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Ducts Matter

hgerhardt

Well Known Member
Years ago, after the original baffle-mounted SW 8406R oil cooler (OC) cracked the baffle a couple of times, the 2nd time also cracking a flange of the OC, I ‘upgraded’ to a remote-mounted SW 10599R fed by 4” SCAT into a little box plenum. That installation was hardly any better temp-wise than the original one, but passable except on very hot days. Well, decided to figure out how to improve on that.

Installed a pair of Bluetooth manometer probes and characterized first the upper/lower cowl deltaP, (7” WC at 155 KTAS) and then upper cowl/face of OC. Found the duct lost 3” WC, or almost half of available pressure! Wow, SCAT sucks. Measured the OC location-to-baffle relationship and designed new ducts with turning vanes and a bellmouth to be 3d printed from nylon-12 via HP MJF process.

Installed and flew with that and holy cow! I now have 0.85” OC duct deltaP, which is a huge improvement. According to the SW performance charts, that improvement ought to increase heat rejection from 350 to 420 BTU/min, or ~20% improvement. Hasn't been warm enough lately to really test the cooling improvement, but one thing is clear: the oil cools off significantly faster in descent than it did before. Also, #3 CHT is now ~10F cooler, despite stealing more of its cooling air. Apparently more air blowing over the tops of the fins helps.

OC duct 1.JPG OC duct 2.jpg
 
Cool! I'll be making a similar change as soon as I can do the testing to document what I have now.

It would be interesting to try that 90 turn without turning vanes and see how much difference they make.
 
very cool

The revolution in 3d design and printing is just starting, and this is one of the most impressive applications of that technology I've seen. I hope some day to use it for my snorkel. I'm sure I'm losing a lot there due to my crappy implementation. I bought one of my daughters a 3d printer hoping she would get into it, but it came DOA. Need to fix it and keep "nudging" her in the right direction. :D
 
Very nice work!

I've been planning to do something very similar this winter. My oil temps have always been at or near 185 during steady state cruise, but are marginal during climbs or slow flight in hot weather (might reach 210-220). I have only a 3" scat with a horrible transition to it above cylinder #4. It's surprising it has worked as well as it has.
 
Years ago, after the original baffle-mounted SW 8406R oil cooler (OC) cracked the baffle a couple of times, the 2nd time also cracking a flange of the OC, I ‘upgraded’ to a remote-mounted SW 10599R fed by 4” SCAT into a little box plenum. That installation was hardly any better temp-wise than the original one, but passable except on very hot days. Well, decided to figure out how to improve on that.

Installed a pair of Bluetooth manometer probes and characterized first the upper/lower cowl deltaP, (7” WC at 155 KTAS) and then upper cowl/face of OC. Found the duct lost 3” WC, or almost half of available pressure! Wow, SCAT sucks. Measured the OC location-to-baffle relationship and designed new ducts with turning vanes and a bellmouth to be 3d printed from nylon-12 via HP MJF process.

Installed and flew with that and holy cow! I now have 0.85” OC duct deltaP, which is a huge improvement. According to the SW performance charts, that improvement ought to increase heat rejection from 350 to 420 BTU/min, or ~20% improvement. Hasn't been warm enough lately to really test the cooling improvement, but one thing is clear: the oil cools off significantly faster in descent than it did before. Also, #3 CHT is now ~10F cooler, despite stealing more of its cooling air. Apparently more air blowing over the tops of the fins helps.

View attachment 3630 View attachment 3631

For those of us that don't have the technology to produce something like these, would you be interested in making another set for me to try?

Thanks,
 
That is really slick!
That's how you get into the RV parts business, LOL.
Now, if you could just make those vanes controllable for cold days....

I also would be interested in parts or the CAD files. Did you do this in SolidWorks?
 
Transitions

To me it looks like before you weren't using all of the cooler’s area due to the poor transition from scat tube to cooler. The new transition has a section forcing air to the edges. This probably really improves cooler performance.JMHO
 
....It would be interesting to try that 90 turn without turning vanes and see how much difference they make.

Your fellow Aero peers recommended the vanes. The increased blockage is overcome by superior airflow. But if you want to do a science experiment by growing a pair of elbows with/without vanes, I'd love to see your results!

