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Oil temperature question

Paul 5r4

Well Known Member
As long as I've been flying my 7A, the oil temps have always been low. I even have a small airflow restrictor plate over the bottom third. My temps typically ran in the 160's range. CHTs are all 350's or little less. I was recently watching one of Mike Buschs online videos and he mentioned that the oil temps we see are coming from the coolest oil in the engine, (because it's oil coming back from the cooler), and that the actual temps can be 25-30 deg hotter. My oil temp probe is mounted where the Lycoming manual calls for it to be. I recently changed oil temp probe and put in the one from dynon. It's reading 175-180 with cht's all good. If the temps inside the engine are indeed 30 deg hotter then I'm running along in the 210 neighborhood. I'm feeling a little confused on the issue. Can the VAF brain help me clear my head on this. Wonder if I should remove the small restrictor plate. Thanks for your thoughts.
 
All is good. You want ~180 degrees as measured on your probe. This does translate to higher oil temps elsewhere in your engine, but that is already taken into consideration for the ~180 degree target.

I typically close off some of my butterfly valve to keep at ~180.

Carl
 
Yes, the Lycmoning OT sensor is in an area that see's oil directly from the cooler, when the vernatherm is closed (oil diverted to cooler). So, when OT's are abover the vernatherm set point, the oil temps in the sump will typically be warmer than the oil temp at the sensor. However, when the OTs are below the set point, I would expect the sump temps to be the same or close. However, the OT sensor is showing the OT of the oil that is being dispatched to the engine for lubrication work.

No concern with sump oil temps of 210. This is well within the normal range for modern oil. This was likely known by the original designers that set the 185* vernatherm temp and this temp has provided good service for many decades. It is a compromise setting, reflecting the need to keep temps below the critical level (around 250) and high enough to remove as much moisture as possible (higher OT's equate to faster H2O evaporation).

high oil temps are MUCH worse than low oil temps and therefore don't recommend more permanent cooler blockage. I would much rather accept consistent 170* temps to ensure that my trip to OSH, with 60 minute taxi at 100* OAT's, did not overheat my oil on depature.

Larry
 
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You want your oil to be at or about the water boiling point 212F. Oil Temp in the cylinder heads near the exhaust valves is about 30F higher than what you are reading. So 180F measured at oil temp probe near oil filter is the bottom of the normal operating.

If oil gets too hot it will coke and provide poor lubrication. Lycomings are air and OIL cooled. If the engine gets too hot of course it affects metallurgy and early wear of key components. Oil starts breaking down at 275F degrees so 245F is max red-line (but not for continuous). 165F degree is recommended Min OT for takeoff in cold weather I recall. A good range 185° to 210° F.
 
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165F degree is recommended Min OT for takeoff in cold weather I recall.

I don't think I could ever get my oil temp to 165F in a Wi winter let alone summer prior to takeoff. I've been using 100F Oil and 200F CHT as a minimum prior to takeoff.
 
165F degree is recommended Min OT for takeoff in cold weather I recall.

Would like the source for that one. Lycoming manual states that if engine will take throttle application without stumbling or other symptoms, it is warm enough for Take Off. Pretty similar to every other engine out there. Though some air cooled engines warn against high RPMs at low oil temps. Not really an issue with a 2700 limit. Personally, my limits are related to cyl wall temp, guessed at by CHT's (concerned with differential expansion with piston)
 
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You want your oil to be at or about the water boiling point 212F.

Last I checked my science, water evaporates at all temperature. Even frozen water does - sublimation. Boiling water evaporates no faster than water at 210* I do beileve that the warmer the water, the faster the evaporation. Maybe that is the point your trying to make; But would like to know how much faster evaporation occurs at 180 vs 150*. I am guessing it is not as much as you think.
 
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And...

The boiling point of water is 212F...at sea level, on a std. day/pressure. At 8500ft, boiling point of water is 196F (std. pressure). And the boiling point is phase change, not evaporation.

