ASTM F2355-05a(2008)
(Specification)Standard Specification for Design and Performance Requirements for Lighter-Than-Air Light Sport Aircraft
Standard Specification for Design and Performance Requirements for Lighter-Than-Air Light Sport Aircraft
ABSTRACT
This specification covers design and performance requirements that apply for the manufacture of lighter-than-air light sport aircraft. Performance requirements for balloons, airships and thermal airships are: proof of compliance; general performance; flight performance; climb; controllability and maneuverability; descent; landing; and stability and control. Structure requirements for airships, thermal airships, balloons and vectored thrust balloons are presented in details. The power plant installation shall be easily accessible for inspection and maintenance. The equipments for airships and free balloons are presented in details. The operating limitations and other information necessary for safe operation shall be established and documented in a flight manual, which will be made available to the pilot upon aircraft delivery.
SCOPE
1.1 This specification covers design and performance requirements that apply for the manufacture of lighter-than-air light sport aircraft.
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory requirements prior to use.
General Information
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Designation: F2355 – 05a (Reapproved 2008)
Standard Specification for
Design and Performance Requirements for Lighter-Than-Air
Light Sport Aircraft
This standard is issued under the fixed designation F2355; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 3.1.3 design useful load—load (other than structure, engine,
enclosure,andsystems)thatalighter-than-airaircraftcancarry
1.1 This specification covers design and performance re-
while achieving the design defining performance requirements.
quirements that apply for the manufacture of lighter-than-air
3.1.4 gross weight—total aircraft system weight(s) at take-
light sport aircraft.
off. The weight limits must be established so that it is: (1) the
1.2 This standard does not purport to address all of the
designed maximum weight at which compliance with each
safety concerns, if any, associated with its use. It is the
applicable structural loading condition is demonstrated, or (2)
responsibility of the user of this standard to establish appro-
the highest weight at which compliance at each applicable
priate safety and health practices and determine the applica-
flight requirement is demonstrated.
bility of regulatory requirements prior to use.
3.1.5 lighter-than-air aircraft—aircraft that can rise and
2. Referenced Documents
remain suspended by using contained gas weighing less than
the air that is displaced by the gas.
2.1 ASTM Standards:
3.1.5.1 Discussion—Airships may include dynamic lift that
F2353 Specification for Manufacturer Quality Assurance
derive as much as 30 % lift from other than buoyancy.
Program for Lighter-Than-Air Light Sport Aircraft
3.1.6 maximum takeoff weight—gross weight limit as de-
F2354 Specification for Continued Airworthiness System
fined by the manufacturer, proven through compliance with
for Lighter-Than-Air Light Sport Aircraft
this specification and placarded on the aircraft as the not-to-
F2356 Specification for Production Acceptance Testing
exceed gross weight.
System for Lighter-Than-Air Light Sport Aircraft
3.1.7 thermal airship—craft with design features to prevent
F2427 Specification for Required Product Information to be
collapse due to forward motion for which buoyancy is created
Provided with Lighter-Than-Air Light Sport Aircraft
or enhanced by heating of the gas in an otherwise unpressur-
3. Terminology
ized envelope.
3.1.8 vectored thrust balloon—craft that can move laterally,
3.1 Definitions:
but is limited to lateral speed by its lack of design features to
3.1.1 airship—engine-driven lighter-than-air aircraft that
prevent collapse due to forward motion.
can be steered, and that sustains flight through the use of either
3.1.9 weight limitations—operational weight restrictions
gas buoyancy or an airborne heater, or both.
(maximum/minimum) as defined by the manufacturer and
3.1.2 balloon—lighter-than-air aircraft that is not engine-
proven through compliance with this specification to demon-
driven, and that sustains flight through the use of either gas
strate controllability.
buoyancy or an airborne heater, or both.
4. Flight Requirements
This specification is under the jurisdiction of ASTM Committee F37 on Light 4.1 Performance Requirements for Airships and Thermal
Sport Aircraft and is the direct responsibility of Subcommittee F37.60 on Lighter
Airships, except as noted:
than Air.
