Introduction
This manual briefly illustrates how to fly OH-1 Ninja in the world of FlightGear. As I'm not a real pilot nor a developer of the real OH-1, I don't know this manual is applicable to the real one, and/or the descriptions here are accurate. I hope this manual helps you fly this cute chopper.
Flight Characteristics
Unlike many choppers in FG, OH-1 has a very powerful helper system called AFCS (Automatic Flight Control System) that improves both stability and controllability of a helicopter. This chapter briefly illustrates how AFCS works.
Automatic Flight Control System (AFCS)
The AFCS is made for improving helicopters' stability and controllability. Unlike airplanes, it is very hard to keep helicopter stable. You can try bo-105 to see how it is difficult to control helicopters. Using AFCS, you can fly OH-1 without using a joystick. However, the AFCS is not perfect, and thus knowing how AFCS works is inevitable to smoothly fly OH-1.
The AFCS for OH-1 has five components:
- Stability Augmentation System (SAS)
- restricts the roll/pitch/yaw rate within a given rate (rate dumper) by taking over up to 10-20%) of human control.
- Control Augmentation System (CAS)
- aids pilots control so a heli's maneuver meets pilots' instinctive control.
- Auto hover
- enables you to easily take off and land.
- Active horizontal stabilizer (probably the real OH-1 doesn't use this one any more, but am not so sure)
- improves pitching stability when accelerating / decelerating
- Semi-automatic coordinated turn (Tail slip adjuster)
- improves stability during turns
- prevents tail slip
How CAS works
There are two different kinds of CAS in generic helicopter AFCS. One is rate control and another is angle control. The CAS in OH-1 (in FG world) uses the latter. When you put the stick to the left a bit and hold it for a while, you'll see OH-1 starts rolling and then keeps its bank angle, while general helicopter or aircraft keeps rolling to the left. If you put the stick more to left, OH-1 start rolling like a regular helicopter or aircraft. This is because the CAS keeps its angle depending on the angle of the stick unless the angle reaches to a certain degree. The same can be applied to pitching direction. CAS is enabled by default, but you can toggle engage/disengage CAS by pressing Ctrl-E.
How SAS works
The SAS restricts the roll/pitch/yaw rate by taking over helicopter controls (up to 10 to 20% in all axis). Since SAS doesn't take over 100% of pilot controls, you can still controls as you like, without "stick wiggling" sensitive adjustment. SAS will take care of it to some extent. SAS is enabled by default, but you can toggle engage/disengage SAS by pressing Ctrl-D.
How auto hover works
The auto hover is like an advanced SAS that takes over almost 100% of pilot control, but a bit different. The difference between SAS and auto hover is that the SAS restricts the roll/pitch/yaw rate while auto hover kills speed of all direction for keeping OH-1 over the current position. To do so, auto hover monitors the velocities of all direction and output the control to kill the velocities. Auto hover and SAS can live together, and SAS will restrict when auto hover outputs very large control for stabilizing OH-1. Though auto hover seems taking over all pilot control while engaged, you can actuate the pedal to make OH-1 spin (pivot turn). Auto hover is disengaged at the startup. You can toggle engage/disengage auto hover by pressing Ctrl-F.
How semi-automatic coordinated turn works
The semi-automatic coordinated turn takes over the yawing control to some extent. While making a left turn, a helicopter tends to slips into the left hand side. When AFCS detects the side slip, it outputs some amount of pedal control for counteracting the slip. Semi-automatic coordinated turn is automatically engaged and disengaged depending on the current speed. As a side effect of this function, OH-1 will make a sudden unexpected yawing maneuver when the speed is about 10 to 20%. This is a bug, and does not occur in a real OH-1, I believe.
Anyway, this function is just an aid and thus is not perfect. It takes over only 10 to 20 % of pilot control, so you still need to actuate the pedal to make a perfect coordinated turn especially in a quick turn with deeper bank angle.
This function is automatically engaged and disengaged, and there's no clear user interface to engage/disengage it. Though semi-automatic coordinated turn through property browser, no keys is assigned (except debug purposes).
How active horizontal stabilizer control works
The active horizontal stabilizer (stabilator) is for stabilizing pitching maneuver especially when adjusting speed and AoA. A helicopter tends to bring its nose up/down while flying, and this makes it harder to stabilize helicopters. To ease this control, the active horizontal stabilizer automatically adjusts the horizontal stabilizer angle for stabilizing the pitching movement. This is just like a combination of horizontal stabilizer and elevators in aircraft, but is controlled fully automatically, and a pilot even don't realizes that this is functioning.
Instructions
Start engines
Press } to start the engines. You'll see no notice but the rotor start spinning. It will take about 10 to 20 seconds for stabilizing rotor RPM, so be patient. Due to weird ground friction of Yasim, OH-1 gradually start spinning to the left while rotor increases its spinning speed. This doesn't happen on the real heli, but don't be mad on this.
