flyrotary@lancaironline.net Mailing List Archive

Hi Will;

Tracy has given you a good rule of thumb for sizing, so I'll just add a few comments.

First the oil cooler. It seems these days that many consider the stock oil cooler to be too restrictive and they may be right so it may be worth investigating other options, however as Tracy just mentioned, he has had good luck with the stock cooler. Which is what I like to hear as I too am using a stock cooler. If I was to change it, the replacement would have to be exactly the same size as I'm not in any mood to do more fiberglassing, painting, etc on the cowl. I believe the stock cooler did change a fair bit over the years and I'm not even sure what year mine was from, but there could be some variation in stock coolers that you may have to consider.

Rads have also changed in preference over the years I've been on this list. Air conditioner evaporator cores seem to have fallen out of favor, but at one time they were quite commonly used likely due to the ease of mounting them directly behind the air inlets on either side of the ever popular RV aircraft and similar airframes. Which is exactly what I have. Tracy, Ed and others also successfully used this configuration if I recall. Tracey may add more here, but I know his RV4 Otter was cooled this way, but his higher powered 20B RV8 likely has more cooling requirements than could be provided for with these coolers.

Your airframe and it's configuration will have a large effect on your choice of cooler(s). What is that you are building? And how far along are you? I made the choice to use a rotary back when I was just building the tail feathers, so engine considerations were always on my mind throughout the building process.

You'll find on this list that nobody will tell you how you have to build your engine install, you left that behind on the other list, however asking questions, posting pics, etc will usually earn a few insightful comments. And at times when the list is quiet it helps to get us talking again.

So when you're at a stage where you can take some pics of your current install, feel free to share them.

Todd, feeling eclipse envy :-(

Todd Bartrim

On Sun, Aug 20, 2017 at 6:42 PM, william Aldridge <flyrotary@lancaironline.net> wrote:

Ok I've spent the last few years on Paul Lamars list and got tired of it. I'm designing and building my own design and was wondering what you guys say is the right size for the water and oil coolers? I plan on p-porting the engine so am expecting 200+ hp. I know there's a lot of factors that go into rad sizing but let's just say i get a moderately efficient cooling system, how much volume do i need? I've got a cross counter flow setup drawn in now that is about 375 cu inches and 10.5 x 17.75 on the face and about 4.5 inches deep. The water cooler will be mounted perpendicular to the airstream with an adjustable exit ramp. For the oil cooler I’m planning on using a standard rx 7 oil cooler that will use a wedge diffuser on the intake and exhaust out shark gills on the side of the cowling. I will also have quite a bit of airflow around the engine itself. That will probably take the airspeed down somewhat but it’s such a slick small airframe that I think it could get uncomfortably close to Vne in level flight, so a little unnecessary drag might be a good thing.

Thanks,

Will Aldridge

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From: Todd Bartrim
Sent: Sunday, August 20, 2017 4:56 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Coolers

Another great example of how tech changes our lives. Back when, we had to guess at what was happening under the cowl. Now a few clicks on Amazon and 2 days later we can have all the investigative tools we need to know instead of guessing.

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Todd Bartrim

On Sun, Aug 20, 2017 at 2:45 PM, Ernest Christley <flyrotary@lancaironline.net> wrote:

Just a point to highlight what Todd was saying about exit ducting.

On the Dyke Delta I built, I had a water cooler under the cowl. The other water cooler and oil cooler were buried in the strakes. The air exited the cooler under the cowl close to the firewall, and was supposed to go down and out the bottom. It didn't do that.

What it did was set up a horizontal whirlwind inside the cowl. The air hit the firewall and then spun around clockwise. I discovered what was happening during the investigation of why some hoses were melting. I constructed a crude dam to force the air out the cowl exit, and saw a significant drop in temps.

All that is to say that the airflow INSIDE the cowl is as important as the flow outside. Today, I would tuft the engine with pieces of yarn on hoses, wires, and engine mount tubes. I have a tiny camera with a 15ft cord that turns my phone into a video surveillance monitor. I'd stick it in various places under the cowl and see how the air flows with the engine running.

On Sunday, August 20, 2017 4:22 PM, Todd Bartrim <flyrotary@lancaironline.net> wrote:

I didn't crunch any numbers in my decision to use this Laminova heat exchanger, I only knew that in climb and level flight I had different cooling between oil & water and figured I could balance it out with this heat exchanger at a small price in weight. It certainly doesn't increase the cooling of the system as a whole.

It should be pointed out that these are not coolers, only heat exchangers. So if a oil/water cooling system doesn't have adequate cooling to begin with, then this will do nothing to address that.

In my case I found that I could climb from 2000' ASL (field) to 10000' ASL in 3 minutes before my coolant temps hit redline, but I still had plenty of room on my oil temps. In level flight my coolant temps would drop but my oil temps would slowly increase to redline. So I figured this would help me borrow from Peter to pay Paul. It still didn't address cooling shortfalls properly.

I believe the biggest culprit in this was the shape and position of my oil cooler inlet which was form over function (hey, it looked good).

Now I have made a lot of other changes which hopefully should address improper cooling airflow. As well as reshaping the oil cooler inlet duct I also did outlet ducting for the oil cooler, intercooler and right coolant radiator. I did not build a outlet duct from the left radiator due to it's close proximity to the turbo exhaust pipe. This interfered with the space required for a proper exit duct and I figured it probably would be a good idea to have some airflow over the turbo. Previously I had only ducted my inlets and left the air to find it's own way out of the cowl through what I believed were adequate sized exits. Ed Anderson spent a lot of time researching cooling air flows and finally was able to beat it into me that exit ducting is every bit as important as inlet ducting.

The other change I made which I hope will have a significant effect is I bought a new set of deep pitch blades for my IVO prop. I also cut it down from 76" to 70". This should give me a higher cruise speed with the accompanying increase in cooling airflow with the same RPM.

So with all these changes it's unknown if this Laminova cooler will have any benefit but I'm certainly not going to remove it as it it's only cost at this point is a few pounds which if I need to get rid of that I'll just start jogging again... not a bad idea anyways :-)

On Sun, Aug 20, 2017, 09:46 Thomas Mann, <flyrotary@lancaironline.net> wrote:

As a side note to these observations there is something to be said about overcooling the engine oil. (i.e. cooling the oil too much at higher altitudes or in cold conditions.)

An oil-to-coolant system help to moderate that scenario.

T Mann

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