This viewgraph presentation describes the icing effects, risk mitigation practices, and icing certifications for various Cessna small aircraft models. NASA's role in the development of simulation tools for icing certifications is also discussed

Hoppins, Jim

NASA Technical Reports Server

A Textron Company
Cessna
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Small Airframe Manufacturer’s 
Icing Perspective
Airframe Icing Workshop
NASA Glenn Research Center
June 9th, 2009
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https://ntrs.nasa.gov/search.jsp?R=20090030608 2019-08-29T18:57:50+00:00Z
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Agenda
 Background/Perspective
 Icing Effects & Mitigation
 Icing Certification
 New Technologies
 Summary and Recommendations
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Background/Perspective
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Product Line
 Cessna currently offer ten models with FIKI* approval
 Two models offer equipment for inadvertent icing
*FIKI = Certification for Flight Into Known Icing
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Aircraft Size/Technology
Bleed Air Thermal Systems
Pneumatic Deicers
Freezing Point
Depressants
Aircraft MTOW Certified Ceiling
Max Cruise 
Speed
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S
t
a
b
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z
e
r
Citation X 36,100 lbs 51000 ft 525 KTAS
Citation Sovereign 30,000 lbs 47000 ft 458 KTAS
Citation XLS+ 20,200 lbs 441 KTAS
Citation CJ4 16,950 lbs 435 KTAS
Citation CJ3 13,870 lbs 417 KTAS
Citation CJ2+ 12,500 lbs 418 KTAS
Citation CJ1+ 10,700 lbs 389 KTAS
Citation Mustang 8,645 lbs 340 KTAS
Grand Caravan 8,750 lbs 184 KTAS
Caravan 675 8,000 lbs 186 KTAS
400 Corvalis TT 3,600 lbs 235 KTAS
350 Corvalis 3,400 lbs 18000 ft 191 KTAS
45000 ft
41000 ft
25000 ft
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Trends
Bus
ines
s
Tur
bop
rop
s
High Speed Cruise
(KTAS)
S
e
r
v
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c
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C
e
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l
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Transport &
Regional  Jets
Regional
Turboprops
Pis
ton
s
Av
aila
ble
Air
cra
ft
Pe
rfo
rm
an
ce
Av
aila
ble
En
erg
y
for
Icin
g S
yst
em
s
FIK
I C
ert
ific
ati
on
Business Jets
FIKI = Certification for Flight Into Known Icing
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 Small leading edges have high water collection rates
 Increases local water catch rates
 Increases relative size of
ice shapes (w/ respect to chord)
 Typically unpowered flight controls
 Majority are fixed leading
edges
Characteristics of Small Aircraft
Citation Mustang
43.2 ft wingspan
737 Next Gen
117.4 ft wingspan
Citation X
63.9 ft wingspan
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Protected Areas
 Small aircraft typically protect a much 
larger percentage of the airframe
 Large proportion of available energy 
is required for ice protection
 Protected areas provide the majority
of aerodynamic effect on small 
aircraft
~90% Protected Area ~30% Protected Area~88% Protected Area
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Icing Effects/Mitigation
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Icing Effects on Small Aircraft
 Scale effects limit the ability of small 
aircraft to operate unrestricted in icing
 Performance effects can be significant
 Current ice protection technology can not 
protect against “severe” icing
 Severe conditions require
 Avoidance
 Monitoring
 Identification and exit
FAA Aeronautical Information Manual:   Severe - The rate of accumulation is such that deicing/anti-icing equipment 
fails to reduce or control the hazard. Immediate flight diversion is necessary. 
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DESIGN
• Aerodynamic Configuration
• Airframe Ice Protection Systems
• Engine Ice Protection Systems
• Air Data Sensors
• Stall Warning/Protection
• System Safety Aspects
CERTIFICATION
• Validation of aircraft performance & handling qualities
(w/ ice shapes)
• Validation of ice protection system performance
• Validation of Operating procedures and Limitations
• Validation of Abnormal & Emergency procedures
OPERATION
• Training
• Preflight planning/exit strategies
• Adherence to operating limitations and procedures
• Avoidance and exit from severe icing
Risk Mitigation
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Icing Certification
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Current Icing Certification
 Icing certification has taken an increasing role in 
mitigating icing risk
 Small aircraft standards amended in 1993
 Large aircraft standards amended in 2007
 FAA Guidance/Policy continues to evolve
 As part of certification, extensive flight testing is 
performed with artificial ice shapes
 Natural icing is typically a validation of the results 
of the artificial ice shape testing
 Artificial ice shapes provide the data used to develop 
performance information, operating procedures and 
limitations
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NASA’s Connection to Certification
 Most small aircraft manufacturers rely heavily on 
NASA developed simulation tools
 LEWICE 2D/3D are the primary ice accretion codes in 
use for certification
 Primarily used for unprotected ice shapes
 LEWICE is also used to provide collection efficiencies 
and impingement limits that are used in designing 
protection systems
 Water catch distributions are also used as input
to heat and mass transfer analysis
 NASA IRT is often used for developing protected area 
ice shapes for certification
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Conservative versus Accurate
 Conservative ice shapes are required for 
certification
 With respect to aerodynamic effect
 However, excess conservatism can have 
unintended consequences
 Too high of stall speeds adversely affects 
approach speeds/landing distances
 Excessive drag can affect performance and 
climb information
 As such, conservative and accurate ice 
shapes are an objective
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Certification Changes
