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Thread: Lower cowl scoop shape

  1. #41

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    Quote Originally Posted by fobjob View Post
    Take a look at my photos section...I have some diagrams on airflow optimization through an oil cooler. In support of those, I was told once that putting a one inch spacer between the baffle and the cooler helped performance. Try running a jet engine without a long inlet duct....

    *that’s NOT to say that scat tubing is an efficient duct.....

    http://www.supercub.org/photopost/se...searchid=10055
    Made some quick sketches based on your ideas in the picture gallery to fit my current oil cooler to try clean up the air flow to oil cooler and cyl#3, tell me if I am on the right track
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    the above sketch would be to fit into this space.

  2. #42
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    Quote Originally Posted by bodumatau View Post
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    Bend that new top baffle up about 30 or so degrees. Extend it to the cowl with an anti chafe seal against the cowl.This will help to smoothly direct the air into the cooler.
    N1PA
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  3. #43
    fobjob's Avatar
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    I agree with skywagon. The problem remains with the bottom of the cooler. It is probably getting too much heated air...Avoid any sudden angles in your deflection baffles. If you could move the cooler rearward, things would be easier. The top baffle as described might also improve CHT on #3.

    *but, since you said that your oil temps were under control in post #32, try the top deflector for the possible improvement in CHT. You might even partially block off the bottom of the cooler to eliminate hotter air flow through the cooler and increase the flow on the back side of #3.....
    Last edited by fobjob; 12-07-2019 at 05:30 PM.

  4. #44

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    Quote Originally Posted by fobjob View Post
    After a LOT of experimentation and measurement, the following things were the most effective at lowering chts.(67 cub, 150hp, @100smph 5500 ft msl. 2450 rpm.)
    1. Ramps in front of cylinders, 20deg F ( to avoid raising front chts, drill 12-1/4 inch holes in each one.)
    2. Boxing in the front of the engine to eliminate air leakage down the front of the engine, 27 deg F
    3. Rear cowling lip, 10 deg F.
    4. Deflection vane over #4, along with reducing the space behind #4, 20 deg F on #4.
    5. Finding a binding rocker arm on #4, another 20 deg F.
    Not effective: extending side cowl cheeks....(45 deg at 1.5 inches protrusion)
    things I am trying: a half round (at least 3 inches diameter) on the bottom of the firewall. Incidentally, the two bottom cowl “vents” are good for 5 deg F each........ all this got me from 390F above ambient to 310F above ambient....fob

    *note that these changes were measured sequentially, not separately.
    Just curious:

    Could you elaborate on your deflection vane for #4? Deflecting air from the side of the cowl, or the top down to #4?

    Also, how did you end up find the binding rocker arm?
    Last edited by motosix; 12-07-2019 at 10:51 PM. Reason: my d@mn spelling

  5. #45
    www.SkupTech.com mike mcs repair's Avatar
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    you guys are only looking at 1/2 of the equation (only pushing air through cooler).....

    if you SUCK air through it, then it's less important if the air is clean entering cooler....

    but yes, a baffle to above the cylinder in his installation would help prevent using that hot air directly off cylinder fins in lower cooler...

  6. #46
    fobjob's Avatar
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    I agree with Mike. Impedance matching on the input and output of heat exchangers is important. Having said that, I’m toying with an exit air matching horn on the outlet of the #4 cooling air. The geometry is complex, but I’m futzing around with it. It’s hard to get too motivated, since I’ve hit all of the low hanging fruit for easy cooling measures. It could always use more, though....
    I was taking the rocker arms off, looking to see if the oil squirt hole was plugged or missing. The split pin bushing was pushed off center, rubbing hard against the metal boss the pivot pin went into. I centered it as a matter of course, and noticed on my next flight a mysterious drop in the CHT. My mechanic had changed two (#4) cylinders and didn’t think to do that, so the problem got moved from old cylinder to new cylinder.....twice..the deflection vane goes from the top of the cowl to the bottom of the rear of #4, mounted on the motor end by that threaded (1/4-20) boss between #2 and #4....tried the same thing on #3, but it didn’t work well, the geometry is different. No pics, it’s dark in there....
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  7. #47
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    Quote Originally Posted by bodumatau View Post
    thanks Fobjob, we have, subsequent to the photos above, put a vertical fence up the front of #1
    Attachment 46043
    roughly the size of the red rectangle, this brought #1 temp in line with #4

