We need to be able to measure our weight-on-wheels with a hard mounted solid axle. Any ideas? The downforce goes to the ends of the axle, so the only place to measure it is the wheel bearing housing.
Ummmm not necessarily.
If you can measure the stress applied by the down force, and add it to the body weight at the solid axle mount you could compute the actual weight on the wheels.
This assumes the down force is applied by a strut (like from a wing) where you could put a strain gauge on the strut to measure its load. If the down force is applied through a large structure which would be difficult to instrument it would not be workable.
It also depends on the degree of precision you need, if you only need a relative value, you might look at an RF tire pressure sensor on the wheels and log how the tire pressure changes (temperature rise would make this complicated), but once the tire reaches a stable temp, the tire pressure should have a correlation to the applied load. If the vehicle is a solid metal wheel that of course is not useful.
Larry