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Thread: PA-12 Gross Weight Increase

  1. #1

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    PA-12 Gross Weight Increase

    There seem to be 2 STCs for PA-12 gross weight increases to 1935 lbs:
    SA190AL - M R Borer Aircraft Svc
    SA689AL - Crosswinds STOL

    How much weight does the conversion add to the empty weight of the plane?

    Generally, what is involved? Just tubing additions? Is it a lot of work or not too much?

    Does anyone know if there are significant differences between the two STCs?

    Thanks, Rod.

  2. #2

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    pa 12 gross increase

    I have the crosswinds stc and yes its a big deal lots of tubes to be added also you have to put the super cub gear on not sure what we gained yet we have to put it on the scales it isn't as much as you may think i'm guessing maybe 150 lbs also i removed the old gear truss by just rebuilding the cabin floor you would also want to put the super cub control system in at the same time ron sullvan has that stc not a small udertaking
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  3. #3

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    Re: pa 12 gross increase

    Leon - Thanks for the info. I didn't realize that you also have to convert to cub gear. I assume that your expected weight of 150 lbs is the weight of the modified fuselage? Do you have any idea what a stock 12 fuselage weighs? I know only that Airframes Inc 18 fuselages are suppose to be 104 lbs; I think their wide body fuselage is only a few lbs heavier.

    I already have a modified control system, not sure which STC.

  4. #4
    klm_ak's Avatar
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    I haven't seen SA190AL, but we installed SA689AL from Charly on my PA-12 last year.

    It is a LOT of work, about 45 tubes and 25 channels.

    I tried to estimate the total weight of tubes and channels, and came up with 17 pounds. Some of these are replacements for stringers that already exist, but including the weight of the additional welds it's certainly over 20 pounds.

    It requires among other things-PA-18 gear & feathers, 8.50x6, 4 tail springs, 3200 scott or maule, and an O-320.
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  5. #5
    Big AK's Avatar
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    rsmarch, consider the change to Cub-style a great improvement unless you'll be doing long x-country from smooth to smooth.

    Cub gear makes float changes and bungee changes less intimidating, and look at all those aftermarket gear available.

    I've got a set of corroded -12/14 gear that are a testament to why new heavy-duty 3" extended -18 gear are a real comfort to me.
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  6. #6
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    PA-12 GW increase

    I've seen it several times and I still scratch my head and say "what the #$%& is all that tubing supposed to do?". There is not much strength in a 3/8" .035 tube laying parallel to the longerons. Its just another big paperwork joke the FAA had someone go through to up the "paper" gross weight of the PA-12/14. They could always carry 1935 lbs safely but the FAA had to see some change to the fuselage to up the Piper numbers. Adding 20lbs aft of the dog leg makes no sense to me at all. This is the area you want to take out weight not add it.

    If you really wanted a PA-12 to haul a load then replace all the 5/8" .028 1025 mild steel diagonal tubes that are installed at every station down the sides, top and bottom of the fuselage long section with 5/8" 4130 .035 chromoly steel tubes. Airframes Inc did this to the PA-18 fuselage they sell. That is why the Airframes fuselage is less flexible and stronger than the Piper original. Crash
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    delete

  8. #8

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    Re: PA-12 Gross Weight Increase

    Thanks for the good feedback here.

    I talked to Roger Borer. He is retired but still has and sells STC SA190AL. He says the two STCs (SA190AL - M R Borer Aircraft Svc; and SA689AL - Crosswinds STOL) are identical. He and Cal Center were partners when they developed the STC. He sells it as a package (I think he said for $350) that includes the gross weight increase, an STC for the required 18 style gear, and an STC for 8.50x6.00 tires (no wheels specified). He says the fuselage gross weight increase by itself adds about 35-40 lbs. He says his gear change adds about 4 lbs if you don't remove the heavy tubing under the seat that the bungees attach to. If you cut those out and put in a cub style seat, then the gear conversion ends up 4 lbs lighter (I'm guessing that the latter may not be part of the STC). He says his gear conversion gets rid on the caster, camber, and toe in and makes the plane easier to handle on the ground and during landing.

    At the moment I'm leaning toward trying to keep the plane lighter and not doing the gross weight increase. The 18 style gear is appealing, but I'll continue thinking about it all and listening to the comments here.
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  9. #9
    Crash's Avatar
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    STC

    There is an STC to just convert the gear over to the PA-18 style and that is something I would always do on a PA-12/14. As for the GW increase STC, I would never suggest doing this mod. I feel it screws up the plane and if I bought one that had it, I would cut it all out and go back to the turtle deck arches and stringers. Bad mod!!! Crash
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  10. #10

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    pa12 gross

    I removed the truss uder the seat by replaceing the bottem of the aircrafft new tubingand every thing else in that area look real good

