flyrotary@lancaironline.net Mailing List Archive

Might be interesting to hear from those flying what rpm it takes to see max oil

pressure.............We have a multitude of oil system variations in the group and

where you take your pressure measurement will have a direct bearing on the

rpm needed for full pressure but if you take it from the far (propeller) end of the

engine like Tracy we should be somewhat on the same page as far as the RPM

needed for full pressure...............Everyone is lubing a redrive (RD1x for most)

and some have the added lube requirements of eccentric shaft jets and/or a

Turbocharger...............

Kelly Troyer
"DYKE DELTA JD2" (Eventually)

"13B ROTARY"_ Engine
"RWS"_RD1C/EC2/EM2
"MISTRAL"_Backplate/Oil Manifold

"TURBONETICS"_TO4E50 Turbo

From: Tracy <rwstracy@gmail.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Sunday, August 21, 2011 7:22 AM
Subject: [FlyRotary] Re: Fwd: oil premix data; info request

To give an actual example of what Lynn described, the 20B installation in my RV-8 is plumbed with -8 oil lines. The oil requirements of the 20B is of course 50% more than the 13B and I still see full oil pressure at anything over 3800 rpm and I'm measuring it at the far end of the oil galley in the engine. The only measure I took to improve oil flow was to clean up the passages in the front housing oil passages near the oil pump.

I did some measurements of pressure drops through the system and did see that the lines and fittings were dropping a significant amount of pressure so I am pushing the lower limit of hose size and anything less would be a mistake. I had some space and routing issues that made -10 lines problematic, otherwise that's what I would have used.

Tracy

Sent from my iPad

On Aug 21, 2011, at 1:37 AM, Lehanover@aol.com wrote:

The oil pump produces a fixed volume tied to RPM. The output is a function of the total resistance to flow of the system which is just about fixed, plus the pop setting of the relief valve, also fixed.

So, if we do not include such things a viscosity changes, foaming, temperature changes, suction side losses and all of the things that cloud the issue,

and just look at the flow, we see that unless there has been a very small hose or gallery size selected, the hose or gallery diameter and volume has no affect at all on pump output, total resistance, or temperature. So the bigger the hoses, in effect the closer you get to a static system where pressure is uniform everywhere. The one effect of larger hoses we want is the lower velocity of the oil. Drag increases at the square of velocity, so a small increase in diameter reduces the velocity and drag and also the amount of heat the pump puts into the oil.

We are also adding some length of hose in excess of the stock system, with more remote filtering and ideal cooler locations and similar, so the larger hose diameter is of some benefit there.

Suppose we have a 200 foot long oil hose in 12" diameter, and another in 1/8" diameter. Both are pressurized with the same size pump turning the same RPM. We have pressure gages at the opposite end next to the relief valve with the pop pressure set at 80 PSI. We also have pressure gages at the pump end. Assume both volumes remain as at rest, what happens when we fire the pumps together?

The large diameter version, the pump builds to just above 80 PSI and the relieve valve pops at the far end about a second later holding the full 80 PSI in the tube, and dumping excess oil with gusto.

In the small diameter version, the pump builds up 150 PSI, and 3 seconds later the relief valve pops at 80 PSI, but just dribbles oil.

The larger system is a nearly static situation, while the smaller system is a very dynamic situation.

Lynn E. Hanover

No, I am not recommending 12" diameter oil hoses.

In a message dated 8/20/2011 1:25:20 P.M. Paraguay Standard Time, dale.rog@gmail.com writes:

Kelly,

I know you asked Lynn, but ...

Things to think about: the original oil system for the 13B was designed to support two 10mm (~3/8") oil paths - one to the main bearings and one to the pressure regulator in the rear (flywheel end) iron. Any volume of oil that exceeds the capacities of those paths will result in excessive oil pressure. Going to an external pressure regulator will solve that problem, but to what purpose? For any given pressure, going from a 3/8" line to 1/2" adds 77% to the volume being pumped; going to a -10 (5/8") nearly triples the oil flow; -12 (3/4") more than quadruples it - you end up pumping a lot of oil - thereby adding heat to it - then cooling it and returning it directly to the sump.

So, how much oil flow do you need for your turbo and re-drive? As much as the engine itself? I rather suspect that having larger than -10 up to the point where the oil supply splits to service the various components won't buy you any advantage except lower oil temps, and that is actually doubtful.

Dale_R
COZY MkIV #0497