Higher Gross Weight Question

[braol]

What exactly is done to the fuselage/wings in the STC SA1-210 to get the higher gross weight? There seems to be a bit of mystery surrounding this topic, in that I have garnered very little information other than the installation of the higher horsepower engine and something about larger bushings that attach the lift struts to the spars (and the required larger holes in the spars, of course). Do the lift strut end attach points then get reamed larger? I would think that this would make the strut attach ends weaker...unless the pins/bolts/bushings that go through these holes have thinner shoulders on them somehow??? Please explain to a new guy. (Oh, and the seaplane version of the BC-12D has a higher gross weight "out-of-the-box." Does the seaplane version already have these larger bushings, etc? How would the seaplane have higher gross weight, if the airframe/wings struts are identical to the "land" plane? The engineering part of my brain is confused.

[3Dreaming]

The seaplane gross weight increase is because the floats produce extra lift. Don't get the idea that without the floats the airplane can support the same weight.

When increasing the gross weight all of the bolts remain the same size. The bushing in the spar as I understand it is to give more surface area to transfer the load to the wood. Without the bushings the wood is more likely to tear from the bolts being pulled under load. There is a added strap that gets welded to tie the front and rear strut attach fittings together. I have not looked at the drawings, but there may also be a heavier root attach fitting.

[braol]

Out of curiosity, was there ever any thought to a smaller gross weight increase STC for a 65 hp equipped airplane (like 1260 or 1300lbs gross)? I know that the CG of the BC-12D is basically impossible to exceed...given the 2-seat arrangement and locations of the fuel tanks... I would assume the structural changes required for the 85hp conversion would translate into a potential higher gross weight for the 65 horse (although not the full 1380)...that's assuming that the 1200lb gross weight limit of the BC-12D came from a structural limitation and not due to meager 65 hp performance.

[3Dreaming]

To increase beyond 1200 pounds I believe that you need both more power and the structural modifications. You can increase the HP to 85 without increasing the gross weight. There is also an option for a weight increase to 1280 for the 85HP airplanes, but it requires the wing modifications.

For certification the airplane is either structurally, limited by climb performance, or both with the 1200 pound gross weight limit. If the gross weight could have been higher you can bet that the airplane would have been certified that way. Back then they were looking for any advantage they could get over the competition. If they could have increased the weight by 5 or 10 pounds you bet they would have.

[Scott]

The c of g moves aft as fuel is burned. It is very posible to exceed the aft c of g limit if you have too much weight in the baggage area. Extended baggage area, even worse.
S

[braol]

The c of g moves aft as fuel is burned. It is very possible to exceed the aft c of g limit if you have too much weight in the baggage area. Extended baggage area, even worse.
S

I just meant under usual conditions...not planes with too much paint, or overloaded, or weighed improperly.

[Robert Lees]

There is no mystery.

Installing a C-85 on the original A-65 mount without the structural mods allows an increase of gross weight to 1280lb.
That is very clearly under the STC now owned by CAP LLC (Terry Bowden of this parish). Link:http://dc65stc.blogspot.com/2018/12/...explained.html

(This was formerly known a long time ago as the Gilberti STC.)

The above link tells you everything you need to know. There is, in my opinion, no reason why a 65hp BC12-D can't operate at a higher gross weight other than no-one has chosen to supplement the original Type Certificate with such a modification! The airframe is certainly strong enough, but as a certified aircraft (in the US) you just cant do it without said supplement.

Rob

[Robert Lees]

There is anecdotal suggestion that CG Taylor wanted the post-war BC12-D (and even possibly the BC-65 before it) to be originally approved under the then CAR4 rules as 1500lb gross weight. But apparently the then CARs were more expensive (?) to certify an aircraft to that higher weight; I can't find evidence of this.

But the fact that his later Chief Engineer, Jack Gilberti, who went on to design the BC12-D-85 and Model 19 and later (after he left Taylorcraft) produced the "Gilberti STC" supports this, in that very little structural mods were required to go from 1200lb to 1500lb gross weight; I wonder if these structural and fuel system mods were simply to satisfy some CAR/FAR (as per the time) requirement?

However: Legally we are where we are. Terry Bowden is your man !

[Ragwing nut]

There is anecdotal suggestion that CG Taylor wanted the post-war BC12-D (and even possibly the BC-65 before it) to be originally approved under the then CAR4 rules as 1500lb gross weight. But apparently the then CARs were more expensive (?) to certify an aircraft to that higher weight; I can't find evidence of this.

But the fact that his later Chief Engineer, Jack Gilberti, who went on to design the BC12-D-85 and Model 19 and later (after he left Taylorcraft) produced the "Gilberti STC" supports this, in that very little structural mods were required to go from 1200lb to 1500lb gross weight; I wonder if these structural and fuel system mods were simply to satisfy some CAR/FAR (as per the time) requirement?

However: Legally we are where we are. Terry Bowden is your man !

post war aircraft have most the mods already done with exception of a few items. The issue is mostly with the prewar planes.

[TC747paul]

I am currently rebuilding N29747 as a deluxe model 19 (85-12) with fuel system mod
Spar Root Bushings need to be increased
Spar Root Straps need a small fitting welded
Strut to Spar brackets need small piece of metal welded to tie front and back of each spar together, small reinforcing at the Strut connection hole
Extended baggage with battery in back
Engine mount needs to be 4" longer (long mount)
I believe this is how a 1,500 gross increase can be achieved on a prewar.
others may know if post wars already have these mods

i agree if your interested Get ahold of Terry and he has all the stuff

[Ragwing nut]

I am currently rebuilding N29747 as a deluxe model 19 (85-12) with fuel system mod
Spar Root Bushings need to be increased Already done on postwar
Spar Root Straps need a small fitting welded Already done on postwar
Strut to Spar brackets need small piece of metal welded to tie front and back of each spar together, small reinforcing at the Strut connection hole
Extended baggage with battery in back
Engine mount needs to be 4" longer (long mount)
I believe this is how a 1,500 gross increase can be achieved on a prewar.
others may know if post wars already have these mods

i agree if your interested Get ahold of Terry and he has all the stuff

you forgot the braces on the fuselage wing attach fittings. also already done on post wars, you should also need 15 rib wings just to increase to 1200 but Terry would need to clarify for the stc.

[3Dreaming]

you forgot the braces on the fuselage wing attach fittings. also already done on post wars, you should also need 15 rib wings just to increase to 1200 but Terry would need to clarify for the stc.

If I remember correctly, terry told me you could do the higher gross weight with 13 rib wings. The 15 rib wing may have had more to do with the increased VNE.

[PA1195]

Also with the extended baggage area the rear floor tubing gets X-braced from a single diagonal. Plus a diagonal rear bulkhead brace tubing, and various attaching lugs for the floor, rear bulkhead, and battery ground. Print #120 has the data.

Gary N36007

[TC747paul]

I see the floor brace, but i dont remember a rear bulkhead brace tube, thanks i will go back and look
thanks

[braol]

Thank You all for the additional information.