KerbalX

Description

The aircraft aims to simulate the basic flight maneuvers of a gyrocopter using an engine-driven propeller for forward thrust and an independent, unpowered rotor in a state of autorotation to generate lift. The main rotor is actively driven or prerotated only for a short duration, in preparation for takeoff. Unfortunately, due to the aircraft’s size, instead of implementing some sort of tilting mechanism for the rotor, I opted for reaction wheels to provide directional control. This choice imparts somewhat unrealistic, hyper-maneuvering capabilities, but, on the other hand, it adds more fun and aerobatic possibilities.

Details

• Type: SPH
• Class: aircraft
• Part Count: 65
• Pure Stock
• KSP: 1.10.0

Built in the SPH in KSP version 1.10.0

Versioning

• rev.B - reduced blades pitch and rotor size diameter, resulting in higher rotor rpm during flight and stability improvement.

To fly:

1. Activate [SAS]. This is necessary mostly during the takeoff phase
2. Hit [Space] to engage prerotation; During takeoff, the main rotor must attain the required rotational speed, enabling the lift force that facilitates its separation from the ground. Initially, a portion of this speed is achieved by powering the engine for 20 seconds using the KAL controller; the remaining necessary speed is generated by the airflow during the takeoff rolling. Hence, it is crucial to commence rolling during or shortly after this interval to augment the rotor speed. Below 200 rpm, the main rotor blades generate highly asymmetric lift forces between their headwind and crosswind positions, making the craft challenging to control. Therefore, it may be helpful to monitor the rotor rpm during this phase by pinning its window on the desktop (as shown in the video below).
3. Takeoff. For a smooth takeoff, in addition to reaching the designated rotor speed, specific airspeed conditions must be met. The [Main Throttle] controls the torque of the pusher engine; throttle up to about 70% and start rolling while correcting the torque-induced skidding. You can pull the stick at about 30m/s, or the craft will take off by itself at about 40m/s. Once airborne, maintain the pitch attitude through throttle adjustments; if you want to climb, throttle up, and vice versa. In level flight, maintain the rotor and airspeed in the range of 250-300 rpm and 30-40m/s, respectively, depending on altitude.
4. Landing. A normal landing requires simply reducing the engine power to allow the aircraft to descend. Power-off landings are also possible by putting the aircraft into a steep descent (to preserve airspeed), followed by a flare at the end.

• The never exceed speed, at which the main rotor exits from autorotation, becoming unable to maintain lift, is about 50m/s. This typically occurs during descents when pushing too hard on the stick without reducing the engine’s power accordingly.

• The aircraft is quite stable and flies well even without SAS, but it handles differently and demands more control inputs than an airplane. Playing with the throttle and monitoring the rotor rpm are key points in flying this autogyro. These are also the features that make this craft insanely fun to fly. Give it a try, and don’t hesitate to let me know what you think.

• In case of customization don’t be surprised that even the slightest change of the parts will completely alter the flight behavior or make it totally unstable.

A side note regarding KSP physics:

As you may already know, the KSP physics engine completely ignores the concept of airfoil. It takes into account only the angle of attack when calculating lift. This is particularly significant when it comes to autorotation in helicopters or autogyros (gyrocopters) because the rotor blade turns backward compared to reality, solely as a result of air deflection. As a consequence of this, a variety of things or phenomena cannot be accurately replicated or behave strangely. For example, in the real world, the blades of a helicopter in a state of autorotation continue to rotate or even increase their speed in the same rotational direction as in powered flight, even if the airflow is now reversed through the rotor disk. In KSP, given the same scenario, the reversed airflow starts to decrease the blades’ rpm and eventually completely reverses their spin direction.