..... I bought one of my daughters a 3d printer hoping she would get into it, but it came DOA. Need to fix it and keep "nudging" her in the right direction. :D

Yes, great idea!! Just keep in mind there are only about 2 processes which are suitable for growing end-use plastic parts for "underhood" applications: SLS and MJF.

I am interested in the source (where can I purchase) the Bluetooth manometer.

I'm using these manometer probes. They are sensitive to heat soak and drift a bit when hot, so get your data in the first 15 min of flight and you'll be good. I also have this kit which I bought to fine-tune refrigerant charge while flying my 'PlaneKool' A/C system. The temp probes from that kit are also good for measuring oil inlet/outlet temps in the oil cooler and comparing to indicated temp on your instrument panel so that you can check Vernatherm performance.

20200905_100504.jpg

For those of us that don't have the technology to produce something like these, would you be interested in making another set for me to try?

Send me your email via PM and I'll send you the .stl files which you can have made at 100's of vendors. Just realize that I designed these specifically for my installation as to the angles and flow directions. If you want to do this right, you ought to measure your airplane's installation and fine-tune the duct geometry. But you can use my files if you like too.

What's the purpose of the vanes? Stiffener? Another source of pressure drop.

The increased blockage of the vanes is overcome by superior airflow.

That is really slick!
That's how you get into the RV parts business, LOL.
Now, if you could just make those vanes controllable for cold days....

I also would be interested in parts or the CAD files. Did you do this in SolidWorks?

Send me a PM with your email and I'll get you the .stl files. I designed this on Siemens NX12, but SolidWorks would work fine too.

To me it looks like before you weren't using all of the cooler’s area due to the poor transition from scat tube to cooler. The new transition has a section forcing air to the edges. This probably really improves cooler performance.JMHO

How about the hugely increased deltaP through the cooler? But yeah, better flow quality would no doubt help too.
 

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With increased airflow going out and through the oil cooler, does that reduce airflow through the cylinders and cause a rise in CHT temps?
 
Your fellow Aero peers recommended the vanes. The increased blockage is overcome by superior airflow. But if you want to do a science experiment by growing a pair of elbows with/without vanes, I'd love to see your results!

Whether or not the vanes help or hurt depends on a lot of factors. One of those factors is the camber and location of the vanes. It doesn't look like yours are cambered at all?

It would be fun to try it. I was going to use Scott McDaniels' idea for an elbow and use a rubber inner tube from an RV-10. Nice smooth surface and a bit more generous radius.
 
With increased airflow going out and through the oil cooler, does that reduce airflow through the cylinders and cause a rise in CHT temps?

#3 CHT is running ~10F cooler than before, the rest the same. I expected a little warmer on 3...
 
Whether or not the vanes help or hurt depends on a lot of factors. One of those factors is the camber and location of the vanes. It doesn't look like yours are cambered at all?

It would be fun to try it. I was going to use Scott McDaniels' idea for an elbow and use a rubber inner tube from an RV-10. Nice smooth surface and a bit more generous radius.

My vanes are not cambered at all, but they are aligned to free-stream. Cambering would have increased blockage but better aero would have probably overcome that; but I did area-distribute them such that the inscribed section of the inner-most vane has the least area and the outer radius the most and those individual areas increase as you go out. I just copied contemporary HVAC duct design as to vane location.

But if you want to do a real test you could have 3 elbows grown with cambered vanes and un-cambered vanes and without vanes just to satisfy your itch. A comparison like that would tell you far more than just using an inner tube and guessing how it might have flowed with vanes. Would cost you about $400 to have 3 flight-worthy elbows made from SLS or MJF nylon-12. With a ground-only test, you could instead grow them from a cheaper process like our own Steve Melton uses.

While science experiments are fun, how much more could you really gain over what I did? You're splitting hairs at this point. I've got .8" WC loss at the oil cooler face vs 3" with SCAT. A different vane arrangement might net you another .1" at best? Which might get you another 5 BTU/min heat rejection?
 
Turning vanes are pretty common in ducts. Every closed circuit wind tunnel I’ve seen has them. Optimizing them is I’m sure a very deep subject and poorly designed ones might be worse than none. But if it’s working well then go with it!
 
A rounded leading edge with a tapered trailing edge and a constant thickness everywhere else is probably good enough.
 
