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LookOut Vario


As an electronic engineer, it is obvious to build your own variometer. As said so done, it only took approx. ten years :-)

Why build yourself? For me, it was to get less noise in the cockpit, and as much automatic help as reasonably possible. And of course because it was fun.

How less noise? Most variometers use a variable frequency to indicate the lift. But since different frequencies have different propagations in the cockpit and thus attenuation, you will have to adjust the volume so that you can also hear the faintest sounds. That means again that the loudest sounds are louder than they needed to be in order to be heard. And this in turn causes the volume of the radio must be more powerful than actually necessary. Haven't you ever tried after a trip of several hours to turn off the sound pollution, and just enjoy the silence?

Therefore, my variometer uses pulses with fixed frequencies instead, where the pulse repetition rate indicates the lift. Each pulse consists of 3 frequencies, in major for lift, and an owl cry for sink. Sound propagation and the perceived volume are thus independent of the lift and can be turned pretty much down, and so goes for the radio volume.

Listening-friendly pulses. Each pulse has a relatively fast "attack" time, and longer "decay" time, ie nothing like square pulses.

A must to keep the sound level low is to adjust the volume of the variometer according to the speed. Have you not tried yourself immediately after landing to turn off the annoying loud variometer? A volunteer test pilot (myself) flew with a test version of the LookOut vario program, which logged all adjustments to the sound made by the pilot during the flight. The test program had no automatic sound control, so the poor pilot had to constantly adjust the sound to an appropriate level. Based on these results, the automatic sound control was programmed. This method also compensated for the slightly different sound pressures that the different sound signals have.

Why is it called LookOut Vario? An important feature of my variometer is that it acoustically indicates if it will pay off to stop and curve, thus achieving a lift better than the set MacCready value. All without having to look at instruments. While curving, the otherwise fixed frequencies will vary a little bit, slightly higher frequencies when the lift is above the MC value, quite useful.

Integration with my Gliding app. If you set the MacCready value on the variometer, this value is of course transferred to Gliding, so final slide e.g. is calculated with the variometer's MC setting, what else? Measurement of the aircraft's IAS is similarly transferred to Gliding, so current headwind or tailwind is used for the final glide calculation.

Automatic switch between sollfahrt and vario. The Gliding app knows whether you fly straight out or curve, so this information is sent continuously to the variometer so that it automatically switches between sollfahrt and vario. This goes faster than switching at a given speed, and straight-ahead flying at low speed under a good cloudstreet takes place in sollfahrt mode. The sound level for sollfahrt indicates how close you are to the optimum. If you move away from the optimum speed, you will slowly be told with a louder sound, if you approach the optimum, the sound will be muted quickly.

Low power consumption. Built with reasonably modern components and a class D output amplifier, so power consumption is low.

Quick start-up, only takes 3-4 seconds. Really good sensitivity and an automatic zero point adjustment that just works, which is one prerequisite for having clearly different sounds for lift and sink.

Conversion and transfer of RS 232 logger and Flarm data to the Gliding app, so that this e.g. can show a Flarm radar display.

The joystick on the stick is used to navigate Gliding's simple menu system. Power supply for logger, Flarm and mobile. Quick connectors to the aircraft's pressure hoses.

Why analog sensors? When I started the project, the analog pressure sensors were much faster than the digital ones. Today, however, the difference is significantly smaller. I tried comparing response time for the LookOut vario against a ColibriII that was set for the fastest possible response time. The difference is noticeable, LookOut vario is 825 ms faster to respond. But ColibriII is also an old fellow. Another advantage of the analogues is purely mechanical, easier to connect to the pressure hoses.

New things I learned. Found out how to improve the contrast on laser printed print layouts by heating them up to 200 degrees for 2 min. Then the black pigment flows much more together so the contrast is 3-5 times as good. Also learned to add solder mask to the prints. And then I finally managed to anodize the front and back plates myself, without having to buy pre-anodised photo-sensitive plates. Sulfuric acid in the fridge is a good thing, but it is not quite easy :-)

For more details read LookOut Vario Description.docx