4.1.1 Proof of Compliance—Each of the following require-
Current edition approved May 15, 2008. Published July 2008. Originally
ments shall be met at the maximum takeoff weight and most
approved in 2005. Last previous edition approved in 2005 as F2355 – 05a. DOI:
10.1520/F2355-05AR08.
critical center of gravity (CG) position. To the extent that CG
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
adjustment devices may be adjusted for flight, these compo-
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
nents will be evaluated in the least favorable recommended
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. position as it affects either performance or structural strength.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
F2355 – 05a (2008)
4.1.2 General Performance—Allperformancerequirements (2) A nose-up pitch from a stabilized descent with a 30°
apply in and shall be corrected to International Civil Aviation nose-down deck angle, and
Organization (ICAO) defined standard atmosphere in still air
(3) Longitudinal upset response shall be evaluated by
conditionsatsealevel.Speedsshallbegiveninindicated(IAS)
analysisortest,orboth,toshowthatitdoesnotresultinunsafe
and calibrated (CAS) airspeeds in knots.
conditions.
4.1.3 Flight Performance—For all flight operations it shall
4.1.8.4 Lateral and Directional Stability:
be shown that control sufficient to safely maneuver or land the
(1) Lateral stability will be demonstrated by maintaining
airship, or both, can be maintained.
thesurfacecontrolsinafixedposition,whichwillinitiallygive
4.1.4 Climb—The following shall be measured:
an unaccelerated level flight condition. The aircraft must not
4.1.4.1 Distance to clear a 15-m (50-ft) obstacle not to
enter into a dangerous altitude during the 2 min that the flight
exceed 213 m (700 ft) from point of lift-off. Compliance with
control surfaces are fixed. A test must be conducted at
the requirements of this section must be shown at each extreme
maximum operating weight, with minimum in-flight turbu-
of altitude and ambient temperature for which approval is
lence.
sought.
(2) Directional stability will be demonstrated by a separate
4.1.4.2 Climb rates of 1.5 m/s (300 fpm) and 0.5 m/s (100
andfulldeflectionofeachdirectionalflightcontrolsurfacesfor
fpm) with one engine inoperable for multi-engine configura-
three full turns of 360° without the aircraft entering any
tions.
dangerous flight altitude during the maneuver. A test must be
4.1.5 Controllability and Maneuverability—The aircraft
conducted at minimum flight weight, with minimum in-flight
shall be safely controllable and maneuverable during takeoff,
turbulence. The demonstrated turn rate shall not be less than
climb, level flight (cruise), approach, and landing.
6°/s (60 s for a 360° turn) in either direction.
4.1.5.1 Demonstrate a smooth transition between all flight
4.2 Performance Requirements for Balloons:
conditions shall be possible without excessive pilot skills nor
4.2.1 Proof of Compliance—Each of the following require-
exceeding pilot forces of 59.1 kg (130 lb) for the foot-operated
ments shall be met at the maximum takeoff weight.
control,9.1kg(20lb)prolongedapplication,or29.5-kg(65-lb)
4.2.2 General Performance—Allperformancerequirements
hand controls, 4.5 kg (10 lb) prolonged operation.
apply and shall be corrected to International Civil Aviation
4.1.6 Descent—The following shall be measured.
Association Organization (ICAO) defined standard atmosphere
4.1.6.1 It must be shown that in the event of the most
in still air conditions at sea level.
critical uncontrolled descent from either: (1) an engine or
4.2.3 Flight Performance—For level flight, climbs, de-
propeller failure, (2) burner failure for thermal airship, (3)
scents, and landing, it shall be shown that control sufficient to
valve leak for either hot air or captive gas airship, or (4) the
safely land the balloon can be maintained.
maximum permitted envelope failure as specified in 5.1.2.