My vanes are not cambered at all, but they are aligned to free-stream. Cambering would have increased blockage but better aero would have probably overcome that; but I did area-distribute them such that the inscribed section of the inner-most vane has the least area and the outer radius the most and those individual areas increase as you go out. I just copied contemporary HVAC duct design as to vane location.

But if you want to do a real test you could have 3 elbows grown with cambered vanes and un-cambered vanes and without vanes just to satisfy your itch. A comparison like that would tell you far more than just using an inner tube and guessing how it might have flowed with vanes. Would cost you about $400 to have 3 flight-worthy elbows made from SLS or MJF nylon-12. With a ground-only test, you could instead grow them from a cheaper process like our own Steve Melton uses.

While science experiments are fun, how much more could you really gain over what I did? You're splitting hairs at this point. I've got .8" WC loss at the oil cooler face vs 3" with SCAT. A different vane arrangement might net you another .1" at best? Which might get you another 5 BTU/min heat rejection?

The key point is that the turning vanes are supposed to actually help turn the flow. They help prevent the flow from separating on the inside of the turn and piling up against the outside of the turn. But it looks like yours are just straight vanes completely upstream of the turn. They divide the flow up but do not initiate any turning. (assuming I am interpreting the shape correctly from the pictures)

If the velocities are low (because the diameter is large) then there is not much to lose in any case, and certainly your measurement is such a low loss that it is probably unimportant to go after additional improvement, even if well-designed TURNING vanes could get the total loss down to 0.3" H2O. Would that be enough of a change to be worth it?
 
Just keep in mind there are only about 2 processes which are suitable for growing end-use plastic parts for "underhood" applications: SLS and MJF.

If you don't mind, how much did it cost to print these? I've been mocking up some duct adapters but I was planning on printing a plug in PLA and making the flight article from fiberglass.

I was also thinking of modding my printer to run nylon but that might not be feasible...
 
Data!

#3 CHT is running ~10F cooler than before, the rest the same. I expected a little warmer on 3...

Interesting story -- thank you for the data points;

15 years ago, I went through almost the exact same exercise: RV-7 with IO-360-A1B6 (200HP Angle Valve) and a too small OC mounted at the rear of the #4 baffle. After cracking the baffle and OC flange, I upgraded to a remote mount SW 8406R OC and used a hand formed duct-to-oil-cooler transition and SCEET ducting. The oil temps dropped to 180F in full power cruise (+24", 2600RPM, 12GPH ~8000DA) and the CHT for #4 was ~20°F cooler than the hottest cylinder.

Flash forward to today: different RV-7, same motor, SW 10599R-T OC with custom duct transition and SCEET ducting. The oil temps are 185-195F at similar power settings, but the CHT for #4 is again ~20°F cooler than the hottest cylinder.

After looking at your post, I have come to a similar conclusion - the duct above the cylinder has a tendency to lower that cylinders temperature - perhaps the movement of air across the top of the fins and whatever acceleration or clean up of the flow causes this.

In any case, it's time for real data -- digital bluetooth manometer purchased and will be here tomorrow!
 

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The key point is that the turning vanes are supposed to actually help turn the flow. They help prevent the flow from separating on the inside of the turn and piling up against the outside of the turn. But it looks like yours are just straight vanes completely upstream of the turn. They divide the flow up but do not initiate any turning. (assuming I am interpreting the shape correctly from the pictures)

If the velocities are low (because the diameter is large) then there is not much to lose in any case, and certainly your measurement is such a low loss that it is probably unimportant to go after additional improvement, even if well-designed TURNING vanes could get the total loss down to 0.3" H2O. Would that be enough of a change to be worth it?

Apparently looks can be deceiving. Here's a cross-section and translucent image of the CAD model. As I said, the fins are fully radiused at the leading edge and tapered somewhat at the trailing edge.

Probably the biggest source of restriction now is the short section of scrunched-up SCAT to allow for engine movement. What I need to look for is a rubber accordion section like you'd find in a car intake system.

OC duct trans.jpgOC duct x-sec.jpg
 
If you don't mind, how much did it cost to print these? I've been mocking up some duct adapters but I was planning on printing a plug in PLA and making the flight article from fiberglass.

I was also thinking of modding my printer to run nylon but that might not be feasible...

