Oil / CHT cooling idea

Where most guys seem focused on speed, I love playing around with keeping my engine nice and cool.

I was considering adding a NACA inlet to the rear side of the lower cowling and running scat tube to my engine mounted stewart warner oil cooler with a cable actuated throttle in the tube.

This does two things: Provides cool air directly to the oil cooler and allows all the air in the cooling plenum to be used for keep the cyl cool.

NACA vents work by creating counter rotating vortexs due to the sharp edge that then entrain the air within the boundary layer - which is low velocity and therefore low drag. I'd run some tube at the oil cooler outlet to the cowl exit as well to prevent over pressurizing the low cowl volume.

Know of anyone who has tried this? I called VANs to discuss it and received the response I expect, "why would you change a design that already works well?" hahaha my answer, "cause I can".

Ken,

One of the faster RV-8's out there (I can't remember who) made a fiberglass scoop to put on the back of the oil cooler and then ducked that to the exit air opening between the exhaust pipes.

this is what I had in mind as well. Also should be able to reduce the inlet size as well.

Ken
Your ideas have merit. The only problem that I can see is that if you do it now you will have no idea if it actually worked. My advice would be to build it stock and then make changes. This way you will be able to tell if there is an improvement in cooling and or performance.
Try a primer paint scheme, it really makes modifications easy.

RV8R999 said:

Where most guys seem focused on speed, I love playing around with keeping my engine nice and cool.

I was considering adding a NACA inlet to the rear side of the lower cowling and running scat tube to my engine mounted stewart warner oil cooler with a cable actuated throttle in the tube.

This does two things: Provides cool air directly to the oil cooler and allows all the air in the cooling plenum to be used for keep the cyl cool.

NACA vents work by creating counter rotating vortexs due to the sharp edge that then entrain the air within the boundary layer - which is low velocity and therefore low drag. I'd run some tube at the oil cooler outlet to the cowl exit as well to prevent over pressurizing the low cowl volume.

Know of anyone who has tried this? I called VANs to discuss it and received the response I expect, "why would you change a design that already works well?" hahaha my answer, "cause I can".

Click to expand...

I tried a NACA inlet in that area to facilitate cooling a fire wall mounted electric fuel pump in a previous life with a previous engine, it did not work. The reason may have been high pressure inside the cowl, so high the NACA inlet did not overcome it, they don't seem to operate like a direct ram air scoop. Air may actually have been exiting the vent but I don't know that for sure.

I do know it did not work - there was a temp gage at the fuel pump and did not change one iota from running quite warm.

That is probably good advice. Establishing a baseline is good flight test discipline anyway. Thanks.

Read the NACA Studies

If you read the actual NACA papers from way back when, they specifically recommend against using them for heat exchangers. They are best for a low drag engine inlet where there is suction

Hans

Yes it's been done as I did a lot of testing with this.

RV8R999 [QUOTE said:

I was considering adding a NACA inlet to the rear side of the lower cowling and running scat tube to my engine mounted stewart warner oil cooler with a cable actuated throttle in the tube.

This does two things: Provides cool air directly to the oil cooler and allows all the air in the cooling plenum to be used for keep the cyl cool.

NACA vents work by creating counter rotating vortexs due to the sharp edge that then entrain the air within the boundary layer - which is low velocity and therefore low drag. I'd run some tube at the oil cooler outlet to the cowl exit as well to prevent over pressurizing the low cowl volume.

Know of anyone who has tried this? I called VANs to discuss it and received the response I expect, "why would you change a design that already works well?" hahaha my answer, "cause I can". [/QUOTE

Click to expand...

Hi Ken, open this link: http://www.vansairforce.com/community/showthread.php?t=12633&highlight=cowling+mods

Click to expand...

AJ, good to see you posting again.

AJ,

....glad to hear you are alive and kicking.

I've got your images and write up stored in a pdf file. It is some of the best cowl work on the planet. I've seen AJ's airplane at OSH....it is magnificent.

I've Conducted numerous wind tunnel and CFD studies during my grad school experience using all shapes and sizes of NACA inlets. Sized, shaped and located appropriately a NACA inlet will allow plenty of airflow for an oil cooler. The size and hence shape isn't the hard part, its correct location on the cowl that will make all the difference and without a full cowl CFD this will be more intuition than science..thats the fun of it.

Ultimately my goal will be to throttle down the exit area as well as inlets and will most likely provide a dedicated oil cooler outlet to the slip stream.

I did something similar in my BD4 and actually had to reduce the size of the NACA inlet as oil temps were in the 170's even in the summer.

Another fun experiment I did for the BD4 was making an exit venturi which really was just a glass shroud over the exit cowl flap. The slip stream was accelerated through the venturi creating a low pressure area at the cowl exit. This dropped my CHTs from the 390's to 340's and increased top speed from 168 to 174 mph (indicated at 1000 ft standard day). The speed increase however wasn't due to a cooling drag reduction as much as it was covering the firewall flat plate area that was exposed (due to the design of the exit hole being forward of the firewall).

