The two-passenger models are similar in design to the army training-machines. They have more powerful upright and V-type four or eight cylinder motors and generate two to three hundred horse-power. The fuselage is built so that the pilot sits in front of or beside the passenger. The control is dual. The machines are mostly tractors, but in a few cases the nacelle is built in front of the plane like a bomber, and the propeller and engine are behind. These pusher types obviate all the blind angles and afford an excellent unobstructed range of vision. They are especially good for hunters, who desire no obstruction in gunning for birds. In case of a crash, however, there is the added danger of having the motor crush the passengers underneath. The Canadian Government has sold over ten thousand of their training-machines to an American company, which is reselling them at a low price to men who wish to own an aeroplane. The aero-mail type is about the same as the two-passenger model in wing spread and fuselage, but the motor is a twelve-cylinder V type and generates anywhere from 250 to 450 horse-power. Cost is not so much a consideration here as carrying capacity. Most of the two-seated fighting-machines built for war purposes can be adapted by the Post-Office Department for this purpose, and plans are afoot to extend the service all over the United States. The big bombing bus type is designed for carrying great numbers of people from one aerodrome to another. These machines are biplanes and triplanes with a wing spread of anywhere from 48 to 150 feet. They are driven by V-type, twelve-cylinder engines generating 400 to 700 horse-power. They have one or two fuselages in the centre but the nacelles are usually forward of the wings, so that nothing obstructs the vision of the passengers. These machines will be sold to transportation companies, which will make a business of carrying people from aerodrome to aerodrome. They are so large and are equipped with so many motors that they are not intended to be landed anywhere except on properly prescribed flying-fields. Several transportation companies are already organized for that purpose. All the above types of aircraft are so designed that pontoons or flying-boats can be substituted for wheels and landing-gear, and so that most aircraft manufacturers can make both. Of course, in most cases the boats and the motors are made by different manufacturers. Several companies, however, construct aeroplanes complete with motors.