
The problem of the necessary power output for our engine was solved by using a Yamaha YZF-R1 motorcycle piston engine.The engine of the Yamaha YZF-R1 is derived from a motorcycle racing engine and its performance to weight ratio is 2.5.The maximum performance of the Yamaha YZF-R1 engine is 110 kW.In addition, neither a reducer nor a built-in engine gearbox is necessary for propulsion of the ducted fan.
The thin-walled shaft (Fig. 2) implements the power transmission directly from the engine to the fan.
The ducted fan and the inlet channel are designed to keep a laminar boundary layer.The fan consist of fourteen rotor blades and seven stator blades.The fan with a outlet nozzle provides 1.8 kN effective thrust.According to our calculation, this thrust should be generate to maintain a maximum speed of 300 km/h.During the landing, a Fowler flap will be used.The landing speed will be 65 km/h.

The design of the inlet channels (3D model)
The inlet channel is designed to keep a laminar boundary layer all along the channel length.In this case, the minimum inner energy of the flow will dissipate.Our boundary layer calculation [5] shows that the optimum channel cross-section taper is 0.54 per 1 m of channel length (Fig. 3).The chord ratio of the inlet channel is 0.64.

Input data for design:
1.The outlet cross-section is given by the fan dimensions.Version No. 12: The final version.The inlet cross-section has been enlarged in the bottom area.The CFD calculation showed that the flow distribution of this channel is relatively uniform.The velocity in the channel cross section varies by max.6 % about the mean value of the flow velocity.

Experiment
The aerodynamic behavior of the final version of the inlet channel design was experimentally tested.For the experimental tests, a model of the proposed channel was made, on a scale of 1:1.934.The model was handmade from glass fiber and a positive form was used.The form itself was made with the use of CAM technology based on a UG model.
The aim of the aerodynamic experiment was to confirm the expected outlet velocity field.The experiment was carried in the wind tunnel of laboratory U 207.1 at CTU in Prague.A five-hole probe was used for investigating the velocity field of the outlet channel.The investigation itself was in two steps.

Version
No. In the first step, the 2D outlet velocity field was determined.The probe position setting and data recording are manual.The field is mapped at 250 points.

Channel
The second step of the experimental measurement is the mapping of the 3D outlet velocity field.Semiautomatic probe setting and automatic data recording are used for 3D mapping of the flow field, see Fig. 7. Outlet velocity map has about 500 points.The two experimental measurements are now in progress and the data is being evaluated.

Conclusion
This paper attempts to demonstrate possibility of applying ducted fan in the design of Micro-light or Ultra-light aircraft.However, only our experimental results will prove the accuracy of the calculations presented here.The preliminary results from the experimental test show that the inner dissipation of the flow energy is below 3 percent and that utilization of the "cold jet" propulsion unit is possible.

Fig. 5 :Fig. 7 :
Fig. 5: Some of the design verions of the proposed channel