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  #21  
Old 09-12-2011, 02:48 PM
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Quote:
Originally Posted by strahler13 View Post
Sunday I climbed to 3500 ft (2,700 AGL) and hit 430 deg. Then straight and level for a few minutes until temps came down. Then into the pattern for a touch and go. On the TNG departure, I kept the same power and speed settings and the temps only climbed to about 385--with a "warm" engine.
Did you have the same beginning CHT on the runway in both cases (CHTs probably fell further during the power-off descent), and did you climb to 3500 after the T&G?
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  #22  
Old 09-12-2011, 03:05 PM
RV8R999 RV8R999 is offline
 
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Originally Posted by DanH View Post
We cannot afford leaks; every molecule must carry away heat.
Our intuition tell us this must be true..but alas there is more going on here than merely plugging leaks. As a quick sanity check I completely sealed my oil-cooler inlet , a 3" diameter leak as well as the inlet to the heater muff, a 2" diameter leak, plus both mag blast tubes 2x1" diameter leaks for a total reduction of 11.775 sq in of leakage area and only saw a marginal reduction in CHTs during WOT cruise, full rich (about 5-10 deg on the hottest cyl) under test day conditions. I only did this once and only long enough to witness the overall change. I returned to base when OT began climbing above 200 deg F and re-opened those inlets. sealing leaks is good, but unless yours is truly horrendous to start with I wouldn't expect much from little dabs of RTV here and there.

As I stated in my first post on the subject, the initial temperature of the engine at T/O has as much to do with the CHT's during the climb as the quality of the cooling system, the A/S during climb and OAT.

When I am able to taxi straight from my hangar to the runway and can get the run-up done without any delays and T/O with CHT's below 300 like I did this AM, I never see CHT's higher than 380 in a 130MPH climb to 6000 ft PA with ground OAT of 82. I did the same thing yesterday but had to taxi all the way to the other runway and took off with CHT's at 365. Max CHT was 415 at about 2000ft but was back down to 375 by the time I leveled off at 5500. The cooling system was doing its job very well. When we add t/o power we create a significant amount of heat very quickly yet the airplane isn't moving fast enough to accommodate for the sudden addition of heat and therefore CHTs rise. A better check of the cooling system is if it brings those temps back down as you stabilize in your climb. Testing during the T/O climb is a poor validation of the cooling system unless you control all the variables very carefully between changes in configuration - i've been experimenting with this for nearly a year now.

Paul is spot on - the climb curve is very flat over a wide range of A/S but cooling capacity increases significantly with A/S. I was climbing at 700fpm at 160MIAS, WOT, earlier this afternoon - CHTs were 320-340's. I won't be happy till I get them below 100 though
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  #23  
Old 09-12-2011, 06:41 PM
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turbo turbo is offline
 
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i was lookin for a similar post on hot chts but this is as good as any to post.

someone had mentioned about taping the front of the cowl seams in the inlet. my chts dropped by 10 degrees F. i was very surprised.
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  #24  
Old 09-12-2011, 06:51 PM
RV8R999 RV8R999 is offline
 
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Yeah Ed, that was me. One of the many incremental things I've done to reduce my CHTs but still if the engine is hot at T/O it is always going to get hotter until the airflow can catch up... no getting around it.
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  #25  
Old 09-12-2011, 07:26 PM
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strahler13 strahler13 is offline
 
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Quote:
Originally Posted by DanH View Post
Did you have the same beginning CHT on the runway in both cases (CHTs probably fell further during the power-off descent), and did you climb to 3500 after the T&G?
Dan,

My monitor starts at 300 deg, if i remember correctly, so i dont know where i start on either run. I did climb to 3500 on the TNG. i just find it hard to believe that the temp from start up, short taxi and take off is higher than a TNG when the temps recently were at 430.

Thanks for thinking,

Mark
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  #26  
Old 09-13-2011, 07:14 AM
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Quote:
Originally Posted by Russ McCutcheon View Post
One note, my IO-360 A1A and Danís IO-390 have angle valve cylinders and oil squirting in the bottom of the pistons, these differences probably contribute to lower CHTs so itís not exactly apples to apples.
Good point Russ....we have no good way of comparing the heat transfer ability of angle valve and parallel valve cylinder heads, other than perhaps estimating fin area. You're probably right in that the angle valve heads likely have more fin.

