Inlet/outlet opening ratio-CHT's

n815vp · #1 08-22-2008, 04:20 PM

Have had higher CHT's for the first 30 hours on a new 0-320 ,rv9a. Allowing for engine break-in, Didn't do anything but think about the newer Vans cowls that have an approx. inlet to oulet area ratio of 1.
Yesterday added (2) louvers (aviation tech products) to the lower cowl and Presto! the CHT's dropped signifigantly.
Don't know what it did to change speed,but don't care. a fast Hot plane doesn't work for me.

flyer46 · #2 08-22-2008, 07:13 PM

I assume you used the LOU-11 or 12

http://www.aviationtechproducts.com/...cessories.html

Which set of louvers did you use? Where did you place them?

Roughly how many degrees did it drop the CHTs??

Thanks for any info you can give on your successful installation. I need some sort of similar modification......or movable cowl flaps.

RV9A FP O320D1A

n815vp · #3 08-22-2008, 08:25 PM

The Lou-11's were installed about an inch forward of the firewall on either side of the lower cowl about 2 inches outboard of the outlet tunnel sides.
The CHT's prior to this mod. would get to 410/420 F in the takeoff climb at 1000 feet with 125 mph, 75/80 F surface.
Today with the louvers it was climbout approx 1200 ft/min to 3000ft full power and CHT's just turning to 400.

flyer46 · #4 08-22-2008, 08:57 PM

Thanks. That is a good data point and definitely a step in the right direction.

N523RV · #5 08-23-2008, 05:55 AM

Has is made any improvement at cruise speeds?

I usually hit 425 on one cylinder on a hot day when climbing out and they stabilize around 380 in cruise.

frankh · #6 08-23-2008, 09:35 AM

A hot O320...Are you sure you glassed in one side of the ramps in the upper half of the cowl..These temps seem a little high.

Also has anyone ever used a cowl flap?

My SJ is a little marginal in a climb on a hot day but cools off nicely in cruise which is what you'd expect.

Seems to me an ajustable cowl flap would be the best of both worlds at th expense of some complexity.

Does anyone have a good design they could post pictures off?

Frank
IO360 now featuring 10% ethanol

L.Adamson · #7 08-23-2008, 09:50 AM

Quote:

Originally Posted by frankh

A hot O320...Are you sure you glassed in one side of the ramps in the upper half of the cowl..These temps seem a little high.

Between this forum, and at the airport, I'm seeing numerous "hot" 0320's on 9's. The owner of the 9A that I've flown.........does have the ramps sealed with glass. I'm going to pass on the info from this thread, regarding the outlets.

However, we do use a high altitude airport, and the summer has been hot. But CHT's are easily running beyond 420 degrees on climbout if you don't keep an eye on it, and lower the climb rate. Cruise is about 380. This is cylinder #3, and there is the air dam in front of cylinder #1.

L.Adamson

N523RV · #8 08-23-2008, 12:36 PM

Frank,

I'm flying with the SJ cowl/plenum. I do have 9:1 pistons for 170hp on my O-320. I just ordered the louvers to install on the bottom of my cowl to see if that brings the temps down. The good thing is that it will be easy to test with/without on the same day to get real numbers, I can just tape over them (on the inside) to get a baseline and then remove the tape afterwards.

I did not trim the cowl exit opening to make it larger. There was an RV-9A at Osh with the SJ cowl and he had trimmed the bottom cowl at an angle to increase the size of the cowl exit area. Mine is just cut straight down.

Matthew

Quote:

Originally Posted by frankh

A hot O320...Are you sure you glassed in one side of the ramps in the upper half of the cowl..These temps seem a little high.

Also has anyone ever used a cowl flap?

My SJ is a little marginal in a climb on a hot day but cools off nicely in cruise which is what you'd expect.

Seems to me an ajustable cowl flap would be the best of both worlds at th expense of some complexity.

Does anyone have a good design they could post pictures off?

Frank
IO360 now featuring 10% ethanol

n815vp · #9 08-23-2008, 02:46 PM

This Rv9a has an air tight plenum with the inlet completely sealed .That's what surprised me regarding my coooling.I thought with the plenum all would be cool. But in my view, with the exit air being restricted the plenum didn't provide the benefit intended.
If you look at RV6a's and older model Rv9a outlets they have more exit area because the tunnel drops down lower.

Bob Martin · #10 08-23-2008, 06:45 PM

You guys that are running hot on climbs......
Have you checked your fuel flow on climb out?
Fuel is used for cooling in the climb at WOT.
Just a thought.