Thanks, flyingagin
The hinge line will be an imaginary line from one or more hinge pivots making an axis of rotation parallel to, and under the flap just aft of the flap LE so that it moves through an arc as it deploys.
It is important to note that in the TR 664, there is mention made of the ability to move the hinge point of the flap as it is deployed so that the position of the greatest coeficient of lift can be measured and recorded. So, they move the flap to a point to achieve the greatest lift numbers, but that point may not coincide precisely with the flap deployment arc. No worries, though, if memory serves, the "ADJUSTED" value differed only very slightly (1%) from the values derived from the "non-adjusted" hinge point, so the slotted flap travel arc should produce results very similar to the reported results.
The hinge point location is best done with templates and a mounting area large enough to experiment with the best hinge point, using the dimensioning in the 664 as a baseline. That would be 0.8081 X C from the leading edge and 0.0475 X C below the chord line.
The problem arises that we are using a flat bottom airfoil, where as they used a NACA 23012 semi-symmetrial airfoil, so the dimension from the chord line is different from that of the big SIG airfoil, so adjusting the pivot line is important to get the gap dimensions called for in the TR.
This will be discussed later when we check the flap rig for the final install.
I used this method: adjusted the hinge point with a T-pin and measured the gap values as the flap went through its arc. Some were too close, some were too far.....and some were juuuust right.
I found that I could approximate the hinge location initially, and then fine tune the arc, and therefore the Flap LE-to-Slot Lip relation according to the dimensions according to the TR. My templates got pretty worn out, though. You can see the multitude of holes where I experimented with the changes in the flap travel at various pivot locations. The discernible "T" was the optimum location and I marked it for later reference.
Andy Lennon's method of flap hinges was sound, but with the advent of the Robart Hinge Pins, it makes things simpler, and cleaner.
I used Andy's hinge build method on my Icon A-5. Although, it is a solidly-designed hinge, it tends to be a bit bulky, so I went with the Robart hinges inside a faired block of hard balsa. Not for the weight advantage, as might be implied, but for ease of fabrication.
Still learning how to use this posting and editing system. I did not want to include that hand made drawing that I took a pic of. Can't figure out how to get rid of it.
Oh well, it is poor quality, but still usable. It is just a profile view of how the mod contours should look. Been a looong time since drafting class.
Blustery day here in Georgia, so perfect weather day to compose build logs
nm