This Franklin 0-805 is a rare prototype air-cooled flat-twelve originally designed for use in remote controlled military drones. According to Wikipedia, the project was cancelled before full production started, and interestingly the same article cites just one previously known survivor–this example now makes two. A whopping 805 cubic inch, 450 HP design, the seller says that they were informed that this one has never been run, adding that it looks clean inside and turns over easily on the starter with good compression. Find it here on eBay in Houston, Texas with an $8,500 BIN.

Initially designed to power a pair of unmanned aerial combat vehicles made by Interstate, the above linked article says that production was cancelled due to project requirement changes. The model number seems to have been chosen based on displacement, which at 805ci equates to roughly 13.2 liters. The big 12 looks complete and in good shape, both of which are pretty remarkable considering that it has probably had a very interesting journey over the past seven decades.

Here’s an info plaque identifying the engine as serial 33. Whether these were consecutive numbers or not isn’t known, but even with very thorough pre-production testing, 33 prototypes seems like a high number. Perhaps the “-2” model suffix is a clue?

An interesting piece of history, its interesting to note how little general aviation engines have changed over the years–any modern Lycoming four-cylinder will bear a strong resemblance to this old 12, though FADEC or Full Authority Digital Engine Controls are finally starting to make manual mixture controls a thing of the past. Hopefully this one will be running soon, at least on a stand, at best in anything with wheels–for some reason an old Power Wagon seems like just the right place for it.