Minimizing CHT while Holding Short on Hot Days

H. Paul Shuch is a Light Sport Repairman with Maintenance ratings for airplanes, gliders, weight shift control, and powered parachutes, as well as an independent Rotax Maintenance Technician at the Heavy Maintenance level. He holds a PhD in Air Transportation Engineering from the University of California, and serves as Director of Maintenance for AvSport of Lock Haven.

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designrs
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Minimizing CHT while Holding Short on Hot Days

Postby designrs » Sun Jun 05, 2016 5:59 pm

The opinions seem to be all over the map on the issue of
CHT mamanagement when holding on VERY hot days:

Everybody seems to agree, wind head-on or from the left:

Otherwise lots of conflicting info:
2,100 to 2,300 from the revised European POH for SportCruiser
1,900 to 2,000 from Roger, as posted on another forum... same numbers from another mechanic I know.
2,750 from fliers at US SportAircraft in Texas
2,700 from other mechanic
3,000 from another individual

What can REALLY be done to maintain CHT temps when holding short in very hot weather?
A Cessna 152 can idle all day in hot weather.
Shouldn't our ROTAX motors be better with the additional water cooling???
Can we do better??
Last edited by designrs on Mon Jun 13, 2016 8:54 am, edited 1 time in total.
- Richard

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designrs
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Re: Minimizing CHT while Holding Short on Hot Days

Postby designrs » Mon Jun 13, 2016 8:53 am

Using Prestone Dex 50/50.
Supposedly that boils at 265 degrees F

Yellow CHT starts at 250.
Red starts at 275
Rotax max is 300 (presumably damage above that)

I tired the 2,000 RPM holding 10 minutes in 95 F OAT.
CHT stayed in the yellow, but it boiled out the coolant reservoir.

It seems that 2,700 RPMs move the coolant faster to prevent boiling??

Comments welcome.
Thanks.

Also, excellent article on ROTAX cooling system:
http://www.rotax-owner.com/pdf/ROAN%20cooling.pdf
- Richard

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MrMorden
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Re: Minimizing CHT while Holding Short on Hot Days

Postby MrMorden » Mon Jun 13, 2016 9:52 am

If you will be there a while, shut down the engine if it gets too hot.

I'm scratching my head as to why your oil temp ranges are different from mine with the same engine type. In my CT max oil temp is 266°F, my yellow starts at 230°F. Roger Lee has stated that any temp below 250°F is no cause for concern, above that you should start mitigating heat somehow. But if you are seeing 250°F on the ground, that seems too high. I personally would not take off if my ground temps were that high.

Saturday I flew in hot weather, ground OAT over 90°F. I climbed out to 4500ft and the oil temp hit about 240°F in the climb, Once I leveled off it started going back down and stabilized at around 216°F with an OAT of 71-75°F. I don't think I've ever seen above 180°F or so on the ground. On very hot days I do sometimes stay in the yellow even in cruise if I'm low enough, 230-235°F.

Your temps look significantly higher than mine, and I'm not sure why.
Andy Walker
Athens, GA
Sport Pilot ASEL, LSRI
2007 Flight Design CTSW E-LSA

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designrs
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Re: Minimizing CHT while Holding Short on Hot Days

Postby designrs » Mon Jun 13, 2016 10:02 am

Andy, Taking about CHT only, not oil temp. (Assume typo in your post above.)
Shutting down the motor due to high temps is not a great idea, as temperatures will continue to climb after shutdown.

Roger & all... if you had high CHT while holding, say 275, couldn't get in the air... what would you do. Fast taxi maybe?

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Re: Minimizing CHT while Holding Short on Hot Days

Postby FastEddieB » Mon Jun 13, 2016 10:13 am

designrs wrote:Shutting down the motor due to high temps is not a great idea, as temperatures will continue to climb after shutdown.



By what mechanism?
Fast Eddie B.
Sky Arrow 600 E-LSA • N467SA
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MrMorden
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Re: Minimizing CHT while Holding Short on Hot Days

Postby MrMorden » Mon Jun 13, 2016 10:28 am

designrs wrote:Andy, Taking about CHT only, not oil temp. (Assume typo in your post above.)
Shutting down the motor due to high temps is not a great idea, as temperatures will continue to climb after shutdown.

