APPENIDX Q. ICE SHEDDING (CONTINUED) You should understand shed-ice trajectories as much as possible before flight-testing. You should also understand the differences between shed-ice trajectories resulting from tanker tests and those from natural icing conditions before accepting tanker testing for evaluating shed-ice trajectories. Reference Q2 provides added information about the use of icing tankers for evaluating shed-ice trajectories.
Ice ingested by the engines should not interfere with the engines’ operation and thrust. The ice protection of airframe surfaces whose ice buildup affects the integrity of the engines should be considered part of the engine’s IPS. Structural damage analyses may be required if ice shed from forward aircraft surfaces can strike downstream surfaces. Also consider shed-ice damage of aircraft components (including control surfaces and their horns, hinges, control cables, and spoilers) and load-bearing structure.
If you do not install anti-icing protection on critical ice shedding surfaces, then you should conduct an investigation to show that ice shed from these surfaces will not cause an unsafe condition. Conduct “ice shedding” investigations during and after icing events. You should evaluate enough events in all intended operational conditions to ensure there is no hazard associated with ice shedding. Besides the usual measurements and observations made during icing tests, we suggest the following instrumentation or observations:
x Motion pictures to record the trajectory of ice released from the aircraft;
x A data acquisition system for turbine-engine-powered aircraft to record exhaust gas temperature, engine pressure ratio, and rpm to detect adverse effects on engine operation; or x Visual examination of the aircraft for damage before and after ice events, especially near the engine compressor and inlet.
In addition, a damage analysis should consider that the most critical ice shapes will shed and impact the areas of concern.
Q.2 REFERENCES.
Q1. “Ice Accretion and Droplet Impingement Codes,” SAE ARP5903.
Q2. “Airborne Icing Tankers,” SAE ARP5904.
Q-2
APPENIDX R. ICE SHAPES R.1 PROTECTED SURFACES.
R.1.1 Preactivation Ice Roughness.
When showing safe flight in icing conditions, applicants should consider the ice accretion roughness on unprotected and protected aircraft surfaces that occurs before the IPS is effective.
Section 8.2.1.2.b, of this AC discusses preactivation ice. This surface roughness may seem small, but the resulting adverse aerodynamic effects may be significant. Also, since safe flight considerations may require adjustments to the uncontaminated aircraft stall protection and other systems, you may need to adjust AFM performance and maneuvering airspeeds of the uncontaminated aircraft (ACs 23.1419-2B, 25.1419-1, 27-1B, and 29-2C). Safe flight considerations for preactivation ice accretion should include acceptable stall warning and safe flying qualities at and above stall warning. Icing conditions event times should include delay times associated with detecting the first buildup of ice, flight crew reaction time to activate the IPS using recommended procedures, and the time required for the IPS to become effective.
Preactivation ice accretion roughness varies with the aircraft’s IPS technology and use as a deicer or anti-icer, the aircraft’s design, and the IPS operating procedures. Therefore, you should determine the preactivation ice roughness for your aircraft and show safe flight before the IPS becomes fully effective. You should base the roughness you select on the time required for the IPS to become fully effective and the icing condition that results in the most critical effects on airplane flying qualities. Figures R-1, R-2, and R-3 are photographs of preactivation ice on the leading edge of a hybrid NACA 23012 2-dimensional icing wind tunnel model. The reader can gauge the sand roughness of the preactivation ice by the grids formed by the one-inch apart chordwise lines and the two 1-1/4 inch spanwise lines along the leading edge of the model.
Castings of the model surface roughness (shown in figures R-1 and R-2) are available from the FAA William J. Hughes Technical Center, Flight Safety Branch. Figure R-1 shows the surface roughness that may build up during the time required for an ice detector to detect ice accretion.
The preactivation time used included 11 seconds for the first deicing cycle of a magnetostrictive type ice detector in maximum continuous icing conditions and an added 30 seconds to allow the pilot to begin recommended anti-icing procedures. You should provide the preactivation ice roughness to the FAA for our acceptance.
R-1
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).
R-2
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.
R-3
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).
R-4
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).
R-5
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.
R-6
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.)
R-7
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).
R-8
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.
R-9
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.
R-10
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°.
R-11