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Working with the Aircraft's Systems

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An aircraft’s systems include electrical, hydraulic, fuel, avionics, flight control, and propulsion sub-systems. In addition to influencing the flight model as appropriate, these systems can be set to fail in X-Plane, allowing pilots to practice dealing with contingencies.

Contents

Creating the Engines

The aircraft’s engine, along with any related propellers, thrusters, and so on comprise its propulsion sub-system.

To begin creating an aircraft’s engine, open the Standard menu and click Engine Specs. The Location tab of the Engine Specs window is the best place to start. There, you can set the number, type, location, and other properties of both the engines and propellers. The parameters available here will vary depending on what type of engine(s) you choose.

To begin, set the number of engines present on the aircraft using the box at the top of the window. A number of columns will appear, one for each engine you specified. Use the drop down menu at the top of each column to set the type of each engine. The engine type will determine what further parameters are available for the engines. It will also affect, among other things, the sounds produced by the engine and the fuel flow it draws.

The following types of engines are available here:

  • carb recip—an internal combustion, reciprocating (piston) engine used to drive a propeller. It uses a carburetor to mix air with fuel at low pressure.
  • injected recip— an internal combustion, reciprocating (piston) engine used to drive a propeller. It uses a fuel injector to mix air with fuel at high pressure. Fuel-injected engines are for more common today than carbureted ones, due partly to their increased reliability.
  • turboprop (free)—an internal combustion, gas turbine engine used to drive a propeller. Gas turbines are more reliable than reciprocating engines. A free turboprop engine is one whose power turbine is not geared to the gas turbine’s compressor, allowing the propeller to operate independent of the compressor speed. This is the most common turboprop design. [tk] right?
  • turboprop (fixed) —an internal combustion, gas turbine engine used to drive a propeller whose power turbine is geared to the compressor. [tk] right?
  • electric—an engine that draws electrical power from fuel cells, solar panels, or the like and uses it to drive a propeller.
  • low bypass jet—an internal combustion, gas turbine engine with a low ratio of air coming into the engine and bypassing the engine core compared to the amount of air passing through the core. Low-bypass turbofans are, in general, more fuel efficient than turbojets but less efficient than high-bypass turbofans. Low-bypass turbofans are often used in jet fighters in conjunction with an afterburner. [tk] check w/Austin
  • high bypass jet—an internal combustion, gas turbine engine which has a high ratio of air coming into the engine and bypassing the engine core compared to the amount of air passing through the core. High-bypass turbofans are more fuel efficient than low-bypass ones, but generally have a lower top speed and greater weight. [tk] check w/Austin
  • rocket—a reaction engine which harnesses the acceleration of mass shooting out of its exhaust nozzle as propulsion.
  • tip rocket—a rocket engine typically attached to the tip of a helicopter’s rotors, used to turn the rotors without the use of a tail rotor. [tk] check w/Austin

The following steps to set up an aircraft’s engines will depend in large part on which engine type(s) you selected. There are, however, a few features that all engine types have in common.

Features Shared by All Engine Types

Regardless of the engine type selected in the Location tab, a few characteristics of the engine must be set. These include the engine’s location, its fuel consumption properties, and the altitudes at which it performs best.

Location

All engine types must have a position specified in the Location tab. This is done using the standard position controls (as described in the section “Fundamental Concepts” of Chapter 3), plus a vertical and side cant. Positive values for the vertical cant will cause the engine to point upward. Positive values for the side cant will cause the engine to angle right (clockwise) when viewing the aircraft from above.

All engine types also have the option to be vectored, using the checkbox beneath the side cant parameter. For information on using a vectored thrust, see the section “Creating Helicopters and VTOL Aircraft” in Chapter 11.

Throttle Settings

In addition to their location, all engines must have a few characteristics of their throttle set. These are found the Description tab of the Engine Specs window, in the General Engine Specs box there. Figure 4.1 shows the parameters relevant to most engine types.

The first of these are the maximum forward and maximum reverse throttle. These control the maximum throttle available in X-Plane with all engines operative (at sea level in standard atmosphere). This can, among other things, be used to fine-tune an engine’s performance to match measured performance in the real world. It is not uncommon to use a maximum throttle of, say, 0.80 in order to match an engine’s real-world performance, as manufacturers will often keep an engine within 75 or 80% of the nominal power to ensure safe, reliable performance. Allowing over 100% power also makes sense when leaving some reserve power for emergency operations.

Note that all engine specifications in Plane Maker are set with respect to full throttle. Thus, if you move the maximum throttle away from 1.00, the engine characteristics set throughout Plane Maker will not match the performance in X-Plane. This isn’t necessarily a problem, but you should keep it in mind.

Figure 4.1: Throttle settings in the Description tab’s General Engine Specs box

For engines that cannot be set in reverse, the maximum reverse throttle will be zero.

Beneath the “max forwards” and “max reverse throttle” parameters is the maximum emergency throttle, which sets the maximum throttle available when an engine failure has occurred. [tk] ask Austin why this is the same??

Next are the low and high idle adjustment boxes. Plane Maker will automatically estimate where the engine idles, both in a low-idle situation and a high-idle one. Use this box to change the idle speed, as a ratio of the default Plane Maker estimate.

