patterson

patterson

Well Known Member
Patron
Topic for discussion.....
I'm struggling with CHT's that are up to 425-430 in climb and wonder what to do....if anything. cruise temps are fine at 350 or less.

I'll bet there are alot of lurkers out there that have real-time experience and we could better learn from what has worked for them...and what clearly does not, and must be addressed or you will be pulling cylinders.... at least.

I've searched the site and learned alot about plenums, cooling, drag reduction, optimal CHT's (very subjective) etc. SO, here's a question to those of you who have flown alot behind normally aspirated Lyc's and taken your engines to and past TBO without a top overhaul. (Rosie?) What did you do re engine management/cooling that got you there? What were your max CHT's in climb? cruise? frequency of oil/filter changes, etc?

If you learned 'the hard way' and required a Top Overhaul or worse, what did you change in your engine management procedures to avoid spending all that down time and $$$ again?
Ron
N8ZD
RV-4 - 175 hours
 
In addition to my RV6, I belong to a flying club which owns 3 Cessnas and a Mooney. It is a very old club which keeps good records. Our planes have historically made TBO without problems. Only the Mooney has a CHT gage. Our planes fly very often. They are flown by pilots with a wide disparity in experience and knowledge. It is my guess that they are frequently climbed with little regard for engine temperature. I'm sure they frequently descend without regard for shock cooling. We didn't even own a preheater until last year (we're in Michigan). What's the key to our engine's longevity? The only thing I can attribute it to is frequent flying and regular oil changes.
 
The answer is simple, fly a lot. 200 hr/s a year should be good enough to make that engine last to TBO (10 years...)
 
Frequent flying (not engine runs, flying)and frequent oil changes. Those are the 2 biggest factors, but by no means are they the only ones.

CHT - IIRC, Lycoming says up to 450*F is OK. I personally don't like that number after looking at a chart showing strength vs. temperature of aluminum. 400*F is (well, will be) my personal max CHT. Does Lycoming know more than me? They sure do. Your call...
 
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The glider club I flew with in the UK had a Chipmunk tow plane with an o-360. It suffered cracked heads multiple times and way before TBO. It was determined that the damage was due to shock cooling (towing a glider up, then pulling back the throttle and coming down). Instruction was given to the tow pilots to keep power on, gradually reducing it after releasing the glider. It takes them a little longer to get down, but to my knowledge instances of cracked heads were all but gone. I never flew the chipmunk and don't know if it had a CHT gauge, but Id' be very surprised if it did.
 
O360 in a Chipmunk?

I used to fly Chipmunks when I was a wee air cadet lad back in the UK...They came with a Gypsy major inverted 6 cylinder inline motor at about 145hp as I remember.

Nice airplanes...Must have looked weired with an o360 sticking out the sides though?

Frank
 
Chipmunk

Art Scholl's and the other Super Chipmunks looked great and flew better. I owned a stock DHC-1 Chimpunk for several years. Standard 145 Gypsy Major was little weak, but still one of the best flying airplanes I ever flew. Push rod controls were superbly balanced and light as a feather.
CHT on a chipmunk...what's that :)
 
Lyc says

Ditto fly every day (fly not start and run up)
Change oil/filter every 25 hours (or so, on a trip I will go longer)

Lyc says:

"For maximum service life, maintain the following recommended limits for continuous operation.

(a) Engine power setting - 65% of rated or less.
(b) Cylinder head temperatures - 400 deg F. or below.
(c) Oil temperature - 165 deg F. - 220 deg F.
(d) Turbine inlet temperature - maintain 100 deg F. on rich side of maximum allowable."



Type certificate for the Lyc O-360

Temperature limits: (Maximum permissible)
Cylinder head 500?F (well type thermocouple)
Cylinder base 325?F
Oil inlet 245?F


There is a BIG diff between Certified CHT red line (500F) and recommended (400F), 100F to be exact, but if you are getting well over 400F you are doing damage. The max allowed or red line is NOT for long life.

My personal Red line is 400F per Lycs recommendation. If I see 410-420F I may allow for short periods but will work to lower temp. You can always level off, reduce climb rate or if level lower power. If you can't keep 400F in level flight (in my opinion) you need more cooling.

Keep in mind NEW ENGINES RUN HOT Why? Because they are tight? No :eek:

The reason new engines run hot is there are no carbon deposits on the new piston top and combustion chamber. The deposit reduces heat transfer. Think of it as a natural coating that works like a ceramic coating, rejecting heat.

OIL THE LIFE BLOOD
Also OIL cooler make, model, installation are important. All Lycs are AIR and OIL cooled. High oil temps exasperate CHT, and vise verse. If oil gets too hot in this area it cooks and leaves deposits on the valve stems, which results in problems. The highest oil temp is on the exhaust valve stem.

The heat in the valve needs to transfer to the valve stem guide and into the cylinder head, fins and than into the air. The oil is in between the guild and stem. You will have valve sticking and problems if you run high oil temp. I like to see no more than 210F, but typically 190F. You can be too cool, 170F is a min. Keep in mind what you read on your Oil Temp gauge is about 20-25F higher at the valve stem. When oil gets to hot it breaks down. This is why early pure synthetic oils did poorly, they could not handle the extreme heat and left more deposits at those high temps. That brings up the topic of OIL: single weight, multi-weight, semi-synthetic, a whole topic onto its self.
 
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4 banger

frankh said:
I used to fly Chipmunks when I was a wee air cadet lad back in the UK...They came with a Gypsy major inverted 6 cylinder inline motor at about 145hp as I remember.

Nice airplanes...Must have looked weired with an o360 sticking out the sides though?

Frank
Click to expand...

Not quite Frank.... :)

It was a four cylinder engine, and I think it was derived from half a WWI V8...

http://en.wikipedia.org/wiki/De_Havilland_Gipsy_Major

One of my first airplane flights was in 1965 in a University of Liverpool Air Squadron Chipmunk... got some great shots of three in formation over the university campus and the two city cathedrals.

I guess the O-360 is a semi-common conversion- made famous by Art Scholl, but not as pretty as the original.

http://www.nasm.si.edu/research/aero/aircraft/dehavilland_chip.htm

gil in Tucson
 
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Yep, the RAF guys at the base had converted it to the O-360 years ago. The other tug plane was a piper pawane with an O-540.

Here's the Chipmunk





And the gliders in que for a winch launch
 
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