On Tuesday, October 28, 2014 9:24:00 PM UTC-7, Andy Blackburn wrote:
On Tuesday, October 28, 2014 5:28:19 PM UTC-7, jfitch wrote:
You are missing my point entirely. A horizontal gust causes actual, real, measurable, and "feelable" vertical acceleration. Ignoring the vario entirely, how can you differentiate it from that acceleration caused by a vertical gust? You cannot without additional information - vertical acceleration is vertical acceleration.

No.

There are transient versus sustained effects that are different for horizontal versus vertical shears (gust versus thermal).

Saying that because a horizontal gust generates lift that it is the same as a thermal that accelerates the glider's frame of reference in a sustained vertical direction is simply incorrect.

9B

Saying that would be simply incorrect - but that is not what I said. A glider is never accelerated in a sustained way. All accelerations the glider experiences are transient, whether induced by a horizontal or vertical gust (excepting turning flight). Once the glider reaches its new velocity, vertical acceleration is zero, regardless of steady state climb rate. This is high school physics. The transient effect is acceleration, this is what you feel. The sustained effect is climb rate, this is what you hope for. But climb rate cannot be felt, only acceleration. When you feel that acceleration, you have about 2 or 3 seconds to determine its cause and react appropriately.

A transient horizontal gust (say ramping quickly from 0 to 10, then back to zero) will be felt as an upward acceleration, followed by a downward acceleration - a bump. But a sustained gust will be felt as an upward acceleration (and an airspeed increase, and a very slight angle of attack reduction, and a lagging variometer up deflection). In nice smooth well behaved air, you might be able to use the more subtle clues to differentiate that from a vertical gust, which will also cause an upward acceleration (and a smaller airspeed increase, a greater angle of attack increase, and perhaps a small momentary lagging downward variometer deflection). In rougher air (mostly what I fly in) sorting this from the noise is practically impossible most of the time. Remembering also that most gusts are neither perfectly vertical nor horizontal, but some random angle in-between.

Of those transient effects, the angle of attack change is probably the easiest to measure, which makes me wonder why this hasn't been pursued more for variometer use. But that signal has a lot of noise in it too.