Beneath the idle adjustments is the “go to Beta below this throttle setting” box. In engines that feature reverse thrust, the Beta range serves to maintain a constant RPM while varying the blade pitch, allowing finer control of the aircraft’s speed while on the ground. Use this parameter box to set the ratio of the joystick’s throttle at which to switch into Beta conditions. For instance, if you wanted to go to Beta when the joystick was at 25% of its throttle range, you would set this box to 0.25.

Beneath the “go to Beta” box is the “go to reverse thrust below this throttle setting.” In engines capable of it, reverse thrust pushes the aircraft backward—quite useful when trying to land a large aircraft in a short distance. Just like the corresponding Beta parameter above, this is set as a ratio of the joystick’s throttle. Both Beta and reverse modes are virtually ubiquitous in both turboprops and jet engines. Likewise, they are uncommon in reciprocating engines.

The final setting in the Description tab which may be applicable to both propeller-driving and jet engines is the “turbine spool-up time,” seen in the bottom of Figure 4.1. This number is determined by the amount of inertia the engine has, and is applicable only to turbine engines, such as turboprops and jets. It is a measure of how long it takes the low-pressure compressor (N1) to speed up to its maximum when the throttle is brought instantly from idle to full. In X-Plane, the actual spool-up time will be affected by atmospheric conditions, the weight of the propeller (if applicable), and the time it takes the pilot to advance the throttle.

Critical Altitude and FADEC Characteristics

Without modification, most engines put out less power the higher they go. The thinner air at high altitudes simply provides less oxygen to burn. Because of this, most aircraft have a critical altitude—a height above sea level above which they can no longer produce full power. At altitudes below this, full power is still available. Figure 4.2 shows the Critical Altitude box, found at the top of the Engine Specs window’s Description tab. In that box, the “critical altitude” setting is specified in feet above mean sea level.

Figure 4.2: The Critical Altitude box in the Description tab of the Engine Specs window

To the right of the critical altitude parameter box are three checkboxes for adding a FADEC, a Full Authority Digital Engine Control. A FADEC system is designed to control all aspects of the engine’s performance. One advantage to having a FADEC is that, on reciprocating engines, it can maintain the perfect fuel-to-air ratio, which means… [tk] ask. The FADEC can also keep a propeller-driving engine within its safe RPM limits, as the second checkbox down in Figure 4.2 notes. Finally, a FADEC can keep the engine from exceeding the maximum allowable thrust, as the final checkbox in Figure 4.2 notes. This can also be done by the automatic wastegate in a turbocharger—in this case, the same box should be checked.

Boost Characteristics

All combustion engines (both jet and reciprocating) can have a boost applied to them. This can come in two forms: an anti-detonant, or a nitrous oxide (N2O) boost. When an anti-detonant is injected into an engine, the engine’s combustion chamber is cooled, increasing the density of the gases in the engine and increasing the engine’s compression ratio. It also serves to cool the engine, allowing it to run at a higher RPM than it otherwise would be able to. Nitrous oxide, on the other hand, decomposes quickly when it is injected into an engine. When it does, it increases the amount of oxygen available during combustion. Like an anti-detonant, the vaporization of N2O also cools the engine.

To tell Plane Maker that your aircraft has a boost, go to the Engine Specs window’s Description tab. There, in the bottom right of the box labeled “Prop Engine Specs,” are the two parameters for boost. Note that, although these are found in the Prop Engine Specs box, they apply to all engines in X-Plane.

Figure 4.3: The boost settings, found in the Description tab of the Engine Specs window

X-Plane will not differentiate between the source of your boost, whether anti-detonant or nitrous oxide. Instead, it just needs to know how much of a boost your method gives. Set the “boost amount” box to the amount of boost you get from the engine, as a ratio to the normal, non-boosted engine’s performance. Thus, if your nitrous oxide system increased the power of your engine by 50%, you would set the “boost amount” parameter to 0.50.

Next, set the “boost capacity” box to the length of time, in seconds, that you can use your boost before it runs out.

To use the boost in X-Plane, simply push the throttle to its the maximum; the boost will automatically kick in.

Specific Fuel Consumption

After setting up the basic characteristics of a propeller or jet engine, you can set the engine’s specific fuel consumption. One box in the SFC/Sound tab (which is itself found in the Engine Specs window) is labeled “Reciprocating or Turboprop Specific Fuel Consumption,” as seen in Figure 4.4. Another is labeled “Jet Engine Specific Fuel Consumption.” These boxes are identical except for the types of engines they affect.

Figure 4.4: The reciprocating or turboprop specific fuel consumption

Using these boxes, you can define the engines’ specific fuel consumption (SFC)—that is, the amount of fuel burned per hour per engine horsepower. This should be set for two altitudes, one low and one high, and each altitude should have a half-power and full power SFC.

For propeller-driving engines, the measurement used here is the brake specific fuel consumption (BSFC), entered in the “Reciprocating or Turboprop” box. This is calculated as fuel flow divided by horsepower (as measured at the engine’s output shaft, before any transmission losses occur).

For jet engines, the thrust specific fuel consumption (TSFC) is used, and it is entered in the “Jet Engine” box. TSFC is calculated as fuel flow divided by thrust.

