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Anyone use louvers to aid in cooling?

Worked great on my F1 for lowering CHTs during climb on a hot summer day.

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Yep, I'm using them. I tape them up on the inside during the winter, all of two months. They sure do help in hot summer climb.
 
Hi Tony,

I installed a cut down version of the louvers shown on the Rocket. I cut mine down to 6 openings per side and installed on the l and r bottom of my RV9a cowl just forward of the fw. I made an aluminum "collar/frame" that has the platenuts on it and mount the louver on the outside attached through the fg of the cowl to the collar on the inside of the cowl using #6 flush ss screws. This way the collar plus the louver "sandwich" the cowl. I use these in the summer and use a blank piece of aluminum over the opening (same size as louver and attached the same way) during the winter. Since the pic I have painted both the louvers and the winter blank to match the plane. The louvers dropped my oil temps, speaking from memory here, about 10 degrees and my chts slightly. If they affected cruise speed it is so small that it is not measurable--and I tried to measure it with before and after runs in similar conditions.

rvdetails015.jpg


Hope this helps.

Cheers,

db
 
Didn't work for me

I installed them on the bottom of the cowling on my RV-4 and my oil temps went up. I read something somewhere about the bottom of the cowl being a high pressure area. Because of that and the increased temps, I removed them. Temps went back to where they were. Slightly high.
 
yes. Helped with CHTs (about 20 deg), but not with the oil temps (firewall mounted cooler). I feel the A's just have too much junk in front of that cowl exit.
I think I lost about 1mph.
 
Before you go to the trouble of mounting louvers, you may want to verify that the lack of exit air is the reason for your high temps. Most installations suffer from a disruption of the airflow into the pressure side (upper) of the cooling plenum. For me and many others, smoothing out that flow has resulted in a significant reduction, almost to the point of too cool. I tweaked the openings on my Rocket and smoothed the top transition and lowered my cylinder temps 40 dF!

Now if you like the look of the louvers, then I doubt it will hurt you and if you are constrained on the output side, the louvers will help. Anecdotal exidence suggests that there are a lot of A models flying that do not have louvers and do not have a problem with high temperatures so I suspect that you can probably fix your problem without them.

I'm not knocking anyone who has used them. Some of the installs are pretty cool, and I'm specifically thinking of Larry Vetterman's solution. If you were going to do it, I'd check out his solution.
 
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f1rocket said:
Before you go to the trouble of mounting louvers, you may want to verify that the lack of exit air is the reason for your high temps. Most installations suffer from a disruption of the airflow into the pressure side (upper) of the cooling plenum. For me and many others, smoothing out that flow has resulted in a significant reduction, almost to the point of too cool. I tweaked the openings on my Rocket and smoothed the top transition and lowered my cylinder temps 40 dF!

Now if you like the look of the louvers, then I doubt it will hurt you and if you are constrained on the output side, the louvers will help. Anecdotal exidence suggests that there are a lot of A models flying that do not have louvers and do not have a problem with high temperatures so I suspect that you can probably fix your problem without them.

I'm not knocking anyone who has used them. Some of the installs are pretty cool, and I'm specifically thinking of Larry Vetterman's solution. If you were going to do it, I'd check out his solution.
Click to expand...

I totally agree, Randy! The first thing is to make sure all of the cooling system elements, such as the baffling, are doing their job. Having good cooling design on the top of the engine and then just expecting the air to find its way out on the bottom is to do only half of the job. Just dumping the output of the oil cooler into the region in front of the firewall is not good design. Outlets should be designed to handle the flow just as well as the inlets. Placing a contracting duct from the outlet of the cooler into a rear-facing opening of about 3-4 sq. in. will solve your oil temp problems. Oh; and louvers are not as good as a single rear-facing opening! Will they work? Probably. But are they as efficient? Definitely not! Anything that's not efficient makes drag!
 
I installed two louvers, one on each side bottom of the cowling on my RV7. They only helped a little in lowering my CHT's, about an avg of 5 degrees. I tried a lot of different things trying to get my temps down and what worked the best ended up being the easiest, cheapest, and quickest solution.

