APPENDIX R. ICE SHAPES (CONTINUED)
a.
b.
Figure R-1. Hybrid NACA 23012 2D (Simulating a 72-inch Chord Airfoil) Model Leading Edge Ice Roughness Before Activation of the IPS. Exposure time included 11 seconds for an ice detector alert and 30 seconds for the flight crew to activate the IPS. The test was performed in 14 CFR part 25, Appendix C Continuous Maximum Icing Conditions. (Static temperature = 14qF, LWC = 0.45 g/m3, MVD = 20 micrometers, spray time = 41 sec., tunnel airflow speed = 195 mph, Model AOA = 4q.) (Reference R1).
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APPENDIX R. ICE SHAPES (CONTINUED) Figure R-2 shows the model’s preactivation surface roughness that occurred during exposure to an intermittent maximum icing condition. The preactivation time included three seconds for the first cycling of the ice detector and 30 seconds for the pilot to begin recommended procedures for actuation of the IPS. Figure R-3 shows the model’s leading edge surface roughness that resulted from a visual observation of ¼ inch of ice accretion and an added 30 seconds of exposure to maximum continuous icing conditions. The 30 seconds allows the pilot to begin recommended deicing procedures.
If you select more than one deicing cycle of an ice detector to avoid nuisance ice detection warnings or activation of the IPSs, then include this time in the preactivation exposure to the icing conditions. Also, flight crews may take up to two minutes to recognize icing conditions and begin recommended procedures for propulsion IPS. When determining the delay time for pilots to begin recommended ice protection procedures, consider the means provided to the flight crews for detecting the first accretion of airframe icing and the flight crew workload. The time required for the IPS to become fully effective varies with each IPS, for example the time for thermally protected surfaces to reach the design temperature. For IPSs that activate components sequentially, consider the time required for activation of the complete system as part of the preactivation exposure to icing conditions.
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APPENDIX R. ICE SHAPES (CONTINUED) Figure R-2. Hybrid NACA 23012 2D (Simulating a 72-inch Chord Airfoil) Model Leading Edge Ice Roughness Before Activation of the IPS. Exposure time included allowing 3 seconds for an ice detector alert and 30 seconds for the flight crew to activate the IPS. The test was performed in 14 CFR part 25, Appendix C Intermittent Maximum Icing Conditions. (Static temperature = 14qF, LWC = 1.95 g/m3, MVD = 20 micrometers, spray time = 33 sec., tunnel airflow speed = 195 mph, model AOA = 4q.) (Reference R1).
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APPENDIX R. ICE SHAPES (CONTINUED) Figure R-3. Hybrid NACA 2301 2 2D Model (Simulating a 72-inch Chord Airfoil) Leading Edge Ice Roughness Before Activation of the IPS. Exposure time included the time required for an observation of ¼ inch of ice and 30 seconds for the flight crew to activate the IPS. The test was performed in 14 CFR part 25, Appendix C Continuous Maximum Icing Conditions.
(Static temperature = 14qF, LWC = 0.45 g/m3, MVD = 20 micrometers, tunnel airflow speed = 195 mph, model AOA = 4q.) (Reference R1).
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APPENDIX R. ICE SHAPES (CONTINUED) R.1.2 Intercycle Ice Roughness.
For continued operation of the deicing IPSs, the flight crew may activate the IPS on visual observation of a recommended monitored surface ice thickness. This ice thickness typically ranges from ¼ to 1½ inches. Figure R-3 shows the surface roughness that may be expected following visual observation of ¼ inch of ice accretion and an added 30 seconds of exposure to maximum continuous icing conditions. The added 30 seconds allows the pilot time to activate the deicing IPS. Since the cycling sequence time may be lengthy for some IPS designs, you should also consider ice buildups on the protection surfaces during the cycling sequence. Other mechanical systems may have different intercycle ice accretion characteristics. You should show that asymmetric intercycle ice accretion resulting from sequential operation of the elements of the IPS does not result in unsafe flight. Alternatively, you may automatically operate the deicing IPS continuously using preselected cycle intervals.
You should determine and prove intercycle ice roughness.
Figures R-4(a) and R-4(b) show intercycle ice roughness for a wind tunnel model using threeminute and one-minute intervals between cycling of the deicing boots in typical icing conditions.
