I fly an Avid Catalina, and have enjoyed it. It came home to the garage for a re-engine, and I couldn't help but try to redesign the cooling system also. The existing system cooled the Rotax 582 with a 140 in^2 radiator hung square out in the wind in front of the engine. It cools exceptionally well in flight, but when idling on the ground, or worse, in a downwind displacement taxi, it was insufficient. A squirt bottle filled with water was a staple.
Here's a couple pictures that show the original rad placement.
I also wanted to clean up the air going into the prop a little bit- my plane is the slowest of it's type that I have ever heard of, and I always blamed the exceptionally bad aero around the canopy, radiator, wing roots and engine cowling feeding into the prop.
Anyway, I mounted the radiator inside, and mocked up a plenum and ducting in plywood, cardboard and hot glue that was robust enough for a static engine run. I don't think there's much ram air pressure to be had at the inlet scoop, since it's so far back on the not-particularly-aero fuselage, but I was counting on airflow over a huge cowl flap on the "pylon" right in front of the prop. It's shown here mocked up in the full-open position. I'd pictured it would be nearly closed during cruise flight.
I started to believe this was a sound enough design that just prop inflow over the cowl flap would provide more than enough cooling even for ground ops. I dreamed of endless downwind displacement taxiing, and dreamed of never again suffering the embarrassment of having the tower at my home airport key up and remark about my opening the canopy at the hold short bars to spray the radiator with a squirt bottle. ("Hey, the ARFF truck can come keep you cool if you need...")
But nope. At around 1000 prop RPM, there's miserably little flow into the inlet, and tufting around the cowl flap is just a completely random mess, and the slope of the temperature graph approaching redline is about the same as with the ducting completely blocked off.
I'm wondering what my mistakes are?
1) I don't understand prop inflow, and there's not as much velocity as I thought there was?
2) I don't understand cowl flaps? The cowl flap is too far open and flow separates? I just eyeballed other slow-speed aircraft's cowl flaps. https://youtu.be/VuAPzvWt1Ps?t=20s
3) Is the aero of the cockpit/sponsons/etc just so foul there's no inflow in the dirtier areas of the fuselage in still air? All the prop inflow comes in cleaner places like over the top or out away from the fuse and wings?
What do other pusher airplanes do? After my attempts and poor results, I look at the Lake and Seabee and wonder how they taxi at all. Geez, is there an internal fan in there?
Here's a couple pictures that show the original rad placement.
I also wanted to clean up the air going into the prop a little bit- my plane is the slowest of it's type that I have ever heard of, and I always blamed the exceptionally bad aero around the canopy, radiator, wing roots and engine cowling feeding into the prop.
Anyway, I mounted the radiator inside, and mocked up a plenum and ducting in plywood, cardboard and hot glue that was robust enough for a static engine run. I don't think there's much ram air pressure to be had at the inlet scoop, since it's so far back on the not-particularly-aero fuselage, but I was counting on airflow over a huge cowl flap on the "pylon" right in front of the prop. It's shown here mocked up in the full-open position. I'd pictured it would be nearly closed during cruise flight.
I started to believe this was a sound enough design that just prop inflow over the cowl flap would provide more than enough cooling even for ground ops. I dreamed of endless downwind displacement taxiing, and dreamed of never again suffering the embarrassment of having the tower at my home airport key up and remark about my opening the canopy at the hold short bars to spray the radiator with a squirt bottle. ("Hey, the ARFF truck can come keep you cool if you need...")
But nope. At around 1000 prop RPM, there's miserably little flow into the inlet, and tufting around the cowl flap is just a completely random mess, and the slope of the temperature graph approaching redline is about the same as with the ducting completely blocked off.
I'm wondering what my mistakes are?
1) I don't understand prop inflow, and there's not as much velocity as I thought there was?
2) I don't understand cowl flaps? The cowl flap is too far open and flow separates? I just eyeballed other slow-speed aircraft's cowl flaps. https://youtu.be/VuAPzvWt1Ps?t=20s
3) Is the aero of the cockpit/sponsons/etc just so foul there's no inflow in the dirtier areas of the fuselage in still air? All the prop inflow comes in cleaner places like over the top or out away from the fuse and wings?
What do other pusher airplanes do? After my attempts and poor results, I look at the Lake and Seabee and wonder how they taxi at all. Geez, is there an internal fan in there?
