FarmBoy's Oil Temp Thread

Extend your inlet edges to keep it parallel with the back of the prop.

Oliver said:

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.

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I'm thinking of viscous entrainment. The faster moving air is at a lower pressure than the stagnant air, air seeks low pressure and so flows out with the free-stream.

Here's a picture of a Beaver:



I see a slight outward contour on the very top of the cowl. I imagine it goes all the way around but that it's hard to see because of the camera angle.

This would increase the size of the low-pressure exit area, and possibly further decrease the pressure just aft of the cowl exit area. Since pressure differentials are the engine in this system, that should increase the outflow of the low-pressure side of the cowling, since the air will try to equalize pressure between that exit area and the area behind the engine.

You guys are mixing CHTs and oil temps into one pot. That doesn’t really work, especially for a guy with no oil cooler that’s trying to manage oil temps.

stewartb said:

You guys are mixing CHTs and oil temps into one pot. That doesn’t really work, especially for a guy with no oil cooler that’s trying to manage oil temps.

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That's a good point.

Until Peter comes up with a way to monitor CHTs there's no way to know if they're good or not.

Though I do think it's a valid assumption that since the temp increase is related to the prop-swap, there's a reduction in pressure differentials under his cowling which SHOULD effect both CHTs and oil temps. But there's no way to know that or not until there's a measurement made.

Come on, FB, quit being so lazy and go borrow that manometer - you've had since last night to get data already! :lol: :lol: :lol:

CamTom12 said:

I'm thinking of viscous entrainment. The faster moving air is at a lower pressure than the stagnant air, air seeks low pressure and so flows out with the free-stream.

Here's a picture of a Beaver:

I see a slight outward contour on the very top of the cowl. I imagine it goes all the way around but that it's hard to see because of the camera angle.

This would increase the size of the low-pressure exit area, and possibly further decrease the pressure just aft of the cowl exit area. Since pressure differentials are the engine in this system, that should increase the outflow of the low-pressure side of the cowling, since the air will try to equalize pressure between that exit area and the area behind the engine.

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Hold your hand out the window of your car at 60 mph, then back in the cabin.
I think more pressure outside air even though is at the same temp and atmospheric press.
This is not new territory, air racers have been trying to address this issue for years - eliminate hot cooling air without adding drag to the airframe.
radically different application but similar concept.

re radial: I was thinking more about fast planes��

Peter, I have an O-200 with an oil filter, no cooler. My cowling is very similar to yours and I have never had an oil temperature issue. In the last 3 weeks that I have been flying, the warmest OAT I saw was last weekend at about 50* F. My oil temp ran about 170* and that’s with the oil tank blanket. I’ve been running 2500 RPM. No blast tube on the probe. I’ll try to get over next weekend if you guys are flying and we can compare cowlings and baffling. It might be interesting to put your spinner setup on mine and see what happens....

Glenn does as well, and no issue. Scott R has a C85 and had similar issues, took the prop back off.
So far only data points seem to be with 85/90 cases, for whatever that’s worth. But not necessarily all of them.
Very little data collected on this, as it is very specific - 85/90, pressure cowl, non-18, composite prop.

I lump it into the low horsepower - high drag - closed cowl - low airflow category.

Pb


Sent from my iPhone using SuperCub.Org

Sounds like you have a handle and a direction.. If they ever get a certified version of that prop I’d love to try it....

CamTom12 said:

That's a good point.
Come on, FB, quit being so lazy and go borrow that manometer - you've had since last night to get data already! :lol: :lol: :lol:

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Well, Dawson is struggling to send it back to Jim, so he can lend it to me, and Tom is over an hour away, by plane, and well it’s snowing and I’ve got the kids.

See? I’ve got all the excuses. Lol. Maybe I do need you to send it. [emoji23]

Pb



Transmitted from my FlightPhone

I have an O200 powered cub. When I replaced my McCauley prop with a 3 bladed carbon fiber prop I experienced exactly what Farmboy has run into. I believe blade profile is an issue. Oil temp went up 20degrees. OAT of 80 yields 210 to 215 oil temp..
I am working on baffling and adding the Piper blast tube. My Amazon.com manometer shows less than 1 inch pressure differential top to bottom inside the cowl.

