Design and Construction of the Mole Mite

2 5% dat um
4390
10 0 0
34 3
644
498
2162
°
10 ,7
316 0
2 5%
dat um
2 34
58 6
8 00
9 2 816 13
Mole MITE Wing Design and construction
Mole "MITE'
G.A.
A lifetime’s interest
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PPL from RAF scholarship while at school
School to Vickers Armstrongs Aircraft shop floor
UAS APO rank and BSc Aeronautical Engineering
2 hrs flying Tiger Moths was a good investment
A career in Business Schools – but no flying !
Family & domestic commitments took over
I desperately wanted to fly again before it was too
late
Almost flying - at last
En route Riga
Northern Norway in the
light of the midnight sun
9 2 816 13
2 5% dat um
4390
10 0 0
34 3
644
498
2162
°
10 ,7
316 0
2 5%
dat um
2 34
58 6
8 00
Mole "MITE'
G.A.
Vs1 VG VF
VA
VC
Vne
Knots
43 62 66
89
90
113
Kph
80 115 121 165 167 210
(MC-30) (81)
(114) (169) (180) (225)
VD
126
233
(250)
Limit flight envelope at mauw
4.50
4.00
3.50
3.00
n
2.50
2.00
1.50
1.00
0.50
0.00
-0.50
-1.00
-1.50
-2.00
-2.50
0
10
20
30
40
50
60
70
80
90
100
110
120
130
Knots
MITE Flight envelope, design speeds
Francis Donaldson in G-LUCL with
builder Richard Teversen looking on
e-Go prototype G-EFUN late 2013
W lb mauw climbing at R ft/min
requires W*R/33,000 hp
Climb rate
Mauw
Power required
Engine shp
Propeller ɳ
Power available
Power for climb
Power for level flight
ft/min
Kg
hp
hp
hp
% available
% available
MC-30
Luciole
800
200
11
22
.8
18
60%
40%
Jodel
D18
770
499
26
85
.8
68
40%
60%
Two main conclusions
• A decent climb rate on low power depends
even more than usual upon containing the
level-flight power requirement.
• An engine problem that allows continued
running at say half the power gives a Luciole
pilot less of an issue to deal with !
Containing the level flight power
required at climbing airspeed
A low-power aircraft benefits
disproportionately from
• A flapped wing that permits a smaller wing
area and lower wing profile drag when clean.
• A low extra-to-wing drag (no open cockpits,
draggy struts are to be avoided,
undercarriage must be well faired etc).
• A long span to contain the power absorbed
by wing induced drag
Pind= [W/b]2* K/ (550 * ½ ρ π V)
Weight
Span
K
Speed
Pind
Rate of climb
Aspect ratio
W lb
b ft
K
V fps
ft/min
MC-30
MITE
Luciole
441
463 lb
22.6
20.74
1.08
1.08
90
90
2.2
2.9
800 ? 800-0.7*33,000/463
= 750
10.3
7.9
Structural elements of the wing
• The narrow box spar reacts normal loads only
Flanges are sized by beam theory for local BM.
The web is sized for the local Shear Force.
Web to flange overlap determines bond stress.
• Wing skin reacts chordal loads & torque around the s.c.
Acquires direct stress from spar flange flexure.
• Ribs maintain the wing section.
Central ribs react crew inertial load on seat & walkway
• The TE False Spar has negligible bending strength
Carries the control surface hinge loads.
Carries shear stress, as it’s part of the torsion cell.
• Centre Section Rear Spar reacts seat & walkway loads.
Flanges of the narrow box spar
• Flanges are laminated from 2 lengths of
pultruded carbon rectangular strip, 20mm wide
and 8mm deep
• These bought-in pultrusions are produced under
controlled conditions.
• Randomly drawn coupons are tested for
consistency of material properties as part of the
acceptance procedure for material stock.
Testing coupons of pultruded
carbon for the spar flange
Advantages of Carbon pultrusions
• Pultruded fibres are much straighter
and more densely packed than a hand
lay-up and thus have superior physical
properties.
