Remote oil cooler inlet screen

[DanH]

Originally Posted by rjcthree

Other posts have stated/suggested that once thermal saturation occurs in the oil cooler, all other things being equal, oil temperature will go up (down) with rising (falling) ambient (OAT) air temperatures, approximately degree for degree. Is that a solid description within the temp ranges we're talking about?

No, not in my opinion. If true, it suggests the cooler isn't large enough. The goal is to have enough cooler to handle the worst case required heat rejection with the airflow available. There is no reason to reach saturation given the availability of more air or a larger cooler.

Plan B: 4" SCEET to feed a new diffuser box, sticking with the 9-row 800074 cooler at the moment. Trying not to make too many changes at once.

That would be a reasonable choice, 50% more area, and if a subsequent step takes you to a larger cooler, you'll need it anyway.

[rjcthree]

Dan?s one word : area. Followed by a Homer-worthy D?oh! How could I be so blind. Most 320s seem to do ok with 7 row AC coolers on the the baffle. Nobody seems ok with 7 rows remote, ever, as far as I can tell, especially fed by 3? SCAT. Face area of the 7 row is about 18 sq in. 3? SCAT is about 7.1 sq in. You simply can?t deliver the required mass flow of cooling air to the cooler that way. Enter my 22 sq in 9 row cooler on a 7.1 sq in feed. It may be better, but....not gonna get there. 4? SCAT is 12.6 sq in. Might get there. Might not. It may need more cooler. I?m going to find out.

Of course there?s more to it than that, but in the ranges we operate, it might be the simple math is a good place to start. I have no excuse, BSME and all. Feeling pretty stupid at the moment.

Now if I could only find a source for a one foot piece of 4? SCAT or SCEET, it would be great. Seems like it?s on backorder until end of July over at Spruce....

[longline]

Rick. drop me a PM or call me at 360 981 5457. I can provide you with 4 inch SCAT for the cost of shipping... which should be minimal.

[blaplante]

I have a 320-H2AD in my RV6A. Somewhere I've read that the H series ejects more heat into the oil than the other 320 series engines. So, from the get go I installed a 13 row remote cooler fed by a 4" duct. Why 13? Well I knew I needed bigger than normal, and I got a deal on it. After break-in I've had zero oil temp issues... and I'm in SoCal periodically flying in the desert. I think sooner or later you'll need to upsize the cooler.

[rjcthree]

Bryan, yes, I understood that too. It's a product of the off the shelf Cadillac lifters Lycoming used. They pump a bunch of oil through the pushrods. Thats also why we have the bigger oil return tubes than just about anything else. It's also generally attributed to less occurance of sticking valves as well, but there may be more to that story. I bet your CHT's are well controlled, right? Mine are. It's also why I went 9 row from the begining, I think mistake #1 was the 3" scat feed(screened at that). I have room to go to 10 rows, not sure I can get 13 in there.

The FAA made it very clear during my airworthiness inspection: it's my experiment. And so it is....

I'll report if the 4" gets it.

[rjcthree]

Updated the classic 9-row to a 4” feed from behind number four, a diffuser into the cooler, and letting the cooler dump unrestricted downward. No other changes were made under the cowling. First pass on the data suggests the oil temp came down 5 degrees, the CHT average went up 10 degrees. The oil temperatures seem more stable regardless of airspeed, engine load. In reference, the average oil temp now floats between 200f and 205f, and the average CHT is up around 360f, with a high of 370f#2 in cruise, which still has some dam. I admit to not climbing at Vy for more than 30 seconds at takeoff; following that I settle into 100kt-105kt at ~ 27” mp. Long story, but works well in the KCLE class B restrictions at KLPR. Max CHT I saw today was 386f on #2.

It appears that the 4” SCAT is flowing more to the cooler, enough to impact CHT and oil temp, but just not enough for my comfort level yet.

Remember, it’s an A model. While I had the cowling off, I was reminded how much obstruction is in the outlet (dropped a flashlight in there....) and no good way the smooth that area for better flow.

Please weigh in on next steps to consider.