    then we cut off the stiffener in front of #2 and replaced it with another underneath
    Attachment 46044
    roughly where the red line is and this brought #2 in line with #1 & #4

    we still have about 20ºF higher temps on #3 throughout the operating range, but I must add that we have our 13 row oil cooler behind #3 stealing air from that back corner.

    we will try the ramp in front of #1 and let you know how it goes.
    Are you having high oil temp, high #3 CHT, or both?

    Here's how I moved my oil cooler, which had previously been mounted behind #4: https://www.supercub.org/forum/showt...l=1#post739392

    I'm willing to bet that adding a baffle between the oil cooler and #3 (similar to what I put here: https://www.supercub.org/forum/showt...l=1#post739404) would help both #3 CHT and oil temps.

    You also need to pay attention to the fin depth on the back side of #3 on a Lycoming. If you add a baffle between the oil cooler and #3, you need to make sure it allows air past the shallow fins. More information here: http://www.vansairforce.com/communit...ad.php?t=37835
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  8. #48

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    Quote Originally Posted by CamTom12 View Post
    Are you having high oil temp, high #3 CHT, or both?

    Here's how I moved my oil cooler, which had previously been mounted behind #4: https://www.supercub.org/forum/showt...l=1#post739392

    I'm willing to bet that adding a baffle between the oil cooler and #3 (similar to what I put here: https://www.supercub.org/forum/showt...l=1#post739404) would help both #3 CHT and oil temps.

    You also need to pay attention to the fin depth on the back side of #3 on a Lycoming. If you add a baffle between the oil cooler and #3, you need to make sure it allows air past the shallow fins. More information here: http://www.vansairforce.com/communit...ad.php?t=37835
    we are happy with our oil temp right now - we did try tape up the bottom third of the oil cooler to feed more air to #3 but that didn't change #3 CHT's and it pushed up the oil temps by 25ºF to 215º.

    we would like to see 20ºF less CHT on #3.

    we have a nice gap at the back of #3 to let air down to the lower quadrant of #3

    I have been toying with your idea of moving the oil cooler down onto the firewall with a scat tube feeding it, just havent built up the courage to do it....

  9. #49
    CamTom12's Avatar
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    Lower cowl scoop shape

    Can you get a more top-down angled pic of #3? Maybe even one from as much of an angled forward image as you can grab and still see the fins on the backside of #3?

    I moved my oil cooler to lower my oil temps (big success there). Since your OTs are fine, I’d try some other things first that might be more “outpatient” level of involvement before you crack open your baffles again to move that oil cooler.

    For your #3, I’d try to build some airflow guides to fit over the cylinder, in front of the oil cooler. I’d do it like the guy does here:


    source: http://www.ez.org/canardpages/pages/...apter_23_7.htm

    Make sure that the airflow guides “stand off” the shallow fins on the back of the #3. I’d use this thread as a resource: http://www.vansairforce.com/communit...ad.php?t=37835

    Fins in open air aren’t necessarily getting airflow through them. If there are fins that don’t tie directly into a path to lower pressure (the lower cowl space), I think you’re not using all the cooling potential on the table. Building an “airflow guide” should be pretty easy to do. And if you’ve got a lot of space back there, they could be temporarily attached for a quick flight test.

    EDIT: I just read through your other thread about the fuel injection system - my comments below have already been covered there by more experienced folks.

