Tuesday, August 11, 2009

My Calculus Book Fails Rocketry

I was flipping through my calculus book this evening trying to avoid actually doing my summer assignments. I noticed that the Handbook of Model Rocketry (6th ed.) was cited as a source. To my disappointment, the authors of the book failed to actually comprehend the chapter on stability.

It shows a picture showing the profile of a rocket, with a triangle (conic) nose, rectangular (cylindrical) body, and a wider triangle for the fin section, as one would for the cardboard cutout method of finding CP. Unfortunately, it then talks about it as though it's a mass profile, and even says that "Rockets are designed with bottom fins large enough that the center of mass is shifted near the bottom of the rocket. This improves the flight stability of the rocket".

FAIL.

The purpose of large fins is to shift the surface area, and center of pressure, to the rear. The center of gravity should be near the front, and specifally in front of the CP, in order to be stable.

It looks like they read about the cardboard cutout method, but substituted mass for pressure.

More explanation later, hopefully.

2 comments:

@eloh said...

You should write a letter to the publisher of your textbook.

They may have you review some material for them one day.

The EGE said...

Heh. I wish. I think I will write them a letter, though.