It has previously been asserted on this list that while the surface to
volume ratio of a rocket declines as diameter increases (by the square); it
is not the case that rockets become relatively lighter as diameter
increases because the wall thickness required to hold a constant pressure
increases as diameter increases; or at least that is what I have previously
understood.
This has gnawed at my ankles for some time, so, because my shop is down
today to bringing in more power, I sat down this afternoon and gave this
some thought.
Numerically, it does not appear to be so: the mass to diameter ratio
increases by a factor of four with every doubling of the diameter.
I assume that the wall thickness doubles with a doubling of diameter to
hold a constant pressure and that wall density is constant. I am
accordingly led to conclude that tank mass decreases by the square (not
linearly) as diameter increases.
Have I misunderstood the previous claims about there being no “volumetric
effect” with scale?
Bill
