Just a small post for the Glider Chronicles today. The weather recently has not been good during the weekends but wonderful during the week. Enough of wistful gazing out of the office window already! It was time to stop being conscientious and take a day off from the work week as sunny skies and a high pressure had been forecast. I used the first sunny day since I know that high pressures can lead to lowering inversions.
Normally as you go higher into the atmosphere the temperature decreases at about 2°C per 1000ft. As the name implies an Inversion occurs when at a certain height the temperature increases for a while as you go up. As thermals rely on warm air rising through the surrounding cooler air, when they hit the height of the Inversion they usually stop rising, unless they are strong enough to punch through. Inversions happen frequently during high pressure weather because the air in a high pressure system is descending which also traps dust in the lower air. Thus in the photographs below you can quite clearly see the line in the sky at the Inversion height.
What this means for the glider pilot on the street is that it clamps down the lift and you cannot go higher than the height of this temperature inversion. This week the inversion was at about 1500ft, quite low. Just about the height you could get from the winch launch.
I had planned to do some more single seater flying in these conditions but an early conversation with an instructor convinced me that converting to fly the high performance twin seater DG1000 would be a fun thing to do for the day, and give me a more tangible goal. Of course the fact that he said it was a good spinning aircraft had nothing to do with my decision! He is also one of the main aerobatic instructors – a skill I would like to work on next year since I think it important to know the limits of the technology you are using.
Once the glider was checked and taken out to the launchpoint, next was to get the ballast weights sorted out. With our combined weight the DG1000 needed all of its tail weights fitted, something that I had not used in other gliders. But they all had to be taken out later when I went solo.
Since we were planning to do some spinning and as this glider could lose a lot of height in a spin we took an aerotow to 4000ft. Of course I did my usual trick with big wing gliders of not using enough rudder as I had done with the Duo Discus. [All thanks to Adverse Yaw explained here.]
As you can see from the aerial photos below, the inversion was quite visible as a line separating the clear upper air from the mucky lower air. A few cumulus clouds can be seen just at the inversion top where the thermals were strong enough to push through. The cloud will then form as the air temperature in that area reaches the dewpoint.
[For the Lashamites among us – in the right-hand photo (if you look hard enough) you can see the old airfield dispersal pans being dug up on the south-east side of the airfield (just ahead of the wingtip). Work is also being done in the north-east corner.]
So what was my impression of the aircraft? Like the Duo Discus she flies beautifully once you get used to the rudder coordination and thanks to those big wings can keep on flying for ages with a glide ratio up in the forties. To date I had been rather intimidated to take it flying, but no more! I am now cleared to fly it off the aerotow and just need another check for winch launching with it. The spins were also great fun but she did come down fast and it was easy to lose 500-600ft by doing a one-turn spin.
Another notable point about this glider is making sure the undercarriage is down and locked before landing. I had heard a number of horror stories about it collapsing on landing because the lever was not far enough forward and was not properly locked. I found it needed some force to lower the undercarriage but it was ok if you made sure you had the reach. You really really did need to make sure the lever was forward, in its detente, and locked against the canopy wall. I have seen some people land with the undercarriage up and it needs about 10 people to go out to it and lift under the wings so the wheel can be put down!
For once the day’s flying included an instruction flight so I have some log book comments by the instructor:
Conditions: Light southerly wind. Inversion at 1500ft.
DG1000 checkout. Spin avoidance and recovery OK. Aerotows OK. Have another winch launch cable break before solo 776 on winch. OK for solo on aerotow.
4000ft dual aerotow. Cable break winch launch. 2500ft solo aerotow.
The photo on the right shows the cockpit panel.
The gauges from top to bottom, left to right are:
ASI – Airspeed Indicator.
ClearNav – Nav computer with control buttons on the joystick.
Turn and Slip indicator.
Altimeter – A small one! You have to crane your neck to look around the joystick.
G-meter – For aerobatics.
Vario 2 – Cannot have enough variometers.
Temperature gauge – Presumably more useful in Scotland wave flights where it can get 30°C below zero.
Radio – The usual type found in the Lasham gliders.
Athough this was primarily a twin seater day, I did also fly the Baby Grob SH7 later which proved to be hard work although I managed some 38mins from a winch launch – good for the conditions. It consisted mainly of scrabbling around from 1000ft up to 1500ft, then losing 500ft flying back upwind and starting to scrabble again. I wont say too much about an earlier winch launch before that which resulted in a slightly low circuit. Not my best!
However it was still a lovely day out and I do really like the DG-1000. I shall not feel too intimidated to get it out flying next time.
As I usually say:
Love those big wings!
Till next time…