• In particular, the properties are
consistent within a manufacturing
batch (if of aeronautical quality!)
• They can be tapered, laminated and
bent rather like wooden members.
Simple restraining jig when
tapering pultrusions
Mechanical grinding completed
Laminated carbon flanges
• Each flange consists of 2 pultrusions
laminated together.
• Top and bottom flanges are symmetrical.
• The flanges are laminated while bent
around a centre-section former.
• The width of the former is the same as the
fuselage and subtends an angle of 9°.
• The spar emerges from the fuselage sides
at 4.5° dihedral.
The spar at the centre section
4,5°
Beech 600*5.5*20 profiled as shown
1.5mm GL1 central lower skin
Laminating the top flange
inside the spar mould
Protection from surface damage
• It is essential to avoid surface damage.
• Barely Visible Surface Damage (BVSD) can be
avoided by encasing pultrusion within a ply shell.
• Internal ply & Beech laminates protect the inner
pultrusion face from fretting damage by soldiers.
• A ply laminate bonded to the external face can be
chamfered, if necessary, to match the section.
• These additional materials erode the comparative
advantage over Spruce only a little.
• The encased MITE spar 24mm wide and 6.32m
long weighs 6.4 kg
The spar at the centre section
4,5°
Beech 600*5.5*20 profiled as shown
1.5mm GL1 central lower skin
Pultruded carbon Vs Spruce I
• VLA ACJ 572(b) permits stresses in carbon up to
40 daN/mm2 or some 58,015 psi
Fcp= 3,530 psi for Spruce, some 16 times lower.
• Because Fcu= 4,700 psi for Spruce, limit load
stress cannot exceed 3,133 psi. The comparison
of allowable stress levels increases in favour of
carbon to 58,015/3,133= 18
• Composite structures are subject to a composite
factor of 1.25 provided the coupon tests
demonstrate adequate consistency .
• The comparison in allowable compression stress
in favour of carbon becomes 18.5/1.25= 15
Pultruded carbon Vs Spruce II
• A Spruce compression flange is about 15% of
the spar depth and the ‘Form Factor’ is
approximately FFu= 0.5+0.5*0.15= 0.58
• FFu*Fbu= 0.58*9,400= 5,452 psi.
Comparison in allowable limit stress falls from
14.8 to 14.8*4,700/5,452= 13
• Density of carbon pultrusions is 1.5 g/cm3 some
3.5 times more than Spruce.
• Specific stress advantage is 12.8/3.5= 3.6
• Carbon pultrusions make a very much more
compact spar flange at about 30% of the weight.
Ready to close up the spar
Encased spar released from the mould
Two last considerations
• Bending 8mm deep pultrusions before laminating
them together to form the 16mm flange at the
centre-section ‘locks-in’ their local bending stress.
• This reduces the remaining allowable stress.
• Reducing the cross-sectional area of the flange to
match the local BM may not be feasible.
• Flange area decreases more or less according to a
square law (rectangular wing).
• But the Normal Shear Force will decrease linearly
to a first approximation.
• The depth of the MITE flange that preserves
acceptable bond stresses to the web becomes the
design criterion around mid-span.
The spar test rig
The proof of the pudding
• The spar weighs about 6.4 kg.
• It supports 722 kg on each wing distributed over
3.16m according to the Schrenk distribution.
• The 1,422 kg total is almost one and a half metric
tons (3,183 lb).
• Load/spar wt ratio = 1,422/6.4= 220
• Photo shows case D4.2 at n= 1.25*1.5*4.2= 7.875g
• Repeated loading gives identical deflections.
• All the elements of structure remain within the
elastic region even at fully factored ultimate
load.
The n= 0 ‘torsion with drag’ test
A4.2 at ultimate combined loads
Building the flight wing
3.1m*1.26m*1.2mm ply with 34mm id
Celebrating the starboard skin safely applied