4.2.3.1 Climb—Each balloon must be capable of climbing
NOTE 1—Procedures must be established for landing at the maximum
at least 300 ft in the first minute after takeoff with a steady rate
vertical velocity attained and procedures must be established for arresting
of climb. Compliance with the requirements of this section
the maximum descent rate within the manufacturer’s specified altitude.
must be shown at each altitude and ambient temperature for
which approval is sought.
4.1.7 Landing—It must be shown that a pilot of normal skill
4.2.3.2 Controllability—The balloon shall be controllable
canachievelandingsinkratesofnomorethan0.77m/s(2ft/s).
during takeoff, climb, level flight, approach, and landing.
4.1.8 Stability and Control:
4.2.3.3 Descent—The following shall be measured. It must
4.1.8.1 Vertical Stability and Control—Stability and control
be shown that in the event of the most critical uncontrolled
of the airship shall be determined at maximum gross weight,
descent from either: (1) burner failure for hot air balloon, (2)
with minimum in-flight turbulence/wind for:
valve leak for either hot air or captive gas, and (3) the
(1) Maximum duration of envelope valve operation (if
maximum permitted envelope failure as specified in 5.2.2.
equipped), during which the airship must not enter into a
Procedures must be established for landing at the maximum
dangerous descent.
vertical velocity attained and procedures must be established
(2) Minimum burner fuel pressures (if equipped), which
for arresting the maximum descent rate within the manufac-
will arrest the maximum descent rate as determined in 4.1.6
turer’s specified altitude.
and climb as determined in 4.1.4.
4.2.3.4 Landing—It must be shown that the pilot can
4.1.8.2 Longitudinal Stability—Longitudinal stability of the
achieve a landing sink rate of not more than 1 m/s.
aircraft will be demonstrated by performing 2 min of flight
4.2.4 Stability and Control—Stability and control of the
without control input for three conditions. In each case, the
balloon shall be determined at maximum gross weight, with
aircraft must not enter into dangerous or unusual altitudes. A
minimum in flight turbulence/wind for:
test must be conducted at maximum gross weight, with a
minimum of in-flight turbulence. The three conditions are 4.2.4.1 Maximum duration of envelope valve operation,
ascent, descent, and level flight.
during which the balloon must not enter into a dangerous
descent.
4.1.8.3 Longitudinal Control—With all engines operating at
maximum power, the airship must be capable of:
4.2.4.2 Minimum burner fuel pressures that will arrest the
(1) A nose-down pitch from a stabilized climb with a 30° maximum descent rate as determined in 4.2.3.3 and climb as
nose-up deck angle, determined in section 4.2.3.1.
F2355 – 05a (2008)
5. Structure Requirements 5.1.7.3 Design Airspeed for Maximum Gust Intensity,
V(B)—V(B) shall not be less than 35 knots or 0.65 V(H),
5.1 Structure for Airships and Thermal Airships (except as
whichever is least.
noted):
5.1.7.4 Maneuver loads considering the maximum forces
5.1.1 Loads—Unless otherwise specified, all requirements
that can be generated by the envelope and surfaces at V(H) and
are specified in terms of limit load.
maximum control deflections, unless placarded to limit deflec-
5.1.1.1 Ultimate loads are limit loads multiplied by the
tion at specific conditions.
factor of safety defined below. Loads shall be redistributed if
5.1.7.5 Gust loads of a discrete gust of 7.6 m/s (25 fps) at
the deformations affect them significantly.
V(H) and 10.6 m/s (35 fps) at V(B).
5.1.2 Factors of Safety—The factor of safety is 1.5, except
as shown in the following: 5.1.8 Control Surface Loads—Control surface loads on the
5.1.2.1 3.0 on castings, airship shall be evaluated at loads defined in flight tests of the
envelope by the envelope manufacturer.