[Reformed SeaSnake]

Rick,

First question (rhetorical, you don't need to reply) is are you generally comfortable with your CHTs throughout the various flight conditions you encounter. If the answer is yes, CHTs are acceptable (climb, cruise, etc.), then where is the Oil temp issue the worst? If oil temp (compared to other metrics for engine stress) is worst at high power and low speed or bad in all speed/power combinations it suggests you need a larger oil cooler (this is what I suspect based on your previous posts). If oil temp is the worst at high speed and high power that suggests you need a less restrictive duct to the oil cooler. I doubt this is the case as there is very little pressure loss through a foot or so of duct. SCEET is better than SCAT and 4" is better than 3", but not much. The issue is not the frontal area of the duct but the pressure loss through it. That is why the screen was so bad. There is a ton of frictional loss passing through that screen.

As our buddy, Dan Bernoulli observed, for an ideal gas, through a frictionless tube, and laminar flow, the size of the duct does not matter; the upper deck pressure would be fully recovered in the oil cooler plenum. Now none of those assumptions apply, and the rougher the duct, the more abrupt the transitions in duct size, and faster the flow (narrower duct) the less well they describe our system. But with ducts less than a couple feet and equal to or greater than 2.5-3" in diameter they are pretty good. So increasing duct size may help a bit and it will help more if the airflow through it is fast (as in the high speed/high power regime), but increasing oil cooler size and thus efficiency will generally help more.

If your motivated to do the calculations, you can take the performance data available from one of the oil cooler manufacturers and calculate your current heat transfer using online calculators for pressure loss in a pipe and estimating upper deck pressure. From there you could take the difference between where your current worst-case oil temps are and where you'd like them and figure out how much larger of a cooler to get to meet your needs.

In a previous post you mentioned that you may not have room for a 13 row. 13 would easily do it even with 3" duct. 10 may be OK, but if a 10 row was the biggest cooler I could fit, I would definitely do the math to make sure it pencils out or call someone in tech support at one of the oil cooler manufacturers to help.

BTW, you also asked in an earlier post about thee impact of hotter OAT on oil temps at steady state. All other things being equal, the hotter the inlet cooling air, the hotter your oil temp will be at any fixed flight condition. It should not be quite 1:1 because the hotter it is outside, the less power your engine makes for a given MP as well. Also the engine cares about humidity, but the oil cooler does not. Water vapor absorbs heat just fine, but it's not so good at sustaining combustion. So on a very humid day you might see your temps get better even if it is warm out.

[rjcthree]

I did some more flying today, and while I have yet to tear into the data, I have a bunch of screen shots from the Dynon at steady state cruising.

In general, the higher the power the higher the oil temp at a given DA. Today I was running about 7200DA due to a cloud deck. OAT 19C/66F. Snapshots:

21.0”mp, 2310rpm, 363F on #2, 129ias/144Tas, 202F OT
21.5”mp, 2360rpm, 362f on #2, 130ias/145tas, 202F OT
22.0”mp, 2390rpm, 366F on #2, 135ias/150tas, 202f OT
23.1”mp, 2490rpm, 373F on #2, 141ias/156tas, 205F OT
24.0”my, 2570rpm, 376F on #2, 146ias, 163tas, 206F OT.

#1 #2,#3 run pretty close, but #2 usually leads by 3-5 degrees, it still has 1.25” of dam in front of it. #4 is lower by about 10f than the others. #4 is where it gets the oil cooler air from.

My climb stayed below 200f at roughly 102-105kts ias at 25”mp, from memory. Not quite WOT. Can’t bust class B airspace.

I think from this, a little more cooler would do me good. I am comfortable with CHT for right now, in that I’ve yet to see 400F at any time( a somewhat arbitrary personal limit) since hour 10 or so. I am already collecting the heat transfer vs flow mass curves to do exactly what you decscribe. I have spoken to pacific oil cooler on recommendations, and they suggested jumping into the HE range, stating the HE has 30%-50% higher heat transfer for a given mass flow, oil and air, seeing as I may have space constraints. I’m still looking for more data to get a clear picture.

It’s flyable now with a little care, but I’ll search for another 10f lower temp. I’m not ready to start cutting holes yet based on the data I have. I’m no longer 215f-220f, so that’s good.

[rocketbob]

With the DA and high ambient temps in the midwest the last few weeks, 205 is a very acceptable oil temp.

[airguy]

Originally Posted by rocketbob

With the DA and high ambient temps in the midwest the last few weeks, 205 is a very acceptable oil temp.

That's about what I'm seeing right now on climbs with my 10-row and 4" tubing, 205-210 for the climb at 1000/min, and settling down to 190-195 in cruise.