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From: "Thomas y Reina Jakits" <rijakits@cwpanama.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-1180320@logan.com>
Subject: Re: [FlyRotary] Re: External Diffusion was [FlyRotary] Re: Remove Turbo
Date: Fri, 16 Jun 2006 19:19:11 -0500
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Hi Steve,

I posted some time ago about a Mustang II, that was going awefully fast. The
owner was helped to finetune drag issues ( ....a lot of it in the cooling
area) by Dave Anders of CAFE RV4 fame.
The most interesting result is cooling-intake is about 135% of the exit
area..!!

Thomas


> Thomas,
>
> I know from what I've read that the larger the inlet the larger the drag.
> Also you need adequate outlet area which I believe (not 100% sure of this
> number) that is 1.2 times the inlet area.  If you use a cowl flap to
reduce
> the inlet area, you'd still need to reduce the outlet area also to achieve
> maximum efficiency.
>
> If I commented further on cooling, I'd only be parroting Ed or Tracey, who
I
> consider to be the cooling gurus.  They certainly have much more
experience
> on the subject, and I relied on their input when working through my
cooling
> issues.
>
> On my plane, I got it to cool adequately for the most part, but I still
have
> improvements to make.  I have plenty of inlet area, and it has more drag
as a
> result.  As I make improvements, I hope to reduce the inlet size and
> resulting drag.  I had so much trouble with high temperatures though, I
just
> wanted to get the cooling under control first, and then work to make it
> better.  I'm using what I (and others) would refer to as brute force
cooling.
> I hope someday to have my system as refine as Ed and Tracey.
>
> Steve Brooks
>
>
> On Friday 16 June 2006 08:37 am, Ed Anderson wrote:
> >  Hi Thomas,
> >
> > Yes, Thomas, you are correct, you can get external diffusion (which is
not
> > necessarily bad) - however, not quite correct about the no drag part.
Any
> > time you slow down more air (whether by external diffusion, internal
drag
> > components inside cowl, larger core than needed or less than optimum
exit
> > airflow, etc) than you need for adequate cooling,   you  are adding
> > unnecessary drag.  It does not matter whether external or internal - if
air
> > is slowed then your airframe is the thing doing the slowing of the air
and
> > opposite and equal reactions, etc.  No free lunch {:>).  You can not
avoid
> > cooling drag - only optimize it for your airframe and flight regime.
> >
> > But, again, if a larger capacity cooling system (which keeps your temps
> > down on take off ) fits better with your comfort zone, then I would be
the
> > last to try to convince you to go smaller.  You've got to stay within
your
> > comfort zone or you simply will not enjoy flying your project.  This
zone
> > is of course different for each individual - what is comfortable for one
> > individual may not be for a second.
> >
> > Ed
> >
> > > Hi Steve, Ed and all,
> > >
> > > I may be wrong:
> > >
> > > Isn't there some selfstreamlining effect when an intake starts to
spill
> > > air
> > > because of backpressure?
> > > What if you start to block off your cooling exit with
louvers/flaps/etc.
> > > to
> > > the point where you reduce cooling air flow speed.
> > > Theory:
> > > If you don't push it through the system it won't produce drag.
> > > Excess cooling air, doesn't even enter the system as it spills past
the
> > > intake (aerodynamic diffusion??)
> > >
> > > Steve said, you can only do so much with flaps/louvers.
> > > Well I guess you can make them big enough to close off enough air to
keep
> > > flow down...
> > >
> > > TJ
> > >
> > >
> > > ----- Original Message -----
> > > From: "Ed Anderson" <eanderson@carolina.rr.com>
> > > To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
> > > Sent: Thursday, June 15, 2006 11:02 AM
> > > Subject: [FlyRotary] Re: Remove Turbo
> > >
> > >> Steve's comments are on the money, Thomas.  Yes, you can certainly
> > >> design
> > >
> > > a
> > >
> > >> cooling duct system optimized for cooling in a climb.  However, as
Steve
> > >> indicated you will then pay with additional drag/weight,etc for each
of
> > >> those many hours at cruise airspeeds.  Many (most?) of us try to
design
> > >
> > > for
> > >
> > >> optimum cooling at cruise (minimum drag) and accept the fact that for
a
> > >
> > > few
> > >
> > >> minutes during/after takeoff we may incur a cooling deficient.  My
> > >> limits are 200F oil and 220 Coolant, so long as my full power
climbout
> > >> does not cause either of those limits to be exceeded, I feel
> > >> comfortable.
> > >>
> > >>  Now, once I have reach 120 MPH IAS I start to get into the
sufficient
> > >> cooling capacity region and all temps start back down.  At cruise my
> > >
> > > cooling
> > >
