In group C is to be found the most profitable source of study for the self-propelling model aeroplane. The glider has no motor and no propeller, but is made on the plan of the motored model in the construction and adjustments. The glider is usually made smaller at first, increasing the size to the actual model later. The glider is more useful for study, if it is made heavier in comparison with the motored model. The glider can be thrown by the hand as if it were a spear, Fig. 216, or it can be thrown by a rubber cord, Fig. 217, or by a springy stick, Fig. 218.
All experiments except those intended for adverse conditions, should be made either indoors where there is no wind, or away from buildings far enough to be out of reach of the whirls that are always present near buildings. Heavy paper can be used for planes in some of the experimenting, and even much may be learned by the use of paper models thruout the whole construction, but a little stiffening with small thin strips as reinforcement is better in most cases.
For the model that is thrown like a spear from the hand, wood is used for all parts. The spine can be 3/4"x3/4"x30", the fore plane 1/4"x2 1/2" in widest part x 8", and the rear plane 1/4"x4 1/2" in widest part x 20".
Bevel off the under side of the front edge of both planes. Fasten the planes to the spine with rubber string, rubber bands will do, this will allow easy adjustment back and forth on the spine. There are many experiments that can be tried with this model. Move the foreplane back, try; move back plane foreward, try; move foreplane foreward; try, and so on. This model and all other models are just the opposite of teeter boards. If too much pressure comes at one end, up it goes, if too much at the other, up that end goes, while the same thing applied to the teeter, that end goes down. It then seems clear at the start that we must have balance fore and aft, as well as right and left, with the kite we must balance right and left, but if the up and down does not quite tally we can counteract by adjustment of the bridle, but on gliders and model aeroplanes, there are no bridles. The little ship must go "all by its lonely".
Another adjustment is possible, and probably will be necessary, and that is tipping of the planes. By the use of little wedges, the front edges of the planes may be tilted up, and by trial we can decide what we think the best angle, which should not be great. Possibly 1/4" might be used under the front edge. It will pay to spend much time in experimentation on these gliders, and it should be carried on until long graceful glides are accomplished.
It will be discovered long before this, that in a very large percentage of cases the arrangement of planes is reversed in model aeroplanes and the large machines. The small planes are placed forward and are used largely as elevating surfaces. A few models have the large plane forward. It will also be noticed in looking over plans of model aeroplanes that a large majority are monoplanes, while in the large machines there are more biplanes.