The efficacy of liquid ice protection systems which distribute a glycol-water solution onto leading edge surfaces through a porous skin was demonstrated in tests conducted in the NASA Lewis icing research tunnel using a composite porous leading edge panels. The data obtained were compared with the performance of previously tested stainless steel leading edge with the same geometry. Results show: (1) anti-ice protection of a composite leading edge is possible for all the simulated conditions tested; (2) the glycol flow rates required to achieve anti-ice protection were generally much higher than those required for a stainless steel panel; (3) the low reservoir pressures of the glycol during test runs indicates that more uniform distribution of glycol, and therefore lower glycol flow rates, can probably be achieved by decreasing the porosity of the panel; and (4) significant weight savings can be achieved in fluid ice protection systems with composite porous leading edges. The resistance of composite panels to abrasion and erosion must yet be determined before they can be incorporated in production systems

Kohlman, D. L.

English

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https://ntrs.nasa.gov/search.jsp?R=19820003179 2020-03-21T11:34:59+00:00Z
(NISI-CR-164966) ICING TUNNEL TESTS CF I	 U82-11052
COMPOSITE POROUS LEADING EDGE FOR USE WITH I
LIQUID ANTI-ICE SYSTEM (Kansas UniT. Center
for Research$ Inc.) 21 p MC IO2/11F I01	 UnclasCSCL 01C G3/05 08296
40%_
RECEIVED
n E! U^ ,u
THE UNIVERSITY OF KANSAS CENTER FOR RESEARCH, INC.
2291 Irving Hill Drive--Campus West
Lawrence, Kansas 66045
	
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/	 p
iICING TUNNEL TESTS OF A
COMPOSITE POROUS LEADING EDGE
FOR USE WITH A
LIQUID ANT'-ICE SYSTEM
KU-FRL-464-3
by
David L. Kohlman
for
National Aeronautics and Space Administration
Lewis Research Center
NASA Grant NAG 3-71
Flight Research Laboratory
University of Kansas Center for Research, Inc.
Lawrence, Kansas 66045
September 1981
t
L•
[	 i
r ^
iTABLE OF CONTENTS
Page
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . 1
SYMBOLS., 
	
. . . 92
TUNNEL DESCRIPTION AND TEST CONDITIONS . . .	 e	 2
MODEL DESCRIPTION. . . . . . . . . . . . . . . . . . . . • . . . . 4
ICE PROTECTION SYSTEM DESCRIPTION. . . . . . . . . . . .	 . . 4
TEST RESULTS	 6
CONCLUSIONS * . . . . . . . . . . . . . . . . . . . . . . . . . . 9
REFERENCES	 10
IINTRODUCTION
	
^i	 Liquid ice protection systems which distribute a glycol-water
solution onto leading edge surfaces through a porous skin have been
	