    ————————————

    Also, since this is an IO, I’m a little out of my experience level, but I just fixed my induction tubes leaks and that really helped bring my cruise CHTs down (on a carb’d motor). May not be as big of a deal for an IO. I used an O-ring set up from the folks that make the SDS EFI (http://sdsefi.com/sdsaero.htm).

    Are your high CHTs only in cruise? Or also in climb out? Might be a plugged Or dirty injector line or tip or something like that?
    Last edited by CamTom12; 12-08-2019 at 10:41 AM.
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  10. #50

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    Quote Originally Posted by stewartb View Post
    If CHTs are the focus? I'd lose that cooler, close the baffle, and put the cooler back on the nose with an outlet duct so it doesn't pressurize the lower cowl. I've got the opportunity to reduce cooler size or eliminate one of my nose mounted coolers right now but my new engine will make more heat so I'll probably leave things alone this go-round. I've dreamed up a few new cooler scenarios for my plane. Like a firewall mounted cooler fed by cowl ducts from the nose. Composite cowls would be easy to incorporate ducts into.
    this is definitely on the agenda, just trying to find the best way to mount the oil cooler, I am not a fan of hanging it on some aluminium angle iron especially if you need to hang it 5 inches below the engine, just too much leverage on the angle iron.... so considering grafting it into the lower cowl like you have done Stewart.

    after some test flying we saw that the right exhaust branch is clearly leaner than the left, right side is cyl#3 & 4, left side is cyl#1 & 2.
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    with #3 running on average 25ºF hotter than the others we assume it is #3 blowing white here, we have changed out the fuel injection nozzle and still the same. what could be the cause? some are saying it can't be an induction leak cause that only affects carburettor engine?
    - sticky rocker or valve intake side and you would loose power but not run lean - you would run overreach cause you can't get the air into the cylinder?
    - sticky rocker or valve on exhaust would mean high EGT's which we dont have?
    - fuel nozzles are all same
    what else could it be? - maybe my cold induction box just somehow feeds a lot of air to #3? is this possible?

    we have done the fuel flow test into cups, we get very close flows across all 4 cylinders, did the test twice, get the same result.

  11. #51
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    Piper pa 25 pawnee. If it will cool a spray plane working the design should cool a cub


    Sent from my iPhone using SuperCub.Org mobile app
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  12. #52

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    some work done tonight, put a scoop on the oil cooler and #3
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    not enough time to finish the top scoop for the oil cooler, test flying tomorrow morning to see if this is a step in the right direction.
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  13. #53

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    What fuel injection system do you have? Yes an intake leak can cause a problem depending on the system. I would expect temps to be different for each cylinder if all nozzles are the same. Cylinder air filling depends on several factors intake runner length/size/bends, valve overlap, RPM. Gami injectors adjust for each cylinder. I would say you need more fuel to #3
    DENNY

  14. #54

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    Quote Originally Posted by DENNY View Post
    What fuel injection system do you have? Yes an intake leak can cause a problem depending on the system. I would expect temps to be different for each cylinder if all nozzles are the same. Cylinder air filling depends on several factors intake runner length/size/bends, valve overlap, RPM. Gami injectors adjust for each cylinder. I would say you need more fuel to #3
    DENNY
    a Bendix RSa5, we are looking at changing the fuel flow to #3 slightly
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  15. #55
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    Here is how I have fabricated the bottom cooling lip. Posterboard and tape to make the pattern/shape.
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    Steve Pierce

    Everybody is ignorant, only on different subjects.
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  16. #56

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    Quote Originally Posted by Steve Pierce View Post
    Here is how I have fabricated the bottom cooling lip. Posterboard and tape to make the pattern/shape.

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    after finishing that bottom cooling lip you were WELL PRACTICED at riveting
    looks awesome

  17. #57
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    Notice the two metal "side curtains" Bellanca added to the boot cowl channel. I assume that helps smoothly direct exit air flow by reducing the chance of turbulent air entering that area from the sides

    Gary[/QUOTE]





    I have never noticed the " side curtains " before. Thank you for pointing that out. It would be neat to hook up a manometer inside the cowling and see how the pressure is effected with them removed.

