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Thread: Borer 3rd seat conversion STC SA5-7

  1. #1
    Steve's Aircraft (Brian)'s Avatar
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    Borer 3rd seat conversion STC SA5-7

    I am in need of the installation instructions for this STC in order to determine if it was installed correctly in a PA-18-150 that I am currently working on. The 337 refers to drawing number 18-1. Any information would be greatly appreciated.

    Thanks.

    Brian.
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    Darrel Starr's Avatar
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    I have the paperwork for the 3rd seat STC I purchased for N18SY in the hangar. I'll try to get out to the hangar over the weekend to take a look. If I have it I will scan and post it.
    Darrel

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    Darrel Starr's Avatar
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    My STC for the 3rd seat (180lb baggage) is from Ronald E. Sullivan. It is SA554AL. I have a drawing with the STC titled "3rd Seat Installation" Drwg No. 7-0, dated 25 Jan 1975. It is a poor quality blue line but I could copy it in sections and hope for the best if that would do you any good.
    Regards, Darrel
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  4. #4
    Steve's Aircraft (Brian)'s Avatar
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    Darrel

    The aircraft I am working on is supposed to already have the Borer 3rd seat conversion. I am not sure if it is installed correctly, therefore need the installation instructions for that particular STC. The aircraft's paperwork does not have it. If the Sullivan STC is the same installation then I suppose it would work in the interim.

    If anyone knows how the Borer STC is supposed to be installed, please let me know.

    Brian.

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    Darrel Starr's Avatar
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    So Brian do you want me to scan the drawing? It will take about 6 sections so I don't want to spend the time if it won't help. Let me know.
    Darrel

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    Steve's Aircraft (Brian)'s Avatar
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    Darrel

    Not at this point, but thanks for the offer.
    I will try to get a picture of what I have so that it can be determined if it is right.

    Brian.

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    Darrel Starr's Avatar
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    Ok Brian. if you later want the drwg just let me know.
    Darrel

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    kase's Avatar
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    I have drawing 18-1. Let me know what part of the drawing your looking for and I can take a picture and email it to you.

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    Steve's Aircraft (Brian)'s Avatar
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    kase,

    Yes, that is the drawing I need.

    Thanks

    Brian.

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    Do you happen to have the the drawing 18-2 rev a. For the stc sa 5-29 ? Weight and balance states 170lb.

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    Steve Pierce's Avatar
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    Quote Originally Posted by Darrel Starr View Post
    My STC for the 3rd seat (180lb baggage) is from Ronald E. Sullivan. It is SA554AL. I have a drawing with the STC titled "3rd Seat Installation" Drwg No. 7-0, dated 25 Jan 1975. It is a poor quality blue line but I could copy it in sections and hope for the best if that would do you any good.
    Regards, Darrel
    Mark Ericson at Dakota Cub redrew this drawing and is what they sent me the last time I bought the STC.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

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    180 lb baggage /3rd seat questions

    So I am building a project and was wanting to know what is involved in this mod. Is it just seatbelt tabs and some additional tube? If so what are the tubing sizes and how are they installed. Any help or photo/ drawings would be appreciated.

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    www.SkupTech.com mike mcs repair's Avatar
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    yes, just an "X" of tubes and add belt attaches

    http://www.supercub.org/forum/archiv...p/t-33713.html

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    [QUOTE=mike mcs repair;618477]yes, just an "X" of tubes and add belt attaches

    Mike thanks for the info-as usual. I however cannot find any photos or drawings. I'm Kinda a new at this and may not be looking in the right places. Is the "X" welded under the floor or to the longerons and what thickness and dia of tube.

  15. #15
    www.SkupTech.com mike mcs repair's Avatar
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    [QUOTE=Beaverpilot;618478]
    Quote Originally Posted by mike mcs repair View Post
    yes, just an "X" of tubes and add belt attaches

    Mike thanks for the info-as usual. I however cannot find any photos or drawings. I'm Kinda a new at this and may not be looking in the right places. Is the "X" welded under the floor or to the longerons and what thickness and dia of tube.
    under baggage floor

    I don't remember tube sizes 3/4"???

  16. #16
    Steve Pierce's Avatar
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    The STC has a good drawing. You have to remove the baggage floor channels, it changes the elevation of the floor.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

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    SchulerJL's Avatar
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    I've never seen a 3rd seat, although heard about them - just curious - anybody have a picture of a couple of people in the back seats? How do you fit two people back there? I have a hard time getting one person in the back seat ( I have some heavy set friends!)

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    Quote Originally Posted by SchulerJL View Post
    I've never seen a 3rd seat, although heard about them - just curious - anybody have a picture of a couple of people in the back seats? How do you fit two people back there? I have a hard time getting one person in the back seat ( I have some heavy set friends!)
    Otta make the 3rd row seat in the back of a Skywagon look plum spacious!
    Remember, These are the Good old Days!