The spinner with the CF prop is different then the McCauley spinner. I need to compare outside diameters of the spinners.

mam90 said:

Sounds like you have a handle and a direction.. If they ever get a certified version of that prop I’d love to try it....

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Once I get the correctly pinned version that works you’re welcome to try mine. Compared to my metal it’s fabulous.
Biggest difference I noticed was ground roll acceleration, but climbout improved substantially (my goal) and cruise held steady. It’s a winner once I resolve oil temp.


Transmitted from my FlightPhone

Just for fun I'd tuft around the lower cowl to airbox opening to see if any air is entering the lower cowling around that seam. Might affect differential pressure if significant. Could be sealed with baffle material. But yea a prop not designed to help flow at the inlet could be a restriction. For example try blowing air through a rotating room fan someday. On motorcycles wheel design can affect handling in crosswinds.

Gary

Someone asked for blade root images. Here are a few when I was playing with a backing prop to help push air in.













Transmitted from my FlightPhone

BC12D-4-85 said:

Just for fun I'd tuft around the lower cowl to airbox opening to see if any air is entering the lower cowling around that seam. Might affect differential pressure if significant. Could be sealed with baffle material.

Gary

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One of the early mods was to add an aluminum flange to better block the top of the airbox opening behind the nose bowl. There was quite a large opening there. I didn’t see any difference but I believe it was just a step in the right direction. Might see a difference with a proper manometer setup.
Probably going to be the culmination of details.


Transmitted from my FlightPhone

One item that hasn't been discussed here is a rolled bottom firewall lip. I have no experience with this, but have read that it can really improve airflow out the cowl, by converting turbulent flow closer to laminar flow, therefore also improve cooling all around. It's pretty clear in your video that the flow out the bottom lip is turbulent.
It would be interesting to see if this helps you with oil cooling.

To the cheek/side cowl point: When I was instructing in a CC-18 Top Cub, which has very large side cowl exits, at -10 to 0 OAT, the oil temperature with the oil cooler (mounted on the aft baffle) completely covered, ran around 94 to 96 degrees F. Yes, lower than human body temperature. We experimented with a couple things, one of which may have involved blocking off those side cowl openings with a plate extended out from the firewall. That got us up to about 150 or so, which I felt was at least acceptable.

I did something similar on my O-320 powered SC in Fairbanks, to get it to run warmer in cold, and that did wonders. Legal?? I always made sure these baffles were removed when the plane came in for maintenance....

But, the point is, increasing the size of those side cowl openings significantly increases cooling.

One thing that nobody has mentioned yet is the effect of openings in the front of the cowl/nosebowl, which put pressure on the lower cowl area, effectively helping to decrease the pressure differential between top and lower cowl. The 11 has an opening to provide cooling to the oil tank, and that opening surely decreases the pressure differential between top and bottom. Super Cubs have air flowing through stock oil cooler up front doing same thing.

MTV

Mike, I was in Bozeman a couple of years ago and there was a small hangar next to the FBO and a guy rolled a Super Cub out. Went over to talk with him, and I think he said they were doing game surveys. The cub had hinged doors that were controllable from the cockpit that could cover the cowl cheek openings. He said they were field approved many years ago. Know anything about this?

Put an augmenter tube around the exhaust outlet? Seems to work for some aircraft.

Gary

BC12D-4-85 said:

Put an augmenter tube around the exhaust outlet? Seems to work for some aircraft.

Gary

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That involves some complex calculations. Diameter vs length and the distance that the end of the exhaust is from the entrance to the tube. I doubt that he wants this on a PA-11 clone.

Oliver said:

Hold your hand out the window of your car at 60 mph, then back in the cabin.
I think more pressure outside air even though is at the same temp and atmospheric press.

Click to expand...

You are absolutely correct! What you're feeling is called Total Pressure. It's both atmospheric (static) pressure and the pressure created by the flow of the air at speed, which is called Dynamic Pressure.

When you create a void in the airstream, it creates a low pressure region. That's why we put "seaplane lips" on lower cowling openings and why the super cub has "cowl cheeks," to create a low pressure region that's NEAR the airstream to help "suck" the air out of the lower cowling.