You can gauge the texture of the intercycle ice by using the grids formed by the one-inch apart chordwise and spanwise lines shown in the photographs. Castings of the intercycle ice in figures R-4 (a) and R-4(b) are available from the FAA William J. Hughes Technical Center, Flight Safety Branch.
For smaller surfaces, such as the horizontal stabilizers of regional air transports, figure R-5 shows intercycle ice roughness on a 2D, 36-inch NACA 23012 airfoil wind tunnel model using three- and one-minute intervals between cycling of the deicing boots.
Figure R-6 shows that the intercycle ice roughness in figures R-4 and R-5 compare favorably with that seen during flight. The wing leading edge deicing boots in figure R-6(a) were cycled just before landing after the aircraft had experienced heavy icing conditions. Figure R-6(b) is a photograph, taken in flight during a revenue flight, of wing leading edge deicing boots’ intercycle ice accretion. The losses in maximum lift, maximum lift AOA, and increases in drag at operational angles-of-attack and as maximum lift is approached underscore the need for proper modeling of the surface roughness of protected surfaces when the IPS is working normally. This is important when showing safe performance and handling qualities in icing conditions.
Aerodynamic effects of intercycle ice surface roughness can be significantly adverse. Figure R-7 shows the aerodynamic effects of intercycle ice surface roughness that resulted from icing wind tunnel and high Reynolds number wind tunnel tests of a 36-inch NACA 23012 airfoil. Texture of the intercycle ice is available from castings of the intercycle ice shown in figure R-5(b).
(These castings are available from the FAA William J. Hughes Technical Center, Flight Safety Branch.) Figure R-8 shows that the aerodynamic effects of uniformly distributed roughness, such as Carborundum grit, do not result in aerodynamic effects similar to those of the tested intercycle ice surface roughness. You should verify the use of uniformly distributed roughness to simulate intercycle ice shapes.
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APPENDIX R. ICE SHAPES (CONTINUED) Figure R-4(a) Hybrid NACA 23012 2D (simulating a 72-inch chord airfoil) mode l intercycle ice before the third cycle of a pneumatic deicing boot. Three-minute boot cycle intervals were used. The test was performed in 14 CFR part 25, Appendix C Maximum Continuous Icing Conditions. (Static temperature = 14qF, LWC = 0.45 g/m3, MVD = 20 micrometers, Spray time = 6:11 min., Tunnel airflow speed = 195 mph, Model AOA = 4q.)
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APPENDIX R. ICE SHAPES (CONTINUED) Figure R-4(b). Hybrid NACA 23012 2D (simulating a 72-inch chord airfoil) model intercycle ice before the sixth cycle of pneumatic deicing boot. One-minute boot cycle intervals were used. The test was performed in 14 CFR part 25, Appendix C Maximum Continuous Icing Conditions. (Static temperature = 14qF, LWC = 0.45 g/m3, MVD = 20 micrometers, Spray time = 6:11 min., Tunnel airflow speed = 195 mph, Model AOA = 4q.)
Figure R-4. Typical Surface Roughness on the Leading Edge of a NACA 23012 Resulting From Normal Operation of Wing Pneumatic Deicing Boots (Reference R1).
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APPENDIX R. ICE SHAPES (CONTINUED) Figure R-5(a). Ice protection design (pneumatic deicing boots) for the NACA 23012 airfoil tested to examine intercycle ice buildup.
Ice shape 290 Ice shape 296 Ice shape 312 Ice shape 322 Ice Shape Angle of Attack (deg.)
Drop MVD (ȝm) Static Temp.
(deg. F) LWC 3(g/m ) Spray Time (min.) Boot Cycle Period (min.)
290 0 20 14 0.45 12 3 296 0 20 21 0.65 12 3 312 0 40 21 0.25 12 3 322 0 40 -4 0.40 3 1 Figure R-5(b). Icing wind tunnel intercycle ice accretions for the figure R-5(a) model.
Figure R-5. Intercycle Ice Roughness for a 2D 36-inch NACA 0012 Airfoil Wind Tunnel Model.