In most cases, the “lo altitude for prop engines” (the low altitude at which you’ll specify the SFC) is zero feet above mean sea level. The “hi altitude for prop engines” may be your cruise altitude, but it doesn’t have to be. Both these controls are found in the left half of the Reciprocating or Turboprop SFC box.

In the right half of each box, the “half power SFC” for each altitude should be set to the specific fuel consumption in pounds of fuel per hour per horsepower of the engine when the engine is at half power. For instance, if a given engine burned 100 pounds of fuel per hour, and it had a 200 horsepower engine, it would burn 0.5 pounds per hour per horsepower. If that was the fuel consumption at your low altitude at half power, you would enter 0.500 in the “lo altitude half power SFC” box.

The “max power SFC” box works the same, but it specifies the fuel consumption at full power for each altitude.

Finally, in the bottom of the SFC box is the engine’s fuel flow at idle, as a ratio of the aircraft’s maximum fuel flow. If your aircraft used 0.1 times the fuel at idle as it does at full power, you would enter 0.10 here.

Note that specific fuel consumption in rocket engines is much simpler than in combustion engines; the SFC parameter found in the bottom right of the Engine Specs window’s Description tab applies at all altitudes, at all power settings, for rockets. It defines the pounds of fuel burned per hour for each pound of the engine’s thrust. Note also that the specific fuel consumption is the inverse of the engine’s specific impulse (Isp), the number usually discussed in relation to a rocket’s fuel consumption.

Engines Capable of Zero-G Flight

Some engines need to be capable of zero-G flight, or sustained flight at a pitch of 90 degrees. This is most often seen in rockets and space ships. To model this in X-Plane, you must tell Plane Maker that the craft has an inverted fuel and oil system. To do so, open the Special Equipment dialog box and check the “inverted fuel and oil system” box in the upper right.

Working with Engines That Turn Propellers

Both of the reciprocating engines, as well as the turboprop, electric, and tip rocket engines all are used to turn propellers (or rotors, as the case may be). In this case, you must specify the number of propellers and their features.

Near the top of the window, right beneath the engine number and type settings, are the settings for the number and type of propellers. In nearly all cases, there will be one propeller per engine.

The following types of propellers are available in Plane Maker:

  • fixed—a propeller whose angle of attack (or blade pitch) is fixed.
  • constant RPM—often referred to as a “constant speed” or “variable pitch” propeller, this propeller will change the blades’ pitch in order to generate greater thrust while keeping a constant number of revolutions per minute (RPM).
  • manual pitch—
  • main rotor—
  • constant tip Mach—this propeller adjusts its speed so that its tips always move at a constant Mach number, usually resulting in a more efficient flight than constant RPM propellers.
  • tail rotor—
  • lift fan—
  • VTOL cyclic—

[tk] descriptions from Austin

Each propeller you specified will have its own column of settings, just like each engine does; the propeller settings will be integrated to the engine settings columns.

Figure 4.5: Some basic propeller settings

Beneath the propeller number and type settings is the “number of blades” control, as seen in Figure 4.5. This number can be set independently for each propeller. Immediately to the right of the number of blades is the direction of spin, also in Figure 4.5. This is set either to clockwise (CW) or counterclockwise (CCW), as seen when looking at the aircraft from behind.

To the right of the blade direction setting are three checkboxes, seen in Figure 4.5. The “engine clutched” and “prop clutched” boxes are used with helicopters and autogyros, respectively. For more information on these, see the section “Creating Helicopters and VTOL Aircraft” in Chapter 11.

The final checkbox in Figure 4.5, labeled “prop ducted,” is used with ducted fans—propellers mounted inside a cylindrical shroud. Ducted fans are also found in Fenestron tail rotors and lift fans (as in the F-35B). A very straightforward ducted fan is found in the Martin Jetpack, as in Figure 4.6.

Figure 4.6: The Martin Jetpack, with its ducted fans (thanks to Flickr user martinjetpack for the photo)

Beneath the engine’s location controls are the propeller settings, as seen in Figure 4.7.

Figure 4.7: The propeller specifications, found in the bottom of the Location tab

The first of the propeller specifications, the prop radius, sets the distance in feet from the center of the propeller to the tip of one of its blades.

Beneath the prop radius are the settings for the propeller’s width. The “root chord” parameter (the left one of the pair) sets the width of the propeller in inches at its base, where it meets the aircraft body. The tip chord, likewise, is the width in inches at the propeller’s tip, where it is farthest from its mounting place on the aircraft.

The minimum and maximum pitch set the range, in degrees, over which the blade can change its angle of attack (pitch). This angle is measured at the propeller’s tip. Constant-RPM and manual pitch propellers, among other propeller types, vary their blade pitch to achieve a desired thrust at a constant blade speed. [tk] be sure with Austin Set the minimum pitch using the box on the left and the maximum using the one on the left. Typically, the minimum pitch is zero degrees, meaning the blades are “flat” against the wind they are moving into.

Beneath the pitch parameters is the “design RPM” parameter. This sets the speed, in revolutions per minute, that the propeller is optimized for.

Next are the “design spd acf, prop” settings. The first (on the left) is the speed of the air, in knots, that the propeller is optimized to have passing through it. For airplanes, this is approximately equal to the forward speed of the plane that you want to optimize for plus half the propwash. For helicopters, it should be the half the propwash only, since a helicopter’s forward speed is only a small component of the airflow into the rotor from above.

