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--- techtalk:ref:engmech07f [2020/10/04 22:40]
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-====== REF: Engine Mechanicals - Sub-07D ======
+====== REF: Engine Mechanicals - Sub-07F ======
+\\
 ====== Liquid Drag vs Fluid Drag ======
+====== Liquid Drag ======
+This is an this example of 'liquid drag' (as opposed to fluid drag, our real life medium). ((Dr Dick of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/122424-breather-diagrams/page2?t=1204854&page=2)) \\
+Consider a 5 gal pail of latex & paint mixer that gets powered from your electric hand drill. \\
+What's the difference between liquid and a fluid? \\
+In this example, it's that a liquid is non-compressible (oil). \\
+A fluid is compressible(air or air-oil). \\
+Stick the mixer in the middle of the pail about 1/2 way to the bottom in the center of the paint mass. \\
+Hit the trigger and the drill wants to twist out of your hand (liquid drag on the mixer). \\
+As the mixer accelerates the paint, the drag reaction at the drill gets less. \\
+And you can see the paint moving fast around the mixer and slow at the pail wall. \\
+Eventually you steer the mixer near the wall to get that stuff mixed and an important change happens. \\
+The reaction at the drill gets less, the drill speeds up and the paint near the mixer speeds up with it. \\
+But the rest of the paint away from the mixer stops moving (as if its hanging in it's own 'miniature sump' away from all the commotion. \\
+That explains the less reaction force on the drill. \\
+You're moving less than the full 5 gal now (and moving that small amount better with less drag) even though the amount in the pail is unchanged. \\
+This is important to understand. \\
+Summary so far: \\
+You're mixing the dickens out of 1/2 gal and cutting 4-1/2 gal out of the picture. \\
+And that 1/2 is really moving and it's taken less force to move it because your moving less. \\
+(less volume don't jive with the density-not volume- as in above) \\
+It's exactly the same if now you change to a 55 gal drum. \\
+/2 gal going fast but 54-1/2 not moving. \\
+So the addition of a sump (containment area) allows a greater quantity of oil (paint) to be present in the case (pail) without any extra drag. \\
+Some of that oil is able to drop out of suspension so it can separate into the sump. \\
+Once the used oil gets sump trapped things are going good. \\
+But there are drag losses geting it to the sump as it flies outward off the rods. \\
+Some will land on the inside of the case near & on the parting seam. \\
+Some will travel down the inner walls of the wheels then fly off to the case wall. \\
+Some will fly up under the pistons where it needs to eventually find its way to the case wall also. \\
+In this chaotic environment, gravity isn't going to do much to drain it down to sump when there are giant flywheels whizzing 1/8" from this case walls. \\
+The wheels are going to set up a following flow on the walls. \\
+The better the following flow, the less oil in commotion. That's good.
+But good movement is because of good dragging. \\
+But drag is bad. \\
+Good dragging sucks power. \\
+So does not dragging because the oil is slow moving. \\
+Oil is now making the fluid more dense. \\
+And what if you got no sump like 99.99% of 76< motors? \\
+This kind of drag is the main liquid drag. \\
+Its a 'no win' situation. \\
+A robbing Peter to pay Paul situation. \\
+====== Fluid Drag ======
+Above, we've touched on the idea that oil in the flywheel cavity of the cases probably creates a drag on the rotating lower end, robbing power. \\
+And the amount of oil probably affects the amount of drag. \\
+More oil = more drag and causes it to increase the density of the fluid. \\
+//Fluid//, not liquid. \\
+This drag is like the drag that makes running in a swimming pool so difficult. \\
+This drag is sometimes the only drag that gets considered. \\
+The idea that 'the dryer the better' don't paint the whole picture. \\
+That drag is smaller than the power used up to physically 'pump' the oil-air fluid as the motor spins. \\
+The more dense the fluid, the more power is lost to pumping it. \\
+No matter the density of this fluid, its the action of the pistons that moves it from the flywheel cavity. \\
+On 76< motors, logically the way to accomplish this is to open the breather valve as the pistons fall so the max amount of 'fluid exhaust' occurs. \\
+Then close the valve as pistons rise. \\
+> motors have a reed valve or umbrella flapper that accomplishes the automatic opening and closing of the 'fluid exhaust port'. \\
+And it is not adjustable. \\
+In this example when the valve closes, then the piston rise creates a giant vacuum in the case. \\
+(with the vacuum being greatest at the highest point of piston travel) \\
+Just after this highest point the pistons start to fall again. \\
+This is when the valve opens again. (max exhaust right?) \\
+This vacuum sucks the previous expelled fluid back into the case resulting in the crankcase not actually getting dry. \\
+> engines deleted the timed open and closed breather valve as is in 76< motors. \\
+The camchest is always open to the flywheel cavity with a one way valve between the motor and the outside environment. \\
+The slang term "FooFoo" comes from the annoying sound that it makes when it gets clogged up with oil residue. ((IronMick of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/128453-crankcase-breathing-cycle/page3?t=1332902&page=3))

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