Look at the lower baffles where they wrap around the cylinders. There is probably a gap between the baffle and cylinders so all that sweet cooling air is not flowing through the cooling fins of the cylinder and escaping out the sides. I was helping a friend do some work on his Tiger and saw that on his these lower baffles were sealed with RTV to the cylinder. At that point I had tried many things along with lots of time and money so why not. Not even half a tube of RTV later my CHT's dropped an avg of 40 degrees.

Give this a try before all the work of installing the louvers.
 
I do have all my baffles sealed up well. I will work to smooth the inlets a bit. Louvers seem like they will help.
 
oil temp

I was just thinking about this. I was thinking about putting it on the top of the cowl. If I remember the top is low pressure the bottom is high. I have the oil cooler behind #4. If I mount the louvers just aft of the oil cooler I think it would drop oil temp. It could raise CHT but mine are low.
 
Tony,

Before you make any big changes, consider that you are still breaking in a new engine, and they tend to run a little warm while the rings seat. Give it another 10 hours or so and see what happens. Also check your baffles like others have suggested.

Did you calibrate the oil temp sender?

A O-320 powered -9 with a fixed pitch prop just doesn't seem like an installation that would require louvers.
 
Has anyone had any experience with using louvers on a Sam James cowl?
My oil temp is fine but my CHTs run high.
My intakes are attached with about 4 inches of accordian type hose to the plenum.
Would this make any difference?

Thanks,

GP
 
Hi GP,

The picture of the red RV9a in this thread is on a Sam James cowl. However, it is on the older long cowl which did not have the honeycomb core.

You indicated you were using "accordian type hose"--are you referring to orange SCEET or SCAT hose?? If yes, I would recommend you go with the rubber system James recommends which is very smooth on the inside. Also, as others have said, before you add louvers, be sure you have a good seal on your James plenum to engine attach, a good seal and the appropriate size openings for the lower baffles, a smooth track for inlet air, and as clean as possible an outlet area.

Cheers,

db
 
another area to look at...

I think that the seal at the top of the engine behind the flywheel is often over looked. A lot of cooling air can escape from the high pressure top of the cowl out behind the spinner if this is not sealed correctly.

Kent
 
kentb said:
I think that the seal at the top of the engine behind the flywheel is often over looked. A lot of cooling air can escape from the high pressure top of the cowl out behind the spinner if this is not sealed correctly.

Kent
Click to expand...

Right on, Kent! I have a friend with an RV-8 that was running much higher temps and he found that the seal you mention had gotten turned forward and was allowing the air out.
 
sprucemoose said:
Tony,

Before you make any big changes, consider that you are still breaking in a new engine, and they tend to run a little warm while the rings seat. Give it another 10 hours or so and see what happens. Also check your baffles like others have suggested.

Did you calibrate the oil temp sender?

A O-320 powered -9 with a fixed pitch prop just doesn't seem like an installation that would require louvers.
Click to expand...

Thanks Jeff,

I spent several hours today redoing my baffle seals. I thought they were pretty good, but found that in fact, there were several leaks. Also, I can see the the inlets are difficult to seal up. I used foil tape and sealed it really well and found the my temps maxed at 198 (versus 215 before).

Still a bit warm, but definitely better, much better. At this point I feel comfortable where there at and I can begin to focus on progressing through my flight testing.

I ordered a set of louvers and am pretty sure I will install them. I am going to wait till I am out of Phase I, so that I have a good baseline set of data.

I still see my CHT's getting warm (430's). I think the louvers will do well to bring them down a bit.
 
apkp777 said:
I ordered a set of louvers and am pretty sure I will install them....... I think the louvers will do well to bring them down a bit.
Click to expand...

