Puma 13.5
Owner’s Manual
VG (Variable geometry)
The variable geometry (VG sometimes called variable billow VB) is used to change the flying characteristics
of the glider while in flight. The Puma has a large travel VG and so the flying characteristics are significantly
altered by the use of the VG. Experienced pilots will constantly adjust the VG in flight (like racing drivers
constantly working up and down the gears in a race car) to match the conditions in which they are flying to
optimise their performance and handling.
As mentioned else where in this hand book, when the glider is rigged the VG cord should be threaded through
the cleat on the speed bar and knotted 5cm from the rope end. (This is a good habit to get into. The knot will
prevent the end of the VG cord being lost up the upright.)
For take off it is recommended that the VG is in the fully released position. (This is with very little cord
sticking from the upright.) In this position the glider is easiest to turn. (You may find with experience, and
especially if aero-towing, that you prefer to take off with some VG pulled on.)
In normal flight, it is easiest to fly with the VG fully released (OFF) although this gives the glider the lowest
performance. As VG is increased the performance progressively improves, however the roll gets
progressively stiffer, the pitch stability margin reduces and the tendency to enter a spin increases. If is
therefore important to always set the appropriate level of VG for the conditions. Low or no VG should be
used when in rough air or close to the ground. When flying in smoother air, at higher altitudes and further
from other pilots, higher VG settings will give better performance. When flying high in smooth thermals VG
settings greater than ½ may be used provided sufficient speed is used (see next paragraph), however always
be ready to release the VG if the going gets rough!
For flying fast or for best glide performance (for example, flying between thermals) use full VG. High VG
settings improve the performance of the glider (in terms of sink rate, glide angle and energy retention)
however also be aware that the roll rate of the glider is significantly reduced especially if flying slowly. When
flying with high VG settings it is better to fly the glider slightly faster than at low settings. This will help
overcome the reduction in roll response and also at higher VG settings the glider will perform better (both in
terms of sink rate and glide angle) at slightly higher speeds.
Do not use full VG
near the ground, near other aircraft or near any other obstacle
.
For flying slowly, near the ground, near other aircraft or other obstacles, in rough air or landing it is
recommended that the VG is close to the fully released position. VG off position will give the most effective
roll control.
When releasing the VG, do so in a smooth manner. Do not just pull the rope out of the cleat and let go. This
will give a needless shock loading to the airframe.
Different pilots fly with different styles and use the VG in different manners. Each pilot should experiment
with the VG to find how best to optimise for the conditions at all ranges of airspeed, for example in very
smooth weak lift (for example wave lift) when high and well clear of the ground and other gliders then a high
VG setting and lower speeds than previously mentioned will optimise the glider performance.
Always be thinking about the VG setting and be constantly adjusting to suit the conditions.
VG MAINTENANCE
Due to the design of the Puma VG, it should be smooth and easy to operate.
To keep it this way, make sure that the ropes are clean and not twisted. Remove grit or dirt from the upright
casting and replace the ropes if they show signs of wear. It is also important to keep the tension strop of the
glider untwisted.
Silicon spray is a useful lubricant which will help maintain easy operation of the VG Spray it both on the
keel in the area of movement of the cross tube junction and its webbing loops and on the VG pulleys in the
lower upright casting and inside the sail.
Pay special attention to VG cord routing when changing uprights. It is possible to miss route the cord
resulting in it becoming difficult to use.
Puma 13.5 hand book-Rev-02
15
Summary of Contents for PUMA 13.5
Page 1: ...PUMA 13 5...
Page 21: ...Puma 13 5 Owner s Manual Figure 4 Checking batten tension Puma 13 5 hand book Rev 02 21...
Page 38: ...Puma 13 5 Owner s Manual Section 3 Assembly Drawings Puma 13 5 hand book Rev 02 38...
Page 39: ...Puma 13 5 Owner s Manual NOSE ASSEMBLY Figure 10 Nose assembly Puma 13 5 hand book Rev 02 39...
