I've noticed that some 7AC Champs have the extended dorsal fin, while others have the original vertical stab with the dorsal extension. Anyone know the rhyme and reason behind which airframes have which tail? I'm seeing several examples for sale that all say they're 1946 7ACs, but with a mix of big tails and little tails.

The "big tails" will have 85hp, while the "small" tails will be 65hp.

You’ll find some small tail 85hp examples also.

When done according to Aeronca and the Type Certificate this is true. There are some STCs for increased horsepower that don't require the dorsal increase.

You will also find A65 Champs with small tails. Note the new 100hp Champs have a small tail.

George

Big tail helps with adverse yaw. Aeronca has a service bulletin allowing 7AC to get the bigger tail. I prefer the little tail because when had I ever deserved something nice? I think only 7AC were given the little tail originally. Champs with more than 65 horses from the factory got the bigger tail.

May be wrong about this but we'll see. I believe that if you put floats on the Champ you had to add the dorsal as well.

Were there 7AC models that came with bigger engines from the factory? Or are these planes with the bigger tails ones that were given the bigger tail with a bigger engine later in life?

I’m not an expert but I believe all 7ACs came with A65s and small tails. The bigger engine champs came with bigger tails to compensate for more left turning tendencies. People found the bigger tail helped with adverse yaw as a positive side effect and Aeronca released a service bulletin allowing 7ACs to get the bigger tail.

One of the ways to add more ponies to an 7AC is to convert it to a later model and this will include switching to the bigger tail, which is why many of the re-engined 7ACs now have the bigger tail.

These airplane have had long lives. Some 7ACs have been given bigger engines and the big tail, then given the original engine and kept the big tail. Other 7ACs got the big tail just for handling qualities improvements. Other champs have been re-engined with various stcs and field approvals.

That reminds me of an old girlfriend.

As I recall the 7CCM was first factory 85hp
7DC had first factory larger tail
Charlie Lasher STC to install 85hp did not require larger tail, nor more fuel tanks, just a firewall brace, lower cowl flange & Hanlon-Wilson exhaust to meet carb heat specs.

A light 7AC with 85hp is a hoot to fly!

All of the sea conversions require additional vertical fins on the horizontal stabilizer.

The factory S7AC did not have larger tail.

More important to figure out is if the conversion ever had a gross weight increase, some did only with no-bounce gear .... that determines if it is LSA qualified, which is less of an issue now with the basic medical option.

Aeronca started putting bigger engines in the Champs for the military in 1947. They basically just used a standard 7AC and added a greenhouse and bigger engine. An L-16A is Champ with a C-85 and the standard small dorsal fin. This airplane became the 7BCM when they returned to the civilian world. The L-16B had a C-90 and and the larger dorsal fin; they are 7CCMs in the civilian world. As a few people mentioned, there are various ways to get the higher horsepower engines into the 7ACs. We have a 7AC that was converted to a 7CCM for use as a duster many years ago. We're going through it now, so you can really tell the difference between the big tail and the small tail. Here's a photo of the frame with the big tail, and then I cropped the photo and circled the two pieces of tubing that are still welded onto the fuselage from the original dorsal fin.

Wow, great content Nick!