5.1.2.2 1.8 on fittings,
5.1.2.3 6.67 on control surface hinges,
5.1.9 Ground Mooring Conditions (when equipped)—An
5.1.2.4 3.3 on push-pull control systems, airship that is normally moored to a mooring mast when not in
5.1.2.5 2.0 on cable control systems, and flight, such as overnight. The mooring mast system shall be
adequate to allow the airship to swing around the mast 360° as
5.1.2.6 5.0 on envelope structures (fibrous or non-metallic
parts) and rigging. wind direction changes. The strength of the mast shall be
sufficient to safely moor the airship in high or gust wind
5.1.2.7 In applying factors of safety, the effect of tempera-
tureandotheroperatingcharacteristics,orboth,thatmayaffect conditions as specified by the manufacturer. Accommodation
shall be made to allow the car to accept these sideward
strength of the balloon must be accounted for.
movements without damage.
5.1.2.8 For design purposes, an occupant weight of at least
170 lb must be assumed. 5.1.10 Control System and Supporting Structure—The con-
5.1.3 Strength and Deformation: trol system structure shall be designed to withstand maximum
forces, and in the case of dual controls, the relevant system
5.1.3.1 The structure must be able to support limit loads
without permanent deformation of the structure. shall be designed for the pilots operating in opposition, if
greater than the control system forces.
5.1.3.2 The structure must be shown by analysis, test, or
analysissupportedbytesttobeabletowithstandultimateloads
5.1.11 Ground Load Conditions—Design features shall
without failure. limit the landing sink rate to less than or equal to 1 m/s (3.3
5.1.3.3 The structure shall be able to withstand ultimate ft/s). Testing by drop test will use a drop height to achieve a 1
loads for 3 s without failure when proof is by static test. When m/s (3.3 ft/s) drop rate. This will be a dead drop test of the car
dynamic tests are used to demonstrate strength, the 3-s require- without envelope lift at maximum takeoff weight.
ment does not apply. Local failures or structural instabilities
5.1.12 Emergency Landing Conditions—Design structure to
between limit load and ultimate load are acceptable if the
protect each occupant from serious injury when the aircraft
structure can sustain the required ultimate load for 3 s.
experiencesthreeindependentultimateloadconditions:1.5-g’s
5.1.4 Proof of Structure—Each critical load requirement
upward, 6-g’s forward, and 3-g’s sideward. Test articles that
shall be investigated either by conservative analysis or tests, or
hold this load for more than 3 s are considered to have passed.
a combination of both.
5.1.13 Emergency deflation systems shall be included to
5.1.5 Proof of Strength—Envelope material, attachments,
handle ground handling failures.
and car frame shall all be demonstrated by test to meet the load
5.1.14 Envelope and Ballonet Pressures (if equipped)—
factor requirement with the required factor of safety. This
Operating pressure limitations for the envelope and ballonets,
evaluation shall include suitable tear resistance testing for the
as limited by flight, structural, and functional, must be estab-
envelope.
lish
...
This document is not anASTM standard and is intended only to provide the user of anASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation:F2355–05 Designation: F 2355 – 05a (Reapproved 2008)
Standard Specification for
Design and Performance Requirements for Lighter-Than-Air
Light Sport Aircraft
This standard is issued under the fixed designation F 2355; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This specification covers design and performance requirements that apply for the manufacture of lighter-than-air light sport
aircraft.
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
requirements prior to use.
2. Referenced Documents
2.1 ASTM Standards:
F 2353 Specification for Manufacturer Quality Assurance Program for Lighter-Than-Air Light Sport Aircraft
F 2354 Specification for Continued Airworthiness System for Lighter-Than-Air Light Sport Aircraft
F 2356 Specification for Production Acceptance Testing System for Lighter-Than-Air Light Sport Aircraft
F 2427 Specification for Required Product Information to be Provided with Lighter-tThan-Air Light Sport Aircraft
3. Terminology
3.1 Definitions:
3.1.1 airship—engine-driven lighter-than-air aircraft that can be steered, and that sustains flight through the use of either gas
buoyancy or an airborne heater, or both.
