> >> >Bill Freeman wrote:
>> >>
>> >> Jerry,
>> >>
>> >> Long EZs are cooling O320s (one I know has been souped and dynoed to
>> >> 176 hp) with a belly mounted NACA duct. Mine is about 4"
deep and about
>> >> 12" wide (from memory, I can measure it if you want) at the outlet.
These
>> >> belly
>> >> NACA ducts work pretty well because they are in a positive
>> >>pressure field when
>> >> climbing. I have a moveable floor in mine, set to about 3" deep since
I only
>> >> need to
>> >> cool 108 hp. Seems like a 12-14" wide and 4-5" deep NACA duct with
>> >> a good diffuser would be a good starting point for a rear fuselage
radiator
>> >> system. An upright radiator with a bell type diffuser dumping out
>> >>into the rear
>> >> fuselage with a pair of exits under the horizontal stab seems worth a
>> > > try. Make the ducts out of two plies of BID glass over a simple
>> >styrene foam
>> >> mold covered with duct tape and melt out the foam with gasoline when
done.
>> >> Mount the rad to the fuselage tubes, sealed to the diffuser, which is
sealed
>> >> to the
>> >> NACA duct.
>> >>
>> >> Might be good to check out what the pressure inside the rear fuselage
is at
>> >> cruise
>> >> in a std Tailwind. If you have a friend with one flying, ask him to
put a
>> >> tube into
>> >> the aft fuselage, run it up to the cabin and connect to
either a water
>> >> manometer
>> >> connected to a static port. This is a critical piece of
info. If the
>> >> pressure is high, you'll need to make an outlet duct and run it to a
lower
>> >> pressure location on the aft fuselage. This would be best
done with a
>> >> pressure survey on a flying Tailwind, looking at the
>> >> exterior pressures at various locations. I would expect the top
surface to
>> >> be low
>> >> pressure, but that is a pure guess. You need an outlet location that
is low
>> >> at both cruise and climb.
>> >>
>> >> What do you think, Paul??
>> >>
>> >> Bill Freeman
>> >
>> >Sounds like a good program to me Bill. I wholeheartedly agree.
>> >Nothing like real world, full scale data.
>> >
>> >Paul Lamar
>
>
>> >Thanks, Bill, Amazing, only one day ago I had exhausted every
>> >possibility I could think of. Now I have some very promising paths
>> >to study. How long is the ramp on your NACA duct? The formula in
>> >Sport Plane Builder calls for a 7º ramp. A five inch deep NACA
>> >duct with a 7º ramp is 40.7" long. I wonder if the ramp can be
>> >steeper? I don't recall ever seeing extremely long ramps on any
>> >NACA ducts. I don't know how to conduct a pressure survey on the
>> >exterior of a flying Tailwind. Directions would be most appreciated.
>> >However, I am confident that I can achieve a low pressure
>> >differential in the fuselage aft of the Rad.--Thanks again, Jerry
>
>Don't forget Bill is only cooling 109 HP.
>
>Check the web site Jerry for a sketch on a water manometer.
>You can plumb into the static pressure tap on your altimeter
>for a reference pressure. Use a bit of porous foam on the
>ends of the pressure measuring tubes. You can also use a short
>piece of small tubing with three or four small holes drilled
>around the ends on the side of the tubing. Pinch the tube shut
>or weld it shut. Place the end of the measuring tube where ever
>you want to measure the pressure. Always measure the pressure
>at the same airspeed.
>
>Paul Lamar
Bill Freeman wrote:
OK, I went down in the basement and picked thru my old templates
and found my Long EZ NACA inlet planform template. It is 12" wide
and 35" long. The start is about 1" wide and IIRC it conforms to the
std NACA design. I think it is about 4" deep "normally" but I have
'shallowed' it by adding a ground adjustable floor for the rearmost
24" or so, hinged at the front edge, so my floor has a kink in it. As
> Paul says, I am only cooling an O-235 low compression 108 hp motor,
but I am only using a 3" by 12" opening. The 4"x12" opening cools
O-320s pretty well, altho most need bigger than stock oil coolers for
O-320s on Long EZs. 36 sq inches for 108 hp, 48 sq inches for 160 hp,
Sounds like about 3-3.33 HP per sq inches inlet. 200 hp/3= 66 sq inches.
40" SOUNDS long, but isn't really, esp since the first part is really
shallow. You need a smooth belly in front of a NACA duct. Take a
wheel pant home - you'll find out that a pair fills up a whole car trunk
and they really look small laying beside the airplane. 40" is not big.
Paul says you need 90 sq inches for 250 hp, most NA 13Bs seem to
be putting out under 200 HP, less in cruise. (200/250)*90 = 72 sq inches.
A 14.5" wide 5" deep NACA duct will have a throat opening of 72.5
sq inches. My calc for aircooled engines indicates 66 sq inches, pretty
darned close to 72 sq inches. Too big is better than too small.
Since the deltaT is lower with a watercooled motor, you should require
somewhate more airflow. { Aircooled submarine. ;-) }
With a proper diffuser ahead of the radiator, a big enough quality
radiator and a low enough downstream pressure for the backside of the
radiator, this should cool 200HP with pretty low drag. A moveable floor
works to control inlet flow, but takes LARGE forces to operate, like a flap
actuator jackscrew, which is why mine wound up being ground adjustable
rather than in-flight adjustable as originally planned. Oh, well -
that's why
they're called experimental.
One additional point that I haven't seen mentioned. When my LE was
running uneven cylinder temps, the solution was to CLOSE DOWN the
baffling over the cold cylinders, which were stealing all the
airflow. Due to
internal shapes, the pressures at the different cylinders were not the same
at the inlet side. To get the same flow, the cylinders exposed to higher
pressure needed to have a higher flow resistance to get the same flow as
the cylinders exposed to lower pressure.
If I had cooling problems with a rad, first I'd be careful to
ensure that there
were no alternate paths for the air to take out of the cowl. It all has to
go thru
the radiator to get out, right? Second, you might even need to
put a bit of a
flow block over part of the rad to keep too much air from going
thru one part,
starving the rest of the area. Perhaps a couple of strips of
0.032"aluminum 1"
wide spaced about 1.5" off the face of the rad to slow down air in
a "too high"
pressure area and send the flow over to the "too low" pressure area. How to
know? Measure the pressure at about 6 differnt points over the face of the
rad in flight, front and back.
How'd I find this out for my bird? Pressure taps all over the whole
engine compartment and a lot of hours staring at a lot of resulting data
numbers
trying to figure out what the data was "telling me". No substitute for
actual field
testing, folks. Then you have to strain your brain to figure out
what the heck
it means, and then come up with a new design and test that. Again, and
again. Experimental. No free lunch. OTOH, I cruise at 150 kts
on 81 hp with
very even cyl head temps and low oil temps. Wasn't free tho.
I've done this on several aircraft, and test data is the ONLY way
to get ahead.
Everything else is throwing darts. Science, guys. Like Paul has
said a couple
of hundred times. When we just tried stuff, we were running in
circles, just
wasting time on theories without any FACTS. Once we had facts (data)
we had to at least come up with theories to match some facts.
Suddenly things
started making sense and getting better. Like eventually proving
that no matter
what you did, a stock sized oil cooler in a O-320 LE would NOT cool it. You
needed more sq inches of cooler, problem solved.
> BIll Freeman