Some reading -- for those of you inclined: https://www.engineeringtoolbox.com/evaporation-water-surface-d_690.html

Check your Lyc. manual for temps & pressure limits and use them. If Lyc. wanted us to worry about the temperature of the oil at the wrist pin on con. rod #4, or the top half of the 2nd main bearing, they would have instrumented it and put it in the book.

Generally speaking, if you follow the book/specs, your engine will be just fine. Your hair will regrow, you'll gain wealth, you'll lose weight, your kids will love and respect you...

Cheers :)

B
 
Good grief. Not that old notion again.
"Good Grief". That dismissive statement is backed up by facts? Proof please.... My comments are based on Lycoming publications. You want your engine oil temp to burn off all the moisture and acids from combustion in the oil. That will not happen efficiently unless the oil temp reads is about 180F. This jives 100% with Lycoming. Old notions rooted in fact is still as true today, where the Lycoming is pretty much the same as 1955.

I don't think I could ever get my oil temp to 165F in a Wi winter let alone summer prior to takeoff. I've been using 100F Oil and 200F CHT as a minimum prior to takeoff.
Read the cold weather Lycoming bulletin. 165F is acceptable. Can you fly or take off with less? Yes. Should you fly around with 100F oil? No and if you can't eventually get 165F you should block the oil cooler.

are you kidding? Would like the source for that one. Lycoming manual states that if engine will take throttle application without stumbling or other symptoms, it is warm enough for Take Off. Pretty similar to every other engine out there. Though some air cooled engines warn against high RPMs at low oil temps. Not really an issue with a 2700 limit. Personally, my limits are related to cyl wall temp, guessed at by CHT's (concerned with differential expansion with piston)
https://www.lycoming.com/content/operating-cold-weather
Third from last paragraph.... I am not kidding, tend to go with the Manufactures recommendations. However I will concede that the bottom of GREEN for Oil Temp on most Certified Planes with Lycoming's is 60F. (some 100F). However if you want to light the fire, take off in sub-zero temps 1-minute after start, with 60F OT, up to you. Lycoming recommends 165F as a MIN operating temperature before takeoff, per Lycoming SB's, SL's and Notices. It is NOT an issue above 40F ambient temperatures. If you can't get 165F you should block your oil cooler.

Last I checked my science, water evaporates at all temperature. Even frozen water does - sublimation. Boiling water evaporates no faster than water at 210* I do believe that the warmer the water, the faster the evaporation. Maybe that is the point your trying to make; But would like to know how much faster evaporation occurs at 180 vs 150*. I am guessing it is not as much as you think.
You posted twice? I have a degree in mechanical engineering so I understand a little about math and SCIENCE! Also your comment ignores OT as recommended by Lycoming. The other part of your comment is irreverent to operation an internal combustion air (oil) cooled aircraft engines. We blow-by a lot of crud unto the crank case, moisture, acids, by products of combustion and raw fuel. That moisture and acids in the moisture, byproducts of combustion are "emulsified" in the oil.... Oil needs to be heated to about 210F to allow the moisture and the nasty volatilies to gas off and go out the vent. This is not opinion. It is Lycoming's recommendation and it is SCIENCE! :) Ha ha I love when people invoke the word SCIENCE as an appeal to authority.

And... The boiling point of water is 212F...at sea level, on a std. day/pressure. At 8500ft, boiling point of water is 196F (std. pressure). And the boiling point is phase change, not evaporation. Some reading -- for those of you inclined: https://www.engineeringtoolbox.com/evaporation-water-surface-d_690.html

Check your Lyc. manual for temps & pressure limits and use them. If Lyc. wanted us to worry about the temperature of the oil at the wrist pin on con. rod #4, or the top half of the 2nd main bearing, they would have instrumented it and put it in the book. Generally speaking, if you follow the book/specs, your engine will be just fine. Your hair will regrow, you'll gain wealth, you'll lose weight, your kids will love and respect you... Cheers :) B
Your sarcasm and humor noted, read my post above. I agree FOLLOW THE MANUAL. The recommended operating OT is 185-210F. Second your comment about when water boils is irreverent when water in solution with the oil. You want to get the moisture emulsified in the oil, which has acids and combustion by products in solution, BURNED OFF.... Leave that in there and let the engine sit you will have corrosion. What kills engines is disuse and not allowing them to run at full operating temperatures. However do what you like. Your engine. Cheers :)



