FarmBoy's Oil Temp Thread

As I've been working on theoretical solutions to a high oil temp issue myself, I've considered a number of thoughts in this thread. Pressure differential is definitely the root baseline, which of course probably creates velocity with a higher pressure delta, and therefore more cooling. But it's based on pressure as the man said.

Not that this will help anyone in this thread regarding plenums, but without a differential test set, one of my first goals was to ensure that my current exit opening and chin spoiler is helping the air leave the lower cowl, and not encouraging it to enter, as if were not a low pressure area.

I taped on some tuffs and clamped my old go pro on the gear to see if I could get an idea of the airflow. You'll see better after about the 6 min mark, as the sunlight doesn't help and I didn't have a closer mounting location. I also taped a short row of tuffs behind the carb air box (it's a PA-11-90).

For the most part the tuffs show as expected. Airflow off the chin spoiler streams on by, and airflow at the edges seem good.
Couple interesting things that I don't truly know the value of yet -
- The leftmost tuff on the row behind the airbox is constantly turbulent and/or some other direction.
- The tuffs in the middle quite often are steaming outwards (sideways), as if the air is somehow being pushed left and right from the center mark. The right side is a little turbulent due to the short exhaust stacks stuck there, which I plan to extend an inch or two.

Anyhow, it was a simple first look today to start down the road of getting good "exhaust" air, which is part of creating the best pressure differential I can. I may add lower cowl louver vents, and I also may look at adding some nose bowl opening enhancements, to help capture more air and drive it into the upper cowl.

Video quality is not great by today's standards - I suggest viewing full screen on a computer to get any value from it.

WTH, no deadstick testing to check unmolested flow?

Glenn

Plenum

Great video!

The lower part of the fuselage is generally a local high pressure area because we have a fixed AoI on the wings. However, the sides of your cowl live in a local low pressure area. If I had a cub-type cowling and had high lower cowl pressure, I’d focus on opening the cowl cheeks.

As it sits, I think yours looks pretty good. I didn’t watch the whole thing but I didn’t see any reversion, or air appearing to enter the lower cowl through the bottom opening.

What engine do you have? Is there an external oil cooler on it? How are your CHTs?

https://www.ebay.com/p/Rupse-Handhe...-Gauge-Barometer/27011372691?iid=332515462420

That’s the manometer I use. Cheap and works good.

Plenum

CamTom12 said:

Great video!

The lower part of the fuselage is generally a local high pressure area because we have a fixed AoI on the wings. However, the sides of your cowl live in a local low pressure area. If I had a cub-type cowling and had high lower cowl pressure, I’d focus on opening the cowl cheeks.

What engine do you have? Is there an external oil cooler on it? How are your CHTs?

.

Click to expand...

I have a no-electric C90, with oil screen and no CHT kit.
It’s been thrashed around in the prop thread but the issue is high oil temps when using a composite prop. With all other parameters equal, removal of a metal prop and installation of a composite prop bumps oil temp 25-30 degrees or more.
185-190-200 becomes 225, and with the right heatsoak and climb I saw 240 one bad day. Swap prop and under 190 again. This makes me believe it’s a lack-of-pressure airflow issue.

I don’t understand how one would open up the cowl cheek openings without rebuilding the cowl doors. And the doors also create part of the top cowl “plenum” seal.

Pb


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cubdriver2 said:

WTH, no deadstick testing to check unmolested flow?

Glenn

Click to expand...

Unmolested airflow? You’ve seen my cub, right?


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https://www.ebay.com/itm/LCD-Digita...ash=item33ad8e5cfb:g:ZZcAAOSwFGNWQ-c9&vxp=mtr Farmboy i wonder if a small rubber hose from the top of the engine to inside could be placed over the end of one of these and get any reading. I cant find a finer reading one. looking. I still think a small pitot sized piece of aluminum tube could very easily be clamped in different places on the engine catching air from top to bottom and hosed to one of these low air speed gauges to see movement would tell alot of things.

Use an old airspeed indicator. Run a line from the pitot connection to the space above the engine and a line from the static connection to the space under the engine.

This site has a chart: http://www.bristolite.com/Interfaces/psi_wind.aspx

For example, a 40-mile-per-hour (mph) wind speed creates a pressure of (0.00256 x (40)^2) = 4.096 pounds per square foot (psf).

