Van's Air Force
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Diameter of oil cooler hoses
- Thread starter Dorfie
- Start date
Certainly not saying 1/2" hose is wrong, because it's really hard to go wrong with a larger hose diameter. However, I would make a few observations.
The objection to -6 hose is inadequate flow capacity, yet builders routinely select and recommend a Meggit (Stewart Warner) 8432 two-pass cooler...which, at 55 lbs per minute, has a oil side pressure drop of 16 psi. The pressure drop for an identically sized SW10599 single pass cooler, at the same mass flow rate, is 3.5 psi.
The oil pump is a positive displacement type, which means the mass flow, in lbs or gallons per minute, is the same for the 3/8 hose or the 1/2 hose, or for either of the above coolers. The differences will be line pressure and pressure drop, some loss of energy to heating, and more power demand.
The pressure delta created by small line size or a two-pass cooler will show up across the vernatherm opening. Since the vernatherm works by closing the bypass opening and forcing all flow through the cooler, it will be required to close and seal against a higher pressure.
The coolers themselves are threaded for -6 fittings...even the huge coolers.
The objection to -6 hose is inadequate flow capacity, yet builders routinely select and recommend a Meggit (Stewart Warner) 8432 two-pass cooler...which, at 55 lbs per minute, has a oil side pressure drop of 16 psi. The pressure drop for an identically sized SW10599 single pass cooler, at the same mass flow rate, is 3.5 psi.
The oil pump is a positive displacement type, which means the mass flow, in lbs or gallons per minute, is the same for the 3/8 hose or the 1/2 hose, or for either of the above coolers. The differences will be line pressure and pressure drop, some loss of energy to heating, and more power demand.
The pressure delta created by small line size or a two-pass cooler will show up across the vernatherm opening. Since the vernatherm works by closing the bypass opening and forcing all flow through the cooler, it will be required to close and seal against a higher pressure.
The coolers themselves are threaded for -6 fittings...even the huge coolers.
That's a good point Walt. I said -6 without thinking, when -6 and 3/8 NPT are not the same thing.
Just about all of the coolers we plumb use -8 hoses. From 912 Rotax to IO540's.
Tom
Tom
Dan,
What you say below is what I have been thinking may be going on with my setup. It is; IO-375, low compression, WWRV200 prop, Meggit 8432R oil cooler, -8 oil lines, feeding air to it via 4" scat to a modified RV10 oil cooler mount on the firewall, have 4" butterfly valve to allow me to close off air, but have certainly not needed to do that... Now about 75 hrs on the engine.
My oil temps were just acceptable in the winter Arizona weather but I was hoping that was mainly because of the brake in process. Flying in the California valley with temps above 100F it is barely flyable if I try to stick to my 200F self imposed oil temp limit. Even in winter temps I am forced to run lean of peak to control oil temps, and CHTs to some extent.
My baffle seals are tight, really. I have tried climbing at higher speeds and that helps some. I am keeping EZ cool cowl flaps open, two of them.
Checked out my vernatherm and it closed off at about 180F as it is supposed to.
Now I am wondering if that vernatherm is bypassing too much of the oil due to the higher 8432 pressures. The seat looked good on the vernatherm.
I plan to measure my differential air pressure on each side of the cooler to have a base line measurement to start with. Then maybe try some SKEET tube to see if it makes any difference. Beyond that, I wonder if anything can be done to the vernatherm to make sure it is not bypassing too much oil away from the oil cooler. Any ideas or adjustments that can be made to it? Do they make different models that might have a stronger spring, or maybe some have shimmed the spring to increase tension?
What you say below is what I have been thinking may be going on with my setup. It is; IO-375, low compression, WWRV200 prop, Meggit 8432R oil cooler, -8 oil lines, feeding air to it via 4" scat to a modified RV10 oil cooler mount on the firewall, have 4" butterfly valve to allow me to close off air, but have certainly not needed to do that... Now about 75 hrs on the engine.
My oil temps were just acceptable in the winter Arizona weather but I was hoping that was mainly because of the brake in process. Flying in the California valley with temps above 100F it is barely flyable if I try to stick to my 200F self imposed oil temp limit. Even in winter temps I am forced to run lean of peak to control oil temps, and CHTs to some extent.
