Oil pump pressure regulator

Thanks for that, will have a think and talk to local Rotax shop before proceeding

Tyler Said:

Hmm, something is not adding up.  The way I read that section is that the maximum amount the normal oil level can be below the prop shaft is 15.75 inches.  I'm going to have to get out my tape measure tomorrow, but it seems to me (despite what the Fig 1. drawing suggests) that the center of the oil pump is a lot less than 15.75 inches below the prop shaft...

I just went out and measured it.

The center of the Oil Pump is about 8 inches below the Prop Shaft.

15 Inches to the Oil level would be Waaaay!!! to low.

This is probably a mistake in the manual.

The Oil level in the tank is about 8 inches from the BOTTOM of the tank, so ~15 from the Prop Shaft to the BOTTOM of the tank might be about right.

What would make more sense is that the drawing is correctly showing the nominal Oil Level At or Above the center of the Oil Pump and there is a typo where the 400mm dimension should have been 200mm(7-7/8") (~8").

I suspect that most installers look at the drawing, get the concept, and successfully install the Oil Tank as intended without ever making specific use of the 400mm dimension.  The picture is worth 400 words.

The ADMN here can refer this question to the Rotax Engineers.

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EDIT:

Even the drawing has a discrepancy.

The description states the Oil level is to be within 400mm of the Shaft, but the drawing pictures the Oil level Below the 400mm reference dimension line.

Yes, clearly there are a few mistakes (or, I'll say "inconsistencies") on those pages in the manual, but what is actually correct?  It does say (and I would agree) that having the normal oil level the same as the oil pump level is "ideal", but implicit in that statement is that other than "ideal" positions are allowable.

As you noticed, in the drawing the "measured" interval there is not accurate, but another odd thing I notice is that it says, "The oil tank (1) must be positioned on its z-axis such that the normal oil level (2) is always between 0 and -400 mm (-15.75 in) on the y-axis."  But surely that measurement (0-400mm) is on the z (vertical) axis.

I am looking forward to the engineers' reply.  I can tell you that there are about a thousand of my type of aircraft flying that have the oil tank level below the oil pump.  Presumably the aircraft designers took that 0-400mm spec at face value.

 I agree Tyler,  Inconsistencies is a good term!

On a running engine, the level of the Oil tank can be quite generous.

The lower limit would be where the Oil Pump can no longer reliably draw the Oil UP to the pump.

The Upper limit would be where the Crankcase pressure becomes excessive in forcing the Oil back into the tank. 

Both of these extremes are likely in excess of a few feet and well beyond the dimensions of any typical fuselage that would be power by a 912 series engine.

The Oil tank position limits on a stopped engine are quite a bit more limited.

While a stopped Oil pump presents a nearly total blockage to any oil flow, given enough time some amount will flow and it is only prudent to assume that ALL the Oil that Can possible flow, Will eventually Flow.

As long as the Oil level in the tank is above the Oil pump inlet, the Inlet hose will not drain, causing the Oil pump to lose its prime.  Making the center of the Oil Pump a practical lower limit.

The upper limit would need to be restricted to the point that if the Oil were to drain into the crankcase to the point of equilibrium, there would still be enough Oil remaining that on the initial engine start, enough of the Oil in the crankcase would begin returning to the Oil tank before the Oil pump had sucked the tank dry.  Making the Center of the Prop Shaft a somewhat arbitrary but Practical Upper Limit.

It is a good practice to "Burp" the Engine, or at least turn the prop through one revolution to confirm there is not an undue amount of Oil in the crankcase or cylinders before any start where more than ~18 hours has passed since shutting down.  Unless there is a puddle of Oil under the plane, it is not absolutely necessary to check the Oil Level as much as it just a good idea to rotate the prop.

All good info and good advice......thanks