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From: "Thomas y Reina Jakits" <rijakits@cwpanama.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-1181553@logan.com>
Subject: Re: [FlyRotary] Exit area smaller than intake was External Diffusion  
Date: Sat, 17 Jun 2006 15:30:40 -0500
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Ed,
there is a mistake as the intake is not 135%bigger than, but 135% of the
exit.
It still makes it 1.35 times bigger than the exit.

I posted this last in April 2005, the latest response to the subject was on
14th of december by Monty Roberts.
It always starts with a question to verify the intake bigger than exit
claim,but "no mistake" that's what it is!

Please search the archive or let me know if you want me to repost the post!
It was about Brian Schmidtbauers Mustang II being the fastest around!
Also menetioned is Dave Anders' RV-4, details in the CAFE report.
I have the essential pages of the Kitplanes article scanned, let me know if
you want them emailed....

It just shows that rules of thumb are not always the best solution. Most
likely just the most economic one to build.....

Thomas

PS: Search "Kitplanes" and go for the 14th Dec.,2005 posts!!


----- Original Message ----- 
From: "Ed Anderson" <eanderson@carolina.rr.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Saturday, June 17, 2006 6:35 AM
Subject: [FlyRotary] Exit area smaller than intake was External Diffusion


> That's very interesting, Thomas.  I too recall seeing in several places
> reference to
> exit area being some multiple of the inlet with the ratios varying from
> 1.2 -1.7.
>  There certainly could be some kind of phenomena I have not hear of or
> read about, but seems strange you would ever have your intake area more
than
> the exit area.  But assuming no error then it would appear to me that
> external diffusion is taking place.
>
>   What  that  indicates to me is that the exit area (what ever size
> it was) provides adequate airflow for cooling flow through the engine
> compartment.(assumption is the engine did not get cooked).  Enough air
mass
> HAD to leave the cowling sufficient to carry away the necessary BTUs of
> heat.  That said, then if the inlets were 135% larger than the exit area,
> then air HAD to be spilling around the inlet or area of external
diffusion.
> The air molecules in this part of the airflow (external to the cowl) then
> contributed NOTHING to carrying away heat from the engine, but do add to
> drag - that left only
> the air that past through the core (or over the cooling fins of the
cylinder
> head) to provide for cooling. Since this air has now been heated and
expands
> to a larger volume, you traditionally need a larger exit area to
accommodate
> this large volume of heated air.   That air must leave the engine
> compartment via the exit. So I just am unable to come up with a scenario
> where having an inlet larger than the exit area would be beneficial.
>
> Having said that, it did just trigger a thought about why this might be
> tried and
> how it might be made to work.
> .
> We do know that for air exiting the cowl to provide minimum drag it
ideally
> should be accelerated back to the airstream velocity before intermixing.
We
> can theoretically do this by taking the larger volume of heat air and
> designing an exit area
> which would  accelerate the air molecules increasing the velocity of the
> exiting air and reducing drag.  However, to accelerate the cowl air
velocity
> to anything really meaningful,
>  would require added energy.  This leads me to believe that  perhaps an
> exhaust augmentation system could be used to provide increased velocity to
> the exiting air using the energy in
> the exhaust flow.  If the exiting airflow velocity is increased over than
> normally associated with exiting air, then more air of course could flow
> through a smaller opening, this would perhaps permit one to have a smaller
> exit area than intake area and still
> get good cooling and low cooling drag.
>
> So with an exhaust augmentation system "helping" the air in the cowl to
exit
> quicker and at a higher velocity, I can see where a smaller exit area
might
> indeed be workable.
>  But, without an exhaust augmentation system, I just don't see how a
smaller
> exit area would be beneficial.
>
> Any mention of exhaust augmentation??
>
> Well that my $0.02 worth on the topic
>
> Ed
>
> Ed Anderson
> Rv-6A N494BW Rotary Powered
> Matthews, NC
> eanderson@carolina.rr.com> Hi Steve,
> >
>
>
>
>
> --
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