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Thread: O-320 STC change during rebuild..

  1. #1
    daedgerton's Avatar
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    O-320 STC change during rebuild..

    In the process of getting my PA-12 back together after the ground loop. The wings are up for rebuild and recover in Pittsburg... Probably not going to recover fuselage as there was no damage and it was recovered with the poly fiber process back in 2008 and hangered ever since. The 12 currently has the Kenmore O-320 STC on it but was thinking about maybe changing to the the Univair / Stoddards STC. I've done most of my research here on it...

    I spoke to Crosswinds about their STC and he said I should just stick with the Kenmore.

    Any thoughts on what would be involved from going from the Kenmore to the Univair/Stoddards? Is it just new engine mount and fabricating cowlings? It would be nice to get that CG a bit further back. Any pics of the Univair / Stoddards would be greatly appreciated.
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    I have the same STC currently and have wondered the same. I just had mine weighed. EW of 1175 with a EW Arm at 12.89. What is your CG currently at?

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    skywagon8a's Avatar
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    Before you go spend a bunch of money for STCs and alterations, why don't you just hang 10 pounds of ballast at the tail? 10 lbs at 200" will move the CG back 1.58". Fly that to see how you like it. Ballast is an acceptable and approved method of moving the CG.
    Make a temporary installation to find out if you like it, then do a more permanent installation.

    Make a simple weight and balance program on your computer. Try different weights, watch the CG move around.
    N1PA
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    daedgerton's Avatar
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    Quote Originally Posted by skywagon8a View Post
    Before you go spend a bunch of money for STCs and alterations, why don't you just hang 10 pounds of ballast at the tail? 10 lbs at 200" will move the CG back 1.58". Fly that to see how you like it. Ballast is an acceptable and approved method of moving the CG.
    Make a temporary installation to find out if you like it, then do a more permanent installation.

    Make a simple weight and balance program on your computer. Try different weights, watch the CG move around.
    But spending money is fun...

  5. #5
    RVBottomly's Avatar
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    Quote Originally Posted by skywagon8a View Post
    Before you go spend a bunch of money for STCs and alterations, why don't you just hang 10 pounds of ballast at the tail? 10 lbs at 200" will move the CG back 1.58". Fly that to see how you like it. Ballast is an acceptable and approved method of moving the CG.
    Make a temporary installation to find out if you like it, then do a more permanent installation.

    Make a simple weight and balance program on your computer. Try different weights, watch the CG move around.
    So now you give me an idea to put in a small baggage compartment near the tail. My shoulder bag typically weighs 15-20 pounds. I often bring it on trips. Might as well put it to good use if it would help.

    Or extra water bottles, cans of beans, etc.
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    Be careful when you put loads at the extreme. While you may be within the CG envelope, moving mass at the far end of the fuselage can have a significant impact on the spin dynamics of the airplane. The inertia of that mass reduces the effectiveness of the rudder in stopping the rotation.


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    skywagon8a's Avatar
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    Quote Originally Posted by dgapilot View Post
    Be careful when you put loads at the extreme. While you may be within the CG envelope, moving mass at the far end of the fuselage can have a significant impact on the spin dynamics of the airplane. The inertia of that mass reduces the effectiveness of the rudder in stopping the rotation.
    If the load is of great significance then I would agree there is a possibility. 10 lbs in a -12 or -18 in this location is not very much. My -18 has this much ballast at the tail with only positive results. I have placed 120 pounds of ballast at the extreme aft end of a Pilatus PC-6 to bring the CG within range with no adverse effects. This was done with a field approval and with concurrence of Pilatus engineering. If a plane had marginal spin recovery characteristics in the first place, then this could be a consideration. A -12 has no issues in this respect.
    N1PA

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    I usually carry 20-30 lbs of tools survival gear most any time I fly. Adding a aft compartment to hold tools and tiedown gear is a no brainer if you want to help with CG.
    DENNY

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    wireweinie's Avatar
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    Use a fat tail wheel.

    Web
    Life's tough . . . wear a cup.
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    O-320 STC change during rebuild..

    Quote Originally Posted by skywagon8a View Post
    If the load is of great significance then I would agree there is a possibility. 10 lbs in a -12 or -18 in this location is not very much. My -18 has this much ballast at the tail with only positive results. I have placed 120 pounds of ballast at the extreme aft end of a Pilatus PC-6 to bring the CG within range with no adverse effects. This was done with a field approval and with concurrence of Pilatus engineering. If a plane had marginal spin recovery characteristics in the first place, then this could be a consideration. A -12 has no issues in this respect.
    The Howard Is a much larger and heavier airplane. With ballast on the tail post, it gets a placard that restricts intentional spins. Mine had about 20 lbs on the tail post to bring it in the forward limit with just the pilot, full oil and full front fuel tank.


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    Quote Originally Posted by daedgerton View Post
    In the process of getting my PA-12 back together after the ground loop. The wings are up for rebuild and recover in Pittsburg... Probably not going to recover fuselage as there was no damage and it was recovered with the poly fiber process back in 2008 and hangered ever since. The 12 currently has the Kenmore O-320 STC on it but was thinking about maybe changing to the the Univair / Stoddards STC. I've done most of my research here on it...

    I spoke to Crosswinds about their STC and he said I should just stick with the Kenmore.

    Any thoughts on what would be involved from going from the Kenmore to the Univair/Stoddards? Is it just new engine mount and fabricating cowlings? It would be nice to get that CG a bit further back. Any pics of the Univair / Stoddards would be greatly appreciated.
    I have the same question.
    really like the 0320 and hope to put carbon prop if/when one is approved.
    not overly nose heavy’due to pa 12 tailfeathers,but I would like to use a shorter mount if it would improve its manners.
    please advise me of your findings,
    thanks
    wb

  12. #12

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    I have a J-5 with PA-12 wings and PA-18 horizontal tail surfaces fitted with a 160 hp O-320. When it had the stock engine mount it was noticeably nose heavy but I went to the Stoddard short mount and she is just so much better - even with the Borer prop. It was necessary to fabricate a new cowling and that needed some fettling to get the cooling right - but the end result is worth it.


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    Don't over look the fairly easy nose weight reduction of switching to a Niagara aluminum oil cooler ,about 5# savings and a light weight starter saving another 4 or 5, both right off the nose and with the added benefit of better cooling and starting.

    And if you do end up recovering the fuselage: move your ELT back to right in front of the jack screw and add the gross weight increase STC, all those new tubes make my 12 almost tail heavy with a long mount
    Staying alive in an airplane has a lot more to do with mastering ourselves than mastering the aircraft.
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