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Thread: FarmBoy's Oil Temp Thread

  1. #1
    Farmboy's Avatar
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    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.
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    cubdriver2's Avatar
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    WTH, no deadstick testing to check unmolested flow?

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"

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    CamTom12's Avatar
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    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, Iíd focus on opening the cowl cheeks.

    As it sits, I think yours looks pretty good. I didnít watch the whole thing but I didnít 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-Handhel...d=332515462420

    Thatís the manometer I use. Cheap and works good.
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    Plenum

    Quote Originally Posted by CamTom12 View Post
    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, Iíd focus on opening the cowl cheeks.

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

    .
    I have a no-electric C90, with oil screen and no CHT kit.
    Itís 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 itís a lack-of-pressure airflow issue.

    I donít 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 ďplenumĒ seal.

    Pb


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    Farmboy's Avatar
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    Quote Originally Posted by cubdriver2 View Post
    WTH, no deadstick testing to check unmolested flow?

    Glenn
    Unmolested airflow? Youíve seen my cub, right? 🧐


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    https://www.ebay.com/itm/LCD-Digital...NWQ-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.
    Last edited by tempdoug; 02-04-2018 at 08:26 AM.

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    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).
    N1PA
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    Quote Originally Posted by Farmboy View Post
    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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    are you sure the composite prop is not pulling harder, working the engine harder?

  9. #9
    Farmboy's Avatar
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    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.


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    Quote Originally Posted by Oliver View Post
    are you sure the composite prop is not pulling harder, working the engine harder?
    We are really going astray from the plenum topic here. Thereís 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 itís a airfoil design difference at the hub/blade root area)
    Pb


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    CamTom12's Avatar
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    Quote Originally Posted by Farmboy View Post
    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.


    Sent from my iPhone using SuperCub.Org
    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?
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    mvivion's Avatar
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    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

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    Farmboy's Avatar
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    SJ/Steve/admin, can we move posts from #21 on over to either a new thread or to the ďCatto prop on C90 ContinentalĒ 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.
    Iíll see what I can do to test them back to back.
    Peter


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    mvivion's Avatar
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    Quote Originally Posted by CamTom12 View Post

    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?
    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

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    Plenum

    Quote Originally Posted by mvivion View Post

    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
    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. Itís 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"
    image.jpg
    Attached Images Attached Images
    Last edited by Oliver; 02-04-2018 at 10:21 AM.

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    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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  18. #18
    Farmboy's Avatar
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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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    Farmboy's Avatar
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    Quote Originally Posted by Oliver View Post
    I've been struggling

    Doug


    Cowl intake: addressing the weak area in the stock cub "plenum"
    image.jpg
    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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  20. #20

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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.

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    Quote Originally Posted by Farmboy View Post
    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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    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.

    image.jpeg

  22. #22
    Farmboy's Avatar
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    There are a few with experience adding louver vents. I believe Poor Joe did, which helped his CHtís.

    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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    Farmboy's Avatar
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    Quote Originally Posted by Oliver View Post
    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.

    image.jpeg
    I think someone discussed this earlier in a different thread, but VGís 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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    CamTom12's Avatar
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    Quote Originally Posted by Farmboy View Post
    (I believe itís a airfoil design difference at the hub/blade root area)
    Quote Originally Posted by mvivion View Post
    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.
    Quote Originally Posted by Farmboy View Post
    If you look at the hub size and airfoil at the blade root, it seems pretty obvious to me as to the cause. Itís the solution that is harder to find.
    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.

    Quote Originally Posted by mvivion View Post
    Actually, what youíd 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 ďflatterĒ. Iím 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...youíd have to build new cowl doors. But....

    MTV
    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.



    Quote Originally Posted by mvivion View Post
    Itís also important to point oint out that the C-90 equipped 11 also has no oil cooler. The ďkidney tankĒ oil sump serves as the ďoil coolerĒ.
    I stole this picture from mam90's post on the catto prop on a C-90 thread

    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:


  25. #25
    Farmboy's Avatar
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    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... CHTís 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.
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    Quote Originally Posted by Farmboy View Post
    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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    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.

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    CamTom12's Avatar
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    Quote Originally Posted by Farmboy View Post
    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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    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-...item25ccb22e76

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    Quote Originally Posted by Farmboy View Post
    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
    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
    2E05A9F3-89C5-4257-A813-B66FDEE5233C.jpg
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    Quote Originally Posted by CamTom12 View Post
    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.
    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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    Extend your inlet edges to keep it parallel with the back of the prop.
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    CamTom12's Avatar
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    Quote Originally Posted by Oliver View Post
    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.
    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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    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.

  34. #34
    CamTom12's Avatar
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    Quote Originally Posted by stewartb View Post
    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.
    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!
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    Quote Originally Posted by CamTom12 View Post
    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.
    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��

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    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 thatís with the oil tank blanket. Iíve been running 2500 RPM. No blast tube on the probe. Iíll 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....
    Mark

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    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 thatís 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
    Likes dryfarmer liked this post

  38. #38

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    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....
    Mark

  39. #39
    Farmboy's Avatar
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    Quote Originally Posted by CamTom12 View Post
    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!
    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 itís snowing and Iíve got the kids.

    See? Iíve got all the excuses. Lol. Maybe I do need you to send it.

    Pb



    Transmitted from my FlightPhone

  40. #40
    Mark Lund's Avatar
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    Feb 2002
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    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.
    Thanks Farmboy thanked for this post

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