How long from start up to take off? (Normally aspirated)

[Hank]

Interesting article! Real data, although skewed by mechanical details particular to the IO-550 engines and Lancair installations. Much if this will apply to our smaller Mooney engines, but in variable manner (the oil return line isn't exposed in my O-360 when the sump falls to 5 quarts, etc.), and I'll never see the altitudes referenced in the "oil loss caused by altitude" section. 

Admittedly, I only scanned the article, will read it in detail later, it's bedtime.

[PMcClure]

5 minutes ago, Hank said:

Interesting article! Real data, although skewed by mechanical details particular to the IO-550 engines and Lancair installations. Much if this will apply to our smaller Mooney engines, but in variable manner (the oil return line isn't exposed in my O-360 when the sump falls to 5 quarts, etc.), and I'll never see the altitudes referenced in the "oil loss caused by altitude" section. 

Admittedly, I only scanned the article, will read it in detail later, it's bedtime.

Engine oil viscosity and Prandtl data should help you doze gently into the night. Lots of good nuggets in this article. The oil viscosity should apply almost universally - although different oils have different curves. The idea is the same - too low temps and the oil doesn't flow. 

[ArtVandelay]

My JPI stops warning me once oil temp hits 90, FWIW

[N601RX]

 

The 1970 model C POH in the download section here on Mooneyspace says the oil temp should be between 100 and 225 for continuous operation.  The lycoming operators manual for the same engine says it should not be below 140 for continuous operation.   I would assume going flying would count as continuous operation.

[carusoam]

PMc,

you have described viscosity as resistance to flow, and dropped the prandl number in conversation!

What kind of engineer/scientist are you?  

Unfortuntely, I was unable to get the first link you posted re oil viscosity.  The Fred Moreno article is a great read.  It is a six page, quick read, of what can happen with real life engine operations.  He described the details of measuring exhaust pressures in an air/oil separator!

Fortunately/Unfortunately, it is mostly IO550 specific.  But, it does give ideas how temperature, oil level, altitude of flight, improved dog house cooling side effects, and other things can accidently cause oil to vent overboard.  Oil Viscosity and air density can have some interesting effects.  Experimental engine installations really leave a lot of unknowns to the consumer...

 

Best regards,

-a-

[Mooneymite]

11 hours ago, PMcClure said:

75 to 100 degrees comes from the science of oil viscosity. There is a noticeable break in viscosity (resistance of flow around these temps. I am not a oil specialist but these temps are what have been commonly used as a rule of thumb with equipment. 

Doesn't viscosity change with oil type?  75-100 applies to W100?  Synthetics?  Or does it make any difference?  I was under the impression that viscosity was a major factor in running a lighter weight oil in the cold months.   If viscosity is oil dependent, then no one temperature is valid for all operators.  Perhaps a chart for oil types/weights?  Perhaps the oil manufacturers have such charts?

Then all we have to do is figure out what viscosity we need to apply takeoff power!

Perhaps this required viscosity was what Mooney was getting out when it said steady oil pressure.....?

[PMcClure]

58 minutes ago, carusoam said:

PMc,

you have described viscosity as resistance to flow, and dropped the prandl number in conversation!

What kind of engineer/scientist are you?  

Unfortuntely, I was unable to get the first link you posted re oil viscosity.  The Fred Moreno article is a great read.  It is a six page, quick read, of what can happen with real life engine operations.  He described the details of measuring exhaust pressures in an air/oil separator!

Fortunately/Unfortunately, it is mostly IO550 specific.  But, it does give ideas how temperature, oil level, altitude of flight, improved dog house cooling side effects, and other things can accidently cause oil to vent overboard.  Oil Viscosity and air density can have some interesting effects.  Experimental engine installations really leave a lot of unknowns to the consumer...

 

Best regards,

-a-

Sorry, I couldn't get the link to work. It was another chart showing the relationship between temperature and viscosity of different SAE oils. Fred Moreno's chart was better.  And to answer your question - I am an Auburn Engineer!! I took a few classes in internal combustion engines and more fluid and thermo classes that I can remember. I probably know enough to be dangerous!!! If I recall correctly the Prandtl number is a ratio of viscosity and the heat transfer ability of oils. At lower viscosity (thinner) oil can transfer more heat. The purpose of oil is to lubricate and transfer heat. Per the chart - both are better at temps above 100F. 

