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Aircraft Front Landing Gear Linear Actuator Design

30 May

School of Engineering
Advanced Mechanical Design
Major Assignment
Aircraft Front Landing Gear Linear Actuator Design
Due Date: 9:00am 29th May 2017
Submission: Hardcopy with a completed ECU coversheet. Submit to Engineering Office, building 23.
Note: Peer and self-assessment will be considered during marking
Your team’s (group of 4 students) task is to design a linear actuator that can lower and raise the front
landing gear of an aircraft. The linear actuator will use a power screw that is driven from a hydraulic
motor via a gearbox. The hydraulic motor specifications are documented below. Your team must
design the entire gearbox and power screw actuator that is mounted between the fuselage and
landing gear linkages, as illustrated in the image below.
The complete design will need to include the following:
Load calculations
Gear sizing
Bearing specification
Shaft design
Gearbox housing design
Power screw sizing
Fastener size specification
And designs of any other fixtures or housings that you require
Figure 1. Schematic of front landing gear linkages / assembly

 

Linkage pivot points
Linkages
Mounts on
fuselage
Motor and gearbox
Main Strut
Linkage pivot points

 

The power screw is attached to the hydraulic motor via a gearbox for the correct torque input to drive
the power screw. The (blue) linkages in Figure 1 are attached to the end of the power screw and the
‘nut’ of the power screw is attached to the top pivot of the main landing gear strut. Turning the power
screw translates the nut along the power screw, which in turn rotates the main landing gear strut
about the top pivot for retracting or raising the landing gear. The main strut and (the upper blue)
linkage are attached to the fuselage as illustrated.
The linear actuator, which comprises of the power screw, nut, pivot attachments, housing(s), gearbox
and hydraulic motor should be
designed as one single device that can be installed onto the landing
gear mechanism. As a result, the linear actuator housing is structural and reacts the motor drive
torques as well as forces during landing gear retracting or raising. Rotating motion between
components should be isolated with rolling element bearings that are adequately sized. There is
no
requirement
for coaxial alignment between the power screw and motor.
The aircraft is designed to operate as reliably as possible to avoid any incidents, however, this must be
within reason to avoid unnecessary weight. As a result, minimum safety factors should be 2 where
required.
The landing gear is specified to be lowered or raised at a maximum speed of 250kmh, and maximum
altitudes of 2000ft. For simplification, the landing gear strut can be assumed negligible and the wheels
are considered the main contributor to the drag forces on the entire mechanism;
likewise the weight
of the assembly can be neglected
. Further, the system is locked when fully retracted and as a result
the linear actuator is isolated from wheel braking loads and vertical loads. There are two wheels
adjacent to one another with the main strut running between the wheels, where the wheels have a
drag coefficient of 3. The aircraft manufacturer has stated that the front landing gear must retract or
raise within 10 seconds
(maximum), where the bottom of the fuselage is 550mm below the main strut
pivot. The link lengths and other associated dimensions are illustrated in Figure 2 below.
Figure 2. Illustration of the key landing gear dimensions (in mm)
The front landing gear wheels (Figure 1 and 2) are 875mm in diameter and 320mm wide.

 

The hydraulic motor (Figure 3) has a maximum operating capacity of 5Nm torque and 3000RPM, and
overall
dimensions (ONLY!) equivalent to the TB0036 hydraulic motor found in the attached Parker
hydraulic motor documentation or
http://www.parker.com/literature/Hydraulic%20Pump%20&%20Motor/_TB_Series.pdf
Notably, different mounting flanges and output shaft options (including dimensions) are available
within the documentation. You are free to select any of the flange and output shaft styles based on
which best suits your design. Your gearbox design must be able to attach the TB0036 motor (
hint: the
gearbox housing and input coupling/gear must match the motor mounting flange and output shaft
respectively
).
Figure 3. Sample hydraulic motor illustration (Note: output shaft and mounting flange may vary)
The overall linear actuator design should include power screw design, nut design, gear design, shaft
design, fastener sizing (where necessary), bearing selection (and any accompanying components such
as seals and clips, etc.) and housing(s) to ensure a completely operating actuator. Fastener
calculations are required to justify the size of any
main structural bolts used in the design. It is a
design requirement that any rotating structural components in the design are located by rolling
element bearings.
Notes and Assumptions:
I. Neglect main strut drag and landing gear weight
II. Ignore thrust bearing friction on the power screw
III. Assume 0.1 friction coefficient between nut and screw of the power screw
IV. Assume there is no loss in aerodynamic drag as the wheel retracts into the fuselage
V. Assume that the hydraulic motor has a constant power curve
VI. The gearbox should be serviceable
VII. The gearbox should include oil fill and drain locations
VIII. This gearbox should be designed for an aeronautical application
IX. The final design should be a complete ready-for-manufacture design

 

The assignment deliverables for the design are as follows:
1. A complete set of design documents for the assembly:
A design report that details (15%):
Product design specification
Manufacturing details (including processes, off-the-shelf components, required
treatments, etc.)
An analysis report that covers (45%):
Load calculations (prior to further analysis)
Strength calculations
Failure analysis calculations of component(s)/assembly where applicable
Finite Element Analysis of structural components
A complete set of manufacturing drawings – fully dimensioned of all parts ready for
manufacture (Note: this excludes the motor, gear tooth profiles and bearings) (
10%)
SolidWorks 3D model (or equivalent CAD model that can be opened within SolidWorks)
of the complete actuator assembly and components. Printed (hardcopy) images of all
the components in your design are required along with electronic files of the parts and
assemblies (
15%)
2.
Presentation: An informal 5 minute presentation of your group’s design to the class during the
final lecture (
5%).
3.
Teamwork: Cooperate as an effective team with suitable load sharing (5%)
4.
Report: All aspects for a quality report, such as grammar, referencing, presentation, etc. (5%)
Note: The
written component (excl. drawings) of the design report should not exceed 10 pages, any
content beyond 10 pages will not be considered in the mark. The
analysis report should not exceed
30 pages, any content beyond 30 pages will not be considered in the mark.

 

 
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Posted by on May 30, 2017 in academic writing

 

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