My baffle seals are tight, really. I have tried climbing at higher speeds and that helps some. I am keeping EZ cool cowl flaps open, two of them.
Checked out my vernatherm and it closed off at about 180F as it is supposed to.
Now I am wondering if that vernatherm is bypassing too much of the oil due to the higher 8432 pressures. The seat looked good on the vernatherm.
I plan to measure my differential air pressure on each side of the cooler to have a base line measurement to start with. Then maybe try some SKEET tube to see if it makes any difference. Beyond that, I wonder if anything can be done to the vernatherm to make sure it is not bypassing too much oil away from the oil cooler. Any ideas or adjustments that can be made to it? Do they make different models that might have a stronger spring, or maybe some have shimmed the spring to increase tension?
Carl Froehlich
Well Known Member
Randy,
I suspect the only problem you have is the oil cooler just being too small for this application.
I too abandoned the Van's angled firewall oil cooler mount as the multiple changes in air direction appeared a disadvantage to me. I have the AirFlow System 2006X cooler horizontally mounted on the left side of the firewall, fed with a 4" scat hose and butterfly valve. The hottest oil temp ever has been 210 degrees after a hard climb on a hot day (stock IO-540 engine). Standard summer cruise has the butterfly valve partially closed to keep oil temps above 180.
I suspect the only problem you have is the oil cooler just being too small for this application.
I too abandoned the Van's angled firewall oil cooler mount as the multiple changes in air direction appeared a disadvantage to me. I have the AirFlow System 2006X cooler horizontally mounted on the left side of the firewall, fed with a 4" scat hose and butterfly valve. The hottest oil temp ever has been 210 degrees after a hard climb on a hot day (stock IO-540 engine). Standard summer cruise has the butterfly valve partially closed to keep oil temps above 180.
As noted, the 8432 loads the vernatherm capsule and spring. it is possible to shim the vernatherm a little by removing the AN seal washer under the body head and substituting a thinner soft aluminum or solid copper washer.
Strictly personal opinion, but a lot of equipment selection in our game is monkey see, monkey do...."everybody" uses an 8432 (or a Framus-brand valve, or a whatever), so that is what gets installed. Here it is really more a case of picking a size necessary to get the results you want. You're like me; you want temps under 200F, 99% of the time, so yeah, maybe you want to install a larger cooler. Others will be perfectly happy with 210F, 50% of the time. To each his own.
If you do swap, a single pass cooler has a far lower pressure drop. You can find the SW/Meggit spec book at:
http://www.oilcoolers.com/stewart_warner_curves.asp
I'm running a remote mounted 10611 (and 1/2" lines). This a direct climb from 200 MSL to 15,000 while holding 125 KTAS, start and end temperatures, IO-390. It's not just a matter of oil cooler size, but it does suggest that an experimenter like yourself can get 'er done if you want to.
I will include a few photos of my oil cooler setup here in case anyone can spot a problem or a way to improve on what I have done.
Can anyone report on changing away from this setup, which I think is fairly common or at least I though it was, and seeing an improvement by going to something else, and what that change involved?
Like the previous post mentions, perhaps to many changes in air direction to be effective?
I will measure pressure differential on this setup and then after some more research, implement a change, based on what I learn from the pressure measurement.
An easy change is to go with SKEET rather than SCAT to see if that puts more air across the cooler. I think the net effect of going with the smooth bore SKEET is that it will act as if the duct is larger, maybe that will help.
I hate the idea of giving up on this high dollar oil cooler. So much for monkey see monkey do approach
Can anyone report on changing away from this setup, which I think is fairly common or at least I though it was, and seeing an improvement by going to something else, and what that change involved?
Like the previous post mentions, perhaps to many changes in air direction to be effective?
I will measure pressure differential on this setup and then after some more research, implement a change, based on what I learn from the pressure measurement.
An easy change is to go with SKEET rather than SCAT to see if that puts more air across the cooler. I think the net effect of going with the smooth bore SKEET is that it will act as if the duct is larger, maybe that will help.
I hate the idea of giving up on this high dollar oil cooler. So much for monkey see monkey do approach
Carl Froehlich
Well Known Member
The pressure differential across the cooler drives the lbm/hr airflow. Changing to SKEET will have little, if any affect.
