way with an undulating motion. If too heavy in front, it will dive; if
too light, it will rise suddenly and slip backwards to the ground. The clip
or the amount of paper in the head must be modified accordingly. This type
is extraordinarily efficient if the dimensions, weighting, and shape are
correct, and one of the easiest possible to make.

Model "B."--The next model (Fig. 128), suggesting by its shape the
Langley steam-driven aeroplane, has two sets of wings tandem. Double a
piece of paper and cut out of both folds simultaneously a figure of the
shape indicated by the solid lines in the diagram. The portion A is square,
and forms the head weight; B indicates the front planes, C the rear planes.
Bend the upper fold of each pair into the positions B1, C1, marked by
dotted lines. Their front edges make less than a right angle with the keel,
to ensure the wings slanting slightly upwards towards the front when
expanded.

The model is now turned over, and the other wings are folded exactly on top
of their respective fellows. Then the halves of the head are folded twice
inwards, to bring the paper into as compact a form as possible. It remains
to open out the wings at right angles to the keel, and then raise their
tips slightly so that the two planes of a pair shall make what is called a
"dihedral" angle with one another.

[Illustration: FIG. 128.--Details of paper gliders: Model "B" above,
Model "C" below.]

Before launching, look at your model endways and make sure that the rear
planes are exactly in line with those in front. It is essential that they
should be so for straight flight. Then grip the keel at its centre between
finger and thumb and launch gently. Mark how your glider behaves. If it
plunges persistently, trim off a very little of the head. If, on the
contrary, it settles almost vertically, weight must be added in front. The
position of the weight is soon found by sliding a metal clip along the keel
until a good result is obtained.

Note that if the leading edges of the front wings are bent slightly
downwards the glider may fly much better than before.

A good specimen of this type is so stable that if launched upside down it
will right itself immediately and make a normal flight.

Model "C."--This is cut out of doubled paper according to the solid lines
of Fig. 128. The three sets of planes are bent back in the manner already
described, but the front planes are given a somewhat steeper angle than the