MIT16_842F09_assn4_sol

MIT16_842F09_assn4_sol - Assignment #4 Solutions 16.899...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Assignment #4 Solutions 16.899 – Fundamentals of Systems Engineering Part I. Vehicle Design and Performance (Aeronautics) 1) In Figure 1, what physical effects cause R to increase as m is increased from 1kg to about 20000kg? What causes the slight decrease as m increases beyond 20000kg? Hint: examine the variables of the Breguet range equation. There are several ways to explain this. This is just one of them: In looking at the BRE, there are three main factors that affect range; engine performance (PSFC), aerodynamics (C L /C D ), and fuel fraction (m fuel /m). From the engine’s perspective, in general a) the less power it has to produce in cruise, the lower the PSFC. At the same time, one wants to b) maximize C L /C D which we know, from the drag polar, occurs when parasite drag equals drag-due-to-lift. Typically, if the aerodynamic condition is satisfied, we’ve done as good as we can in minimizing the power required. Finally, we want c) as much fuel as possible without overstressing the a/c. When the aircraft is very light, the best improvement we can make is in terms of c) since the stress limits are easily avoidable by adding relatively low amounts of reinforcement (in terms of mass), and it is relatively easy to meet a) and b). This is true for a range of mass that continues upward until stress limits become very costly to increase (i.e. the amount of mass required to reinforce is no longer worth the range gained by the increase in fuel mass). This is related to the square-cube law as described below in the answer to number 3. At this point, it is also no longer easy to meet the requirements of a) and b). That is, although it may be possible to fly at the condition for which parasite drag equals drag-due-
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 11/08/2011 for the course AERO 16.810 taught by Professor Olivierdeweck during the Winter '07 term at MIT.

Page1 / 4

MIT16_842F09_assn4_sol - Assignment #4 Solutions 16.899...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online