Oliver said:

This is not new territory, air racers have been trying to address this issue for years - eliminate hot cooling air without adding drag to the airframe.
radically different application but similar concept.
re radial: I was thinking more about fast planes

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Ha! I'm with you, but that's not really an apples to apples comparison to a C-90 cub :lol: :lol: :lol:

Farmboy said:

Someone asked for blade root images. Here are a few when I was playing with a backing prop to help push air in.
Transmitted from my FlightPhone

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Huh... well, if I was being super picky I might say there seems to be less twist at the root than a "true" fixed pitch prop. Maybe that's the difference? Less local AoA on the prop near the cowl openings, where the prop linear speed is low... I don't know.

Grasping at air-inlet straws here, but how's your spinner line up on the cowl openings?

I think a manometer reading is where I'd go next.

mam90 said:

Mike, I was in Bozeman a couple of years ago and there was a small hangar next to the FBO and a guy rolled a Super Cub out. Went over to talk with him, and I think he said they were doing game surveys. The cub had hinged doors that were controllable from the cockpit that could cover the cowl cheek openings. He said they were field approved many years ago. Know anything about this?

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Roger Stradley or one of his pilots. I’ve seen an airplane in Fairbanks with something similar a long time ago. I think that one was field approved at Phillips Field Aviation a long time ago, in a galaxy far, far away.

MTV

Thread drift for controllable Cub cowl side closures: Bachner's Aircraft at extinct Phillips Field in Fairbanks sold a kit...son Andy had one on his Cub as I recall and there was another on a red A-model that belonged to John Lincoln. Adjustable side closures and moveable lower cowl flap. Polar Bear hunter equipment. We made fixed side closures and I still have the patterns in an old Blazo fuel box somewhere. Bolted to firewall with riv-nuts and screws in my case.

But that's not the cooling enhancement Farmboy's after. If you think about it a prop rotating at cruise rpm partially blocks or at least disrupts cooling air unless the base next to the hub is an airfoil - fan design.

Is there an oil cooler on the engine now? Get a factory unit or install a remote with an adapter plate off the C-90's blocking cover like Steve's Aircraft sells https://www.stevesaircraft.com/oilcooler.php or maybe something like this oil screen replacement adapter and a remote cooler: http://www.aircraftspruce.com/catalog/eppages/cont-remoteoil.php?

Gary

CamTom12 said:

You are absolutely correct! What you're feeling is called Total Pressure. It's both atmospheric (static) pressure and the pressure created by the flow of the air at speed, which is called Dynamic Pressure.

When you create a void in the airstream, it creates a low pressure region. That's why we put "seaplane lips" on lower cowling openings and why the super cub has "cowl cheeks," to create a low pressure region that's NEAR the airstream to help "suck" the air out of the lower cowling.



Ha! I'm with you, but that's not really an apples to apples comparison to a C-90 cub :lol: :lol: :lol:

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Yikes, sorry, thought I was responding to “plenum”
post all this time, sorry..

thanks CamTom for reply

mvivion said:

One thing that nobody has mentioned yet is the effect of openings in the front of the cowl/nosebowl, which put pressure on the lower cowl area, effectively helping to decrease the pressure differential between top and lower cowl. The 11 has an opening to provide cooling to the oil tank, and that opening surely decreases the pressure differential between top and bottom. Super Cubs have air flowing through stock oil cooler up front doing same thing.

MTV

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That’s a good point. A successful fix that I’ve heard of on some SCs with high temps and a front mounted oil cooler is to seal the carb air box and oil cooler to the lower cowl better. Sometimes folks with different starters cover the hole in the lower cowl in front of those as well.

Makes me wonder about how all those engines out there with poor baffling and holes all in the lower cowl are running in normal temps? Making less power? Cooler OATs?

My particular airplane had zero temp problems in a cooler OAT region. When I moved it to the Deep South I started having oil temp issues and started digging into the air cooling system. My CHTs have always been in normal range but oil temps ran high in high OATs. I’ve got it figured now but it took a ton of data, experimentation, and head scratching to get there.

FB will get it figured too, hopefully we can help him along the way!

CamTom12 said:

... seal the carb air box .. to the lower cowl better.

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Piper has a closer for this which is on the plans. Just for experimentation I left it off on my Lycoming build in order to see what effect it had. Guess what, I had no temperature issues so never bothered to make and install the part.