The second parameter, the design speed of the propeller, is the maximum airspeed, in knots, of the propeller at its tip. If the propeller would otherwise exceed this speed, X-Plane will sweep it back in order to stay at or below this speed. For propellers that should not be swept back, simply enter a very large number here.

Based on the radius, design RPM, and design speed of the propeller, Plane Maker will automatically calculate an angle of attack for the length of the propeller. To modify this angle of attack, see the section “Customizing the Propeller” below.

The final setting for propellers in the Location tab is the engine-to-gear ratio, found at the bottom of the window. This is the number of times the engine rotates for each rotation of the propeller. This is most commonly set to 1.000: for each rotation of the engine, the propeller rotates once.

Setting the Engine Details

After setting the engine’s location and the basic features of its propeller, you can set the details of its engine performance, such as its horsepower and the RPM for various modes.

Most of these details for a propeller-driving engine are set in the box labeled “Prop Engine Specs,” located in the Engine Specs window’s Description tab and shown in Figure 4.8. Other engine details, like the maximum throttle and the critical altitude, are common to all engine types, and are described in the section “Features Shared by All Engine Types” above.

Figure 4.8: The Prop Engine Specs box, found in the Description tab of the Engine Specs window

In the upper left of this box is the engine’s maximum allowable power. This is the maximum horsepower output at sea level with standard atmosphere.

Beneath the “maximum allowable power” control are the RPM values at which the engine redlines and idles. The redline RPM sets the maximum allowable rotations per minute for the engine, and the idle RPM sets the speed at which the engine turns when the throttle is set to zero. Reciprocating engines typically redline between 2,000 and 3,000 RPM.

Beneath the redline and idle RPMs is the “transmission losses” parameter. All aircraft lose some power in the transference of energy from the engine to the actual turning of the propeller; this is power lost to the transmission. The “transmission losses” box sets this loss as a ratio to the full power coming from the engine. Thus, a value of 1.000 here would mean that 100% of the power from the engine is lost in the transmission. Airplanes typically have losses between 0.00 and 0.02.

Note that the “transmission losses” value should include all drags on the engine, including any generators, belts, chain drives, etc. which take away from the engine’s output.

The center column of the Prop Engine Specs box has three boxes, corresponding to three different engine RPM limits. The top box, “top of green arc,” sets the maximum engine RPM that can be set using the prop control in X-Plane—the maximum RPM seen under normal operation. This should probably be close to the engine redline RPM set to the left.

Beneath the “top of green arc” box is the “bottom of green arc” parameter. This sets the minimum engine RPM that can be set using the prop control in X-Plane.

The final RPM limit here is the “minimum prop governor engine RPM,” found at the bottom of the center column of values. This parameter sets the lowest RPM that can be obtained in X-Plane by pulling the prop control back. This does not take into account reverse, Beta, or feathered modes. For these, you will simply set the propeller pitch using the controls in the bottom of the General Engine Specs box to the left and X-Plane will automatically calculate an appropriate RPM. (For information on setting these pitches, see the section “Customizing the Propeller” below.)

In the column to the right of the engine RPM limits are a few miscellaneous settings. The top one, “engine-start fuel intro time” sets the time (in seconds) it takes fuel introduction to go from zero fuel flowing into the engines to the idle amount during the engine’s start process.

Beneath the “fuel intro time” is the “throttle advance time idle to max” parameter. 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. For turboprops, this is the amount of time it takes the low-pressure compressor (N1) to bring in torque when the throttle is brought to its maximum.

Note that the final settings in the Prop Engine Specs box, both of which deal with the boost, are described in the section “Boost Characteristics” above.

tk non-jet exhaust from bottom of SFC/Sound tab

Customizing the Propeller

The propeller is initially created in the Location tab of the Engine Specs window. As discussed in the section “Working with Engines That Turn Propellers” above, the Location tab specifies the propeller’s size, pitch, and design RPM. In many aircraft, though, there is much more to the propeller than that.

In the far left of the Description tab in the Engine Specs window is a box labeled General Engine Specs. The top half of the box deals with the throttle settings of many or all types of engines, and is thus described in the section “Throttle Settings” above. The bottom half, however, is all about propellers.

Figure 4.9: The bottom half of the General Engine Specs box

The first characteristic of a propeller that can be set is the feathered pitch of the prop, as seen at the top of Figure 4.9. This sets the pitch of the propeller, in degrees, when it is feathered. A featherable propeller is one whose blades can be rotated to be parallel to the air flowing over them. In the case of engine failure, feathering a propeller reduces the drag it generates by a huge amount. For instance, Figure 4.10 shows a C-130 Hercules with the blades of its propellers angled to attack the wind with as small a profile as possible; its propellers are feathered.

Figure 4.10: A C-130 Hercules with its propellers feathered

Beneath the feathered pitch of the propeller is its Beta pitch, seen in Figure 4.9. This sets the pitch of the propeller, in degrees, when it is in its Beta range. In engines that feature it, the Beta range serves to maintain a constant RPM while varying the blade pitch, allowing finer control of the aircraft’s speed while on the ground.