Fun fact I had a 1959 PA23-160 Pilper Apache with two O-320 160HP engines. I bought it around 1990 with 1800 hours since engines were new, replaced about 5 years earlier. It was flown by previous owner about 300-400 hours a year. I flew it about 150-200 hours/yr for two years and sold it with 2200 hrs on the engines. All cylinders were high 70's. I used 1 quart every 8-10 hours as long as I kept the oil level under 6 qts. This shows you what flying an engine and keeping it within limits can do to add longevity.

BTW More fun facts, LYCS with 8 qt capacity need to be run under 6 qts or less.... Why? More than 6qts will just get blown out. Why? It is a FAR engine certification requirement they have reserve oil capacity for a leak and having reserves to get on ground. With a wet sump Lycoming put that reserve oil there, which in turns increases oil consumption. It reduces overall crankcase volume, increases case pressure and oil splash, which goes out vent. You are far better putting in a PINT in at a time every few flights, verses topping 6 Qts to 7 Qts. I ran min between 5.5 to 6 qts but tried to shoot for 5.7 Qts for local. If cross country I'd fill to 6 Qts. I would put in just a tad every few hours or flight to keep that level.
 
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That moisture and acids, by byproducts of combustion are "emulsified" in the oil.... Oil needs to be heated to about 210F to allow the moisture and the nasty volatilies to gas off and go out the vent. This is not opinion. It is Lycoming's recommendation and it is SCIENCE! Ha ha I love when people invoke the word SCIENCE as an appeal to authority.

I believe that the bulk of the water is NOT in suspension in the oil, though some is. Most remains in a gaseous state, until shut down and cooler temps allow it to condense and rest on top of the oil. Assuming I am wrong and it IS all in suspension, where is your data that says the water precipitates out of suspension in oil at 210 and not at 150.

Larry
 
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"Good Greif". That dismissive statement you made is based on no facts. Proof please.... My comment is based on Lycoming publications. You want your engine oil temp to burn off all the moisture and acids from combustion. That will not happen efficiently unless the oil temp read is about 180F. This jives 100% with Lycoming Oil Temp Green band 185-210F. Lycoming allows 165F for cold weather operations... What is your point? Old notions rooted in fact is not bad, when it is true.

Read the cold weather Lycoming bulletin. 165F is acceptable.

https://www.lycoming.com/content/operating-cold-weather
Third from last paragraph.... I am not kidding I tend to go with the Manufactures recommendations. However I will conceed that the bottom of GREEN on most Certified Planes with Lycoming's is 60F. However if you want to light the fire, take off in sub-zero temps 1-minute after start, with 60F up to you. Lycoming recommends 165F as a MIN operating temperature per Lycoming SB's, SL's and Notices.

You posted twice? I have a degree in mechanical engineering so I understand a little about math and SCIENCE! Also your comment ignores OT as recommended by Lycoming. The other part of your comment is irreverent to operation an internal combustion air (oil) cooled aircraft engines. We blow-by a lot of crud unto the crank case, moisture, acids, by products of combustion. That moisture and acids, by byproducts of combustion are "emulsified" in the oil.... Oil needs to be heated to about 210F to allow the moisture and the nasty volatilies to gas off and go out the vent. This is not opinion. It is Lycoming's recommendation and it is SCIENCE! Ha ha I love when people invoke the word SCIENCE as an appeal to authority.