If you really are against getting the right size cooler, then try mounting the current cooler horizontally. You might gain a few lbm/hr increase in airflow.
Carl
If you really are against getting the right size cooler, then try mounting the current cooler horizontally. You might gain a few lbm/hr increase in airflow.
Carl
Gaylon
Active Member
Mount it horizontal
I changed my oil cooler mounting location 1 month ago and have seen better delta p on the oil cooler (2007x) from stock location. I am near 40 degrees angle at this time only because I used a 45 degree plenum. I will be changing to a horizontal position soon once I get the straight plenum. I will also be working on smoothing out the lower firewall lip so the air flows better out of the cowling. I have a Show Planes cowl so this isn't directly comparable to the stock cowl. I did change my vernatherm out to the bypass spring. This didn't necessary seem to help, like others claimed on VAF, but it did lower temps slightly and I wont pretend to put a value on the amount it dropped.
I performed Vx, Vy and straight and level flight testing to characterize the delta P before and after all my changes so I have the data to back up the relocation of the oil cooler. I still get into the 200's (200-215) for oil temp but once in cruise the temp will go back down the 190F whereas before it would never go back below 200F. It is overall a much better setup with better oil temps.
I wont comment about what happens with the oil temps with the POD attached, that's another story.
My engine is a Barrett 9:1, cold air, FM300. I will see about posting a picture.
I changed my oil cooler mounting location 1 month ago and have seen better delta p on the oil cooler (2007x) from stock location. I am near 40 degrees angle at this time only because I used a 45 degree plenum. I will be changing to a horizontal position soon once I get the straight plenum. I will also be working on smoothing out the lower firewall lip so the air flows better out of the cowling. I have a Show Planes cowl so this isn't directly comparable to the stock cowl. I did change my vernatherm out to the bypass spring. This didn't necessary seem to help, like others claimed on VAF, but it did lower temps slightly and I wont pretend to put a value on the amount it dropped.
I performed Vx, Vy and straight and level flight testing to characterize the delta P before and after all my changes so I have the data to back up the relocation of the oil cooler. I still get into the 200's (200-215) for oil temp but once in cruise the temp will go back down the 190F whereas before it would never go back below 200F. It is overall a much better setup with better oil temps.
I wont comment about what happens with the oil temps with the POD attached, that's another story.
My engine is a Barrett 9:1, cold air, FM300. I will see about posting a picture.
A little more info to share:
I spoke with a tech rep at Pacific Oil coolers yesterday. He said it would take about 40PSI of differential pressure to cause the oil to bypass. Since the 8432R has a pressure drop of about 16 PSI at 55 lbs per minute it is very doubtful that is causing high oil temps.
I see 64 PSI oil P in cruise, add the 16 PSI assumed pressure drop and it might mean the vernatherm sees 80 PSI against the seat. If what the rep said is correct it would mean the vernatherm should not bypass until 64 PSI plus 40PSI = 108 PSI. (Am I doing this right?)
If I remember right, Dan figured it might bypass at 90 PSI. If so I only have a 10 PSI margin and that might not be enough..
He also stated that the 8432R is the most efficient oil cooler and that going to a larger cooler would not gain much in lower temps, maybe 5F or so. There are hundreds if not thousands of these coolers in use on the Mooney M20 series and they work fine in that application for both 180HP and 200HP engines. Anybody have Mooney time and can share what the oil temps run, or do they even instrument it?
He thinks my self imposed 200F limit is too conservative and he would not get worried until it got up to 235F.
Just another data point as far as I am concerned. I will still get the air pressure measurements and learn what can be done from that side. Still need to verify the oil is not bypassing through the vernatherm.
Randall
I spoke with a tech rep at Pacific Oil coolers yesterday. He said it would take about 40PSI of differential pressure to cause the oil to bypass. Since the 8432R has a pressure drop of about 16 PSI at 55 lbs per minute it is very doubtful that is causing high oil temps.
I see 64 PSI oil P in cruise, add the 16 PSI assumed pressure drop and it might mean the vernatherm sees 80 PSI against the seat. If what the rep said is correct it would mean the vernatherm should not bypass until 64 PSI plus 40PSI = 108 PSI. (Am I doing this right?)
If I remember right, Dan figured it might bypass at 90 PSI. If so I only have a 10 PSI margin and that might not be enough..
