• If You Are Having Trouble Logging In with Your Old Username and Password, Please use this Forgot Your Password link to get re-established.
  • Hey! Be sure to login or register!

Borer 3rd seat conversion STC SA5-7

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....
 
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....
 
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....
 
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.
 
... 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.
 
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!
 
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
 
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:
Interesting to learn the history of the modification.

Here is a stock baggage floor.
20150110_081256.jpg

and a 180 lb. Borer STC'd baggage floor.
20150110_081353.jpg

Several people asked me why you have to change the baggage floor channels on a PA18, one reason is to weld all the way around the tube, the other is interference with the rudder cables. Fairleads in the pictures below.

Stock baggage floor.
20150110_081207.jpg

Borer STC'd 180 lb floor.
20150110_081343.jpg
 

Attachments

  • 20150110_081256.jpg
    20150110_081256.jpg
    920.5 KB · Views: 1,957
  • 20150110_081353.jpg
    20150110_081353.jpg
    705.6 KB · Views: 2,075
  • 20150110_081207.jpg
    20150110_081207.jpg
    1.5 MB · Views: 1,932
  • 20150110_081343.jpg
    20150110_081343.jpg
    708.6 KB · Views: 2,000
Great info as usual from you guys! I am considering this mod for my project, to be able to carry more baggage legally. I have bought the wipline 2000 Lbs kit, and FA Dodge extended baggage, so there is room for more weight! :)
but my question is where do I buy this STC? Does Dakota cub sell the Sullivan STC?
i will soon have an aerospace approved welder to weld the FA Dodge float fittings on my cub, would be great to install this mod at the same time..
 
Steve, will it be necessary to trim the aluminum side panels, and the aft baggage panel since the floor is raised a bit? If I remember correctly, the panels is "resting" on the L- angles?
 
Call Ron Sullivan at 907-345-4630 Anchorage or 907-262-4630 Sterling for the STC. I don't have anymore contact info for him. You do need to trim the side panels at the bottom since it does raise the floor.
 
Last edited:
When the 3rd seat is occupied does the cross bar get installed before flight or just stowed? Are there any structural concerns for flying the aircraft without the crossbar? A friend of mine will be at Javron tomorrow taking another look at Jay's kit. There was some question as to whether it was SOP to fly with the cross bar removed with using the 3rd seat. Another question was where the 3rd seater would sit if you put the floorboards down on the longerons like an ag model.
We plan on using the 3rd seat option regularly for medical work here in the Andes of Bolivia. Its got to be better than walking right?
 
The cross bar is supposed to be installed in flight. You can physically move the fuselage. I know people who fly without it but I wouldn't.
 
Unless you have a sufficiently wide passenger, the bar should be installed during flight.
 
Last edited:
Thanks guys! Now the talk of emergency egress problems really makes sense. It's hard to believe the FAA signed off on that STC. Usually they aren't that brave. We'll give this some more thought. Probably need to limit the use of the 3rd seat to agile folks.
What about the two tubes that cross the fuselage to support the bottom part of the rear seat? Are those structurally important as well. I've noticed that some planes have the rear seat bottom removable.
 
On my -A model, the crossbar is bolted to the rear seat-back and the whole assembly, seat-back and all, comes out (up 1") when the crossbar-to-fuselage pins are pulled. To get out from the 3rd seat - which, BTW, I don't have - you pull the pins and throw out the whole seat-back. It's not that complicated but should be shown and practiced at least once.
 
In an emergency you do what you have to do. However, I note that most Super Cubs that have all the mods can legally carry about 100 lbs less than my J-3. So if you are going to go out seriously overweight, why worry about an STC? I would bet it takes the 2000 lb gross weight increase to be able to carry three and still have enough fuel to go anywhere.
 
Back in the day, all the hunting guides in Alaska commonly hauled 3 people around in their cubs.
We always stuffed the guides in the baggage area, then put the bar across, then loaded
The "sport" and away you went, it took a hell of a long time to get the tail up with the guides
Weight back there, so you just adjusted the flying to match the load........ when I bought my first
Super Cruiser we quickly realized the huge advantage, to having all that extra weight forward
Up under the wing, with both of them in the rear seat position. You could lift the tail up in half
The distance , and you didnt have to shoot the approaches like you were in a Navaho, to keep
The tail from stalling out from underneath you! Of course we all used GI packboards for a backrest
For the rear seat, that also lets the 3rd seat persons legs come up past the other persons hips.
Its certainly very uncomfortable to say the least unless you are a tiny person.........a 6 ft guide in the
Baggage is going to have the back of his head push so far forward his view will be mostly of his knees?
If your planing on an STC ( which no one had or even heard tell of) making a cub fly better with the 3rd
Person you may be unpleasently surprised.....,....jm2cw
 
-Bob
I hear what you are saying...We are planning to go experimental so STCs and gross weight shouldn't be an issue. If we buy a Cub that is already built we'll be sure to put the 2000 lb. kit on it. If we build a kit, Jay has tested his wings to 2200 lbs. Besides that we'll be trying real hard to keep the empty weight to 1100 lbs. or less.
-TurboBeaver I am definitely paying attention to your comments about the tail being heavy. If we build we'll go with a widebody to get skinny people side by side in the back seat and a pod to put any luggage underneath. With wider people we will just have to know our limits.

In general I am gathering that the 3rd seat is pretty unpopular but I think we'll still end up using it a lot. I've personally shared the backseat of a 1960 (narrow body) 182 with two other adults on a 20 min flight. When the options are squeeze or walk, most people squeeze in ;-)
 
I put the 3rd Seat/180 lb baggage STC in about everything we rebuild but don't bother with the seat belt fittings.
 
Ron Sullivan Contact Information?

I have a phone number for Ron Sullivan of 907-561-2550 but it has been disconnected. That same number is listed on Atlee Dodge's website. I called them and they are checking. A google search resulted in contact info of Airframe's site of 907-345-4630 or 907-262-4630. The later has an answering machine for someone with a different last name. I left a message at both numbers. Would like to purchase the 180 lb baggage STC. Thanks.
 
Back
Top