The International Cessna^® 170 Association

This is more of a curiosity than anything, but I've been wondering about the appearance of dorsal fins on straight 170s (1948s). The more I look at them the more I see straight 170s with the dorsal fin seen on the As & Bs. It's not listed in the IPC for the '48, so it doesn't appear to be factory. The dorsal fin first appears on the '49 A models.

I imagine that some people added them over the years, but it seems like there is a rather large population of them... more than I would expect from the occasional owner getting the urge to make the change.

Does anyone know the story on this? Was it a factory option from later in the production run? Or were there really just a bunch of people over the years that decided to add it on their own?

TCDS Item 609 authorizes its installation on the '48 model. Mine has it also.

Sg

Well that makes sense... d'oh, didn't think to look on the TCDS

I'd be interested in hearing about what your logbooks say. Is there any record of the dorsal fin being installed after it left the factory?

And so since there where so many more A & B's, they are easier to find after you flip over or some other such yucky thing.

The fin was added in 1949 to increase directional stability with floats. It wouldnt pass the FAA test without it. This is according to the Bill Thompson book CESSNA WINGS FOR THE WORLD.

So, we have float pilots to thank for that graceful dorsal fin, eh? Thanks guys!

However, the 48 has been installed on floats by field approval.

I bet it wouldn't be easy to get that done any more