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RV12 Hot Weather Operation, Overheating

D_C

I'm New Here
2010 RV12 Rotax 912

I have a friend with an RV12 and now that our summer weather amounts to 90 degree plus ambient temperatures he doesn’t fly and just goes home.

He has worked at getting the prop pitch optimized along with other fixes but is pretty much grounded when it’s hot out.

He said owners in other hot climates just limit there flying to early mornings.

Are there any good modifications that would allow operation on hot days?

Getting the coolant type and mix correct likely helps. I believe it is oil temps that cause his distress.

Can flying on hot days be done?

Thank You
 
I’ll go out on a limb here…

Use 50/50 mix DEXCOOL – either mix yourself from concentrate with distilled water or purchase 50/50 already mixed.

Synthetic oil is much better for high temperature. Petroleum motor oils don’t tolerate elevated temperatures well - oxidation and coke formation can occur.

I use MOBIL 1 RACING 4T FULL SYNTHETIC MOTOR OIL in my RV-12 for over 600 flight hours. This oil is 100% synthetic and has special gear lubricating formulation needed when engine and gear reducer share same oil. This is same design consideration for motorcycle where engine and transmission are housed in same case and share same oil. Very important that oil have formulation for lubricating power transmission gears.

My RV-12 is an early SN with muffler located very close behind the oil cooler. In summer months I see oil temps in the yellow arc during extended climb. Temps return to high-green arc in cruise flight.

Disclaimer: Having said the above, Rotax and Van’s only authorize use of AeroShell Oil Sport Plus 4 in 912ULS engine...

Also, minimize/eliminate ground operations and use a cooling fan at the open oil access door when airplane is parked for any duration with expected restart and return to flight. See… https://vansairforce.net/community/showpost.php?p=1522183&postcount=135
 
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We have seen a number of construction errors over the years that have contributed to high oil and coolant temperatures.

One that has occurred quite a few times is the air inlet opening on the lower front of the cowl not being trimmed properly. This causes a restriction of cooling airflow.
It also causes the oil cooler to be positioned closer to the muffler than was designed (which was fairly close already). This contributes to higher oil temps as well.

In hot ambient temps, oil temps that go into the yellow range for a short period of time (such as doing a climb) is not unusual with Rotax 912 powered airplanes and is not a problem as long as it doesn't continue to climb and get close to red line, and as long as it comes back into teh green range in cruise flight.
 
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Thank You Scott. It looked to be a good quick-build by an experienced builder (who had built several other Vans aircraft).

Still good to examine those possible adverse conditions.

Appreciate the information.

DC
 
Thank You Scott. It looked to be a good quick-build by an experienced builder (who had built several other Vans aircraft).

Still good to examine those possible adverse conditions.

Appreciate the information.

DC

Repeat builders have made the mistake.

If you post a photo of the cowl inlet I could verify.
 
We are hitting 115F here in Phoenix. That means minimum operating oil temp is only 7 degrees higher. I can’t fly if I get delayed n taxi and run up without flirting with redline CHT and Oil T on climb out. The guys at the flight school in a nearby hangar are flying both the 12 and 12iS SLSA’s. They tell me it’s like day and night between the two with overheating being no problem in the iS. I don’t think it is strictly a builder issue.
 
Are you sure the high indicated temperatures are accurate. There’s a design deficiency with the D180 legacy 12. A very small ground side voltage drop to D180 will have large indicated errors at high engine temps. Vans uses a single 22 gauge wire from the D180 to the Vans “switch panel” and then an 18 gauge wire from the Vans panel to the airframe with a total calculated voltage drop in the wiring of 110mv. This could give an error of 30 degrees higher then actual at the top end. The Vans design is dependent on the instrument attach screw to “improve” the grounding and shunt some of that drop. The resistance of that connection will vary between installations and with the torque on the attach screw. A better solution is to fill the empty D180 connector ground pins and tie those wires to the airframe ground.
 
We are hitting 115F here in Phoenix. That means minimum operating oil temp is only 7 degrees higher. I can’t fly if I get delayed n taxi and run up without flirting with redline CHT and Oil T on climb out. The guys at the flight school in a nearby hangar are flying both the 12 and 12iS SLSA’s. They tell me it’s like day and night between the two with overheating being no problem in the iS. I don’t think it is strictly a builder issue.

I didn't say it was a builder issue.

I said that it can be a builder issue. That would make it worthwhile to investigate.

There are also different personalities in different engines. When the red prototype got to high time on the engine and had it replaced, the oil temps on the replacement engine ran 10-15 degrees warmer than the previous engine, with everything else being exactly the same.
 
