flybymike wrote:If you are flying over high or undulating ground on the QNH and do not (and indeed cannot) know the ground elevation beneath you, then how can you know the high and low key altitudes?
Using a process known as judgement. You look at your landing area and judge your height and the angle you are above it.
Then fly a circuit round it, adjusting your distance to keep the angle above your landing area about the same as you will need for the approach. This gets you to finals at a position where you can make an approach using half to two thirds airbrake.
Two things:
You do NOT use your altimeter. They are very unreliable in gliders because the lack of vibration means that they can stick. And also you don't know the height of the terrain.
You plan your circuit relative to your landing area because that's the only thing that you can rely on having. You don't use secondary references because they won't be there.
If you don't have a landing area you have a problem, but it's not a circuit planning problem.
Gliders tend not to make radio calls in the circuit but where we do, such as at Aboyne, all we call is downwind. All we're saying is "coming ready or not". Going around is not usually an option. I don't recall anyone calling high/low key.