Regarding airspeed and groundspeed: as an RC pilot, we are concerned about BOTH. Flying RC is like flying in perpetual ground-reference maneuvers.

The plane neither "knows" nor cares about groundspeed. Groundspeed is only relevant when the plane needs to track in relation to some point or path that is ground-based (like the runway, or the RC pilot's viewpoint), or when we are trying to figure out how long it will take to get somewhere. It has ZERO EFFECT on how the plane flies.

This may help: imagine the plane flying on a calm day. Now the earth mysteriously starts spinning faster, but the air does not change. No thinking person could imagine the airplane instantly changing its flight behavior just because the earth below it (which it is not touching) has changed speed.

Of course, the plane will APPEAR to be flying at a different speed to a ground observer if there is any wind. Example: flying at 40kts into 40kt headwind will result in the plane appearing to hover in place. I see this often with my powered gliders. If you are at full power (or gliding) and still not gaining ground, the only option is to drop the nose to pick up AIRSPEED, which naturally will increase GROUNDSPEED (assuming steady wind).

As RC pilots, it is critical to fully get our heads around this concept if we really want to be proficient pilots. It's not that hard. And the trig stuff and wiz wheels are only required if you are trying to plot ground track or groundspeed.

There is also a difference between INDICATED airspeed (or pressure airspeed) and TRUE airspeed (the actual velocity of air molecules passing over the plane), but at the altitudes and conditions we fly RC, this difference is usually not much of a consideration.

Matt