These 3 parts cost $400 at 3d Hubs.
$400 sounds like a lot of $$$ for some plastic parts. But the labor involved with making something like this from fiberglass (and nevermind trying to integrate vanes into that), makes 0.4 AMU's totally worth it.
 
Years ago, after the original baffle-mounted SW 8406R oil cooler (OC) cracked the baffle a couple of times, the 2nd time also cracking a flange of the OC, I ‘upgraded’ to a remote-mounted SW 10599R fed by 4” SCAT into a little box plenum. That installation was hardly any better temp-wise than the original one, but passable except on very hot days. Well, decided to figure out how to improve on that.

Installed a pair of Bluetooth manometer probes and characterized first the upper/lower cowl deltaP, (7” WC at 155 KTAS) and then upper cowl/face of OC. Found the duct lost 3” WC, or almost half of available pressure! Wow, SCAT sucks. Measured the OC location-to-baffle relationship and designed new ducts with turning vanes and a bellmouth to be 3d printed from nylon-12 via HP MJF process.

Installed and flew with that and holy cow! I now have 0.85” OC duct deltaP, which is a huge improvement. According to the SW performance charts, that improvement ought to increase heat rejection from 350 to 420 BTU/min, or ~20% improvement. Hasn't been warm enough lately to really test the cooling improvement, but one thing is clear: the oil cools off significantly faster in descent than it did before. Also, #3 CHT is now ~10F cooler, despite stealing more of its cooling air. Apparently more air blowing over the tops of the fins helps.

View attachment 3630 View attachment 3631

If someone produced similar ducting for the RV-10 set up, I would buy them tomorrow !!!
 
Whether or not the vanes help or hurt depends on a lot of factors. One of those factors is the camber and location of the vanes. It doesn't look like yours are cambered at all?

... and use a rubber inner tube from an RV-10. Nice smooth surface and a bit more generous radius.

Or use SCEET tubing instead of SCAT, which would likely help the OP's flow a little more.
 
Apparently looks can be deceiving. Here's a cross-section and translucent image of the CAD model. As I said, the fins are fully radiused at the leading edge and tapered somewhat at the trailing edge.

Probably the biggest source of restriction now is the short section of scrunched-up SCAT to allow for engine movement. What I need to look for is a rubber accordion section like you'd find in a car intake system.

View attachment 3674View attachment 3675

Beautiful parts !!!
 
Are there any RV'ers that could make me a set?

I'll give you the stl files and then you can upload them at 3dHubs.com and have a set grown for yourself. Easy-peazy. Just give me an email to send the files to.

Or are you asking if someone will design a set specifically for your installation?
 
Very true, but with your new ducting, that short piece could be replaced with sceet.

Sorry, misunderstood your question. I bought the SCEET specifically for that short piece. However, that joint has to compress and expand; that's why the room for the duct is 3" and I cut the SCAT to 4" and compressed it an inch to allow for that.

SCEET in its relaxed state is nice and smooth; you're right. But, if you compress it in length, it has bigger bumps internally than SCAT does.

What I really need here is a rubber bellows like you'd find in a car intake system.
 
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Apparently looks can be deceiving. Here's a cross-section and translucent image of the CAD model. As I said, the fins are fully radiused at the leading edge and tapered somewhat at the trailing edge.

Probably the biggest source of restriction now is the short section of scrunched-up SCAT to allow for engine movement. What I need to look for is a rubber accordion section like you'd find in a car intake system.

View attachment 3674View attachment 3675

Ah, I see. Thanks. Yes, in the pictures it is not evident that the vanes are really dividers that go all the way through the turn.
 
Cool! I'll be making a similar change as soon as I can do the testing to document what I have now.

It would be interesting to try that 90 turn without turning vanes and see how much difference they make.

When I worked in the power industry, I got to see the difference on a large scale. We had adjacent scrubbers, with 20 foot diameter inlet ducts. In one, the turning vanes had corroded away, in the other they had just been replaced. The fans pulling gas through those scrubbers operated at significantly different loads. I can't recall exactly how much different, but I seem to remember a significant bias (several percent) in the fan damper demands. On a 9,000 hp fan, that means a lot!
 
This is a wonderful application for 3d printing--I have been looking for ways to use my printer to improve potential performance and looks on my RV-10. I'd love to be able to give these a try.
 
