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From: Steve Brooks <prvt_pilot@yahoo.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] External Diffusion was [FlyRotary] Re: Remove Turbo
Date: Fri, 16 Jun 2006 09:15:51 -0400
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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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