j	 shown to be very effective. Numerous airplanes in Europe already
	
,.	 employ such systems as standard equipment. Tests recently conducted
	
f	 in the NASA Lewis Icing Research Tunnel confirmed the efficacy of
a liquid system on general aviation airfoils and generated some data
on required flow rates (Ref. 1).
All liquid ice protection systems currently in use, as well as
the one described in Reference 1, use a sintered stainless steel
mesh as the porous skin through which the glycol is distributed.
While the stainless steel is strong, rigid, and smooth and functiuns
very satisfactorily, iL is relatively heavy, accounting for approxi-
mately 50% of the total weight of the hardware of such a system.
The desire to reduce this weight, coupled w'th the advent of airplanes
almost totally constructed of composite materials, has stimulated
investigation of alternate porous leading edge materials, particularly
composites.
This report presents the results of a test of a composite porous
leading edge panel in the Lewis Icing Research Tunnel and compares
those results with the performance of the previously tested stainless
steel leading edge with the same geometry.
{SYMBOLS
c 
	 section lift coefficient
LWC	 liquid water content, g/m3
T	 total temperature
V	 free stream equivalent airspeed
WS	 wing station, in
a	 angle of attack
TUNNEL DESCRIPTION AND TEST C01,MITIONS
The NASA Lewis Icing Research Tunnel (IRT) ig a closed-cycle,
refrigerated tunnel with a rectangular test section 1.83 m (6 ft.)
!	
high by 2.74 m (9 ft.) wide by 6.1 m (20 ft.) long (Figure 1).l
Maximum tunnel airspeed is 134 m/sec (300 mph). A natural icing
cloud is simulated by injecting a water spray upstream of the test
section.
The area of interest on the test model is confined to that
region in the center of the test section where the icing cloud is
most uniform, covering a cross-sectional area of .9 m (3 ft.) high
by 1.5 m (5 ft.) wide. The liquid water content (LWC) of the cloud
can be varied from about .5 to over 2 g/m 3 with volume median droplet
diameters in the range of 10 to 20 microns. The tunnel airflow
temperature can be varied from -28.9°C (- 0°F) to ambient.
3
For this series of tests, two test section equivalent airspeeds
were chosen, namely 49.2 m/sec (96 knots) and 90.3 m/sec (175 knots).
These speeds ccrrespond to the best rate of climb speed and the
2
cruise speed of a typical high performance, single-engine airplane
and duplicate the speeds used in Reference 1.
Since the LWC and water drop size ranges of the IRT icing cloud
depended upon tunnel airspeed, operating envelopes for LWC and drop
size were plotted for the givcm airspeeds of interest, 49.2 m/sec
and 90.3 m/sec (Figure 2). From these two tunnel operating envelopes
i
the extreme values and several midpoint values of LWC and drop size
were chosen as the icing cloud test conditions (Figure 2). The LWC
and drop size varied then from .65 to 2.4 g/m 3 and 11 to 20 microns,
respe^cively. Figures 3 and 4 illustrate where the tunnel icing
cloud test conditions are located on the continuous maximum and
intermittent maximum icing condition curves specified in FAR Part
25 (Ref. 2).
The type of ice (i.e., glaze or rime) that formed on the airfoil
depended primarily on the tunnel total air temperature. To produce
glaze ice, the tunnel total air temperature was set at -3.9°C (25°F);
and to produce rime ice, it was set at -15°C (5°F). The ambient or
outside air temperature (OAT) corresponds to the static air temperature
in the tunnel test section. For the two airspeeds chosen, namely
49.2 r./sec and 90 . 3 m/sec, the OAT's for glaze ice were -5.1°C and
j
•-7.8°C, respectively; and the OAT's for rime ice were -16.2°C and
-
18°C, respectively. The true airspeeds were 43 . 7 m/sec and 85.3 m/sec
^.	 at T - 5 °F and 44.7 m/sec and 86 . 9 m/sec at T - 25°F.
(1	 MODEL DESCRIPTION
I The wing section tested was taken from an actual single-engine,
light airplane. The original wing tapered from a NACA 64 2A215 airfoil
3
at the root (WS 0) to a NACA 641A412 airfoil at the tip (WS 216).
The wing incorporated a modification proposed by Raymond Hicks (Refs.
3, 4) of NASA Area Research Center. This modification, which adds
thickness to the forward 30 percent of the upper surface, increases
ci
 , reduces Cd at high CR , and improves stall characteristics.
max
A typical "Hicks" modification is shown in Figure S.
The wing section tested was fastened securely to the turntable
on the floor of the tunnel, using the spar fittings that are used
to attach the wing to the fuselage of the airplane. A clearance
of one-half inc}: was allowed between the outboard end of the wing
segment and the ceiling of the six-foot high test section of the	 i
tunnel. The centerline of the tunnel was at WS 58 of the original
wing. Table 1 gives the airfoil coordinates at WS 58, where the
wing chord is 63.25 inches. The chord tapers 1.1 inches per foot
of span, and the wing is twisted 0.167 degrees per foot of span
(washout). Figure 6 shows the wing section with composite leading
edge installed in the NASA Lewis Icing Research Tunnel.
ICE PROTECTION SYSTEM DESCRIPTION
The system tested consists of porous composite panels attached
to the leading edge of the wing, and a pump that distributes a
glycol based fluid from a tank to the panels through plastic tubing.
4
..^wTM.^...+..,:n.,-t ^•.
	
