1. No category

Light Aircraft manufacture and
materials
Comparison of materials, specific buckling
stiffness.
Comparison of materials for specific stiffness (E/ro)
column buckling ( E/ro^2) and panel buckling ( E/ro^3)
250
150
100
E/ro^2
E/ro^3
E/ro
50
Titanium alloy
7075 alloy
6082 alloy
Steel 8.8
Fir
Spruce
Balsa
Birch ply
Epoxy matrix
UDCFRP
WCFRP
UDGFRP
0
WGFRP
E MPA /g/cc
200
E/ro
E/ro^2
S
F
te ir
e
60 l 8 .
82 8
70 allo
Ti 75 y
ta
ni allo
um y
al
lo
y
W
G
F
U RP
D
G
F
W RP
C
F
U RP
E DC
po
F
xy RP
m
a
B trix
irc
h
pl
y
B
al
s
S a
pr
uc
e
specific strength MPa/g/cc
Specific strength of materials
UTS/ro
500
450
400
350
300
250
UTS/ro
200
150
100
50
0
St Fir
ee
60 l 8
82 .8
70 allo
Ti 75 y
ta
ni allo
um y
al
lo
y
W
G
F
UD R P
G
FR
W
P
C
F
UD RP
Ep C
ox FR
P
y
m
a
Bi trix
rc
h
pl
y
Ba
ls
Sp a
ru
ce
£/kg
Relative cost of materials
cost/kg
80
70
60
50
40
cost/kg
30
20
10
0
Considerations
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Metals – design for fatigue, corrosion
●
Isotropic - best for 3D loads
●
Bolted and rivetted joints good in metals
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Wood – drainage/ventilation, considerations apply as for composites
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Composites – Impact, drainage ( esp. foam),service temperature, repair schemes
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Wood and composite Orthotropic – best for 1D or 2D loads
●
Rivetted joints unsuitable for thin composite or wood panels
●
Fibres must be aligned with primary load paths
●
Through-thickness peel and shear loads must be carefully considered
●
Slot together joint features best – avoid peel loaded joints
●
●
Carbon composite strain limit around 0.4% to allow for joints, repairs and to avoid
damage growth after impact
Special factors applicable for temperature degradation and variability of production (
see CS-VLA AMC 619)
Design process
●
Sketch ideas for layout, calculate flight envelope, weights, loads
●
Simple hand or XL spreadsheet calculations
●
Optimise layups using laminate analysis program to obtain
A,B,D stiffness matrices
●
Refine calculations and weight estimates
●
Apply laminate analysis to FE program e.g. Nastran
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Check answers are in line with initial hand calcs
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Optimise FE design
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Build it and load test unless experienced with very similar
previous analysis models
CFM Shadow uses many different
materials to good effect
●
●
Fibrelam fuselage
structure
Extruded light alloy
boom
●
Foam ribs
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Ply leading edges
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Extruded spar caps
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Pultruded U/C legs
Classic Cessna 150 light alloy semi-monocoque. Wing has few ribs
and uses stiffeners, postbuckling at ultimate load. Poor
payload/empty weight compared to Jodel.
ARV super 2 – all light alloy, with super plastic formed fuselage
belly pan. Now called Opus in USA with Rotax 912 engine.
The Jodel with wood construction is
light and efficient
Columbin MC30 Luciole – even
lighter!
Columbin Luciole uses wood, foam
and carbon pultrusions.
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97kg empty, 200kg max
25bhp Briggs and
Stratton V twin
100kt on 5 litres/hr
Wing uses wood spar
with carbon pultruded
spar caps and foam ribs
Wing is quickly
detachable from
fuselage
Spar construction
Wing skin bonding under partial
vacuum
Ply skinned wood fuselage
Fuselage with wing connection
Spar to fuselage carry-through
structure
V twin Briggs and Stratton
conversion, direct drive
The Mosquito used innovative design with wood to achieve excellent
performance, pioneering modern composites design practice
Mosquito construction
●
●
●
●
ply/balsa/ply fuselage sandwich monocoque,
with reinforcements built into the core
Fuselage 80% fitted out in 2 halves, hydraulics
in one side, electrics in the other
ply/spruce stiffeners/ply wing skin sandwich
panel production
Laminated spruce spar caps with plywood
shear webs
Composites allow smooth aerodynamic shapes and laminar flow
Glass/Epoxy UD fibres make an effective spring
undercarriage
The A.I.R. Atos has a cantilever carbon leading edge D box with
folding ribs for transport, flaps for takeoff/landing, 15m span, 40kg,
20:1 glide and 150fpm sink rate
Firewall uses reflective and intumescent coatings
e.g. Technifire
Storch uses mixed construction with extruded light
alloy tailboom, strutted wing can be folded
Prepreg/autoclave – high cost/high performance process
with some problems.
