THE REASON WHY WE DO NOT USE THE ACCELEROMETER TO INTEGRATE THE VARIOMETER
Many pilots ask us the reason why we do not integrate the variometer by an accelerometer.
As you know, Compass introduced the C-Probe some years ago. This instrument, between others, has a gyro and an accelerometer. It would be not big deal to use this hardware to integrate the variometer.
This idea was soon abandoned because we are convinced that it would not lead to any real improvement. By integrating an accelerometer, the vario becomes more responsive, but we found a problem. If the pilot starts to turn (or already is in a turn) the accelerometer feels not only the lift force, but the response of the sensor is affected by the angular velocity. This can false the variometer’s reliability, in terms of climb rate. Therefore, to compensate, it becomes necessary to perform a series of calculations. But, in turn, this operation increases the electronic noise. As consequence, the variometer becomes less precise, and the unit is compelled to use some more bits to sample the data.
Another problem is that the accelerometer registers all the movements of the pilot’s harness: the oscillatory movements in pitch and roll. The result is very annoying in flight, if the sensitivity is much! But at this point the accelerometer becomes useless.
Another question is: the human vestibular apparatus is better than any accelerometer to measure the vertical accelerations. So we do not really need the accelerometer while entering in a thermal: we are able to feel and distinguish in an optimal way. We need a precise variometer in the moment the system (our otholits) is stabilized (when we are inside the thermal and the acceleration stops and turns in a plus or less constant climb). For further explanations see the Compass Wiky: “the myth of flying without a variometer”.
Noted that we mount a very precise barometric sensor and we process data at 24 bit, the result is that the responsiveness and reliability of our “traditional” variometer is still better than its integration with an accelerometer.
This is demonstrated even by the pilots users: if they set the Compass instrument at maximum responsiveness, they find too much annoying the increased sensibility of the variometer.
Ultimately, in our opinion integrating the vario by an accelerometer does not lead to any improvement and could be distracting for the pilot. With a great sensor and processing the data to 24 bit, integrating variometer with an accelerometer is not worth