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----- Original Message -----
From: "Ernest Christley" <echristley@nc.rr.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Monday, April 04, 2005 8:23 PM
Subject: [FlyRotary] Re: Cooling Inlet Areas/Bernie's RV9
> Al Gietzen wrote:
>
> > Doug;
> >
> > I agree with your ‘rule-of-thumb’ numbers. My analysis came up with
> > coolant inlet area in sq. in. of 1/3 the HP (.33) for climb out on a
> > 90F day. It assumes a 120kt climb speed for my Velocity. I used 45% of
> > that additional for the oil cooler. Assumes scoop efficiencies of 85%
> > or better.
> >
> > Al
> >
>
> snip
>
> > Second, even if cooling can get out, if it can't get in, it can't be
> > there to cool the heat exchangers. Rule of thumb: 0.3 sq. in. of
> > cowling inlet air opening per HP. 200 HP x .3 = 60 sq. in. Note: This
> > assumes a reasonably shaped inlet cowl which has been discussed online
> > often. IMHO: Berni's plane inlet shape and inlet cowl is fine, but I
> > question his inlet opening _area_.
> >
> snip
>
> > Don't mean to start another stream of threads on an old subject, but
> > we sweated over this one for 3 months and 3 systems and one might save
> > a lot of time by comparing ones system to these simple "works great"
> > rules of thumb which are the result of LOTS of technical and
> > experimental work.
> >
> > Doug Dempsey
> >
> > N6415Q and RV7 in process
> >
> > Colorado, USA
> >
>
> Don't won't do demean or dismiss your experimental work in any way, but
> Ed is running with half the inlet area, and unless something has changed
> with his new found power, he'd doing just fine. Just to be sure that
> we're all talking apples, I can confidently quote him at 28 in^2 inlet
> for coolant, which I believe is half of what you recommend above.
> Reality isn't meeting theory at eye level here, and everyone will be
> much better off if we know why.
>
> --
> This is by far the hardest lesson about freedom. It goes against
> instinct, and morality, to just sit back and watch people make
> mistakes. We want to help them, which means control them and their
> decisions, but in doing so we actually hurt them (and ourselves)."
>
I am running with 28 sq inches of total inlet area, much more outlet area
than Doug mentions and not producing 200HP continuos. My best estimate
based on fuel flow is I produce around 180HP perhaps a bit more on a cooler
morning.
I agree apples and oranges get compared frequently. But, rules of thumb
are just that - generally a place to get started. I don't think anyone
would say that a rule of thumb means the "optimum" for a specific
installation. Just good enough. I have a rule of thumb that says given
enough surface area and airflow you WILL cool. Not too helpful though and
certainly does not address the cooling drag you may impose. I mean if your
rule of thumb says you have to have sufficient area to let the hot air out
and sufficient inlet to let the cold air in - well, OK, I can buy that - but
not too useful. If you put numbers to it like Doug has done that becomes
more useful but is not the final answer.
For some of us, rules of thumb are simply a gore to understand what's behind
them. How did they come about, what do they mean? To others they are a
heaven - sent- answer that does not require listening to or reading this
sort of stuff {:>).
So I am not certain we need to necessarily even attempt to explain Rules
of Thumb, they are simply a starting point that experience has shown will
work (most of the time).
Ed A
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