_.	
_	
,e-^•--•- ^•---^•....5`.,,^.^'•.-^a:-.---,,... 	 3s.....,.,.	 ..n.:-^.	
-^--^-..,•,•F"^R'•.Y.,,-,,,.^,9T,aAf••_
X11 The fluid exudes from *.ie porous panels onto the surface of the wing,
providing ei ther an anti-icing capability by dissoving the supercooled
water droplets and preventing the formation of ice, or a deicing
capability by chemically breaking the bond of established ice. A
^I
t	 significant feature of the system is that protection is obtained
aft of the panels by the flow of the fluid along the chord to the
trailing edge, thus preventing the formation of ice anywhere aft
of the active leading edge.
The porous leading edge panel used in this test was attached
to the original wing leading edge, as shown in the cross-sectional
drawing in Figure 7. The width of the porous region is 8.7 cm.
The panel is divided spanwise into three separate porous sections.
Referring to the vertical position of the wing in the tunnel, the
upper and lower sections are 20.3 cm . long and the middle section is
30.4 cm long. The maximum thickness of the panel is 3.2 mm.
iThe flow rate into each section was controlled independently by
three variable positive displacement pumps.
The fluid reservoir behind the porous leading edge skin consists
of a composite backing panel and a thin polyvinylfluoride sheet that
separates the fluid from the porous leading edge. The Purpose of the
polyvinyl fluoride sheet, whose porosity is much lower than that of-
the composite skin, is to distribute the glycol evenly over the
entire active portion of the panel, regardless of the chordwise
pressure distribution changes that occur as angle of attack changes.
Pressure tests showed that the net porosity of the leading edge panel
was much higher than that ' of the original stainless steel panel.
5
This resulted in uneven distribution of glycol. This is discussed
more fully in the following section.
The fluid used in this test is composed of 801 monnethylene
glycol and 202 deionized water.
The edges of the active portion of the panel must be placed
such that extreme positions of the stagnation points for which
icing protection is required are no closer to the edge than approxi-
mately 1 cm. This ensures that the fluid will always be distributed
on both the upper and lower surface of the wing. Figure 7 shows
the location of the stagnation pointe on the leading edge for each
angle of attack used in this test.
The composite skin consists of two outer layers of Kevlar and
a middle layer of fiberglass in a resin matrix. The composite panel
was designed and manufactured by Fiber Haterials, Inc., of Biddeford
Maine.
The weight of the composite panel was 390 grams, about one-third
that of the previously Masted stainless steel panel of the same
dimensions.
TEST RESULTS
Normal operation of the glycol-exuding porous leading edge
system is in the anti-ice mode; that is, the glycol flow rate is
sufficient  to prevent any ice from forming on the wing. This is
possible as long as the glycol-water solution on the surface main-
tains a freezing temperature below the ambient air temperature.
The solution freezing temperature increases as the ratio of the
6
f(	 water catch rate to the glycol flow rate increases. A series of
runs was conducted in the Lewis IRT to determine the minimum glycol
I.	 flow rate at which anti-icing could be maintained.
The method of determining the glycol flow rate corresponiing
t.
with the anti-ice threshold wits as follows. At a given flight
I condition, the flow rate was set to be well above the anti-ice
l	
threshold. The flow rate was then reduced in steps, allowing
!.	 stout 30 seconds for the system to stabilize at each point, until
small flecks of ice began to appear on the leading edge in the
vicinity of the stagnation point. At the anti-ice threshold, the
small ice flecks, ranging up to about 3 mm in diameter. would form
and then be swept downstream in less Lhan one minute. A glycol
flow rate lower than the threshold value would cause the ice flecks
to persist, gradually growing into larger patches before being
shed from the wing.
To obtain the minimum anti-ice glycol flow rates, all three
sections were used simultaneously during each run to establish
