• Hybrid Operation

Hybrid operation has received significant attention recently in several industries, such as wind farming [8] and automobile manufacturing [9]. Such a device generally uses two or more diverse forms of power sources in various situations, shown as Figure 1.

**Figure 1.** Parallel hybrid electric vehicle mechanism [10].

The basic principle is that the different motors work better at different speeds; the electric motor is more efficient at producing torque, or turning power, and the combustion engine is better for maintaining a high speed (better than a typical electric motor) [11]. Changing power sources with appropriate timing and in the right circumstances facilitates energy efficacy and fuel efficiency. Abundant hybrid models (i.e., the Boeing Fuel Cell Demonstrator Airplane, Hybrid FanWings) have been presented in order to take advantage of each and handle uncertainties [11]. This hybrid methodology is proposed, taking benefits of both the conventional power source (i.e., a turbine engine's consistent output) and an electricity power system (i.e., fastest response for utility) [12] so as to enhance safety if engine failure happens.

#### **3. Conceptual Framework and Design for Experiment**

This drone application proposal [4] is shown as Figure 2.

Figure 2 explains the sequence for the operation procedure of the proposed hybrid mechanism. Generally speaking, (1) A turbine engine offers the power for rotor head speed; (2) if the turbine engine suffers from lack of fuel/engine failure, (3) the electricity power system offers auxiliary dominance so as to (4) keep the full rotor head speed for a helicopter.

**Figure 2.** Proposed theoretical foundation of the hybrid mechanism.

Moreover, this experiment contains the following sections:


**Figure 3.** The hybrid mechanism proposal.

In more specific terms, number in Figure 3 denote the following:


Operationally, once we start the turbine engine (12), this engine rotates the first output shaft (121) and the first bevel driving gear (122) so as to drive first bevel gear (123). Consequently, through the first transmission gear (111), the one-way bearing module (113) is driven to turn the driver shaft for the propellers (11). Finally, the propellers (22) revolve at a specified speed so as to provide sufficient thrust for lifting the remote control helicopter. In more specific terms, we set the turbine engine's (12) output shaft rpm to 9000; the gear ratio between the first bevel driving gear (122) and the first bevel gear (123) was 1:4. Accordingly, the rpm of driver shaft for propellers (11) was 2250. However, the realistic rpm reaches only 70–80% (1575–1800) of the calculated result due to aerodynamic drag [13,14].

On the other hand, if accidentally, the turbine engine suffers from lack of fuel/engine failure, the electronic motor (13) works right away to drive second output shaft (131), second driving shaft (132), and second v-shaped teeth gear (133) so as to rotate first v-shaped teeth gear (116). Consequently, the second transmission gear (112) and one-way bearing module (114) are driven to turn driver shaft for the propellers (11). Finally, propellers (22) revolve at specified speed so as to provide sufficient thrust

for lifting the remote control helicopter. In more specific terms, the electronic motor's (13) maximum rated output shaft rpm/v is 520 KV. The gear ratio between the second v-shaped teeth gear (133) and the first v-shaped teeth gear (116) is 1:11. Accordingly, the rpm of driver shaft for propellers (11) is 520 KV × 44.4 V/11 = 2099. However, the realistic rpm reaches only 70–80% (1469–1679) of the calculated result due to aerodynamic drag [13,14].

Figure 4 represents a transparent model for Figure 2.

**Figure 4.** Transparent model.

Figure 5 represents the complete hybrid mechanism proposal in the conversion kit.

**Figure 5.** Complete hybrid mechanism. (116- first v-shaped teeth gear, 123- first bevel gear).

*Symmetry* **2020**, *12*, 33

#### **4. Discussion**

We successfully test ran and flew this newly designed R/C helicopter, as shown in Figure 6.

**Figure 6.** The new design of an R/C helicopter.

Operationally, we used a radio control transmitter to maintain the main blades' rpm at 1500 for both turbine engine and electronic motor power sources, respectively. Generally speaking, the maximum speed for the tip of the helicopter's blades is approximately 180–220 m/s. In other words, the speed is around 0.55–0.66 Mach at standard atmospheric pressure (i.e., the environmental temperature might have moderate influence on the speed) [15]. So as such, 1500 rpm × 0.9 m × 2 × 3.14 = 141.3 m/s which is roughly 70% of the maximum speed mentioned above for producing much less vicious variations in altitude or velocity of the helicopter [16]. The pitch administered to the main blades was between –5 and 10 degrees. This new design R/C helicopter started to lift at the pitch of 2◦ and hovered at that of 4.5◦. The propellers are of the controllable-pitch type so that they could have a low pitch when taking off and a higher pitch for high speed, horizontal flight [16].

Empirically validated, within 1 second, the electricity power system offers supplementary motive force as soon as the turbine engine shuts down (and/or has a flameout). Furthermore, the electricity power system offers sufficient dynamism for the above helicopter (9.5 kg) not only hover at a specific altitude but also ascend to the sky. The capacity of those batteries is adequate for this model helicopter to fly for 5 minutes. In other words, the 5-minute airtime is a very safe and satisfactory period of time for a harmless landing. Through this hybrid mechanism, two individual power sources are interconnected to make either turbine engine or electronic motor flight possible [16].

This paper contains both theoretical and experimental pioneering research, presenting a model for the solution to an engineering problem: the fastest way to solve the crisis of unavoidable/unpredicted engine failure for helicopters. In the near future, we hope to apply this practical evidence in the helicopter industry for decreasing human injuries and/or fatalities. The ultimate purpose of this manuscript is to save people's lives.

For any specific helicopter, the hybrid mechanism needs to be redesigned for adaptation. The impending electricity power system (i.e., kW output of an electric motor, capacity of an electricity amperage supplier, and measurements of batteries) needs to be redefined. In other words, the overall weight-to-power ratio must be re-calculated.

The findings of this study solve only the lack of fuel/engine failure jeopardy. We might need to conduct some other experiments for straightening out personnel mistakes and/or mechanical failures.

#### **5. Patents and Recognitions**

In Figure 5, the complete hybrid mechanism is in the process of patent application on the date of submission for publication. The conversion kit which contains new, reinforced helicopter body frames (Patent pending) won a Gold Medal in the 2016 Kaoshiung International Invention and Design Expo. In Figure 6, both Triple Blades' Flybarless Main Rotor Head Complete System (Patent M584707, Taiwan, R.O.C.) and Triple Blades' Tail Rotor Assembly (Patent M584706, Taiwan, R.O.C.) won Gold Medals in the 2016 Kaoshiung International Invention and Design Expo. Additionally, the latter innovation obtained The Award of the President of the Jury in the same exhibition [17].

**Author Contributions:** Conceptualization, methodology, and experimental project administration (construction of this experimental R/C helicopter, and test flight), K.K.-S.C.; writing—original draft preparation, K.K.-S.C.; writing—review and editing, M.-L.T. and Y.-J.C.; confirmation of the rigidity of the materials in the construction of this experimental R/C helicopter, J.-L.L. and R.H.-L.H. All the authors have read and approved the final version for submission. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** This work has been supported by the KingTech Turbines and MingDa Technology Corp.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

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