Introduction

The INAV nav launch mode, also known as Autolaunch, is a very useful feature. You can use it for all kind of planes that need to be hand-launched. With this helpful feature, it is much easier to throw-launch a plane. Its also much safer than throwing a plane with a propeller spinning at 10,000 rpm; especially if you have a pusher plane.This guide will take you through everything you need to know to setup nav launch. In general, the Autolaunch feature works out of box for most planes. Just enable the mode and you are good to go. But, with the default settings , for a good launch you’ll need to have a setup with:

  • A perfect thrust to weight ratio.
  • A perfect throw, at the right angle, and with good speed.
  • And a little bit of luck.

If your planes are too important to you to trust them to pure luck, thankfully we’ve got your back. In this guide we will explain the launch mode in detail. We’ll show you how to find better settings for your plane and make Autolaunch as easy. As simple as throwing a paper plane; except of the fact that your plane will keep flying! This guide will show how to get the perfect setting to autolaunch correctly, so no need to shake and bake, which is a very bad technique. See here to understand why.

Autolaunch settings

The first thing to know: The relevant Autolaunch settings are not (yet) accessible through the configurator GUI. This would make it much quicker to setup nav launch. You need to do the necessary changes in the CLI. There are an infinite number of possible combinations for these settings. They all need to work together to make your plane launch well. But, if you understand each option and how to decide the best values for your needs; it makes life much easier. In the following tables you will find all the options. We will show how to set them to make Autolaunch better tailored to your specific needs.

The thing that is crucial is that you have a plane that flies stable. We talk more about this in other articles. But simply, you want a plane that can fly well in manual and in angle modes, with no trims. You also want a plane that doesn’t “freak out” because the PIFF values are set too high. This means you’ll need to get your plane to a point where it’s ready for the Autolaunch.

If you decide to use Autolaunch for your maiden, this is not recommended. Make sure that you select a good, close preset in the Preset page. It must closely fit your plane, and select low PIFF values. Especially for smaller wings; these should be maxed at PIFF 8, 5, 50 for pitch and roll. Yaw can be even lower, at 5,0,50. We don’t really need an I gain on yaw.

Main settings

CLI name and default valueDescription
nav_fw_launch_max_angle = 45Max throwing angle that is allowed to be accepted as a valid launch throw
nav_fw_launch_thr = 1700Motor throttle value during launch procedure
nav_fw_launch_idle_thr = 1000Motor throttle value when armed and before launch
nav_fw_launch_motor_delay = 500Wait time after throw, before motor goes to launch throttle power
nav_fw_launch_spinup_time = 100Time for incrementally increase the throttle from idle to launch throttle to avoid motor stall
nav_fw_launch_climb_angle = 18Angle to climb at during launch sequence

How to choose each setting

nav_fw_launch_max_angle

The launch angle depends on the way you launch your plane. If you have a standard fixed wing, like a 4 channel trainer or a Talon style; you probably launch it with one hand under the fuselage and throw it like a big paper plane. In this case the default angle of 45° is totally fine. This will avoid accidental launch detection when carrying the plane after arming it.

For flying wings. If you launch with a wing throw, 45° is fine too. We do not recommended a wing throw, because Autolaunch could flip it and crash into ground with full throttle. If you decide to do an over-head launch, by throwing it backwards over your head. You need to set this value much higher. It is fine to select 180° in this case.

nav_fw_launch_thr

The launch throttle is mostly depending on 2 factors:

  1. The thrust to weight ratio of your plane.
  2. The capabilities of your hardware: battery, ESC, and motor power capabilities.

We recommend a value where your plane is close to hover. Hold the plane in your hand nose up. Throttle up slowly until you feel the plane become light. You want it to feel like it would not climb if you let it go; of course do not do that! That will be your launch throttle.

If the plane is very big and has a low thrust ratio, set this to 2000. Also check the current that is needed to obtain the selected throttle value on the bench. Your battery, ESC, and motor need to tolerate this current for about 10 seconds. Ensure the current is within the limits to avoid overheating and damage to the power system. See Determining throttle setting for more information on this topic.

nav_fw_launch_idle_thr

By default, the idle throttle is set to 1000 which means no throttle. This is totally fine on standard props. There are 3 scenarios where you can, or even should, select a higher value. T have the motor already spinning before you throw it.

Scenario 1: You have a very low thrust to weight ratio, or a very heavy plane

Idle throttle will give you an extra push when throwing the plane. This helps to gain speed faster, and avoid a stall or height loss. A Good value here would be 1200-1400 depending on your motor power. Be aware, that the motor will spin at relative high speed as soon as you raise the throttle after arming!!!

Scenario 2: You are using a folding propeller.

It can be very stressful for your motor, props and even fuselage if a folding propeller is spinning instantly to 100% power if it is folded. So, you can use a low value like 1100 to make sure the prop is open and in balance before launch.