    Jonny
    Last edited by Jonnyo; 12-18-2019 at 02:24 PM. Reason: Photo did not transfer
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  18. #58
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    Quote Originally Posted by bodumatau View Post
    thanks Fobjob, we have, subsequent to the photos above, put a vertical fence up the front of #1
    Attachment 46043
    roughly the size of the red rectangle, this brought #1 temp in line with #4

    then we cut off the stiffener in front of #2 and replaced it with another underneath
    Attachment 46044
    roughly where the red line is and this brought #2 in line with #1 & #4

    we still have about 20ºF higher temps on #3 throughout the operating range, but I must add that we have our 13 row oil cooler behind #3 stealing air from that back corner.

    we will try the ramp in front of #1 and let you know how it goes.



    I took a brand new 4 way, digital CHT set and stuck them through the top of a closed, 5 gallon metal can, with a pin hole vent. I put the can on the stove and brought it up to 200 degrees. I turned off the stove and let things stabilize for a few minutes. 2 readings were 9 degrees apart and the others were around 5. I think it's great that so much quality work is going into this, but just because it's digital doesn't mean it's perfect. For me, 20 degrees is zero.

    Jonny
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  19. #59
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    We went thorugh all these same problems with our banner tow Huskies. When you rob air from the cylinders to run it through an aft mounted oil cooler you heat up the cylinders, which then heat the oil. No problem in regular service. Aft coolers are neat and clean, but in extreme cases, you might consider just mounting the cooler under the firewall like so many Restiicted Category banner planes.

    I have couple of Harrison GPU coolers which used to be the standard for south Florida banner ops. Makes anything run cool in high temps. Seal up you rear baffle, fix up a generous cooling lip and you're on your way.

    If you are curious pm me and I'll send you a foto. I paid very little for the coolers, and I'll gladly pass it onto you. It worked great for us for years.

  20. #60
    fobjob's Avatar
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    Replacing my front mounted Harrison with a drop-in replacement Niagra Cub Cooler eliminated all oil temp issues.....

  21. #61

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    So....since my last post I have added ramps in front of both cyl #1 & #2, added a "top ramp" to help direct the air DOWN from the top of my baffle plenum, this seems to have helped at cruise speed, 2400rpm and 85Kts TAS, I am seeing CHT's of 350, Oil of 180 and I can EVEN lean about 150º of EGT.... wow..... but..... at slow flight (below 40kts IAS she still ends up running over 400º CHT and creeping over 200J Oil.

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    here you can see the first "top ramp" and the ramp in front of cyl #1, both seemed to help so I went ahead and completed the "top ramps" and built another front ramp for cyl #2

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    here you can see my second "top ramp", after this I closed the gap with another "top ramp"

    I have really tried to find a spot in the front of the cowl for the oil cooler but this BCSC cowl is SO tight up front and SO tight around the cylinder heads and intake manifold and exhaust branches that I came up with another idea that I would like to bounce off the forum members before trying out.....
    WHAT ABOUT trying a NACA duct on the right hand side of the cowl, just below the cylinder heads out of the way of the intake and exhaust -> this NACA duct is then ducted to the 13 row oil cooler mounted on the firewall behind cyl #3 (more space this side) and the exit air is SCAT tubed down to a separate exit scoop on the lower right side of the cowl... see pic below for rough location

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    please try and ignore the strap, we were fitting the new lower scoop, which I will share if it makes a difference...
    under the strap you can see the rough dimensions (cryptic... I know) for the NACA duct..... any opinions on whether it will work? think there will be enough air to draw in from the side of the cowl?
    Last edited by bodumatau; 01-23-2020 at 02:30 PM.

