Engine temps and leaning.

[docmirror]

TS Alpin makes or made some cowling louvers that are popular on skywagons. I don't know if they're STC'd for a skyhawk...

You might try that...

And exhaust pipe fairing is supposed to decrease positive pressure through the hole ...

The same offering came on the Bonanza gill doors about 1963 or so. Many of the IO-520 engines have the louvers on the gill doors, and I've heard it helps quite a bit. The early O-470s don't often have them. For the Bonanza, it is not an STC to cut the louvers, just a minor mod done on 337. Not sure what the paperwork would be on a 172 cutting into the lower cowl area for air exhaust, or even if it would help, but it might.

http://www.barnstormers.com/listing_images.php?id=1017435&ZOOM=b7bf61137cc9e9216eb247f75067776f

 

[txflyer]

The same offering came on the Bonanza gill doors about 1963 or so. Many of the IO-520 engines have the louvers on the gill doors, and I've heard it helps quite a bit. The early O-470s don't often have them. For the Bonanza, it is not an STC to cut the louvers, just a minor mod done on 337. Not sure what the paperwork would be on a 172 cutting into the lower cowl area for air exhaust, or even if it would help, but it might.

http://www.barnstormers.com/listing_images.php?id=1017435&ZOOM=b7bf61137cc9e9216eb247f75067776f

Many wagon owners have them. My 0-470 does not as you say. I don't need them because mine runs on the cool side already. Never have exceeded 400 but I don't have individual cylinder temps so I wouldn't know if one is running hot either.

I don't know skyhawks, but another thing to check are the heater hoses and ram air box on the cabin heat mounted on the firewall. I know mine just dumps the hot air right back out into the engine bay when you are not using cabin heat.

There may be some room to play with all that heat being rammed around the muffler and blown out into the engine bay.... maybe some louvers in just the right place ...

 

[Tom-D]

Not sure what the paperwork would be on a 172 cutting into the lower cowl area for air exhaust, or even if it would help, but it might.

It's quite common to see the lip trimmed on the 170 and early 172. most claim it to be a minor mod.

It will add about 1 mile per hour to the cruise speed, but does nothing to the 0-300 temps.

 

[docmirror]

It's quite common to see the lip trimmed on the 170 and early 172. most claim it to be a minor mod.

It will add about 1 mile per hour to the cruise speed, but does nothing to the 0-300 temps.

Didn't know the O-300 had a problem with temps in the 172. I can understand the 175 having cooling issues, but not the 172.

 

[Tom-D]

Didn't know the O-300 had a problem with temps in the 172.

They don't..

I was referring to the cowl mod question.

 

[Stewartb]

For cowls without cowl flaps where guys struggle with high temps it's popular in Alaska to add a cooling lip to increase lower cowl negative pressure. I added cowl lovers to my own big motor 180 and helped a couple of friends do the same. 10* was the average improvement. With 180s the bigger issue is inadequate fuel flow and once that's solved the CHT woes disappear. TS Alphin has been gone for several years. Some outfit in Maryland has his STC and I think Skywagons City got his inventory. I bought my louvers from Sywagon City. Lost the STC I'd bought years ago from the Skywagons Club and installed them as a minor alteration. Subsequently finally got my carb dialed in and solved my problem so wouldn't do the louvers if I had to do it over. These days my temps are excellent and my temp spreads are very close, even in cold weather when lean is accentuated. But that's thread drift and has little to do with the OP.

FYI. http://www.globefiberglass.com/images/COMANCHE/CESSNA/GF055200-41.htm

 

[UngaWunga]

Took it up for some experimentation yesterday. About 60deg out. Take off at full throttle, got 800fpm climb at 77knots. Engine temps were good, fronts a little hotter than the rear.

Cruising at 2500', 2400rpms, the rear cylinders started getting hotter than the front. Ended up with 1.25 fingers out on the mixture to keep rear cylinder temps down.

Lowered rpms to 2300, and the engine temps evened out. About 1.5 fingers of mixture kept things even. Interesting that dropping 100rpms made that difference. Why would it do that?

Also noticed that pushing the mixture in another 2 notches, the engine picked up rpms. Peak power over peak lean, I guess. Learning process for me.

As for the baffles, pictures...
You can see in the last picture that the baffle is too short, and gets pushed back. Need to fix that.

