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  #1  
Old 04-14-2021, 04:56 AM
Mtherr Mtherr is offline
 
Join Date: Nov 2020
Location: Montréal, Canada
Posts: 58
Default Temperature control on O-360

Lycoming recommends not exceeding 400F CHT for continuous operations and Mike Bush, recommends not exceeding 400F CHT, period. Max cooling rate should also not exceed 50F per minute.

Well, no matter how hard I try, seems I cannot always respect those limits; especially when doing circuits.

On first takeoff, after warm-up and run up, I will get temperature on no 3 cylinder reaching 415 to 430F. This with reduced throttle and decreased angle of climb (faster speed) (90-110KT).

While I seem OK to control cooling rate on descent and landing, I cannot get much less than 55F/min doing circuits, after climb and when turning downwind.

Interestingly, i can keep CHT lower than 400F when climbing doing circuits, but the rate of ascent is not what I was dreaming about with a RV.

Any tricks? Opinion?
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  #2  
Old 04-14-2021, 05:30 AM
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 5,880
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It is not a slow speed airplane. Some cool better than others and while you can help that with some attention to the cooling, operation is important too. When working in the pattern, throttle back early and climb with lots of horizon showing. Cooling increases with the square of the speed. Heat is generated with higher engine rpm and power. Assuming always rich in the pattern. Adjust accordingly and if your bird is exceeding temps compared to others, then look for cooling improvements.

I have CS prop and reduce to 2500 at 200ft and throttle back more for patterns than for normal climb. The thermal mass of the system helps slow temperature rise, but find it necessary to go to a near by airport in lean cruise to cool it off before doing more circuits.

You can lower temps up to 20-30F if the cooling system has leaks. You likely do. Timing plays a big part in heat generation, so be sure it is not advanced at your altitude and speeds. Throttling back is less helpful if the timing advances. It sounds like cooling improvement is something you need to address. Do some research using google to search the site, and post pictures for feedback on specific areas of interest. Details greatly matter in sealing the baffles, small holes, gaps between baffles and case etc. There are many opportunities for air to bypass the fins.

Have fun in developing your plane and procedures.
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Last edited by BillL : 04-14-2021 at 05:35 AM.
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  #3  
Old 04-14-2021, 06:06 AM
Bcone1381 Bcone1381 is offline
 
Join Date: Dec 2015
Location: Chelsea, MI
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Your #3 cylinder is running hot, while 1,2, and 4 are OK.

The casting of the cylinder from the factory on the Rear of #3 creates an air dam preventing proper airflow if the baffling is installed IAW the vans baffle kit instructions. There are ways to create a gap to open up the dam and allow airflow to pass over this area. That might help.

Read this thread.
https://vansairforce.net/community/s...ad.php?t=37835
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  #4  
Old 04-14-2021, 06:19 AM
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rv8ch rv8ch is offline
 
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Quote:
Originally Posted by Mtherr View Post
...
Interestingly, i can keep CHT lower than 400F when climbing doing circuits, but the rate of ascent is not what I was dreaming about with a RV.

Any tricks? Opinion?
What kind of prop do you have? A 360 should get you some really good climb performance - if you are not getting that, might need to check some things.
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  #5  
Old 04-14-2021, 07:49 AM
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AlexPeterson AlexPeterson is offline
 
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What is your fuel flow and RPM during the climb where you see the high cht's? Carb/injected? Mixture plays a dominant role in CHT's. Also please report the OAT, since CHT will track that.
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  #6  
Old 04-14-2021, 08:24 AM
Robin8er Robin8er is offline
 
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Location: Socal
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Try a higher speed climb. Try 120 knots, that helps significantly with mine.

Outside air temp plays a big roll too. If OAT is 60 degrees or less, I have no issues. If it's warm out, I have to pay attention and keep the speed up.

Lots of threads on trying to get the back cylinder to cool. I have the same issue in mine. I've worked my baffeling alot and it has helped, I still have a little more work to do.

I live in a very hot area, I'm planning on adding a cowl flap just to help with temps in the hot summer.
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  #7  
Old 04-14-2021, 08:34 AM
Mtherr Mtherr is offline
 
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Location: Montréal, Canada
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Bcone, thanks! I will look into this. Great information

Mickey. Sensenich FP 72X85. I was still climbing above 1000fpm, but to control temperature, I was reducing throttle significantly.

Alex. I have to go back and pay attention. At full throttle, I was above 60 litres per hour (17gph), full rich. My engine is not injected (O-360-A1A). It is not yet hot here in East Canada. Yesterday was 16C (60F) when I was flying.

From the various responses. Should I understand that it is not normal to go into the 400s on initial climb?
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Last edited by Mtherr : 04-14-2021 at 11:37 AM.
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  #8  
Old 04-14-2021, 08:42 AM
Robin8er Robin8er is offline
 
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Quote:
Originally Posted by Mtherr View Post
From the various responses. Should I understand that it is not normal to go into the 400s on initial climb?
It isn't preferred, but depending on how good your baffling is, timing, how aggressive you climb will all effect your CHT. It will be a bigger problem in the summer and when the plane is heavier.

It is preferred to keep your CHT below 400, but short periods of time in the lower 400's aren't a big problem in my opinion. You will likely need to do some work with the baffling to try too cool the rear cylinder more. I will admit that I routinely hit 400-430 on initial climb in the summer, but I work really hard to keep it below that. I have perfect temps in cruise. Its just an airflow issue. You likely need to seal gaps and try to get more airflow to those back cylinders to bring the temps down. Its a lot of trial and error.
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  #9  
Old 04-14-2021, 11:21 AM
Mtherr Mtherr is offline
 
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Anyone using the EZ Cool Cowl Flap (Antisplat Aero) or anything similar?
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  #10  
Old 04-14-2021, 11:37 AM
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DanH DanH is offline
 
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Michel, the folks saying climb at a higher airspeed are entirely correct. Dynamic pressure is the source of the pressure differential which forces cooling mass (air) down through the fins. Available dynamic pressure increases by roughly 50% when going from 100 to 125 knots.

RPM reduction is also effective. The old NACA papers said "Cooling demand is proportional to mass flow". Our engines are air pumps with mass flow roughly proportional to RPM.

Having boosted cooling mass flow and reduced combustion mass flow, the next job is to increase heat transfer. You want every molecule of air which passes through the cowl to carry away as much heat energy as possible. This is where effective baffling and zero leakage come into play. Cowl exit air temperature is a pretty good yardstick. Some guys with hot engines have rather cold exits.
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