[shortstuffsushi]

How much weight do you think it would realistically take to alter flight in a plane of this size? For instance, if both the pilot and passenger weighed e.g. 200lbs and sat toward the left of the plane, would that considerably (or perhaps even just perceptibly) impact flight? Same for some of the other variables, is there an appreciable different for things like magnetic variation? Wind, of course, seems reasonable - the others I've heard less about. I don't fly, and have never been in a small engine craft.

[sokoloff]

Fore and aft weight distribution matters a lot in terms of how the airplane flies. Side to side not as much. (Most single-engine airplanes have more moment arm of fuel weight change in the wings than moment arm of two people sitting on the left side of the airplane.)

Fore and aft changes in center of gravity affect how far the center of mass is from the tail control surfaces and the amount of negative lift the tail has to contribute. I can feel the difference when my (fairly small framed) family moves around in the back cabin.

Aft weight distribution makes the airplane far more sensitive in pitch, reduces drag from the tail negative lift, which slightly increases climb rate and/or forward speed for a given power setting.

[pilot7378535]

Not sure about the plane from the original post; it looks pretty hefty. And lateral weight is so close to the center of mass that it's unlikely to have much effect. What's more of a concern is having a bunch of weight far from the plane's center of mass, where the weight tries to lever the plane end over end, increasing the risk of a stall. I heard about a crash where the pilot's seat adjuster didn't lock, so when he took off his seat slid all the way back (just a few inches) but that was enough to cause a crash. Could theoretically happen to any size plane, but matters more with little light planes like those in general aviation.

I have no idea if "Spirit Airlines weight distribution issue" actually happened, but it's funny so I'll share: https://youtu.be/YvfYK0EEhK4

Magnetic variation in my area is +20° (west) off true north. So if I want to follow longitude line true north I need to fly such that the compass reads 20° NEN. And don't forget to account for the hunks of metal inside the airplane, which can affect the compass differently depending on your heading.