No limits, please! By all means, impose a limit on your own work, then make the low number of polygons a key selling point; but a cap would deny other developers the freedom to make up their own mind. Computer hardware is improving so fast that any imposed cap would be out of date immediately. Also, the practical limit is not only determined by hardware, but also by the aircraft type and choices made by the developer. For example, mapping the Plane Maker panel to the cockpit object has a disproportionately high drain on resources. If you make an aircraft with purely analogue instruments (no VDU/LCD displays at all) and do without the Plane Maker panel altogether, the effect on frame rates is enormous. I switched from a 2048x2048 Plane Maker panel to 3D animations and gained 6.0 FPS instantly. On my system, I found that each 100,000 polygons "cost" 1.0 FPS, and that this was linear up to the overall limitation of VRAM. Without the Plane Maker panel I was able to add 600,000 polygons with no net change in FPS.