Roger & all... if you had high CHT while holding, say 275, couldn't get in the air... what would you do. Fast taxi maybe?


Oh, I thought you were talking oil temp, not CHT (even though you clearly said CHT, LOL).

But CHTs run even cooler than oil temps in my airplane. I rarely see more than 220°F on CHT even on a hot day in the air, and 140-160°F on the ground.

Something still doesn't sound right.
Andy Walker
Athens, GA
Sport Pilot ASEL, LSRI
2007 Flight Design CTSW E-LSA

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designrs
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Re: Minimizing CHT while Holding Short on Hot Days

Postby designrs » Mon Jun 13, 2016 10:31 am

SportCruisers run hotter CHT... (Different cowling? radiator? Oil cooler?) requires some management.
I'd love to look at your CT and ROTAX installation Andy.
- Richard

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designrs
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Re: Minimizing CHT while Holding Short on Hot Days

Postby designrs » Mon Jun 13, 2016 10:51 am

FastEddieB wrote:
designrs wrote:Shutting down the motor due to high temps is not a great idea, as temperatures will continue to climb after shutdown.



By what mechanism?


Lots of heat retained in the motor and components... shutdown... then no moving air, oil or water cooling systems. CHT temps climb. Check your CHT at shutdown, then compare 3 minutes later.
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Re: Minimizing CHT while Holding Short on Hot Days

Postby FastEddieB » Mon Jun 13, 2016 12:44 pm

designrs wrote:
FastEddieB wrote:
designrs wrote:Shutting down the motor due to high temps is not a great idea, as temperatures will continue to climb after shutdown.



By what mechanism?


Lots of heat retained in the motor and components... shutdown... then no moving air, oil or water cooling systems. CHT temps climb. Check your CHT at shutdown, then compare 3 minutes later.


Sure, heat will move around some, but I think my point was that once you remove the overall heat source (the running engine) the overall temps must ultimately begin to cool.

In any case, if CHT's were getting uncomfortably warm, I still think shutting down the engine while waiting is an option worth considering.
Fast Eddie B.

Sky Arrow 600 E-LSA • N467SA

FastEddieB@mac.com

Nomore767
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Re: Minimizing CHT while Holding Short on Hot Days

Postby Nomore767 » Mon Jun 13, 2016 1:55 pm

Last time I flew I was looking to see how the ambient heat was affecting my 912 ULS.

Oil pressure usually around 60 and EGTs 1300. The oil temp was consistently 219 which is a bit higher than normal average. If it goes above 212 then I believe any moisture present will be boiled off. The CHTs started at around 150 and peaked at 190.

Oil temp and CHT seem to be the biggest variables in my Rotax depend ending on seasonal temps. In the winter I use metal tape to restrict cooling airflow so as to raise the CHTs into the low green in order to gain some cabin heat.
My airplane came new with the coolant right at the minimum level in the reservoir and its never moved.

When I brought the RV-12 home from Oregon summer of 2014 I did have numerous times where the oil temps were nudging the upper yellow and I resolved this with steps climbs. Once in cruise at around 7000-9000 away from the summer and desert heat the temps settled down albeit a bit higher than in cooler weather.

Not sure what panel you have but on my Dynon SkyView you can set the screen widgets as you want. Mine were factory set and I've gone through the setting process to familiarize myself but changed nothing.

I'm wondering if your screen settings may not be set right as to ranges and limits etc and so you may be seeing 'abnormal' readings? Have you run this by the dealership in Addison?

For myself in current ambient temps I can start and by the time I've taxied to the runway the temp will have just reached 120F and so I can exceed 2500 rpm and also complete the run-up.( In the winter I may have to wait till the temp comes up, less so with the metal tape.) At my uncontrolled field delays or traffic aren't an issue so I can get airborne pretty quickly. That said I've not experienced the high temps that you're reporting, even here in 'tropical Carolina'.

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Re: Minimizing CHT while Holding Short on Hot Days

Postby MrMorden » Mon Jun 13, 2016 2:24 pm

designrs wrote:SportCruisers run hotter CHT... (Different cowling? radiator? Oil cooler?) requires some management.
I'd love to look at your CT and ROTAX installation Andy.


I'll try to get some pics for you.
Andy Walker
Athens, GA
Sport Pilot ASEL, LSRI
2007 Flight Design CTSW E-LSA


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