Info source.

hgerhardt,


Do you have a link on the knowledge source you used to figure out how to design the vanes (spacing, etc.)?


thanks
 
I put a single turning vane in this elbow, but it was strictly TLAR design, and I have no idea if it was really needed or not.

The 3-D printed parts are lovely, but a simple glass duct built on a foam form is a whole lot easier on the budget.
.
 

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hgerhardt,
Do you have a link on the knowledge source you used to figure out how to design the vanes (spacing, etc.)?
thanks

I work with aerodynamicists and propulsion engineers. They all said I need to use vanes. None had had any rules-of-thumb, so went to my friend google and got the below. From that deduced that the inscribed areas between the vanes should increase as the radius gets larger.
Screenshot 2020-10-23 112724.jpg
 
Interesting

I would tend to think turning vanes would not want to be spaced like that. The balance you are trying to strike is the wall losses of the turning vane against the pressure loss caused by airflow going around a corner. The tighter radius would have a higher delta P, so to offset I would have guessed that the spacing between the vanes would be the exact opposite, and be wider at the small radius. But I believe you're well into the second-order effects at this point. The big gains were made by replacing the rough SCAT tubing with a smoother wall 3D printed part. The next gain was putting in any turning vane at all. The spacing and number of those vanes you're definitely into the diminishing returns portion of the show.

Caveat: I am not an aerodynamicist, but have done modeling and testing or gas flows for process equipment (spray dryers, mostly), as well as portions of my airplane, including CFD using Fluent. There is a lot of work on gas flows in elbows, especially in cases where particulate is carried in the flow, as it leads to erosion of the outside of the elbow and failure of the piping. We also could not use turning vanes, due to cleanability and cleaning verification requirements. There are various ways of addressing this that have to do with expanding or contracting the pipe diameter and/or changing the circular cross section. But most of those solutions take up more space than you have available.
 
Years ago, after the original baffle-mounted SW 8406R oil cooler (OC) cracked the baffle a couple of times, the 2nd time also cracking a flange of the OC, I ‘upgraded’ to a remote-mounted SW 10599R fed by 4” SCAT into a little box plenum. That installation was hardly any better temp-wise than the original one, but passable except on very hot days. Well, decided to figure out how to improve on that.

Installed a pair of Bluetooth manometer probes and characterized first the upper/lower cowl deltaP, (7” WC at 155 KTAS) and then upper cowl/face of OC. Found the duct lost 3” WC, or almost half of available pressure! Wow, SCAT sucks. Measured the OC location-to-baffle relationship and designed new ducts with turning vanes and a bellmouth to be 3d printed from nylon-12 via HP MJF process.

Installed and flew with that and holy cow! I now have 0.85” OC duct deltaP, which is a huge improvement. According to the SW performance charts, that improvement ought to increase heat rejection from 350 to 420 BTU/min, or ~20% improvement. Hasn't been warm enough lately to really test the cooling improvement, but one thing is clear: the oil cools off significantly faster in descent than it did before. Also, #3 CHT is now ~10F cooler, despite stealing more of its cooling air. Apparently more air blowing over the tops of the fins helps.

View attachment 3630 View attachment 3631

It's probably mentioned somewhere, but I didn't see it:

What did you print these out of? ASA? PETG?
 
It's probably mentioned somewhere, but I didn't see it:

What did you print these out of? ASA? PETG?

I used the HP-MJF process with nylon 12 (PA-12) for these ducts.

For hot "underhood" applications such as this, I'd only use the HP-MJF or SLS processes with nylon 12. With all the various vendors out there nowadays, it's so easy to email your stl file, wait a week, and have robust, high-quality parts.
 
I used the HP-MJF process with nylon 12 (PA-12) for these ducts.

For hot "underhood" applications such as this, I'd only use the HP-MJF or SLS processes with nylon 12. With all the various vendors out there nowadays, it's so easy to email your stl file, wait a week, and have robust, high-quality parts.

It would be interesting to find out if this could be printed in PA-CF (nylon carbon fiber) filament. I have a couple of rolls I'd like to try out.
 
Would love to have this for a -10.

This is really great work!

Anyone grabbing these files and modifying them for a RV-10 install? I would like to explore this approach when I get there.
 
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