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I'm not joint this "thread" on "theoretical calculations" becasue I need
more info on how I'll set up my cooling system - I already know what I'm
going to do - use two GM a/c cores like the other successful operators of
rotary powered RV's. Just mount them "better" I hope - see earlier post
(today?) re "cowl with no holes so I can cut and shape my own holes where I
want them."
In other words, I'm not planning to "base" my cooling system on "theoretical
calculations". Like I posted a couple of days ago, I just "harvested" my
two big a/c cores that I'm going to use (assuming they fit under the engine
like I want, otherwise, I'll call Frigid Air dot com in Fl and get him to
put my eyes on later model cores that might fit better.)
- I'm chiming in because the new fellow on the list is asking questions
and is planning to write a book.
- If I were to publish a "how to do it" treatise or e-mail or book on
cooling, involving calculations, I'd simply want present something like Ed
has done - cancel out all the common terms and get down to the things that
can or ought to be controlled in the "design" and "operational limitations"
areas, so anyone would be able to plug in values for their own application
and do something like look at the extreme hot days.
The value of "theoretical calcs", like in Ed's masterful DIE (EdDie) thing
on intake tuning effects, is to see if "theory" and "test/practical data"
are in reasonable proximity to each other.
I'm all for empirical design (e.g., copy Tracy or Jim Mosur or . . . .) but
when you start digressing from their inlet shapes, outlet shapes, locations
(move from Lyc cooling holes to "F-15/P-51 straight thru ramps/difusers"
lower down on the cowling), change from A/C cores to some custom radiator of
x,y,z dimensions, and play with different cowl flap arrangements, then you
ought to be able to "predict" the effect on cooling of each change you make.
You want to be at least moving in the "right direction", not doing something
that runs counter to the laws of physics.
Sorry I worded my thing about hot days so that some extrapolated meaning
beyond what I intended. Hey, I don't have much to contribute - I "take" a
lot more than I "give". I'm just trying to "give" a bit about how I plan to
do my cooling, because I think it will be a significant "step" in the ages
old "iterative design improvement process".
Now, what I'd really enjou is peer review/comments on my design stuff, not
hot day calculations.
David Carter
----- Original Message -----
From: "Ed Anderson" <eanderson@carolina.rr.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Friday, November 21, 2003 2:07 PM
Subject: [FlyRotary] Re: radiator
>
> Subject: [FlyRotary] Re: radiator
>
>
> >
> >
> > Great post, Al.
> >
> > Just a comment on one of the "assumptions" we all start with when
> > discussing estimation of cooling system sizes for hot weather: How much
> hp
> > is being developed, i.e., how much heat is to be rejected?
> > - I wonder if everyone is "assuming" that they must calculate
radiator
> > areas based on heat being generated/to be rejected while generating 100%
> > power, i.e., 160 or up to 180-205 for a n/a rotary, depending on what
you
> > think you will be getting?
> SNIP
>
> > So, these become "constants" to be applied at the outset of setting up
> > (calculating) our "heat to be rejected" value, which value is the
starting
> > basis of all subsequent calcualtions of radiator size, pressure drops,
> > velocity changes, etc, etc, that the equations work on.
> > - In other words, if I have a 160hp engine, I should NOT design my
> > cooling system to reject 160hp worth of heat on a hot summer day climb
> out.
> > I should be using some lower value that was objectively arrived at as
> > discussed above.
> >
> > David Carter
> >
>
>
> So good points, David. While I agree with you (in theory {:>) the down
> side is - if you are betting your cooling on implementing a "near perfect"
> cooling system with no margin for that 160HP on a Hot day, and if it
turns
> out your cooling system capability is less than you plan for (for any
number
> or reasons) OR you ARE producing 160HP on that hot day, then I think you
may
> find yourself with over temp problems.
>
> The one thing that I have learned is that all the theory does is get you
> closer to an approximate answer. There is still that semi mysterious
world
> of imperfect implementation that can (will?) result in less that your
> planned performance in a cooling system.
>
> If you find yourself with a bit "too Much" cooling, the worst is you are
> going to loose a bit of top end speed (I don't like the cost of running at
> top speed - but others may not mind the fuel burn). On the other hand, if
> you plan your cooling system "too close" and you are off on the inadequate
> side - then you could have a major redo and additional expenses.
>
> You will likely find that if you do plan your cooling system for cruise
then
> you are likely to overheat on climbout. My cooling system has 50% more
> cooling capacity at cruise than I need, but my coolant temp will still get
> up past 210F on a hot day climb out. Remember, you almost always have to
> pick some performance point for the design of your cooling system - be it
> take off , climb or cruise. Whatever point you pick - if you are not
> operating on that point for some regime of flight, you could either have
> excess cooling capacity (not a disaster) or inadequate cooling capacity
> (that could hurt). True, fans and cowl flaps can aid in minimizing excess
> cooling capacity, but you can encounter less than expected in that arena
as
> well.
>
> Keep in mind that the rotary reportedly does not withstand overheating as
> well as the old V8s etct. While I do not think it is as delicate in this
> area as I once did (and they have improved the design of the castings over
> the years), I know you can overheat them without really trying hard(don't
> ask me how I know).
>
> >From my decade of listening to folks with problems getting the rotary
> powered aircraft into the air, inadequate cooling initially has been a
> problem for at least 80-90% of them (including Tracy Crook, yours truly
and
> a number of others). Yes, you can assume our knowledge of what it takes to
> cool a rotary in real world was inadequate at that point, but it wasn't
> because we didn't attempt to use the best information available as well as
> our best educated guesses {:>). I have noticed that more recent launches
do
> seem to be doing better in the cooling area which is good to see.
>
> One reason for the "cooling issue" that it is difficult to optimize for
all
> flight regimes as there is the wide range of power you may produce. At
take
> off, most of us want all the power we can get (say 160HP) at which I am
> producing approx 5000 btu of heat that needs to be rejected by the
> radiators. On the other hand at fast cruise I am producing apporx 80HP at
> 7.5 GPH that produces 2500 BTU of heat for the radiators to get rid of.
So
> there is a 2 fold difference in cooling capacity needed. If I optimized
for
> the 2500 BTU cruise figure at 170 MPH TAS at 81 HP, I could get by with
one
> evaporator core and still have a 17% reserve cooling capacity at cruise.
> However, if I go to take off with the one core, I will be overheating
until
> I reach an airspeed of approx 145 MPH TAS. The question is - would I feel
> comfortable overheating (and by quite a bit) until I reach 145 MPH TAS and
> the answer in my case is - NO. You on the other hand, might be willing to
> accept that.
>
> Not to discourage you from using every tool in planning for your optimum
> cooling system, but I think you need to be careful about trying to cut it
> "too fine" with standards. Additionally each homebuilt and its engine
> installation is different. Even the Lycoming guys (and you would
certainly
> think they would have settled on a standard decades ago) still have
problems
> (in some cases) getting their cooling sorted out.
>
> But, this is just based on my experience, Perhaps we are to the point
that
> "point design" for a cooling system will be successful with smarter more
> experience folks who will bring it off. So best of luck in your cooling
> design.
>
> FWIW
>
> Best Regard
>
> Ed Anderson
>
>
>
>
> >> Homepage: http://www.flyrotary.com/
> >> Archive: http://lancaironline.net/lists/flyrotary/List.html
>
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