  22. #62

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    I like the ideal of the NACA duct.
    DENNY

  23. #63
    skywagon8a's Avatar
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    Quote Originally Posted by bodumatau View Post
    So....since my last post I have added ramps in front of both cyl #1 & #2, added a "top ramp" to help direct the air DOWN from the top of my baffle plenum, this seems to have helped at cruise speed, 2400rpm and 85Kts TAS, I am seeing CHT's of 350, Oil of 180 and I can EVEN lean about 150º of EGT.... wow..... but..... at slow flight (below 40kts IAS she still ends up running over 400º CHT and creeping over 200J Oil.

    That portion of the baffle which is in front of the cylinder fins (not the cylinder head) ought to be shortened and aligned with the center (up & down) of the fins for the cooling of the steel barrel. You have no temperature measurements of this section. Overheating here can damage the piston rings. You could also cut the section in front of the aluminum head back to the center to increase the cooling on the head fins.
    N1PA

  24. #64
    mvivion's Avatar
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    The ducting on the side of the lower cowl works on Huskys and the Carbon Cubs, both of which tend to run warm. The Huskys use a cowl vent like this:

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    Here's a picture of one of the newer Carbon Cubs:



    Which might not be efficient enough for your needs. But, either this or an outward opening duct like the earlier CC might help:


    This would be the first thing I'd try-it's pretty well documented to help cylinder head cooling. The latter could be made so it's adjustable. There's a similar kit for the Cessna 185.

    MTV
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  25. #65

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    Quote Originally Posted by skywagon8a View Post
    That portion of the baffle which is in front of the cylinder fins (not the cylinder head) ought to be shortened and aligned with the center (up & down) of the fins for the cooling of the steel barrel. You have no temperature measurements of this section. Overheating here can damage the piston rings. You could also cut the section in front of the aluminum head back to the center to increase the cooling on the head fins.
    copy that NP1A, #1 has never been a problem though only #3, but I hear you, I will trim it back a little.

  26. #66

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    Quote Originally Posted by mvivion View Post
    The ducting on the side of the lower cowl works on Huskys and the Carbon Cubs, both of which tend to run warm. The Huskys use a cowl vent like this:

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    Here's a picture of one of the newer Carbon Cubs:



    Which might not be efficient enough for your needs. But, either this or an outward opening duct like the earlier CC might help:


    This would be the first thing I'd try-it's pretty well documented to help cylinder head cooling. The latter could be made so it's adjustable. There's a similar kit for the Cessna 185.

    MTV
    These are all sucking air OUT of the cowl, do you think there will be enough positive pressure along the side of the cowl to let enough air INTO the NACA duct?

  27. #67

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    pictures are worth a 1000 words, so here goes trying to explain a bit better what I want to do:
    Click image for larger version. 

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    RED would be the NACA duct INLET
    YELLOW the ducting to and from the oil cooler
    BLACK is the oil cooler on an ali frame mounted on the firewall
    BLUE is the separate outlet scoop to suck air through the system.

  28. #68
    skywagon8a's Avatar
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    Quote Originally Posted by bodumatau View Post
    I am seeing CHT's of 350, Oil of 180 and I can EVEN lean about 150º of EGT.... wow..... but..... at slow flight (below 40kts IAS she still ends up running over 400º CHT and creeping over 200J Oil.
    These oil temperatures are perfect. I would leave the oil cooler as it is.

    Is this 400º CHT on more than one cylinder or for a considerable period of time? If so perhaps just increase the fuel flow a bit during that time with the mixture control.
    N1PA

  29. #69

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    at FULL RICH during slow flight my CHT's creep up toward 425 and my oil also creeps up to 210, so I definitely want to get my oil cooler to have its own air supply, I think that would give me some more leeway on the CHT's if I give the cylinders the air back that the oil cooler is taking.

    my mission profile rarely is cruise at 2400rpm, maybe for 30 min max to get somewhere interesting, the majority of my time I want to spend on my first notch of flap at between 25&40Kts and 2000rpm, so I need that slow flight cooling to work properly.
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  30. #70

