Optimal Empty CG for a PA12

A Goldilocks question?

I have received a number of inquiries about the CG of the 12 I am selling and can only tell them that the Empty CG is 12.99 (I think). Is that considered nose heavy, tail heavy, or just about right?

I built it with some battery location flexibility (firewall, under the front seat, or in the baggage compartment) so that the CG can be easily changed to suit the end user’s preferences. I imagined a 260 pound pilot would want the battery in the back whereas a 170 pounder might like it on the firewall or under the seat.

So then, is there an optimal Empty Center of Gravity position for a 180 HP PA12? And at what position is a 12 considered “nose” or “tail” heavy?

Thanks.

Fly it and then determine how to set the plane up right.
mine is very different if I have a Borer or a Composite prop on.
I have added weight in different places to make the plane “balanced” as I go through the speeds and the flap settings. Once it is balanced I find my bird is balanced on the stick throughout its loading of stuff. From 10 gallons and myself to “full” gross passengers and items in the extended baggage and in the cargo pod, not much change in how it feels on the stick and flying performance. Add a passenger and 2-3 cranks nose trim down all set then. Be a 170 or 250# person
so to me not a “best” CG number as they are so different than a stock plane.
Mine borer prop LW battery LW alternator LW starter 35 # in the extended baggie pushing 13.49” 1300#
take the weight out of the extended baggage and the nose feels heavy and need to trim a lot more than set up as I fly my bird. With it in the EB adding passenger and stuff really doesn’t change things much. Set up or the trim.

There is no ideal CG for every pilot. Some guys want nothing more than to fly empty with minimum fuel and make videos. Some want to pack it full and fly distances. Part of getting acquainted with any airplane is moving to load fore and aft to see how that plane responds. It’s so easy now with apps that have W&B calculators. Do a few test flights to find your sweet spot. When I built my -12 I wanted the CG to be close to original with the stock engine.

Sometimes it just depends on the mission. Flying 1600# of fish off a beach with a 185? You get what you get. Flying a moose out in a 12 or a load of caribou meat? You get what you get again. In either case it going to be tail heavy. You probably want to set it up on the front of the envelope with just the pilot in there.

"Optimal CG" means different things to different people.
An aft-ish CG generally makes the airplane cruise faster & stall slower, and generally handle lighter.
However, an aft-ish empty CG often doesn't leave much allowance for cargo.
A forward-ish empty CG might make the airplane cruise slower, stall faster, and handle heavier,
but gives you much more loading flexibility.

Having owned 4 different Super Cruisers , I will be first to admit most have forward CG's mainly because of the length of the engine mount to get the aircraft certified as a 3 place airplane. However even with a short mount these PA-12 that have an empty weight north of 1200lbs certainly fly and stall very different than the ones that are south of 1100. A 1300 lb PA-12 feels like a completely different model Piper aircraft, than one that's just over 1000 lbs......
An 1150 lb one with 11.5" cg would be a good place to start. Good Luck.
E

Thanks, everyone.

All during my build I read and re-read Bill Rusk’s thread about building a Javron Cub. I constantly worried about what my empty weight and CG would come in at. Prepping 3 options for the battery location helped lessen my anxiety. From your answers it sounds like a CG of 11.99 with the battery currently in the baggage compartment couldn’t be better. That’s a huge relief. Thanks.

Adopting a “no unnecessary frills” attitude was critical to achieving an empty weight of 1120 lbs.—only 20 pounds over my target. I think that is pretty good considering it has 180 hp driving 3-blades.

Bill’s zealous effort to save every ounce possible on his Javron build was beyond my capacity, but his thread focused my attention on keeping a keen eye on total weight. Bill Rusk’s insight should be required reading in every builders workshop. By meticulously documenting his build and sharing his knowledge, insight, and skill with us he made us all better builders. was invaluable. Kudos.

Some good info in this thread. My empty CG is 12.9 at 1,175 pounds. Me (170), full fuel (216) and gear behind the back seat (~20) I am at 13.9 and 1,581 pounds. I'll have to add some weight to my extended baggage and see how it handles.

Are you all aware of this note in the PA-12 TC? A-780

Empty Weight C.G. Range
(+9.5) to (+13.3)When empty weight C.G. falls within this range, computation of critical fore and aftC. G. positions is unnecessary. Range is not valid for non-standard arrangements.


Long ago this note appeared on some TCs.

skywagon8a said:

Are you all aware of this note in the PA-12 TC? A-780

Empty Weight C.G. Range
(+9.5) to (+13.3)When empty weight C.G. falls within this range, computation of critical fore and aftC. G. positions is unnecessary. Range is not valid for non-standard arrangements.


Long ago this note appeared on some TCs.

Click to expand...

I just did a W&B in Foreflight with empty weight (1,175), half fuel (108 ), pilot (170), Passenger (227), behind rear seat baggage (60), most aft position extended baggage (10) and I'm at max gross (1,750) with a CG of 17.0" which is still within my aft limit (18.6"). With all that said, I need to spend some time flying in this configuration to familiarize myself with the difference in flight characteristics. Hotrod180's post helped solidify some stuff for me. Simple explanation that makes the points.