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A Method of Desensitizing Wooden Propeller HubMounting Bolt Security To Environmental Effects andSub-Optimal Maintenance TechniquesOrHow To Keep Your Wood PropOn Your Plane With Less WorkMarc J. ZeitlinJuly 31, 20082:30 PM – 3:45 PMForum Tent 06 – Utah Valley University PavilionSeptember 8, 2008Rutan Derivative Canard ForumSlide #1

What Will I Talk About? Characteristics of Wood PropsNeed for MaintenanceProposed Solution – Representation / TheorySpecific SolutionPrior Art / ProposalsPre-Flight TestingFlight TestingCurrent ConfigurationGyroscopic IssuesIncreased Robustness / Decreased SensitivityCost / Weight PenaltyAvailabilityQuestions / AnswersSeptember 8, 2008Rutan Derivative Canard ForumSlide #2

Characteristics of WoodProps Relatively softLow crush strengthLow stiffnessSusceptible tomoisture / humidity/ shrinkage /expansionSeptember 8, 2008Rutan Derivative Canard ForumSlide #3

Need For MaintenanceExamples of Wooden Propellers: Sensenich–50 hrs or annually Hertzler–every 25 hours, anytime goingbetween different climates Jabiru–every 25 hours Miles Gemini–every 10 hoursTechnique (not usually specified): Remove safety wire Loosen bolt first to break static torque Ensure movement – measure torque while turningSeptember 8, 2008Rutan Derivative Canard ForumSlide #4

Proposed Solution –Representation / Theory - 1 Prop Bolts very stiff – Prop Hub size determines forceProp Hub(Somewhat Squishy)Before CompressionSeptember 8, 2008Very StiffSpring(Prop Bolt)After CompressionRutan Derivative Canard ForumHub shrinks,compression forcefalls, bolts cannotcompensateAfter ShrinkageSlide #5

Proposed Solution –Representation / Theory - 2 Same motion of hubSmall change in spring force – SOFTER SPRING DETERMINES FORCE CHANGESoft SpringBefore CompressionSeptember 8, 2008After CompressionRutan Derivative Canard ForumAfter ShrinkageSlide #6

Specific Solution Belleville Washers Flexible arrangements– use serial stack Force/deflectioncurves adjustable –can obtain anyforce/deflectionrequiredSeptember 8, 2008Rutan Derivative Canard ForumSlide #7

Prior Art / Proposals Jabiru - recently switched to belleville stacks on certainengine prop combinations Miles M65 Gemini w/Cirrus Minor II Engines, from 1947– used belleville stacks Paul Lipps / Vance Jaqua – belleville stacks installed onLancair 235 w/O-320 Burt Rutan proposal 25 years ago – never tested Independently proposed to me by 3 sources – c-a mailinglist; web forum; co-workerSeptember 8, 2008Rutan Derivative Canard ForumSlide #8

COZY MKIV Installation Took proposals, didcalculations, pickedhardware Determined 6-stack wouldprovide more thanadequate expansion /shrinkage capabilitySeptember 8, 2008Rutan Derivative Canard ForumSlide #9

Pre-Flight Testing - 1 Two boltshave stacks of6 bellevillescapturedbetween twowide areawashers – 4standard boltsCan see goodlinearitySeptember 8, 2008Bolt Torque / Washer Compression vs. Turns0.303530Torque - L0.25Torque - RCompression - L25Compression - R0.20200.15150.1010Washer Compression - (in) FindHardwareBolt Torque (ft-lb) 0.05500.0000.511.522.533.54Bolt TurnsRutan Derivative Canard ForumSlide #10

Pre-Flight Testing - 2Washer Compression vs. Bolt Torque0.200.18Compression - LTotal Washer Compression (in) Remove“turns” fromthe equation– just showwashercompressionvs. appliedtorque Still verylinearCompression - 5Bolt Torque (ft-lb)September 8, 2008Rutan Derivative Canard ForumSlide #11

Pre-Flight Testing - 3 Switch from sixstd. bolts to sixbolts – all withBellevillewasher 6-stacksChange in slopeas “slop” istaken out ofsystem (bothtypes of boltingsystems) – thenmore torque forsamecompressionneededSeptember 8, 2008Hub Compression vs. Bolt Torque0.030Compression - Std0.025Hub Flange thickness (in) Compression - t Torque (ft-lb)Rutan Derivative Canard ForumSlide #12

Pre-Flight Testing - 4 Six boltswithbellevillewasher 6stacksSeptember 8, 2008350.040TorqueHub Compression0.035Individual sion (in)30Torque (ft-lb) Very lineartorque andcompressionwith boltturnsWasher / Hub Compression / Bolt Torque vs. Bolt Turns100.01050.00500.000012345Bolt TurnsRutan Derivative Canard ForumSlide #13

