What does the location of of the fuel in the spar vs inboard wing affect the plane?
The fuel can go out to the wingtips, increasing the rotational moment, much like a figure skater extending his arms. This causes the spin to flatten and increases the rudder force needed to stop rotations. NASA did a study of spins using a modified AA1. They had to use a small parachute in the tail to stop some of the spins.
We have all jumped in different N-numbers of the same model and found the planes were very different, and time in your specific plane is going to make you the most comfortable.
Interesting point. One of the biggest adverse surprises I ever got while flying was on one of my early solos, where I had been scheduled to do a cross country. The Piper Colt I had been scheduled in was down for maintenance, so the flight school put me in one I had never flown before. I had trouble from the start, not being able to find the starter switch. There was a switch in the same place I was used to from other Colts, but it had been disconnected and the switch had been moved. I thought the battery was dead, but after the flying school folks laughed at me, they explained where the switch really was. Then I took the plane up, and I am sure I had secured the door, but it popped open nonetheless on takeoff. The climb was dismal. When I got to pattern altitude I closed the door, but since it was a hot day and the flight was not going well, I decided to go around the pattern and land before anything else could go wrong. I did a power off approach (bad idea in retrospect) figuring that a steeper approach limited the likelihood of an overshoot and go around. I approached at 65 mph, the standard approach speed, as indicated by the manual and my previous experience. I had made a very good turn to final, but although I thought I was a little high and might have to slip, the touchdown point stayed exactly in the same point on the windshield and just got bigger and clearer, with little or no control input. I was flying with my right hand, as I had in all my dual flights (which says something about the instruction). When I raised the nose in an attempt to round out, the plane just continued in a straight line to the runway. Apparently the airspeed indicator was off, and other students had been told to fly their approaches at 85 mph, of which I was completely unaware. I landed very hard on the two mains, then the nose came down, I had a short bounce, during which I kept the nose up, and the plane stopped in a very short distance.
The flying school later said that I had caused substantial structural damage. I think the plane may well have had some of that damage before I got in. Certainly there may have been something wrong with the door frame, which in turn may have lowered pressure at a static port under the panel, raising indicated airspeed.
Although I now know to keep one hand on the throttle during final and round out, I still think this shows how different one plane of a model can be from another. I would have profited greatly had someone merely clued me in to the indicated airspeed others were using for approach in that airplane.