As altitude increases, air density decreases. At altitude, the  atmospheric pressure that acts on a given volume of air is  less, allowing the air molecules to space themselves further  apart. The result is that a given volume of air at high altitude  contains fewer air molecules than the same volume of air at  lower altitude. As altitude increases, density altitude increases,  and glider takeoff and climb performance is reduced. Temperature changes have a large effect on density altitude.  When air is heated, it expands—the molecules move  farther apart, making the air less dense. Takeoff and climb  performance is reduced, while the length of runway required  for landing is increased. Consider the following METAR for two airports with  same altimeter setting, temperature, and dewpoint. Love  Field (KDAL) airport elevation of 487 feet versus Denver  International (KDEN) at 5,431 feet. KDAL 240453Z 21007KT 10SM CLR 25/15 A3010 RMK  AO2… KDEN 240453Z 24006KT 10SM FEW120 SCT200 25/15  A3010 RMK AO2… The computed density altitude for Love Field is 1,774 feet;  for Denver, 7,837 feet—almost twice the density altitude  increase compared to the increase for Love Field. The effects  of attitude and temperature are significant, a fact pilots must  consider when computing aircraft performance. and allowances must be made for the winds, indicated or  expected. It is a lot easier to lose altitude than it is to make up  altitude when the glider is down low. When gliding toward an  object on the ground in the presence of crosswind, such as on  final glide at the end of a cross-country flight, the glider pilot  should keep the nose of the glider pointed somewhat upwind  of the target on the ground. For instance, if the crosswind  is from the right during final glide, the nose of the glider is  pointed a bit to the right of the target on the ground. The  glider’s heading is upwind (to the right, in this case) of the  target, but if the angle of crab is correct, the glider’s track is  straight toward the target on the ground.  [Figure 5-3] Headwind during landing results in a shortened ground  roll, and tailwind results in a longer ground roll. Crosswind  landings require the pilot to compensate for drift with the  proper flight control input, such as a sideslip or a crab. Glider  pilots must be aware of the apparent angle versus the rate of  descent. The glider descends at a constant rate, but the different  groundspeeds will result in different approach angles. These  different approach angles require specific techniques to ensure  safe touchdowns in the landing zone. For example, if landing  in a strong headwind, the glider pilot should plan for a closer  base leg to allow for the apparent steeper approach due to the  slower ground speed. Another technique would be the delayed  extension of spoilers or drag brakes and accepting the faster  airspeed to counter the headwind component. In the case of a  tailwind and an apparent lower angle of approach, the glider  pilot can use more spoiler or drag brake extension or slipping  or a combination as allowed by the GFM to touchdown in the  landing zone. In any condition, the glider pilot must make  allowances for the current conditions of wind and density  altitude to ensure a safe landing in the landing area. A glider  pilot must respond to the current conditions and amend the  traffic pattern and/or modify their procedures to compensate  Wind affects glider performance in many ways.  Headwind  during launch results in shorter ground roll, while  tailwind causes  longer ground roll before takeoff.  [Figure 5-2]  Crosswinds  during launch require proper crosswind procedures or control  input to track along the runway.  During cruising flight, headwinds reduce the groundspeed  of the glider. A glider flying at 60 knots true airspeed into a  headwind of 25 knots has a groundspeed of only 35 knots.  Tailwinds, on the other hand, increase the groundspeed of  the glider. A glider flying at 60 knots true airspeed with a  tailwind of 25 knots has a groundspeed of 85 knots. Crosswinds during cruising flight cause glider heading (the  direction in which the glider nose is pointed) and glider  track (the path of the glider over the ground) to diverge. In  a glider, it must be remembered that crosswinds have some  head or tailwind component that results in a lower or higher  true groundspeed. When planning the landing, the wind  effects must be factored into the landing pattern sight picture  5-3 Wind Temperature Altitude Figure 5-2.  Apparent wind effect on takeoff distance and climb-out  angle.  34 34 W i n d Takeoff and climb-out: no wind  Takeoff and climb-out: 25-knot headwind