Variometer build for gliding aircraft

If you’re flying through the air in a non-powered vehicle your rate of descent is something that you want to keep any eye one. With that in mind, [Adrian] decided to design his own Variometer (translated) what will have a place in the cockpit next to the other instrumentation. It emits a pitch whose frequency is dictated by the rate at which altitude is being lost or gained.

He went with a PIC 24FJ64 microcontroller to drive the device. It’s reading data from an MS5611 barometric pressure sensor. This measures changes in air pressure associated with a change in altitude. As a user interface he chose one of SparkFun’s Nokia 5110 LCD screen breakout boards. He also went with one of their boost converts which lets him power the device from just one battery cell. The case itself is cut from several layers of plastic using a CNC mill.

In the video after the break you can see how sensitive the device is. Moving it just a few feet up or down has an immediate effect on the sound and the displayed data.

Comments

  1. Hack Man says:

    Uhhhh just how weather resistant is that case?

  2. jc says:

    well, building your own avionics certainly sounds very safe !

    • jc says:

      not only that.. looks like it actually measures pressure in the cockpit. Not even hooked to the pitot static system. VERY safe.

      • hpux735 says:

        It’s a variometer. Not exactly required equipment. He obviously flew just fine before he built it.

      • jc says:

        @hpux735:
        fake instruments don’t belong inside cockpits. Especially ones that could make the pilot believe his vertical speed is different than it really is. What’s the point of having it there anyway? if you can’t trust it, it only serves to distract you.
        Just a thing to fly off and smack you in the head when you run into rough air or have some kind of control surface failure or something. That’s what it’s apparently good for.

      • nickleaton says:

        not only that.. looks like it actually measures pressure in the cockpit. Not even hooked to the pitot static system. VERY safe.

        To measure altitude, you don’t connect to the Pitot.

  3. James Fowkes says:

    Building your own vario is safe enough, you shouldn’t ever be using it near the ground, unlike your ASI or altimeter. Even with those, your primary flight instruments are still your eyes and ears.

    The major drawback with this vario is that most glider (sailplane, not hang-glider) varios are “total energy compensated”, meaning that they only respond to changes due to the static air pressure, not the speed of the glider. Hence needing to be plumbed into the pitot-static system.

    The point of a vario is to tell you when you’ve gaining extra potential energy as a result of vertical movement of the surrounding air. With a non-compensated vario, if you pull up sharply, the electronics will see this as a gain in total energy (kinetic + potential). You’ve actually just momentarily sacrificed airspeed for height, for a gain of (less than) zero.

  4. Adrian says:

    Hi guys, this is a prototype, and works really well (better that my comercial vario) It is a instrument for paragliding, hang glider… No problems for the case… “cockpit” is an instrument holder (camera, vario, phone and gps on it).

  5. geonomad says:

    A few clarifications.

    The photo shows that Adrian is flying a powered paraglider. So the comment about non-powered aircraft seems a bit off.

    There is also no cockpit, so there is no problem having a hand-held variometer. Most of us do.

    The point of a variometer is to indicate the change in altitude, up or down, in order to recognize rising air that can extend the paraglider flight (powered or not). It is not
    a safety device.

    PPGs rarely have any pitot measurement of airspeed, as it has to be far from the pilot and the propellor, which means sticking it out on some kind of boom. It is done, but not often.

  6. Rich says:

    It’s fairly common for sailplane instruments to get their static pressure from the cockpit.

    Cheap, sensitive electronic instruments are often used in addition to less sensitive mechanical instruments that are deemed to be more reliable.

    It would be cool if he could add a gyro, to work out where in a turn the lift is.

    • jc says:

      but the cockpit is a pressure vessel. Its a little similar to empty bottle flying through air. Sure it isn’t totally closed but I don’t think you can accurately measure static characteristics from inside the cockpit. If you farted hard enough, the vario could think you’re descending rapidly, lol

      • gregman_1 says:

        On an unpressurized aircraft, the cockpit will maintain the same pressure as the ambient air outside the aircraft. This is actually on purpose, as it means you can construct the doors or canopy and areas surrounding the cockpit out of the thinnest material possible, and in the most convenient shape possible, saving lots of weight. But all this argument is moot, this is intended for a powered paraglider (which can still be used as a glider, hence the vario), and has no enclosed cockpit to worry about. The lack of airspeed compensation is troubling, though, as without it, it’s just an audible VSI and not really a variometer.

      • jc says:

        @gregman_1:
        that would be correct if the pressure inside the cockpit was always the same and changed at the same rate as outside air pressure, which it really can’t. And the whole point of a VSI is to be sensitive to pressure changes and show altitude change. Just think about it: what’s the point of having static ports (or pitot static tubes) on unpressurized aircraft then? Aren’t they useless by your logic?

  7. adrian says:

    Hi guys, It is a prototype and work really well (better than my comercial vario). The “cockpit” is an instrument holder (camera, phone, gps and vario go fit with velcro on it). Its a standard instrument used by paraglider, hang glider… pilots. No rain, no storms!… when flying :)

  8. Mik says:

    Nice job! Working on my own Hang gliding vario myself. I’m glad some real pilots eventually got to the comments instead of the armchair critics. Weatherproofing isn’t really ever a concern for even commercial varios. If you’re attempting to soar in rain or even a thunderstorm, you’re doing it VERY wrong

  9. nickleaton says:

    The problem is far more difficult than people realize.

    If you measure altitude, and the preasure sensors are pretty good for this, they can detect small changes in altitude. However, that also makes them pretty good microphones and they will pick up on noise.

    In practice, you aren’t interested in the rate of change of altitude. You’re interested in the change of total energy. Your speed and height combined.

    For example, speed up by diving. Large rate of change of altitude, but you can get it back, by slowing down by climbing. Measuring total energy is important. Then your rate of descent depends on speed. If you want to know what the atmosphere is doing, you need another adjustment.

    The other thing is that thermals are turbulent. Fly into one and you can get a gust increasing your measured flying speed. That would produce a false increase in measured energy.

    Fitlering is a big issue.

  10. sarah ward says:

    this sounds excellent. a chea backup audio vario is what all paraglider and hang glider pilots need. it tells us where the thermals are so we can use this lift to gain height for cross country flight. that is all it is for … staying airborne. it is not used for navigation or imc flight, so there should be no controversy here.

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