Howto – X-Rotors

Whatever is your preferred simulated flight activity with our AW139, from mountain rescue to off-shore operations, you may have already encountered the need to trim your helicopter. In this article we’re going to explain ho to achieve a proper trim for both rotors and flight controls to ensure your flight is comfortable and efficient.

WHAT IS TRIMMING

Trimming means fine tuning your aircraft’s attitude. This is useful in simulated flights as well as in real ones to achieve maximum operational efficiency in terms of lower fuel consumptions, less pilot’s effort and comfort for your passengers. Trimming is related to each of your axis – pitch, roll and yaw – and each function is nicely reproduced and managed from the cyclic and collective sticks.

FORCE TRIM

As the real AW139, our helicopter spots a force trimming device which allows you to get maximum control over the flight attitude. On the interseat MISC panel you have the Force Trim (FT) switch, when both autopilots are engaged (AP1, AP2 on the interseat panel) this little switch puts the AW139 autopilot from SAS mode (Stability Augmentation System or hands-on-controls) to ATT mode (Attitude or hands-off-controls).

ATT mode enables two distinct functions:

Couples the Flight Director (FD) to servos. Once a FD mode is selected (ie. HDG, ALT, etc…), this function allows the helicopter to fly autonomously and can be switched off by pressing CPL button (when it’s green) or by putting FT switch back to OFF;
Freezes your cyclic in position. This function in particular is needed to fly hands-off controls, as in reality. The cyclick stick can be kept in position at the desired forward speed and nose pitch angle. To temporarily unlock the cyclic, keep your hands on it and release the locking system by pushing the FT REL button on the cyclic stick. You can even assign a key or a joystick button to it. Pilots normally leave the FT switch ON.

When ATT mode is ON, the cyclic hat switch trims the cyclic left or right. Pressing it up or down increases or decreases airspeed when IAS (indicated air speed) FD mode is activated. When ATT mode is OFF, pressing it left or right set the heading bug left or right. Pressing it at the center activates the HOV (hovering) mode, see here for details.

CLTV/YAW TRIM

At the right of the FT switch there’s the Collective / Yaw Trim switch. Once activated it allows you to:

Freeze your collective and pedals in position. Unlock them by using the CLTV/YAW REL switch below the collective stick. You can assign a key or a joystick button to it. When the CLTV/YAW trim switch is ON you can trim the collective up or down with the left hat switch (the one at the right controls the third external light spot below the fuseleage); normally the same hat switch has the function to set the reference target up or down once a FD collective mode (ie. ALTA or VS ) is activated;
Trim your yaw left or right with the collective hat switch (left one). This function is really useful on longer leveled flights to achieve comfort and optimize fuel consumptions. You can reset the yaw trim by pressing the switch on top;

Here’s a first article of a series dedicated to trouble-shooting. In this one we’ll explain how the auto-hover is operated on our AW139 version 4.00.

THE BASICS

What you need to get first is how the auto-hover works in this very first release. Basically it works as the real one, once activated it will reduce all your X and Z axis velocity vectors to zero knots, in other words it will decelerate your horizontal directions until the helicopter will stay in position without speeding up, unless you decide. The Y axis, or vertical direction and speed, will be controlled through the collective. The more you raise it the higher the ascending speed and vice versa. Yaw, or nose heading around Y axis, is controlled with the pedals. Once activated, the autopilot attempts to keep the your heading steady. In adverse weather conditions, you may be asked to act a little bit more on the pedals. As explained in the guide provided with the product, auto-hover shoudn’t be engaged above 20 KTS. This is the limit speed above which the helicopter will have to reduce too much speed to keep the helicopter nearby where desired. Engaging the auto-hover abobe 20 KTS may give unpredictable results.

TYPES OF AUTO-HOVER

We’ve been actually implementing two types of auto-hover.

Type A is hands-ON-controls is untied to the FT (force trim) system of the aircraft, in order to leave the pilot more control on the rolling and pitching axis. It’s designed to help out during manouvers, approaches, in adverse weather conditions and can be used to decelerate the aircraft.
Type B is hands-OFF-controls and is tied to the FT (force trim) system. This is the stablest hovering mode and lets you put your hands off flight controls. When type B is engaged the nose pitches up +10° as described in this article. Being in conjunction with flight trim means that you can trim the direction and speed of auto-hover. As the real one, never exceed 60 KTS in this mode.

OPERATING INSTRUCTIONS

The two modes are mutually exclusive. They can be switched by switching ON (type B) or OFF (type A) the FT (force trim) switch on the MISC panel and then pressing HOV (hovering) mode button below on the FD (flight director) panel.

When Type B is engaged and no joystick is present, the collective raises automatically to the right blades pitch value, in other words it lets you achieve an automatic take-off, putting your aircraft steady ±5 ft.

CHANGES ON THE MFD

HOV mode is designed to reduce horizontal speeds to zero, as in reality. This means you will always control the ascent or descent of the helicopter through the collective. When activated, the HOV mode changes the HSI on the MFD with a compass showing the velocity trend and direction, just like the real one.