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Thread: Converting Aeronca Chief to C-85-12

  1. #1

    Question Converting Aeronca Chief to C-85-12

    I am contemplating converting my 1946 Chief from an A-65-8 to a C-85-12 since I have to remove the A-65 for a bearing failure. My wife hates my having to hand-prop, and on chilly days, I don't like it much, either. Having an electrical system for powering radio and GPS would be great, too.

    I would like to hear from anyone who has converted under the Lasher STC-- any installation issues? Any interference w/ firewall? Weight and balance issues? Where did you put the battery? Any stories I ought to hear would be most appreciated. Note that my airplane has the larger dorsal fin and modified firewall, as if it were converted at some time in the distant "logs-lost" past.

    Thanks,

    Hunter

  2. #2

    Join Date
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    I'm an Aeronca project owner, but can't help much with your question other than to point you to the National Aeronca Association forum. I'm sure someone there has experience with the engine swap. You can join for free or you can just search through the existing threads without signing up. Here's a link to the board:

    http://www.joea.com/phpBB2/

  3. #3

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    As a type certificated aircraft you will need to work with an A&P/IA to handle the paper work. Such as FAA form 337. There is no reason that you can not do all the work yourself. However you will need their licenses to do the above. Do not do the work and then contact the above or your EAA technical counselor later. They need to be in the loop as the work progresses.
    First. go on line to FAA.Gov and look up the TCDS (type certificate data sheet) for the 11AC. It may allow you to make the conversion with out an STC.
    Second. Research all the data that makes up the Super Chief (85 HP). Many years ago I did a simeler conversion to a 7AC chanmp. and Found that the small stuff. Like the fuel line size and structural tubing changes required and matching the propeller were more important than just swapping the engine. I believe that you will find that the C85 and A65 use the same mount.
    It is a simple and good conversion. Go for it and enjoy.

  4. #4

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    I'm going thru this on a '41 J4A. Depending on the available fuel head, you may have to replace the carb. See the C-85 type certificate data. The oil tank may also have to be swapped out to clear everything.

  5. #5
    Max Torque's Avatar
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    Hunter,

    You don't need an STC to convert your 11AC Chief to a C-85 engine. Check the TCDS - A-761. In it, you will find:

    "III - Model 11BC, 2 PCLM, ApprovedAugust 26, 1947(Model 11AC eligible forconversion to Model 11BC when accomplished in accordance with Aeronca ServiceLetter No. 17.
    The nameplate must be re-stampedwith the proper model designation and the letters "CONV" added. Theairplane serial
    number should not be changed.)"
    To convert to a C-85-8F, it's pretty much just a log book entry. To convert to a C-85-12, it will entail some additional substantiation to show the...gentlemen...in the FAA (should it ever come under scrutiny) that the -8F and -12 are the same with only minor differences as listed in TCDS E233. The -8F and -12 are under the same Type Certificate (E233).
    "You have to be alive to spend it..."

  6. #6
    My '46 Chief has been converted to A-75, but still no electrical system. I can't offer any helpful tips except to say,"I like the power on climb out".
    Mine has plenty of compression. It is about all the compression I want pull through when propping, especially when it doesn't start right up. Depending on your age and physical stamina, I think the C-85 will surely need the electric starter. I wish mine had it.
    Have fun!!

  7. #7

    Join Date
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    Hunter, By way of adding to your project thinking I have two bits of info that may help.
    1) You may have 'lost logbooks' but the FAA has all the 337's ever filed as well as all the pre 1958? 'annual airworthyness inspections'. Email the FAA (www.faa.gove and search aircraft records) or call the Aircraft Registration Branch at 866 762-9434. Ask the nice folks for the "Blue plate special" and for the total of $5 (it may have gone up to $10) you will get all the FAA file data on a CD or paper if you prefer killing trees. There are 3 parts, ownership, inspections and 337s. These will include all the documentation on your aircraft from original airworthyness cert through all the liens etc. That may help you determine if someone already installed a -12 engine on that airplane. Even if the mechanics of the day did the install as a 'minor alteration' (log book entry because it is approved on the TCDS) the early 'annual inspection reports' (done every year until about 1958? will show the engine installed at the time of that inspection).
    2) I had a 7AC that had been converted to a C85-12 using the Lasher STC but they also changed to the later (7EC) engine mount. This moved the whole engine slightly forward. It always flew sort of nose heavy solo but we carried a 35# shot bag strapped into the back seat. You would have to do the wt and bal math for the 11 series (carefully..please) before you decide. There is also about a 13# difference in weight between a wood prop and a metal prop. The wood prop, that far forward might get you back more toward the 'comfortable end' of the CG envelope.

  8. #8
    RRHaldeman's Avatar
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    Lightbulb Conversion experience

    Hunter,

    I recently completed the conversion of my 7AC Champ under the Lasher STC. I installed a C85-12F, added a Sky-Tech starter and an Odyssey battery, without a charging system. The C85-12F was modified by the O-200 conversion. I used an A&P, IA to work with me. You will need to use a C85-12F if you want the starter for several reasons: it accepts the starter on back of the engine and you don't need to modify the firewall. It is good that you have the enlarged dorsal fin and modified firewall (with additional supports) because they are called for in the Lasher STC. You can see a few pictures of my project here:
    http://s900.photobucket.com/albums/ac207/RRHaldeman/
    RRHaldeman
    1979 Cessna 182Q N42RH
    1946 Aeronca Champ N83729

  9. #9
    Max Torque's Avatar
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    Awesome RR! Good on ya! Good information. How does it fly compared to the old -65?
    Tom
    "You have to be alive to spend it..."

  10. #10
    RRHaldeman's Avatar
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    Quote Originally Posted by Max Torque View Post
    How does it fly compared to the old -65?
    Tom
    Faster, climbs like a bandit.
    RRHaldeman
    1979 Cessna 182Q N42RH
    1946 Aeronca Champ N83729

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