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Dixon's Notes

4. Lifted Index, Reverse Launch

This is the 4th article in a series on weather and flying pointers. Contact me or the USHGA for the previous articles which are important for following the thread of these discussions. Spend time with your flying group reviewing your experiences, knowledge and lessons. A recent local club discussion reminded members to be supportive in making wise flying decisions as opposed to challenging each to daredevil activities. A serious accident had recently occurred where there was some possibility that the pilot felt pressured into flying demanding conditions. Do your own homework on the weather and make your own decisions on whether to fly - you're the one who gets to either enjoy the flight or suffer through it.

The "lifted index" is the "thermal index" at the 18,000 ft msl level, which is generally higher than the realm we fly within - so we'll simply look at the thermal index, which is the surface puddles of heat compared to any level above the ground. When you gather temperatures at different AGL's you can chart how strong the thermals may develop. Air basically cools at 5.5f/1000ft. i.e. if it's 100f at sea level you'd expect air at 10,000ft above sea level to be 45f. If the "sounding" (see previous articles) shows that the air at 10,000ft was 35f then you have a -10 thermal index. The stronger the negative number, the stronger the thermals, usually.

Different ground surfaces heat differently - a golf course is pretty "cool" compared to an exposed dirt field. Take a thermometer and place it on different surfaces to get an idea of how much heat can develop on the ground - you'll be shocked. You'll find temperatures of 130f within 10 minutes midday on some "hot" surfaces. We take the forecasted high for the day and the temps we get from actually measuring the surface heat and split the difference to derive a "puddle" temperature basis, i.e. forecasted high for Denver is 85f and the dirt slope below Lookout Launch showed 115f after 10 minutes, so the puddle temperature would be around 100f. We'll use 6,000ft as our ground level and compare this 100f to a reported 32f at 12,000msl. This give us a thermal index to 12,000msl of -35 (VERY STRONG!!). You will also want to note the barometric pressure level and keep some notes as to how the flying went for you, or your buddies. Didn't like the air because it was too bumpy? Learn to anticipate it by knowing the models of thermal index, pressure, and the other factors we discussed in previous articles. We'll talk about the "K" index in the next article.

Now that you have practiced inflating the glider in a reverse position, let's get the brakes in hand so that you can bring the glider up and turn around to a forward/flying position. We find that pilots achieve much higher launch success rates if they smoothly inflate the glider to its flying position and rotate to the forward position without hesitating. Pilots who try and stand in a reverse position kiting their gliders with the brakes in hand have a higher aborted launch rate, which isn't good for the glider and can be dangerous.

Add the brakes to your hands by putting your right hand on the carabineer on your right side and follow the rear riser to the brake handle, detach it and now do the same with your left hand - the brakes are now in their proper hands so that when you inflate the glider and rotate forward they will be in the correct flying position. Be sure to now retake the front risers ("A's") so that the front riser attached to your left hip is in your right hand and the one attached to your right hip is in your left hand - which is what you've been practicing since the last article. Practice inflating your glider and making the rotation to a forward facing position in different wind conditions and on varying degrees of slope at least 100 times, and do so in a soft user friendly field. Bring the glider up, turn and go forward while looking primarily at the horizon. While running forward you will develop a feel for the glider position over head, the better you get at feeling the glider the better pilot you will be - so this is a terrific exercise all the way around. You should challenge yourself to practicing this in no wind and in high wind conditions while on flat ground and slopes, as well as in gusty/switchy conditions. In no wind make sure you have the glider in a very well laid out horseshoe shape with all the lines cleared. Be sure the slope behind you is a known quantity - remove things that may trip you. Take 3 or more quick steps backwards while looking for some pressure on the leading edge of your glider. When the leading edge loads lift your arms so that you rotate the glider up and into the flying position and then smoothly make your rotation to your forward/flying position. A slope really helps in making a no wind launch, but practice is the real key, we'll discuss forward launches in the next article.

In high winds you'll want to practice moving towards the glider as it moves up off the ground and then feel the point in which you should then take a couple of steps backwards while releasing the front risers and adding a bit of brakes to keep the glider from shooting overhead. Don't lift the glider too fast in high winds without stepping towards it or it can pull you off your feet and then drop you while it overshoots and then folds in on itself. Be ready to apply the brakes even while you're making your rotation to a forward facing position.

We have noticed that pilots who have trouble ground handling not only have launching difficulty but frequently have trouble flying in turbulent air. If these skills are difficult for you then you should fly in soft conditions. Learning ground handling in gusty/switchy conditions is best, steady ground handling winds can overdevelop a pilot's sense of competence. Finding the right atmospheric conditions for good ground handling will help you model the best conditions for actually flying. If you want to eventually fly in dynamic thermal conditions you need to have a sense of the air and the intuition to react accordingly. Become "one" with your glider and be ever vigilant of the atmosphere you fly within.