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What have you guys used for an air outlet in the top of the cowl for the turbo cooler radiator fan? Looks like the factory used some small soffit vent type things. Has anyone tried a small Naca vent facing backwards (so it doesn't scoop air in flight), or any other alternatives?

Also, I guess by default if you follow the plans, the radiator fan blows air up through the radiator and out the top of the cowl. Would it not make more sense to have it suck fresh air down from the top? Or maybe the fan works better as a pusher anyway... How have you guys done it?

Chris

I used 3 inch instead of 4 inch soffit vents that I found on amazon. They are only 1/8 inch thick and have bendable tabs for mounting underneath. I plan on using some RTV on a couple of the tabs to keep them from moving in the hole and permit removal if ever needed. My radiator is mounted directly underneath that spot. The vents come in different colors with or without bug screens. I opted out of the bug screen just to permit more air flow. Manufacturer for my vents is Maurice Franklin and part# is RBLT-200. I don't remember the retailer but a search on amazon should do the trick. They are aluminum and very reasonable in price.

I have wondered for a while if this would be a good addition to a NA Aerovee to let the heat out on the ground. Any thoughts?

I have a lot of thoughts on this topic, none of which are conclusive.

I have a Waiex-A Turbo Aerovee. I could not find room to install the radiator/fan near the top of the cowling; instead, mine is located near the cowling exit. This is not ideal, but at least it is in the proximity of fresh air. It also probably disturbs my cowling-cooling airflow in-flight (it's not directly obstructing the exit-opening, but it is taking up some space near the bottom-center of the engine mount.)

All that aside, I didn't need to consider the actual radiator airflow when I decided to add the upper cowling air vents anyways (I used 2 - 3" vents from Amazon.) Afterall, the Turbo is the hot part and it's relatively close to the top of the cowling, so why not add vents? Also, the vents are on the low-pressure side of the baffles, so I figured they could only benefit the exit-area of my engine cooling.

Unfortunately, I have no data or experience to say whether the vents help or hurt anything.

In-flight, I am very much limited by CHT. I'm currently exploring more options to optimize my airflow/baffle setup and I suspect exit-area is a culprit, despite my top vents. I'm not sure those top vents do much in-flight, and I primarily base that statement on the fact that I have had absolutely no change in any sort of residue on my windshield/cowling near those vents. With the amount of fluid-leakage around the engine that I've been fighting (and mostly solved), none of it is ending up on the top of my plane.

On the ground, after shutdown, whether my cooling system is running or not, I don't feel appreciable airflow using my hand above the vents. Much more heat seems to be coming from the cowling inlets. This is not to say that airflow isn't happening, I've just noticed that it's not as much as I expected it to be.

My impression is that the top vents probably don't hurt, but they don't do much good (unless you actually had a cooling fan that directly flows air through them.) Take all of this with a grain of salt, my evidence is poor.

Spaceman wrote:Has anyone tried a small Naca vent facing backwards (so it doesn't scoop air in flight), or any other alternatives?

In my understanding, a backwards naca duct is basically the same as a hole. It might look better, but it doesn't perform better. The aerodynamics of a naca duct don't work in reverse. I'm curious about this topic though, and am considering cowl flaps, or come other style of suction-type duct to improve exit airflow (like the Sonex-B cowling side-ducts?)

Rynoth wrote:

Spaceman wrote:Has anyone tried a small Naca vent facing backwards (so it doesn't scoop air in flight), or any other alternatives?

In my understanding, a backwards naca duct is basically the same as a hole. It might look better, but it doesn't perform better. The aerodynamics of a naca duct don't work in reverse. I'm curious about this topic though, and am considering cowl flaps, or come other style of suction-type duct to improve exit airflow (like the Sonex-B cowling side-ducts?)

Yeah, I did a little more research after posting this the other day and found the same info. The tapered naca shape apparently doesn't do anything special backwards. It would be nice for engine cooling if it caused extra air to be sucked out but I guess that wouldn't really be a factor for the turbo cooler anyway since it'll be mostly used on the ground at low or no airspeed.

I guess I'm just looking for something that looks nice and doesn't add much drag or add positive pressure to the aft area of the engine bay.... A little reverse ramp like a tiny version of the B-model cowl exits would probably work. I was kind of thinking something like this:
https://www.aircraftspruce.com/catalog/ ... ckkey=6854
Although that actually looks pretty small and I'm not sure how I'd direct the air from the radiator to that vent.

I also need to consider that whatever opening I put on the top of the cowl would be a rain funnel if I ever park and get rained on, and all my firewall electrical stuff is pretty much right below where the radiator is, so I'll need to have a way to cover or plug the opening too.