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parts of the aircraft during operation, particularly in the case when the tire is damaged and
continues to spin when stowed. As shown in Fig. 6.6, the maximum grown outside
diameter (DG) and section width (WG) are determined using the expressions [25, p. 8]
DG = D + 2(1.115 - 0.074 AR)H (6.14)
and
WG = 1.04W (6.15)
where D is the specified rim diameter, H is the maximum section height, W is the
maximum section width, and AR is the tire aspect ratio defined as
AR
H
D
= (6.16)
The values for the radial and lateral clearance, i.e., CR and CW, respectively, are calculated
using the expressions [25, p. 9]
C W at
MPH
MPH
MPH
MPH
MPH
R = G
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250
225
210
190
160
.
.
.
.
.
. (6.17)
and
CW = 0.019WG + 0.23 (6.18)
The constant coefficients found in Eqs (6.14), (6.15), and (6.16) are based on the
maximum overall tire dimensions, plus growth allowance due to service and the increase in
diameter due to centrifugal force.
55
Figure 6.6 Clearance envelope for aircraft tires [25]
Based on the clearance as determined above, the minimum radial and lateral distance
between the tire and surrounding structures are calculated as follows [25, p. 9]
R
D
x C
G
= + R
2
(6.18)
W
W
x C
G
= + W
2
(6.19)
S
C C
x
= W R
+
2
(6.20)
Given the minimum allowable distances obtained using Eqs (6.18), (6.19), and (6.20), a
clearance envelope is established around the truck assembly. Then, using the kinematic
analysis as outlined in the previous section, the boundary of the envelope is re-established
in the retracted position. Note that the envelope is represented in the kinematic coordinate
system, while the boundaries of the landing gear wheelwell are in the aircraft coordinate
system. Recall that the origin of the kinematic reference frame is defined in the aircraft
coordinate system. Thus, simple algebraic manipulation would bring both sets of data
under the same coordinate system, whether it be the airframe or the kinematic reference
frame. Stowage boundary violations can then be identified by comparing both sets of data
for discrepancies.
38
January 2008 • www.machinery.co.uk
The exceptional strength-to-weight
ratio of carbon fibre composite has
ensured its evolution into the material of
choice for a growing number of
applications, predominantly in the
aerospace and motorsport industries.
However, this innovative material
poses a number of manufacturing
challenges for those more familiar with
processing conventional metal or plastic
components. The Delcam-hosted seminar
provided around 70 delegates with the
opportunity to learn about them.
Graeme Cartwright, the sales manager
of CMS Group (UK), talked in detail about
the strides his company has made in
recent years to develop machines capable
of handling composites.
CMS now has a range of 3- and 5-axis
machining centres suited to applications
such as machining carbon fibre
honeycomb parts in the aerospace sector,
body and interior automotive
components, sports equipment, as well
as a variety of machining tasks in the
marine industry, such as producing
mould and plugs for yacht hulls and the
trimming and chamfering of decks.
Special features of CMS machines for
composite machining include enclosures
designed for dust and noise containment,
high level electrical protection against
carbon fibre dust, special vision panels to
protect against carbon fibre dust abrasion
and
a CNCcontrolled
dust
extractor on the Yaxis
to accommodate varying
lengths of cutting tools.
UK customers using CMS technology
for composites machining include Lola
Composites, Brookhouse, the Advanced
Composites Group, Atlas Composites and
WJ Todd.
TECHNOLOGY AT WORK
The very nature of carbon fibre
composite materials results in the
generation of high cutting forces when
undertaking machining operations which
can lead to delamination. To overcome
this difficulty, SGS Carbide Tool has been
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