KerbalX

Description

The aircraft tries to simulate the basic flight maneuvers in a gyrocopter that uses an engine-driven propeller for forward thrust and an independent, unpowered rotor in state of autorotation, to generate the lift. The main rotor is actively driven or prerotate only for a short duration, in preparation for takeoff. Unfortunately, due to the aircraft size, instead of some sort of tilting mechanism for the rotor, I opted for reaction wheels to provide directional control; this gives kind of 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 achieve the required rotational speed at which the lift force generated enables its separation from the wall. A portion of this speed is initially obtained by powering the engine for 20 sec using the KAL controller; the remaining necessary speed is generated by the airflow during the takeoff rolling. Thereby, it is mandatory to start rolling during, or shortly after this interval, in order to increase the rotor speed. Under 200 rpm the main rotor blades generate very asymmetric lift forces between their headwind and crosswind positions making the craft very hard to control. Therefore, during this phase, it may be useful to keep track of the rotor rpm by pinning its window on the desktop (as in the video below)
3. Takeoff. For a smooth takeoff, besides the designating rotor speed, the airspeed condition must be met. The [Main Throttle] controls the the torque of the pusher engine; throttle up to about 70% and start rolling while correcting the torque induced skiddings; you can pull the stick at about 30m/s or the craft will takeoff by itself at about 40m/s. Once airborne, the pitch attitude is maintained through the throttle settings; if you want to climb, throttle up and vice-versa. In level flight, the rotor and the air-speed should be maintained in the range of 250-300 rpm and 30-40m/s, respectively, depending on altitude
4. Landing. Normal landing requires simply to reduce the engine power letting the aircraft to descend; power-off landings are also possible by putting the aircraft into a steep descent (in order to preserve the airspeed), followed by a flare at the end

• The never exceed speed, at which the main rotor exits form autorotation becoming unable to maintain the lift, is about 50m/s. This usually happens on descends 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 flies different and demands more control inputs than an airplane. Playing with the throttle and monitoring the rotor rpm are the key points in flying this autogyro, or a real one. …and these are the same 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 it will make it totally unstable.

A side note regarding KSP physics:

As you may already know, the KSP physics engine totally ignores the concept of airfoil. It takes into account only the angle of attack when it calculates the lift. This is especially important when it comes to autorotation in helicopters or autogyros (gyrocopters), because the rotor blade turns backwards than in reality, only as a result of air deflection. Deriving from this, a whole bunch of things or phenomena cannot be replicated or behaves strangely. For example, in real world, the blades of a helicopter in state of autorotation, continue to rotate or even to increase their speed, in the same rotational direction as it was in powered flight, even if the airflow is now reversed through the rotor disk; in KSP, given the same scenario, the reversed now airflow starts to decrease the blades rpm and eventually will completely reverse their spin direction.