3.1.2 balloon—lighter-than-air aircraft that is not engine-driven, and that sustains flight through the use of either gas buoyancy
or an airborne heater, or both.
3.1.3 design useful load—load (other than structure, engine, enclosure, and systems) that a lighter-than-air aircraft can carry
while achieving the design defining performance requirements.
3.1.4 gross weight—totalaircraftsystemweight(s)attakeoff.Theweightlimitsmustbeestablishedsothatitis:(1)thedesigned
maximum weight at which compliance with each applicable structural loading condition is demonstrated, or (2) the highest weight
at which compliance at each applicable flight requirement is demonstrated.
3.1.5 lighter-than-air aircraft—aircraft that can rise and remain suspended by using contained gas weighing less than the air
that is displaced by the gas and includes gas.
3.1.5.1 Discussion—Airships may include dynamic lift aircraft that derive as much as 20% of their 30 % lift from something
other than buoyancy.
3.1.6 maximum takeoff weight—gross weight limit as defined by the manufacturer, proven through compliance with this
specification and placarded on the aircraft as the not-to-exceed gross weight.
3.1.7 thermal airship—craft with design features to prevent collapse due to forward motion for which buoyancy is created or
enhanced by heating of the gas in an otherwise unpressurized envelope.
3.1.8 vectored thrust balloon—craft that can move laterally, but is limited to lateral speed by its lack of design features to
prevent collapse due to forward motion.
3.1.9 weight limitations—operational weight restrictions (maximum/minimum) as defined by the manufacturer and proven
through compliance with this specification to demonstrate controllability.
This specification is under the jurisdiction of ASTM Committee F37 on Light Sport Aircraft and is the direct responsibility of Subcommittee F37.60 on Lighter Than
Air.
Current edition approved April 1, 2005. Published April 2005.
This specification is under the jurisdiction ofASTM Committee F37 on Light SportAircraft and is the direct responsibility of Subcommittee F37.60 on Lighter thanAir.
Current edition approved May 15, 2008. Published July 2008. Originally approved in 2005. Last previous edition approved in 2005 as F 2355 – 05a.
For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
F 2355 – 05a (2008)
4. Flight Requirements
4.1 Performance Requirements for Airships and Thermal Airships, except as noted:
4.1.1 Proof of Compliance—Each of the following requirements shall be met at the maximum takeoff weight and most critical
center of gravity (CG) position. To the extent that CG adjustment devices may be adjusted for flight, these components will be
evaluated in the least favorable recommended position as it affects either performance or structural strength.
4.1.2 General Performance—All performance requirements apply in and shall be corrected to International Civil Aviation
Organization (ICAO) defined standard atmosphere in still air conditions at sea level. Speeds shall be given in indicated (IAS) and
calibrated (CAS) airspeeds in knots.
4.1.3 Flight Performance—For all flight operations it shall be shown that control sufficient to safely maneuver or land the
airship, or both, can be maintained.
4.1.4 Climb—The following shall be measured:
4.1.4.1 Distance to clear a 15-m (50-ft) obstacle not to exceed 213 m (700 ft) from point of lift-off. Compliance with the
requirements of this section must be shown at each extreme of altitude and ambient temperature for which approval is sought.
4.1.4.2 Climb rates of 1.5 m/s (300 fpm) and 0.5 m/s (100 fpm) with one engine inoperable for multi-engine configurations.
4.1.5 Controllability and Maneuverability—The aircraft shall be safely controllable and maneuverable during takeoff, climb,
level flight (cruise), approach, and landing.
4.1.5.1 Demonstrate a smooth transition between all flight conditions shall be possible without excessive pilot skills nor
exceeding pilot forces of 59.1 kg (130 lb) for the foot-operated control, 9.1 kg (20 lb) prolonged application, or 29.5-kg (65-lb)
hand controls, 4.5 kg (10 lb) prolonged operation.