A lot of kidney tank Continentals have cold outside air ducted from the lower nose bowl directly to the kidney tank.

skywagon8a said:

Piper has a closer for this which is on the plans. Just for experimentation I left it off on my Lycoming build in order to see what effect it had. Guess what, I had no temperature issues so never bothered to make and install the part.

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Yeah, it’s weird how some installs are fine and others struggle with temps.

It sure would be nice if there was a smoking gun that was consistent across all engines. But from what I’ve seen it’s properly maintaining pressure differentials and directing airflow that helps the hotter installs.

So after I got back from an 3/4 day breakfast, I thought it would be a good time to start playing with variables affecting the oil temp, as OAT is climbing and I was running a pretty solid 185 all way back.

After having none I now have two borrowed manometers to test the pressure differential in the cowl, and since CamTom12's is quite compact I had run the hoses and stuck it in the cockpit the other day. Pretty much ran a differential of 2.50-2.60" of water at 2350 in level flight as an average. Checked that a few times this morning.

Once back I clamped on my "nostril" idea to try and capture more air and better pressurize the upper cowl. It was a test case and therefore looks didn't matter, but I expected to get some increased pressure.


Sadly and a bit of a surprise to me, it had zero effect on pressure differential, and no affect on oil temp.

So...my conclusion is the air must not be leaving, and therefore you can't push more air into an area that is already full. So, let's go back to the "increase the vacuum" path.

I have roughly a 2" chin spoiler that I had early last year, but never truly tested to see if it was making it better or worse. So I took some duckbills and bent down 3/4" of trailing edge closer to a 90 degree angle to the flight path, and test flew it.

Oil temperature dropped roughly 5 degrees, and pressures stayed constant.

**As much as I had hoped the manometer would be a great source of reliable data, in all these tests it has really failed me. The pressure differential really didn't change with any of my modifications, but does change with rpm/speed - A change of rpm up into the 2400 range will bump the differential into the 2.75-2.85" of water range, and correspondingly going slower. (Unfortunately the oil temp doesn't drop with increased pressure at higher speed, for obvious reasons)

So the next test, to confirm the validity of the previous one and remove any doubt of the additional chin spoiler helping, was to simply remove it all together. Once again, pressure stayed constant, but oil temp climbed a full 12-15 degrees over the previous test. OAT was constant, or perhaps a degree or two cooler.

So in summation of today's tests -
~ Can't increase ram air.
~ Manometer does not see to be a good test data method, as it's just not fluctuating with any changes other than airspeed. Removing the composite prop and reinstalling the metal prop may be a telltale test on this, but some doubt has risen about maybe it not being a pressure issue.
~ Oil temp will fluctuate easily with changes, so perhaps should use that as the data point.
~ Cubcrafters wasn't aware that I had rear openings, but they (And Tom Ford) suggested rebuilding the doors to increase the rear opening size. I'd have to measure, but I anticipate the opening is 1.5"-2" at the wide point. Tom seemed to think that the Super Cub runs a 3" and greater opening on the cowl doors. I'd rather not rebuild the doors yet, but it's an option.

Knowing that the chin spoiler is making a difference encourages me to test that further. I had previously drawn up an idea of a "carbon-cub-style" center lower cowl addition, that would come off the back of the airbox that already hangs out and then fan out a bit to the back edge of the cowl. I may bend up a few pieces to test this, similar with the carbon cub, where the large center tunnel should provide a good draft behind it, right below the oil sump.

The other thing I had forgotten about, but might as well test is to throw a piece of tape on the cowl doors and stick on some leftover VG's, to see if it helps or hinders the sucking of hot air out of the cowl. There's been opinions on both sides of that idea as well.

pb

Seein' as how it's not mine I'd try two things. May have been discussed already. Round the outboard edge of the firewall with something stuck on or whatever (like a half-moon piece of foam facing the engine). The sharp outboard edge where the doors and lower cowl overlap creates resistance to flow...think venturi shape. And or add a small lip to the rear door edges before making them bigger. Look at the NACA cowl for a radial. Some have an outward flare at the rear. Maybe some thin 1/16" lexan broke in a 45* bend stuck on with something temporary.

An initial design of the NACA cowl, spinner, firewall shape, and rear flare if present: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930091667.pdf

Gary

You definitely get a E for effort.