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FIELD REPORT, SERIAL No. 1552
AIR SERVICE INFORMATION CIRCULAR
(AVIATION)
PUBLISHED BY THE CHIEF OF AIR SERVICE, WASHINGTON, D. C.
Vol. III · July 15, 1921 No. 241
REPORT ON COOLING SYSTEM TESTS OF DH-4 AIRPLANE
EQUIPPED WITH EXPERIMENTAL AUXILIARY RADIATOR . IN
THE PROPELLER SLIPSTREAM
Prepared by Engineering Divison, Air Service
McCook Field, Dayton, Ohio, February 15, 1921
WASHINGTON
GOVERNMENT PRINTING OFFICE
1921
Ralph Brown Draughon
LIBRARY
MAR 2 8 2013
Non•Cepoitory
Auburn University
l' + I +
~' REPORT ON COOLING SYSTEM TESTS OF DH-4 f\JRP,t~l'>l
EQUIPPED WITH EXPERIMENTAL AUXILIARY RADI~
ATOR IN PROPELLER SLIPSTREAM.
OBJECT OF TESTS.
To determine on the production DH-4 the required
additional radiating surface, placed in the propeller
slipstream, to insure satisfactory cooling at any given air
temperature.
To determine the relative cooling value of a square foot
of surface in a nose position and in the slipstream of the
propeller about one-half its diameter back.
CONCLUSIONS.
An auxiliary radiator, for the DH-4, with deep core
section made of seamless copper tubes (hexed ends) with
a length 30 to 35 times their diameter and a total surface
of 55 square feet fitted below the fuselage near the front
landing gear struts will insure satisfactory cooling performance
at a ground temperature of approximately 38° C.
(100° F.).
In the unobstructed slipstream of the propeller, and
about one-half its diameter back the cooling value of
1 square foot of radiating surface equals approximately
1.56 square feet of surface in a nose radiator similar to that
in the DH-4. The ratio of frontal area to total area while
giving this relative cooling value is-
Nose radiator core, 1 to 53.
Propeller slipstream core, 1 to 70.
RECOMMENDATIONS.
It is recommended that an auxiliary radiator conforming
to A. S. drawing No. X-28519 be used on all DH-4 airplanes
requiring satisfactory cooling in air temperatures
between 23° C. (73!° F.) and 38° C. (100° F.), and also
that all DH-4's so equipped have their nose radiators
fitted with the full length shutter, A. S. drawing No. 045521.
DATE AND PLACE.
These cooling tests were conducted September 9, 1919,
June, 1919, and November 14, 1919, at McCook Field,
Dayton, Ohio.
GENERAL DESCRIPTION AND DIMENSIONS.
AIRPLANE.
The airplane used was P-82, S. C. No. 30723, a production
DH-4 except for alterations enumerated below.
In addition to two fixed Marlin guns forward, and two
Lewis guns on a flexible mount in the rear, which were
carried on the test, provision was made for mounting two
fixed guns in the pilot's cockpit shooting forward and
downward through the landing chassis, and two fixed
guns in the observer's cockpit shooting rearward and
downward. During the tests these last four guns were
not carried, although their mountings with two Aldistype
sights on the side of the fuselage were in place. The
total weight of the airplane as tested was 3,994 pounds,
80 pounds of which represent the addition to the cooling
system described below. The average weight of the
DH-4 equipped as a fighter is approximately 3,915 pounds.
COOLING SYSTE'M.
The nose radiator was a production Mayo with square
air cells, vertical water passages being spaced 5/16 inch
from center to center. The depth of the core was 4k
inches. The radiating surface of the core amounted to
approximately 312 square feet, 52.8 per cent, being direct.
An auxiliary radiator, see figures 2 and 3, was fitted
directly below the fuselage and just forward of the front
pair of landing gear struts, and piped in series with the
nose radiator . Its chief characteristics are given below:
Overall dimensions.
Width, 23i inches; height, 101 inches; depth, 11 inches.
Core.
Width, 23! inches; height, 9 inches;' depth, 10 inches.
Weight full, 80 pounds; empty, 53 pounds.
Frontal area, 1.47 square feet. Total cooling surface,.
100 square feet; 96 per cent direct.
Tubes.
:;:. D. 0.36 inch, hexagonal expanded ends, 0.44 inch
across flats; length, 10· inches; wall, 0.006 inch seamless
copper. Number in use, 1,260.
Water temperatures were taken by distance reading
Boyce thermometers. one being placed in the line between
the engine and the nose radiator, and the other in the pipe
elbow between the auxiliary radiator and the pump.
The air temperature was taken by a spirit-in-glass thermometer
placed high up on one of the wing struts, protected
from the sun.
SHUTTE RS .
The stand.ard production half shutt.er was kept full
open throughout the climbing test.
PROPELLER.
