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Rutan Derivative Canard Forum Slide #1July 19, 2007
A Method of Desensitizing Wooden Propeller Hub
Mounting Bolt Security To Environmental Effects and
Sub-Optimal Maintenance TechniquesOr
How To Keep Your Wood Prop
On Your Plane With Less WorkMarc J. Zeitlin
July 26th, 2007
2:30 PM 3:45 PM
Forum Tent 06 Sportys Pavilion
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July 19, 2007 Rutan Derivative Canard Forum Slide #2
What Will I Talk About? Characteristics of Wood Props
Need for Maintenance
Proposed Solution Representation / Theory
Specific Solution
Prior Art / Proposals
Pre-Flight Testing Flight Testing
Current Configuration
Increased Robustness / Decreased Sensitivity Cost / Weight Penalty
Questions / Answers / Availability
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July 19, 2007 Rutan Derivative Canard Forum Slide #3
Characteristics of Wood
Props
Relatively soft Low crush strength
Low stiffness
Susceptible to
moisture / humidity
/ shrinkage /
expansion
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July 19, 2007 Rutan Derivative Canard Forum Slide #4
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 hours
Technique (not usually specified):
Remove safety wire
Loosen bolt first to break static torque
Ensure movement measure torque while turning
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July 19, 2007 Rutan Derivative Canard Forum Slide #5
Proposed Solution
Representation / Theory - 1 Prop Bolts very stiff Prop Hub size determines force
Prop Hub
(Somewhat Squishy)Very Stiff
Spring
(Prop Bolt)
Hub shrinks,compression force
falls, bolts cannot
compensate
Before Compression After Compression After Shrinkage
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July 19, 2007 Rutan Derivative Canard Forum Slide #6
Proposed Solution
Representation / Theory - 2 Same motion of hub
Small change in spring force SOFTER SPRING DETERMINES FORCE CHANGE
Soft Spring
Before Compression After Compression After Shrinkage
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July 19, 2007 Rutan Derivative Canard Forum Slide #7
Specific Solution Belleville Washers
Flexible arrangements use serial stack
Force/deflection
curves adjustable
can obtain anyforce/deflection
required
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July 19, 2007 Rutan Derivative Canard Forum Slide #8
Prior Art / Proposals Jabiru - recently switched to belleville stacks on certain
engine 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-worker
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July 19, 2007 Rutan Derivative Canard Forum Slide #9
COZY MKIV Installation
Took proposals, didcalculations, picked
hardware
Determined 6-stack would
provide more thanadequate expansion /
shrinkage capability
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July 19, 2007 Rutan Derivative Canard Forum Slide #10
Pre-Flight Testing - 1 Find
Hardware
Two bolts
have stacks of
6 bellevilles
capturedbetween two
wide area
washers 4
standard bolts
Can see good
linearity
Bolt Torque / Washer Compression vs. Turns
0
5
10
15
20
25
30
35
0 0.5 1 1.5 2 2.5 3 3.5 4
Bolt Turns
BoltTorqu
e(ft-lb)
0.00
0.05
0.10
0.15
0.20
0.25
0.30
WasherCompression-(in)
Torque - L
Torque - R
Compression - L
Compression - R
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July 19, 2007 Rutan Derivative Canard Forum Slide #11
Pre-Flight Testing - 2 Remove
turns from
the equation just show
washer
compressionvs. applied
torque
Still very
linear
Washer Compression vs. Bolt Torque
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0.20
0 5 10 15 20 25 30 35
Bolt Torque (ft-lb)
TotalWasherCom
pression(in)
Compression - L
Compression - R
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July 19, 2007 Rutan Derivative Canard Forum Slide #12
Pre-Flight Testing - 3 Switch from six
std. bolts to six
bolts all withBellevillewasher 6-stacks
Change in slopeas slop is
taken out ofsystem (bothtypes of boltingsystems) thenmore torque for
samecompressionneeded
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+Flangeth
ickness(in)
Compression - Std
Compression - Belleville