> > >> temps are normally around 160-170F for both oil and cooling - which
> > >> could indicate that I still have a bit too much cooling capacity (and
> > >> therefore cooling drag). Ideally at cruise, I would like to see oil
and
> > >> coolant at 180-185F.   However,  since I don't wish to exceed my
> > >> establish limits in climbout, I accept that I probably have more
cooling
> > >> drag at cruise than I
> > >> need to have.
> > >>
> > >> If I were flying a Bush plane in and out of hills and valleys
carrying
> > >
> > > heavy
> > >
> > >> loads and at relative slow speeds, then I would opt to optimize the
> > >
> > > cooling
> > >
> > >> system for takeoff and climbout.  If I were flying a canard type I
would
> > >
> > > opt
> > >
> > >> to optimize the cooling system for cruise.  With an Rv I'm someplace
in
> > >
> > > the
> > >
> > >> middle {:>).
> > >>
> > >> Like most of areas when discussing aircraft, cooling is another one
of
> > >
> > > those
> > >
> > >> "compromise things"
> > >>
> > >> Ed
> > >>
> > >> Ed Anderson
> > >> Rv-6A N494BW Rotary Powered
> > >> Matthews, NC
> > >> eanderson@carolina.rr.com
> > >> ----- Original Message -----
> > >> From: "Steve Brooks" <prvt_pilot@yahoo.com>
> > >> To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
> > >> Sent: Thursday, June 15, 2006 9:51 AM
> > >> Subject: [FlyRotary] Re: Remove Turbo
> > >>
> > >> > Thomas,
> > >> > You could design a cooling system for extended climb, but you would
be
> > >> > adding
> > >> > significant drag to the aircraft.  There is only so much you can do
> > >> > with
> > >> > cowl
> > >> > flaps.
> > >> >
> > >> > I believe that most builders (and also most certified aircraft)
design
> > >> > cooling
> > >> > for cruise, and tolerate temperatures climbing somewhat in climb.
> > >> > There
> > >> > do
> > >> > have to be tolerable limits, however.
> > >> >
> > >> > I'm afraid that if I built my cooling system to maintain temps on
an
> > >> > extended
> > >> > climb, at full power, on a 95 degree day, I would have much cruise
> > >> > speed
> > >> > when
> > >> > I leveled off.
> > >> >
> > >> > I've seen several discussion on this group, where people leveled
off
> > >> > for
> > >
> > > a
> > >
> > >> > while, or reduce power and go to a cruise climb, in order to let
thing
> > >> > cool
> > >> > back down.
> > >> >
> > >> > On my aircraft, the oil temperatures are fine, but coolant is
marginal
> > >
> > > on
> > >
> > >> > hot
> > >> > days.  On a 95 degree day, I could only get to about 2000 feet AGL
> > >
> > > before
> > >
> > >> > my
> > >> > coolant temperature was at redline.  Leveling off and reducing
power,
> > >> > cools
> > >> > it down, and then I can increase power and continue climbing at a
> > >> > cruise
> > >> > speed.
> > >> >
> > >> > I have some more gains that I can make on mine cooling system by
> > >> > making improvements in air flow.  Currently I have some dead space
> > >> > below the radiators which I'm sure allows some air to roll back
out.
> > >> > I also have
> > >
> > > a
> > >
> > >> > couple of spots that are allowing air to leak through, which I need
to
> > >
> > > fix
> > >
> > >> > as
> > >> > well.
> > >> >
> > >> > Steve
> > >> >
> > >> > On Wednesday 14 June 2006 09:30 pm, Thomas y Reina Jakits wrote:
> > >> >> ""
> > >> >>
> > >> >> > While it doesn't make sense to try to have sufficient cooling
for
> > >> >> > climb,
> > >> >> > I think that I can still make some air flow improvements and get
a
> > >> >> > little
> > >> >> > better cooling.
> > >> >> >
> > >> >> > Steve ""
> > >> >>
> > >> >> Steve, what makes you think/believe that!?
> > >> >> I always assumed that one would design/plan for the worst case
> > >
> > > scenario:
> > >> >> Slow/steep/pro-longed max power climb....
> > >> >>
> > >> >> You always can close the flaps/louvers (streamline/reduce drag)
when
> > >
> > > you
> > >
> > >> >> change into a less severe regime.
> > >> >> But what good is a 250hp engine if you can't use it for more than
2
> > >> >> min....
> > >> >> I would at least want a 5 min limit for T/O-power. As Rotaries go,
> > >> >> they
> > >> >> will hold up fine with max power for cruise/racing/etc. fine too -
> > >> >> but
> > >
> > > if
> > >
> > >> >> you can't cool it.....
> > >> >>
> > >> >> What if you are in line on really hot day? You might not even get
2
> > >> >> min
> > >> >> of
> > >> >> max power.
> > >> >> I would rather err on the wild side of cooling - you always can
cut
> > >
> > > down
> > >
> > >> >> and close off, once you know your ride...
> > >> >>
> > >> >> TJ
> > >> >>
> > >> >>
> > >> >> --
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> > >> >> Archive and UnSub:
http://mail.lancaironline.net/lists/flyrotary/
> > >> >
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> > >
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