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Flight modes in Ethos

The power of flight modes

Flight modes are a really cool feature of Ethos. At their simplest, they allow you to switch quickly between different trim settings. However they offer many other ways to make the pilot's life easier. In this article, I'll explain how to set up your flight modes, and how to use their power to the full.

Sailplane example

Let's suppose that you're flying a sailplane, and it enters a thermal. To take advantage, you might want to:

If you made the adjustments manually, the thermal would be gone before you finished! But by setting up a special flight mode, you could accomplish all three operations at the flick of a switch.

The same applies for other phases of flight like cruise, landing and so on. By setting up a flight mode for each phase, you can react faster to changing conditions.

The active flight mode

Every model has one or more flight modes available, including a 'default' flight mode. Ethos maintains a simple rule:

The flight mode which is active is called the active flight mode. When a flight mode is active, all its associated trim settings, mixers, special functions etc. go live.

Since only one flight mode is active at any moment, each one should represent a temporal phase of flight independent of other flight modes. An example of a good combination is 'Launch', 'Cruise', 'Thermal' and 'Landing'.

An example of a poor combination would be 'Landing' and 'Crow brakes', since their functions overlap. In general, flight modes should be broad in scope rather than being tied to specific mixers.

Managing flight modes

Flight modes are managed in the Flight modes screen. This is where you can add, delete and modify flight modes.

The screen displays all the flight modes belonging to the current model. These comprise the Default flight mode, followed by (optional) user-created flight modes.

Flight mode list

Flight modes menu.

Let's look at these in more detail:

The Default flight mode

The default mode is always present. It's shown at the top of Flight modes screen, with a blank Active condition.

If you don't create any flight modes, then the default flight mode will always be active - without you knowing, or needing to know. Think of it as your 'fallback' flight mode if none other is active.

Flight mode list

The default flight mode.

The initial name is 'Default Flight Mode' but you can change it to something more meaningful.

User-created flight modes

The real power of flight modes is realised when you create additional flight modes.

To create a flight mode, click the '+' at the top right of the Flight modes menu. This opens the flight mode editor. The key parameters are name and condition:

Flight mode editor

Flight mode editor

Flight mode priority

Every flight mode has a priority. Priorities are important where flight modes are defined with different activation methods — they allow Ethos to mediate when there's a conflict.

The priority is simply the position in the list - the higher up the list, the higher the priority.

The exception is the default flight mode, which is at the top of the list, despite being lowest priority.

Flight mode editor


How Ethos determines the active flight mode

Ethos uses a simple rule to select the active flight mode:

Let's look at an example. The screenshot below shows a typical setup for an F5J electric sailplane. There are five flight modes. Highest priority is Power. Next is Landing, followed by Cruise and Speed. The lowest priority flight mode is Thermal (since it's the default).

'Power' mode is activated by pulling the throttle stick (logical switch THROTTLE UP). Landing mode is activated by pulling the crow stick (logical switch CROW STICK DOWN).

Flight mode list

Flight mode list. Active conditions are a mixture of logical and physical switches.

Suppose the crow stick is pulled, while the throttle stick is at idle. Let's examine how Ethos chooses the active flight mode:

The active flight mode is always highlighted in the list.

Flight modes and trims

Trims can operate in two ways with respect to flight modes.

The behaviour is defined in the Trims menu.

Trims menu

Trims menu

Putting flight modes to use

So far, we've seen how flight modes are managed. In this section, we'll learn how to put them to use!

There are essentially three contexts in which Flight modes can be employed: (a) to enable/disable mixers, (b) in special functions and (c) in logical switches. Let's look at each in turn:

Enabling/disabling mixers

A mixer may be linked to one or more flight modes. With a sailplane, for example, a crow compensation mix would be enabled in Landing mode, and disabled in all other modes. Or, on a slope racer, snapflap might be enabled in Normal and Speed modes.

To link a mix to specific flight modes, open the mixer menu, and tick the relevant fields in the Flight modes filter. The flight modes are shown by their priority ('D' for default, '1', '2', '3' etc.)

Mixer active in FM3

Mixers menu showing mixer active in FM3

To trigger special functions

Flight modes can be used as conditions in special functions. One common application is for a flight mode to announce itself using a Play track action:

Special functions for flight mode announcements

Special functions for flight mode announcements

In logical switches

Flight modes can also be used as in logical switches. For example, you might want some behaviour within a flight mode to change depending on the position of a switch. In the code below, LSW10 is true if flight mode 1 is active and SA is down

Logical switches with FM as condition

Logical switch with FM1 as one of the operands

Programming flight mode switches

In this section, we'll look at the most common way of activating flight modes, namely using a switch.

For up to three flight modes

For selecting up to three flight modes, a single 2- or 3-position switch is sufficient. Here's a typical scheme for three flight modes:

And here's how it might be implemented in the Flight modes menu. Note that only two extra flight modes are required, since the third position will naturally fall back to the default ('D') flight mode.


1:speed condition=SA-up

2:cruise condition=SA-mid

For four or more flight modes

If there are four or more flight modes, two or more switches will be required. Below is a typical scheme for four flight modes. From the user's point of view, it works like this:

And this is how it might be implemented in the Flight modes menu:


1:speed condition=SA-up

2:cruise condition=SA-mid

4:thermal_2 condition=SF-down

Let's check that it works. Imagine that SA is down, and SF is up. Ethos starts from the Speed flight mode (the first flight mode with a condition). The condition evaluates to False (since SA is not up). So Ethos steps the next flight mode (Cruise). Its condition is also False. And on to Thermal_2, which is also False.

Having exhausted the list, Ethos falls back to the default condition (Thermal_1) - as intended.

Note that no logical switches are needed, even though the condition for thermal_1 is logically 'SA-down and SF-up'.


Sometimes it's useful for a flight mode to be activated without user intervention. An example is an electric model with a 'Power' flight mode. Instead of requiring a switch, Power mode should be activated automatically when the motor is running.

To determine if the motor is running, we define a logical switch to check if the motor output is above the 'idle' value (−100%). Next, we specify the logical switch as the condition of the Power flight mode:

LSW1 CH7 > -100%

FM1:Power ActiveCondition=LSW1

(Digression: for safety, there should also be an arming switch which is independent of flight mode. The state of the arming switch will determine whether the motor can actually run.)

Similarly, a Landing mode might be activated by pulling on the throttle stick. When the stick is at the top, it carries a value of 100%, so we can use the following code to activate Landing mode:

LSW1 Thr < +100%

FM1:Landing ActiveCondition=LSW1

Landing mode would typically activate a Butterfly mix.

Wrapping up

Flight modes are a powerful feature in any RC system, and particularly so in Ethos thanks to the multiple contexts in which they can be employed.