M6RV6 wrote:Comments worth every penny you spent!!
GT

Lol

I'll look into all that stuff, GT! My first step towards the cooling fixes is new baffle rubber. Then I'm going to start experimenting with that tab. I'm hoping I can just bend it back flat to fill the gap behind it. The actual "blister" should create its own vacuum without needing a tab. Right now I need all the help I can get, though.

I only measured 3.something inches different between high and low pressure sides of the cowl. Lycoming says I need at least 5 to properly cool the O-320.



No progress on the wiring tonight, my boss had a get together at his place. Tomorrow after work I'm heading straight over to the hangar to try and get it buttoned up to fly and an in-flight MOC complete before nightfall. Not likely though. Tomorrow I'm supposed to head to Gilbert's to get help putting the new baffle seals in.

.....a wet Beaver....

That's a pretty slick looking cowl, much better looking than the OEM.

What I think needs to be understood is that trying to get the air out of the bottom of the cowl is the problem. It's just about the worst place on the airplane to do that. Your cooling system has to work harder to get the air out there than it would be to get it out on the top or sides of the cowl. The Cessna "gills" that they put on the side of the Skywagon cowls make a big difference. My hangar neighbor (54 C-180) said his oil temperatures went down 20 degrees and CHT went down 10-15 when he put those gills on.

I'll bet you $100.00 and a steak dinner that if you moved the air exits to the side of the cowling and closed off/smoothed over the hole in the bottom you'll see lower temperatures at all flight modes AND higher cruise speed. Same inlets, same total exit area, just substitute two properly designed "gills" on the side.

Glad to chit-chat about this possibility, online or off.

EZFlap wrote:That's a pretty slick looking cowl, much better looking than the OEM.

What I think needs to be understood is that trying to get the air out of the bottom of the cowl is the problem. It's just about the worst place on the airplane to do that. Your cooling system has to work harder to get the air out there than it would be to get it out on the top or sides of the cowl. The Cessna "gills" that they put on the side of the Skywagon cowls make a big difference. My hangar neighbor (54 C-180) said his oil temperatures went down 20 degrees and CHT went down 10-15 when he put those gills on.

I'll bet you $100.00 and a steak dinner that if you moved the air exits to the side of the cowling and closed off/smoothed over the hole in the bottom you'll see lower temperatures at all flight modes AND higher cruise speed. Same inlets, same total exit area, just substitute two properly designed "gills" on the side.

Glad to chit-chat about this possibility, online or off.

The sides of the bottom of that cowl are flush with the bottom of the fuse. That "tunnel" at the bottom sticks out and creates a natural vacuum behind it. It'd all be more efficient if my baffles weren't leaking high pressure air. Hopefully once I fix them I can remove the "tab."

I really feel like it would be a potato po-tah-to situation by moving the cowl exit from the bottom to the sides of the cowl. No engineering data to back that up, just intuition.

My question about the cessna "gills" is whether they are in addition to or replacing the standard cowl flaps? Do the cowl flaps open not cool that motor?

If they are in addition to, it makes me feel like more exit:entrance ratio is required instead of the efficiency of the specific location

Cessna gills are in addition to cowl flaps... Do you have the ramps in your upper cowling..??. I know on the RV's the upper cowl ramps smoothing out behind the opening helps with cooling...

Yup, ramps are installed. CHTs are really well balanced except for #3.

As I recall, there was a seaplane version of the Pacer which had gills or non-or-semi adjustable gills on the side of the cowl. Maybe it was on the 160hp /cs prop version? You might see if you can google up a pic, it might give you some ideas.

CamTom12 wrote:Yup, ramps are installed. CHTs are really well balanced except for #3.

Number 3 is the front right cylinder? If that's correct and redoing your baffling doesn't help, maybe you need to cut that ramp down a bit. It looks to be higher then the left side, which maybe isn't letting eoungh air flow on the front of the cylinder. I'm not a pro, just trying to help by looking at the pictures.

On 4 cylinder Lyc, #3 is copilot side rear cylinder. Usually the hottest one.

Troy Hamon wrote:On 4 cylinder Lyc, #3 is copilot side rear cylinder. Usually the hottest one.

Gotcha. So really, cutting the ramp down would help as more air would flow through right? From the picture it just seems that the ramp is a good inch or 2 higher on the right then the left...

Backyard landings.

CamTom12 wrote:
That "tunnel" at the bottom sticks out and creates a natural vacuum behind it.

I really feel like it would be a potato po-tah-to situation by moving the cowl exit from the bottom to the sides of the cowl. No engineering data to back that up, just intuition.

.
FWIW, my intuition is that your tunnel indeed creates a small localized negative pressure just behind it, but that is only relative to the pressure field in that area. Wherever you put that tunnel, you get a slight reduction in the pressure just behind the tunnel, whatever that surrounding pressure is..