Next in Figure 4.9 is the “reverse pitch of prop” setting. Like the previous parameters, this defines the pitch of the propeller, in degrees, when it is in reverse-thrust mode.

The “propeller mass ratio” parameter determines the density of the propeller, which affects how easily the propeller speeds up and slows down. This is set as a ratio to the density of solid aluminum. Aluminum has a density of 2700 kg per cubic meter, so if your propeller had a density of, say, 1000 kg/m3, you would set this to 1000 / 2700 = 0.37.

The next parameter down in Figure 4.9, “tip weights on rotors,” is used in helicopters and VTOLs only; for information on these aircraft, see the section “Creating Helicopters and VTOL Aircraft” of Chapter 11.

The final two parameters in the General Engine Specs box are for constant-Mach propellers. These set the speed of the propeller’s tip at full and half throttle, respectively, as a ratio of the speed of sound. X-Plane will automatically interpolate between these values at other throttle settings.

At this point, most of the characteristics of the propeller have been set, from its pitch settings to its weight. What we have not yet discussed is fine-tuning the shape of the propeller. For instance, in our discussion of the Location tab, we set the width of the propeller at its root and tip, and we set the length of the propeller’s blades. What about the width of all the points in between? We also have not touched on the twist of the propeller, the angle of incidence for each “slice” of the propeller.

Each of these shape settings is controlled by the Propeller tab of the Engine Specs window, as shown in Figure 4.11.

Figure 4.11: The Propeller tab of the Engine Specs window

Each blade of the propeller is broken into nine pieces, and each piece has three parameters that can be set. These parameters are the chord ratio, chord offset, and angle of incidence, as seen in Figure 4.12.

Figure 4.12: The three settings for each slice of the propeller

The “chord ratio” parameter controls the width of each slice of the propeller. This is set as a ratio of the default width of each chord, which Plane Maker finds by linearly interpolating between the root and tip width.

The “chord offset” parameter sets the amount up or down that the center of each propeller piece is shifted. This is set as a ratio of the chord width. For instance, if a certain section of the propeller needed to be shifted in the opposite direction from the way the propeller turns by one-tenth the width of the propeller at that point, you would set that piece’s chord offset to 0.100.

The last option available in the Propeller tab is the angle of incidence for each piece. By default, Plane Maker will calculate an appropriate angle of incidence based on the radius, design RPM, and design speed of the propeller. To modify the angle of incidence, first check the box labeled “check here to set prop element incidence manually.”

The final element of the propeller’s shape which we have yet to set is its cross-sectional shape (the airfoil it uses). To define this, open the Airfoils window from the Expert menu. The first tab at the top of the window, labeled Props, is used for the propeller’s airfoils. For information on using the controls in the Airfoils window, see the section “Setting a Wing’s Airfoils” in Chapter 3.

Setting Up Solar Cells

If solar cells on the wings are to be used (in part or in whole) to power an electric engine, the two solar power settings in the SFC/Sound tab must be set appropriately. Shown in Figure 4.13, these are the solar cell coverage on the wing, as a ratio of the whole wing area, and the solar cell efficiency, as a ratio of perfect efficiency.

Figure 4.13: The solar panel settings

Most solar cells have an efficiency between 5% and 20% (a ratio to perfect efficiency of between 0.05 and 0.20). At noon, the sun puts out about 1400 watts of power per square meter in space, which is reduced to about 1000 watts per square meter at sea level. A good guess for middling altitudes is 1100 watts from the sun. The equation to find the power in watts available from the solar cells is:

Wings surface area x Solar cell coverage x Solar cell efficiency x Power coming from the sun

Divide this number by 760 to convert the power in watts to horsepower.

Working with Jet Engines

Jet engines are much simpler to set up in Plane Maker than propeller-driving engines. Use the Location tab of the Engine Specs window 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 exhaust. Check the “vectors” box in that tab if the engine will vector (and read more on setting up a vectoring engine in the section “Creating Helicopters and VTOL Aircraft” of Chapter 11).

After setting the engine’s location, you can set the details of its performance, such as its thrust characteristics and N1 speed, using the Engine Specs window’s Description tab.

The Description tab’s “Jet Engine Specs” box, seen in Figure 4.14, controls the relevant parameters here.

Figure 4.14: The Description tab's Jet Engine Specs box

The parameter in the upper left, the engine’s maximum allowable thrust, defines the thrust output at 100% N1 (the low-pressure compressor) speed, as measured under standard atmospheric conditions. Note that many engine manufacturers rate their engines at their take-off thrust, which is often not 100% N1. Thus, the thrust specifications from a manufacturer may be under-rated.

Beneath the maximum allowable thrust is the “afterburner thrust inc,” the increase in thrust provided by the afterburner. This will be added to the value in the “maximum allowable thrust” field when the afterburner is at full power.

Beneath the afterburner increase is the “max efficient inlet mach,” the maximum speed as a proportion of the speed of sound at which the inlet can pass air into the engines efficiently. The geometry of any intake will allow it to funnel air into the engine only up to a certain speed; past that, the force of shock waves hitting the inlet make it much, much less efficient. Many real aircraft have variable intake geometries as a means of counteracting this effect and extending the maximum 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. This parameter does not affect the flight model; it is used only to enable RPM gauges in jets, and to scale the pitch of sounds based on N1 speed. [tk] right?