Your sarcasm and humor noted, read my post above. I agree FOLLOW THE MANUAL. The recommended operating OT is 185-210F. Second your comment about when water boils is irreverent when water in solution with the oil. You want to get the moisture emulsified in the oil, which has acids and combustion by products in solution, BURNED OFF.... Leave that in there and let the engine sit you will have corrosion. What kills engines is disuse and not allowing them to run at full operating temperatures. However do what you like. Your engine. Cheers :)



Fun fact I had a 1959 PA23-160 Pilper Apache with two O-320 160HP engines. I bought it around 1990 with 1800 hours since engines were new, replaced about 5 years earlier. It was flown by previous owner about 300-400 hours a year. I flew it about 150-200 ours for two years and sold it with 2200 hrs on the engines. All cylinders were high 70's and oil use (as long as I kept the oil level under 6 qts) was about 1 quart every 8-10 hours. This shows you what flying an engine and keeping it within limits can do to add longevity.

BTW More fun facts, LYCS with 8 qt capacity need to be run under 6 qts or less.... Why? It is a FAR that engines have reserve oil capacity. With a wet sump they put that reserve oil there, which in turns increases oil consumption. It reduces overall crankcase volume, increases case pressure and oil splash, which goes out vent. You are far better putting in a PINT in at a time every few flights then topping it over 6 qts. I ran min between 5.5 to 6 qts. I would put in just a tad every few hours.

Agree with the sentiment about disuse.

Speaking of books --

from the Lycoming nnn-360-xxx manual - 8th Edition Part No. 60297-12

OPERATING CONDITIONS
Average *Oil Inlet Temperature
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)
* - Engine oil temperature should not be below 140?F (60?C) during continuous operation.

----

from the Lycoming nnn-320-xxx manual 3rd Edition Part No. 60297-30

OPERATING CONDITIONS
Average Oil Inlet Temperature
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?F to 90?F 180?F (82?C) 245?F (118?C)
0?F to 70?F 170?F (77?C) 225?F (107?C)
Below 10?F 160?F (71?C) 210?F ( 99?C)

----

Interesting differences at the bottom end of ambient :eek:

Like you said -- it's your engine :)
 
Agree with the sentiment about disuse.

Speaking of books --

from the Lycoming nnn-360-xxx manual - 8th Edition Part No. 60297-12

OPERATING CONDITIONS
Average *Oil Inlet Temperature
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)
* - Engine oil temperature should not be below 140°F (60°C) during continuous operation. Like you said -- it's your engine :)
Ha ha I was about to post that.
As far as oil capacity I mentioned, shocked to see 2 Qrts. Mins. 6 Qts is my max and 5.5 Qts min to keep from blowing out out vent.

OIL SUMP CAPACITY
All Models (Except AIO-360 Series, O-360-J2A) ...............................................8 U.S. Quarts
Minimum Safe Quantity in Sump
(Except – IO-360-M1A, -M1B; HIO-360-G1A) ..................................................2 U.S. Quarts
IO-360-M1A, -M1B; HIO-360-G1A..................................................................4 U.S. Quarts
AIO-360 Series .................................................................................................Dry Sump
O-360-J2A.................................................................................................6 U.S. Quarts

Ref Lycoming Operators Manual O-360, October 2005; Part No. 60297-12
 
An irrelevant fact

As noted previously, water does not have to be 180F to completely vaporize. The medical industry standard for DRYING moisture cured substrates, example casting tape, is heating materials to 120F. Other potential corrosives suspended in the oil are probably temperature, agitation and time dependant.
 
Paul, yes, remove the air side blockage. You can use it down there in LA. As you noted, it appears the OT sensor yielded an incorrect reading.

Back to the vigrous discussion off topic.
 
Read the cold weather Lycoming bulletin. 165F is acceptable. Can you fly or take off with less? Yes. Should you fly around with 100F oil? No and if you can't eventually get 165F you should block the oil cooler.

Please reread my post...this isn't a debate...I was simply sharing the facts of my operating circumstances. I didn't say you should fly around with 100F oil...I said it was near impossible to get my oil 165F in the winter in WI...prior to takeoff. I would have to do a full power static runup for 10 minutes with limited head cooling to see 165 prior to takeoff, even after preheating my oil to 60F+...I don't know anyone that does or recommends this.