Take-off with auto hover
The first operation after starting the engine is to engage auto hover. When it is engaged, you'll see a message Auto Hover engaged on the top of the screen. When the rotor rpm becomes constant, start hovering by gently pulling the collective half the way up. As you pull the collective, OH-1 goes up higher. The most important thing in auto hovering is the "gentle collective control." You must not rapidly pull or push the collective, or OH-1 easily goes unstable even CAS/SAS are engaged. Another thing that you need to know in FG world is that you can control collective using the same keys assigned to throttle in aircraft, except its direction is opposite (page-up decreases power, and page down increases it).
When the altitude reaches several feet, its time to make up which direction to go. Actuate the tail rotor (the same as rudder in aircraft) with auto hover enabled. Thanks to auto hover, you are floating on the same spot and make a very stable "Pivot turn." Probably you feel you can be a exhibition heli pilot.
To start flying forward, disable auto hover, and then, gently push the stick. OH-1 brings its nose a bit down and starts flying forward. When the speed reaches about 10-20kts, you may encounter unexpected yaw movement. This is caused by a side-effect of automatic coordinated turn (doesn't occur on a real OH-1, and yes, it is a bug....). You can use stick to counteract this weird behavior.
In auto hover mode, you must not actuate collective rapidly, otherwise OH-1 rolls left to right and/ or pitches front to back. You also must not enable auto hover if OH-1 flies more than 20 kts, otherwise OH-1 will climbs up almost vertically and goes unstable. Though OH-1 will becomes stable shortly after the vertical climb, it is very dangerous and thus must be avoided.
Take-off without auto hover
If you want to make a straight-forward take off without hovering up, simply pulls the collective to half the way up (Pressing Page-down until the speed indicator on HUD becomes center). when OH-1 starts flying up, gently pushes the stick and the OH-1 start flying forward. Keep pulling the collective to increase the altitude and speed. you can balance the speed and altitude using both stick and collective. Needless to say, the gentle control is the most important key.
Climb
You can climb OH-1 by pulling collective, and/or pulling the stick. a helicopter climbs up for losing its speed. Thanks to CAS and SAS, you don't have to worry about the balance among collective, stick, and pedal. The AFCS takes care of it. All you have to do is to concentrate on monitoring speed and altitude. The service ceiling of OH-1 is about 16,000 ft (4,880 m).
Low altitude flight
Since OH-1 is an observation helicopter, it needs to stably conduct a very low altitude flight. Thanks to AFCS, OH-1 can make a very low altitude flight, just like a snake is sneaking around. You can fly OH-1 at a few feet high with 80 kts, moving left to right to see how stable it is.
Cruise
The cruise speed for OH-1 is about 120 kts. You must not exceed 145 kt, or the rotor reaches its stall speed. If the rotor stalls, OH-1 goes nose-up and start climbing, which induces continuous pitching front and back that makes OH-1 very unstable. OH-1 in FG has a speed warning sound, which continuously ticks sound in the cockpit view.
Approach and Land
Decrease the speed by pushing the collective as pulling the stick. OH-1 decreases its speed and altitude when the collective and the stick is well balanced. The nose will be up about 5 to 10 degree (depending on the current speed) while descending. Important thing in approaching is to keep an eye on the landing point, as well as the gentle descent and slow down. When the speed reaches 10 to 20 kts, you can use auto hover. When auto hover is engaged, pushes down the collective slowly. OH-1 will be gently touches down. The key point in landing is to know where to engage auto hover. Auto hover force kills the speed so OH-1 moves either forward or backward while entering the auto hovering state. For accurate landing, you need to gently slow down to almost zero kt, and then enable auto hover. Though you can adjust the position in auto hover mode using stick and the pedal, but it is not that effective, so the positioning before the auto hover is important. (I hope I can implement more effective position adjuster in auto hover mode, but I'm not so sure if the real OH-1 has such function).
Shut down engines.
Welcome back. Simply press { to shut down engines. that's it.
Manual Flight Mode
Though it is not recommended, you can try manual flight mode. To enter the manual flight mode, you need to:
- disengage CAS (pressing Ctrl-E)
- disengage SAS (pressing Ctrl-D)
- disengage Auto hover if engaged (pressing Ctrl-F)
You will see how OH-1 is unstable without AFCS just like (or more than) other choppers in FG.
Even in manual mode, active horizontal stabilizer and semi-auto coordinated turn are enabled. To disable these, you need to do so using property browser. The instruction will be written soon, hopefully :-p
Gauges
No gauges are available at this moment.
Key Bindings
- Ctrl-D
- Toggle SAS (Stability Augmentation System; improves stability)
- Ctrl-E
- Toggle CAS (Control Augmentation System; improves controllability)
- Ctrl-F
- toggle Auto Hover
- "}"
- Starts engines
- "{"
- Shuts down engines
- Page up/down
- Collective