He also stated that the 8432R is the most efficient oil cooler and that going to a larger cooler would not gain much in lower temps, maybe 5F or so. There are hundreds if not thousands of these coolers in use on the Mooney M20 series and they work fine in that application for both 180HP and 200HP engines. Anybody have Mooney time and can share what the oil temps run, or do they even instrument it?
He thinks my self imposed 200F limit is too conservative and he would not get worried until it got up to 235F.
Just another data point as far as I am concerned. I will still get the air pressure measurements and learn what can be done from that side. Still need to verify the oil is not bypassing through the vernatherm.
Randall
cajunwings
Well Known Member
Oil Temp
He also stated that the 8432R is the most efficient oil cooler and that going to a larger cooler would not gain much in lower temps, maybe 5F or so. There are hundreds if not thousands of these coolers in use on the Mooney M20 series and they work fine in that application for both 180HP and 200HP engines. Anybody have Mooney time and can share what the oil temps run, or do they even instrument it?
Have lots of time in Mooneys with angle valve 200 hp motors(IO-360-A3B6) Cruise oil temps usually run around 180-185 in the summertime at ROP settings if you run LOP then 10deg cooler. Only time oil temp is a issue is climbing at higher altitudes like 7000' and above with higher than standard OAT.
Don B
RV 9 Rebuild in Progress
He also stated that the 8432R is the most efficient oil cooler and that going to a larger cooler would not gain much in lower temps, maybe 5F or so. There are hundreds if not thousands of these coolers in use on the Mooney M20 series and they work fine in that application for both 180HP and 200HP engines. Anybody have Mooney time and can share what the oil temps run, or do they even instrument it?
Have lots of time in Mooneys with angle valve 200 hp motors(IO-360-A3B6) Cruise oil temps usually run around 180-185 in the summertime at ROP settings if you run LOP then 10deg cooler. Only time oil temp is a issue is climbing at higher altitudes like 7000' and above with higher than standard OAT.
Don B
RV 9 Rebuild in Progress
Another piece of the puzzle
I talked with Doug Hamerton at Aerosport today about my oil temp problem. He agreed that it is a good idea to try to keep temps under 200F but felt going up to 215 or so will not hurt it, and quoted the Lyc spec of 245F redline.
He has not heard of others having problems from the vernatherm bypassing, but agreed that it would be good to check it's operation. I proposed one way of doing this would be to eliminate the vernatherm and put a plunger and spring etc. in place, fly it that way and compare temps. (I need to learn more about the parts involved and verify for sure just how they function, more reading here will help...)
The kicker is that he looked up my engine build records and verified that I do indeed have oil squirters shooting oil up to the pistons, so that may explain at least some of the higher oil temperatures I am seeing. He said built they built IO-375s with and without squirters over the years and mine got them.
Anybody have an approximate figure as to how much temperature rise the squirters add to the oil temperature?
Randall
I talked with Doug Hamerton at Aerosport today about my oil temp problem. He agreed that it is a good idea to try to keep temps under 200F but felt going up to 215 or so will not hurt it, and quoted the Lyc spec of 245F redline.
He has not heard of others having problems from the vernatherm bypassing, but agreed that it would be good to check it's operation. I proposed one way of doing this would be to eliminate the vernatherm and put a plunger and spring etc. in place, fly it that way and compare temps. (I need to learn more about the parts involved and verify for sure just how they function, more reading here will help...)
The kicker is that he looked up my engine build records and verified that I do indeed have oil squirters shooting oil up to the pistons, so that may explain at least some of the higher oil temperatures I am seeing. He said built they built IO-375s with and without squirters over the years and mine got them.
Anybody have an approximate figure as to how much temperature rise the squirters add to the oil temperature?
Randall
BillL
Well Known Member
Your 200F limit could be raised to 210/220 range without issue from oil degradation (oxidation) standpoint. I don't know about oil-to-bearing temps, but that would be indicated by the Lycoming limit.
Regarding your installation, something that might help more than a hose change is the sharp edge entrance and exit to that 4" hose. Vena contracta is where the flow "necks down" due to the sharp edge - effectively reducing the diameter by 20-30%. Depending on the velocity at entrance, (your pressure drop across the cooler will define that) you could easily see 20% increase in flow with a 1" diameter radius at the entrance. Probably a pain to make, but it would be cheaper than other changes. After you get pressure drop (and temp rise) data on that cooler it might be interesting to add the radius and quantify the improvement.
