topic: Aircraft Development

Instrument Alignment

Instruments in X-Plane are positioned based on their center position. Because an instrument with an odd width or height might have a center that is a fraction of a pixel wide, fractional instrument coordinates are allowed.

Guidelines

Here are some guidelines for positioning your instruments for maximum visual quality:

• For best quality, leave the instrument scale at 1.0.  If you scale the instrument, the graphics card will blur your art. To make a small instrument, use small artwork!
• The base layer and overlay layers should all have the same even-odd status.  In other words, if your base instrument texture is 57 pixels wide, your overlay should not be 54 pixels wide.  All widths and heights should be either all-odd or all-even.
• If your textures are even, your instrument should be centered on a whole-pixel position, e.g. (254.0, 127.0).
• If your textures are odd, your instrument should be centered on a half-pixel position, e.g. (254.5, 127.5).
• When these rules are followed, Plane-Maker’s preview should match X-Plane when the panel is not scaled.
• If you violate these rules, the particular visual errors you get will vary based on the particular instrument, the type of alignment mistake, and possibly even your graphics card.

Test Airplane

This test airplane package demonstrates all possible instrument alignment combinations for non-scaled instruments, both correct and incorrect. Download the zip file here.

This picture illustrates the panel test:

Some notes:

• When an instrument is misaligned, there may be no visible error, a full pixel error, or in the case of rotating panels, blurry pixels.
• The error may be different for each layer of the instrument.

Creating Generic Instruments

The Rotary

• The rotary can be used as a single image layer, but with dynamic lighting. Set it to no click, one image.
• Rotary can be used behind an image to get “dynamic lighting” onto a background. (But – don’t make it too large – spot lights affect overlays UNIFORMLY. Burns VRAM. No shadows!)
• Rotaries can be used with rheostats – set the rheostat to no -1 layer on top of the rotary with no click, customize hot spots. Same trick works with triggers.
• Put a rotary (no click 1 phase) as a face plate over a pointer, but set the pointer itself to clip, to ensure that if the pointer exceeds its “masks” bounds it disappears.
• Key frames must be continuous EXCEPT for rotaries – use to re-arrange enums. See Non-Monotone Key Frames.
• Rotary key frame output < 0 means it disappears. Use for annunciators. Don’t need transparent frame. Save VRAM.
• Rotary key frame > digits WRAPS. USe for repeating animation like trim wheel.

Using Rotaries With Plugins

You can use a rotary as a way to get “mouse clicks” in a plugin:

• Set the rotary mode to “momentary”.
• Create a custom dataref handler.
• Your dataref’s “set” handler will be called once on a down click and once on an up click. The down click will have a value of the number of frames – 1, and the up will have a value of 0.

There is one complication with this method: if you are using the “get” function from your rotary to make the light flash, then you may not receive “set” messages, because the sim won’t write back to your dataref the same value you returned. (Thus if you use “1” for “lit”, you won’t get down-clicks in a 2-phase rotary.)

The solution: rotaries will modulo their number of frames. So for a two-phase rotary, return 2 & 3 from your plugin, instead of 0 and 1. The graphics will look the same, but you will still get writes of “0” and “1” on click.

Driving The Same Dataref With Multiple Rotaries

You can use multiple “push-button” rotaries to set the same dataref between two values. For example, say you want to have (3) push-buttons on your panel and they all set the dataref between zero and another value as follows:

• Push-button #1 to drive the dataref to either 0 or 1,
• Push-button #2 to drive the dataref to either 0 or 2
• Push-button #3 to drive the dataref to either 0 or 3.

You would set the gen_rotary properties to Positions = “2” and Rotary Type = “Push Button”. Your graphic image should be designed with two (2) phases.

You should then set-up the key frame table as follows:

For Button #1:

Dataref Value ––––––––—–––– Image Number

          0                            0
          2                            0
          3                            0
          1                            1

For Button #2:

Dataref Value ––––––––—–––– Image Number

          0                            0
          1                            0
          3                            0
          2                            1

For Button #3:

Dataref Value ––––––––—–––– Image Number

          0                            0
          1                            0
          2                            0
          3                            1

When a button is pushed, X-Plane looks for Image #1 in the key frame table (the highest image for a 2-phase image) for that button and notes what the dataref should be set to by the associated “Dataref Value”. At the same time all other buttons with that dataref are set to zero.

All of the enum values for the dataref must be individually listed in the keyframe table (you cannot set up a range). The last key frame needs to be the “1” frame.