...what Scott is talking about can be seen here in a Kitplanes magazine article, this cowling was incorrectly trimmed. I have seen a few like this as well, they forgot one step in the KAI. I still seem to have the opposite issue here in Niagara as I still have 1" wide tape across my oil cooler in order to keep temps up in the green, in the winter I had 3" tape across.

https://s28490.pcdn.co/wp-content/uploads/2019/05/rv-intake.jpg
 

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...what Scott is talking about can be seen here in a Kitplanes magazine article, this cowling was incorrectly trimmed. I have seen a few like this as well, they forgot one step in the KAI. I still seem to have the opposite issue here in Niagara as I still have 1" wide tape across my oil cooler in order to keep temps up in the green, in the winter I had 3" tape across.

https://s28490.pcdn.co/wp-content/uploads/2019/05/rv-intake.jpg

Thanks Scott, that is exactly what I was talking about.
 
I fly in areas that experience seasonal temperature inversions, where I start at an airport that's 1034 ft and the inversion temps increase all the way up to 5500 or 6000 ft before I get above the dirty air or haze and the temps aloft finally start dropping.

You'll want to back out of the throttle a bit and decrease your climb rate to moderate the oil temperature, to keep it in the green, below 230 F.

Particularly true in South Western States of the USA, maybe the region you fly it, too. Keep an eye on your OAT, as well as your oil temp.
 
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Mike,

Before I start up OAT and Oil T are within a few degrees. I’m confident the overheat is real.

Rich

Rich, the error is not linear. Look at it this way; at 70F the sensor will output 2.2 volts, a loss of .1 volt will not be noticeable. But at 255F the sensor will output .115 volts, with a 110mv drop on the ground side of the D180, it will only see 5mV. This error will peg the indicator.

As I said the design is very dependent on the D180 attach screw. I was never able to get below a 25mv drop without adding the redundant grounds to the unused D180 power ground pins. The additional grounding got it down to less than a 5mV drop. Four, 2-inch #20 wire for the pins soldered to a 15-inch length of #12 wire bolted to the avionics bay floor.

side note, with a 25mv drop (the best I could get with the as built design) an engine at 240F will indicate 255F. I found that unacceptable. YMMV
 
Appreciate the many good and detailed replies.

I spoke to the owner of the RV-12 that prompted the original post.

Many of the suggestions he had already applied and processed and he appreciates the post (I forwarded him the link for him to follow). He seemed particularly interested in the Grounding issues and poor quality of the Dynon sensors.

Also, the temperature operating restrictions differ between Rotax and Vans Aircraft with the latter being more restrictive.

In any event, he is following up on the suggestions and appreciates any other possible diagnostics and or fixes.

Thanks Again.
 
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I operate out of Salt Lake International Airport and fly in a range of temperatures. Yesterday when I landed the density altitude was 7,000 ft (the airport elevation is 4,226 ft). If I depart to the east, I have to immediately climb to 10,500 feet to clear the mountains. In winter, there is often snow and ice lining the runways and taxiways.

I've found the RV-12 to be remarkably versatile in this environment notwithstanding its obvious limitations. Given the airline traffic, I often have to wait for landing and departing heavies. If you aren't careful, oil and cylinder temps can skyrocket or stay well below the green depending on the season while you are on the ground. As long as I keep a decent nose angle, I've never had trouble with temps while in the air.

When you are on the ground, the key is to find the right idle speed to maintain the right temperature. I've found that idling around 2,000 rpm is too slow in the heat. There's just not enough air flowing through the radiator. Even after the engine is warmed up, I have to maintain at least 2,500 rpm, while "idling" to keep the air moving across the radiator. That helps keep CHTs in the green. It is counter intuitive to add throttle to lower temps, but it works for me (to a point).

For winter, the Van's radiator baffle works great. I had mixed results with the oil cooler and installed an oil thermostat. The airplane warms up much faster and maintains temps much better with the thermostat in the cold.

As long as you recognize the airplane's limitations, plan your schedule around them (e.g., fly in the mornings in the Summer, etc.), the airplane will perform well. You just have to be patient with it sometimes - it is a flying compromise.
 
Also, check SL-00021. I remember reading some early exhaust systems placed the muffler close to the oil cooler. The new one moved the muffler aft which made a big difference on hot summer days in my dad’s rv-12.

And Scott’s post on keeping the temperature within range is excellent.
 
Mike, good point on nonlinearity of error, but hard to believe that both CHT sensors (old style coolant sensors) and the oil T sensor are all in error.

Rich
 
Rich,
What we see as a temperature gauge is actually a volt meter displaying a valve from a lookup table.

Any voltage drop along the D180 ground path and all three displayed engine temperatures will indicate an error. The error is nonlinear and increases dramatically with sensor temperature.

The issue is not the sensor, the problem is the D180 can’t see all the voltage from the sensor(s) because of the offset of the ground side voltage drop.
 
Maybe, Mike, but being an operator at heart (Navy and Civilian nuke program) I tend to believe my indications. Once tried to transition a guy in 116F and he dawdled on taxi and run up. We ended up in a cautionary landing after 10 minutes in the air due to ahi CHT’s and a oil T, and even got an “Out of operating range” message for the avionics. When everything quacks like a duck it’s probably a duck.
 
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