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Hi,

On several occasions, I experienced that the coolant temperature has reached close to the max of 120 degrees C when on the ground.

I did some tests to find out what causes this and what can be done to mitigate high coolant temperatures on the ground.

I wanted to share my results and ask if any of you guys had similar issues and possible solutions? 


My setup:

Bristell NG5 with Rotax 912 iS
Propeller: DUC 3-bladed Swirlblack in-flight adjustable
Coolant: Prestone premixed 50/50
Coolant radiator, roughly 32x16 cm mounted low behind the propeller

TLDR; RPM of 2500 and facing aircraft into the wind makes a big difference on coolant temperature while on the ground.

 

Day 1 test conditions:
OAT: 13 degrees C
Wind: 7 kts, aircraft faced into the wind.

I did 5 test runs with different settings, in between the test runs I let the engine cool back down. The test runs are 11 minutes each and I started the timer once the coolant temperature had reached 80 degrees C

1st test: 2000 RPM, Lane A & B on, prop 100% (fully fine propeller pitch)
2nd test: 2000 RPM, Lane A only (to force the engine out of ECO mode, which gives lower EGT, however, oil temp is N/A), prop 100%
3rd test 2000 RPM, Lane A & B on, prop 70% (prop slightly course, similar to a fixed pitch prop)
4th test 1650 RPM, Lane A & B on, prop 100% 
5th test 2500 RPM, Lane A & B on, prop 100% (Gave lowest coolant temperature but the highest oil temp)

Coolant temp: https://imgur.com/a/wdhla9D
Oil temp: https://imgur.com/a/rcmBkZD

Day 2 test conditions:

OAT: 7 degrees C
Wind 11kts 

I did 2 test runs, one with the aircraft facing directly into the wind and the other facing opposite the wind. 2000 RPM, prop fully fine, and both Lane A & B on. 11 minutes test runs, the timer started when coolant reached 80 degrees C

1st test: Facing directly into the wind 
2nd test: Facing opposite the wind. (At the end of test run the coolant temp was 22 degrees C higher than the previous test

Coolant temp: https://imgur.com/a/vs0s3oH
Oil temp: https://imgur.com/a/jTPkjRR

 

 

 

 

 

  

9209_1_test 1 coolant.png (You do not have access to download this file.)
9209_1_test 1 oil.png (You do not have access to download this file.)
9209_1_test 2 coolant.png (You do not have access to download this file.)
9209_1_test 2 oil.png (You do not have access to download this file.)
9209_1_temp_coolant_oil.xlsx (You do not have access to download this file.)
  • Re: Rotax 912 iS oil & coolant temp while on the ground

    by » 3 weeks ago


    Hi Tobias

    The OEM usually picks the prop and the coolers for their aircraft design.  It should be noted that the injected engines by design will always run hotter on the ground than a carb version.  This is explained in that the inlet air has no fuel and therefore no cooling effect of the fuel vapor in the inlet plenum or intake runners.  (it is added just above the inlet valve) A number of OEM have solved this in hotter environments by doing the same thing a modern car or truck has done, with an electric fan for ground running.  Small thermostatic controlled fans can be used to help you on hot days.

     

    Cheers

     


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