XR Flight Operations Manual Version 3.0
Copyright 2006-2018 Douglas Beachy. All Rights Reserved.
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Dynamic Pressure Gauge showing pressure in kilopascals
Try to keep the dynamic pressure between 8 and 20 kPa (
kilopascals)
initially,
depending on velocity. This will supply the SCRAM engines enough oxygen without
the ship being too low in the atmosphere and generating excessive heat, which
wastes fuel. If you fly your ascent correctly you should be able to reach Mach 17-20
before the engines reach their operational limit and you shut down the SCRAM
engines and switch to the main engines for orbit insertion.
Another important gauge to watch during SCRAM ascent is the
SCRAM Diffuser Temp
gauge; this shows the temperature of the diffuser in each engine where the incoming
air is compressed before it is combined with SCRAM fuel and ignited.
SCRAM Diffuser Temperature Gauge
The diffuser chamber walls are cooled by the cryogenic SCRAM fuel right before it is
injected; the operational limit of the engines is 8000 Kelvin. Since the SCRAM
engine is a RAMJET variant, the speed of the ship determines the temperature of the
compressed air in the diffuser. As you approach thermal limits the temperature of
the compressed freestream approaches the temperature of the ignited fuel/air
mixture, and so the thrust produced (and therefore engine efficiency) is reduced.
Once the engines reach their thermal limit they are unable to accelerate the ship any
further; at that point you should shut down the SCRAM engines and switch to the
main engines.
Note: the computer will automatically throttle-down the SCRAM engines as the
diffuser temperature approaches 8000 Kelvin, so do
n’t
be afraid to run the engines
right to the edge. As long as y
ou don’t run the
main
engines alongside the SCRAMS
the SCRAM engines will never overheat on an ascent running on SCRAM engines
alone.
However, remember to close the SCRAM doors (CTRL-G, or use the
switch on the upper panel) before you engage the main engines!
Otherwise
the diffuser temperature may exceed 8000K, which will overheat and likely damage