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 window 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 (and read more on setting up a vectoring engine in the section “Creating Helicopters and VTOL Aircraft” of Chapter 11).

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 window.

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.

Beneath the three thrust settings is the engine’s optimum altitude, the altitude at which the rocket achieves maximum thrust, in feet above mean sea level.

In the upper right of the Rocket Engine Specs box is the “nozzle exit area” parameter, the size of the exhaust nozzle. This is used only to calculate how large an exhaust flame to display in X-Plane.

The final parameter in the Rocket Engine Specs box is the engine’s specific fuel consumption (SFC). Specific fuel consumption in rocket engines is much simpler than in combustion engines; this parameter applies at all altitudes, at all power settings. It defines the pounds of fuel burned per hour for each pound of the engine’s thrust. Note that the specific fuel consumption is the inverse of the engine’s specific impulse (Isp), the number usually discussed in relation to a rocket’s fuel consumption.

Working with Twin- and Multi-Engine Aircraft

Creating multiple engines in Plane Maker is quite straightforward; in the Location tab, each engine has its position defined independently (as described in the “Location” section above), as well as its propeller characteristics, if applicable, as described in the “Customizing the Propeller” section above. Engines of the same type (propeller-driving, jet, or rocket) are assumed to have the same characteristics—that is, all propeller-driving engines on an aircraft will have the same maximum allowable horsepower, the same redline RPM, and so on.

The only thing significantly different about setting up multiple engines is the use of the Engine Specs window’s Transmission tab. This, of course, applies only to engines that turn propellers.

Most aircraft designs will have one transmission per engine. Thus, a single-engine aircraft will have a single transmission, a twin-engine aircraft will have two transmissions, and so on. Exceptions are designs which use a common transmission to connect multiple engines to multiple propellers, as seen in the V-22 Osprey, as well as helicopter designs, where all rotors are geared together.

The number of transmissions is defined in the far left of the Transmission tab, seen in Figure 4.16.

Figure 4.16: The Engine Specs window's Transmission tab

To the right of the “number of transmissions” parameter are the transmission settings for each engine and each propeller; engine settings are in the center of the window, and propeller settings are on the right. With multiple engines created in the Location tab, there will be one row of settings for each engine. Note that the topmost engine here corresponds to the leftmost engine in the Location tab, and the topmost propeller here corresponds to the leftmost propeller in the Location tab.

Each engine can drive one transmission, as defined in the “transmission that this engine feeds” box. Each propeller, in turn, can be driven by one transmission (set in the “transmission that feeds this prop” box). Thus, in a twin-engine plane, the port-side engine might feed transmission 1, and the port-side propeller would be fed by transmission 1. The starboard-side engine, then, would feed transmission 2, and the starboard-side propeller would be fed by transmission 2.

For information on setting up transmissions in helicopters and other VTOL aircraft, see the section “Creating Helicopters and VTOL Aircraft” in Chapter 11.

Setting Up Electrical, Hydraulic, and Pressurization Systems

The electrical and hydraulic sub-systems of an aircraft are used to drive instruments, lighting, and flight controls. The pressurization system keeps the air pressure in the cabin at a comfortable level. These systems are modeled in Plane Maker using the Systems window, found in the Standard menu.

Configuring the Electrical System

The electrical system is configured using the Systems window. The Electrical tab sets the sources of electrical power, as well as the number of buses and inverters, so it is a good place to start when setting up the system.

Note that the aircraft will have one battery for every battery button present on the 2-D instrument panel, and one generator for every generator button on the panel.

Figure 4.17: The Systems window’s Electrical tab

In the Sources box, the parameter on the left sets the battery’s capacity, measured in watt-hours. The battery will only be considered if more amperage is required by your electronics than is available from the generator, as might occur in a generator failure or when taxiing in some aircraft. A good estimate for light aircraft is a 1,000 watt-hour battery.

If the aircraft also has an air-driven backup generator to power the electrical system, check the box on the right side of the Sources portion of the window.

An aircraft will often have several different electrical distribution networks, called buses. These buses are often separated and powered by separate generators and batteries so that the failure of one bus will not cause electrical failure across the rest of the aircraft. In this case, a switch inside the aircraft will “tie” the buses together so that the still-working buses can power the failed ones.

Set the number of buses, batteries, and generators using the corresponding parameters in the “Batteries, Generators, and Buses” portion of the window. If you have more than one bus, specify which bus each battery and generator feeds using the input boxes at the bottom of the “Batteries, Generators, and Buses” box. Finally, if the buses are always tied, check the box labeled “buses always cross-tied.” In this case, all engines and batteries will feed all buses.

Finally, the “Inverters” box in the Electrical tab specifies the number of power inverters and which systems are connected to them. Inverters are most commonly used for backup power, turning DC power from the batter into AC power for (most) electronics. [tk] right?

With the backbone of the electrical system configured, you can use the Systems window’s Bus 1 and Bus 2 tabs to specify how much amperage each electrically-powered subsystem requires and from which bus it draws its power. To the right of each subsystem’s label are up to four checkboxes, corresponding to buses 1 through 4 (with buses 1 and 2 corresponding to the top two checkboxes and buses 3 and 4 to the bottom two checkboxes). For instance, in Figure 4.18, the de-icing subsystem’s window heater is drawing 6 amps from bus 1.