  11. #11
    cubunltd's Avatar
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    I have done the Charlie Center grossweight increase on several PA12's and yes it is a lot of work. And yes some of the tubing additions don't make sense, but it is the only legal way to get the increase in gross weight and it causes no adverse affects on the aircraft. Adds about 30 lbs. with the PA18 gear. If you add the 3" 0r 6" gear it spreads the wheel base out and makes for good ground handling qualities. I'm using Charlie center's 180 hp conversion and it makes for a nice flying and performing PA12

  12. #12

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    gross weight increase

    The PA-12 and PA-14 are identical behind the back seat. The PA-12 has a gross weight of 1750. The PA-14 has a gross weight of 1850. In a way, Piper demonstrated that the PA-12 could have had a gross weight of 1850 when they built the PA-14 without changing the structure but they were not building the 12's anymore. Piper probably limited these plane's gross weights based on the limited horsepower of the stock engine and the available rate of climb at gross rather than the ultimate structural strength of the rear of the fuselage. When they went from 12 to the 14 they simply bumped up the gross weight 100 lbs to accommodate the extra seat.
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  13. #13

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    Hmmmm.....

    Hmmmm, certainly makes one seriously consider an experimental, doesn't it?

    Mike

  14. #14
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    RPURCELL has correctly guessed the limitations on the PA-12, at least if information received from a long-time FAA guy is correct.

    Piper limited the gross weight on the PA-12S due to the limited climb rate. They limited it to 1838 pounds.

    I heard, from a source involved in the testing that Cal Center kept adding tubes until nothing bent during the required drop tests in order to get the STC.

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    What are typical empty weights folks are seeing on their PA-12's? The plane I'm looking at is 1265.0 empty. This means unless you weigh less than 161 you can't even solo with full fuel. On floats you could weigh 201. Not much (legal) utility here....

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    What are typical empty weights folks are seeing on their PA-12's? The plane I'm looking at is 1265.0 empty. This means unless you weigh less than 161 you can't even solo with full fuel. On floats you could weigh 201. Not much (legal) utility here....

  17. #17
    StewartB
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    BSEC,
    I think 1225# is a realistic weight for a modified 12. Add the extended wings and the panel in the plane you refer to, and 1265# is believable. I know of a nice looking 160hp 12 that's well over 1300#. I've heard stories of light ones. You're right about the "legal" useful load being too small. That's why most of us have the GW increase, with it's added weight. My 12 will have a useful of right at 700#, or slightly more (I hope!)
    SB
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  18. #18
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    my PA12 has a modified top deck and most all 1025 replaced. I left the 12/14 gear truss in place as it added tremendous strength to the fuselage at the area affected most by rough landing (except for the tail) The seat was modified with different upholstery and If you can live without taking it out or moving it back and forth this works fine. I also have the 18 gear fittings with a combination of Rogers STC and Ron Sullivan's STC. As for gross weight increase Crash is right as to the illogical tubing installed???

    The PA18--12/14 will easily carry the weight. Legal??? but really how many cubs do you know that structually failed due to over weight?

    The PA12 without the wing mounting being changed is greatly hindered in its ability to carry a large load without it plowing through the air. Charly has overcome this with his modifications but it is really hard to justify the cost especially if you are starting with an "original" 1025 fuselage. That is where John Mitchell was on the right track up in Canada. (he had some "short comings" as to his business decisions but his airplanes performed well and he did not totally #$%^k up a good design.

    my 12 and others will do about 95% of what a Modified SC will do and have the interior room advantage.

    It is my opinion that if you add flaps, move the ailerons out , put on a Hendrixs tail, beef up the aft section of the fuselage, and do as Crash suggested, and if on wheels add the 6" extended SC gear you will be pretty happy. the Short mount is a plus if you don't mind sacrificing some aft loading? I really like my long (original beefed up) mount and the ability to load all the crap you want in the baggage. the 8' gear spread adds tremendous stability and with 31" tires it rotates in about 25% less ground roll (light) then stock gear on a flapped 160 hp 12.

    Light is always better and mine weighs slightly less then 1200lbs.


    just an opinion--Tim
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  19. #19
    klm_ak's Avatar
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    My -12 was 1162 before I started modifying it. Big tanks, wheel ski brackets and reservoir, gross weight increase and two doors later it is now 1222 (1314 on skis).
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  20. #20
    PA12driver's Avatar
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    Sound about right!

    Tim

  21. #21
    skukum12's Avatar
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    12 weight

    my 12 tips the scales at 1172. 29's, 3 inch cub gear, hendrix tips, flaps, o320, borer and cub tailfeathers. oh yeah, light starter and alternator.

  22. #22
    PA12driver's Avatar
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    Sounds about right! Post some pictures?

    Tim

  23. #23
    jr.hammack's Avatar
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    pa-12 gross weight increase

    tim,
    my pa-12-160 with 29'' bushwheels,extended flaps,pa-18 gear,hendrix tips,dan's battery stc,l.w. starter&alt.,weigh's 1207 lbs.


    see all at ruidoso if you make it.

    jr. & j.d.

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