  19. #19
    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by Steve Pierce View Post
    ...You have to remove the baggage floor channels, it changes the elevation of the floor.
    ???

  20. #20
    Steve Pierce's Avatar
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    It raises the baggage floor.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

  21. #21
    Steve Pierce's Avatar
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    The rudder cables would hit the "X" tubes and there is some interference with the dogleg as well.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

  22. #22
    wireweinie's Avatar
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    Quote Originally Posted by Steve Pierce View Post
    It raises the baggage floor.
    Hi Steve
    Do you have a pic or drawing of this? About every other Cub here has the third seat stuff and I've never seen a difference in the baggage floor. I was under the impression that it was just the 'butt brace' and seat belt tabs. Does it make a difference whether the dog leg has been flipped?

    Web

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    Any one have a copy of the stc that they would let me look at and see if this is what I want to attempt. I would be grateful.

  24. #24
    Eddie Foy's Avatar
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    What is the dogleg? My Cub has the 3rd seat mod but I don't have any drawings.

    Eddie

  25. #25

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    The dog leg is the three tubes located at the back of the stock baggage compartment with the shortest tube on the bottom left looking aft (stock) or the top right of inverted. It is common to flip this (mod) for extended baggage compartments. Photo failure it looks like a "Y"
    Last edited by Beaverpilot; 01-08-2015 at 05:05 PM. Reason: Tried to insert a photo

  26. #26
    Steve Pierce's Avatar
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    Here is the factory dogleg and 180 lb Sullivan STC installed.
    Click image for larger version. 

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    Last edited by Steve Pierce; 06-05-2017 at 12:02 PM.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
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  27. #27
    mvivion's Avatar
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    The third seat conversion has the third person sitting aft of the person in the passenger's seat...in other words, in the original baggage compartment. Hence the increase of the baggage area weight limit to 180 lbs, and the addition of seat belt tabs in the aft corners of the baggage compartment.

    It helps if someone is actually going to sit back there (a uniquely bad idea in any but an emergency) to have a narrow passenger seat back in your rear seat, so that the aft passenger can rest their feet on either side of the "middle" passenger.

    This modification originally came about as a result of the polar bear guides hunting off the coast of NW and western AK. They typically operated with two Super Cubs, one with the guide and client, the other with an assistant guide and lots of five gallon gas cans.....till some of these guys figured out how to increase fuel capacity.

    Once they found a bear, the guide would land, and if that went well, he and the client would stalk the bear or vice versa, as the case may be. The assistant guide would land and if they killed the bear, they'd skin it and load the hide and skull in the assistant guide's plane, and launch both planes for AK.

    On the other hand, if the guide broke his plane landing, the assistant guide would find a safer place to land, they'd put gas in that airplane from the cans, all three would board that plane, and they'd fly back to AK.

    At some point, the FAA objected to the notion of three guys flying home in one two passenger aircraft.....hence the development of the third seat conversion.

    In matter of fact, now that polar bear hunting with aircraft is illegal, the third seat conversion is most frequently used to stiffen the airframe in this area and to increase the legal load capacity of the main baggage compartment.

    MTV

  28. #28
    Ursa Major's Avatar
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    Quote Originally Posted by mvivion View Post
    The third seat conversion has the third person sitting aft of the person in the passenger's seat...in other words, in the original baggage compartment. Hence the increase of the baggage area weight limit to 180 lbs, and the addition of seat belt tabs in the aft corners of the baggage compartment.

    It helps if someone is actually going to sit back there (a uniquely bad idea in any but an emergency) to have a narrow passenger seat back in your rear seat, so that the aft passenger can rest their feet on either side of the "middle" passenger.


    MTV
    I always wondered why my rear seat back was narrower than other super cubs. It has the 3 rd seat mod - makes perfect sense now.
    Mike

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    Quote Originally Posted by Steve Pierce View Post
    Here is the factory dogleg and 180 lb Borer STC installed.
    Click image for larger version. 

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    Steve, the tubes that have the green tape on it, is this part of the 2000lb gross kit?

  30. #30
    Steve Pierce's Avatar
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    The small diagonal tube is. The horizontal tube is the bottom of the back seat, front tube. Springs are removed and we might have replaced the perforated tube with a solid tube I can't remember.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

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    Beaverpilot do you have an A-model with the removable rear seat? I seem to remember you asking something about an ag frame some time back. It would look like thisClick image for larger version. 

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    and you would want STC SA5-29 for the baggage floor on the lower longerons. If you have a stock frame disregard.

    chuck

  32. #32
    nanook's Avatar
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    The third seat mod is a floor beef-up that allows you to put up 180lbs (limit) in that area. Very few people actually use the mod for a third person. Good luck getting out of that area if you are on fire or sinking....

