Concepts
Design Idea 1: A VTOL Hybrid
This Section explores the feasibility and various designs of a hybrid between a helicopter and a fixed-wing. An initial design was drawn and further research was done including research for similar aircraft.
Design Idea
The idea of this aircraft is to combine the VTOL capability of a helicopter, and a cruise speed and efficiency of a fixed-wing aircraft. The rotor will produce the initial lift needed for the aircraft to take off. there are various methods of propulsion in this idea which will be discussed later. Multiple options for the rotor operation are available for this hybrid design:
Locking the rotor blades during the cruise.
Allowing the rotor to slightly spin when not needed.
Lastly, which is the most probable option, allow the rotors to act as a gyrocopter.
Multiple engine layouts were thought of during the designing process.
a single turbine to power the rotor and two separate jets or turbofan to produce thrust for cruise
single or multiple turbines that power the main rotor that can be disengaged to power propellers to produce forward thrust.
a single turbine for the main rotor and a turbofan with a ducted thrust system for forward propulsion that may even help during the VTOL operation.
During my research, a similar aircraft was found using a very similar configuration. The aircraft discussed here is the Sikorsky S72 developed in the 80's.
Discussion
Various advantages are present in this design. One of the biggest advantages is that the aircraft's size is relatively compact for a VTOL while it also has a fixed-wing component incorporated into it. However, a large volume of the fuselage is actually utilized for various mechanical components required for the operation of the aircraft. The aircraft itself can only carry what seems to be an inadequate amount of fuel considering it may require up to three different engines. This leads to a problem where the passenger cabin may be cramped with limited cargo space. This problem can be alleviated by extending the fuselage width. Another issue with this design is the fact that, despite the various powerplant configurations, the engine driving the rotor will be inactive which meant that the engine will pose to be a dead weight during cruise. This problem persists unless the same engine can also provide forward thrust which will require the aircraft to be redesigned to utilize a propeller for forward thrust.
Design Idea 2: A Tiltrotor
Although multiple tiltrotors were already produced, it is still very rare for this technology to be utilized. This page will explore various designs that may improve upon the tiltrotor idea, their advantages as well as their disadvantages.
Description
Figure 2, A Rotex Kaman K-1200. Image courtesy of Wikipedia[1].
As noted in the introduction, various tiltrotors are already produced and used worldwide. The most notable tiltrotor in production is the V22-Osprey researched and manufactured by Bell Helicopters and Boeing. This design is to introduce a civilian tiltrotor that is compact enough to land within the criteria's requirement 20m by 20m area. This was achieved by tilting the rotors inward at a slight angle and allow the blades to sync and interfere with each other. This interfering rotor design was largely inspired by the KAMAN K-Max helicopter seen in the image on the left [1]. This concept will be discussed later.
This design is easily scalable for passenger needs as well as cargo size requirements. In the initial concept sketch pictured, the rotor diameter is estimated to be between 8m and 10m. the length of the aircraft would roughly be 10m which allows for spacious room for up to 5 passengers and a pilot as well as a spacious cargo area toward the rear.
This design would require two turbine engines located at the wingtips of the aircraft. At this current stage, various tail designs are considered. One of the options is to utilize an H-tail design which would allow for a shorter vertical stabilizer in order to avoid any possibility of the rotors cutting into the V-stab. Another one is to utilize a standard tail design or a T-tail but depending on the location of the rotor, the first option may be the only option feasible for this aircraft.
Discussion
Some major flaws are present in the current concept sketch. The biggest one being the fact that the heaviest components of the aircraft will need to be supported at the wingtips. This may create some material challenges as stronger materials may be more expensive or even inaccessible. Various adjustments on the sketch may also be required as in its current state, the rotors may strike the fuselage during the transition. This concept, while being the heaviest may also be the most capable and expandable. Due to the standard simple shape of the cylindrical fuselage, it can easily be shortened or lengthened depending on the need. This concept is largely inspired by the current designs of various airliners around the world. This aircraft may also benefit from the tilt-rotor design which may allow it to go faster than conventional helicopters.
Design Idea 3: Tilting The Wing on Water
A lot of tilt-wing designs were already produced throughout history. Unfortunately, none of them ever came to production due to various reasons. This concept will have a similar basic idea and improve upon the tilt-wing concept.
Description
Figure 2, Kaman K16B Tilt-Wing Prototype[2].
Very few modern aircraft are built for a water landing. This was a common way of building large aircraft early in the 30s, 40s, and part of the 50s. Currently, only a handful of modern purposely designed amphibious aircraft and most of them were built for fire fighting and SAR such as the Canadair CL 415 and the Canadair CL 215. Some passenger and personal aircraft mostly consist of pontoon equipped land-based aircraft such as the Twin Otter, Beaver, and Cessna 204. However, in the more recent years, a handful of purposely designed amphibious passenger and personal aircraft started to emerge. Some of these aircraft include the Seawind which is a four-person aircraft with a range of almost 2000km or 1040nm to be exact and the Icon A5 which utilizes a foldable wing and a range of 427nm with the state of the art safety features.
