General comments

I finished the discussion of rockets by presented one typical performance trade for rocket nozzles. In this context we talked about ideally-expanded, underexpanded and over-expanded nozzles. For each we talked about the impacts on momentum flux and pressure forces in the thrust equation and the impacts on nozzle weight. We did one PRS question in connection wiith this discussion.

We then took 20 minutes to cover Chapter VII of the notes. As with the rockets, this allows you to connect design parameters to vehicle performance. The important part of this material is understanding the behavior of simple turbojet engine cycles. A necessary complication along the way is expressing the fairly straightforward equations for thrust and efficiency in terms of principal design parameters, design contraints, and flight conditions--this makes them appear more complicated. There is a PRS question that we didn't get to (PRS#2). This question is about at the level that I would like you to understand the behavior of turbojets. You should also know what the principal design parameters and constraints are for these engines (like compressure pressure ratio, and turbine inlet temperature).

Responses to 'Muddiest Part of the Lecture Cards'

(6 respondents, 65 in class)

1) I made it through the first test in 16.05; do you knnow if everything we covered there should be enough to survive here? (1 student) You should be able to do fine on this Unified material without seeing any of 16.05. If you are having troubles with it however, come and see me. I am happy to go over any of the material in more detail.

2) How valid is the expression for thrust that we derived since we assumed (among other things) perfect component efficiency? (1 student) When you get through 16.05 (if you aren't in it already), you can do the back-to-back comparison between ideal and non-ideal cycle analysis. You can also refer back to thermodynamics from the fall semester where we did a back-to-back comparision of an ideal analysis to the on-line MIT powerplant data -- we predicted 53% ideal cycle efficiency, compared to 28% measured efficiency. So the answer one gets is not very good, BUT the trends in performance with many of the typical design parameters are well captured.

3) Where can we find the Excel code? (1 student) Send me an email requesting it and I will give it to you.

4) No mud (3 students).