  33. #33
    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by nanook View Post
    The third seat mod is a floor beef-up that allows you to put up 180lbs (limit) in that area. Very few people actually use the mod for a third person. Good luck getting out of that area if you are on fire or sinking....
    thats what I was always told is the person back there is usually dead after a crash.... didn't make it feel nice then when I got to ride back there, plus the rear shoulder harness mount bolt kept bumping my head as we flew along....

  34. #34
    nanook's Avatar
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    I know of one fatality in a float plane on the middle Yukon, couldn't get out (of the 3rd seat) and drowned. I'm sure there are more....

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    My airframe is built up as an "A" but experimental. I am in the process of Finnishing it and would like to use proven technology/ methodology to enhance its usefulness (for me) I doubt I will ever get 180lbs back there but it would be nice to have that capability. I just finnished installing the floor mounted seat belt tabs and the overhead shoulder harness tube also and I am flipping the dog leg as we speak. So is the short diagonal (2000#) brace worth my time and passenger comfort. As I understand it it keeps the door frame from racking under the heavy loads. I would like to see a drawing of this passenger seat mod. First I am a noobie to all this and haven't seen a real stc and second curious as to the process.

  36. #36
    skywagon8a's Avatar
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    Quote Originally Posted by Beaverpilot View Post
    ... but experimental. ......... I doubt I will ever get 180lbs back there but it would be nice to have that capability. ....... So is the short diagonal (2000#) brace worth my time and passenger comfort. As I understand it it keeps the door frame from racking under the heavy loads. ......haven't seen a real stc and second curious as to the process.
    Key word experimental. An stc is permission to do something to a certified airplane. When an stc is issued there has to be something done to justify the issuance. It is my understanding that the small diagonal is for the purpose of justifying a gross weight increase. While it may stiffen the fuselage, it is doubtful that it makes a great deal of difference. I would not hesitate operating a Cub without these two diagonals. I'll give an example of fuselage stiffness. Have you ever flown a Citabria on floats in rough water? The fuselage twists and wiggles all over the place. It is a wonder that the door doesn't pop open. A Cub doesn't do this without the small diagonal.

    If you are not likely to carry 180 pounds in the baggage very often, leave the X brace out. For the few times you want to carry a heavy load, just drop in a piece of 1/2" plywood to distribute the load. A human's rear end will concentrate the load in a small (for most) area. A baggage load will generally be distributed over a larger area spreading the load over a larger area.

    Just my opinion.
    N1PA

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    TurboBeaver's Avatar
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    Mtv, has explained the old guide set up pretty well, however one should remember none of the guides I
    Knew ever
    Used the factory seat backs, most of us just used a packboard(that is much narrower) so the guides
    Legs would fit passed the "sports" sides, I have an old picture of a guide circa late 70s that is 6'2"
    Stuffed into the 3rd seat ! His head is pushed down right into clients, very uncomfortable for them
    But he never once complained, loved to fly and hunt!

  38. #38
    mvivion's Avatar
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    Quote Originally Posted by TurboBeaver View Post
    Mtv, has explained the old guide set up pretty well, however one should remember none of the guides I
    Knew ever
    Used the factory seat backs, most of us just used a packboard(that is much narrower) so the guides
    Legs would fit passed the "sports" sides, I have an old picture of a guide circa late 70s that is 6'2"
    Stuffed into the 3rd seat ! His head is pushed down right into clients, very uncomfortable for them
    But he never once complained, loved to fly and hunt!
    I've often wondered how many Super Cubs are out there somewhere on the bottom of the ocean......

    MTV

  39. #39
    nanook's Avatar
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    The smarter "old" guides used two supercubs when out polar bear hunting...

  40. #40
    TurboBeaver's Avatar
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    Far as I know All of the old guides used two planes, one to track the bear, one to haul the client, the spotter cub flew low to track and almost never hauled a passenger, the other cub flew behind and above with the client only, never heard of anyone flying a thrid person unless someone wrecked. So third seat flying really wasnt an issue flying for White bear hunting, all that was before Atlees tanks , so the standard
    Set up was 4 of the stanndard 18 gal tanks, so 72 gals on board! Most liked to hunt over on the Russian coast so lots of fuel was a big plus.
    On the other hand lots of other guiding in Alaska did involve flying the guide stuffed into the baggage for short flights so save the time and fuel to make an extra trip. This of course was when the PA 12 really shined, having the guides weight up under the wing was a big advantage, compared to trying to lift your tail in an 18 with even a lightweight guide in the "third seat position".
    Last edited by TurboBeaver; 01-10-2015 at 06:17 AM.

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