'41 bc12 cg

[Tim Larsen]

Hi All,

I've been flying my BC12 for about 5 years now, but I hadn't really been concerned with the CG since I was flying the same set-ups my instructor/partner was using when he transitioned me into it.
Now I'm stretching out into more of an XC mode and want more CG info.
In my "manual", it gives me 2 flying CG ranges: "+14.5 to +19.7 OR +14.8 to +17.9"

Why are there 2 ranges? Does it have to do with a wood vs. metal prop?

Thx,
Tim

[Bigdog]

The Type Certificate Data Sheet/Aircraft Specification is your friend. Look for the section of your specific model and you'll find the CG range. Most have a landplane and one or more seaplane configs. You'll also find the CG arm for seats, baggage and fuel shown as something like (+23), (+40), etc.

[Tim Larsen]

Thank you, Greg. Much appreciated.
Tim

[Ragwing nut]

Hi All,

I've been flying my BC12 for about 5 years now, but I hadn't really been concerned with the CG since I was flying the same set-ups my instructor/partner was using when he transitioned me into it.
Now I'm stretching out into more of an XC mode and want more CG info.
In my "manual", it gives me 2 flying CG ranges: "+14.5 to +19.7 OR +14.8 to +17.9"

Why are there 2 ranges? Does it have to do with a wood vs. metal prop?

Thx,
Tim

Determining CG range is pilot 101 stuff. Maybe time for a refresher.

[Scott]

I seem to recall that if your empty C of G is toward the aft limit, the gross C of G range is different. This is because the C of G always moves aft as you burn fuel so if the empty CofG is already aft, a restriction is needed on the loaded Cof G.

[Bigdog]

I seem to recall that if your empty C of G is toward the aft limit, the gross C of G range is different. This is because the C of G always moves aft as you burn fuel so if the empty CofG is already aft, a restriction is needed on the loaded Cof G.

The CG range is aerodynamic and doesn't change unless something like the addition of floats changes the aerodynamics. You may be thinking of the empty weight CG range where if you load without exceeding any of the useful load limits (pax, baggage, fuel) then you can't mathematically get out of the aerodynamic CG range.

[Scott]

Huh?
the cofg moves aft as you burn fuel from the main tank. It is a mathematical certainty and has nothing to do with aerodynamics.
S

[Bigdog]

Huh?
the cofg moves aft as you burn fuel from the main tank. It is a mathematical certainty and has nothing to do with aerodynamics.
S

Sure, the loaded CG changes with the load. Burning fuel changes the load. But you asked about the CG range, i.e. limits. The forward and aft <LIMITS> do not change unless the aerodynamic configuration changes. Your role as a pilot is to assure the loaded CG stays within the range. The T-craft is simple - the limits do not change with gross weight. Some do. Others have different limits for aerobatics. Our CG envelope of limits vs GW is just a rectangular box.

[Scott]

Well the Tcraft is not that simple.

If the empty c of g as weighed ends up toward the aft limit of the range, the gross c of g range is different... the aft loaded limit is further forward to ensure the aft limit is not exceeded during flight.

So, for the OP, as my memory returns on this, check your empty c of g on your weight & balance report, against the spec in the type certificate. There's a note in there somewhere about empty cofg position. You're empty cofg position will dictate which cofg range you need to use when loading your aircraft.
S

[Bigdog]

Well the Tcraft is not that simple.

If the empty c of g as weighed ends up toward the aft limit of the range, the gross c of g range is different... the aft loaded limit is further forward to ensure the aft limit is not exceeded during flight.

So, for the OP, as my memory returns on this, check your empty c of g on your weight & balance report, against the spec in the type certificate. There's a note in there somewhere about empty cofg position. You're empty cofg position will dictate which cofg range you need to use when loading your aircraft.
S

OK, I'll play. Let's say I have a BC-12D. If my empty CG is 17.5", what is the CG range to use? If the empty CG is 18.5" now what is the CG range to use?

[Scott]

Ok I've probably left the OP thoroughly confused. My BC12D empty wieght cofg is within the range so I haven't had to think about landing cofg which is what this is all about.

Assuming your BC12D has the A65 you have two ranges to concider:
empty: 14.8 - 17.9
Loaded: 14.2 - 20

If your empty cofg from your w&b report is forward of 17.9 then you can load the aircraft anywhere within 14.2 - 20.

If the empty cofg is not within the empty range, then you must calculate your landing cofg position Ie the cofg after you've removed your calculated fuel burn, transferred fuel or not, dropped your propaganda leaflets, etc. Etc. To ensure you won't exceed the aft loaded cofg for landing.

This all sounds odd, but if your aircraft has an updated tailwheel, tubing repairs/ splices, lights etc in the empenage area, it's likely the empty cofg is close to or past the empty aft range. It actually doesn't take much weight because the arm at the tail is very large.

as I've demostrated, once you've confirmed your empty cofg is forward enough, you can forget about all this (until you change anything configuration wise)
S

[Hank Jarrett]

Huh?
the cofg moves aft as you burn fuel from the main tank. It is a mathematical certainty and has nothing to do with aerodynamics.
S

The CG RANGE is aerodynamic and doesn't change if the configuration is constant. The CG itself DOES change as fuel is burned or loading shifts. The requirement is that the actual CG does NOT exceed the CG

[3Dreaming]

The CG RANGE is aerodynamic and doesn't change if the configuration is constant. The CG itself DOES change as fuel is burned or loading shifts. The requirement is that the actual CG does NOT exceed the CG

Limits.

[Ragwing nut]

The CG RANGE is aerodynamic and doesn't change if the configuration is constant. The CG itself DOES change as fuel is burned or loading shifts. The requirement is that the actual CG does NOT exceed the CG

CG RANGE can move on certain aircraft based upon weight. Bellanca Super Viking is one example.

[Hank Jarrett]

CG RANGE can move on certain aircraft based upon weight. Bellanca Super Viking is one example.

Changing the weight IS changing the configuration. On most planes the weight change alone doesn't have enough impact to worry about, but on some it does. If you own one where it does it would be in the specifications for the plane.