Figure 4.18: A single electrical subsystem, drawing 6 amperes from bus 1

In addition to the subsystems, there may be a base load on each of the buses—that is, some number of amps drawn at all times, regardless of what other electronics are powered on. The base load for each bus is set in the upper left of the Bus 1 tab. Note that generator loads will be affected by the bus that each system is attached to, and the amperage drawn from it.

If the bus powering a system fails in X-Plane—that is, if the battery and generator for the bus are off, the bus cross-tie is off, and there is no APU running for the bus—that system will fail.

Configuring the Hydraulics System

The hydraulics system is configured in the Systems window’s General tab. Here, the boxes labeled “Hydraulic Sources” and “Hydraulic Systems that Depend on Hydraulic Sources” represent the basics of the hydraulic system.

Figure 4.19: The “Hydraulic Sources” and “Hydraulic Systems that Depend on Hydraulic Sources” boxes of the Systems window’s General tab

X-Plane can model up to four hydraulic pumps: one powered by the electrical system, one powered by a ram air turbine, and two powered by the engine. Check the boxes in the Hydraulic Sources portion of the General tab corresponding to the pumps your aircraft uses.

Each type of pump has a different max pressure, set beneath the pump’s checkbox. The units on the maximum pressure are not specified; the hydraulics modeling is not detailed enough for the units to matter, so they can be anything. The only thing that matters here is the ratio between the different pumps, and it only matters then in the case of failure.

To the right of the hydraulic sources are the systems that depend on the hydraulics. If the hydraulic pumps fail, the systems represented by each checked box will also fail.

Most of the systems here are self-explanatory. The final one, the stick shaker, is a device that rapidly vibrates the control yoke as the aircraft approaches a stall. In X-Plane, this is indicated by a loud noise. If the stick shaker box is checked near the bottom of the “Hydraulic Systems that Depend on Hydraulic Sources” box, the stick shaker will fail along with the hydraulic system.

The box labeled “manual reversion” controls the extent to which, following a hydraulic system failure, the flight controls continue to operate. This is set as a ratio of their normal full operation.

The group of settings in the middle specifies how the landing gear fails in the event of a hydraulic failure. If the landing gear depends on hydraulics, it can have one of three behaviors in the event of failure: it can remain retracted, remain extended, or extend and remain there if the craft’s indicated airspeed is below a certain threshold. Select the radio button appropriate for your aircraft here. If the “fail down below…” option is selected, you must also set the threshold speed, in knots indicated airspeed.

Configuring the Pressurization System

An aircraft’s pressurization system is set up using the Pressurization box (seen in Figure 4.20) found in the General tab of the Systems window. There, use the “maximum allowable pressurization” field to set the cabin pressure that the system is capable of providing, measured in pounds per square inch (psi). Standard atmosphere on Earth is 14.7 psi at sea level.

Figure 4.20: The Pressurization box, found in the General tab of the Systems window

To the right of the maximum allowable pressurization is the emergency pressurization altitude. When the “dump to emer alt” button is pressed in the aircraft’s panel in X-Plane, this is the altitude that the pressurization system will match.

Checking the top box on the far right, labeled “auto-manage pressurization,” will cause X-Plane to control the pressurization, maintaining the air pressure of 7,500 feet above mean sea level until the maximum allowable pressurization is reached.

Checking the bottom box on the far right, labeled “dump pressure below 1000 ft,” will cause the pressurization system to equalize pressure with the outside air when the altimeter reads 1000 feet.

Configuring the Avionics System

The avionics system is comprised of the electronics used on an aircraft, including the systems used for navigation, communication, and the monitoring of other systems’ performance. Most of the avionics setup in X-Plane is performed when designing the panel, as described in Chapter 5, Creating an Instrument Panel. When designing the panel, you will add the specific instruments your aircraft uses.

Configuring Instrument Performance Ranges, Display Limits, and Colors

Prior to adding the instruments themselves (again, as described in Chapter 5, Creating an Instrument Panel), you can configure the instrumentation’s “back end,” the features of the instruments which will change based on your aircraft’s specifications. This includes performance ranges, which are set in terms of red-line, yellow, and green ranges. Additionally, it includes the instruments’ display limits, such as the maximum speed displayed by the airspeed indicator.

The aircraft’s performance ranges are set using the Limits 1 and Limits 2 tab of the Systems window (found in the Standard menu). These tabs are used to set the operational and limiting temperatures, pressures, voltages, etc. of various systems on the aircraft. This information should be available in the aircraft’s Pilot’s Operating Handbook (POH). Note that this information is not used in the flight model; it controls only what the instruments display.

Figure 4.21: The columns for redline, yellow, and green ranges in the Limits tab

In addition to setting the red, yellow, and green ranges for the aircraft’s systems, the Limits 1 and Limits 2 tabs determine the units used in displaying torque, temperature, and power.

To configure the colors used in the instrument displays, open the Systems window from the Standard menu and select the Arc Colors tab. Here, you can set the (decimal) RGB values for each of the three standard ranges. By default, the “green” arc has an RGB value of (0, 1, 0), the “yellow” arc a value of (1, 1, 0), and the red a value of (1, 0, 0).