If that tunnel is located on the high pressure (bottom) side of the cowl, you will have lower pressure (just behind the tunnel) than the high pressure surrounding field. If you put the same tunnel on the lower pressure (top or sides) of the cowl, then the pressure (just behind the tunnel) will be lower than than the low pressure surrounding field.

The entire cooling system operates on a pressure differential between the air intake and exhaust. What I'm saying is that it will take more horsepower/drag/entropy to create an equally low pressure on the top or sides of the cowl than it will to create the equally low pressure on the bottom.

The tunnel (or ANY air exit) is like a guy swimming upstream. The guy can swim at 3 mph. He's going to make a lot better progress if he is swimming against a 2 mph current than he would against a 4 mph current..

EZFlap wrote:The entire cooling system operates on a pressure differential between the air intake and exhaust. What I'm saying is that it will take more horsepower/drag/entropy to create an equally low pressure on the top or sides of the cowl than it will to create the equally low pressure on the bottom.

I think you may have written this backwards, but I get your point. With the airplane at any alpha other than 0 deg, there'll be more localized low pressure above the cowling than below the cowling. That makes sense.

But having said that, I'm not going to custom fabricate a new cowl and reverse the baffles to create a top-cowl exit. That's a lot of work and I enjoy flying. Maybe if this was a project plane, or something I had in R&D. It'd be neat to see if there truly is a difference though.

I'm willing to bet that I'll see adequate cooling with functional baffle seals, but we'll see!

Crzyivan13 wrote:Backyard landings.

Shut up.

A1Skinner wrote:Gotcha. So really, cutting the ramp down would help as more air would flow through right? From the picture it just seems that the ramp is a good inch or 2 higher on the right then the left...

That ramp actually is supposed to direct air over the #1 so it can get forced through #3. The problem is that my baffle seals have deteriorated and created a number of gaps and wrinkles near the #3. I did a bunch of research and it turns out this is a problem that other guys have had with the stock RV baffle rubber. Gilbert Pierce had similar symptoms to be in his Clipper (same baffle system), replaced the rubber and fixed the problem. My rubber seals are actually older and probably worse than his were when he replaced his. Hopefully it'll take care of the problem.

We were supposed to link up this weekend for the fix, but my wife had a bunch of stuff she needed help with so I had to cancel. Soon!

http://headbergaeroclub.homestead.com/RV10/Bottom_Cowl.jpg

Well maybe someone else can make it work?

M6RV6 wrote:http://headbergaeroclub.homestead.com/RV10/Bottom_Cowl.jpg

Well maybe someone else can make it work?

Holy louvers, Batman!

CamTom12 wrote:

M6RV6 wrote:http://headbergaeroclub.homestead.com/RV10/Bottom_Cowl.jpg

Well maybe someone else can make it work?

Holy louvers, Batman!

Wow! Somebody was really trying hard to solve a cooling problem !

CamTom you're correct... I meant to write that it would take LESS energy to exit the air on the top of the cowl than the bottom. But, I think it would be good enough for most airplanes that exiting the air on the sides probably gives you 3/4 of the benefit you would have gotten from a top exit, with a lot less effort and re-design of the cowling. For a top exit, you're really looking at a total re-design to an updraft system, where with the side exit you can still leave the existing downdraft system mostly alone.

The overall point is that exiting the air on the bottom is the worst way to do it, and almost anything is better.

That's not to minimize the fact that a poorly designed air intake at the front of the cowl can cause its own set of problems, such as contributing to a complete reversal of intended cooling flow at high AoA on some airplanes.

Had some free time this afternoon so I fabbed up a template for my new battery box:







I need to cut the back down a bit, but I'm going to "test-fit" in the plane first to make sure I have enough material for mounting and that my template holes line up right.

I planned on forming the final out of sheetmetal, but today I got to thinking that Kydex might be cool. Still deciding. Also, my ALT Out indicator light came in today from digikey. Actually, that's where I got the cardboard for my battery box template.

Hopefully I can get it all buttoned up this week.

CamTom12 wrote:Had some free time this afternoon so I fabbed up a template for my new battery box:







I need to cut the back down a bit, but I'm going to "test-fit" in the plane first to make sure I have enough material for mounting and that my template holes line up right.

I planned on forming the final out of sheetmetal, but today I got to thinking that Kydex might be cool. Still deciding. Also, my ALT Out indicator light came in today from digikey. Actually, that's where I got the cardboard for my battery box template.

Hopefully I can get it all buttoned up this week.

Thoughts about Kydex is what happens to it when you battery fries?? will it just melt or burn? Just a thought!

M6RV6 wrote:Thoughts about Kydex is what happens to it when you battery fries?? will it just melt or burn? Just a thought!

That's a good thought George, thanks!

Sheet metal sounds better in that case for sure. Now to find a brake to borrow!