Cowl bottom lip

[6643]

N1940V » Sun May 29, 2005 5:34 pm

Carl Chitwood wrote:
If your engine is already operating within the proper range, it is possible to make it run too cool by improving the cooling too much, particularly in cooler climates.

The lip and larger plenum inlet holes are required by the Thompson STC; However, the STC was conceived with an improperly timed O-200 that was running hot. The dill rods (the previous owners of the STC, not Randy,) hacked the cowling up before they figured out that their engine was out of time.

Cessna 120/140 cowls and baffles are well designed, and do not need to be modified in order to properly cool a few more inches of engine displacement. I installed the Thompson STC and did not add the lip or hog out the plenum holes, and the only problem I ever encounter is getting the oil temp to hit 180 at OAT's less than 70F.

Paul Domeier
N1940V

[6643]

Michel Charette » Sun May 29, 2005 6:39 pm
Ok, as promised here are the pics of my lip arrangement.

The first pic is from outside, and below. The second pic is from inside, and the top. There are 2 round lips as the one shown, each side of the gascolator.

I bet you never saw a 140 equipped that way ! With an outside air temp of 43 deg.F at 2400 RPM last fall, I had 140 deg.F of oil temp., EGT of 1400 and CHT of 300 (both single point) and they always seem to be around these values, only the oil temp increasing a little.

My AME kind of likes the lip but is thinking about replacing it with a more kosher one... thus my original post.

cowling_lip1.jpg (14.67 KiB) Viewed 20662 times

cowl_lip2.jpg (28.97 KiB) Viewed 20662 times

MichelC (ex-caretaker of C-GNCJ)

[6643]

John von Linsowe » Sun May 29, 2005 7:47 pm

Michel Charette wrote:
There are 2 round lips as the one shown, each side of the gascolator.

I find the curved firewall mounted sheet metal interesting. RV fliers round this exit on the lower firewall with a noticeable increase in speed. The sharp corner apparently provides a fair amount of turbulence and therefore drag.

John von Linsowe
Webmaster
Association Web Coordinator
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N2165V 1948 C-140
N293MA 2004 Citabria 7GCBC
N9JV Maxair Drifter

[6643]

N1940V » Mon May 30, 2005 10:04 am

Michel

That looks more like some sort of strange attempt at streamlining than anything else. The "lip" we've been talking about is a small strip of metal that hangs out in the wind to add suction at the rear cowl air exit. Your installation is very very different.

As you said your plane is harder to heat up than cool, I'd either remove the mod and not install the cooling lip, or just leave it alone if it doesn't cause any problem with Canadian regs.

It's amazing the weird, funky and downright stupid things former owners have done to these planes over the years. At some point along the way, some idiot had braced the tail surfaces of 1940V with flying wires. The wires are long gone, but the hardware remains.

Paul Domeier
N1940V

[6643]

bzzt » Mon May 30, 2005 2:40 pm

Paul,
Just curious, is there any indication N1940V was previously used as a floatplane? That would give an indication for use of flying wires on the tail.
Buzz
N3034N

[6643]

Joe Mortland » Mon May 30, 2005 6:32 pm

If anyone were to ask me what that rolled sheetmetal, on the firewall was, I couldn't even BEGIN to give an answer! Maybe it's to help prevent vaporlock?

[6643]

N1940V » Mon May 30, 2005 8:11 pm

bzzt wrote:
is there any indication N1940V was previously used as a floatplane? That would give an indication for use of flying wires on the tail.

No, and no. This wasn't float plane stuff, it was flying brace wires ala Pitts Special. I ought to throw some on for a weird picture one of these days.

Paul Domeier
N1940V