Scenario 3: If you want to launch your wing with a wing throw

With a wing throw, it makes sense to give it a high idle throttle value. This avoids a strong yaw spin when throwing the wing and makes your launch more stable. Half to two thirds of the launch throttle value is recommended in this case. An example, if your launch throttle is 1700 this should be set to 1350-1450.

We recommend to keep Motor Stop feature enabled to avoid motor spin on arm. It will spin at idle throttle as soon as you rise the throttle stick on the remote.

nav_fw_launch_motor_delay

This delay brings extra security, especially for pusher planes. By default, this is set to 500ms. But, this time may be too long; and the plane will hit the ground before the motor has full power, which would suck. This is especially for smaller planes which quickly lose speed because of low weight. Therefore, you should lower this value. We recommend a value of 200ms.

For tractor planes, with the propeller on the nose, you can even set this to zero. Do not set this to zero on pusher planes! The propeller could hit your hand with full speed.

nav_fw_launch_spinup_time

As soon as the launch is detected and after waiting for the motor delay time; the Flight Controller will power up the motor. By default, the throttle will rise smoothly from idle throttle to launch throttle in a time frame of 100ms. This is important to avoid motor stall, especially for bigger props and folding props.

For planes with 8-10-inch props we recommend even 200ms and more on larger propellers. You can test this on the bench to make sure the motor gets full power without stuttering, but be careful.

nav_fw_launch_climb_angle

After launch throttle, this is the most important value and it depends on a multitude of factors. Motor Power, weight of the plane, throw speed, and possible lift. Big planes or motor glider with a very high lift ratio and low thrust. In this case, keep a low climb angle like the default 18°.

Small planes with a low thrust to weight ratio should keep a lower angle. But because they can quickly loose speed while motor goes to full power, keep the angle to at least 20°. Then the FC can pitch harder up to gain back height. Also, a bit higher P-Gain in PIFF controller can help to get a quicker climb angle.

For other planes we recommend 25-30°. But make sure the plane can sustain speed at this climb angle without stalling.

If you have a high speed setup and a lot of power, select a very steep climb angle. During the first second or two, while the plane is accelerating; the backwards G-forces could make the FC “think” it is already climbing. This can even cause a nose down in some conditions. Therefore, the thrust for launch should never be higher than the plane could hover on its propeller. Better slightly lower to get a quick and correct climb angle.

Optional settings

CLI name and default valueDescription
nav_fw_launch_accel = 1863Needed G-Force when throwing to detect launch
nav_fw_launch_detect_time = 40Time in ms the launch acceleration needs to be exceeded to accept the launch
nav_fw_launch_min_time = 0Time to ignore any stick input after launch sequence has started
nav_fw_launch_timeout = 5000Time for the launch sequence to run. After that the Plane will switch to the actual active flight mode
nav_fw_launch_max_altitude = 0The maximum altitude to be reached. Upon reaching, the plane will switch to the selected flight mode
nav_fw_launch_end_time = 2000(INAV 2.6+) Time for the transition of throttle and pitch angle, between the launch state and the subsequent flight mode [ms]

How to choose each setting

nav_fw_launch_accel

In most cases it is not necessary to change this value. This means, the FC need to detect a force of 1.8G to accept the launch throw. For big and heavy planes, this can be lowered because they are harder to throw. But be careful, because launch detection will be more sensitive and accidentally launch activation could happen.

nav_fw_launch_detect_time

This should not be changed for throw launches. It is a good value to get a reliable launch detection. For a catapult launch you can set this a bit higher, depending on the length of the catapult. But it is more useful to rise the motor delay time than the detect time.

nav_fw_launch_min_time

If you launch your plane while you have your remote in the other hand; it can be safe to set some delay here. Especially on some remotes with very sensitive sticks. This can avoid accidental Autolaunch aborts when the remote gets a shake during the throw. We recommend to not go above 2000 (two seconds). This will allow you to gain control and abort a launch as soon as possible if needed. This means for a full two seconds you will not be able to control your plane.

nav_fw_launch_timeout

Sometimes the default 5000 (five seconds) can be a bit short. Especially if in you need to take the remote, put on your FPV goggles, take a seat in a camping chair, crack open a brewski, and open some Dorritos. So it is always a good idea to rise this value up a bit. In theory this can be set up to 60 seconds (value 60000). But then the plane will fly far away. This is the time to wonder if you have your home position to set at first arm? You ask Marc to tell you a funny story about this topic. Set a value that is comfortable for you and your surroundings.

nav_fw_launch_max_altitude

By default, this value is disabled. But if you want the plane to always climb to a specific height; it makes sense to put a value here. The value is the height in cm. The plane will then abort the launch sequence as soon as the set height; or as soon as the timeout is reached. To make sure the height is reached, you need to set launch time high enough, especially at flat climb angles. But we recommend to not disable launch timeout, otherwise this could cause a flyaway.

nav_fw_launch_end_time

The launch end time is mainly a cosmetic feature. In older INAV versions, after ending the launch sequence, the plane rapidly switched into the flight mode that is set on the radio. If ANGLE mode is set on the radio, the nose was pushed down hard to level out, after the launch is complete. The new Launch-Transition feature introduced in INAV 2.6 levels out the plane gently during the set timeframe (in ms) before switching to the selected flight mode. This results in smooth transition from Launch into other Flight Modes like POSHOLD, ANGLE, RTH or WAYPOINT.

