On Tuesday, October 28, 2014 4:39:56 PM UTC-7, wrote:
On Wednesday, October 22, 2014 2:03:48 AM UTC+11, jfitch wrote:
On Monday, October 20, 2014 4:24:46 PM UTC-7, wrote:
On Friday, October 10, 2014 3:50:54 AM UTC+11, wrote:

Excellent questions and observations.



I am focused on the S80 and Butterfly primarily because they have an artificial horizon but also would like a unit that can filter out horizontal gusts that cause me/us to think we have entered a strong thermal. It also would seem that the instantaneous wind readings would be very helpful when flying convergence lines.



You have a built in filter that can eliminate false readings due to gusts. It's called your backside. If you can't feel the acceleration, it's not there.

Acceleration due to a a vertical or horizontal gust are not discernible by the human backside. Both result in an increase in lift: the former due to an increase in the angle of attack and the latter due to an increase in air speed. Both can be used to gain energy, but you will find circling in the latter a pointless exercise. Which is why every variometer manufacturer is trying to differentiate them.

A horizontal gust does NOT produce acceleration. That's why you can't feel it. If you cannot sense vertical acceleration it's not there, despite what your instruments are telling you.
To put it another way: if your vario is telling you that you are accelerating upwards at 5 knots (500 fpm or over 8 feet per second) and you cannot feel it, then you can ignore it as a gust. Why look for a complex technological solution to something so simple?
A vertical gust is a different matter. I presume by vertical gust you are referring to a vertical movement of air. What distinguishes a vertical gust from lift?

A horizontal gust most certainly does produce acceleration, at least on this planet. It will cause a horizontal acceleration due to direct drag on the airframe, and a vertical acceleration due to an increase in lift. To refresh your memory, lift = dynamic press x coefficient of lift x wing area. The instantaneous coefficient of lift does not change at a horizontal gust (nor obviously does wing area) but dynamic pressure increases as the square of the velocity. If the gust is from ahead and say 10 knots flying at 50, you have a sudden increase in lift of 44%, therefore you will feel 1.44 Gs upward acceleration momentarily.

A vertical gust is what we call lift, though it can be quite transient, then we call it turbulence. A vertical gust increases airspeed slightly, but increases angle of attack and therefore coefficient of lift markedly. That causes vertical acceleration due to increased lift, and horizontal acceleration due to an increase in induced drag. A 10 knot vertical gust encountered at 50 knots will only give you about 1.2 Gs though, since lift/angle of attack is approximately linear.

Your variometer might also be confused in various ways (lag, TE comp, acceleration effects) but the accelerations described above are very real. In gusty conditions (or better still a high wind shear gradient) it is possible to extract energy from horizontal gusts, sufficient to soar. It has been done in full size sailplanes and is routinely done in RC gliders.