I have weighed it
I’m seeking the forward and aft limits and datum point in order to confirm I am safely within limits.
This makes me wonder how much you know about weight and balance? What did you use for a datum when you weighed the plane? What did you use for a reference when you leveled it for weighing?
This is the FAA Type Certificate for a PA-18: http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/ab203ab0e89895af862572090071f7cd/$FILE/1A2.pdf
Notice on page 6 that the datum is the wing leading edge. Some people use an arbitrary number ahead of the leading edge in order to not get confused with
+ &
- arm numbers. If you use a spread sheet on your computer the + & - numbers are a non event. I use the wing leading edge because it is a known hard point from which I can measure rather than a point in space. The point in space just means more math which can be done wrong.
The
Leveling Means on page 6 says:
"Plumb from PK screw in upper door frame channel to center punch mark on enclosure door rear hinge."
We know that you do not have this on your plane. Alternatively you can refer to page 10 on the T.C.
Landing Gear item 202: Tires are located at (
+2) This means that when the plane is level you can drop a plumb bob from the wing leading edge and measure to the center of the axle 2". Another method of determining that the plane is level is to place your level on the firewall between the upper and lower engine mount fittings. The firewall should be plumb. We know this from the fuselage drawings. You may or may not have access to this drawing.
This is the FAA's weight and balance handbook:
https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/media/FAA-H-8083-1.pdf
Some airplanes do have published empty CG limits. There are no published empty weight limits for a PA-18. The published limits are applied when the plane is loaded for any particular flight. You can refer to the T.C. for the seat, fuel, baggage and other moment arm locations.