That said, engines are engines. Some percentage of combustion energy is simply heating the parts, so more HP equals more cooling requirement. Substitute a 200 or 210 HP engine in place of a 180 and you must increase system cooling capacity. Put another way, my IO-390 generates about 15% more waste heat than an O-360. Given the same cowl (thus the same cooling air mass), the only way to increase capacity is to increase the temperature rise of the mass. That's exactly what additional fin area would do. A parallel valve owner can do the same by making absolutely sure all his fin area is in full contact with cooling mass.

I doubt the oil squirters result in much CHT reduction. All piston contact is with the cylinder barrel at some distance from the head.

Quote:
Originally Posted by RV8R999 View Post
Our intuition tell us this must be true..but alas there is more going on here than merely plugging leaks.
Yep......

Quote:
Originally Posted by turbo View Post
someone had mentioned about taping the front of the cowl seams in the inlet. my chts dropped by 10 degrees F. i was very surprised.
.....although chasing them down is worth the effort.
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  #27  
Old 09-13-2011, 09:26 AM
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jjconstant jjconstant is offline
 
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Default cylinder metalurgy affect on CHT?

I've seen it suggested that ECI cylinders tend to run hotter than Lycoming. I have an ECI engine, 9:1 pistons and PMags and have been doing similar baffle and climb angle things to reduce CHT's incrementally. I think I'm almost there but I was wondering what the brain trust thought about differences between manufacturers/metallurgy explaining some of the lack of troubles some folks are having vs the CHT issues others are having.

Would a Poll be useful, ie "at 120kt climb on an 80 degree day, do you typically see CHTs over 400 degrees? What engine, compression ratio and ignition do you have"? I have no idea how to set up a poll like that or how to phrase it so it would yield useful data.

Jeremy Constant
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  #28  
Old 09-13-2011, 11:29 AM
RV8R999 RV8R999 is offline
 
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Default oil squirters

interesting point about the oil squirters. I have them in my Xp-360. I've wondered if during the first t/o when OT is typically way below steady-state if the increased viscosity reduces cooling effectiveness? This would be a good test.
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  #29  
Old 09-13-2011, 07:58 PM
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AlexPeterson AlexPeterson is online now
 
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Mark,

Lasar ignition systems do have a 5 minute (I think that was the amount) timer on initial power up, which prevents any timing advancement beyond baseline. The idea is to allow time for climb out without extra heat that might result from advanced timings at less than SL MAP's. I don't recall if the timer is reset when doing mag checks, which disables the EI also, or just on initial power up.

However, your issue seems to be the opposite... but, this timer could explain your first flight observation in some way not yet contemplated.

The cht trip point (where baseline timing kicks back in) on the Lasar system might be something fairly high, like 450, but check this. Not relevant, but it was mentioned.

You have not mentioned what power settings and, most importantly, what mixtures you are using during climb out. I can climb on a 90F day from 1k' to 10k' and not see any cht's over 380ish. My oil will climb to around 210, but will fall again after leveling off. On leveling out, my summertime cht's will run in the 310 to 340 range, depending on OAT. This takes some mixture control though. BTW, I'm running injected O360 with dual Lightspeed EI's. I previously had a Lasar system, and it did run hotter than the Lightspeed, no clue why.

On climbs, one can either run WOT and full rich, which will certainly keep things cool, or one can dial back to no more than 24/24 and lean things to LOP, if the engine is balanced in terms of when each cylinder reaches peak egt. (Tons of stuff in these forums about this.) If I were to climb at 24/24 at peak power type of egt settings (say 100 - 150 ROP), I would easily go over 400F on that same climb.

Come on up to MN this winter, you'll not have any cht problems!
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Last edited by AlexPeterson : 09-13-2011 at 08:01 PM.
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  #30  
Old 09-14-2011, 06:03 AM
PeterP PeterP is offline
 
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Sometimes high CHT can be related directly to fuel flow, or lack of I should say. Everything else can be perfect but if there`s not enough fuel for the HP it will be high CHT. I have a mildly hotted up parallel valve built by a good shop. Servo was the same as on a 180 HP 360 so changed it to one off a 540, get an extra 12 litres at WOT, problem gone. May be check your fuel flow as well.

Regards Peter
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