Ultimate-Jets

Here is a short description on how to setup the Weatronic MUX box and telemetry sensors on the Weatronic system.

The MUX box is a sensor interface that plugs on the SCU port of the receiver. It enables the receiver to send you the data that is collected by the sensors.

It requires two servo cables to be plugged to the receiver. One goes to the SCU port and the other one to a servo output via a Y cable or to a battery port. The other cable is only just a power supply cable.

On this picture you can see the black "batt" cable at the bottom that goes to the receiver Y servo cable ( power supply ). The blue plug goes to the SCU input slot of the receiver.

Once the MUX box is connected to the receiver, power up the system. You will see the MUX box green and red LEDs flashing for a little while and then, the red should extinguish and the green become steady.

Once this is done, plug the DV4 module to the laptop via the USB port and open up the GigaControl software.

Go o the MUX box tab.

You should see this:

The MUX box 1 tab on the top left has turned green and shows the device type and serial number.

You can now plug the required sensors to the available slots.

The pitot tube:

It is a great little device that works on the Prandtl principle. The front of the tube measures the dynamic pressure, while the annular hole measure an average static pressure around the tube. The rounded shape of the tube front assures that the dynamic pressure is read correctly in a reasonable range of angles of attack.

The back of the pitot tube will be connected to the pressure sensor by two very tiny silicone tubes. One is blue and connect to the blue nipples, whereas the other one is white an connects to the non colored nipples. It is essential to ensure that the silicon tubes are not pinched when installing them.

The  pressure sensor is a very tiny little cube with a servo plug on its back.

The servo plug HAS to connect to the A1 input of the MUX box as this is the only input that accepts this device.

The pitot tube has to be installed in a free flow environment, as streamlined as possible and at least 40 cm away from any fuselage surface. The best location for a jet is a the front of the nose. Make sure that the pitot tube is aligned vertically and horizontally with the symmetry axis of the fuselage.

Note that when you are at the field and switch the receiver ON, the pitot system goes through a boot up sequence and zeroes. It is important at that point to keep it protected from any wind interference. I found out that putting an open cells foam hood on the pitot before switching ON was doing the trick.

To make sure that the zero was done properly, I have a little trick: just place the model nose in the wind after the foam hood is remove. HAve a look at the MUX box live data. You should read the wind velocity.

When all the connection is done, enable the pitot sensor in the MUX box tab under sensor A1.

The sensor name is 250 km/h pitot speed sensor. 5 Hz sampling rate should be enough for most users ( 5 readings per second ). ote that the 450 km pitot is the same device with the little tab at the bottom of the cube welded. I have not fund this as necessary so far. My pitot was able to record speeds as high as 300 km/h without problem.

Once this is done you should see some live data on the right column. It shows in meters per second. The voice output can be configured in mph though. So no panic here...

Now you could test the system by using a compressor and gently send air into the front of the tube at a distance of 1". You should see the live speed increase a bit.

Then the speed output can be configured in the voice output tab to broadcat MUX box, A1 speed, in mph. However, at this stage of the software version, the warnings are still programmed in meters per second. So if you want to be warned of a low speed of 50 mph, you will need to set it as 27 m/s. However the voice warning will say " caution, MOX box speed fifty miles per hour ".

The 125c temperature sensor:

It is a tiny device that can plug on any analog input  of the MUX box ( A1 to A4 ). Once you have plugged the device and installed it in the fuselage, you can configure the MOX box tab. Here is an example where I set up the temperature sensor on A2.

Then select some sample rate to enable the sensor:

Using a this sensor can be useful to monitor a fuselage temperature at the back of the turbine. However you cannot use it as an EGT sensor as the max reading is 125c. There is a specific device to get EGT readings.

The benefits of the pitot tube over the remote GPS device is twofold. First of all you will have a continuous reading of your speed. With the remote GPS device, the speed will only read when the sensor is looking at the sky and has acquired the satellites. Then the pitot tube will give you an air speed whereas the GPS device will give you a ground speed.

Here is an example of a flight with the pitot tube speed. It is the red curve on the bottom window.

If you want to monitor your approach speed at 1,3 vs and get the system to give you a caution when you reach this speed, I would highly recommend the use of the pitot tube. This is very useful for heavily loaded scale jets. It will enable you to nail your landings every time.

Below is an example of a stall conducted at landing flaps on the Scorpion Mk2. The stall speed is 12.8 m/s or 46 km/h or 28 mph. The approach speed is 1.3 Vs or 17 m/s, 60 km/m, 38 mph.

Additionally you can use the device to monitor your speed in flight and give you a warning when approaching a stall condition.

I typically setup the voice output for the pitot tube as followed:

Control channel= flaps

1. flaps up: minimum speed caution at 1,3 Vs

2. takeoff flaps: maximum speed caution at Vr

3. landing flaps: minimum speed caution at 1,3 Vs

Where Vs is the stall speed for each flap configuration as established by doing a stall test with the pitot tube logging enabled.

The voice output file should show something like this:

On this example the 3 values of 1.3 Vs have been inserted for the 3 flaps settings. I get a caution callout when I reach this value in all situations.

Written by Olivier Nicolas — September 17, 2013

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