In the latest edition of Soaring magazine there is an article about TLAR. For those not familiar with TLAR, it is a landing approach teaching method that is based on angles as opposed to elevations and distances.
Using angles automatically compensates for variations in altitude. On downwind , if you are high, you fly further away from the runway, if you ar low you fly a shorter pattern. The TLAR method is superior and safer than trying to teach fixed distances and specific altitudes for turns.
However, I found a problem with something said in the article, but being the author a very recognized figure in the world of soaring, I was hesitant to write about it. I am refering to the dip angle between the glider and the runway on the downwind leg.
The article states "The pattern shpuld be flown so on the downwind leg, opposite the touchdown point, the pilot is about 600 feet above the ground looking down at the touchdown point at a 45 degree angle". That angle looks too high for me, and I think it could be dangerous.
I've always thought that angle should be more around 25 degrees, which would produce close to a 1-on-2 slope, as opposed to the 1-on-1 slope of 45 degrees.
The 25 degree angle will put you at around 1300 feet from the runway, or close to a quarter mile away when you are at 600 ft agl.
Getting too close to the runway prevents the pilot from having a good base leg where you can better judge your position to enter the very important base-to-final turn. In the worse case scenario, being too close will force you to use very steep banks or going for a button hook turn. New pilots and many old pilots may try to force the turn with rudder, and we all know how bad that can end.
Is 600 ft too close? I'd say it is. I'll use a typical example. In calm conditions, many gliders fly a pattern at 50 knots. In theory, the radius of a 45 degree bank turn flown at that speed is 220 ft. But that doesn't take into consideration that you start the turn from zero bank, bank to 45 degrees, stay in the bank and unbank back to zero, so at the end you have a spiral turn, followed by a circular turn, followed by another spiral. If we assume it takes 2 seconds to bank to 45 degrees, the net effect is that your turn has an equivalent radius of 310 feet. When I repeat the calculations with a 30 degree bank, the equivalent radius of the turn is 440 feet.
I am trying to spare you from the equations, but if you don't believe me, look at your flight traces in google earth, or just using google earth, measure the distance from the location of your downwind leg to the runway. On your home airport, you should have a good idea of more or less where that is.. I assure you that nobody is flying at 600 ft, it would scare you. Also, take a look at the angle to the runway when you are flying. Definitely not 45 degrees. Even on your chair as you read this look down to your left or right at 45 degrees and imagine the runway is at the floor.A little steep?