Reduce your Skyhawk CHT!

[idahoflier]

Shout out to @Pilawt for recommending the Maple Leaf exhaust fairing! I just got my Skyhawk back after installation today and the fairing works!

I had my engine overhauled last fall and had a JPM 730 installed at the same time. Prior to the JPM, I only had an EGT gauge and was shocked at the CHT's I was seeing. As winter progressed to spring and summer it only got worse. I had to stagger climbs in order to keep my hottest cylinder below 420°F (my personal limit) and in cruise I always was right on the edge of 400°F trying to get as lean as I could.

I have an Air Plains O-360 conversion and speaking to one of their technical folks I was told I could expect CHT's between 420°F - 430°F during climb out. That was disappointing, but at least I knew my baffling wasn't at fault. Lycoming recommends CHT's less than 400°F for maximum cylinder life so I had resigned myself to the fact that my cylinders would likely not make it to TBO.

One back-country departure (necessary to be leaned for maximum power) a couple weeks ago one cylinder jumped up the 436°F before I could enrichen and pull power to get it cooled. That was my fault, however the CHT went from 390°F to 436°F in less than 60 seconds.

Anyway, today was a pretty good test as the ambient temperature was 95°F, the warmest by far I have flown this summer. I was able to takeoff and climb to my cruising altitude and all cylinders were under 400°F. I estimate my hottest cylinders are running at least 20°F - 25°F cooler. As I fly more I will pull my JPM data for comparison but I really think this was a worthwhile addition.

So if you have a Skyhawk running a bit hot, consider the Maple Leaf exhaust fairing. It will likely cost 1 AMU installed but I think it's worth it...

 

[charlie]

Flying ours for the first time later today......

 

[GMascelli]

in case anyone was wondering what the exhaust fairing looked like.

 

[bnt83]

O-320-E2D in the "lead sled" Cessna 177. This engine is run hard pulling an airplane that's a tad too large for the HP. I should mention it is stock 150 horse. #4 will run all the way up up to 415F on longer climbs on a hot day, but usually starts cooling off by itself after passing 5k MSL or so. My Dad thinks it should stay under 380F during climbs (after reading Mike B which is advice for Continental engines ) which isn't possible.

We have the exhaust fairing as well as the fixed cowl flap fairing (cowl flap is a 177 part and not applicable to the 172)

 

[EdFred]

Trying to wrap my head around why an exhaust fairing would affect CHT - or even EGT for that matter. It's not affecting airflow to the cylinders, or oil cooler, or anything else from what I can see. Unless somehow it helps 'pull' the air through the cowl better?

 

[bnt83]

Trying to wrap my head around why an exhaust fairing would affect CHT - or even EGT for that matter. It's not affecting airflow to the cylinders, or oil cooler, or anything else from what I can see.

Basically controls airflow around that area of the cowl better. The OEM hole in the cowl is pretty large and it looks like it catches air to me, reducing the pressure differential of air above and below the engine and reducing cooling.

 

[wheaties]

420-430!? Aluminum loses rigidity as the temperature goes up. Also, most oils don't survive higher temps past 400. So you're effectively pushing a weakened metal part running at high rpms with lessened lubrication every time you take it above 400.

 

[dtuuri]

Trying to wrap my head around why an exhaust fairing would affect CHT - or even EGT for that matter. It's not affecting airflow to the cylinders, or oil cooler, or anything else from what I can see. Unless somehow it helps 'pull' the air through the cowl better?

Not saying I know, but it looks like an augmenter tube arrangement to me. Exhaust gas providing motive flow for a larger volume of air through the opening around the tube, like a "jet pump".

 

[bnt83]

420-430!? Aluminum loses rigidity as the temperature goes up. Also, most oils don't survive higher temps past 400. So you're effectively pushing a weakened metal part running at high rpms with lessened lubrication every time you take it above 400.

I find it interesting that Lycoming O-320-E2D red line CHT is 510F yet a Continental IO520 redline CHT is 460F

A Continental C75 redline CHT is 550F, I think its the hottest I have ever found.

Pratt Wasp Jr is also 550F

The O320 we have is 1940 ish hours since new with most of its life being operated without an engine monitor, like most flight school aircraft.

 

[idahoflier]

Trying to wrap my head around why an exhaust fairing would affect CHT - or even EGT for that matter. It's not affecting airflow to the cylinders, or oil cooler, or anything else from what I can see. Unless somehow it helps 'pull' the air through the cowl better?

