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Australian innovation in small aircraft design : A case study
Answers
Why is MDF craftwood being used?
- Cheap
- Easy to machine
- No grain isotropic strength characteristics: equal strength in any direction.
- Strong enough to withstand bumping or slight fall.
- What is meant by "lift" and "drag".
Lift is an upward force developed on a wing surface from airflow over it. Drag is a resistance force encountered by the aircraft as it moves forward through the air. The amount of drag depends on the shape of the aircraft and the surface finish.
- What is meant by "stall".
Stall is a sudden loss of lift on the wing causing the nose to dive. Severe stall leads to loss of control of the aircraft.
- How can you tell this aircraft has stalled?
The tufts in the centre section of the wing are no longer aligned with the flow. Thus a loss of lift has occurred.
- Why is welded steel used rather than aluminium alloy?
Aluminium alloy is more difficult to weld reliably and more bulky for the same strength. Aluminium takes up more space. Weight differences are not significant.
- How might the frame be checked for fatigue cracks? (ultrasonic, X-ray, etc.)
Ultrasonic or X-ray testing to determine if there are any internal flaws or cracks that could weaken the structure.
- What material would be used to "skin" this aircraft? (duralumin)
Duralumin as this material has good formability and strength characteritics.
- What is the difference between a monocoque, semi-monocoque and framed structure?
With a monocoque structure all the material is in a shell as in an egg. A semi-monocoque has some structure to reinforce the shell. A framed structure has the entire load carried by the frame itself.
- What type is the P99L aircraft and why is this innovative?
A combination of monocoque and framed, which is innovative because of the combination. The framed structure produces a protective cell and the monocoque follows more conventional methods.
- What is the difference between a strutted wing and a cantilevered wing?
A strutted wing is hinged at the fuselage with a strut between the wing and the fuselage. A cantilever is built into the fuselage so that the maximum bending loads are carried at the intersection of the fuselage and wing.
- What purpose does the strut serve in a strutted wing?
The strut prevents bending moments at the hinge by going into tension.
- What type of wing does this plane have?
A strutted wing because the location and shape of the cabin prevents the wing being supported on a main spar which would have to be large enough to resist the large bending moments set up at the wing root.
The applied loads can be either static or dynamic. What is the difference between these two load types?
Static loads do not take into account motion, so they are just determined by the object's own weight when stationary.
Dynamic loads take into account the acceleration of the distributed masses of the structure.
After design, calculation and other factors are complete, a prototype will need to be built. What is a prototype and what purpose does this serve in the design of a new aircraft?
A prototype is a real working example that is as close to the final production aircraft as possible. It will undergo rigorous testing, close observation and further engineering evaluations.
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