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RV-8 Cowl Vents

 
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Matt Dralle
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Joined: 08 Nov 2005
Posts: 26320
Location: Livermore CA USA
PostPosted: Mon Aug 08, 2011 9:53 am    Post subject: RV-8 Cowl Vents Reply with quote
At 07:04 AM 8/8/2011 Monday, you wrote:
Quote:
Dear Fellow RV-8 Builders, I now have 13 hours on my 0360 Lyc. Still having # 1 CHT get too hot before TOC. So I have to throttle back and stairstep up to altitude. Temps should be stable by now with 13 hours. So I bought from Avery the bottom cowl louvers to improve airflow. Talked to a couple RV-8 drivers both said the vents lowered CHTs about 20 degrees. Question is how is best to mount? What shape and size hole(s)? The bottom of the vent plate is flat while the cowl bottoms have compound curve surfaces. What is best for looks and effectiveness and strength? Hope to hear from someone, Bill of Georgia N288WP

Hi Bill,

I have an IO-390 210hp on my RV-8 with the standard cowling. I don't have any trouble with CHT's (generally well under 400f) and my oil temps are generally in the low 180'sf. If I take off on a hot day at sea level and climb hard, I can get the CHT on the hot cylinder to go over 400 but by that time I'm at 8000 ft and simply decreasing my angle slightly will bring it back down. The only "non-stock" aspect of my installation is the giant oil cooler I added to the back of the baffle. Its about twice the size of the stock one.

Before you start cutting holes in your cowling, you might want to do some more investigation into the cause of the overheating. Might be indicative of something else. Plugged oil line to that cylinder, maybe a blocked fuel injector on that cylinder? Try swapping the injectors between the hottest and coolest cylinder and see what impact this has on the CHT.

Here's some info on the oil cooler installation that has worked well for me:

http://www.mattsrv8.com/users/display_log.php?user=MattsRV8&project=638&category=2972&log=90253&row=84

Matt
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Matt Dralle
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PostPosted: Mon Aug 08, 2011 11:44 am    Post subject: RV-8 Cowl Vents Reply with quote
Matt:
I just made a simple mod that you should try before doing anything drastic like cutting holes in the cowl.  On my 6A I duct taped on 2 wedges cut out of wooden 2x2  that were about 1.5" wide from the narrow edge back to the 3/8" wide trailing edge.  They are about 5" long.  They were nearly identical with the plastic rudder trim wedges that Avery sells.  I put these on the bottom of the cowl where the exhaust pipes come out with the wide edge flush with the aft edge of the cowl.  I saw an immediate drop in oil temps of at least 10 deg. F and probably 20 F.

Last week I replaced them with 2 of the Avery rudder trim tabs, painted to match the plane and curved a bit to match the shape of the cowl.  I think these work  the same way the louvers work: The air going past the trailing edge causes a slight decrease in pressure that helps draw more air through the cowl.  I only had to drill 4 screw holes in the cowl to mount them "permanently".  I can remove them any time I want just by taking the screws out..   The cowl is otherwise a stock Van's cowl.

I need to do some more flying (I'm in Tucson where there's plenty of hi temps this time of year)  to test this, but the few flights I have done are very encouraging.  I'll send pictures if you like.

--
Tom Sargent, RV-6A
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