 

[UngaWunga]

Those are intercylinder baffles, and the Lyc has them too. Often find them loose or beat up so they let a lot of air escape. Another bad spot is the aft side of the aft cylinders; the baffle is supposed to be held tightly against the fins as it curves down and under the cylinders, yet I often find the wires missing. When the airplane is in flight and there's a lot of air coming in, those baffles flex away from the cylinder fins if they're not tied properly.

Dan

The weather is crappy here today. If I have a chance, I'll head over and pop the top cowl off to take a look at that.

 

[pigpenracing]

Took it up for some experimentation yesterday. About 60deg out. Take off at full throttle, got 800fpm climb at 77knots. Engine temps were good, fronts a little hotter than the rear.

Cruising at 2500', 2400rpms, the rear cylinders started getting hotter than the front. Ended up with 1.25 fingers out on the mixture to keep rear cylinder temps down.

Lowered rpms to 2300, and the engine temps evened out. About 1.5 fingers of mixture kept things even. Interesting that dropping 100rpms made that difference. Why would it do that?

Also noticed that pushing the mixture in another 2 notches, the engine picked up rpms. Peak power over peak lean, I guess. Learning process for me.

As for the baffles, pictures...
You can see in the last picture that the baffle is too short, and gets pushed back. Need to fix that.

It doesn't sound to me that you have problems. I am not shut why you are leaning at low altitude anyway???? I think you are overthinking everything and trying to fix something that isn't broken. If you want good mileage at cruising speed climb to 8000 feet and you can lean it a bunch then.

 

[mtuomi]

On long climbs the rear cyls will obviously run hotter than front ones. The delta is then defined by the baffles and cowlings.

The intake system/cylinder head/cam design on every single certified airplane engine is absolute rubbish, that is not a consideration for this problem.

 

[MauleSkinner]

You can see in the last picture that the baffle is too short, and gets pushed back. Need to fix that.

Yup...that'll make for a pretty big hole.

 

[Dan Thomas]

The intake system/cylinder head/cam design on every single certified airplane engine is absolute rubbish, that is not a consideration for this problem.

They're not absolute rubbish, but they're not as good as they might be. I, for one, know that I wouldn't be able to do any better without spending a gazillion dollars on R&D and prototyping. These engines have a far different job that an auto engine, which loafs along at 25% power most of the time, has little restriction on weight and RPM, is built in the millions of units, and usually has plenty of room available. Just try designing and building something that MUST be light and strong and compact and reliable and affordable and efficient: a lot bigger job than it appears. And do it for a tiny market while dodging lawyers and insurance companies and the FAA. There are plenty of reasons why we're still flying ancient designs.

SMA, for example, had spent one billion dollars on its 230-HP diesel engine for the 182 by 2011 when I was working on one of the 50 then flying. 50 engines after a billion dollars spent. And they were still working the bugs out of it. How much money is SMA going to make off it?

Dan

 

[bnt83]

How much money is SMA going to make off it? Dan

Before the liability trial lawyers win or after?

 

[mtuomi]

The fact that the used rpm and power range is so narrow on a plane makes designing the intake system alot easier.
A simple double plenum design would work great. It would save space, be lighter and much much more efficient, but they weren't around when these engines were designed, and the manufacturers are too lazy to improve them anyway.

They're not absolute rubbish, but they're not as good as they might be. I, for one, know that I wouldn't be able to do any better without spending a gazillion dollars on R&D and prototyping. These engines have a far different job that an auto engine, which loafs along at 25% power most of the time, has little restriction on weight and RPM, is built in the millions of units, and usually has plenty of room available. Just try designing and building something that MUST be light and strong and compact and reliable and affordable and efficient: a lot bigger job than it appears. And do it for a tiny market while dodging lawyers and insurance companies and the FAA. There are plenty of reasons why we're still flying ancient designs.

SMA, for example, had spent one billion dollars on its 230-HP diesel engine for the 182 by 2011 when I was working on one of the 50 then flying. 50 engines after a billion dollars spent. And they were still working the bugs out of it. How much money is SMA going to make off it?

Dan

 

[UngaWunga]

Update. Got that baffle seal replaced, and now cylinder #4 temps are lower. Cylinder #3 are down a little, but still higher than all the others. Cruising at 5500 last weekend at 2300rpms, EGT temps were relatively even with a little leaning. Bumping up rpms to 2400 or 2500 had the rear EGT temps climb, leaning didn't seem to change things too much. So I ran at 2300 rpms.

I'll have the plane in a hanger soon and will pop off the cowling to poke around at the other baffles.