The design of propeller used was 0800, S. C. No. 74656,
on the test of the 100 square feet auxiliary radiator.
The cooling tests were run in the usual manner and the
observations made, recorded, and corrected as shown on
the following data sheets:
(3)
ANALYSIS OF RESULTS AND DISCUSSION.
The temperature difference between the . mean temperature
of the water and that of the air reaching the
radiator which any cooling system will maintain under
the I]lOst severe operating conditions is a measure of its
effectiveness. In service this most severe condition is
during full throttle, full climb with airplane carrying its
military load. The Air Service requires satisfactory performance
when the ground temperature equals 32° C.
(90° F.) and with this condition a mean temperature
difference of 60° C. is necessary to keep the hottest engine
water from boiling and to prevent its remaining at
unsafe temperatures.
The plotted test on page 8 (fig. 4) shows that the cooling
system on the production DH-4 operates on a temperature
difference of 72° C. The test on page 9 (fig. 5) shows
that the same cooling system with the addition of the 100
square foot auxiliary radiator operates on a mean temperature
difference of 48° C.
On page 10 (fig. 6) the estimated required performance is
shown of a cooling system adequate for conditions where
the ground temperature is 38° C. (100° F.) from a standard
United States temperature curve. This is for summer
service in such regions as Texas, the Mexican border,
etc. It is evident that a mean temperature difference of
approximately 57° C. is then necessary.
Since cooling varies directly with amount of surface
and inversely with temperature difference, the product
of surface and its temperature difference, when divided
by any given temperature difference, will give the amount
of surface necessary and, obviously, this same product
divided by any given surface will give the necessary
temperature difference. That is
Where
T =mean temperature difference using surface S.
S =total radiating surface which gives temperature dif-ference
T.
T1=mean temperature difference required.
S 1 = surface required.
Substituting
3124~72 =468.
This 468 is the number of square feet necessary in a nose
radiator to give the temperature difference obtained in
the test shown on page 9 (fig. 5); that is, it would equal the
effectiveness of this 312 square feet in the nose plus the
100 square feet in the auxiliary radiator in the propeller
slip stream. •
Then 468-312=156, which is the surface in the nose
equal to 100 square feet in the propeller slip stream, or
4
1 square foot in the slip stream equals 1.56 square feet in
the nose under DH-4 conditions.
Now
312
5:;:
72
=392, which is the surface necessary in
the nose to give the required temperature difference of
57° C. (previously decided upon as necessary for service
flying in the summer in the South).
And 392--312=80 the necessary increase in ·the nose to
give this desired performance. Above it was shown that
100 square feet in the slip stream equaled 156 square feet
in the nose.
Then by simple proportion
100 : 156 : : X : 80.
Or
10
~~
80
=51.3. This, then, is the required surface
in square feet for an auxiliary radiator in the slip stream
to give a temperature difference of 57° C. under these
conditions.
As the tubes in this test radiator were considerably corroded
it is estimated that the same cooling effectiveness
could be obtained under the same conditions with some
5 to 10 per cent less surface made up of clean polishedtubes.
However, in an auxiliary radiator half this size
and half this height a considerably larger portion of its
surface would lie close to the fuselage where the rate of
air flow is reduced to an extent estimated at from 10 to
15 per cent under these conditions. On the strength of
the foregoing an auxiliary radiator containing better
tubes and having 55 square feet of surface was designed,
built, and tested with the results shown on page 11 (fig. 7),
where the mean temperature difference between 2,000 and
4,000 feet proved to be 57.6° C.
Subsequently a superior type of extruded copper radiator
tube was developed and adopted for use in· the Air
Service. This tube is 0.268 inch outside diameter with
0.006 inch wall and can be secured in any length up to
and including 9 inches. (See A. S. Dwgs. M-1317,
M- 1318, and M- 1337.)
The designs of the 55 square foot auxiliary radiator described
above were altered to take this new standard core,
considerably reducing its over-all dimensions except depth
(front to rear), which was increased from 8 inches to 9
inches. This radiator is so designed that it may be
easily installed in the field. No additional piping is
required. The old pipe (on the production DH-4)
leading from the nose radiator to the pump when cut to
proper length fits the inlet and outlet of the new auxiliary
radiator. This addition to the system weighs full 61
pounds and empty 40 pounds. (For complete details
see A. S. Dwg. 046118.)
j
...
5
Fm. 1.-DH-4 with auxiliary radiator of 55 square feet giving satisfactory cooling at ground temperature of 38° C. (100° F.). (This radiator superseded
by smaller one of same surface with standard .268 inch tubes, A. S. Dwg.)
53058.:._21- 2
fj
Flo. 2.-Production DH-4 equipped with experimental auxiliary radiator of 100 square feet.
7
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Fm. 3.--Production DH-4 equipped with experimental auxiliary radiator of 100 square feet.
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Air Service Information Circulars
