John shared his brother's enthusiasm.  "Fine!" he cried, with sparkling eyes.  "Why, that's almost a neutral condition, as she is!  Buddy, if we can apply this principle to a full-size machine--and I don't know why we can't--we shall have solved the biggest problem facing airplane designers to-day.  With a machine weighing only a trifle more than her load of fuel and baggage, she will not only fly a lot faster but go a lot farther, with a given supply of fuel, than the present-day planes. And what is more, she could attain good speed with a single engine of reasonable power, where now many machines are handicapped with the burdensome weight of an extra power-plant.  When will she be ready to test out?"