4.1.6 Descent—The following shall be measured.
4.1.6.1 It must be shown that in the event of the most critical uncontrolled descent from either: (1) an engine or propeller
failure, (2) burner failure for thermal airship, (3) valve leak for either hot air or captive gas airship, or (4) the maximum permitted
envelope failure as specified in 5.1.2.
NOTE 1—Procedures must be established for landing at the maximum vertical velocity attained and procedures must be established for arresting the
maximum descent rate within the manufacturer’s specified altitude.
4.1.7 Landing—It must be shown that a pilot of normal skill can achieve landing sink rates of no more than 0.77 m/s (2 ft/s).
4.1.8 Stability and Control:
4.1.8.1 Vertical Stability and Control— Stability and control of the airship shall be determined at maximum gross weight, with
minimum in-flight turbulence/wind for:
(1) Maximum duration of envelope valve operation (if equipped), during which the airship must not enter into a dangerous
descent.
(2) Minimum burner fuel pressures (if equipped), which will arrest the maximum descent rate as determined in 4.1.6 and climb
as determined in 4.1.4.
4.1.8.2 Longitudinal Stability—Longitudinal stability of the aircraft will be demonstrated by performing 2 min of flight without
control input for three conditions. In each case, the aircraft must not enter into dangerous or unusual altitudes. A test must be
conducted at maximum gross weight, with a minimum of in-flight turbulence. The three conditions are ascent, descent, and level
flight.
4.1.8.3 Longitudinal Control—With all engines operating at maximum power, the airship must be capable of:
(1) A nose-down pitch from a stabilized climb with a 30° nose-up deck angle,
(2) A nose-up pitch from a stabilized descent with a 30° nose-down deck angle, and
(3) Longitudinal upset response shall be evaluated by analysis or test, or both, to show that it does not result in unsafe
conditions.
4.1.8.4 Lateral and Directional Stability :
(1) Lateral stability will be demonstrated by maintaining the surface controls in a fixed position, which will initially give an
unaccelerated level flight condition. The aircraft must not enter into a dangerous altitude during the 2 min that the flight control
surfaces are fixed. A test must be conducted at maximum operating weight, with minimum in-flight turbulence.
(2) Directional stability will be demonstrated by a separate and full deflection of each directional flight control surfaces for
three full turns of 360° without the aircraft entering any dangerous flight altitude during the maneuver. A test must be conducted
at minimum flight weight, with minimum in-flight turbulence. The demonstrated turn rate shall not be less than 6°/s (60 s for a
360° turn) in either direction.
4.2 Performance Requirements for Balloons:
4.2.1 Proof of Compliance—Each of the following requirements shall be met at the maximum takeoff weight.
4.2.2 General Performance—All performance requirements apply and shall be corrected to International Civil Aviation
Association Organization (ICAO) defined standard atmosphere in still air conditions at sea level.
4.2.3 Flight Performance—For level flight, climbs, descents, and landing, it shall be shown that control sufficient to safely land
the balloon can be maintained.
4.2.3.1 Climb—Each balloon must be capable of climbing at least 300 ft in the first minute after takeoff with a steady rate of
F 2355 – 05a (2008)
climb. Compliance with the requirements of this section must be shown at each altitude and ambient temperature for which
approval is sought.
4.2.3.2 Controllability—The balloon shall be controllable during takeoff, climb, level flight, approach, and landing.
4.2.3.3 Descent—The following shall be measured. It must be shown that in the event of the most critical uncontrolled descent
from either: (1) burner failure for hot air balloon, (2 ) valve leak for either hot air or captive gas, and (3) the maximum permitted
envelope failure as specified in 5.2.2. Procedures must be established for landing at the maximum vertical velocity attained and
procedures must be established for arresting the maximum descent rate within the manufacturer’s specified altitude.
4.2.3.4 Landing—It must be shown that the pilot can achieve a landing sink rate of not more than 1 m/s.
4.2.4 Stability and Control—Stability and control of the balloon shall be determined at maximum gross weight, with minimum
in flight turbulence/wind for:
4.2.4.1 Maximum duration of envelope valve operation, during which the balloon must not enter into a dangerous descent.
4.2.4.2 Minimum burner fuel pressures that will arrest the maximum descent rate as determined in 4.2.3.3 and climb as
determined in section 4.2.3.1.
