very informative. correct me if I am wrong but from that going to forward sloping blades will make them harder to drive but will produce more wind pressure at lower speeds and will also produce a more forward directed wind ??
The forward curved blade drives air off the tip of the blade faster and increases the volume of air the fan can handle. For the cleaning shoe, this is a good thing. It won't increase the pressure under the sieve, but it will increase the airflow. A reverse blade will build more static air pressure for a given fan speed, but the air flow will be slightly less. A reverse bend blade is great for pumping air through a grain bin full of grain where higher static pressures are required. A forward curved blade will pump more air, but at a lower static pressure, such as a leaf blower where a large amount of air is used to move light material. A straight blade is the best of both worlds. If you look at the cleaning fan in a 9500 or 9600, they have a rather unique series of curves that Deere used to increase both air scavenging, (getting air into the fan,) and air volume required for the shoe and the precleaner. ( Only to leave huge gaps in the airways to the pre cleaner for all that extra air to escape!!
)
The 7720 T2, and to more of an extent, the 8820 T2, required a lot of air for the bigger shoe, compared to the earlier models, and the small side openings were terribly inadequate to get any kind of air volume, evenly under the shoe to do a really good job of cleaning in high trash conditions. They tend to drive most of the air up through the middle of the shoe and leave the outside of the shoe short of air. Grind up some really dry canola and try to put everything over the shoe, and it fails miserably because you can not get an even flow of air under the chaff to effectively separate the canola. There just isn't a really good way to get a nice even, consistent airflow under the shoe to do the job. The increased side openings helped the 7720 quite a bit, allowing more air to get into the fan early and toward the outer edges of the shoe, but were not enough for the 8820 to get reasonably even airflow under the shoe. (Canola blows over in the center and sloughs over on the outside of the chaffer.)