Some people just like that Bonanze look! :D

Two things you can check to see if it helps. You might trim the output opening back an inch or two to increase the outlet size. I did that on my RV-6 and it helped. Also, make sure on the inlet on your right side that you can easily fit your hand up inside. The cylinder is pretty close and if you don't trim the upper cowl lip back, the air pressure can build up here and really limit the flow over the cylinders on this side.
 
f1rocket said:
Some people just like that Bonanze look! :D

Two things you can check to see if it helps. You might trim the output opening back an inch or two to increase the outlet size. I did that on my RV-6 and it helped. Also, make sure on the inlet on your right side that you can easily fit your hand up inside. The cylinder is pretty close and if you don't trim the upper cowl lip back, the air pressure can build up here and really limit the flow over the cylinders on this side.
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Thanks Randy, I am focusing on the inlets. That seems to be where the problem is. I've taped up the inlets to smooth things out. I will glass it all when I find the contour I want. I am pretty happy with where I am at for now. The engine only has about 8 hrs tach time, so it might come down on its own a bit.
 
Not sure I would want much cooler oil temps.

I have no idea why people want their oil temps much bellow 190?.

Heating it up helps rid the oil of moisture and other nasty stuff that builds up.

Most people change the oil in their engines way before it actually breaks down so I doubt running in the 200? range is ever going to cause any problems and in fact most likely will prevent some.

Now if your one of those people that go 100+hrs on an oil change, that might be different....
 
Brantel said:
Not sure I would want much cooler oil temps.

I have no idea why people want their oil temps much bellow 190?.

Heating it up helps rid the oil of moisture and other nasty stuff that builds up.

Most people change the oil in their engines way before it actually breaks down so I doubt running in the 200? range is ever going to cause any problems and in fact most likely will prevent some.

Now if your one of those people that go 100+hrs on an oil change, that might be different....
Click to expand...

I am really targeting 190. Still a bit high though at 198-200. I agree that 180 seems low. I was up in the 215-220 range, that was too high.
 
elippse said:
Placing a contracting duct from the outlet of the cooler into a rear-facing opening of about 3-4 sq. in.!
Click to expand...

Paul,
3 to 4 square inches? thats all? I am about to do a duct off my oil cooler and if thats all the outlet size needs to be, that will be much easier.
 
apkp777 said:
I am really targeting 190. Still a bit high though at 198-200. I agree that 180 seems low. I was up in the 215-220 range, that was too high.
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If I'm between 180 & 200, I feel great! With the Van's cooler shutter, I can raise winter temps from 150 ......up to 200-205 F. 180 is not to low, as water evaporates at these temps (previously mentioned) and doesn't require boiling.

Look up Lycoming's thoughts on engine temps. They say about the same thing.

L.Adamson ---- RV6A
 
Why 215 F

f1rocket said:
I'm not sure this is true. I believe sustained oil temp over 200 F is less than ideal, although it is within the normal operating range for a Lyc.
Click to expand...

I got this from a guy I know here in Montana who runs over 15 planes in his business, mostly for pipeline inspection. He had all kinds of cam wear/pitting problems until they started blocking off the oil coolers to achieve 215 F. Now they go past TBO with zero cam problems. These are planes that run regularly. He told me he thought that it was because it boiled all the water out of the oil.

Hans
 
C-FAH Q said:
Paul,
3 to 4 square inches? thats all? I am about to do a duct off my oil cooler and if thats all the outlet size needs to be, that will be much easier.
Click to expand...

Don't fixate on size and forget the "contracting" part. And as I recall, Paul runs a dedicated cooler intake. Compared to a back baffle air source, I'll bet he has higher pressure available at the cooler and thus at the cooler duct exit.
 
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Oil Temps to Remove Moisture:

Ref the discussion on oil temps and what is required to remove moisture.

My understanding is that Lycoming references 180 degrees as a good temp because of the location of our temp probes. Most of us have the temp probe located on the back of the engine in close proximity to the return line for the oil cooler. Due to this proximity, the oil temp at this location is not what the oil temp is in the engine case---the engine case oil could be as much as 25 degrees hotter--plenty hot to boil off any moisture--especially at altitude since the boiling point goes down as you gain altitude. After hearing this I was still skeptical so I flew the plane, landed, noted the oil temp just before shut down, removed the dip stick, attached a digital temp probe to it, and ran it down into the crankcase. Sure enough it was still significantly hotter than the temp gauge showed prior to shutdown--and yes the guage had been verified for accuracy.

You can also look at the Lyc schematic on the oil circulation. That probe location may be the coolest spot on the engine!!

