flyrotary@lancaironline.net Mailing List Archive

I’ll go out on a limb here for an explanation of the roof ridge material, if i recall correctly when Tracy showed me his RV8, at the cowling air exit point underneath he had taken some aluminum flashing or gutter material (basically cheap flat sheets of aluminum) and riveted them to the firewall in such a way to create to create a shape to smooth the exit air leaving the cowling, that was it. He said it didn’t increase speed but it made a noticeable increase in cooling

Essentially the air doesn’t want to turn through 90 degrees abruptly, so if you picture a side profile of an aircraft firewall, where it meets the cowl at the bottom and round off those sharp edges where the air exits the cowl, then you get the extra cooling benefit Tracy’s talking about,

Alex Molteno

On Sun, Feb 23, 2014 at 10:17 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

From: shipchief@aol.com

Subject: Re: [FlyRotary] Re: [Fly Rotary] Vortex Generator in air duct

Date: Fri, 21 Feb 2014 23:26:19 -0500 (EST)

To: flyrotary@lancaironline.net

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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