Is this normal?

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  • Updated 3 years ago
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Ok, so I cleaned the underside of the deck and waxed it. I used Windex to clean it and then applied some ProtectAll All Surface Care product. It contains, among other things, Carnauba wax. That's the first pic. After mowing my dry front yard I have a bit of grass stuck to the underside. Kind of what I'm used to seeing without using any sort of product I usually just clean the underside with a whisk broom after a mow. No waxing or other products used. What I hadn't paid attention to in the past was how there is a much heavier buildup/coverage on the side of the deck away from the exit chute side. That's the second pic. Anyway, does it seem  normal that the non-exit side would have more grass stuck to it than the exit side?
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Posted 3 years ago

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And after - 
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Please ignore the condition of the blade. I know it needs sharpening.
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Troutboy

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I think it is normal/  Less on exit because the air flow carries clippings out,  less air flow on other side, clippings stick.  Just my opinion based on fluid dynamics and engineering.
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Oregon Mike, Champion

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Thanks. Yeah, I don't know much, ok anything, about those things so that seems to make sense.
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Blue Angel, Champion

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I was thinking the same; increased airflow as well as the profile of the deck opening up and allowing the grass clippings to move outward.
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Egocentric

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I went down and looked at my housing.  I have 20 inch so it may not be exactly the same as yours.  If you consider the height between the top of the blade and the highest point of the dome of housing, you will find that the height stays roughly consistent from about 5 o'clock spinning CCW to about 11 o'clock  (12 o'clock being the front of the mower deck).  At roughly 11 o'clock the height increases steadily as it spins CCW and heads out the exit chute.  Then from 7 o'clock to roughly 6 o'clock there is a fairly rapid decrease in the height and you are back to 5 o'clock.  So maybe a way to think about this is that there is a rotating pressure wave that is somewhere around the blade, ain't smart enough to say where exactly but for our purposes let's say that it is between the top of the blade and the dome of the housing.  Think of it as a bubble of pressure directly above the blade.  When the blade is passing from 5 o'clock to 11 o'clock, the instantaneous geometry of the pressure boundary is constant and the air is relatively  compressed.  That is it is at a higher pressure because geometry of the pressure bubble has less volume.  As the blade passes from 11 o'clock heading to the chute the volume expands, and a result the pressure in the bubble is decreasing. 

Now within the bubble is all this swirling grass particulate.  Some of it get slammed into the wall.  The higher the pressure the higher the velocities of the particulate and the more inclined it may be to stick to the wall.  

That is kind of a guess of what is going on.  If I was still employed, I could talk to some people that could tell you exactly what is going on.  Alas I am out to pasture.  Oh wait, that is a good thing, but there is the loss of rubbing shoulders with some really bright folks. 

If it makes you feel any better here is a quote:  


I am an old man now, and when I die and go to Heaven there are two matters on which I hope for enlightement. One is quantum electrodynamics and the other is the turbulent motion of fluids. And about the former I am rather more optimistic.
  • Sir Horace Lamb 1932
Sir Horace Lamb FRS[3] (/læm/; 27 November 1849 – 4 December 1934)[4] was an English applied mathematician and author of several influential texts on classical physics, among them Hydrodynamics (1895) and Dynamical Theory of Sound (1910).[5] Both of these books are still in print.  Wikipedia.