Oil Breather Tube Orientation

RW,

I think, what you are suggesting is that, by supplying higher relative pressure, to the hose, may create a venturi. The venturi could create a vacuum in the breather, exacerbating the tendency for oil droplets to be drawn out of the tank. I agree - a possibility I had not considered..

I am not sure what you mean, in the context used, by "neutral pressure" - please expand?

The term "neutral pressure" suggests to me, the same as. The same as what?

My understanding of the NOTCH is that the pressure downstream of the notch, should be not be a vacuum ie any tendency to have a vacuum at the end of the breather should be nullified/counteracted.

My limited understanding of how to do this, is that a positive air pressure,  equal opposite to the negative, needs to be introduced to the breather, thus creating a neutral pressure, that will not draw oil droplets out of the tank. This is not the same as introducing a "neutral pressure"

Without air pressure sensing (altimeter) equipment and multiple hoses within the cowling, I don't see how anything but a guess can achieve anything like an acurate equal/opposite air pressure (where to place the NOTCH & how big should it be???).

The best I can do without more precise direction/testing equipment, is try for a posative air pressure, at the end of the breather hose, in the hope that this will overcome the possibility of a low (negative?) pressure area, in the cowling exit air (breather exit) to be  transferred to the breather .

The best way to do this would be using a Y fitting with the posative air pressure, being directed against the flow of breather air - no chance of a venturi effect. I will explore the availability of a Y fitting (may have to make one)😈

Sean, by neutral pressure I should have used the aviation term, static air pressure.  As it relates to  aviation is defined as:

Hi All

Blow-by and small amounts of evaporating water create a permanent gas flow that must escape through the vent line. If checking the oil level of a cold engine by turning the propeller a few times by hand can build up enough pressure to force oil into the oil tank, then you can imagine the gas flows that have to escape into the oil tank and through the vent when the engine is running. A blocked oil tank vent inflates the oil tank, leading to oil loss through bursting hoses and engine damage.

Of course, Rotax does not want the vent flow to be disturbed by dynamic pressure or negative pressure, but this is of secondary importance and Rotax does not explicitly point this out. The most important thing for Rotax is that the vent remains open under all circumstances and does not ice up. That is why the notch is there as a last resort in case the end of the vent does ice up. Strong negative pressure at the end of the vent facilitates escape, especially of oil droplets.

Gas pressure is constantly escaping from the vent hose, so the vent hose is not a pressure equalizer in the sense that static pressure is sought or generated, but rather it is intended to prevent the escaping gas from being impeded in any way by unfavorable circumstances. Carburetor ventilation moves small amounts of air, if any, while oil tank ventilation constantly releases something, which is something completely different.

If you wanted to use the oil tank vent hose to tap into the ambient pressure at various points within the engine cowling via a Y-piece, you would not be tapping into anything, but simply clearing a path for the pressure, i.e., the gas/oildust flows from the crankcase, to escape. Mainly to where the pressure is lower.

The notch is not about aerodynamics and Venturi. There is no real Venturi effect at the end of the vent hose. For this to occur, there would have to be an inflow, a constriction, and an outflow, which is not the case at the end of the hose. If there were a significant effect here, Rotax would have pointed it out long ago and offered a solution.

The notch is the last safeguard against clogging, e.g., due to icing—as Rotax also states. The end of the hose is simply at risk if icing conditions occur. The crankcase vapors have to go somewhere; they have no place inside the engine cowling. If you want to avoid the consequences of oil vapors at all costs, you have to collect them; you cannot prevent them.

Greetings