I happily get 165F+ airborne with my oil cooler blocked in the winter.
 
You want your oil to be at or about the water boiling point 212F.

My goodness, after putting my washing out on the clothesline to dry for decades I had convinced myself that they were actually drying...but I guess not...you learn something new on VansAirforce every day. :D
 
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My goodness, after putting my washing out on the clothesline to dry for decades I had convinced myself that they were actually drying...but I guess not...you learn something new on VansAirforce every day. :D
You must be kidding and trolling me? Ha ha. OK let's just nip this in the bud. It is a strawman argument that water evaporates below boiling. I never said water does not evaporate below boiling. Nope. Clouds form in the sky, as water vapor condensing that evaporated from ocean, lakes and rivers. Sure these bodies of water are not boiling. When I boil water I see water vapor (steam) come off before the bubbles. OK.

Fun fact, water (we are talking liquid H2O) can evaporate (go from liquid state to gas or vapor) at ANY TEMP, just slower at lower temps. At 32F H2O freezes and reaches it "triple point". Water can go from solid to gas without going through the liquid state, and it is called "sublimation" (phase transition). Water is an amazing element and expands when it freezes.

The gases in the crankcase is more than pure H2O. There is H2O mixed with nitric oxide (NO), nitrogen dioxide (NO2), and carbon monoxide (CO) and unburnt fuel and acidic byproducts.

Nothing I am saying is controversial and not sure why I got you all "triggered". Ha ha. Lycoming says 185F is min OT for normal Ops. They recommend 165F OT Min in cold temps. In extreme conditions 140F OT is the Min for continuous operations. Low OT is not the normal complaint of pilots in lower 48

I believe that the bulk of the water is NOT in suspension in the oil, though some is. Most remains in a gaseous state, until shut down and cooler temps allow it to condense and rest on top of the oil. Assuming I am wrong and it IS all in suspension, where is your data that says the water precipitates out of suspension in oil at 210 and not at 150.Larry
Yes good point. Also what happens, when you shut down lots of hot high humidity air fills your crankcase; it will condense to liquid water as your engine cools and cover all the metal parts inside your engine. The next time you start most of water is still there and oil mist gets mixed like a blender as the camshaft, crank and gears in accessory start mixing it like an oil water milkshake. This is why you want to get your engine up to normal operating temperature to get all the moisture out the oil and engine... Also oil has viscosity and needs to flow and create film boundary in the "Babbitt" bearings. Too cold the oil will not flow properly.
 
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You must be kidding and trolling me? Ha ha. OK let's just nip this in the bud. It is a strawman argument that water evaporates below boiling. I never said water does not evaporate below boiling.

These days, that is known as a "Fake News" response.

To be specific, what you wrote was...

"You want your oil to be at or about the water boiling point 212F. Oil Temp in the cylinder heads near the exhaust valves is about 30F higher than what you are reading. So 180F measured at oil temp probe near oil filter is the bottom of the normal operating."

...which is simply not true on several levels.

Most notable? The boiling point of water is irrelevant.

Nothing I am saying is controversial and not sure why I got you all "triggered". Ha ha. Lycoming says 185F is min OT for normal Ops. They recommend 165F OT Min in cold temps. In extreme conditions 140F OT is the Min for continuous operations.

Actually no, no, and no.

Lycoming's recommendations vary, apparently depending on who created the particular manual, and who (if anyone) reviewed it, even across a relatively small publication date range for the same engine. I will use the IO-390 as an example, since I have watched and read most of the new manuals as released.

None call out 185F "min OT for normal ops". The Lycoming Operation Reference Manual IO-390 Series (June 2007) for the IO-390-EXP states:

G. For maximum engine life, the desired oil temperature should be maintained between 165°F (73.8°C) and 200°F (93.3°C) in level-flight cruise conditions.

