Some more obscure questions...

General information about Wing42's Lockheed Vega.
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Vitus
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Some more obscure questions...

Post by Vitus » 09 Jul 2018, 12:52

Here are three obscure question for which I am curious to find out the answers. Maybe some of you may be able to shed some light:
  • What is the oil flow rate for an oil pump on a P&W R-1340 SC1 under different engine speeds under ideal conditions (e.g. viscosity in the normal range)? I'm currently working under the assumption that it's around one liter per second, but it feels a bit excessive.
  • Since oil temperature is measured on the upstream, I'm still wondering how it is possible to get to a temperature of ~50C. Are there two separate oil tanks, one that's in circulation and a reserve tank from which more oil is feed into the cycle when needed?
  • Am I right to assume that the oil pump that pumps the oil from the sump back into the tank, has the same specs as the upstream pump? If so, am I then right to assume that during normal operation the sump gets continuously pumped out dry as long as the engine is running?
edit:
  • How hot does the crankcase get at normal operation?
  • How hot will the pushrods get?
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Jarek
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Re: Some more obscure questions...

Post by Jarek » 09 Jul 2018, 20:16

Maximum oil flow for this engine should be 60 pounds per minute at 75deg C and rated rpm (2200).
This gives around 0.45 kg/sec.
Oil grade for this test = 1100 (SAE 50, MIL-L-6082)

AeroShell 100 SAE 50 oil specs:
Density @ 15°C kg/l = 0.886
Kinematic viscosity@ 40°C cSt = 230
Kinematic viscosity@ 100°C cSt = 19,7

Please note presence of oil pressure relief valve which controls the oil pressure. It will close entry circuit if the pressure is gone (eg. engine stops).

There is a single oil pump with 3 sections, one pressure sections and 2 scavenge ones. One section directs oil to the oil tank, second to the front case through the push rod tubes. So it cools them this way.

Jarek
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Re: Some more obscure questions...

Post by Jarek » 09 Jul 2018, 22:47

This report may also be useful,even as a reference - with data series for single cylinder of R-1340, as head and barrel are the hottest elements. As barrel goes upto 300degC, pushrod temp. will be way way less and should increase with distance from the crankcase. There are rubber joints between oil lines on lower cylinders, these should not exceed 90-100 degrees for rubber (if this is not other material).

Correction of temperatures of air-cooled engine cylinders for variation in engine and cooling conditions:
http://www.dtic.mil/dtic/tr/fulltext/u2/a800840.pdf

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Vitus
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Re: Some more obscure questions...

Post by Vitus » 10 Jul 2018, 12:47

Thanks for your reply Jarek.
I previously spent quite some time researching engine oils and its properties. Your data is for modern, synthetic oil, which didn't exist in the 1920s. So, I opted for four types of mineral oils for the Vega: SAE-10W, SAE-20W, SAE-30 and SAE-50. All calculations for viscosity, kinematic viscosity, density, etc. are already implemented, they just don't take much of an effect just yet (see pages 6+7 of the debug panel - shift+9). Interesting that the density of modern oils is so low. I'm dealing with mineral oil with a density of ~0.89kg/l :o

As you may know, I am currently working on the heat-exchange module. Each component of the engine is calculated separately, it has physical properties like mass, heat capacity, geometry, etc.etc. Then I create relationships between the components ad define them by the type of heat-exchange (i.e. conduction, convection, radiation). At present, this module contains around 30 different components and around 100 relationships.

I am now at the point of tuning the parameters, which is why I asked my questions above. I need to have a rough idea of how hot each component gets to compare my calculations.

Thanks for the paper you linked, it's very much relevant to this work!!
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Jarek
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Re: Some more obscure questions...

Post by Jarek » 10 Jul 2018, 19:07

You're welcome, I'm glad to help as it is a huge work.

PS. Please notice that figures are for Aeroshell 100, not W100 (blend with additives) - this is straight mineral oil used for break-in periods. It matches specification given by P&W for the flow test.
I'm dealing with mineral oil with a density of ~0.89kg/l
So it's the same :) 0.89 is the typical density for straight mineral oils from current production.

Recommended oil specs from P&W handbook, year 1936 (sq inch/h converted to cSt)

Temperate oil:
Kinematic viscosity@ 40°C cSt = 225 (maximum permitted)
Kinematic viscosity@ 100°C cSt = 17-19

Torrid oil:
Kinematic viscosity@ 40°C cSt = 325 (maximum permitted)
Kinematic viscosity@ 100°C cSt = 20-22
opcond.png
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Tailspin45
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Re: Some more obscure questions...

Post by Tailspin45 » 10 Jul 2018, 22:03

As far as I know there was only a single oil tank, although some had the oil cooler built into.

Attached is page 4 of the 1340 overhaul manual that describes in detail how the lubricating system works.

No pressure or temperature mentioned, however.
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R-1340small_pdf.jpg
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