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Oil cooler ins and outs printer friendly version
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dannparks
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Posted Sunday, July 8, 2012 @ 01:57 AM  

I'm taking a final look at the oil cooler arrangement and I have a question for those with oil coolers. Most setups I have seen have a duct to exhaust the hot air through the back of the baffles to the lower pressure area in front of the firewall (first pic). I have some concern about all that hot air heating up the mag (and the generator and voltage regulator in my installation). Has anyone had problems or mag failures because of the heat off the back of the oil cooler on the firewall?

I was thinking about a second option of adding a small NACA-type inlet on the top-front of the cowl that would put air directly through the cooler and the hot air would exit through the cylinders -- not by the firewall (second pic). This makes the air through the cylinders warmer, but no hot air blasting on the mag (and other electrics).

Should the hot air on the electrics be a concern? Is it a big enough issue to warrant looking at a new intake design?

Thanks for any advice or suggestions.

--------------------
Dann Parks • RF4D #4051 N2188 • now flying!
Pictures at: https://picasaweb.google.com/111628310900713778468/RF4D_N2188?noredirect=1

Jorgen
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Posted Sunday, July 8, 2012 @ 06:11 AM  

Hi Dann,
I think Bob Grimstead measured temperatures under the cowl when he tested a ram-air carburettor setup:

http://sbeaver.com/cgi-bin/fournier/cutecast.pl?session=topOC7ORfut6eVJvgHZ0oFBfUd&forum=17&thread=677

If Bob's measured 20-40C higher temp below the cylinders is true I wouldn't worry too much about heating your mag+ electrickery too much. That said I remember reading somewhere about a french Fournieteer who had odd problems that turned out to be a faulty mag. It tested normal on the bench, but failed when heated (faulty spool?). I don't remember how much it needed to be heated to fail, anyway it sounded more like a faulty mag than a temperature problem.

May the 4's be with you/ Jörgen

milnerd
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Posted Sunday, July 8, 2012 @ 11:26 AM  

Hi Dann,

One problem with your proposed idea is that the air pressure on either side of the oil cooler will be the same so I think that you will get no airflow through the cooler. The high velocity air coming into the cowling increases its pressure as it slows down. Whether the air is coming into the plenum on top of the engine via the main air intakes, or your proposed NACA scoop, the static pressure inside the cowling will be the same. By venting the discharge of the oil cooler through the baffle at the rear of the engine (which is in the low pressure zone of the cowling) you are creating a differential pressure across the cooler that will keep the air moving through it.

If you are concerned about excessive heat on the magneto you could shield the mag or use large diameter SCAT tubing to duct the hot air from the cooler outlet and down to a point lower down below the mag. Make sure that you don't discharge the hot air on your gascolator though as that could create additional problems for yourself.

Bob Grimstead runs his engines as hard as it is possible to and he exhausts the oil cooler down the back of the engine and has never had magneto problems as far as I am aware, so perhaps it is not a real issue in practice. Bob also flys his Fourniers more ours a year than most too. One would think that if a problem were going to occur in this area Bob would be the first to see it.

Best regards,

Dave

dannparks
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Posted Sunday, July 8, 2012 @ 11:47 AM  

The pressure differential (or potential lack of it) is a real question. I'm sure if the idea had merit, someone would have tried it in the last 40 years. I had planned to put some cool air tubes in the mag area and on the voltage regulator, maybe that will be enough. The voltage regulator should be kept below 150 F.

I noticed that Ray (jb92563) has almost the same setup that I am doing with the Diehl case generator and slick mag, and the oil cooler venting out the back. Ray, if your checking out this thread, have you had any issues with the hot air over the back of the engine? Where is your voltage regulator mounted?

--------------------
Dann Parks • RF4D #4051 N2188 • now flying!
Pictures at: https://picasaweb.google.com/111628310900713778468/RF4D_N2188?noredirect=1

jb92563
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Posted Monday, July 9, 2012 @ 11:14 AM  

Dan,

No issues with the voltage regulator nor the Mag.