[PMcClure]

30 minutes ago, Mooneymite said:

Doesn't viscosity change with oil type?  75-100 applies to W100?  Synthetics?  Or does it make any difference?  I was under the impression that viscosity was a major factor in running a lighter weight oil in the cold months.   If viscosity is oil dependent, then no one temperature is valid for all operators.  Perhaps a chart for oil types/weights?  Perhaps the oil manufacturers have such charts?

Then all we have to do is figure out what viscosity we need to apply takeoff power!

Perhaps this required viscosity was what Mooney was getting out when it said steady oil pressure.....?

Each oil type has it's own curve. I couldn't find a specific one for all oil types we use in aviation. But I found several examples of graphs for the SAE oils used for cars. Even though they have the same shape, they are slightly offset from each other. I read somewhere that SAE 50  = w100, not sure about that. But lower viscosity oils have more flow at lower temps. It makes a good case for synthetic and lower viscosity oils in cold weather. 

I don't think there is a magic number, but 100F seems to be a good rule of thumb. And oil pressures and temperatures and viscosity are all related. But I wouldn't recommend ignoring temp and only focusing on pressure. The first thing I look at when I start the engine is pressure. As long as I have it, I turn my attention to other things. Before take off, I like to see oil temp and oil pressure in the green. Never focused on CHT except I get worried when ATC makes me idle for 10 minutes on a hot day. 

 

Here is a link to Shell's page....http://www.shell.com/business-customers/aviation/aeroshell/knowledge-centre/the-aeroshell-book/_jcr_content/par/textimage_1433441235.stream/1445042093501/281ec318e13a1739d0a798f601b7330a514cc1f8d08258b1157216fa806075c6/aeroshell-book-3peo.pdf

A few things I note -

1. viscosities are given at 40C and 100C. 40C is 104F. I wonder if that is where the 107 reference came from?

2. The last page shows the curve for different oils (log scale)

3. 15w50 has 64% the viscosity of 100w at 40C (104F) but the same as 100W at 100C.

4. Fred's chart on my previous link seem to exaggerate the curve compared to Shell's numbers.  

Maybe some engine designer out there can tell us what viscosity number is needed to go. Based on this info, I'll keep running 15w50 and look for over 100F and good pressure before launching. Other conditions, locations and engines may do better with a different answer. 

 

Edited June 28, 2016 by PMcClure
added Shell Data Sheet

[carusoam]

Go War Eagles!

The viscosity curves show a huge change from room temperature up to operating temp.  Even more significant as the starting temps go below 0°C on cold days...

something to add to the thought process when heating up an engine.  The OilT probe is only telling the temp in one spot, not the temp of the bulk of the oil in the sump.

Chem Eng note: high viscosity and low viscosity liquids don't like to mix very well.  It may take extra time to get all the oil in the engine participating in the process....

-a-

[Hank]

War Eagle, Mr. McClure!

We really need to meet for lunch sometime. I even took some thermo electives. 

[PMcClure]

Hank - let's meet in Auburn sometime soon. My son is there and I try to get down there a couple of times per month.  

 

[N601RX]

I have bad memories from my thermo classes at Auburn.  

[PMcClure]

20 minutes ago, N601RX said:

I have bad memories from my thermo classes at Auburn.  

I had Dr. Dyer. Who did you have?

 

[N601RX]

Maples and Burch.  If your passing over Talassee around lunch stop by and Hank and I can pick you up for lunch.

Is your son a ME?  We have several openings as well as coop and intern positions. 

[PMcClure]

15 minutes ago, N601RX said:

Maples and Burch.  If your passing over Talassee around lunch stop by and Hank and I can pick you up for lunch.

Is your son a ME?  We have several openings as well as coop and intern positions. 

PM sent.

[Hank]

4 hours ago, N601RX said:

I have bad memories from my thermo classes at Auburn.  

That's cause you're a EE. Those crazy circuits classes nearly ended me.

 

[jetdriven]

Aeroshell W100 is 50W oil, there is no 100 weight oil in aircraft engines.