Maylon or one of our engine builders could probably shed more light on this and please correct me if any of this is in error.

Cheers,

db
 
db1yg said:
Oil Temps to Remove Moisture:

Ref the discussion on oil temps and what is required to remove moisture.

My understanding is that Lycoming references 180 degrees as a good temp because of the location of our temp probes. Most of us have the temp probe located on the back of the engine in close proximity to the return line for the oil cooler. Due to this proximity, the oil temp at this location is not what the oil temp is in the engine case---the engine case oil could be as much as 25 degrees hotter--plenty hot to boil off any moisture--especially at altitude since the boiling point goes down as you gain altitude. After hearing this I was still skeptical so I flew the plane, landed, noted the oil temp just before shut down, removed the dip stick, attached a digital temp probe to it, and ran it down into the crankcase. Sure enough it was still significantly hotter than the temp gauge showed prior to shutdown--and yes the guage had been verified for accuracy.

You can also look at the Lyc schematic on the oil circulation. That probe location may be the coolest spot on the engine!!

Maylon or one of our engine builders could probably shed more light on this and please correct me if any of this is in error.

Cheers,

db
Click to expand...

Thanks for testing that. It's conventional wisdom and mostly legend that drove the idea of higher oil temps to evaporate moisture.

I think one of the problems some people have with corrosion is when the plane is only used for a short flight and the temps never really get up at all.

It makes perfect sense however that 180 at the gauge is probably 200-220 at the hot point of the engine. I am not sure the temperature that oil really begins to break down, but I am sure it's gotta be near 300 or so.

Fortunately, it seems that my high oil temp situation is stabilizing. I just got back from 2.6 hours of flying at high power settings 70 degree OAT's at altitudes and never saw the temps go above 195. What a relief on that one. BUT, now I am looking at my CHT's and finding that the temps get pretty hot in the climb (440). Thus the subject of my original question. Should I use louvers to help with the CHT's.
 
Tony, if you are 13 hours on a new engine....wait a bit. Let the engine break in before fixing cooling problems that may go away.
 
DanH said:
Don't fixate on size and forget the "contracting" part. And as I recall, Paul runs a dedicated cooler intake. Compared to a back baffle air source, I'll bet he has higher pressure available at the cooler and thus at the cooler duct exit.
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I have an SW10578B cooler on my plane, with four oil modules-five air channels. It calls for 20lb/min of cooling air at the center of the chart. The six oil module-seven air channel model would probably require 50% more or 30 lb/min for a 180 HP engine. With air at 0.076 lb/cu ft, this would require a flow of 392 cfm, 6.54 cfs. At 190 mph, 278 ft/sec, that would require an inlet area of 3.38 sq. in. into the free-stream. With a cooling air temperature rise of 100F above ambient, the outlet area would need to be 4 sq. in. to have the outlet velocity match free-stream. The pressure drop on mine at chart center is 6" H2O. At 190 mph, 8000' density altitude, stagnation pressure is 1.025" Hg, or about 14" H2O, which should be more than adequate to give the required flow.
 
elippse said:
At 190 mph, 278 ft/sec, that would require an inlet area of 3.38 sq. in. into the free-stream. With a cooling air temperature rise of 100F above ambient, the outlet area would need to be 4 sq. in. to have the outlet velocity match free-stream.
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Paul, I'm sorry but after consideration I must question the above sizing recommendation.

Assuming 190 mph and 8000 feet doesn't reflect the reality of hot day climb....lower dynamic pressure and higher standard air temp. That's the critical requirement for an oil cooler.

At 190 mph, I think you also neglected the effect of the 6" H2O pressure drop across the cooler.

The above also assumes you have 100% dynamic pressure recovery....which isn't valid unless you build an excellent external intake dedicated to the oil cooler. As previously noted, full pressure isn't available with an air source tapped from the rear baffle wall.