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July 19, 2007 Rutan Derivative Canard Forum Slide #13
Pre-Flight Testing - 4 Six bolts
with
bellevillewasher 6-
stacks
Very linear
torque and
compression
with boltturns
Washer / Hub Compression / Bolt Torque vs. Bolt Turns
0
5
10
15
20
25
30
35
0 1 2 3 4 5
Bolt Turns
Torque(ft-lb)
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.035
0.040
Compression(in)
Torque
Hub Compression
Individual Washer
Compression
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July 19, 2007 Rutan Derivative Canard Forum Slide #14
Pre-Flight Testing - 5 Same slight
change in
slope as slopis taken out
Stillpredictableand relatively
linear withBolt Torque
Might beeasier tomeasure turns
rather thantorque,however
Hub and Washer Compression vs. Bolt Torque
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.035
0.040
0 5 10 15 20 25 30
Bolt Torque (ft-lb)
Compression(in)
Hub Compre ssion
Individual Washer Compression
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July 19, 2007 Rutan Derivative Canard Forum Slide #15
Flight Testing - 1 First few flights two bolts with bellevilles four standard bolts
Calcs show prop will stay even if two bolts dont
See washers NOT completely compressed allows for shrinkage AND expansion of
Prop Hub
No difference from standard installation perceived - ~3 flight hours accumulated in thisconfiguration at various speeds, RPM, flight attitudes near 1 million cycles for fatigue
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July 19, 2007 Rutan Derivative Canard Forum Slide #16
Flight Testing - 2 Next few flights four sets of belleville washers, two standard bolts
Have confidence based on previous flight hours
Run another ~3 hours build ~2 million cycles on first set, ~1 million onsecond set
Again, fly various RPMs, flight attitudes, speeds, G-loading
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July 19, 2007 Rutan Derivative Canard Forum Slide #17
Flight Testing - 3 Next set of flights all six bolts with belleville washer stacks
Built more confidence based on previous flights
Run another ~3 hours build ~3 million cycles on first set, ~2 million onsecond set, ~1 million on third set
Again, fly various RPMs, flight attitudes, speeds, G-loading
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July 19, 2007 Rutan Derivative Canard Forum Slide #18
Flight Testing - 4 Remove two bellevilles from each stack now have 4/bolt
Run another ~40 hours build ~13 -15 million cycles on all belleville
washers Again, fly various RPMs, flight attitudes, speeds, G-loading
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July 19, 2007 Rutan Derivative Canard Forum Slide #19
Current Configuration
Using 7 bolts couldreduce to 6.5 andremove hardened washerto save ~0.1 lb.
Added AN3 bolts toFRONT of crush plate
Will be able to addspinner backplate /mounting structureWITHOUT having toremove/touch prop bolts
Dont have to havebackplate BETWEENprop and prop extension
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July 19, 2007 Rutan Derivative Canard Forum Slide #20
Increased Robustness /
Decreased Sensitivity Maintenance
simplification
(measurespacing, # turns)
Maintenance
frequency
reduction
(Jabiru from
25 hrs. to 1/yr.
example)
Safety enhanced
Hub Compression Force Loss vs. Hub Shrinkage
0%
10%
20%
30%
40%
50%
60%
0 0.002 0.004 0.006 0.008 0.01 0.012 0.014
Hub Shrinkage (in)
HubCompressionForceLoss(%)
Standard
Bellevilles (6-stack)
Bellevilles (4-stack)
Bellevilles (2-stack)
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July 19, 2007 Rutan Derivative Canard Forum Slide #21
Cost / Weight Penalty
~3.5 lb for Bolt SAE-2 Flange with 7 CrushPlate and 6 washers/stack (~2.5 lb in current
configuration 4 washers/stack)
Approximately $120 gets replacement bolts,
bellevilles, flat washers
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July 19, 2007 Rutan Derivative Canard Forum Slide #22
Questions / Answers /
Availability
My Email: [email protected]
Website: http://www.cozybuilders.org/
Currently ONLY configured for bolts 3/8
bolt configurations may be tested in the future.
I can supply Bellevilles at cost+; Bolts availablefrom Saber MFG, washers from ACS, Wicks, etc.