the independent flow rate values from each section. During the
first day the center section was inoperative due to a teak in the
tube fitting. Flow rates are presented in terms of specific flow
rate: milliliters of glycol per square centimeter of active panel
per minute.
Figures 8 through 11 present results of the anti-icing tests
for four different icing conditions. The anti-ice threshold is
defined in terms of glycol specific fluid flow as a function of
liquid water content (LWC).' In examining the data, several con-
clusions may be readily drawn.
l^
It is clear that anti-ice performanca was achieved at all
conditions tested using the composite leading edge panel. Although
sngl^ of attack had relatively little effect on the anti-ice flow
rate, there was a wide variation in the performance between the
I.
three separate panels. There was .zlFo a considerable amount of
r^
scatter in the definition of the ant : . .,cing threshold flow rate
for a given condition.
More important, however, is the comparison between anti-ice
flow rates for the composite panel and the previously tested
stainless steel TICS panel. It is obvious that much higher total
flow rates were required for the composite panel than for the
stainless steel panel.
1
The porosity of the composite panel is believed to be the
I	 cause of this discrepancy. Bench tests as well as pressure measure-
!
=ants of the glycol during test runs showed that the composite panel
was much more porous than the stainless steel panel. Thus the back
pressure in the reservoir of the composite panel was relatively
low. Therefore, the stagnation pressure on the outer surface of the
leading edge was able to inhibit glycol flow at the stagnation point,
forcing more glycol out near the edges of the porous panel. This
process could be observed clearly by eye in the IRT. Since the need
for anti-ice protection is greatest at the stagnation point, much
more total fluid was required to achieve that critical protection at
the stagnation point.
The problem of non-uniform distribution of fluid through the
►?orous leading edge can probably be solved by merely decreasing the
8
porosity of the composite porous panel system. Construction of
such a panel and further testing to verify this has been proposed.
CONCLUSIONS
Tests of a composite porous leading edge panel in the SAM
Lewis IRT have led to the following conclusions:
1. Anti-ice protection of a composite leading edge was
possible for all simulated flight conditions tested.
2. Glycol flow rates required to achieve anti-ice protection
were gener-.1y much higher than those required for a
previously tested stainless steel TKS panel (Ref. 1).
3. Tha low reservoir pressures of the glycol during test
runs indicated that more uniform distribution of glycol,
and therefore lower glycol flow rates, can probably be
achieved by decreasing the porosity of the panel.
4. Significant weight savings cs.» be achieved in fluid
ice protection systems if composite porous leading edge.
panels can be used. Composite panels weigh about one-
third the weight of comparable stainless steel panels.
S. The resistance of composite panels to abrasion and erosion
must yet be determined before they can be incorporated
in production systems.
9
RBYMMCBS
I, 1. Kohlman, D. L., Schweikhard, W. G., and Albright, Alan E.,
"Icing Tunnel Tests of a Glycol-Exuding Porous lwading Edge
Ice Protection System on a General Aviation Airfoil," NASA
Contractor Report 165444, September 1981.I,	
2, Federal Aviation Regulations, Part 25, Appendix C - Airworthfnese
Standards: Transport Category Airplanes, Department of
Transportation, Federal Aviation Administration,. Washington,
D.C., June 1974.
3. Hicks, R. M., and Schairer, E. T., "Effects of Upper Surfs---a
Modification on the Aerodynamic Characteristics of the NACA
632-215 Airfoil Section," NASA TM 78503, January 1979.
4. Szelazek, C. A., and Hicks, R. M., "Upper-Surface Modifications
for C 	 Improvement of Selected NACA 6-Series Airfoils,"
max
NASA TM 78603, August 1979.
10
RS I
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TFST CHAMHER	 ! ^®
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SPRATS
	