I did however have some vaporization in my fuel lines if I taxi or idle for a long time on a hot day (15min+) but since I wrapped my exhaust pipes and put some aluminum shields around the fuel lines that problem is gone as well.

Once the plane is in the air the airflow does a great job keeping everything nice and cool.

My normal Oil Temp in the air is 90C and midway in the green zone so it should not be a problem.

On the ground you can get the oil temps up to the yellow zone if reving the engine for a long time, maybe more than 30 minutes with the cowl on, so the heat can build up but even then I had no mag or regulator problems.

--------------------
Ray
RF4D #4057 N-1771 Rectimo 1400cc
http://picasaweb.google.com/jb92563/FournierRF4D
http://www.touringmotorgliders.org

Bob Grimstead
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Posted Tuesday, July 10, 2012 @ 08:02 AM  

Hi Guys,

Those magnetos do not like to get too hot, neither does any component in the fuel system.

Adding an oil-cooler's excess heat to that already generated by combustion of a 1400cc+ engine into a small, tight cowling designed for normal flight with a 1200cc engine will always cause some kind of overheating problems.

However... I got both my magnetos overhauled as soon as I got the Fourniers, and had new coils fitted, to bypass the common issue of Fournier magneto coil breakdown due to overheating.

In Dann's case, if he can make a NACA scoop at the front of his cowling like that, and put another, separate outlet behind the oil coooler, exiting into the low-pressure air at the convex rear upper surface of his top cowling, he should get a good flow through the cooler without adversely affecting lower cowling temperatures.

The tricky bit will of course be obtaining an adequate seal between the ducting and the cowling, but ducts open at the top combined with compressible foam seals on the undersurface of the cowling should do the trick. Best of all, this does not much change the lovely flowing cowling lines, so that would probably be a very good mod.

I would love to see details when you're done Dan, and then I shall blatantly copy your design (only with your approval, of course).

I have always been concerned that the opening at the back of the oil cooler (its outlet) is robbing/diverting/by-passing much-needed air from going down through the cylinders and more importantly the heads. Your solution of using completely separate ducts for the oil cooler will completely sidestep that issue, and seems like such a good idea, I bang my head against my monitor that I didn't think of it myself!

Yours, Bob

--------------------
Flying and displaying Fournier RF4Ds VH-HDO and G-AWGN, building replica RF6B G-RFGB and custodian of RF6B prototype F-BPXV

dannparks
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Posted Sunday, July 15, 2012 @ 05:47 PM  

The concept of the air path going in and out through the top of the cowl is intregueing. Especially since the scoops and channels could all be done in fiberglass and be part of the cowl. I do want to be sure i'm not overthinking this and trying to solve a problem that won't really exist for my installation and use. I might just build it "stock" at first and see if there are any issues. And then modify the cowl if needed.

Are there any others with an oil cooler that have some experience to share?

--------------------
Dann Parks • RF4D #4051 N2188 • now flying!
Pictures at: https://picasaweb.google.com/111628310900713778468/RF4D_N2188?noredirect=1

Jorgen
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Posted Sunday, July 15, 2012 @ 06:43 PM  

Hi again Dann,
it must be the lower temperatures I fly in, but I rarely see temperatures that are too high (maybe I should check my temp gauge?). We did the annual last Friday (I'll post pics of how I detach my baffles in another thread) and compressions were all good, nothing special with the plugs either. I do have an oil cooler, I think it was fitted at Nymphsfield in the UK when XST (then G-AVNX) got 1400 pots. Possibly they fitted the oil cooler to cure a problem that was later cured by drilling out the carb inlet (too lean mixture(?)- as we have discussed in other threads)- I don't know for sure since I haven't gotten around to ask Dave Bland about it yet.

Anyway, Mike Woollards oilcooler fitting sits furhther back compared to yours Dann. Also, there is no hole or duct through the baffle plate behind the oil cooler (or the casing's plate behind the baffles for that matter) and still I have no cooling problem. Maybe my baffles are so "not tight" that I do get "in and out" flow through the oil cooler- or maybe it's just cool to fly in Sweden. So very cool!

May the 4's be with you/ Jörgen

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