(Oil) Cooler theory

[zkvii]

Hi,

I'm still in the early stages of flight testing and fighting high oil temps. I've had a couple of good runs but the good seems more linked to outside air temp rather than anything else - ie. 15C day / 5C @ 4000' everything is within green - but warmer, 26C day / 15C @ 4000' oil temps are red lining after about 20 mins (takeoff -> 4000' S&L @ 150+ kts). CHTs are all sensible, 400-420. Oil pressure is always good, > 70 psi @ the high temps (eg. upto 115C)

Just for the record / background, this is a brand new engine (TMX OF-360) so I expect some heat for a few hours, I've checked the verntatherm, oil temp probe accuracy and changed from NDM to SW 8604R cooler. Leg and main fairings are installed too. Some improvments but all pretty small amounts.

We do have a custom cowl inlet / plenum which may be the source of my grief but changing the cowl is big work and I want to confirm before hacking it around.

So questions:

• Plenum 101 - can someone confirm I'm not actually that interested in 'air flow' into the plenum, what I want is a good pressure delta between upper and lower segments?
  
• What pressure delta should I be aiming for across the oil cooler?
  
• Intake / Outlet ratios - I know this has been debated / covered before, can some with the SJ cowl give me some details - ie. inlet diameter and outlet shape for side/side RVs.
  
• We are a nose dragger and currently I don't have an upper intersection fairing on the cowl - could this be seriously hurting our cooling flow?

We are currently working on the inlet shapes a bit and also setting up instrumentation across the cooler so at least we can measure what we are getting right / wrong.

All rather frustrating...... but it seems to fly well

Carl

[SebsRV7A]

Walter Tondu shows his pressure test for the cooling on his web site:
http://www.rv7-a.com/phase_1_page2.htm

I put a plenum in my -7A and also have cooling issues at high temperatures. I'm on my third mod of the inlet and getting ready to do the 4th. I almost cooked my engine on the first flight. It's reasonable now except climb ROP at higher temperatures. Since everything else in the plane is stock, I can only conclude that the inlets are my problem. I also hope to get some missing speed with a better inlet smoothing.

If you have a big slot open in the bottom of the cowling without the intersection fairing, I'd say it's probably allowing higher than desired pressure in the lower cowl. You could duct tape it closed for now as a test.

I changed to the real SW cooler from the one Van's sells and moved it from the firewall (remote) to the back of the baffles. That was the biggest difference after my earlier mods to the plenum inlet. I also have issues with CHTs in the climb, adding evidence to my theory of an inlet problem.

There was an article in Sport Aviation on inlet mods on a Lancair 360. I'm planning on trying to do something along the same lines. I'm going to try to do as little mod to the cowl as possible as it's already painted, but I think I'm going to suck up getting round inlets for the efficiency.

Hope this helps. Let us know how any mods you do help out.
Seb Trost
RV-7A (220 hours)
Cameron Park, CA (O61)

[robbieattaway]

Give me a call, maybe I can give you some information that will help.
602-538-6087.