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"I performed Vx, Vy and straight and level flight testing to characterize the delta P before and after all my changes so I have the data to back up the relocation of the oil cooler."
Gaylon,
Can you post the results of the pressure delta across your cooler before and after the change?
That would give me a nice comparison since I am ready to fly and measure mine.
Randall
Gaylon,
Can you post the results of the pressure delta across your cooler before and after the change?
That would give me a nice comparison since I am ready to fly and measure mine.
Randall
Bill,
Thanks.
The vena conracta information is interesting, but like you say what a pain to build that into that rear baffle.
It would be somewhat easier to do the rounding of the entrance by making the entrance smaller but I suspect that would eliminate any possible gain.
I have a 4" flange mounted to the baffle. They should make it at 5" with the rounding built in, that would make it easy to deal with if there is room for the 5" flange. I notice the smaller 1" flanges have a small amount of rounding machined into them. I mounted them with the flange to the inside of the baffling to take advantage of it.
A machine shop might be able to turn one out on a lathe and then it could be mounted to the inside like I have done with the other little ones.
As for the SCAT vs SKEET, I have read that the rough corrugated interior of the SCAT effectively reduces the diameter of the tubing by some amount, maybe not 20% but I was hoping to see some difference.
Thanks.
The vena conracta information is interesting, but like you say what a pain to build that into that rear baffle.
It would be somewhat easier to do the rounding of the entrance by making the entrance smaller but I suspect that would eliminate any possible gain.
I have a 4" flange mounted to the baffle. They should make it at 5" with the rounding built in, that would make it easy to deal with if there is room for the 5" flange. I notice the smaller 1" flanges have a small amount of rounding machined into them. I mounted them with the flange to the inside of the baffling to take advantage of it.
A machine shop might be able to turn one out on a lathe and then it could be mounted to the inside like I have done with the other little ones.
As for the SCAT vs SKEET, I have read that the rough corrugated interior of the SCAT effectively reduces the diameter of the tubing by some amount, maybe not 20% but I was hoping to see some difference.
Rostra Vernatherm specifies a cracking pressure of 60 to 90 psi with oil at 195F. However, understand that cracking pressure is the result of several factors.
First, the vernatherm capsule must extend the plunger 0.160" between 160F and 185F.
Second, the depth of the vernatherm well must be 3.280", assuming a 0.0625" gasket under the head of the unit. If someone has cut a chamfer on the bypass opening, the well dimension would require reduction to compensate, as the valve cone would extend further into the hole.
Three, compressing the vernatherm's bypass spring 0.050" should require 15-20 lbs of force.
Given standard dimensions, the valve should seat at 183~187F. At the 195F given for cracking pressure, the valve is firmly seated and the bypass spring is slightly compressed. A bad capsule, an over-depth well, or a weak spring would all cause bypassing at some lower pressure, as would an off-center bypass opening or asymmetrical chamfer.
Am I saying any of these things are present with your installation? No.
Yes, it is efficient (more heat rejection for the same mass flows), probably a function of its high internal oil velocity stripping away more boundary layer. That's what you get in trade for the big pressure drop.
However, we're interested in total heat rejection. The operative words are "..at the same mass flows".
Go to the SW specs. If you look at the heat rejection plot of the 8432, you'll see it rejects 525 BTU at 55 lbs of oil flow and 45 lbs of airflow. The 10611 is 1.5 inches taller. The plot says it rejects about the same 525 BTU at 60 lbs oil flow and the same 45 lbs airflow. Wow...a cooler that big, and the same heat rejection? Nope.
Look at the air side pressure drops. The small face area of the 8432 requires 12.5" H2O to get that 45 lbs of airflow. The 10611 only requires 7.5" H2O to get the same 45 lbs of airflow.
At 125 KTAS in a climb, you'll be lucky to have a 5" H2O delta between upper and lower cowl volumes. At 5", the 8432 would only have about 27 lbs airflow, so heat rejection drops to 400 BTU. The 10611 would flow about 37 lbs air, so heat rejection would be about 475 BTU.
Bring on the monkeys!
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