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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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