What are three structural reasons carbon fiber is often taking the place of aluminum?
Carbon fiber is less susceptible to corrosion and fatigue while also having a higher strength to weight ratio. This means vehicles can last longer and be lighter which decreases the structural loads over the vehicle's service life. A draw back, however, is that improper design and materials selection can negate the benefits of composites and actually add more weight so careful consideration must be taken in design to get the full benefit of carbon fiber.
What is a tolerance intended to represent?
A tolerance is a statistical baseline that is effectively a limit of producibility. If the tolerance is tighter then less parts are able to be produced but the product is more 'ideal'. A level of six-sigma is the gold standard where there are roughly three defects per million units. However, this is not always practical. Therefore, a tolerance represents a trade-off of design goals and production capability to achieve an acceptable number of defects,
During the Space Shuttle program why were the main engines throttled down before going full throttle to reach LEO?
Atmospheric flight vehicles fly indirectly based on speed but as a direct result of pressure. To reach low Earth orbit (LEO) the Shuttle must accelerate to a speed where it is in a state of constant free-fall to avoid the pull of microgravity bringing it back to Earth. However, as the Shuttle speeds up through the atmosphere the air density decreases slower than desired for structural limitations. Therefore, 'max q' was called out to let the astronauts know when they can continue unrestricted. Maximum dynamic pressure on the airframe, max q, was the limiting factor for the Space Shuttle launch. Dynamic pressure is one of the most important concepts in aerospace.