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Mat, The difference between my PSRU and tracy’s is in mine, the prop shaft is running on oil fed timken taper bearings which are designed to take end thrust. The oil return at the front was to ensure that oil got to the front bearing before returning to meet up with the oil return from the rear of the redrive, and from there to the sump. Tracy only has the one return from the rear as he only has to lubricate the planetrys with a sealed bearing taking the prop loads at the front, that requires no oil. Mine has a higher reduction which in hindsight I think is not worth the extra cost. That is the basic difference. Neil. From: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Monday, May 24, 2021 6:53 AM
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: [FlyRotary] Re: Fwd: PSRU oil pressure I've always had a crankcase breather filter on the engine, but while I was testing I wanted to see what kind of actual pressures were developed inside the system. It was more a FYI. I guess in my subject I should have clearly stated this is Neils PSRU design. Waiting for Neil to chime in on the difference between his and Tracy's PSRU, but the prop shaft bearings ride on Tapered Roller Bearings. The oil inlet is on the front half with 1/4npt return on the side. There is also a 3/8npt return on the bottom of the rear section.
My whole post was basically saying, gravity return isn't enough. The psru still gets pressurized even with the smallest of restriction. Putting a vent line on top, turns into another pressured outlet for the oil to return. Still, a vent line on top I'd recommend to help the returns.
I have a temperature prob in the PSRU. I could be wrong, but having the psru gears pressurized would cause more heat? I'll see what the datas shows.
Ok, Here is my third comment. Yes you should absolutely vent your crankcase. In addition to the stock vent located on the oil filler neck, I also eventually installed an additional 1/2 in. vent. Both of these lines go through an oil/air separator which is vented in the low pressure slipstream and drained out the gear leg. And still it is not perfect, but improved since the early hours. As an aside, I can tell you that increased blow-by is usually the first indication that I am due for an engine rebuild (among several other more imminent indications like a sudden loss of power). I recommend keeping track of blow-by (how much oil is caught by the oil air separator). If you start getting a lot of oil in the can, you will need a rebuild soon. I played around the past few days with oil and psru. I added a psi gauge on top of psru,and vented the housing back to the oil dipstick tube. I have an oil breather tube from the fill port. We should have a vent on the oil crankcase. Without it, I did a pull and turned off the engine and 5psi stayed within the system until I cracked open the dipstick to relieve the pressure.
On Neil's PSRU, the oil inlet is on the front half. The front drain is on the side, which connects to the back drain that is an10, then to the oil pan.
Anyways, the stock psru inlet restrictor was 9/64. Once warmed up and running at 2200rpm static on the ground, engine oil is about 100psi for me. PSRU pressure was about 2.5psi and lots of oil was venting back into the oil dipstick tube. I kept on sizing down the restrictor until 1/16th. That mostly kept the vent clean and clear of any pressure build up inside the psru.
I'm not sure why Tracy recommends having the psru fuel of oil, maybe uses different bearings then Neil's? From a truck gear case perspective, plantey gears only need a coating of oil, not full and pressurized. I'm probably wrong, but throwing it out there. ?.?
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