The usual autumnal SW gales have finally arrived and the ridge has been working well for the last month or so. However, recently there have been several issues for Pilots that we need to learn from and make sure we don’t repeat these experiences.
Getting caught in rain and flying back to Matamata on a compass heading.
Just try watching the compass when you are flying in clear air towards a known point. The compass will swing as much as 30 degrees as you accelerate, depending on your heading and angle of bank. There are at least 3 different effects which contribute to the errors:
Angle of Dip error – which is about the way the magnetic flux changes in relation to the equator and the Poles,
Acceleration Error, which causes a turn to the South and deceleration error, a turn to the North.
Turning Error. The compass is also affected by the centrifugal force generated in a coordinated turn and is worst when turning North and South.
The obvious solution is not to get caught in rain! Keep an eye on the Western horizon and if there is an approaching rain squall that you can see the extent of, fly North or South of the squall until it has passed. Be aware the ridge can go very weak for a while after a squall has gone through. If the squall or front is as far as you can see in all directions, make an early decision to return to the airfield.
Getting caught in the Curl Over, also appropriately known as the “Clutching Hand” effect.
Just like a wing, the airflow accelerates over the top of the Kaimai Range and has the same downward flow behind the ridge. A recent experience with one of our Pilots produced a sink rate of 14 knots and a loss of three thousand feet to penetrate back to the windward side and the lift. On a ridge flight a couple of weeks ago, Tony Davies noted a wind speed of 57 knots at 3000’!
Keeping a good visual reference to ground based features is essential to avoid being drifted back into the curl over. Often, the smoothest lift can be found in the pressure wave, well in front of the ridge. For example, on Labour Weekend Saturday, there was still 2~4 knots of very smooth lift over the Waihau river.
Getting caught in rapidly forming orographic cloud and ending up on the Tauranga side of the ridge.
Especially in pre-frontal conditions, with high humidity and hazy visibility, a wisp can rapidly develop into a large cloud within a few seconds. With no horizon or ground refence and the high wind speed over the top of the ridge, means you can easily be blown over the back and if you are lucky enough to avoid the terrain on the way, the landing options are few and far between.
We all like to gain as much height as possible, but especially on a good ridge day where there is plentiful lift everywhere, you have no business flying right up against cloud base. Keep a good eye on what is happening in front and behind you and think of how many other gliders may be hovering around at cloud base near you and the consequences of a mid-air, or ending up in cloud and losing control of the aircraft. Did you know that the average time for loss of control in cloud is 178 seconds? (Last 10 years in Australia for 111 occurrences.) As soon as you notice you are getting close to cloud base, open the airbrakes fully and descend to keep clear, keeping in mind the relevant speed limitations of the aircraft. Make the decision early and play it safe!
The CAA rules require us at or below 3000’ AMSL 0r 1000’ AGL, to remain clear of cloud and in sight of the ground.
Be careful too, of emulating what you have done with an Instructor by yourself. Your Instructor likely has hundreds of hours learning how the ridge operates in different wind conditions. On the right day, it can be delightfully easy, it can also be very tricky and I would strongly recommend you have a very good briefing with any of our Instructors if you are contemplating going North of Thames, or flying on the West Coast, where the landing options are pretty much non-existent, unless the tide is out and of course, that will change during the time you are flying.