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From: "rijakits" <rijakits@cwpanama.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-861271@logan.com>
Subject: Re: [FlyRotary] Re: rule of thumb and RV-3 sizes-
Date: Fri, 8 Apr 2005 07:01:40 -0500
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Hi Barry,

I agree that augementation plays a serious role in these two planes.
It was never metioned or opposed or other, they just found the right
combination/optimization of various areas in their system to make it work
contrary to the "rule of thumb" of 150% (or whatever number) the exit area
hat to be bigger than the intake. Obviously this ROthumb does not care too
much about drag reduction.

Thomas J.

> 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
> >
>
>
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