At least on my N model the hole in the cowl for the exhaust pipe has about a 20° incidence to the relative wind and it gets worse in a high nose attitude like climbs. That creates positive pressure and reduces airflow. I spoke with the designer and he said that the fairing creates a slight vacuum...

 

[nrpetersen]

Our 172M was cold blooded as we didn't note things were warm until it got over ~ 330 DegF. We kept the cyl fins clean and the baffles tight and rigid.

It may be time for some testing. There should be about 5 to 6 inches of water pressure across the baffle system at cruise. Or?

 

[UngaWunga]

in case anyone was wondering what the exhaust fairing looked like.

View attachment 88758 View attachment 88759

$1000 for that and for someone to install it?

 

[EdFred]

$1000 for that and for someone to install it?

R&D + FAA = bend over.

 

[idahoflier]

$1000 for that and for someone to install it?

Yeah, it's a pricey addition for a piece of fiberglass. The part itself + STC was something like $300.00. Their site says 1-2 hours to install (not including painting), but my shop took a bit longer. Could they have done it faster? Maybe, but they did a great job so I'm not unhappy.

As I mentioned earlier I just had my first run O-360 overhauled. Looking at the logs it had 3 jugs replaced, one twice. I suspect it was due to heat because flying by the book with an EGT guage they all likely got cooked. If this saves one cylinder replacement then I'm ahead...

 

[midwestpa24]

Trying to wrap my head around why an exhaust fairing would affect CHT - or even EGT for that matter. It's not affecting airflow to the cylinders, or oil cooler, or anything else from what I can see. Unless somehow it helps 'pull' the air through the cowl better?

With air cooled engines it doesn't take much to have an impact on cooling. Even a baffle folded the wrong way putting the cowl on will have a huge effect. I can see how this probably optimizes the air flow over the opening in the cowl to promote more cooling.

 

[PaulMillner]

the CHT went from 390°F to 436°F in less than 60 seconds.

That sounds like moderate detonation going on... 2 degrees per second CHT rise. I understand this was a max performance takeoff, but a little richer wouldn't affect power more than a percent or two, but might stop the detonation.

It would be interesting to know what your fuel flow is during normal climbs... I'm guessing an additional one to two GPH might well suppress those high CHTs in the climb.

Paul

 

[PaulMillner]

O-320-E2D in the "lead sled" Cessna 177. This engine is run hard pulling an airplane that's a tad too large for the HP. I should mention it is stock 150 horse. #4 will run all the way up up to 415F on longer climbs on a hot day, but usually starts cooling off by itself after passing 5k MSL or so. My Dad thinks it should stay under 380F during climbs (after reading Mike B which is advice for Continental engines ) which isn't possible.

We have the exhaust fairing as well as the fixed cowl flap fairing (cowl flap is a 177 part and not applicable to the 172)

Well... it *is* possible! GAMI's recommendations for long cylinder life, based on cylinder metallurgy, are the same for Lycoming and Continental... and Mike Busch doesn't think Lycomings should run warmer either.

Are you certain all four of your cylinder baffle springs are in place, and adjusted properly? Can you post a picture of your baffle seals? There are some tricks common to the Cardinal that you might be missing... there are different dash number carburetors of varying richness... do you have fuel flow instrumentation?

The Braly mod, takes five minutes to install the simple version, will improve cooling on #2 and #3... details on the Cardinal Flyers website, www.cardinalflyers.com

Paul

 

[idahoflier]

That sounds like moderate detonation going on... 2 degrees per second CHT rise. I understand this was a max performance takeoff, but a little richer wouldn't affect power more than a percent or two, but might stop the detonation.

It would be interesting to know what your fuel flow is during normal climbs... I'm guessing an additional one to two GPH might well suppress those high CHTs in the climb.

Paul

The CHT rise was < 1°/sec, but it's possible there was light detonation going on. I'll pull the jpi data when I get a chance to take a look. I doubt it though because the DA was around 9,500 and the engine wouldn't be able to make much over 60% power if that. I think the GAMI/Red Fin folks would have that just outside of the possible detonation zone. There is a bit more than a 1% - 2% penalty running full rich on takeoff at that DA and unfortunately I don't have the luxury of fine tuning the mixture on the takeoff/climb out.

No fuel flow data, I was too cheap to splurge on that but I don't really miss it. I always run full rich during takeoff/climb - when I can...

One more data point, took off yesterday with an OAT of 100°. Climbed from 2,540 to 7,500 WOT and CHT peaked at 409° on the hottest cylinder. This fairing works!