[shorbird]

Has anyone on this forum tried to use surface mounted NACA ducts only to supply air to a oil cooler plenum, rather than ducting air from the back of the engine cooling plenum?

Thank you for any assistance.

 

[Gramps1]

NACA Ducks

I have a NACA duck that I plan on adding to the left side of my RV-7A's Same James Cowl with a 4" hose feeding a plenum mounted on the oil cooler attached to the engine mount. I have a O-360 A1D engine running 9:1 pistons, Airflow Performance fuel injection, Dual LSE III ignition and with squirters on the cam and piston skirts. Figure a lot of heat is going to be absorbed by the oil. I got the NACA duck from Prescott Enterprised in Lockart Texas and have modified the rectangle shape to a 4" round and made the fiberglass plenum for the oil cooler.

regards,

Tom Parks N620CF

 

[Caveman]

Has anyone on this forum tried to use surface mounted NACA ducts only to supply air to a oil cooler plenum, rather than ducting air from the back of the engine cooling plenum?

Thank you for any assistance.

Yes. I have an RV-7 with IO-360 M1B, running 9:1 pistons. I can run with the door completely closed during this time of the year... but I have a big oil cooler too, (SW 8432R).

It was 77 deg. f. on the ground during our flight today and my oil temp never went above 200 degrees even on take-off. My set-up with the door will drop the temperature 30 deg f. when I open it on a warm day. But I did not need it today.

There is a down side and that is it makes removal and reinstallation of the lower cowl a pain in the rear. I'm not sure if I'd do it again with my particular engine. I need to fly it in some of our 100 plus degree heat this summer before I'd recommend going to all the trouble. (I only have about 50 hours on the airplane and have been flying since the end of October).

If you have the angle valve engine with piston skirt oil squirtters then I'd proably say go for it.

 

[shorbird]

Thank you for the responses;

I have a fire breathing HIO-360 w/11:1 NFS pistons E/I, F/E and all that good stuff. I have a James plenum which cools the cyls more than adequately. I have two 3" scat ducts running off the back of the engine plenum to two separate, 180 hp S&W firewall mounted oil coolers (w/plenums).
Doesn't work, too hot at summer temps. The eng plenum is nearly water tight and the top and bottom of the cyls are baffled to the point where the cyl head temps are within 25 degrees of each other. But, not enough air, for what ever reason, is going out the back of the James plenum via the scat, to the coolers. I don't want to continue with two coolers and space is very limited. So, I now have a single 540 S&W cooler that I would like to firewall mount and feed via two 2.5" scat tubes from two NACA 2.5" ducts (one per cowl side). My cowl sides are metal so I don't want to make the cut-outs for the NACA ducts without seeking out others who may have experience with this type of setup. I don't have the space to mount the cooler behind the #4 cyl.

Thanks again for any comments or suggestions.

 

[Shockwave]

Before cutting up your cowl, would you have room to try 4" or 4 1/2" scat tube off of the plenum to your new cooler?

 

[nucleus]

NACA Ducts are not for Heat Exchangers

I know people use them, but NACA ducts are not designed for heat exchangers, not really a positive pressure design.

Hans

 

[N941WR]

Before cutting up your cowl, would you have room to try 4" or 4 1/2" scat tube off of the plenum to your new cooler?

Here is what we made for a friend's O-360 and it seemed to solve his problems:

It took us one evening to make and was bolted in place the next morning.

 

[BrentHumphreys]

I have no experience at this but it seems to me that your issue might be on the low pressure side, if the plenum is tight, and you have plenty of Ram air coming in, then perhaps the pressure on the oil cooler side is not low enough to draw enough air for cooling.

As mentioned before it could be that there is too much restriction in the SCAT as well.

 

[Ron Lee]

Brent made my point. Make sure that the pressure differential between the high and low pressure sides is adequate. If not, fix that problem.

 

[f1rocket]

The size of your SCAT tubing is likely your problem. If you mount your cooler on the firewall (which I would not recommend) you have to get more smooth airflow to the cooler than what you can pump in 2.5". The key is not only size, but smooth airflow as well.

The fact that you have a plenum means that you should have more than enough pressure. On my Rocket with a plenum, my cooler works too well and needs an adjustable door.

If you can squeeze a 4" SCAT tube in there, that's what I'd try first. However, there are many factors which influence the effectiveness of the cooler. A set up on one person's engine can be duplicated on another's with different results. Fluid dynamics are really complicated and interesting!

 

[Caveman]

I have a fire breathing HIO-360 w/11:1 NFS pistons E/I, F/E and all that good stuff. I have a James plenum which cools the cyls more than adequately. I have two 3" scat ducts running off the back of the engine plenum to two separate, 180 hp S&W firewall mounted oil coolers (w/plenums).
Doesn't work, too hot at summer temps.
Thanks again for any comments or suggestions.

Do a search for A.J. Judy's modifications (RV969WF). E-mail him and ask if he would mind if you copied his oil cooler set up.

 

[scsmith]

Might be some other things going on here...

Normally, the 180 hp sized SW coolers use a 3" scat. The 540 sized ones should have at least 3.5", and in hot areas, 4" scat (although most people find they cool too much and need to throttle the cooler flow)

My very first step would be to try 3" scat for each of your two existing coolers. thats more air than a single 4" scat. Its a 40% increase in air flow from what you have now.

