Vertical tail fin extension

[PurpleHonker]

Service Letter 17 (Converting a 11ac to a 11bc with C-85) requires a p/n 7-792 vertical fin extension (making a Big A__ Chief). Does anyone know where the regulatory requirement is? I suspect the question has been previously answered on this forum but I haven't found it. It is probably somewhere in FAR 23, having to do with tail volume vs horsepower, or some AC but again, where?? I'm restoring N3703E with the Wagner O-200 STC and have to go through a conformity inspection since the Airworthiness Certificate has been lost and there's no entry in the FAA database and I'm trying to make sure I've got all bases covered.
Cliff Goldman

[rkittine]

I have the Large Tail on my Chief, which was done via the Service Letter Conversion to a C-85-12 (Don's Dream Machine engine with 0-200 parts). My understanding was that was just a requirement of the Service Letter established by Aeronca and that the other STC conversions, as the Wagner, did not require it. I have read all the plus's and minus's, but really like it on a seaplane. Bill Pancake could for sure explain.

Bob

[Paul Agaliotis]

AS Bob pointed out, the regulatory requirement is the Service Letter. By following the Service Letter, completely, the aircraft will be in a "properly modified condition". Should you chose to use other "approved" documents you would follow their instructions. If it does not require the big tail, or is optional, those instructions are are valid for the modification.

Bob does a lot of floatplane work, so if you are considering this be sure to use the proper documentation for your modification.

Paul

[bsafran]

Just a few thoughts about vertical fins. I used to have a 7AC fuselage repairing business and had a wonderful jig that let you build either style tail. Instead of a lot of welding, you can take the easier route and bolt on a modification. Whatever method you use, be sure you are ending up with an accurate alteration.
I was looking down the flight line at one of the Middletown fly ins with Bill Pancake and noticed a group of large tail planes parked close together. I asked Bill why the dorsal fin shapes were so different. No two were alike. He laughed and said that airplane rebuilding was a little looser in the old days and not so adherent to specs like today's FAA/lawyers demand. He said a common practice was to take the leading edge off of a J-3 horizontal stabilizer and modify it to bolt onto the Aeronca tail (he even admitted to doing this himself). I had a bolt on part in my shop and couldn't wait to get home and lay it on my Cub tail. Sure enough, I had a bogus part!
If you are going to make the mod, the dimensions and shape must conform to Aeronca Drawing 7-450L Frame Assembly- Fuselage (look in the bottom right hand side of the drawing). The dimension are also on Aeronca Drawing 7-792 Fin Assembly - Clamp On. Univair sells the bolt on version ($706.81). We were asked to quote a price for converting on a few fuselages we were repairing. At that time, the Univair price was a little over half of what it is today. We could not do the required work for less than the bolt on, so no customer went the welded route.

[rkittine]

I agree with bsfran regarding doing it right as there have been a lot of quick fix alternatives installed out there. Same with the conversion to floats and the addition of either the twin small vertical stabalizers on the horizontal stabilize or the single dorsal fin. Then I see a lot of people leaving them on when the plane goes back on wheels, where they are supposed to come off.

Bob

[MikeB]

While I have flown both the big and small dorsal fin Champs, etc. I've owned a 7AC, L16 and 11CC Chief all have the big fin. Some purists don't like the look of the big fin but I'm OK with it. I think I find the big tail a little more stable in the air but it gives the wind extra area to push on when taxing in a crosswind and as mentioned before the Wagner STC doesn't require installing the big tail. I'd think using the Wagner STC with the 0200 installation (that's what I have in my L16) should cover the regulatory basis as it's "recommended but not required".
Mike

[Richard Murray]

With all due respect to the assembled knowledge base on this site, the Wagner STC specifies " To convert to the larger engines the aircraft is brought up to the Model 7CCM-90hp conversion"



To the best of my limited knowledge the only way a 7AC can be converted is by Service Letter 15, which requires the addition of the bolt on dorsal tube.

http://aeronca.celinaux.com/SL/SL-15.pdf

While the Wagner STC is generously vague and allows for ample interpretation by the installing mechanic, I don't believe you can avoid the larger fin as has been suggested.

[rkittine]

That is interesting Dick though that is the Wagner STC and I think everyone is talking about the LASHER STC. Good question for Bill though. In any case, both my Don's Dream Machine Chief and my 7CCM had the bigger dorsal fin.

Bob

[MikeB]

As Dick noted (and I've always said) the Wagner STC leaves a lot open to "interpretation" or up to common sense. I understand Dicks point regarding service letter 15. Wagner STC is specific in that the "Clamp on dorsal fin (specification #618) is recommended but not required under the STC". That would be SA 372 for the 7 series. I've also scanned through SA 57RM as applies to the 11 series with the Lycoming and 0200 installation and I can find no mention of the extended dorsal fin. Old "Buzz" made things a lot easier for us when it came down to installing the 0200 engine but he left a lot of details out too. When I was in the process of putting a starting and charging system on my 0200/L16 I pointed out to my IA that the "basic electrical system may be used as on the Chief SA57RM" and he concurred. However, I went the field approval route with the Sky-tec starter and no charging system although I do have approval to install the 12 amp B & C generating system. I just haven't installed it yet as that opens up another 'can of worms'. Obviously there must have been some reason why the dorsal fin extension was added when the larger engines were installed but I wonder how much different it would make.
Mike

[rkittine]

http://johnpropst.yolasite.com/resource ... ev%208.pdf

[PurpleHonker]

Hey guys, thanks for all the comments. I should have enough ammo should the inspector question the big tail. He's owned Aeroncas in the past so is familiar with them and (are you sitting down?) reasonable to work with but -- that bear's asleep, I ainta kickin im -- I just want to be armed in case. Incidentally I have field approvals to install the B&C 12 amp alternator and to substitute 3/32" pop rivets for PK screws on Chief wings if anyone needs one.
Cliff Goldman