Determining throttle setting

The throttle setting is very important when we setup nav launch.The first thing to understand is that the throttle setting influences thrust. But there isn’t a one-to-one correlation between throttle setting and thrust. What this means is that the best throttle setting for your plane will be plane specific. We would love to tell you a value at this point that you could use for all your planes. But, you will need to perform this test for each plane.

When you look on your receiver page in the INAV configurator. You will notice that as you move the throttle up and down the values change. In a perfect world the very bottom of the throttle range is 1000. 1000 represents ”no throttle.” In reality it may be something like 980. If you haven’t calibrated your transmitter in a while this may be the best time to do it. You should also set the endpoints in your transmitter to get the perfect 1000-2000 range. You only need to do this for the sticks. It’s common for the sticks to be of a bit, and it won’t affect performance of the plane. But for the rest of this example, we’ll talk as though your throttle was perfectly calibrated.

There are 2 ways that we can get the throttle setting. One is using the transmitter and estimating the throttle value. The other is to use the INAV setting page, where we can see the exact value. I’ve just mentioned the advantage of using INAV. But the disadvantage is that you have to be careful of the USB cable too. Either way, you will need the flight battery in the plane, and have it in manual mode.

Transmitter method

If you are using OpenTX; to make this easier you can set up a telemetry screen showing the throttle input value. This will range from -100 to 100 when you move your throttle stick. The reason to set up a page rather than just use the channel monitor, is the page has bigger text. This will make it much easier to read. We can apply a calculation at the end to get the close figure.

Hold your plane nose up with one hand. With the other you’ll need to work your throttle. You may want to do this outside. With the throttle off you will feel the full weight of the plane in your hand. As you fire up the throttle the plane will become lighter. When it feels like it’s just about ready to fly out of your hand, note where the throttle position is.

If you don’t have OpenTX or a value in the -100 to 100 range; you will need to estimate the value. The throttle all the way off is 1000 and full throttle is 2000. If you’re at half throttle the number would be 1500. Thus 1250 would be ¼ throttle and 1750 would be ¾ throttle. Estimate your throttle value based on the above values. Use this value for nav_fw_launch_thr.

If you have a value between -100 and 100. To calculate the value for nav_fw_launch_thr, follow this formula.

nav_fw_launch_thr = (((Throttle + 100) × 10) ÷ 2) + 1000

To break this down, I will show an example where the throttle value in the transmitter was 15. So just over half throttle.

nav_fw_launch_thr = (((15 + 100) × 10) ÷ 2) + 1000
nav_fw_launch_thr = ((115 × 10) ÷ 2) + 1000
nav_fw_launch_thr = (1150 ÷ 2) + 1000
nav_fw_launch_thr = 575 + 1000
nav_fw_launch_thr = 1575

The INAV method

Make sure that the USB cable will stay clear of the propeller(s). Go to the outputs page in INAV configurator. Hold your plane nose up with one hand. With the other hand, enable the motors. With the throttle off you will feel the full weight of the plane in your hand. Slowly raise the throttle with the master slider. The plane will become lighter. When it feels like it’s just about ready to fly out of your hand, note where the throttle position is. It is displayed in a few different places on that page. Most notably in the blue bars that rise with the throttle. This is the number to use in the nav_fw_launch_thr setting. Make sure to disable the motors as soon as possible.

Is your plane ready?

One of the most important assumptions we make about Nav Autolaunch is that your plane is setup well. What you need to keep in mind, is that for a short period of time the plane is flying itself. So, let’s use some common sense. First of all, go somewhere that you’re able to launch the plane that is away from people and property. Sometimes things go wrong, and we just want to be sure that we keep your risk exposure low.

The second thing is, if your plane is flying wonky, don’t play with this mode. You are going to want to focus your efforts on getting your plane flying well. A flight controller helps a good plane fly better. But it can only do so much for a plane that isn’t set up well. We cover this topic more in other articles. But the gist is to make certain your plane can fly well in the manual mode without trims. Then use servo auto trim and autotune to make certain your plane is flying well in the stabilised modes. If the plane is pitching down in stabilised modes, you can correct this with board alignment. You want to add low values like 1 or 2. However a good autotrim should fix this.

The last thing is that you’ll want to make certain that you can bring the plane back to you. If your radio has a range of 1km and your plane is flying faster than 60km/h; you will fly out of radio range before you’re ready to fly. Hopefully your NAV RTH is set right. You can also add Nav RTH or POSHOLD to NAV Autolaunch. This means that the plane goes into its NAV RTH or POSHOLD routine after the launch is complete. This can allow you more time to get your goggles on. You will want to have RTH set up correctly and fully tested before you enable this feature.