The first all metal monoplanes were developed during World War I. These were faster, but it was quickly realized that they did not climb well. Although more powerful than the initial airplane engines, the engines of World War I did not have enough power to lift the all-metal monoplanes quickly enough.
Wood, iron, and aluminum are possible materials for making aircraft wings. How do the densities of these materials compare? The density of water is 1 g/cm3 by definition at standard temperature and pressure. Wood floats in water so its density must be less than 1 g/cm3. Its density ranges from 0.45 to 0.85 g/cm3. Iron and aluminum do not float, so their densities must be greater than 1 g/cm3. Iron's density is equal to 7.9 g/cm3 and aluminum's density is equal to 2.7 g/cm3. So, in theory, it should be possible to reduce the weight of an airplane by utilizing aluminum instead of iron. Aluminum is about 1/3 the density of iron. But there is a problem: aluminum is not strong and alloying does not strengthen the material the way it does in bronze and iron. Aluminum needed to be strengthened, but how?