Parachute Descent Speed m/s
The speed at which the drogue parachute, strop and a short length of cable descends.
Initial Glider Angle deg
The angle of the glider to the horizontal at the start of the main climb.
Glider Flying Speed kts
Airspeed of glider during the main climb.
Glider Mass kg
Glider with pilot and ballast.
Cable Mass per unit length kg/m
Cable Diameter m
The diameter in metres.
Ground Run Acceleration m/s2
Used to calculate the length of runway used in the initial phase during acceleration to flying speed.
Ground Run Constant m
Length of runway used in initial phase after acceleration to flying speed when the glider rotates into the main climb.
Glider Lift/Drag Ratio :1
The lift to drag ratio of the glider in the climb under a high wing loading.
Max Launch Angle deg
The angle of the cable to the horizontal at the end of the winch launch.

Launch Heights

deg kts

AD Weather Station

Winch Master

There are many risks when conducting gliding operations from an airfield. One risk, especially to third parties, arises from the use of a winch to launch gliders. At Cotswold Gliding Club, under certain wind conditions, gliders can be launched to heights in excess of 2000ft. If there was a launch failure, for example, and the cable broke near the top of a launch with only sufficient cable remaining attached to the cable's drogue parachute to stabilise its decent, the parachute, weak link and strop assembly could drift in the wind and fall to ground outside the bounds of the airfield causing damage to property or in the worst case injuring or killing a person.

A risk assessment of this possibility has been undertaken and a suitable mitigation strategy has been formulated to ensure that there is a very low probability that the cable or parachute could fall on adjacent property or persons. The principal mitigation will be to site the winch and launch positions after consideration of the prevailing wind conditions. To help the Duty Instructor to determine the best position for the winch and launch positions a computer application has been developed (called Winch Master) which is available as an Android application for a mobile phone or tablet and this web page which can be used on the briefing room computer. The application shows on a map the probable drop locations for a range of winch locations.


User Guide

When you first load the WinchMaster page the wind direction and speed are obtained from the club's weather station sited above the club house.

The winch and launch positions are set automatically based on the wind setting. You can move them by placing the mouse over them and clicking then dragging to a new location. After the move a new set of launch solutions is displayed.

To change the wind move the yellow ball on the wind compass. Moving it out to the rim increases the speed and moving to the centre decreases the speed. After a change a new set of launch solutions is displayed.

Click on "Settings" to change the model parameters. A new set of launch solutions will be shown when you click on "Recalculate". The initial settings are for a K21 glider and the cables and chutes used at Aston Down. The model assumes a worst case scenario whereby the the pilot flies the glider to the best of his ability to achieve the highest launch directly over the runway.

Click on "Reset" to clear all shown launch solutions.


Robert Corbin - 1 Aug 2018