Farmboy said:

I have a no-electric C90, with oil screen and no CHT kit.
It’s been thrashed around in the prop thread but the issue is high oil temps when using a composite prop. With all other parameters equal, removal of a metal prop and installation of a composite prop bumps oil temp 25-30 degrees or more.
185-190-200 becomes 225, and with the right heatsoak and climb I saw 240 one bad day. Swap prop and under 190 again. This makes me believe it’s a lack-of-pressure airflow issue.

I don’t understand how one would open up the cowl cheek openings without rebuilding the cowl doors. And the doors also create part of the top cowl “plenum” seal.

Pb


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Click to expand...

are you sure the composite prop is not pulling harder, working the engine harder?

Regarding cowl pressure, a simple $35 manometer like camtom posted a link to is the best info, and just as simple.
Or borrow one from your friends. [emoji57]


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Oliver said:

are you sure the composite prop is not pulling harder, working the engine harder?

Click to expand...

We are really going astray from the plenum topic here. There’s more discussion in the c90 thread and Catto prop threads.
Simple answer is I believe the load range is different, but if you can spin the same or greater rpm at WOT or throttle position, then load should be similar.
(I believe it’s a airfoil design difference at the hub/blade root area)
Pb


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Farmboy said:

Regarding cowl pressure, a simple $35 manometer like camtom posted a link to is the best info, and just as simple.
Or borrow one from your friends. [emoji57]


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Click to expand...

Speaking of which, let's start a new thread for this. PM me your address and I'll mail you mine to borrow for a bit. I've got some major maintenance coming up this spring so I won't me needing it for a couple of months.

I'd REALLY like to see a before/after pressure reading with metal/composite props (if you don't mind all the switching around). I'll look for your new thread and ask a few more questions there. I have a guess and it'd be neat to see if I'm right or not.

And you're right, cowl cheeks would be pretty tough to open easily... Maybe a simple lip around the outside edge, almost like a gurney flap?

It’s also important to point oint out that the C-90 equipped 11 also has no oil cooler. The “kidney tank” oil sump serves as the “oil cooler”.

Second point: Farmboy, does your airplane have the blast air tube from the top deck to the oil temperature sensor, as came stock, or has that been removed? On these installations, there was a blast tube from the aft baffle top that connected to a scat hose, which then connected to a box surrounding the oil temperature probe. Apparently, this was done to reduce oil temperature readings, caused by an unfavorable location of the oil temp probe. Removal of that assembly and blockage of the hole in the aft baffle will result in somewhat higher indicated chts.

That, of course has nothing to do with the change between props, which is interesting. That difference could be as simple as a difference in blade contour close to the hub, modifying airflow through the cowl. Maybe.

MTV

SJ/Steve/admin, can we move posts from #21 on over to either a new thread or to the “Catto prop on C90 Continental” thread?

Thanks, Pb

CamTom, thank you, but I believe two of my friends in the region have one as well. I just need to go borrow it.
I’ll see what I can do to test them back to back.
Peter


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CamTom12 said:

And you're right, cowl cheeks would be pretty tough to open easily... Maybe a simple lip around the outside edge, almost like a gurney flap?

Click to expand...

Actually, what you’d need to do is make longer cowl doors in the rear, and keep the tops of the cowl doors relatively flat. The curvature of the doors would be “flatter”. I’m not describing it well, but look at a CC-18 Top Cub cowl. Those cheeks really stick out to clear the (slightly wider) O-360.

Not saying it would be easy...you’d have to build new cowl doors. But....

MTV

Plenum

mvivion said:

That, of course has nothing to do with the change between props, which is interesting. That difference could be as simple as a difference in blade contour close to the hub, modifying airflow through the cowl. Maybe.

MTV

Click to expand...

Summer months with the metal prop I ran a blast tube to the rear case, as did the former owner. There are huge debates on the value of this, backed up with data from someone (Jerry Burr maybe) who did extensive testing.
All I can say to that, is with temp increase oil pressure drops. With temp decrease oil pressure rises.

With the composite prop install the blast tube no longer could keep up.