Sounds good.

Ken

In my research and studies, I have come to a similar conclusion. I think the most efficient way to supply a cooler is it's own dedicated duct. As you can see from Alan's posts, beside his awesome glass work, is that a NACA duct will work fine when properly executed.

I am working on my cowling right now. I mounted my cooler to the firewall and will supply it with a dedicated inlet. The outlet will also be ducted to the single round exhaust pumped exit.

There many ways to "skin a cat", just as long as they are done well.

The side of the cowling is probably one of the lower pressure areas on the airframe.
I'm using the cowl side for my oil cooler air exit. I'm just ground running now, but it seems to be working fine.
Although I'm an 'alternate engine builder' I'm using a stock cowl, with a few mods.
Just my 2 cents, but if you experience a need for more oil cooler air flow...after trying the stock set up, you might try ducting the cooler exit air out the side thru a reverse facing scoop (extractor). IF you must, otherwise I'd advise you to duct the oil cooler exhaust air out the bottom as already mentioned.
One thing is for sure. If you change anything, build time gets a LOT longer. Ask me how I know this, or just check my link.
Build it stock, change it later.

SHIPCHIEF said:

The side of the cowling is probably one of the lower pressure areas on the airframe. ......

Click to expand...

I agree.

The attached image depicts the side Bonanza vents I copied and built and they are a reason the IO360 cht's and oil run cool, too cool in fact. Beech invented them about 50 years ago and they work.

The vents were installed to facilitate cooling with the Subby H6 and were almost removed when the Lycoming was installed. But one test flight changed my mind. I taped them shut with duct tape wanting to observe temperatures just using the stock cowl exit. There was no change and I thought coming in to land, they will be removed.

But after shut down I saw why there was no change. The internal lower cowl pressure had blown the duct tape off the cowl and they were taped tight. With that I decided to leave well enough alone. I don't think there is any drag with them as the airplane goes as fast as Vans numbers and somedays a bit faster. The max CHT observed so far is 405 and that was a WOT climb to 10,000' last summer to see how long it would take to get up there. (8 minutes, 26 seconds ) Oil temp with that climb was 185 or 190.

I believe you get good cooling by running air across the engine, lots of it, and one way to do that is having a copious amount of exit area. The standard Vans inlet is about 45.5 inches square and the exit 49 which equals 107%. That works for many guys.

My cowl was modified at least 4 times trying to cool the H6. I undid some of it going to the IO360 but I still have the Bonanza vents and a 5X16 bottom exit. Total area is 108 inches which computes to an exit ratio of about 237%.

Now I know that much exit area is not suppose to work in terms of drag and there is no science to qualify why the engine runs cool and airplane flies like it does, but it does. I suppose I could make some changes to perhaps see an improvement in performance. But I spent about 4 years trying to cool that H6 (never did conquer the beast) and flying around with a Lycoming that never over heats is such a pleasure, I think I will leave it all alone.

At present the side vents are taped shut on the inside to facilitate getting the oil temp up a bit. Even with the air shut off, oil temp still runs around 160. This is with the SW8432R mounted like in the RV-10 with a 4" scat tube from aft of #4 baffle.

I also believe another reason this thing is running like it is, is because it is not a 200+HP engine. (it turned up 187 on the Barrett dyno) There is a lot more heat generated with engines like what Alan Judy and others are running. And of course the faster you go, the more drag becomes an issue.

Oil cooler cooling

Have you read my thread "Oil cooler cooling". I was thinking to install a "Advanced Aero Components " Naca Scoop large on the left side of the lower cowling and connect it directly the the SW oil cooler through a " scat tubing.
This naca scoop seems to be the best I have found around but its price is a big deterent ($ 225). Teh advantage of doing this will be to entirely devote the air going through the SJ plenum to the 4 cylinders equally. Cylinder # 4 is presently with a CHT 40F higher than # 1, 2 and 3 due the air going to theoil cooler mounted on the firewall through a 3" scat tubing.

I've concluded after 1 year of flying my -8, a an oil cooler air source seperate from cyl cooling air isn't warranted. My oil cooler is mounted low in the cowl on the engine mount and fed cooling air via 3" scat from the #4 cyl baffle. As it is now, I have the inlet covered 50% and still do not see OT above 190, even during extended climb in the Florida Summer heat. I experimented with blocking the OC inlet in varying degrees to observe changes in CHT (particularly #4) and have determined it doesn't vary much at all if any as a function of OC inlet area.

Thanks for the follow up.
Our hangar nieghbor has an RV-4 with a custom oil cooler arrangement.
He mounted the cooler dead center on top of the crankcase on the front side of the rear baffle. The air flows right straight thru it and he controls the air flow seasonally with a partial blocking plate at the back.
He claims more even cylinder temp as well.
It is strong and simple.