Looking to minimize excess heat in cowl.

[kiloxray]

Hi, I have been flying the hawk for about 3 years now. I have a carb temp sensor installed, and always have a carb temp 10 degrees hotter that OAT.
I have decided this is robbing power and I am looking to lower the temps in the lower half of the cowl.

I have wrapped the exhaust with fiber glass tape so far, but I am now looking at how the carb heat dumps when not in use. I have a typical air box fro ACS, modified with the dump hole on the bottom of the box. I would like to find out what is the best way to dump this hot air out side the cowl rather than inside the cowl. has anyone else done this?

Thanks, Eric Klokstad

O-540 - hartzel- vetterman exhaust

[Enewton57]

The carb air box that I purchased from Aircraft Spruce had a 2" pipe sticking out the bottom. I guess the idea is to cut a hole in the bottom of your cowling and let the pipe stick out. When carb heat is off, the hot air exits the pipe through the bottom. I didn't like the idea of cutting a hole in my cowl bottom, so I cut the pipe off and let the air dump into the cowling. I just made sure the cowl exit was plenty big to give a good exit. I also made nice 2" lip at about a 45 degree angle at the exit.

[Battson]

Is it possible your carb heat door shutter could be leaking hot air into the carb?

[N3UW]

I would also agree with Battson. With the volume of air going into the intake I would find it hard to see the heat inside the cowl would heat up the intake that much. I would think you are getting so type of leak of hot air into the intake.

[fly_n_low]

My ACS airbox rides low in my cowl so I cut the dump tube almost flush but I also cut the hole in the bottom of the cowl. I also have gills. I've never noticed my carb temp being much over ambient but I'll have to pay attention the next time I fly.

http://www.foxflier.com/bearhawk/2011/Aug11/P8300024.JPG

Regards,

Ted

[jaredyates]

I don't think it is uncommon for a Lycoming to read a carb temp higher than ambient cowl temp and real carb air temp. Since the carb is mounted to the sump, you can get some energy transfer to the carb body, which in turn causes the carb temp probe to read erroneously high. If your carb temp doesn't require the grounding of the carb threads, you might try temporarily securing it somewhere inside the cowl near the carb to see how it changes. I remember reading someone's opinion that it was not advisable to wrap the exhaust, since it can inhibit the ability of the pipes to transfer energy away from the cylinders and into the surrounding air. This is apparently part of the strategy for cooling the engine, according to that source.

[Battson]

I have heard the same about wrapping exhausts in air cooled engines... especially the aviation variety.
But it could have been some other reason too... memory lagging...