This aircraft concept was designed with amphibious operations in mind. It incorporated mid-wing mounted engines that can tilt for VTOL operation. The tilting rotor also contained the other half of the wing section which would allow for uninterrupted thrust downward during VTOL operation. The thought of this system is the fact that it might be simpler to tilt the rotor than tilting an entire section of the wing. However, tilting the rotor requires a stronger and shorter wing section. This idea provides a larger wing section area which meant that the wing design can utilize a higher aspect ratio design. This aircraft's design is highly inspired by the amphibious VTOL experimental aircraft Kaman K16B built in the 60's as seen in Figure 1.
Discussion
Some major flaws are present in the current concept sketch. The biggest one being the fact that the heaviest components of the aircraft will need to be supported at the wingtips. This may create some material challenges as stronger materials may be more expensive or even inaccessible. The aircraft's balance may also be finicky since the rotors must be placed exactly where the center of gravity is for VTOL operation. This complexity might be relieved by the addition of a third tilting rotor which may allow some balance for the aircraft's VTOL operation.
Design Idea 4: A Futuristic Wing Design
This design utilizes an infinity wing design which can often be seen in RC planes. However, only a handful of experimental passenger aircraft utilizes this design.
Description
This design is to utilize a single or up to two turbine engines which will be positioned on the rear half of the aircraft. The turbine or turbines will provide power to two lift fans located on the wings through a gearbox and clutch system. The turbine will also power a propeller for forward thrust during the fixed-wing operation which can be disengaged during VTOL. Two mini jets are located on the front canard of the aircraft that will provide some balancing thrust during VTOL as well as the optional forward thrust for the fixed-wing operation. This system also has its own benefit as the lift fans can be powered by electric motors instead.
Discussion
This aircraft is relatively simple in terms of mechanical complexity. However, this aircraft may be difficult to analyze due to the little information there is for infinity wing configuration. This aircraft also utilizes a canard design which can prove to be maneuverable but unstable.
Design Idea 5: A Futuristic Amphibious Aircraft
This design is meant to revive the concept of flying boats with a twist of advanced technology. This aircraft's VTOL capability will be achieved by using 3 fans/rotors where one of which is to be tilted for forward thrust.
Description
This aircraft concept design is largely similar to the third concept design. Both aircraft feature high-wing configurations with an amphibious fuselage. The main difference between the two planes is how the VTOL system is set up. This aircraft also utilizes a twin-boom design in order to accommodate the two turbine engines and a tilt-rotor in between the booms. The twin-boom design allows for the rotor to be placed in between them and be utilized for both VTOL and forward propulsion. A large aspect of this aircraft was inspired by the German WWII plane BV-138 as seen in Figure 1. This aircraft was used as a reconnaissance and patrol aircraft used by in WWII[1].
Figure 3, Drawing of a Blohm & Voss BV-138[3].
The nature of the aircraft's design allows two different propulsion set up for this aircraft. The first set up utilizes the two turbine engine and a gearbox set up to power the three different rotors or fans. A more advanced set up utilizes a hybrid electric system where each of the rotors(or fans) will be powered by an electric motor. In this setup, batteries will be elegantly set in the rear of the cabin as a backup and the turbines will generate electricity.
Discussion
while having three different lifting components allow this aircraft to be relatively simple to balance, this aircraft contains some critical flaw in its current concept state. The rear rotor is meant to provide both lift during VTOL operation as well as forward propulsion during fixed-wing operation. The tilting of the rotor may prove to be difficult in the current position as it must change the direction of thrust mid-flight during the transition in order to do perform both functions. It is critical to design the rear rotor in a way such that it can rotate while providing both VTOL and forward thrust required during transition. One way of doing this is by attaching the rotor to the aircraft using a structure span between the boom or by utilizing the tail as a mount for the rotor. Doing this would allow the rotor to rotate forward during transition and provide lift up and forward at the same time.
Reference
[1] “Kaman K-MAX,” Wikipedia, 31-May-2021. [Online]. Available: https://en.wikipedia.org/wiki/Kaman_K-MAX. [Accessed: 20-Jun-2021].
[2] “Kaman K-16B,” Wikipedia, 18-Dec-2019. [Online]. Available: https://en.wikipedia.org/wiki/Kaman_K-16B. [Accessed: 24-Jan-2021].
[3] “Blohm & Voss BV 138,” Wikiwand. [Online]. Available: https://www.wikiwand.com/en/Blohm_%26_Voss_BV_138. [Accessed: 20-Jun-2021].