Compression Algorithms CSCI 2720 Spring 2005 Eileen Kraemer.
Or How To Keep Your Wood Prop On Your Plane With Less Work · • Small change in spring force –...
Transcript of Or How To Keep Your Wood Prop On Your Plane With Less Work · • Small change in spring force –...
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Rutan Derivative Canard Forum Slide #1September 8, 2008
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 Work
Marc J. ZeitlinJuly 31, 2008
2:30 PM – 3:45 PMForum Tent 06 – Utah Valley University Pavilion
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September 8, 2008 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• Gyroscopic Issues• Increased Robustness / Decreased Sensitivity• Cost / Weight Penalty• Availability• Questions / Answers
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September 8, 2008 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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September 8, 2008 Rutan Derivative Canard Forum Slide #4
Need For MaintenanceExamples of Wooden Propellers:• Sensenich – 50 hrs or annually• Hertzler – every 25 hours, anytime going
between 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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September 8, 2008 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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September 8, 2008 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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September 8, 2008 Rutan Derivative Canard Forum Slide #7
Specific Solution
• Belleville Washers• Flexible arrangements
– use serial stack• Force/deflection
curves adjustable –can obtain any force/deflection required
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September 8, 2008 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 on Lancair 235 w/O-320
• Burt Rutan proposal 25 years ago – never tested
• Independently proposed to me by 3 sources – c-a mailing list; web forum; co-worker
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September 8, 2008 Rutan Derivative Canard Forum Slide #9
COZY MKIV Installation
• Took proposals, did calculations, picked hardware
• Determined 6-stack would provide more than adequate expansion / shrinkage capability
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September 8, 2008 Rutan Derivative Canard Forum Slide #10
Pre-Flight Testing - 1• Find
Hardware
• Two bolts have stacks of 6 bellevilles captured between two wide area washers – 4 standard bolts
• Can see good linearity
Bolt Torque / Washer Compression vs. Turns
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September 8, 2008 Rutan Derivative Canard Forum Slide #11
Pre-Flight Testing - 2
• Remove “turns” from the equation – just show washer compression vs. applied torque
• Still very linear
Washer Compression vs. Bolt Torque
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Bolt Torque (ft-lb)
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Compression - LCompression - R
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September 8, 2008 Rutan Derivative Canard Forum Slide #12
Pre-Flight Testing - 3• Switch from six
std. bolts to six bolts – all with 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
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Compression - StdCompression - Belleville
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September 8, 2008 Rutan Derivative Canard Forum Slide #13
Pre-Flight Testing - 4
• Six bolts with belleville washer 6-stacks
• Very linear torque and compression with bolt turns
Washer / Hub Compression / Bolt Torque vs. Bolt Turns
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Individual WasherCompression
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September 8, 2008 Rutan Derivative Canard Forum Slide #14
Pre-Flight Testing - 5• Same slight
change in slope as “slop”is taken out
• Still predictable and relatively linear with Bolt Torque
• Might be easier to measure turns rather than torque, however
Hub and Washer Compression vs. Bolt Torque
0.000
0.005
0.010
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0.025
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0 5 10 15 20 25 30
Bolt Torque (ft-lb)
Com
pres
sion
(in)
Hub CompressionIndividual Washer Compression
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September 8, 2008 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 don’t• See washers NOT completely compressed – allows for shrinkage AND expansion of
Prop Hub
• No difference from standard installation perceived - ~3 flight hours accumulated in this configuration at various speeds, RPM, flight attitudes – near 1 million cycles for fatigue
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September 8, 2008 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 on
second set• Again, fly various RPMs, flight attitudes, speeds, G-loading
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September 8, 2008 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 on
second set, ~1 million on third set• Again, fly various RPMs, flight attitudes, speeds, G-loading
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September 8, 2008 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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September 8, 2008 Rutan Derivative Canard Forum Slide #19
Current Configuration
• Using 7” bolts – could reduce to 6.5” and remove hardened washer to save ~0.1 lb.
• Added AN3 bolts to FRONT of crush plate
• Will be able to add spinner backplate / mounting structure WITHOUT having to remove/touch prop bolts
• Don’t have to have backplate BETWEEN prop and prop extension
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September 8, 2008 Rutan Derivative Canard Forum Slide #20
Gyroscopic Effects and Belleville WashersAnalysis by David Dannemiller
Assumptions:• Weight of Prop: 16 lb.• Prop Hub Dia.: 7 inch• Prop Diameter: 64 inch• Maximum
Pitch/Yaw Rate: 90 deg/sec
• Prop Bolt Tension: 3000 lb.
Safety Factor: 9
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September 8, 2008 Rutan Derivative Canard Forum Slide #21
Increased Robustness / Decreased Sensitivity
• Maintenance simplification (measure spacing, # 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)
Hub
Com
pres
sion
For
ce L
oss
(%)
Standard
Bellevilles (6-stack)
Bellevilles (4-stack)
Bellevilles (2-stack)
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September 8, 2008 Rutan Derivative Canard Forum Slide #22
Cost / Weight Penalty
• ~2.5 lb for ½” Bolt SAE-2 Flange with 7” Crush Plate 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, flat washers
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September 8, 2008 Rutan Derivative Canard Forum Slide #23
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 Bolts available from Saber MFG, washers from ACS, Wicks, etc.
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September 8, 2008 Rutan Derivative Canard Forum Slide #24
Questions / Answers
• My Email: [email protected]
• Website: http://www.cozybuilders.org/