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Aircraft Overhead Bin. by Sam Donaldson Gerard Mouatt Francis Gillis Rob Harmer. Introduction.
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Aircraft Overhead Bin by • Sam Donaldson • Gerard Mouatt • Francis Gillis • Rob Harmer
Introduction The mechanism chosen for this project is an aircraft overhead bin mechanism. Its purpose is to cover storage compartments on an aircraft where passengers store carry-on luggage so it is accessible during the flight. It is designed to take up as little space as possible while having enough space for small carry-on luggage. A simple design is required in order to limit weight on the aircraft.
Abstract • The aircraft overhead bin mechanism is designed to pivot between “open” and “closed” positions. When broken down, or simplified for analysis, it is seen as a classic four bar linkage. There are two rockers connected to a grounded link which provide oscillatory motion for the door panel. The upper rocker is linked to the bottom corner of the panel and has limited motion. The lower rocker connected to the upper corner of the panel has approximately a 90 degree window of motion. This Grahsof mechanism has range which allows for small carry-on luggage to be stored in the compartment. The panel’s motion is designed so gravity will keep the mechanism open while a latch will keep the door closed. Although not shown, a stopper is required to halt the opening motion of the door which in turn provides safety for passengers.
Brain Storming • Need to convert the Mechanism to a classical four bar linkage. • Some restraints are needed on this mechanism in order to slow the rotational speed down.
Degrees of Freedom • Gruebler’s Equation • # DOF’s = 3L-2J1-J2-3G • L = the number of links • J1 = the number of 1 DOF joints (full Joints) • J2 = the number of 2 DOF joints (half Joints) • G = the number of ground links • Aircraft Overhead Bin • 3(4) – 2(4) – (0) – 3(1) = 1 Degree of Freedom
Grashof Condition • Grashof Equation • S= length of shortest link • L= length of longest link • P= length of one remaining link • Q= length of other remaining link • S+L ≤ P+Q • Aircraft Bin Mechanism • S= 7.489 • L=12.968 • P=9.170 • Q=9.434 • 7.489+12.968 < 9.170+9.434 • Case I (Grashof Double Rocker)
Critical Parameters • One way Damper • A one way damper limits the velocity of the door upon opening. This is why we kept the angular velocity (ω2=.25 rad/s) and acceleration (α2=rad/s2) small. • Rotational Stopper • The stopper should keep the door from opening to far and swinging into a passenger’s head. It must allow clearance for small luggage placement. • Weight • A simple design will aid in keeping the component’s weight down.
Position Results • The results obtained during the analysis of this mechanism were reasonable with respect to its function. The position analysis was done both analytically and graphically. AutoCAD was used for the graphical analysis. The values for all of the angles were very close between the two methods and supported the function of the mechanism. When the bin was in the closed (crossed) position, all of the values (a, b, c, d, θ2) needed for calculation were obtained by drawing the original picture from the textbook in AutoCAD. When the bin was in the open (open) position, there was no value given for θ2, so a value had to be assigned. The value 330 was chosenby drawing the four bar linkage in AutoCAD, estimating where the door would stop and then measuring θ2.
Velocity & Acceleration Results • Values needed to be assigned to 2 and 2 in order to make calculations for velocity and acceleration. An educated guess had to be used to assign those values. The values were first guessed as 2 = 3 rad/s and 2 = 2 rad/s2. After using those values to make the appropriate calculations, the final values for 3,4,3, and 4 where outrageously large. We found that if 2 was changed to 0.25 rad/s, and 2 was left at 2 rad/s2, the final values were much more reasonable. In comparing our results from graphical and analytical analysis, as well as from the working model, we believe they support the real-life functionality of this mechanism. **For a detailed look at all of the results, view the filename project.xls on this CD**
Conclusion • With the completion of our analysis, we found that a damper was need to slow the rotation of the mechanism. If the bin were to open using gravity it would be moving at speeds to high for the long term reliability required. It would have to be a single direction damper that would have to be around 7 kN-m-s to achieve the appropriate angular velocity. There would also need to be a stopper installed in a position to keep bar “a” from swinging under 330 degrees. This would help keep the seated passengers from being struck by the door while also allowing as much possible clearance for luggage and access to the seats beyond the bin. While reconsidering the design of this mechanism, one strong possibility would be for the bin door to swing up. This would be a more practical and safer design.
Sources • AutoCAD 2006 • Norton, Robert L. Design of Machinery: an introduction to the synthesis and analysis of mechanisms and machines. McGraw- Hill, 2004. • Norton, Robert L. Working Model Software. McGraw-Hill, 2004.
