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Date: Thu, 07 Apr 2005 22:19:16 -0500
From: Barry Gardner <barrygardner@mindspring.com>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: rule of thumb and RV-3 sizes-
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Thomas J,

The key line in that article followed the size of the exhaust: "is 
augmented by exhaust flow." Exhaust augmenters really work according to 
Contact magazine and others. This article is just more evidence of that. 
Apparently the augmenter is so effective that it allows what would 
ordinarily be a restrictive outlet on the back of the heat exchanger.

Barry Gardner
Wheaton, IL

rijakits wrote:

> Al,
> I did mean "intake"!
> On both their planes, the Mustang II and the RV-4 the intake area is 
> biiger than the exit!!
> As mentioned, if you need I can email the scans of the mag! You also 
> might want to read up on: http://www.cafefoundation.org/aprs/RV-4.pdf
> Thomas J.
>
>     ----- Original Message -----
>     *From:* Al Gietzen <mailto:ALVentures@cox.net>
>     *To:* Rotary motors in aircraft <mailto:flyrotary@lancaironline.net>
>     *Sent:* Wednesday, April 06, 2005 11:29 PM
>     *Subject:* [FlyRotary] Re: rule of thumb and RV-3 sizes-
>
>         ..cut
>
>         Note: the exhaust area requirement is greater than the inlet
>         combination of oil and coolant due to the now considerable
>         hotter air temperature. Rule of thumb: Coolant air inlet
>         opening for 200 HP coolant cooled engine ~60 sq. in., oil
>         inlet opening ~30 sq. in. equals a total opening of 90 sq. in.
>         A good place to start with exhaust opening is 1.4 times the
>         inlets or 126 sq. in. Close the exit area down with cowl flaps
>         to as little as 80% of the inlet combination at cruise conditions!
>
>         ...cut
>
>         I do understand that an air-cooled installation is a different
>         animal, but by the end of the day ( or at the cowl exit...for
>         that matter) everything is air cooled. The interesting thing
>         is that both run a intake/exit ratio of 78%, the intake (I
>         think you meant ‘exhaust) being bigger - just about confirming
>         the above statement!
>
>         Schmidtbauer mentiones the " rule of thumb" - exit about 150%
>         of inlet.
>
>         I think for our purposes, the 1.5 ratio is more applicable
>         than 1.28. It can be lower IF you have well shaped entrance
>         and exit ducting. Typically we focus on entry ducting, and
>         then have rapid expansion at the exit from the core – sudden
>         expansion pressure loss; losing all momentum and then, usually
>         a rather sudden acceleration out a fairly small opening.
>         Definitely less than optimum.
>
>         I don't think there is a great difference on the amout of
>         cooling necessary, as the efficiency of both engines are
>         fairly close. So some heat goes out the exhaust and the rest
>         has to be cooled. For sure you need different ducting, but the
>         amount of heat energy should be about the same and you want to
>         get rid of it with the least drag, either way.
>
>         You’re right. The biggest difference is the higher rejection
>         temp, and larger delta T of the air on the air-cooled engines
>         allows for a lower air flow rate.
>
>         Al
>