24ST3 Aluminum VS. 2024T3
Posted: Sat Feb 24, 2007 2:56 pm
I am not a member yet, and do not own a 170. I own an aircraft repair facility for GA aircraft, 22 years as A&P mechanic and 16 as IA. I should know the answer to the question below, but don't, and would like to draw some knowledge from the older, err more experience gentlemen. Here goes.
What, if any, is the difference between the aluminum, 24ST3 used in older (pre 1960) and modern 2024T3?
It appears that the changeover occurred in the mid and late 50's with most manufactures, I guess until the surplus was exhausted.
My reason for asking is this: My shop has rebuilt/restored four 170's and two 195's in the past 12 months; a noteable increase of aircraft owners spending big money restoring older aircraft. I know this trend started 20 years ago, but I've noticed a considerable accelleration in the past few years. I also notice that the degree of corrosion is much worse on the aircraft using the older designation 24ST, even in the same vintage aircraft. I would like to note however, that the corrosion on the 24ST3, in most cases only effect the surface and rarely do I see exfoliation, intergranular or other types of corrosion. This is in contrast to 2024T3 which seems to resist surface attack more than 24ST3, but I see more corrosion under metal-to-metal joints and exfoliation type corrosion with 2024T3.
These observations have very littile to do with the age of the aluminum, nor the location of the aircraft; 3 of the aircraft had documented repairs when they were young (1, 3, and 11 years old) were I could observe the new skin (2024T3) along side the old skin (24ST3). In all cases the 24ST3 had moderate to severe surface corrosion with very little between metal-to-metal joints, and the 2024T3 had very little surface corrosion and more metal-to-metal.
All examples were unprimered internal surfaces.
What, if any, is the difference between the aluminum, 24ST3 used in older (pre 1960) and modern 2024T3?
It appears that the changeover occurred in the mid and late 50's with most manufactures, I guess until the surplus was exhausted.
My reason for asking is this: My shop has rebuilt/restored four 170's and two 195's in the past 12 months; a noteable increase of aircraft owners spending big money restoring older aircraft. I know this trend started 20 years ago, but I've noticed a considerable accelleration in the past few years. I also notice that the degree of corrosion is much worse on the aircraft using the older designation 24ST, even in the same vintage aircraft. I would like to note however, that the corrosion on the 24ST3, in most cases only effect the surface and rarely do I see exfoliation, intergranular or other types of corrosion. This is in contrast to 2024T3 which seems to resist surface attack more than 24ST3, but I see more corrosion under metal-to-metal joints and exfoliation type corrosion with 2024T3.
These observations have very littile to do with the age of the aluminum, nor the location of the aircraft; 3 of the aircraft had documented repairs when they were young (1, 3, and 11 years old) were I could observe the new skin (2024T3) along side the old skin (24ST3). In all cases the 24ST3 had moderate to severe surface corrosion with very little between metal-to-metal joints, and the 2024T3 had very little surface corrosion and more metal-to-metal.
All examples were unprimered internal surfaces.
