Cowl bottom lip

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Michel Charette » Mon May 16, 2005 7:36 pm

Is the 1948 C-140 supposed to have that "lip" at the bottom openning of the engine cowling sticking out for about 1/2 inch in the airflow as I have seen on many 120/140s ?

Mine does not, but has an extension instead narrowing the cowl bottom opening plus rounded lips on the bottom of the firewall, a la homebuilt, each side of the gascolator (approx 5 inch diam. bend).

My AME would like to see a more standard layout to make sure we keep those new cylinders of mine properly cooled. The previous owner seems to have made some temperature measurements and they seem to work (have some graphs in my paperwork), but they are definitely not original looking !

My C-85-12F has the C-150 exhaust STC. You can see a little bit what I mean on the attached picture.

cowl_lip.jpg (238.85 KiB) Viewed 13345 times

MichelC (ex-caretaker of C-GNCJ)

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Dale Radeleff » Mon May 16, 2005 8:35 pm

Michel,

I made a post in your parts wanted ad about this but the "48" lip may be longer then the one on the "47" and earlier models. Also, it looks like you may have your stacks reversed. I believe that the slant of the pipe is supposed to go the other way, something having to do with keeping pressure on the exhaust instead of sucking it out, I could be wrong but the other way is how I see them on 150's.
An error does not become truth by reason of multiplied propagation, nor does truth become error because nobody sees it.

Mohandas Gandhi

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Victor G » Mon May 16, 2005 10:38 pm

Michel,

The cowling lip you refer to is required for C-90 and 0-200 engine installations. It is not needed for any C-85, although I suppose if your engine was running hot, it is a Cessna part and would be able to be installed with minimal fuss.

The cowling lip you have is something unique to your airplane, I've never seen one like that. Do you have a 46 or a 1947 aircraft? A 46 cowling drops down lower (towards the ground) than a 47. Thus a 47 has more benefit of a cowling lip than a 46 would.

Your exhaust pipes are backwards. Spent a lot of time talking with people who should know, and the sum total of what everybody said, who's opinion I respect, says the slope of the exhaust pipe should match the slope of the cowling. Mostly to keep the hot exhaust gases off the cowling. I've tried turning them both ways and was unable to perceive even the slightest difference in power.

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David Sbur » Mon May 16, 2005 11:28 pm

The cowling lip you refer to is required for C-90 and 0-200 engine installations.

Guess I better research this. My 0-200 installation does not have this. I have an 'early' lower cowl. Plane is June of 1946, SN8748. My engine runs cool and often is difficult to get the oil temp up into the 180's. CHT rear/left is usually in the low to mid 200's except on climbouts. I have the Emmett/now Thompson STC for my installation, but I don't recall any requirement for a lower cowl lip. Does this draw more air through the cowl for cooling or what/how exactly does such a thing work?

Dave Sbur/Vancouver WA
N110V C-140 #8748 Member#6597
Asso. Rep. Washington State
Learn from my problems-it's cheaper!

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Michel Charette » Tue May 17, 2005 7:38 am

Well, well, well... So my exhaust pipes are reversed ??? You learn eveyday in here ! I'll have that fixed on my next visit to my AME, for sure !

As for the lip, indeed, I have not seen any like that before, thus my asking. So apprently, I would not need one ? If anyone could post a pic of what they should normally look like on a 1948, I would appreciate. I have the C-85 engine.

Makes me think... we should organize a clinic somewhere on the east coast where we could have you guys look at our planes. Then we could fly away with a nice list of things to do !!!

Our planes are old and it seems lots of funny things have been done to them by well intent people, but the results are not always so good ! I'm learning, I'm learning !

Thanks guys !

MichelC (ex-caretaker of C-GNCJ)

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Victor G » Tue May 17, 2005 7:57 am

If you look in the TC under "optional engines" part of the C-90 install is to install Cessna doubler (p/n XXXXXXX) (i.e. the cowling lip).

I have both 0-200 STC's of about 15 years ago and the one I used to install my 0-200 required the cowling lip, and I need it, my engine oil runs on the warm side. I don't recall what the other STC said and it's at home and not available to look at right now. I'll check on it though.

If you look at a 46 cowling vs a 47 and later, the lower lip of the cowling on a 46 hangs down more into the slipstream and I suspect provides for better cooling. (no facts here) My 47 needs all the help it can get I'm thinking of enlarging the lip on the bottom.

Michel, I would have to see your airplane, or better pictures, my guess is you could remove what's been added and you would be back to an original arrangement. And it would probably work just fine.

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Michel Charette » Tue May 17, 2005 8:03 am

Victor, next time I go the the airport, I will take much better pics and post them here.

I don't have the figures with me now but I'll give you my temps as well.

About the exhaust pipes, is it only the stacks that are reversed ? Can they be simply turned faceward or it needs more work ? I never looked at that area that carefully so I don't remember how they are mounted...

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Randy Thompson » Tue May 17, 2005 9:15 am

I don't think that I would be so quick at this pipe reversal thing. When you start looking around you will see them both ways. I prefer the slant to be forward. Someone went to great lengths to center your stacks in the cowl opening. Most of them are curved and will come out of the cowl in different places when reversed. Yours look long enough that they can be recut to face forward and only some will think they are correct then. Like Victor said the engine doesn't run any different.
I agree that if you just removed that extra sheet metal the cowling would look original. In a hot climate the proper cowling lip provides extra cooling.

A&P IA. Holder of STC for O-200A's in 120, 140 & 140A's. Engine overhauls on C-85's ,C-85's with O-200 crankshaft, C-90's and O-200A's
State Rep for California

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Dale Radeleff » Tue May 17, 2005 10:05 am
Randy is right, swapping stackes from one side to the other (which is what you would have to do) may well change the position of the stacks causing you to have to move the holes (something I have to do on my left side. Just trim them with a band saw to match the cowling contour and save yourself the grief.

The cowling lip hanging down in the slipstream causes a vacuum that pulls more air through the cowling giving you better overall cooling of the engine and hence lower oil temps I found when I put mine on it also change the trim slightly so beware the first time you takeoff after you put it on.
An error does not become truth by reason of multiplied propagation, nor does truth become error because nobody sees it.

Mohandas Gandhi

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Michel Charette » Tue May 17, 2005 1:09 pm

So if I deduce from what some of you guys are saying, the lip thing is more a seasonal issue then... have it in in summer to reduce temps and then remove in winter to keep warmth inside ?

I will have a look tonight on the temperature charts I saw in my plane's documentation and report back. It probably ran hot at some point because it seems the previous owner went to quite an effort to make sure this arrangement was efficient. He is known to be a good homebuilder and teaches a/c maintenance at a local college, so I don't want to dismiss what he did too fast. By the way, I had them off last summer and when we replaced my cylinders, we could definitely tell that some of them had run hot. Was it partly the extra long taxi at Oshkosh ? Perhaps... So I did not take any change and put them back. But the temperatures on both my CHT and EGT (single point) look very similar than before !

As I said, I'm learning all the time and one of my main source of information is to ask quaestions here on the forum. And I have to say I feel priviledged and lucky to be able to do just that ! Some of you guys are a wealth of information and experience with the type. This alone pays tenfold the membership fees !!! As a first time owner, you can't beat that !

Thanks all for your input ! I'll get back with more details...

MichelC (ex-caretaker of C-GNCJ)