300 Ml H. TES
SECTION 6'.9'
CONTroI t00r	 R	
I 
• 
w
J try •	 SHOP
Figure 1. - NASA Lewis Icing Research Tunnel.
2.4	 12.4, 201
	
/	 i V • 49.2 ml sec
E
100,
	 I
1.6
zo	 //	 01L5, 15)	 11.55,201
c	
///
L 2	
/	
/,oo	 Il.i6,111
	
,' JILJ, 151	 V - 90.3 MsecJ	 /
.8 — (L 16,15) J^	 (. 8, 15)
(.65, 11)
41C	 12	 14	 16	 18	 20
DROP SIZE, pm
Figure 2. - IRT Operating Envelopes and Test Points.
1R
11
® CONTINUOUS MAXIMUM
ICING CONDITIONS
(STRATIFORM CLOUDS)
2.4 A(2.	 201
IRT OPERATING
^ 2.0- 15)ENVELOPES	 ^^^ 
	
I r V - 49.2 rriSKL 5,I/	 Y
►= r(1.16,111,^
	 ,',rIL 16,15)	 I
L 6 o ;	 (L 0, 15)	 (L 55,20)
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V - 90.3 misec
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a 18,1510	 AIR TEMPERATURE
.8 +320 F,
0 4 X L65, 11) -	 F +1	 FJ
-22° F"
40 12	 14	 16	 18	 20	 22	 24	 26	 28	 30
DROP SIZE, pm
Figure 3. — Continuous Maximum icing Conditions (ref. 	 1)
and IRT operating envelopes.
3.2 r 0 INTERMITTENTMAXIMUM ICING
2.8 1
 r
CONDITIONS
E , (CUMULIFORM CLOUDS)
a' IRT
2.4	 OPERATING V • 49.2 misec
w ENVELOPES  (L 55 20)
0 2. 0	 IL 5,15), -AIR TEMPERATUREU
^ 1
a
1.6	 (1.:6 329 F
0 1.2
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_(0.6511) 1.8,15)i
-^^ F^
I	 i	 I4l-- _^- _
10	 12	 14 16	 18 20	 22	 24	 26	 28	 30
DROP SIZE, pm
Figure 4.	 - Intermittent '4aximum icing Conditions	 (ref.	 1)
and IR.T operating envelopes.
12
NACA 64,A412
— — — — Proposed Modification
0.1
y/c 0
	
-0.1 l	 1	 1	 1	 1	 1	 1	 I	 1	 1
	0 	 0.1	 0.2	 0.3
	 0.4
	
0.5	 0.6	 0.7	 0.8	 0.9	 1.0I	 x/c
1.
Figure S. - Hicks Modification on a NACA 64 1A412 Airfoil.
r
r
13
IT
Figure 6. - Winb with Composite Porous Leading Edge
Installed in the NASA Lewis IRT.
ORIGINAL PAGE IS
OF FGGR QUALITY
14
al Wing Contour
anel
Stagnation Point
Location
a•0.50
a • 1.2°
a°7.8°
a • 12.5°
1	 2 3c m
Figure ]. - Cross Section of the T.K. S. Porous Panel
Inst alled on the Test Wing at WS 58.
•^Y
15
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,06
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v .04
u
u
a
o
0
V = 9 G Kr
T= 2^°^
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UPPER PANEL — 140 C-UAC,
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CALL	 REVISED DATE Figure 8. - Anti-ice Thresholds of a
CHECKI
	
Composite Porous Panel at
A►PD	
sV = 96 kt T = 25°F. 
A ►►D
UNIVERSITY OF KANSAS
tV
t
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9
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V = 9G Kr
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	 d
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M^pOLE PRU^^ OWE-- FLAG
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PAGE IS	 _..
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CALL	 REVISED DATE Figure 9. - Anti-ice Thresholds of a
CHECK	 Composite Poroas Panel at
APPD	 V = 96 kt , T = 50F.
A7PD
	
UNIVERSITY OF KANSAS
	
PAGE 17
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	 V = k_7'5 Kr
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CALL	 REVISED DATE Figure 10. - Anti-ice Thresholds of a
CHECK
	
Composite Porous Panel at
AP.D	 V = 175 kt, T = 25°F,
a = 7.3°AIPD
UNIVERSITY OF KANSAS
	
PAGE 18
r-
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V = l ?5 K r
T = 5° F
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Composite Pnrous PWIVI :ItCHECK
V -	 175 kC ,	 T =	 5tF.APPD
APPD
UNIVERSITY OF KANSAS PAGE	 19
.E; 10 7196 Fit MC,ON.


Icing tunnel tests of a composite porous leading edge for use with a liquid anti-ice system

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