Pre-Flight Testing - 5 Same slightchange inslope as “slop”is taken outStillpredictableand relativelylinear withBolt TorqueMight beeasier tomeasure turnsrather thantorque,howeverSeptember 8, 2008Hub and Washer Compression vs. Bolt Torque0.040Hub Compression0.035Individual Washer Compression0.030Compression (in) 0.0250.0200.0150.0100.0050.000051015202530Bolt Torque (ft-lb)Rutan Derivative Canard ForumSlide #14

Flight Testing - 1 First few flights – two bolts with bellevilles – four standard boltsCalcs show prop will stay even if two bolts don’tSee washers NOT completely compressed – allows for shrinkage AND expansion ofProp Hub No difference from standard installation perceived - 3 flight hours accumulated in thisconfiguration at various speeds, RPM, flight attitudes – near 1 million cycles for fatigueSeptember 8, 2008Rutan Derivative Canard ForumSlide #15

Flight Testing - 2 Next few flights – four sets of belleville washers, two standard boltsHave confidence based on previous flight hoursRun another 3 hours – build 2 million cycles on first set, 1 million onsecond setAgain, fly various RPMs, flight attitudes, speeds, G-loadingSeptember 8, 2008Rutan Derivative Canard ForumSlide #16

Flight Testing - 3 Next set of flights – all six bolts with belleville washer stacksBuilt more confidence based on previous flightsRun another 3 hours – build 3 million cycles on first set, 2 million onsecond set, 1 million on third setAgain, fly various RPMs, flight attitudes, speeds, G-loadingSeptember 8, 2008Rutan Derivative Canard ForumSlide #17

Flight Testing - 4 Remove two bellevilles from each stack – now have 4/boltRun another 40 hours – build 13 -15 million cycles on all bellevillewashersAgain, fly various RPMs, flight attitudes, speeds, G-loadingSeptember 8, 2008Rutan Derivative Canard ForumSlide #18

Current Configuration Using 7” bolts – couldreduce to 6.5” andremove hardened washerto save 0.1 lb. Added AN3 bolts toFRONT of crush plateWill be able to addspinner backplate /mounting structureWITHOUT having toremove/touch prop boltsDon’t have to havebackplate BETWEENprop and prop extension September 8, 2008Rutan Derivative Canard ForumSlide #19

Gyroscopic Effects andBelleville WashersAnalysis by David DannemillerAssumptions: Weight of Prop: 16 lb. Prop Hub Dia.:7 inch Prop Diameter:64 inch MaximumPitch/Yaw Rate: 90deg/sec Prop Bolt Tension: 3000 lb.Safety Factor:September 8, 20089Rutan Derivative Canard ForumSlide #20

Increased Robustness /Decreased Sensitivity Maintenancesimplification(measurespacing, # turns)Maintenancefrequencyreduction(Jabiru – from25 hrs. to 1/yr.example)Hub Compression Force Loss vs. Hub Shrinkage60%StandardBellevilles (6-stack)50%Hub Compression Force Loss (%) Bellevilles (4-stack)Bellevilles (2-stack)40%30%20%10%0% Safety enhanced00.0020.0040.0060.0080.010.0120.014Hub Shrinkage (in)September 8, 2008Rutan Derivative Canard ForumSlide #21

Cost / Weight Penalty 2.5 lb for ½” Bolt SAE-2 Flange with 7” CrushPlate and 4 washers/stack (current configuration) 1.75 lb. for 3/8” Bolt SAE-1 Flange with 6”Crush Plate and 4 washer/stack(currently in testing) 120 gets replacement bolts, bellevilles, flatwashersSeptember 8, 2008Rutan Derivative Canard ForumSlide #22

Availability Washers, etc. Currently configured for 1/2” bolts and 3/8” bolts others may be tested in the future. I can supply Bellevilles at cost ; Prop Boltsavailable from Saber MFG, washers from ACS,Wicks, etc.September 8, 2008Rutan Derivative Canard ForumSlide #23

Questions / Answers My Email:marc zeitlin@alum.mit.edu Website:http://www.cozybuilders.org/September 8, 2008Rutan Derivative Canard ForumSlide #24

Belleville washer 6-stacks Change in slope as "slop" is taken out of system (both types of bolting systems) - then more torque for same compression needed Hub Compression vs. Bolt Torque 0.000 0.005 0.010 0.015 0.020 0.025 0.030 0 5 10 15 20 25 30 Bolt Torque (ft-lb) Hub Flange thickness (in) Compression - Std Compression - Belleville