On Sunday, September 18, 2016 at 5:42:36 PM UTC-7, Sean wrote:
I thought accurate straight line glide computer wind accuracy required a fixed compass (aka LXNAv) for the best not thermaling wind detection sensitivity. My S10 is going to have a compass module shortly. But I really can't imagine a need that that much wind accuracy. The wind where you are now isn't the problem. It's accurate anticipation of what the wind is 1, 5 10 and 20 miles ahead, just like sailing, but much less critical.

Am I right or wrong on the compass module?

I believe the butterfly an fixed compass built in, and this is the reason that it is more energetic on updates? Correct?

The Butterfly (Air) vario wind is inertially derived and calculated many times a second. As far as I know they are the only ones really doing this. I'm pretty sure they use air speed, GPS speed, etc for long term calibration, but the instantaneous wind is derived from the MEMS sensors. For example I will get an accurate instantaneous wind in my motorglider with the engine running. The tail pitot is in the prop wash and indicates about 45 knots over the actual speed. The Oudie or XCSoar will say I have a 45 knot headwind whenever it is running. The Air vario gives accurate wind, even with it running.

It is pretty difficult to get an independent verification of the wind vector. Headwind and tailwind component not that hard in stable conditions. Circling, unless very close to the ground, will only give you a vague notion. In the western mountains at least, the wind is quite dynamic in and around thermals, a fact that iGlide uses as a thermal centering device.

The instantaneous wind IS of immediate interest at least some times. I have found many days (in western mountains again) when there is a rather abrupt shear at say 14,500 ft. The cloud bases are 15,500. But you are heading upwind. When you hit the shear you leave the thermal. Going downwind, obviously carry it right to the cloud. This information is verifiable by checking TAS agains GPS speed. But most soaring instruments determine this too late to be of much use. There are other times when wave was dipping into the boundary layer again producing a sudden change of instantaneous wind. When I saw this I knew to look around for wave. I have discovered there is often a strong south wind blowing up the Minden valley late in the afternoon above about 12,000 ft. Never saw that before on other instruments, I'm not in it long enough for their filters to figure it out. Yet it can be exploited by flying down the middle of the valley rather than cutting straight across which seems otherwise more logical. Again these readings can be verified by observing TAS and GPS speeds.