What happened with Auk XIII, and what did the boys notice about the rocket when it was recovered in October Sky?
The flight of Auk XIII was very similar to that of its predecessor, Auk XII, launched just a little while earlier. Upon ignition, it "jumped from the pad...leaned over, puffed a big cloud of smoke, and sped off into the sky." When it reached its highest point and fell back it disappeared into a dense thicket of trees. The boys could hear it hit the branches of a large oak as it approached the ground on its descent.
Since O'Dell had knocked over Quentin's theodolite in his excitement at the rocket's launch, the boys were unable to get a reading of its altitude, but it was clear that Aux XIII had not reached the height of Aux XII. When the boys recovered the rocket, they found that, like Aux XII, its nozzle was completely worn through. Billy suggested that maybe the heat created by the rocket candy was too intense for the nozzle as it was created, but, upon closer examination, Sonny noticed that the nozzle actually appeared to be corroded. From this observation, Quentin was able to deduce that the problem was caused by rapid oxidation; heat combined with a steady flow of oxygen had worked together to destroy the rocket's nozzle. It was evident that the next step in the experiments would have to be the discovery of a material that would be capable of withstanding both heat and oxidation (Chapter 11).
Auk XIII is loaded with rocket candy. It jumps off the pad, leans over in a cloud of smoke, and jets off into the sky. When it lands in a clump of trees, the boys are in such a rush to recover it that they knock over the theodolite that could have given them an altitude reading. They know that it did not go as high as Auk XII, however.
When they recover the rocket, the boys notice that the rocket's nozzle has been worn out. At first, they think it was blown off, but then Sonny recognizes that the nozzle has signs of corrosion. Quentin realizes that it's the same oxidation process he has seen in science class, caused by a high heat with a steady supply of too much oxygen. Therefore, the boys resolve to find a material for the rocket's nozzle that can resist heat and oxidation.