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Borer 3rd seat conversion STC SA5-7

Very interesting development: understood the frame modifications, BUT:

What about the CoG shifting to the back when fully loaded, does it exceed the limits?

A tail heavy plane would be very damgerous to fly, besides exceeding the original MTOW.

Any Weight and Balance considerations and tale off n lamding caracteristics chamge?


Inviato dal mio iPhone utilizzando SuperCub.Org
 
Weigh the plane if the W&B is not relatively recent and do the math.

I have flown a Cub with a far forward CG that required significant ballast to fly solo (it could not be loaded beyond aft CG while obeying the baggage weight limitations and the 1900 lb MLW), a 185 that needed a little ballast in the extended baggage to be legal with two people up front, and a 185 with aft CG issues when running around with any significant load. None of the owners were aware of the CG issues that they should have been aware of because they did not bother to do the math (although they all had reasonably recent W&B's...).

The Cub I last flew is not exceptional in any respect. I can carry maximum weight in the extended baggage and baggage area (180 lbs), half tanks (18 US gallons), and a 190 lb passenger and be at the aft CG limit. Normally I cannot fit 180 lbs of stuff into the baggage area, so most of the time heavier passengers are no issue.
 
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This is an EX Cub. 180 hp. Full lightweight electrics with a Catto prop. No issue with the 3rd seat. I use it routinely.20190314_090332.jpeg20190227_175132.jpeg
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This is an EX Cub. 180 hp. Full lightweight electrics with a Catto prop. No issue with the 3rd seat. I use it routinely.View attachment 42020View attachment 42021
View attachment 42018View attachment 42019
For anyone trying to visualize how this, came into being was Alaskan guides needing to haul the client and afield guide in the Cub at the same time to save making TWO trips back in the 50's everyone started hauling guides in the baggage compartment. So when hiring guides the often considered short/ lightweight fellas
For this very reason! Anyway almost all Cubs used by professional guides were set up with a "GI" packboard as the passenger "seatback" two small holes were drilled in the plywood seat bottom to accommodate the two pins that were already in thr packframes. Note at top in 1st picture. The frame then leaned back against removeable crossbar. A boat cushion was an added luxury for the person in the baggage, hardly ever used. The guide then got settled into the baggage first: Then the crossbar was droped in place; then the packframe as droped in. The client then got into the rear seat; leaning up against the packframe; same as if was on his back. This positions the guides legs going past his sides , passing beside the packframe on both sides. See pics below for what this looks like. About ever Cub in Western Alaska had one of these packboards in it in the 70's /90's that was used for guiding. Hope this helps all that have not seen this before; ;-)

Sent from my LM-X210 using SuperCub.Org mobile appIMG_20190320_100540875.jpgIMG_20190320_100603790.jpg
 

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This raises another question which has probably been beat to death already. I know a PA-12 is designated 3 place, even if they will carry up to 5. (No, don't even think about asking) What about carrying an infant or toddler in a 2 place like a PA-18 or Bird Dog? Is it legal to have "2 people" on board within the weight limit of seat and seat belt? If so, when does 2 small people (kids) exceed the limit?
 
This raises another question which has probably been beat to death already. I know a PA-12 is designated 3 place, even if they will carry up to 5. (No, don't even think about asking) What about carrying an infant or toddler in a 2 place like a PA-18 or Bird Dog? Is it legal to have "2 people" on board within the weight limit of seat and seat belt? If so, when does 2 small people (kids) exceed the limit?
About 1988 I saw an Eskimo gentleman, land his Aeronca Sedan in McGrath and he and Momma got out of the front seat and a small boy probably 8 years old. Rear seat passengers included 3 young girls looked bout 14/12/10.
Then momma went back and got 2 more young boys from the extended baggage![emoji19] maybe 4/6 years old! Momma took all the kids to trading post for goodies n ice creams.
Daddy went into McGuires for a few frosties!!! Lol. I walked by the Sedan and he had the rottonest 30" Airsteaks
I had ever seen. I would not have attempted one T/O with them empty in a J3........
They loaded via reverse osmosis, he then pulled out and layed the whip to that old tired C145, (bet she hadnt been inspected in 20 years) And it sounded as weak as well water , might have been makin 100hp maybe. But up came that big tail and in bout 6/700 ft; she came right off flat and climbed out like a single engine Otter off the top of the wing; and headed out west! Just a normal day for a man, and a Sedan, and 6 kids![emoji6]

Sent from my LM-X210 using SuperCub.Org mobile app
 
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I saw a Mooney land at PLY. When it puled up four adults climbed out and then the pilot opened up the outside baggage door and four youngsters jumped out.
 