The original 390-A manual (revised 2009) simply says:

For maximum engine life, maintain desired oil temperature (sic) is 180F.

...with the same in the "B" manual, complete with grammatical error.

The AEIO 390 manual (April 2012) doesn't list a max life recommendation, only minimums of 140F for takeoff and 170F for cruise.

The HIO 390 manual (Oct 2017) lists the same 140F takeoff minimum, despite allowing 2800 RPM....and it returns to the optimum oil temperature for maximum engine life statement of 165F to 200F.

The latest IO-390 C (Jan 2017) and D (March 2020) manuals include this line...

The best way to decrease the risk of engine corrosion is for the aircraft to be in flight at least every 30 days for at least 1 continuous hour at oil temperatures between 180°F to 200°F (80°C to 93°C), depending on location and storage conditions.

...but then go on to state in another section "Oil Temperature (for maximum engine life) 180ºF"

Oh yeah, recall the "140F for takeoff" listed above? Almost all the manuals otherwise state...

"Engine is warm enough for take-off when the throttle can be opened without the engine faltering and the oil pressure is not less than the minimum pressure specified in this operation reference manual.

Point is, there is not a lot of basis for claiming one particular number is best. Digging around in Lycoming specs to prove it is a lot like digging around in the Bible...a decent preacher can find support for almost any view, and make it sound good come Sunday morning ;)
 
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Point is, there is not a lot of basis for claiming one particular number is best. Digging around in Lycoming specs to prove it is a lot like digging around in the Bible...a decent preacher can find support for almost any view, and make it sound good come Sunday morning ;)

As I was going thru my morning reading, I came upon this thread again and asked myself, am I going to learn anything new here by clicking on this thread again!
Sure as taxes, well worth clicking. I can?t say I learned much as what temp the water boils but sure enough, now I understand the preacher's word when one day up is up and another day up is down.

THANK YOU Dan, again.
 
Lycoming says 185F is min OT for normal Ops.

Sorry George, but I'm with Dan on this one.... you almost certainly just made up that 185F minimum. Show me where you got it from.

My Lycoming IO-360 Operators Manual states quite clearly that the "desired" oil operating temperature for continuous operations is 180F. That's not a minimum value either...it's the ideal medium temperature. Incidentally Lycoming don't provide a minimum temperature for take-off but Superior call for 75F.

The Sky Ranch Engineering Manual states that for the IO-360 the "desired oil temperature should be within the range of 160F to 245F with 180F being a medium value. Oil temps should not be below 165F during continuous operation."

So there you have it...180F is the figure to aim for...it's Lycoming's ideal temperature. And it makes sense because that temperature will be recorded at the oil filter adaptor and the actual temperature of the oil in the sump will be about 30F higher (ie about 210F).

The reality is that continuous operating temps in cruise of 180F plus or minus 15 degrees (ie. temps in the range of 165F to 195F) are ideal. Outside of that range pilots probably need to take a further look at their set-up.

We can't have pilots fretting unnecessarily that their oil temps aren't always over 185F in continuous operations. ;)
 
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On a related note.....has anyone ever noticed change in engine noise associated with oil temp?

I perceive an audible low frequency rumble at lower oil temps, maybe below 140 or so. Sort of a background gear train harmonic on takeoffs and climbs on very cold days. It goes away as temps rise. Not sure if it corresponds in anyway with the opening of the thermostat, but maybe.

Might be a throwback to my days of driving Navy helos, when your ears were always tuned into a variety of gear whines, vibrations and harmonics.
 
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On a related note.....has anyone ever noticed change in engine noise associated with oil temp?

I perceive an audible low frequency rumble at lower oil temps, maybe below 140 or so. Sort of a background gear train harmonic on takeoffs and climbs on very cold days. It goes away as temps rise. Not sure if it corresponds in anyway with the opening of the thermostat, but maybe.

Might be a throwback to my days of driving Navy helos, when your ears were always tuned into a variety of gear whines, vibrations and harmonics.

Yes, but then I also am an old helicopter person.
 
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