●
De-bulking required every 4
plies
●
High energy usage
●
Thermal stresses/warping
●
Expensive equipment
●
Traditional high-end aerospace
process
Vacuum bag processes
●
●
●
●
Wet-preg/vac bag process
gives better properties than
bucket and brush
Widely used for gliders,
motorgliders, microlights
Messy process
Resin infusion process setup
and process control more
complex
●
Clean process
●
Low void content
Stabilator sandwich skin vacuum
bagged
RFI and RTM
●
●
●
●
●
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RFI similar to resin
infusion but allows
toughened resins
Easier to get uniform
infusion over an area
Vacuum stack compacts
during cure
RTM requires precision
closed tools
Good for small parts e.g.
Propeller blades
Process control and
preform production critical
Good finish with tight
tolerances on all surfaces
Winding, Wrapping and pultruding
●
●
Filament winding or
prepreg tape
wrapping for torque
tubes and pressure
vessels
Pultrusion and
pulwinding give high
quality constant
section parts at low
process cost
Finishing composites
●
●
●
●
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Polyester gel coats favoured over
epoxy for UV resistance – but check
compatibility with epoxy gelcoat
Brushed gel coats typically 1mm
thick
Spray gel coat 0.5mm thick, more
uniform colour dispersion and
metallic effects possible, air fed
mask and fume extraction required
Structural composites generally
white to minimise surface
temperature ( 54C)
Lightest finish is to prime/surface
then 2K acrylic paint – but very
labour intensive
CT production
• CT rear fuselage is
monocoque sandwich
• Aramid used on inside
skin
• Reinforcing bulkheads
carbon with ply inserts
• Finish is by primer/filler
then sanding and
painting
Slotted H-joint features in the Beech Starship
Wing construction in a mould
Mouldless methods
Mouldless methods - shells
Foldaplane concept for 2D
curvatures
Now for something completely
different
Which does different things
QuikR – a 3D sports motorcycle
●
Tailless flexwing configuration gives low empty weight and low parts
count
●
Empty 220kg, loaded 450kg
●
50-100 mph hands off, electric trim
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Lateral trim by nosewheel steering
●
Range 400 miles at 80mph
●
38mph stall, 120mph Vne
●
1200fpm climb at max AUW on Rotax 912s
●
Quick fold topless wing
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Seamless mandrel drawn 6082-T6 17swg tube airframe
●
Extruded 6082 aerofoil struts
●
Polyester mouldings with spray gel coat
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Extruded trike basetube and main pylon
Fittings etc designed and optimised on CATIA/ABAQUS
Sail reinforcing aramid bands and washout rods, composite tip fins,
short aerofoil struts, pullwound carbon battens
QuikR sail production
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18 hours precision sailmaking, +- 1mm all over
Advanced technology sail materials include Polyant HTP square sail main
body, PX10T leading edge, X05 aramid unidirectional reinforcement bands,
Mylar .040” leading edge stiffener with APS system.
In flight strain gauging carried out with extensometer
Sails produced on mylar templates with raised tape edges, shape is
transferred with a 4h pencil
●
Sail is assembled with seamstick double sided tape
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Simple automatic tape folder/adhesive applicator for making batten pockets
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Sewn together with Tenara spun PTFE UV proof thread
●
Continued airworthiness testing by Bettsometer ( needle with calibrated
spring balance)
Sail loft with batten tape folder, raised tables and mylar template
with thick tape profiles
The last word on the subject!
Scrapheap biplane build and flown
in 3 days with 4 people
Sailmaking for BAE Cayley glider
Pilcher triplane replica
Booster carbon fibre auxiliary power unit with folding propeller and retractable
undercarriage