Aircraft Weight and Balance

AviaTop

Generic PA-18-150 profile with modified parameters.

On Google playstore for Android
 
The 3rd seat mod, is used mainly for a structural beef-up! There is no way to get out of the 3rd seat in an accident. I work with a guy, whose father drowned in the Yukon River, he couldn’t get out of the far back seat before the Cub on floats went under. Fire is another concern… If you have 2 pax to move, make two trips…
 
Some who use the 3rd seat leave the crossbar out for those and other reasons.
Those "some" are exercising poor judgement from a safety perspective. That crossbar is in there for structural purposes holding the two sides in position to serve their structural purposes. Do you have any idea of where the landing loads go in a hard landing when the rear wing carry through is trying to compress down towards the up push of the landing gear? Hint: that crossbar is holding the fuselage sides in place so that they can do their jobs without buckling. That little diagonal tube in the 2000# STC is helping for that same purpose.
 
Double buckling is legal.

Just curious where to find a reference for this? Google only came up with two passengers using a single seat belt on a divan/lounge while en route in the FARs. Everything else was about double buckling in cars.
 
Pete…..My understanding is that DJs past mission for his cub was transporting villagers needing medical attention from high altitude areas. If I was one of the natives in dyer need of a doctor and my two options were a multi day trip in the back of truck down the mountain or sitting in the 3rd seat of a cub without a crossbar for 30min, I’d probably pick the cub. Neither option sounds very appealing.

Good on David for doing what he does. His 4 place solves this problem!
 
Pete…..My understanding is that DJs past mission for his cub was transporting villagers needing medical attention from high altitude areas. If I was one of the natives in dyer need of a doctor and my two options were a multi day trip in the back of truck down the mountain or sitting in the 3rd seat of a cub without a crossbar for 30min, I’d probably pick the cub. Neither option sounds very appealing. Good on David for doing what he does. His 4 place solves this problem!
Understood.......however, promoting the practice could give some people the wrong idea that it is safe to do under most all conditions.
 
As to the risk here, KevinJ nailed it. I have met many people in the mountains with major, life altering injuries from vehicle accidents. Yes, including truck rollovers when they were riding in back. A missionary friend was killed in a bus roll over. Bolivia is famous for the "death road" from La Paz to North Yungas. Many roads we drive are actually more hazardous but less traffic and therefore lower death toll. We have started a small rehab center to help rural folks with Physical Therapy after spinal injuries. One of our current patients was in a minivan with a dozen others when the driver fell asleep on a mountain road. There were fatalities. She had a good chance to walk again but received almost no treatment for 8 years. Another patient in a similar accident was thrown clear and then crushed by the rear of the car as it continued to roll slowly down the hill. She lived for 8 years in a room on a steep hill with no wheelchair access, caring for her child and cooking for her family by dragging herself around on the floor. The latest patient had her accident at 16, is now a 20 year-old paraplegic who has never received even a single PT session.

I've learned that risk is relative here.

Using the 3rd seat, crossbar in OR out is certainly not the safest in my opinion. It would not be my choice in the lower 48 for regular ops.
 
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".
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An old time guide told me a story to the effect that one of the polar bear guides wrecked a Cub on landing or takeoff, so they loaded guide, client and assistant guide in the other cub and flew back to shore. At some point, one of these deals was met by an FAA Inspector. An emergency was declared, of course, etc etc. But, according to this gent, that was the impetus to develop the third seat mod.....to make legal what they'd been doing occasionally anyway.

Of course, nobody was weighing things during those conversations, I'm sure.

MTV
 
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