National Aeronca Association Bulletin Board

I found a C-90 locally and I'm wondering if there is a STC or service letter for the installation. Is there any way of keeping the small tail as well?

Any advice would be appreciated

John

Hi, There is both. My C-90-8 was put it with the service letter, which required the larger vertical dorsal fin, which can be bolted on and recovered over it. It also required a new engine mount and some modification to the cowling and the addition of two strengthening rods in the front of the airframe. There is also a Lasher STC, though I do not have the details on it. If you wade through the STC list, you will find it. As the C-90 is actually 95 hp for take off, it still is uner 100 hp so it does not trigger the more agressive spare inspection AD. - Cheers - Robert

Sorry, I forgot, but Bill Pancake can tell you the exact Service Bulleting Number. My aircraft is now listed as a 7CCM - Serial number is 7AC-931 and the data plate shows 7AC-CONV

Don's Dream Machine has an STC for the C-85 with 0-200 parts in an Aeronca. I used that STC when putting my C-85 conversion in my Chief. I believe he also has one for the C-90.

Go to http://www.aeronca.com and click on Service Letters. Take a look at SL 13, 14, 15 and 16. These are factory (FAA approved) instructions to install a larger engine. The upgrades are for the Continental -8 series (no electrical) series of engines.

If you want a starter and/or generator, then the Charlie Lasher STC will let you install the -12 series engine. His STC is very flexible and allows optional modifications or additions, like the dorsal fin, mufflers, firewall mods, etc. etc.

I am using the Lasher STC. I am currently in the middle of building up a C85-12F for my Champ that will have the SkyTec starter (STC), which is shorter, and will not require a firewall and fuel tank modification. Also no generator, so I'm still going to be legal "non-electric, no transponder". But I will install the Odyssey battery (FAA approved for Piper Super Cub) which has enough power to provide many starts and run a Narco XCOM radio between recharges (trickle or solar). The battery, cables, switches and the radio will be installed and approved on a Form 337.

Be aware that the smaller Continental four cylinder engines, C75 and C85 are FAA approved under Type Certificate E-233. The C90 and O-200 are on a different Type Certificate E-252. While many part numbers are the same between the two types, be careful swapping parts. That is where the Don's Dream Machine STC comes in, he can install some of easier to find O-200 parts in the C85 engine.

Larry Clark
ATP, A&P, I.A.
1946 7AC N84096

Building on the previous comments, here is a summary of the various conversion options:
Service Letter 13 covers the conversion of a 7AC to a 7BCM with a C 85-8 engine
Service Letter 14 covers the conversion of a 7AC to a 7DC with a C85-8 engine
Service Letter 15 covers the conversion of a 7AC to a 7CCM with a C90-8 engine
Service Letter 17 covers the conversion of a 11AC to a 11BC with a C 85-8 engine
Service Letter 56 covers the conversion of a 7AC to a 7EC with a C 90-8 or C 90-12 engine
Service Letter 60 covers the conversion of a 7EC to a 7GC with an O-290 D2B engine
In addition to these service letter conversions there are at least two STCs covering conversions.
The Lasher STC provides various provisions for converting a 7AC to aircraft similar to 7BCM and 7DC using a C 85-8 or C 85-12 engine. The STC also covers the conversion of a 7BCM from a 85-8 to 85-12 engine. The Lasher STC does not address other engines such as the C 90.
I do not have a copy of Buzz Wagner's STC but their STC listing indicates that their STC covers the installation of o-235 and O-200 engines in 7AC aircraft.
In addition to the service letters and STC's listed above, there are other STC's for engine modifications. Aircraft Specilaties has an STC for modifying a C 85 engine with O-200 crank, pistons, and rods. The resulting engine is still a nameplate C 85 engine. Don Sword at Don's Dream Machines has a number of STCs including the installation of O-200 parts in a various model continental engines and the conversion of various -12 engines to -8 engines. Don has a very nice website and provides full service including turnkey engine repair and conversions.
Note that the engine conversion STC's address the conversion and modification of the engines but do no not address the installation of the converted engines into aircraft. You still need a Service Letter procedure or STC such as Lasher's or Wagner's STC to address the installation of the engine in a specific model aircraft.
As noted before a full copy of the Service Letters are available on Todd Trainor's Aeronca.com web site or on his DVD. A full listing of all STC's with a summary of their application on the FAA.gov website.