A 3.38 sq in inlet is roughly 2" diameter. A 4" sq in exit is about 2.25" diameter. Don't want anyone thinking they can plumb their oil cooler with 2" SCAT off the rear baffle.......;)
 
full of hot air

I realize that a small scat tube will probably not work for me off my rear baffle mounted cooler. The actual size cut out of my rear baffle is 4x3 inches. I am not having cooling issues with my 200 hp angle valve at this time, but rather am looking at cleaning up the airflow for some speed. I am in mid form of my airbox that will mount to the back of my cooler and plan on using a 3" scat tube routed down to the lower cowl exit area between the exhaust pipes. If that works, great, if not, will try a 4 inch scat tube. So far the foam block looks like a peice of free form art that was sculpted by chance.;)
 
I thought this was an interesting bit from the article referenced earlier

"One more finding from the NACA reports; to further aid cooling, you should paint the engine with a VERY thin black enamel. The paint should not be thicker than .002 " This will improve cooling by three (3) percent over bare metal. If the paint is thicker than .005" you get no benefit and in fact thicker paint will insulate the cylinders. Use black RTV for the wraps and paint everything under the cowling with a thin coat of black high temperature grill paint. "

Also, am I the only one that takes several days to figure what DanH is talking about? That guy is a genius.
 
DanH said:
Don't want anyone thinking they can plumb their oil cooler with 2" SCAT off the rear baffle.......;)
Click to expand...

I totally agree, Dan! Anyone who uses corrugated tubing anywhere in a cooling airstream is asking for trouble. I'm all for people taking the time to build smooth, diverging or contracting ducts for their induction, engine, and oil cooling flow. What I keep trying to point out is that the airplane, for all of its beautiful paint job, is just a half-vast project if you ignore good aerodynamics for cooling! The plenum has high-pressure, low velocity air. Using corrugated tubing of a cross-sectional area smaller than the oil cooler inlet face means that you will not get adequate flow. This is because in going from a smaller area to a larger area requires the flow to slow down, and the effective cross-sectional area of this kind of tubing is much less than its measured dimension. Then dumping the outlet in front of the firewall without making a nice converging duct that points to the rear outside of the cowling further adds inefficiency. I have one acquaintance that was always having trouble with hot engine and oil temps on climbout, but he wouldn't reshape the cowling to stop the problem, as he didn't want to ruin his paint job. I have another acquaintance who races at Reno. He has dual turbosuperchargers with long runs of corrugated tubing from the air inlets to the turbo. As far as he's concerned, the turbo suction will make up for the pressure drop through the tubing. But the compressor outlet temperature will be higher since it is based on the inlet-outlet pressure ratio, which means he will need additional inter-cooler air which means more drag!
One of the things that we have going for us on takeoff and initial climb is that it takes a while for the engine and oil to get hot, since the engine has so much thermal mass. During this time we get additional cooling from the rich mixture at the lower altitudes and higher power settings. You can see this reflected when you look at the engine charts of cooling air requirements vs power and altitude. It takes just about as much cooling flow at 75% power lean as it does at 100% power rich. Plus guys using FP props seldom operate anywhere near 100% power. Mine runs 79% static and 86% at rotation and initial climb under sea-level conditions. Either design and build the cooling system right initially or suffer the consequences in over-heating and/or more drag and have to apply band-aids such as louvers and such!
 
SCAT is also very bad for airflow because of the corrugations. They set up a lot of resonate waves resisting flow. The exact loss over a smooth walled "pipe" vs a corrugated one will be hard to predict due to flow rates, velocty, duct length, curves etc. But it can be huge.

My oil cooler is ducted off of a rectangular hole in the back left baffle (stock Van's cowling inlets feeding a modified Sam Jame's plenum) that is about 2.5" x 3.5". The smooth rectangular duct is gently curved 45 degrees down and gradually opening to the size of the entire face of the oil cooler. I use a generally poorly regarded Posi-tech cooler that gives me great cooling - 200 degrees max during long climb outs on hot days. I must reduce cooling flow (via a duct mounted door) for all other flight regimes to get oil temps above 165.

Improved design does work. I will be continuing work towards reduced drag as time and motivation permit. Thanks to inspiration in threads like this. Hope to get some data at the SARL race in July.
 
