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60 4. WORKING WITH THE AIRCRAFT’S SYSTEMS
efficient inlet speed.
At the top of the middle column in the Jet Engine Specs box is the compressor area, given
in square feet. Specifically, this is the frontal area of the engine compressor, calculated as π times
the radius of the compressor for engines with the whole of their (round) compressors open to drag
effects. The compressor’s frontal area only has a significant effect on drag at low throttle settings.
Beneath the compressor area is the minimum N1 for fuel introduction, set as a percentage of
N1’s maximum speed. If fuel is introduced into the engine prior to this speed, a hot start (a start
that exceeds the maximum temperature the engine is designed to handle) may ensue. Beneath the
minimum N1 is the fan RPM at 100% N1, measured in rotations per minute.
At the top of the far right column in the Jet Engine Specs box is the “engine-start fuel intro
time”-the time, in seconds, that it takes to go from no fuel to idle fuel flow during the engine’s
starting process.
Beneath the fuel intro time is the “throttle advance time from idle to maximum.” This sets the
time in seconds that it takes the engine to go from idle to full torque if the throttle is commanded
instantly from idle to full. It is, more accurately, the time it takes N1 to bring in torque when the
throttle is moved to full.
The final parameter in the Jet Engine Specs box is the thrust-reverser deployment time, the
time in seconds that it takes the thrust reverser to deploy and retract.
Working with Rocket Engines
Rocket engines, like jets, are quite simple to set up in Plane Maker. Use the Location tab of the
Engine Specs dialog box to set the position of the center of the engine’s thrust (as described in
the section “Features Shared by All Engine Types” above). For a jet engine, this center of thrust
is usually the center of the exhaust nozzle. Check the “vectors” box in that tab if the engine will
vector.
After setting the rocket engine’s location, you can set its other characteristics using the “Rocket
Engine Specs” box (seen in Figure 4.15), located in the Description tab of the Engine Specs dialog
box.
Figure 4.15: The Rocket Engine Specs portion of the Description tab
Here, there are three parameter boxes for thrust. From left to right, these set the maximum
thrust of the rocket engine, in pounds,
• at sea level,
• at the engine’s design altitude, and
• in a vacuum.
In X-Plane, the engine can put out full thrust in all three conditions, though real rockets are
not always able to do so.