If that doesn't work, or you are really set on the external door approach, first, note A.J. Judy's pictures - but his oil cooler intake door extends out into the flow, it is NOT an NACA inlet, it just happens to be shaped that way. He is suppying ram air into his cooler plenum through that door.

Also, on your twin cooler set-up - one possibility is that the way you have the oil lines plumbed may affect the way the oil is circulating through the coolers. Do you have them in series or parallel? If you split the flow in parallel, does the orientation of the Tee fitting create any preference toward one cooler or the other? I would not recommend plumbing them in series - too much oil pressure drop and you will not circulate enough oil through the coolers.

Another thing to note on your Sam James cowl, they have much smaller intake holes than the Vans cowl. With a plenum, they surely cool well, but there is not a lot of excess airflow to do a lot of other things. I'm less familiar with the outlet area of the S.J, but I would guess it is also smaller. So, you may not have much pressure differential for your coolers, as others have suggested. I doubt this is the problem, or others would have had similar.

 

[shorbird]

I am presently using two 3" scat tubes, one to each cooler. The coolers are connected in series and the oil line runs were kept simple and as short as possible. After reading all of the above excellent advice I'm going to try one
4" scat to a firewall mounted 9 plate cooler w/ plenum on top and an exit ducted to the top of the cowl exit, near the exhaust.

Thanks everyone for the info, I appreciate all the thoughtful posts.

Dennis

 

[Randy]

You can purchase a Magnehelic pressure gauge for less than $50.00 on ebay. I got mine for $35.00. Put one probe on each side of the cooler and you can measure the pressure differential. It can be a great tool for getting a good baseline measurement before making changes, then you can measure again and see how well the changes worked. A range of pressure from 0" to 15" of water column worked well for me. It is easy to run some plastic tubes out through the vents etc. to get a quick measurement. A little Gorilla tape will keep them from flapping around.

There are some good ideas from people with experience here, but nothing beats actually measureing that air pressure.

The stuff just does'nt always behave the way we would logically think it should.

Randy C

 

[scsmith]

pretty sure series routing of coolers is bad

The coolers are connected in series and the oil line runs were kept simple and as short as possible.
Dennis

I'm pretty sure its a bad idea to route the oil coolers in series. There is too much pressure loss for the oil flow through both coolers, and you won't flow much oil. Its like having your vernatherm stuck half way closed.

 

[shorbird]

Randy, we are working on a simple setup now to check the differential pressure across the coolers and agree that I should stop chasing my tail on this and get some definitive data. I have spent many hours closing down the cyl baffling in order to get ideal cyl cooling and hopefully invite more air to inter the oil coolers. Perhaps if I can create a low pressure on the exit side of a larger cooler near the cowl exit, adequate cooling will result.

Steve, we went around and around on that one and you may be correct. In any case, I need the room to reinstall my inverted system so one larger cooler will have to be the solution. I have always preferred firewall mounting the oil cooler and have had success with this method on two other aircraft (miniplane/ W-10 Tailwind). Both had conventional aluminum baffling where the top of the cowling creates the top of the cooling plenum and of course, both had lots of cooling drag.

To note; Prior to my new cowl and the new James plenum, I had been using only two, 2" scat tubes running off the back baffle to one firewall mounted 180 hp 7 plate S&W cooler to this high output HIO-360. I never saw oil temps above 190 even while turning 3100 rpm. The plenum screwed up the oil cooling but made the airplane 10 mph faster. I'll take the speed and fix the cooling.

 

[Mike S]

The plenum screwed up the oil cooling but made the airplane 10 mph faster. I'll take the speed and fix the cooling.

Hope your cooling fix doesnt cost 10 mph

 

[Bill Wightman]

How does this look?

If you mount your cooler on the firewall (which I would not recommend) you have to get more smooth airflow to the cooler than what you can pump in 2.5".

Randy, I'm interested in why you wouldn't recommend a firewall mounted cooler. I know its done on certified aircraft routinely, but I also I know some Rv'ers who have had problems with this setup. Are your reservations primarily centered around getting enough air to the cooler?

Here's what I've got going. My 8 is still in the build, and the engine hasn't been run so I can't tell you how it will work. The SCAT tube used here is 3" diameter going to a 9-row Positech cooler:

My focus is on achieving high differential pressure across the cooler face - all of it - along with ample area in the duct carrying the cooling air. Whaddya think??

 

[f1rocket]

My primary issue is that it seems to be less effective than other installations and I believe it has more parts and takes up more room. For the record, I don't like to mount the cooler on the rear of the baffle either. The problems with cracking baffles is well known. I think a far superior installation is to mount the oil cooler to the engine mount using some .063 brackets and cushion clamps. Then build a plenum chamber that bolts to the front of the oil cooler and ramps off the back of the baffle. Some rubber strips provides an effective seal and allows the engine to shake all it wants. This gives you a straight shot of air over the top of the cylinders and right into the cooler resulting in excellent cooling.

Bill, your installation may work just fine. Fly it first and see. Many others have used the firewall approach with success.

BTW, the short bolts are just there to hold things together temporarily. When it was permanently installed, I used long bolts and sleeves between the flanges of the cooler.

 

[RV7Guy]

Slick!!!!

Randy,

That is slicker than snot on a wet doorknob!!! Appears to be a great and relatively simple solution to an ongoing problem.

I agree with the firewall mounted coolers. I tried it and couldn't get enough airflow with 3" SCAT and no room for 4". I ended up baffle mounting and have had a couple of minor issues.