X-Mozilla-Keys:
Fredmoreno@aol.com wrote:
Interesting page, work referenced in one of Miley's papers. I had not seen
the original. Could you provide a reference name and number so I can search
for it? Need to add to my library which is woefully short on aircraft
propulsion stuff.
Great book Fred. Out of print and hard to find used. UCLA has a copy
back in the stacks that is in real bad shape. McGraw Hill 1953
Lib. of Cong. # 52-6541 Another technical classic.
With regard to testing radiators, I can offer the following.
1) Generally it is better to suck through the radiator test rig rather than
blow through it. The velocity distribution of the fan is usually skewed, and
the high level of turbulence exiting the impeller can affect pressure drop
measurements. Means building m ore duct work and using more duct tape, but
might as well do it right the first time and generate better quality data.
2) When building the test rig, put a bell mouth on the inlet to smoothly
guide the air into the inlet. Same reason; uniform velocity distribution
with low turbulence level. I made such an inlet for my test rig by cutting a
length of 2 inch PVC water tube from Home Depot lengthwise on the table saw
(two passes) to get two half cylinders. These were then mitered on the
corners and screwed to the plywood inlet and tastefully finished with a bit
of duct tape to provide a rectangular bell shaped inlet to the plywood duct.
I measured the velocity profile with a small hand held air velocity meter
attached to the end of wooden dowel (so my hand would not affect the flow
pattern), and it was quite good. Such a velocity meter is available from
Omega (www.omega.com). Request their thermocouple catalog (The Temperature
Handbook), about as thick as a phone book, and in the current edition go to
page L-40 for the model HHF22 digital anemometer for $119. While we are on
instrumentation, I recommend the 4 channel type K thermometer model HH501DK
page XXXV (new product) for $95 which includes 4 thermocouples, and I ordered
some spare thermocouples page A-16 model TSC-GG-K-30-72, 30 gage type K, 6
feet long, glass braid insulation $68 for a 5 pack. I plan to use for
measuring under cowl temperatures and feed the wires back through the
firewall.
3) A trick I have read about is to minimize the turning loss entering the
radiator is to orient the fins parallel to the incoming flow (which makes the
tubes perpendicular to the incoming flow). In this way the flow does not
have to turn around each sharp fin leading edge which creates a loss
approximating one local velocity head. If one uses an automotive radiator
with oval tubes, the flow turns over the front end of the nicely radiused
tube when entering the radiator reducing the entry loss (which is usually
less than 10% of the total loss, but worth saving if possible). Means the
radiator tanks must be oriented parallel to the centerline of the airplane.
It is not essential, but a nice finesse.
Fred
Just a quick note. I tried it today. What an eye opener. Most of the air
came out on the sharp end. The wedge shaped duct was about 20 inches
long,
ten inches wide on the rad side and about eight inches high where it fed
from the squirrel cage blower.
Zero pressure at the squirrel cage end and about one inch
of water on the sharp end. Looks like we need a bell shaped duct here
too to get even flow through the rad. As luck would have it I had the
tubes oriented as suggested above by Fred.
I will have to get one of those airspeed meters.
Very important to seal everything as well as possible.
Pictures in a few days.
Paul Lamar
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