Are there any planes that used Aluminum tubing instead of chrome-molly steel in their fuselages? I haven't noticed any and was just wondering if their is a reason for it? I know it is a lot harder to weld and more expensive but wouldn't it work better and be lighter?

I believe a version of one of the Rans models (S6?) used aluminum structure for the fuselage aft of the cabin area, with steel tubing forward of that. I think the steel tubing was for crash-worthiness reasons.

BD-4
bolt-together aluminum angle fuselage,
aluminum (irrigation ) tube spar

--Bill

The Larid series of aircraft produced in the 1930's used an aluminum tube truss fuselage structure. The aluminum tubes were joined with welded steel tube clusters. The tube ends slid into the steel clusters. The clusters were held together with wire cross bracing. This system places the wires in tension and the tubes in compression. By using this method they produced a very strong, lightweight, and rigid structure.

Also from the late 1920's and early 1930's the Boeing F4B series of fighter aircraft also used an aluminum truss fuselage. In the case of the Boeing square tubes were bolted together with aluminum gussett plates.

During WWII student Navy aircraft mechanics at the Philladelphia Naval Shipyards assembled N3N-3 trainers. They resembled the N2S Stearman but were actually a totally different airplane. One of the big differences was the bolted together aluminum square tube truss fuselage.

There are probably many more from this era but these were all that came to mind.

I scrapped out an Airstream trailer once, it had been crushed in a rollover. Aircraft grade construction, just like they say, until I got down to the lower longeron (?), the bottom plate of the structure was bolted to the steel frame with plain old steel carraige bolts, and the dissimalar metal corrosion was pronounced, right where you really wanted the strength. I hope Airstream changed that, it just seemed like a bad deal.