Another innovation which Hawke planned for the machine was a mica window in the forward part of the fuselage, which would enable them to see what was passing below them, without leaning over or altering the angle of the planes.
While the boys worked and followed directions, Hawke explained the parts and their use on the machine. Fred and Fly proved themselves the most accomplished at first, owing to their previous experience with mechanics and aeroplanes. Gray also had a previous knowledge of the possibilities of aeronautics, and it was not long before all of the boys were intelligently working on Hawke's model and making progress.
Mr. Phipps rode over from the ranch almost every day to see them at work, and was much pleased with the rapid advance his son was making. Entirely recovered from the accident, Herb was as useful as any of his companions, and, besides evincing a great deal of mechanical skill, which he had never been called upon to display before, he readily grasped the principles Hawke continually ground into his pupils.
"You see, Dad," Herb said, when the rancher had inquired, on the occasion of one of his visits five or six days after work had been begun, about the use of the propeller, the particular part on which Herb was working, "the propeller is everything on an aeroplane. It's got to be made just right, or the whole thing goes to smash. If it wasn't for the propeller the machine wouldn't go at all," he finished triumphantly.
"Oh, indeed," remarked the southerner, an amused twinkle in his eye. "And what's the reason for that?"
"Well, yuh see," replied Herb, seriously, not noticing the smile playing about his father's mouth, and anxious to display his newly acquired knowledge, "it's the thing that moves the machine forward, and it has almost everything to do with the pitch and speed. The surfaces of the aeroplane are called the skin, and there is some friction of air against these surfaces, and that is called skin friction. Well, yuh see, the propeller has to make the machine move through the air with the smallest amount of skin friction. It has to travel through as large an amount of air as possible in a certain time, and take as little power as possible. Yuh understand?"
"Oh, yes," exclaimed the rancher, unable to restrain a short laugh. "How about that, Hawke?"
"He's right," responded the aviator, slapping his young pupil on the back. "He's got the dope exactly."
"Yes, but a good deal depends on the operator," chipped in Fly, who was ambitious to excel as an aviator, and could scarcely wait until the machine was finished to try his hand.
"I'm working on the box-girder," said Dunk, feeling called upon to give an account of himself.