George;
I haven’t been following this
thread, and stepping in here may reflect that; but I don’t really understand
your question. The size of the inlet opening is determined by the amount
of heat you need to reject, best taken as corresponding to something close to
the climb power. That; with the density and specific heat of air, gives
you the cfm required. When you know that, and the approximate climb speed
of your application, you can calculate the required inlet opening.
Having done all those calcs, I (or ED, I’m
sure) could scale those numbers for you fairly readily to your power level and
speed.
Other things follow from there;
including the face area of the rad. Optimally, you’d like to have a way
of adjusting inlet and exit areas for absolute minimum drag; but that’s
very complicated. If you can do one of those, adjust the exit area. If
both are fixed and you want least drag, you can size the inlet for something
closer to cruise speed, and add the complexity of the spray-bar idea for added
cooling during high power regimes.
It’s good to have some sort of
control over the amount of cooling to maintain engine temps within some
reasonable range. If the cooling system is sized for climb on a hot day,
a thermostat is a way to maintain temps for other regimes. There is the rare possibility
of a thermostat sticking closed, but that is something that hopefully would be
noted before takeoff.
Not that I advocate this approach, but I
have a setup that doesn’t require any pilot intervention and serves quite
well. I have 2 coolant radiators, one which can handle the cooling for normal
cruise (both coolant and some of the oil heat), and one (connected in parallel)
that can handle maybe 30-40% more (in the wing root with presumably a fairly
low drag inlet/outlet. The second has an in-line thermostat, so only comes into
service during high-power operation, or very hot days. I have an oil/air
cooler that handles normal cruise power, and small oil/water exchanger (in
parallel) that keeps the oil temps at a safe level for high power by
transferring heat to the coolant. Yeah; the plumbing is a little more
complicated, but I like the way it works.
(Sorry, it seems what starts out to be a
simple answer always turn into more complicated discussions).
Al G
-----Original Message-----
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of George Lendich
Sent: Monday, January 25, 2010
2:31 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re:
Wedge/Oblique Duct
I have been thinking about this, if
I use A1V1=A2V2 to solve for the inlet opening size, how do I know if the speed
of air through the duct is correct i.e. 10% for cruise and 30% for climb.
Also If I use the Cessna 171 speed
of approx 100 K for cruise = 10 K through core, 70 knot climb and approx 20 K
through core. Do I then use the climb speed to calculate inlet air openings and
attach an adjustable louver exit OR I suppose I could do as Tracy does and
calculate for cruise and attach a spray bar.
I'm still a little confused on the
best approach.
BTW it's Australia Day today -
arrival of the first fleet.
George, For the bell
shaped duct, what I have read in K & W it appears they say the inlet
area should be between 0.25 – 0.40 of the core area. The more
slowing of the air velocity that needs to be done by the diffuser before the
core that is needed appears to call for lower area ratio values of Ai/Ab (area
inlet/area core). In the example plotted of an streamline duct in K&W
the chart shows the area ratio was 0.40.
From: Rotary
motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of George Lendich
Sent: Wednesday, January 20, 2010
6:16 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re:
Wedge/Oblique Duct
If Ai is .33 Ab and .44 Ab for the
wedge ducts, what's it for the bell shaped duct - is there any similar
drawing?
----- Original Message -----
Sent: Wednesday,
January 20, 2010 3:39 AM
Subject: [FlyRotary]
Wedge/Oblique Duct
George, here are two figures from
K&W – one could be described as a “Wedge” figure 12-6 and
the other one a “streamline” wedge figure 12-12.
Always dangerous for me to try
to interpret what K&W are really saying, but from what I get from these two
figures, it would appear that the “streamline” wedge permits you to
use a smaller inlet (Ai = 0.30 Ab) for the same performance (same losses) that
you get with a larger opening Ai = 0.44 Ab for the pure Wedge. But, that
is just my take on it.
The slight bump (where the 64 deg
angle is annotated) of the Streamline wedge may be to increase the boundary
layer velocity to delay separation of the boundary layer in that far
corner where duct meets core.
Ed
Ed Anderson
Rv-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com
http://www.andersonee.com
http://www.dmack.net/mazda/index.html
http://www.flyrotary.com/
http://members.cox.net/rogersda/rotary/configs.htm#N494BW
http://www.rotaryaviation.com/Rotorhead%20Truth.htm
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