Surrounded by online newspaper comic strip historians and collectors, I'm aware of the shortcomings of my knowledge. Almost everyone out there knows more than I do about almost everything. Still I'll offer what I do know in hopes it will help someone somewhere fill in some blanks. In return I hope you'll fill in a few of mine.
AP Newsfeatures' Scorchy Smith surely must deserve a prize for the greatest number of artists to draw one adventure strip. We're all familiar with its early days. In 1930 John Terry started the feature, modeling its hero after Charles Lindbergh. We have seen examples of Terry's scratchy, rather clumsy artwork (So unpopular was Terry's version that most online sources actually ran Noel Sickles' art, not Terry's).
We also know that Terry became ill and young Noel Sickles imitated the creator's style for a while until it became clear Terry wouldn't return. Then Sickles began changing to his own personal style. In the process he revolutionized comics. Sickles left Scorchy in 1938 when AP refused him a raise. For a while he assisted on other people's strips, but finally Sickles moved on to a distinguished illustration career.
Bert Christman replaced Sickles. Thanks to the people at Big Fun Comics we can see a long run of Christman's work. He was an able successor. Not only did he draw exceptionally well, he also (in my opinion) wrote better stories. Christman might have become a big name had he not joined the Flying Tigers and died in combat.
This part of Scorchy's history is well-documented. Afterward things get fuzzy. An article in Il Fumetto by Franco Fossati says Christman was succeeded by one Howell Dodd. The only Howell Dodd I turned up was a prolific magazine illustrator who painted lots of “men's sweat” illustrations in the 1950's. From his career dates he could have worked on Scorchy. I found a 1946 pen-and-ink drawing by Dodd that suggests he would have done a nice job. However I can find no further info.
Next in line (1939) was Frank Robbins, another young man who made his name on the strip. Though his approach was cartoonier than Christman's, Robbins' rich blacks and dynamic staging worked well on Scorchy. Sometime during Robbins' five years' stay on the feature a Sunday page began. Impressed by this young artist, King Features stole Robbins away from the AP in 1944. At King Robbins created another flyboy, Johnny Hazard.
Robbins was replaced by Ed Good. Good was a Canadian comic artist who later did much work in American newspaper strips and comic books. I've never seen a sample of his Scorchy.
According to the Who's Who of American Comic Books, Good drew Scorchy through 1950. Fossati cuts him off in 1946, which seems a likelier date. His replacement was Rodlow Willard, one of the most painful adventure strip artists I've encountered. Here's a sample from an Italian translation of one of his continuities. The sequence begins on 14 January, but no year is given. It's amazing that Willard ran the feature for eight years, considering that as time passed he only got worse.
Willard was succeeded by John Milt Morris. Morris seems to have taken over circa 1954. I haven't seen a sample of his Scorchy, either. However the one sample I've seen of Morris' strip work makes me wonder if Willard wasn't so bad after all! I've found no biographical information about Morris.
In almost every source, Scorchy's saga ends with Morris, crashing the strip ignominiously in 1961. Hardly anyone mentions the two artists who actually saw the strip out: George Tuska and A. C. Hollingsworth. I've seen several Tuska Scorchy dailies. They were drawn in Tuska's Buck Rogers style. This jibes with lambiek.net's note that Tuska was “main illustrator” on the strip from 1954 to 1959, when he left to take over Buck. Interestingly, lambiek.net says Tuska assisted on Scorchy back in 1939, which would have been in the early Robbins days.
Where this puts Morris, I don't know. It does suggest a term for A. C. Hollingsworth: 1959-1961. Hollingsworth, one of the few (two, perhaps?) African-American artists of 1950s American comics, is worth an entire article. Several of his Scorchy dailies and Sundays are available online. 
Though variable in quality, they're generally rather good. The last of the old-school Scorchy Smith style was gone by the time Hollingsworth took over; his work owed more to Wallace Wood than to Noel Sickles. It seems as if Scorchy became a space pilot in his last years. These Sundays take place on other planets. The day of the earthbound flyboy was over, as was the day of Scorchy Smith. It had been quite a ride.