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APPENDIX R. ICE SHAPES (CONTINUED) Figure R-6(a). Residual ice following cycling of the deicing boots after an inflight icing event and before landing.
Figure R-6(b). Wing deicing boots intercycle ice accretion photographed during revenue service.
Figure R-6. Wing Deicing Boots Residual and Intercycle Ice Buildups.
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APPENDIX R. ICE SHAPES (CONTINUED) Re = 7.5 × 10°, Ma = 0.21 Clean Ice shape 290 Ice shape 296
1.0 Ice shape 312
0.8- Ice shape 322
0.4 -0.6- -4 -2 6 8 10 12 16 18 20 œ (deg)
0.080-
0.070-
0.060-
0.050 Ca 0040-
0.030-
0.020 -0.08- 0.010 -0.10 3 10 12 14 16 18 2 0.000- 4 6 8 10 12 14 16 18 20 a (deg) a. (deg) Figure R-7. Aerodynamic Effects Resulting From Deicing Intercycle Ice Shapes for a 2D 36-inch NACA 23012 Airfoil Wind Tunnel Model at a Reynolds Number of 7.5x10°.
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APPENDIX R. ICE SHAPES (CONTINUED)
2.0 Re = 7.5 x 10°, Ma = 0.21 Clean 40-grit sandpaper 80-grit sandpaper Ice shape 290
0.2
0.0- -0.2 -0.4- -0.6- 042024681 14 16 18 20 a (deg)
0.080
0.070
0.060
0.050-
0.00 0.000 Ca 0.040- -0.02
0.030 -0.04
0.020 -0.06
0.010 -0.08 -0.10- "2 4 6 8 10 12 14 16 18 20 00000-5-6 4 2 0 2 4 6 8 10 12 14 16 18 20 a (deg) a (deg) Figure R-8. Aerodynamic Effects of Distributed Roughness Along the Leading Edge of a NACA 23012 Airfoil (c = 36 inches, Re = 7.5x10°, M = 0.21) (Reference R2).
R.1.3 Runback Ice.
Water not evaporated by a thermal IPS and unfrozen water during near-freezing conditions may run aft of the ice protection surfaces and form runback ice. During near-freezing conditions, the freezing fraction (n) of the water is less than 1.0.
Figure R-9 is a photograph of runback ice for a 36-inch NACA 0012 duty airfoil model after 5 minutes of exposure to icing conditions. The model was equipped with an electrothermal IPS.
The IPS ran wet (surface temperature of about 50°F with an icing wind tunnel static temperature of O°F). The tunnel icing conditions were mixed-phase, with 20 um liquid water drops. The R-12
APPENDIX R. ICE SHAPES (CONTINUED) LWC was 0.35 g/m3 and the IWC of the shaved ice was 0.35 g/m3. Appendix C does not include mixed phase icing conditions. However, the runback buildups shown have similar characteristics to those produced in Appendix C liquid-phase conditions.
Figure R-9. Lower Surface Runback Ice on a 36-inch NACA 0012 Airfoil Model. The model was equipped with an electro-thermal IPS. The IPS ran wet with a constant protection surface temperature of about 50qF. The mixed-phase icing cloud exposure time was 5 minutes.
(Static Temperature = 0qF, LWC = 0.35 g/m3, MVD = 20 micrometers, IWC (shaved ice) =
0.35 g/m3, tunnel airflow speed = 120 mph, model AOA = 0q).
Computer codes may be unable to estimate the characteristics of the runback water or the resultant ice shapes. Some codes may be able to estimate the mass of the runback ice. Until computer codes are developed and accepted, determine runback ice empirically by natural icing tests, icing tanker tests, or icing wind tunnel tests.
You determine and verify runback ice buildups. Consider the effects of runback ice resulting from a 45-minute hold when showing the safe flight. The required water catch may be impractical to get in natural icing conditions. Instead of natural icing tests alone, use icing tanker, icing tunnel tests, or analyses with flight tests to determine runback ice buildups. You can then flight test simulated ice shapes to evaluate the effect of runback ice on aircraft flying qualities. For thermal IPSs that do not evaporate the impinging water under holding conditions (running-wet systems), evaluate the shedding and engine ingestion of runback ice from airframe and engine inlet surfaces.
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