 Certification ice shapes are transitioning 
from a single operating point to scenario 
based shapes
 Takeoff ice, Final takeoff ice, En route ice, 
Holding ice, Approach ice, Landing ice, 
“sandpaper” ice
 Large droplet rulemaking define scenarios 
for recognition and exit of conditions
 Requires transitions between Appendix C and 
Appendix X icing conditions
 Current available version of LEWICE does 
not address such scenarios
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Future Icing Certification
 Draft rulemaking has 
been proposed for SLD
 Options include:
 Unrestricted operations
 Unrestricted in a 
portion
 Detect and exit
 Simulation and 
compliance methods 
are limited
 Interim methods focus 
on detect & exit
FZDZ
FZRA
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Icing Tunnels * * * *
Codes ** ** **
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Icing Tunnels * * * *
Codes ** ** **
Tankers
Icing Tunnels *
Codes ** **
Tankers
Icing Tunnels *
Codes ** **
Tankers
LEGEND Updated FEB 2009
*
**
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Unprotected Areas
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It may be possible to test small scale installation effects, but large scale installations are not currently feasible
Current 2D capabilities exist with large droplet effects, but limitations exist in the use of 3D codes for simulation of Appendix X effects
The capability exists today and is suitable to be an element of a means of compliance, or is readily achievable based on current experience
The capability is possible, but has not been demonstrated, or there is limited or no validation.
The capability is unknown, or does not currently exist
Detection Methods Air Data Sensors
FZRA
MVD > 40µm
IPHWG
Phase IV 
Review
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Icing Tunnels * * * *
Codes ** ** **
Tankers
Icing Tunnels *
Codes ** **
Tankers
Icing Tunnels *
Codes ** **
Tankers
LEGEND Updated FEB 2009
*
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Unprotected Areas
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It may be possible to test small scale installation effects, but large scale installations are not currently feasible
Current 2D capabilities exist with large droplet effects, but limitations exist in the use of 3D codes for simulation of Appendix X effects
The capability exists today and is suitable to be an element of a means of compliance, or is readily achievable based on current experience
The capability is possible, but has not been demonstrated, or there is limited or no validation.
The capability is unknown, or does not currently exist
Detection Methods Air Data Sensors
FZRA
MVD > 40µm
IPHWG
Phase IV 
Review
Small Aircraft 
Emphasis Area
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Simulation Efforts
 As illustrated, much work remains to mature 
SLD simulation methods
 With individual icing tunnel tests on the 
order of $500k to $1M, no individual 
manufacturer has the resources to mature 
simulation methods
 This effort is best accomplished through 
joint efforts between NASA and industry
 Benefits flying public by improving safety
 Conserves limited resources
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Balance of Needs
 Much of the funding for icing research 
appears to have shifted towards engine/ice 
crystal research
 This area is less mature than SLD and requires 
significant research and development
 However, the maturity of the SLD simulation 
methods will likely have a larger near term 
impact on icing safety
 Continued development of both the ice 
crystal and SLD technical areas is 
recommended
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New Technologies
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New Technologies
 Continued interest in new technology ice 
protection systems that balance design 
parameters
 Energy requirements
 Aerodynamic effects
 Weight
 Reliability
 Affordability
 Severe icing detection methods
 For both Appendix C and SLD
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Summary and Recommendations
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Summary
 NASA’s simulation tools are essential for 
aircraft development and certification
 Artificial ice shapes developed using these 
tools are fundamental to the certification 
process
 Continued maturation of SLD simulation 
tools are essential for future certifications
 Particularly combined effects of SLD with ice 
protection systems
 Potential accretions aft of protected areas
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Needs/Recommendations
 Atmospheric research that supports a detect 
and avoid strategy
 Aircraft level simulation of icing effects
 Current certification standards provide a 
rigorous evaluation prior to field operations
 Provides the basis for any aircraft specific 
training that may be required
 Computational simulation of ice accretions 
during scenarios
 Changing icing and aircraft conditions, etc.
 Aligns LEWICE with current regulatory 
requirements
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Needs/Recommendations (cont.)
 Performance of ice shapes with well defined 
separation features is fairly consistent with scale
 Can be readily simulated in scale wind tunnel 
tests
 Roughness based ice shapes still present 
challenges with respect to scale
 Reynolds number issues
 Ability to effectively model roughness based ice 
shapes is critical for design and certification
 Improved predictability of full wing stall 
behavior
 Ties in with aircraft level simulation of icing 
effects
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Recommendations:  NASA’s Role
 Provide technical leadership
 Roadmaps, consortiums, industry cooperative 
programs
 Fundamental research to be used in 
simulation methods
 Continued support of development and 
certification tools (with focus on SLD)
 Proactive approach to icing safety
 Addresses the issue before the aircraft are 
placed in the field
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Questions?
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Small Airframe Manufacturer's Icing Perspective

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