Propeller Fatigue Limits and Evaluation

AC 35.37-1B · FAA

Public domain · FAAAdvisory Circulars

Overview

The Propeller Fatigue Limits and Evaluation (AC 35.37-1B) is a public-domain FAA advisory circular, republished here as a free chaptered HTML edition with a linked table of contents and the official PDF.

Publisher: FAA
Document: AC 35.37-1B
Pages: 25
Chapters: 5

Key points

This advisory circular provides guidance for demonstrating compliance with § 35.37, which pertains to propeller fatigue limits and evaluation.
The document is directed at propeller manufacturers, modifiers, and foreign regulatory authorities, but it is not mandatory or regulatory.
Fatigue limits for propellers are established for components such as the hub, blades, and blade retention components, which are critical for safety.
The fatigue evaluation must consider various loading conditions, including steady and vibratory stresses experienced during flight and ground operations.
The endurance limit for composites is typically projected to be at least 500 million cycles, while for aluminum, it is at least 100 million cycles.

Frequently asked questions

Who is the intended audience for this advisory circular?

The guidance is directed to propeller manufacturers, modifiers, and foreign regulatory authorities.

Is the guidance provided in this document mandatory?

No, the material is neither mandatory nor regulatory and does not constitute a regulation.

What are fatigue limits in the context of propellers?

Fatigue limits refer to the material and structural databases used to support the fatigue evaluation of the propeller on an airplane.

What factors are considered when establishing fatigue limits?

Fatigue limits are developed with an understanding of the propeller component, material, failure mechanism, environment, and loading, including service damage.

What is the projected endurance limit for aluminum propellers?

The endurance limit for aluminum is normally projected to be at least 100 million cycles.

Appendix

3/24/11 AC 35.37-1B

Appendix

Appendix. Figures

Figure 1

LOAD AND LIFE FACTORS

Typical S-N Diagram Load Factor LOAD (Linear Scale) Life Factor CYCLES (Log Scale)

Figure 2

COMPOSITE BLADE DAMAGE DEVELOPMENT Residual Strength Load Capacity Applied Load Damage 1.0 II I III Cycles

A-1

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Appendix

3/24/11 AC 35.37-1B

Appendix

Figure 3

EXAMPLES OF BLADE TEST RIGS

RO O T ZERO ME AN S TRES S TEST

H ub F ixture B lade First fla twise Electr om echanical V ibrat ory t ip m od e S haker m otio n • Peak str ess n ear t he bl ade r oot • R ra tio equa l z ero, doe s not m at ch flight lo ad s for b lad e root • Re son an t test

TIP ZER O M EA N S TR ESS TE ST

H ub F ixture B lade S ec ond fla twise Elec tr om echanical V ibrat ory t ip m od e S haker m otio n • Peak str ess n ear t he bl ade t ip • R ra tio equa l z ero • Re son an t test

M EAN STRE SS TES T

S te ad y B e nding Lo ad S te ady C ent ri fuga l Loa d H ub Fixtu re V ibrat ory Lo ad B as e H ydra u lic Sh ake r • Peak str ess n ear t he bl ade r oot • R ra tio adjust ed fo r f lig h t cond it ion s im ulated • Forc ed res pons e te st

A-2

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Appendix

3/24/11 AC 35.37-1B

Appendix

Figure 4

FLAW GROWTH DATA

Test performed at constant amplitude

Assigned growth rate

Flaw Area (% of maximum)

0 5,000,000 10,000,000 15,000,000 20,000,000

Cycles

Figure 5

COMPOSITE FLAW GROWTH RATE

Growth Rate - % of growth rate at limit load 1 10 100 1000 Alternating Moment - % of limit load

A-3

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Appendix

3/24/11 AC 35.37-1B Appendix Figure 6

Typical Crack Growth Curve Shape

1.00E-02 Kc or final failure 1.00E-03 1.00E-04 1.00E-05 da/dN Linear portion with slope "m" 1.00E-06 1.00E-07 1.00E-08  Threshold Kth 1.00E-09 1 10 100 1000  K A-4

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Appendix

3/24/11 AC 35.37-1B Appendix Figure 7 HUB AND BLADE RETENTION TEST RIG Centrifugal Load 2 4 Stub Blade Vibratory Bending Load Steady Bending Load Propeller Shaft Adapter Hub Mounting Base Notes: Loads are applied to each blade stub Vibratory bending is simple harmonic loading and 90 degrees out of phase from blade stub to blade stub Steady bending is maintained at all times Centrifugal loading is maintained at all times A-5