Aluminum oil cooler lines?

[judoka5051]

Hey All,

I noticed in "Speed with Economy" that the author installed aluminum tubing oil lines after mounting his oil cooler to the engine (eliminating the hoses). Since reading that I've often wondered why I haven't seen one RV with that setup. It would be lighter than hose, that's for sure! I'd like to find out if it's practical and safe, or not.

Thanks, Lance

[penguin]

Hi Lance,

Early Super Cubs use steel lines running from the back of the engine to the front, with the cooler at the front in the center. Most people use flexible hoses, but hard lines will certainly do the job. There is clearly a risk of cracking using aluminum tubing - do you feel like taking that risk? The consequences are severe if you should get a crack, and the gains small.

If you choose this route perhaps a very regular and thorough inspection regime would be prudent to spot any potential cracking as early as possible?

Hope this helps, Pete

[Toobuilder]

Generally speaking, hard lines are superior to hose assemblies in every respect. That being the case, hose assemblies are reserved for those areas that have a lot of relative movement or maintenance issues dictate. A baffle mounted oil cooler has a great deal of relative movement between it and the fittings in the engine case. So if you want to run hard lines, you will need to figure out a way to allow some movement of the oil cooler yet support its weight. At this point you will do a cost/benefit analysis between engineering this complicated mount system, or just popping for the expense and weight penalty of the hose.

I went down this road when I rebuilt the -8... With the exception of a short hose between the firewall and fuel pump, I replaced every flex line FWF with a stainless hardline and it turned out great. I saved a bunch of weight and got rid of that nasty, oil soaked orange fire sleeve junk. I even had a nice set of stainless hard lines made for the oil cooler and hoped that I could address the relative movement thing with some nice 90 degree bends in the lines, but to no avail... The mount cracked anyway. Ultimately I gave up and made some nice short hoses which work just fine. Someday, I'll take another run at building a sliding mount, but for the time being the hoses are not much of a penalty.

[hgerhardt]

Robinson helicopters use aluminum hard line to plumb their oil coolers. The R44 even has two oil coolers, plumbed in series. See http://www.robinsonheli.com/R44IPC.html and go to chapter 4, Powerplant, page 4-7C.

[Sam Buchanan]

Originally Posted by judoka5051

Hey All,

I noticed in "Speed with Economy" that the author installed aluminum tubing oil lines after mounting his oil cooler to the engine (eliminating the hoses). Since reading that I've often wondered why I haven't seen one RV with that setup. It would be lighter than hose, that's for sure! I'd like to find out if it's practical and safe, or not.

Thanks, Lance

Originally Posted by Toobuilder

Generally speaking, hard lines are superior to hose assemblies in every respect. That being the case, hose assemblies are reserved for those areas that have a lot of relative movement or maintenance issues dictate. A baffle mounted oil cooler has a great deal of relative movement between it and the fittings in the engine case. So if you want to run hard lines, you will need to figure out a way to allow some movement of the oil cooler yet support its weight. At this point you will do a cost/benefit analysis between engineering this complicated mount system, or just popping for the expense and weight penalty of the hose.

The original poster said he was considering mounting the oil cooler to the engine. No relative motion.

Seems I recall some older RV-4's having small oil coolers mounted on top of the crankcase. The RV-4 cowl apparently is quite efficient.

[skylor]

Originally Posted by Sam Buchanan

The original poster said he was considering mounting the oil cooler to the engine. No relative motion.

Seems I recall some older RV-4's having small oil coolers mounted on top of the crankcase. The RV-4 cowl apparently is quite efficient.

There is some relative motion with a baffle mounted cooler because the baffles aren't that rigid and they flex quite a bit from the weight of the cooler when subjected to engine vibration. Something to consider...

Skylor

[Sam Buchanan]

Originally Posted by skylor

There is some relative motion with a baffle mounted cooler because the baffles aren't that rigid and they flex quite a bit from the weight of the cooler when subjected to engine vibration. Something to consider...

Skylor

No..........the original poster inquired about a cooler mounted to the ENGINE, not the baffles.........

[Ironflight]

The RV-1 at one time had the cooler mounted in front of the sump (no cross-over exhaust, so it had plenty of room), I imagine on a bracket that picked up the sump screws. So there ARE places to put it other than the baffles. I don't however, know how it was plumbed.

[judoka5051]

Well, that's certainly food for thought. I had given consideration to mounting the cooler on the baffles and using loops to allow for motion, but the more I think about cracking oil lines, and the fun that I'd have with that... Anyway, I'll either figure out a way to secure it firmly to the engine, or use long runs of tubing and a short hose to absorb motion if I put it somewhere vibration will be a problem. I'm trying to keep the plane under 1000 lbs, and you know how fast it all adds up!

Thanks, Lance

[Toobuilder]

If you can't tell from any of my posts on the subject, I'm not a real fan of hose assemblies, but the fact is, if you're doing the normal location on the baffles then you will not experience much of a weight penalty going with hose. There will be some, for sure, but proper routing can keep them pretty short. It's one area where a trade study really needs to be done to know for sure if the hardlines are an advantage.