Air powered governor--???

[Brian Rupnow]

This is something I have watched a video on, but never seen in person. It was a guy using a model T car engine to run a belt driven buzz saw from a drum attached to the rear axle in place of a wheel. The engine had it's stock fan at the front of the engine, which blew a strong stream of air back over the engine when running. The carburetor which mounted on the side of the engine and had a throttle spring that would normally make the engine rev up to it's highest rpm. The throttle lever also had a large piece of sheet metal attached to it, so that when the engine was running, the air stream from the fan blew against the sheet metal and forced the throttle back into a position which let the engine rev up to a bout 2000 rpm.---So, the strength of the air stream from the fan overcame the force of the spring. When they started to cut a log with the buzz saw, the engine revs dropped off, the fan slowed down, and with lesser air stream from the fan the spring advanced the throttle to give more revolutions per minute. It would advance the throttle until it was back to the desired 2000 rpm, then the air stream from the fan would overcome the spring. It appeared to react very quickly and maintain the speed of the buzz saw very well, with no notable lag time. ----Brian

 

[gartof]

This is something I have watched a video on, but never seen in person. It was a guy using a model T car engine to run a belt driven buzz saw from a drum attached to the rear axle in place of a wheel. The engine had it's stock fan at the front of the engine, which blew a strong stream of air back over the engine when running. The carburetor which mounted on the side of the engine and had a throttle spring that would normally make the engine rev up to it's highest rpm. The throttle lever also had a large piece of sheet metal attached to it, so that when the engine was running, the air stream from the fan blew against the sheet metal and forced the throttle back into a position which let the engine rev up to a bout 2000 rpm.---So, the strength of the air stream from the fan overcame the force of the spring. When they started to cut a log with the buzz saw, the engine revs dropped off, the fan slowed down, and with lesser air stream from the fan the spring advanced the throttle to give more revolutions per minute. It would advance the throttle until it was back to the desired 2000 rpm, then the air stream from the fan would overcome the spring. It appeared to react very quickly and maintain the speed of the buzz saw very well, with no notable lag time. ----Brian

That's how governors work on lots of small air cooled engines like Briggs and Stratton.
You could put one on your fan cooled engine. Another opertunity to select the perfect spring.

 

[Nerd1000]

On small air cooled engines this is usually implemented as a plastic 'flapper' vane next to the flywheel that gets pushed outwards by the airflow from the centrifugal fan blades on it. Would be a good solution for a small stationary engine style model.

 

[Brian Rupnow]

Actually, I knew that about the small Briggs and Stratton engines, but had kind of forgotten about it.