If you look at the hub size and airfoil at the blade root, it seems pretty obvious to me as to the cause. It’s the solution that is harder to find.

Pb



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I've been struggling with high heat issues since last build. here's a summary of what worked:

Confirm airtight baffling
confirm your carbs jetted correctly
confirm you're not over propped
block off flywheel area
increased "seaplane lip" lower cowl
clean up cowl intake with molded scoops to clean up intake airflow
reduce drag on airframe, faired gear legs, bungee covers, get rid of baby Bushwheel

Ive experimented with lots of other stuff but these had the most significant results.

following brek-in, Lycon O320, I could go right past 450 CHT's climb on a warm day.

Following mods listed above resulted in temps rarely exceeding 400 climb out on a hot day, cruise 2450 - 350 hottest (#3)


something I would consider experimenting with: adding a VG's or a lip near trailing edge of cowl doors. I'm convinced there's an air dam created by cool air racing past cowl exits accounting for pressurized lower cowl.
it would be interesting to explore some more

Doug


Cowl intake: addressing the weak area in the stock cub "plenum"

Making new cowl doors isn’t difficult. Here are a few pics including the MCS high tech and super secret spacer used to set the gap.





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In the interest of simplicity, I like the idea of adding lower cowl gills like cub crafters does, and better snouts on the nose.




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Oliver said:

I've been struggling

Doug


Cowl intake: addressing the weak area in the stock cub "plenum"
View attachment 35038

Click to expand...

Doug,

The cowl inlets are something I plan to address. Internal ramps as you show, but also edging the outer surround to capture more air and direct it in. Particularly on the outer edge, where the cowl curves away to the side panel and where the blade starts gaining an aggressive airfoil.

In an ideal world, adding a manometer, CHT and Manifold pressure setup would provide very good info as to the differences between props.

Pb


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Louvers can be useful when there isn’t another path for air to exit, but in a standard Cub cowl there is an open path. It’ll be interesting to see if louvers help, hurt, or do nothing. I added cowl louvers to my Cessna to lower CHTs while cowl flaps are closed. It helped in that mostly closed cowl condition. It’s hard to translate the louver advantage to a typical Cub cowl, but I’ll be watching to see what you learn.

Farmboy said:

In the interest of simplicity, I like the idea of adding lower cowl gills like cub crafters does, and better snouts on the nose.

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Click to expand...

I tried this with some results: I think the resulting turbulent air passing the cowl exit is where gains are made though.
supporting my earlier theory.

There are a few with experience adding louver vents. I believe Poor Joe did, which helped his CHt’s.

The beauty is that you can put them closer to the side, which is a naturally lower pressure area than the bottom cowl, as noted by others earlier.
The unsure part is if there is room to add an appropriate size vent, without sucking heat from my side mounted carb and cabin heater shrouds.

Pb


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Oliver said:

I tried this with some results: I think the resulting turbulent air passing the cowl exit is where gains are made though.
supporting my earlier theory.

View attachment 35040

Click to expand...

I think someone discussed this earlier in a different thread, but VG’s on the side of the cowl cheeks would increase or decrease low pressure at the opening? I believe the answer was it would make it worse, not better.

Pb


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Farmboy said:

(I believe it’s a airfoil design difference at the hub/blade root area)

Click to expand...

mvivion said:

That, of course has nothing to do with the change between props, which is interesting. That difference could be as simple as a difference in blade contour close to the hub, modifying airflow through the cowl. Maybe.

Click to expand...

Farmboy said:

If you look at the hub size and airfoil at the blade root, it seems pretty obvious to me as to the cause. It’s the solution that is harder to find.

Click to expand...

This was kind of along the lines of what I was guessing. I'd be curious to see pictures of the roots of both props, but purely out of curiosity so if you're busy or forget to do it, no worries.

mvivion said:

Actually, what you’d need to do is make longer cowl doors in the rear, and keep the tops of the cowl doors relatively flat. The curvature of the doors would be “flatter”. I’m not describing it well, but look at a CC-18 Top Cub cowl. Those cheeks really stick out to clear the (slightly wider) O-360.

Not saying it would be easy...you’d have to build new cowl doors. But....

MTV

Click to expand...