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f1rocket said:
I'm not sure this is true. I believe sustained oil temp over 200 F is less than ideal, although it is within the normal operating range for a Lyc.
Click to expand...
Sometime ago, I called a Lycoming tech rep and was informed that 180? is considered the ideal oil temp. That phone conversation validated what I found inside my copy of the Lycoming engine operating manual:

OPERATING CONDITIONS

*Oil Inlet Temperature

Average
Ambient Air Desired Maximum
Above 80?F 180?F (82?C) 245?F (118?C)
Above 60?F 180?F (82?C) 245?F (118?C)
30? to 90?F 180?F (82?C) 245?F (118?C)
0? to 70?F 170?F (77?C) 245?F (118?C)
Below 10?F 160?F (71?C) 245?F (118?C)
 
Is there a replacement for corrugated scat tubes available?
Click to expand...

SCEET tube....like SCAT but has a liner. Not perfect, certainly better.

My oil cooler is ducted off of a rectangular hole in the back left baffle ...that is about 2.5" x 3.5". The smooth rectangular duct is gently curved 45 degrees down and gradually opening to the size of the entire face of the oil cooler.
Click to expand...

Nice Gary! Do post a picture if you have one. It's the sort of very practical thing anyone can do.
 
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Sat down this AM with some code written (by a qualified friend) for liquid/air heat exchangers. The analysis revolved around a 30 lb/min air mass requirement, more or less the center of the chart for a SW 8432 or 10599. What sort of inlet and exit size is required? For these examples I used a 3-1/2" diameter inlet, an arbitrary selection. The math assumes the cooler has its own dedicated external inlet and exit.

In climb (100 mph):
30 lbs/min is 0.5 lbs/sec (wdot), so the exit requirement (a6) is 0.10 sq ft, 14.4 sq in or a diameter of about 4.3".



At WOT (200 mph for an average RV):
The 0.10 sq ft exit is now too big, flowing 0.84 lbs/sec. Just like a cowl exit, it could be throttled. A smaller exit would reduce mass flow and increase velocity, decreasing cooler drag.



And like Forrest, that's all I have to say about that.
 
exit air

So,
Let me pose another question/scenario......
Instead of letting the air from a baffle mounted cooler, just dump into the firewall area, and assuming that it would be next to impossible to build a smooth duct system to route the air to the lower rear cowl, which would be a better choice for the most air flow and least drag?

A) Not changing and let it dump to the firewall area or
B) Routing the exit air from the cooler out the side of the cowling in front of the wing?

Note, I do not have cooling issues, but rather I am trying to decrease cooling drag to gain some speed. Once I find a reasonable exit solution I realize that I can start to decrease my inlet sizing.
 
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Oil Cooler Outlet

When my friend installed an O-320 in his Lancair 235, from whom I was able to purchase his previous O-235, he tried using the oil cooler which I now have. 'Not good! So he purchased the larger cooler and we mounted it vertically on the firewall with a NACA duct on the side of the cowling feeding it. The outlet side was next to the cowling, so we made two cuts about an inch long and about the width of the cooler apart in the cowling, heated it along the forward edge and pulled the back edge out about 1/2", then filled in the sides where we made the cuts. This formed a nice little outlet of about 3 sq. in. and gave him kool oil temps!
 
gereed75 said:
SCAT is also very bad for airflow because of the corrugations. They set up a lot of resonate waves resisting flow. The exact loss over a smooth walled "pipe" vs a corrugated one will be hard to predict due to flow rates, velocty, duct length, curves etc. But it can be huge.

My oil cooler is ducted off of a rectangular hole in the back left baffle (stock Van's cowling inlets feeding a modified Sam Jame's plenum) that is about 2.5" x 3.5". The smooth rectangular duct is gently curved 45 degrees down and gradually opening to the size of the entire face of the oil cooler. I use a generally poorly regarded Posi-tech cooler that gives me great cooling - 200 degrees max during long climb outs on hot days. I must reduce cooling flow (via a duct mounted door) for all other flight regimes to get oil temps above 165.

Improved design does work. I will be continuing work towards reduced drag as time and motivation permit. Thanks to inspiration in threads like this. Hope to get some data at the SARL race in July.
Click to expand...

How about posting some pictures of your set up?
 
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