Problems that arise when using an (arbitrary) value of GLOW
Problems that arise when using an (arbitrary) value of GLOW
(1) The initial guess for GLOW results in unrealistically
low values of Wi.
Wi can often be zero or even negative!
(2) There is a definite relationship between Wi and Wp,
called the
Propellant mass fraction, Lp, which the resultant values
of Wi and Wp
must satisfy. That relationship is Lp = Wp/(Wp+Wi). Where
Lp is
specified by the designer as 0.7, 0.8, even 0.9
(3) A proper range for the GLOW can be systematically
found using the
check formula for Propellant mass fraction, Lp, above.
For example,
Lp = 0.8 indicates a stage which is 80% propellant mass
and 20% inert
mass. If the pair Wi, Wp are equal to or less than 0.8
it indicates the
GLOW is in a realistic range.
(4) This technique is laborious but it works for SINGLE
stage rockets.
Can it be applied to multistaged vehicles too?
Copyright (c) 2000 by Rainier Anacker