This would give two planes with a sustaining surface of 360 square feet.

But the sustaining surface is only four times as great.

The smaller the sustaining surface, the higher the speed.

One square foot of sustaining surface for every pound of the total weight will be sufficient for security.

But this time he quickly shook out a portion of his reefed sustaining surface and slowed down in time.

The weight, compared with sustaining surface, if expressed in understandable terms, would be equal to sixty pounds for every square foot of surface.

We have an aeroplane with a sustaining surface of 300 square feet which weighs 900 pounds, or 30 pounds per square foot of surface.