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Charlie and all;
The vortex generator must look larger in the pic than in real life. The prototype is .4" tall, the one in the pic is about .5" tall. I mounted it just aft of the divergent throat and wanted to be sure it's tall enough to snag some air.
I'm planning to keep it and re-shape the duct as per Steve Boese' reference. The cowl inlet is mounted higher than the cooler, so the airflow still needs to be pulled down before it gets squeezed thru the cooler core. The co-ordinates provided will need some interpretation for diagonal flow across the face of the cooler. It's not like I could make a fiberglass part accurate to .01 X or Z anyway? The cut down and re-make will also reduce weight and give more access, so I'm looking forward to doing it.
I did make a flow ramp for the jacket water Radiator, without the knowledge of this study, just a general description from this group. The 'no ramp' version worked 'ok'. The cardboard trial ramp was a big improvement, and the final fiberglass over foam version is a real winner. There is a future possibility that I could switch to a smaller lighter radiator. Lets just say it's not a problem, so it stays while I work on other things!
-----Original Message-----
From: Charlie England <ceengland7@gmail.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Sun, Feb 23, 2014 2:59 pm
Subject: [FlyRotary] Re: Vortex Generator in air duct
I'm not Tracy, but might be able to help. Ridge vent is porous foam that's normally placed between a slot cut on a roof ridge and the cap. It allows air to flow out of an attic without letting insects in. Tracy packed it in the back of his wedge diffuser to limit the excess flow and force more air through the forward part of the core.
BTW, the vortex generator looks pretty big. Have you tried several smaller ones spread across that surface? Most VGs I've seen are only about 1/2" tall. Multiple smaller ones might get the job done with less resistance to flow.
FWIW,
Charlie
On Feb 23, 2014 3:18 PM, "Jeff Whaley" < jwhaley@datacast.com> wrote:
I'm not sure about the roof-ridge material either but perhaps he meant cutting small strips from an aluminum ridge-cap, allowing the peaks slight protrusion into the air stream and riveting on the flats -- there are strips available for fastening to the
lower roof used to prevent large build-ups of ice -- they resemble vortex generators. I'm happy to see you are enjoying the experimental part of your homebuilt. Yes, the thermostat will limit your minimum temperature which is a great asset in cold weather.
If you are turning air 90 degrees 2 times you'll need excellent ducting. In contrast to vortex generators, several contributors to this list are really pinching the air at the back of their plenumns; if you allw too much space in that location most of the
air will pass through the core in a relatively small (1/3 surface) area.
Stay with it ...
Jeff
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Jeff;
That's a good point. I've heard of that 1:1 ratio, however, I'm using the stock Mazda oil cooler with a 170F Thermostat. In my case, it will always be above 170 by some margin, then ambient effects will have their way.
I was pleased the Vortex Generator worked so well for such little effort. I thought I should share it. I'm agreeing with you that winter is a good time to start flight testing, and also I probably need more improvement as the weather warms.
Tracy suggested 'roof ridge material', which I couldn't figure out. Perhaps he meant a loose strand media that serves to slow the air flow through the back where most of the air naturally passes, so that some of the air must pass thru the front of the cooler
also?
My son Peter suggests the next step could be a partial scoop half way back that directs some air to the forward part of the cooler.
-----Original Message-----
From: Jeff Whaley < jwhaley@datacast.com>
To: Rotary motors in aircraft < flyrotary@lancaironline.net>
Sent: Fri, Feb 21, 2014 1:44 pm
Subject: [FlyRotary] Re: [Fly Rotary] Vortex Generator in air duct
All improvements are good; however, you can expect a 1:1 degree rise in your operating temperatures relative to ambient air temperature.
If 185F is the cruise result on a 40F day – you should expect 245F in cruise if the air temperature reaches 100F. In other words, you’re not quite there yet; winter is an excellent time to experiment with a liquid-cooled engine as there
is little chance of overheating. Realistically, if you want <200F oil temperature at 100F you need to see <140F oil temperature wit OAT 40F. It is not easy to design for both ends of the spectrum …
Jeff
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