Yeah, I'm tracking what you're saying. That's what I was originally imagining, but FB reminded me that the cowl doors have to seal against the felt on the sides of the baffles, those would also have to be modified to seal against the now wider doors, right?

I think if you increased the frontal area of the trailing edge of the cowl cheeks, it might create a larger low pressure region behind them which should cause the air pressure lower cowl to fill, trying to equalize. I don't think it'd be as effective as a larger cowl cowl cheek opening, but I think it'd be more effective than the small openings on their own. It'd definitely be easier to test with some stick on wedges or something to that effect.

But Peter, I wouldn't stress this part until you've confirmed/denied a pressure differential problem.

mvivion said:

It’s also important to point oint out that the C-90 equipped 11 also has no oil cooler. The “kidney tank” oil sump serves as the “oil cooler”.

Click to expand...

I stole this picture from mam90's post on the catto prop on a C-90 thread

View attachment 32887

Interesting... Has anyone tried building a baffle system around the kidney tank and pumping it with a blast tube? Similar to a firewall mounted oil cooler? Or shoot, even building a strap-on set of metal fins to increase surface area? With or without a blast tube, that helps radiate heat like this mod for oil filters:

I considered all sorts of sump cooling thoughts, and even added a second blast tube onto the tank itself.
But the end game is to gain more airflow, for if the oil temp is high... CHT’s are probably there too.



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The oil tank may be worthy of a plenum. Feed it with a scoop on the belly and duct the outlet air so it doesn’t interfere with the bottom cowl pressure. Maybe use it to preheat the cabin heat supply.

Farmboy said:

I think someone discussed this earlier in a different thread, but VG’s on the side of the cowl cheeks would increase or decrease low pressure at the opening? I believe the answer was it would make it worse, not better.

Pb


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Click to expand...

I'd be interested to see a back-to-back on this as well if anyone has the time/motivation.

Just thinking through it: VGs cause a vortex, which reaches up into the free-stream air and brings some of that energy down into the boundary layer and re-energizes it. That extra energy helps the boundary layer stick to the low-pressure surface of an airfoil longer, delaying stall.

The boundary layer is slower than free-stream air, I'd be willing to bet that adding VGs to the cowl sides would help increase the size and "strength" of the low pressure region behind the cowl cheek opening. But I could be way off on that. My old instructor says "everything affects everything," so sometimes the answer isn't as intuitive as you'd think.

Farmboy said:

I considered all sorts of sump cooling thoughts, and even added a second blast tube onto the tank itself.
But the end game is to gain more airflow, for if the oil temp is high... CHT’s are probably there too.



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Click to expand...

Here's an idea for a temporary install to gather data if you're interested in CHTs:

http://www.thermomart.com/14mm-under-spark-plug

https://www.ebay.ie/itm/4-Channel-K...Temperature-/162348019318?hash=item25ccb22e76

Farmboy said:

Doug,

The cowl inlets are something I plan to address. Internal ramps as you show, but also edging the outer surround to capture more air and direct it in. Particularly on the outer edge, where the cowl curves away to the side panel and where the blade starts gaining an aggressive airfoil.

In an ideal world, adding a manometer, CHT and Manifold pressure setup would provide very good info as to the differences between props.

Pb


Transmitted from my FlightPhone

Click to expand...

Mot so much “ramps” but more like “tubes” to get the air past all the sharp eddy causing features of cowl entrance
kind of a scrappy looking prototype but very promising results so far

CamTom12 said:

I'd be interested to see a back-to-back on this as well if anyone has the time/motivation.

Just thinking through it: VGs cause a vortex, which reaches up into the free-stream air and brings some of that energy down into the boundary layer and re-energizes it. That extra energy helps the boundary layer stick to the low-pressure surface of an airfoil longer, delaying stall.

The boundary layer is slower than free-stream air, I'd be willing to bet that adding VGs to the cowl sides would help increase the size and "strength" of the low pressure region behind the cowl cheek opening. But I could be way off on that. My old instructor says "everything affects everything," so sometimes the answer isn't as intuitive as you'd think.

Click to expand...

K, think of a stream of 90 mph cool (thick) air rushing past an opening of stagnant hot (thin) air.
not a good scenario if you are trying to eliminate the hot air.
radials have a pronounced lip all the way around the cowl.