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    Ducting those NACA inlets to the cooler? That might work but I'm not sure that's a high pressure area of the cowl so inlet pressure may not be what you need it to be. Louvers increase air exchange through the cylinders by increasing outlet flow because that area is in negative pressure. I'd think you'll need to move those ducts forward to an area of impact air. In the Carbon Cub examples they're using plenums. I know of a couple of SQs that have recently done plenums to improve cooling. Hot rodded parallel valve engines are hard to cool in Cubs. You aren't the only one searching for solutions. Most of those guys are moving coolers to the nose, by the way. Robbing air from the top to blow on an aft mounted cooler worked on O-320s. It isn't working as well with higher output engines.
    Last edited by stewartb; 01-24-2020 at 09:08 AM.

  31. #71
    mvivion's Avatar
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    Quote Originally Posted by bodumatau View Post
    These are all sucking air OUT of the cowl, do you think there will be enough positive pressure along the side of the cowl to let enough air INTO the NACA duct?
    it seemed to me the biggest issue is high CHTs. These cowl mods increase air flow through the cowling, and should help reduce CHTs. And, they’re relatively easy to install, and proven on a number of platforms.

    As Pete said, I wouldn’t be that concerned about the oil temps.

    MTV

  32. #72
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    Of the examples shown, I like the location of this one the best. It is in a location where the airflow will be the most effective.



    When I had a turbo in my 185, it ran hot. Cowl vents similar to these dropped the temperatures considerably. Also bringing down the CHTs will in turn bring down the oil temps. Fix the CHTs and the oil temps will fall in line.
    N1PA
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  33. #73

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    Quote Originally Posted by stewartb View Post
    Ducting those NACA inlets to the cooler? That might work but I'm not sure that's a high pressure area of the cowl so inlet pressure may not be what you need it to be. Louvers increase air exchange through the cylinders by increasing outlet flow because that area is in negative pressure. I'd think you'll need to move those ducts forward to an area of impact air. In the Carbon Cub examples they're using plenums. I know of a couple of SQs that have recently done plenums to improve cooling. Hot rodded parallel valve engines are hard to cool in Cubs. You aren't the only one searching for solutions. Most of those guys are moving coolers to the nose, by the way. Robbing air from the top to blow on an aft mounted cooler worked on O-320s. It isn't working as well with higher output engines.
    yes exactly Stewart, this is what I am worrying about

  34. #74
    Jonnyo's Avatar
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    NACA Scoop LOCATION

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    Quote Originally Posted by bodumatau View Post
    These are all sucking air OUT of the cowl, do you think there will be enough positive pressure along the side of the cowl to let enough air INTO the NACA duct?





    Your drawing locates the NACA duct at the point, on the side of the cowl, where that maximum suction is trying to lift the paint off the cowling. Trying to overpower that suction and make air enter the cowling is not going to work. If the NACA duct was installed 10 inches forward; where the side walls of the duct would be able to generate two strong vortexes would be more viable. The 2 vortexes are what makes the suction, in the other direction, to draw the air into the duct.

    A short walk at Oshkosh would provide a hundred examples of where not to install a NACA duct. Remember, even on a Formula 1 or Nascar vehicle the duct is probably in a compromised place because of other more important considerations. Race cars are also optimized for much higher Reynolds numbers. Airflow starts to behave radically differently below 50 miles per hour. Narrow your search for data to the mid 1950s on the NASA Technical Reports Server. The reports from that era have excellent nuts and bolts data and discussions. The more modern stuff is not very helpful.

    Jonny
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  35. #75
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    Lower cowl scoop shape

    Those guys are right, I doubt a NACA duct will work well there. The sides of cowlings are generally a low pressure region. On the other hand, a regular inlet with a scoop behind it will probably recover all the pressure you need to feed that oil cooler.

