There has been discussion on how high gliders are when they come off the hi-start

A bit of math shows that we are considerably above 400 ft when we come off the line. The information below is provided for your review.

Givens:
- Club hi-start
-- 100 ft of rubber
-- 500 ft of line
-- Hi-start stretched 300 ft at launch (100 paces from slack line)

-- Total length at launch is : 100 + 500 + 300 ft = 900 ft.

Assumptions:
- Hi-start is slack when glider flies off the line. This is normally NOT the case. Most pilots feed in up on the climb to get as much lift as possible. This is especially true in winds above 5 mph when it is possible to “kite” the glider up keeping the line stretched. Most pilots will dip down, buiding speed near the top of the arc and zoom up when coming off the line for greater altitude. We will assume a “fly-off” on a slack line, with no zoom.

- Rubber sags when glider flies off the line. We will assume the apparent length is 50 ft due to slack.

- Thus: Line length when flying off = 500 ft + 50 ft of rubber = 550 ft

- The line angle when the glider flies off is usually between 50 and 70 degrees, depending on the pilot skill, type of glider, and wind. The chart below summarizes:

Degrees = degrees above horizon (line angle)
Sine = arc sine of degrees above horizon
Line length = fixed at 550 ft
Altitude = Sine(degrees) x line length
Degrees Sine Line Length Altitude
10 0.1885 550 104
20 0.3703 550 204
30 0.5388 550 296
40 0.6880 550 378
45 0.7536 550 414
50 0.8124 550 447
60 0.9078 550 499
70 0.9706 550 534
80 0.9986 550 549
90 1.0000 550 550

From the table we see that even a rookie glider pilot can come off the EAM hi-start with a slack line at 45 degrees above the horizon and still be at 414 ft in altitude. In truth, a 45 degree line angle is a really mediocre launch. Most of us have line angles between 50 and 70 degrees when we come off the line.