(2) The value of h, is of the order of 25 to 30 ft-lb/in.2 for aircraft hose. The value of β is approximately 0.2 to
(3) For example, the M3A1 thruster is designed to bypass gas into a 3/16-inch (inside diameter) A hose at the
end of its stroke. The parameters from chapter 6 are:
Thruster: Pf = 5,700 psi
Vd = 1.30 in.3
γ = 1.25
Vt = (0.1 † + 0.0276Lt) in.3
Lt = tube length, in.
St = 0.59Lt
(4) These values are substituted in equation (49) using ht = 26 ft-lb/in.2 and β = 0.3. The curve which results is
given in figure 51 as hose pressure, Pt, versus hose length, Lt, and it follows the experimental curve
closely enough to confirm the choice of the various parameters.
Figure 51. Experimental and calculated bypass pressure for MSA1 Thruster.
c. Locked-Shut Requirements.
(1) An estimate of the locked-shut pressure in a thruster can be obtained from the equation of state by making
a few assumptions:
In terms of charge weight, C, and propellant impetus, F,
Vt = initial thruster volume
(2) The factor 0.54 is estimated as follows:
(a) The peak pressure is assumed to occur when only 90 percent of the propellant has been consumed.
(b) In systems that use propellants with "large" webs (w>0.3), it is safe to assume that the pressure is
reduced by about 40 percent due to dissipation of heat to the walls of the device.
† The additional 0.1 in.3 is for end block and gas volume, etc.