5. Structure Requirements
5.1 Structure for Airships and Thermal Airships (except as noted):
5.1.1 Loads—Unless otherwise specified, all requirements are specified in terms of limit load.
5.1.1.1 Ultimate loads are limit loads multiplied by the factor of safety defined below. Loads shall be redistributed if the
deformations affect them significantly.
5.1.2 Factors of Safety—The factor of safety is 1.5, except as shown in the following:
5.1.2.1 3.0 on castings,
5.1.2.2 1.8 on fittings,
5.1.2.3 6.67 on control surface hinges,
5.1.2.4 3.3 on push-pull control systems,
5.1.2.5 2.0 on cable control systems, and
5.1.2.6 5.0 on envelope structures (fibrous or non-metallic parts) and rigging.
5.1.2.7 In applying factors of safety, the effect of temperature and other operating characteristics, or both, that may affect
strength of the balloon must be accounted for.
5.1.2.8 For design purposes, an occupant weight of at least 170 lb must be assumed.
5.1.3 Strength and Deformation:
5.1.3.1 The structure must be able to support limit loads without permanent deformation of the structure.
5.1.3.2 Thestructuremustbeshownbyanalysis,test,oranalysissupportedbytesttobeabletowithstandultimateloadswithout
failure.
5.1.3.3 The structure shall be able to withstand ultimate loads for 3 s without failure when proof is by static test.When dynamic
tests are used to demonstrate strength, the 3-s requirement does not apply. Local failures or structural instabilities between limit
load and ultimate load are acceptable if the structure can sustain the required ultimate load for 3 s.
5.1.4 Proof of Structure—Each critical load requirement shall be investigated either by conservative analysis or tests, or a
combination of both.
5.1.5 Proof of Strength—Envelope material, attachments, and car frame shall all be demonstrated by test to meet the load factor
requirement with the required factor of safety. This evaluation shall include suitable tear resistance testing for the envelope.
5.1.6 Load Factor:
5.1.6.1 Positive— n = 1.5 (comprised of a maneuvering load multiplied by a gust load factor).
5.1.6.2 Negative— n=0.
5.1.6.3 Additional load considerations shall be evaluated for selected design airspeeds and resultant dynamic pressures.
5.1.7 Design Airspeeds—The selected design airspeeds are equivalent airspeeds (EAS) except as provided in specific
requirements.
5.1.7.1 Design Stall Speed, V(SI)—shall be calculated based on area, lift coefficient estimates, and maximum negative boyance.
5.1.7.2 Design Maximum Level Flight Airspeed, V(H)—V(H) is the maximum speed obtainable in level flight with all engines
operating at maximum continuous power and the airship loaded to achieve minimum drag.
5.1.7.3 Design Airspeed for Maximum Gust Intensity, V(B) —V(B) shall not be less than 35 knots or 0.65 V(H) , whichever is
least.
5.1.7.4 Maneuver loads considering the maximum forces that can be generated by the envelope and surfaces at V(H) and
maximum control deflections, unless placarded to limit deflection at specific conditions.
5.1.7.5 Gust loads of a discrete gust of 7.6 m/s (25 fps) at V(H) and 10.6 m/s (35 fps) at V(B).
5.1.8 Control Surface Loads—Control surface loads on the airship shall be evaluated at loads defined in flight tests of the
envelope by the envelope manufacturer.
5.1.9 Ground Mooring Conditions (when equipped)—An airship that is normally moored to a mooring mast when not in flight,
suchasovernight.Themooringmastsystemshallbeadequatetoallowtheairshiptoswingaroundthemast360°aswinddirection
changes. The strength of the mast shall be sufficient to safely moor the airship in high or gust wind conditions as spe
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