Finally, you can set the range of values displayed by opening the Limits window from the Standard menu. Here, two tabs are used for setting the range of values displayed on “round” instruments and two tabs are used for digital instruments.

In the case of round instruments, check the box next to a measurement (such as VVI, ITT, N1, etc.) to set (in order from left to right):

  • the minimum value displayed,
  • the maximum values displayed,
  • the angle on the dial at which the minimum value is displayed, and
  • the angle on the dial at which the maximum value is displayed.

In setting the angles, 0 degrees is the top of the instrument. Angles can be positive or negative, and can even be greater than 360 if you would like the dial to wrap around.

To use a different (compressed) scale for the high-end of an instrument’s range, check the box on the right of the angle settings labeled “halve over.” Then, beginning at the value you select, the scale will be halved, so it will take 2 units to move the instrument hand the same amount that 1 unit moves it at the low end of the scale. This is most often used in the airspeed indicators of high-speed airplanes, where it allows a greater range of speeds to be “compressed” into the display.

In the case of digital instruments, checking the box for a measurement allows you to set the offset, scale, and the number of digits used in displaying that measurement. The offset is a value added to the X-Plane value when displaying this measurement in the panel (this may be positive or negative). The scaling value will be multiplied by the X-Plane value to determine the number displayed in the instrument panel. The “digits” value determines the total number of digits used in displaying this measurement, while the “decimals” value determines only the number of decimals used.

Setting V-Speeds and G Limits

In addition to red, green, and yellow ranges, the instruments need standard operating markings. These include “v-speeds” (such as the maximum cruise speed, stall speed, and so on), as well as g limits. With the exception of the g limits, these will not be factored into the flight model; they may, however, be used in the airspeed indicator. To set these, open the Viewpoint window from the Standard window. There, on the left side of the Default tab, you can set the following:

  • Vmca, the minimum speed below which you can still steer the aircraft with one engine disabled and the other at full throttle
  • Vso, the speed below which the airplane will stall with the flaps deployed
  • Vs, the speed below which the airplane will stall with the flaps retracted
  • Vyse, the optimal climb speed with one engine disabled
  • Vfe-m, the maximum allowable speed for fully extended flaps
  • Vfe-1, the maximum allowable speed for first-notch flaps
  • Vle, the maximum allowable speed for extended gear
  • Vno, the maximum allowable speed for normal operation
  • Vne, the maximum allowable speed (the craft’s airframe will fail if this speed is exceeded by more than about 25%)
  • Mmo, the maximum allowable mach number
  • Positive g limit, the maximum allowable positive g load (the craft’s airframe will fail if this limit is exceeded by more than about 50%)
  • Negative g limit, the maximum allowable negative g load

Note that, unless noted, all values above are in knots.

If you cannot find official g limit values, 4.0 is a good guess for most general aviation aircraft. At g loads more than 50% above these values, if the appropriate settings are enabled in X-Plane, structural damage will occur—probably in the form of a wing being torn off!

Note that, depending on your engine configuration, some of the values listed above may not be visible. Any of these markings can be left off the instruments by simply setting their values to zero. Note also that, though X-Plane does not take these speeds into account for performance prediction, it may use them for niceties like the plane’s starting speed when selecting an approach.

Configuring the Autopilot

The Autopilot is separate


Figure 4.22: The Autopilot box, found in the General tab of the Systems window


Radio altimeter in Systems -- >General


Configuring the Starter

The engine’s starter is very simple to configure. X-Plane comes good defaults for the starter and battery strength, but you can increase or decrease the starter strength as a ratio of X-Plane’s default. To do so, use the “starter strength ratio” parameter, located in the “Starter” box of the Systems window’s General tab, and seen in Figure 4.23.

Figure 4.23: The Starter box found in the General tab of the Systems window

[tk] starter is electric versus air driven??

Configuring the Fuel System

The aircraft’s fuel system is configured using the Weight & Balance window, launched from the Standard menu. To begin setting it up, go to the Weight tab and enter the maximum amount of fuel, in pounds, that the aircraft can carry into the “fuel load” parameter box.

Next, move to the Tanks tab. In this tab, there are nine fuel tanks able to be added. Each tank holds a ratio of the aircraft’s maximum fuel, which is set using the “tank #x ratio” input box. The total of all tanks’ ratios must add up to 1.000. For instance, if an aircraft had two fuel tanks, one in each wing, each tank might hold 0.5 of the total fuel.

Use the “fuel pump pressure” setting to set the relative pressure of the fuel tanks. This will determine which tanks are emptied first if more than one is selected. For instance, If tank 1 should empty a little bit before tank 2 and long before tank 3 when all 3 tanks are selected, you might set their fuel pump pressures as in Table 4.1.

Table 4.1: Relative fuel pump pressures
Tank 1 20 psi
Tank 2 17 psi
Tank 3 10 psi

Finally, the fuel tanks can be placed on the aircraft using the standard position controls (as described in the “Fundamental Concepts” section of Chapter 3). When placing fuel tanks, you are really only placing the tanks’ center of gravity; X-Plane assumes the tanks are physically large enough to hold the weight of fuel you have specified.

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