    It’ll add drag, but I’d put money down that you’d never notice it.
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  36. #76

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    Some progress...... We have a new lower cowl outlet, for now a fibreglass one and if it works we will make it out of carbon, the greybeard who made it for me insisted on extending past the firewall by about 4 inches to get better air flow at the outlet, I am not convinced it is better, it SURE LOOKS A LOT BETTER than our original added on to add on
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    Our old one
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    Temps unfortunately stayed about the same, still fine in a high powered cruise (2400rpm) but need to watch the temps when below 40KIAS.

    then I tried an "eyebrow", not the prettiest but it seems to have given me about 10°F better temps in both my CHT's and Oil temp
    Click image for larger version. 

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    This tells me that I need more air for my cylinders (as many of you have already kindly pointed out) and the best solution would be to move my oil cooler out of my cylinder plenum which I haven't done cause it would mean down time for the plane till I get it finished.....

    I hear what all of you are saying about my NACA DUCT idea, why I chose that is because my lower cowl is so tight that I hardly have any space on the bottom and lower corners because of my vetterman exhaust really filling the cowl up, I need to figure out what kind of scoop I can put on the lower front of the cowl and how big it needs to be to satisfy a 13 row oil cooler, can anyone help me with this? Oil cooler is about 140mmx140mm (5.5"x5.5") and I want it to cool at 30KIAS, is there data about how many CFM these coolers need to work at which temp and is there a formula to work out how much a scoop will scoop at certain speeds?

    Sent from my SM-G930F using SuperCub.Org mobile app
    Last edited by bodumatau; 02-13-2020 at 05:54 AM. Reason: mobile app loaded same photo twice

  37. #77
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    You are fighting two different temperatures (oil & CHT) at the same time. CHTs effect the oil temp so when you do one, the other is also effected leaving a mystery in your mind. Separate the two. Temporarily remove the oil cooler from the engine compartment and mount it on the landing gear cabane V. Close the hole in the baffle and tackle the CHTs. Once the CHTs are solved you can then address the oil temps. Who knows, perhaps just moving the oil cooler outside will solve the whole issue? Some of the banner towing Cubs mount their oil coolers outside.
    N1PA

  38. #78
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    Lower cowl scoop shape

    I’ve got similar cooling problems at full power Vy climb, and have been talking through it with a guy on the RV forums. Here’s some pointers he’s given me:

    At that low of airspeed, you don’t have enough total pressure (static plus airspeed) to cool much of anything...

    You might need to do some major cowling work to get there.

    At 1000’ and 70 KIAS, the available air pressure is only around 3.3-ish inches of water. Assuming you had no losses in the lower cowl, that’s still not enough to cool your motor if you’re applying power.

    You’ll have to take advantage of the prop wash as much as you can, which means air inlets further away from the spinner.

    This is a NASA data collect from an Aztec, using a pressure rake.



    Note the reduced pressure region near the spinner. The main takeaway here is that if part of your inlet is close to the spinner you could set up a spanwise flow from outboard to inboard which does nothing for your cooling. You would need to open your inlets up and move them away from the spinner.

    Here’s some carbon cub inlets. They do a good job of this.







    How do yours measure up? Mine need to grow and shift outward some. Until I get the time to do that I just fly faster.
    Last edited by CamTom12; 02-13-2020 at 08:15 AM.

  39. #79

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    Move the cooler back to the nose, duct the outlet air so it doesn't pressurize the lower cowl, close the big hole behind #3, and 95% of the battle will be won.

  40. #80

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    Quote Originally Posted by stewartb View Post
    Move the cooler back to the nose, duct the outlet air so it doesn't pressurize the lower cowl, close the big hole behind #3, and 95% of the battle will be won.
    we have tried Stewart, the previous 10 row cooler was fitted under cyl #2, it rubbed on: lower cowl, starter motor, fuel pipe, induction box and stole air from cyl#2, the 13 row won't even come near to fitting in there without making a big block that sticks out the front of the cowl, so I would rather move it underneath where I can take the intake further away from the prop and let the air exit in a controlled way.

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