Glass vs. Translucent Glass

X-Plane has two modes of glass instrument lighting. Both take the light levels from an instrument light level rheostat and light the instruments overlays, ignoring spot lighting. The difference is in how they fade:

• Glass instruments are opaque except for their alpha channel, drawing over what is behind them. As they get dark, they fade to black. Thus they can be used to form masks as well as glass instruments, but they will only appear to blend in over a pure-black background.
• Translucent Glass Instruments draw additively – the alpha channel is not needed and has no effect. As they get “dark” they become more translucent – that is, they add less. They cannot be used for masks, but they will draw over any background, allowing for screen backgrounds that are not pure black.

Needles

• Generic needles can be offset – save VRAM!
• Needle can act as a heading bug, via offset and drag.

Rheostats

• Rheostats can have overlays – save VRAM.
• Set rheo step 2 to 0 to get incremental movement.

Pie

• You can customize the colors of the pie – the-2 overlay image has 3 color swatches for the “green”, “yellow” and “red” tinges, which are chosen based on the dataref range. So you can pick any color for your pie.
• If you ned more than 3 colors, make two overlapping pies and use show-hide to switch between pies at certain dataref ranges.
• You can make a pie that is a thin line rather than thick by putting a black pie in front of the white pie, but give the black pie a smaller radius. After 930 you can simply use the offset parameter.

Groups

After X-Plane 930 groups can be hidden using filters. This can be used in a few ways:

• If you need more filters (E.g. hide an instrument based on a number of conditions) simply put the instrument into a group – now you can filter the instrument or the group.
• You can hide non-generic instruments by putting them inside a group.

Pointer Instead of Rolling For Tapes

gen_rolling is meant for a mechanical drum style instrument but it will not work if a large section of the “drum” is visible…thus while it seems that it should be usable as a tape, it is not. (The instrument does not work as a tape because not enough “extra” texture is provided at the top and bottom).

After 940 you can use a vertical pointer with a wrapping key frame table to make a looping tape.

Misc

• Key frame tables can be clamped by doubling an output value, e.g. (-1,0) (0,0) (1,1) (2,1)
• You can also clamp one side of a key frame table and wrap the other side. To do this you’ll need to repeat a value. For example: (0,0) (0,0) (100,100) will make a key frame table from 0->100 that can be wrapped at the top but will clamp at the bottom.

Upgrades to Aircraft for X-Plane 10.40

X-Plane 10.40 fixes a few bugs where:

• The bug fix applies once you save your aircraft with Plane-Maker version 10.40 or newer; older planes will maintain compatibility with the old and buggy behavior.
• You may need to edit your aircraft when running under the new non-buggy code (by re-saving your aircraft).

In other words, these are bugs that were fixed, where aircraft may have been relying on the buggy behavior.  We strongly recommend you re-save your aircraft and re-check these items.

High Altitude Fuel Consumption for Jets

This applies only to jet aircraft: X-Plane 10.36 and older incorrectly interpolated between the 50% and 100% N1 fuel flow SFC numbers. If your 100% and 50% N1 SFC numbers are not the same, the new, correct interpolation will change your fuel consumption at high altitudes.

• If your 50% SFC is higher than your 100% SFC, you will see lower fuel consumption.
• If your 50% SFC is lower than your 100% SFC (this is not usual) then you will see higher fuel consumption.

Billboard Light Sizes

Before X-Plane 10.40, the size of lighting billboards for named and param lights was fixed in pixels. This meant that as a user increased screen size, the lights looked smaller, relative to the scene, and everything looked dark.

X-Plane 10.40 changes this behavior to keep lights consistent relative to the screen.  When you save your aircraft for X-Plane 10.40, this will apply to your aircraft too.

You may have to make your lights smaller – the larger the screen where you authored your lights, the larger the increase in size you will see relative to X-Plane 10.36.

Once you have re-tuned your light sizes, their appearance in X-Plane 10.40 will be consistent for all users.

Check Engine Oil Pressure

X-Plane 10.36 and earlier incorrectly failed to feather the prop on low oil pressure for twin props. Once your aircraft is saved in 10.40 this logic will work; if you set the oil pressure to be too low in your aircraft, you may find the prop spontaneously feathering itself. Fix this by changing the red line oil pressure in Plane-Maker.

Propeller Beta & Reverse Models

Everybody always asks, and few ever understand, how the propeller beta and reverse models work in X-Plane.

Everything here applies to single and multi-engine propeller planes in X-Plane, and also applies to REAL KingAirs and Lancair Evolutions and the like (planes with PT-6 engines) because they work mostly the same way. To simulate non-PT-6 airplanes, use the info in this document to see how X-Plane works, and then tweak the inputs into Plane-Maker as needed to suit your propeller-driving engine.

So let’s start with the REAL airplane description, and then move on to entering data into Plane-Maker after that.

Real Airplanes

The Red Knob: the Condition Lever

If this is all the way forward, then you are at FLIGHT idle. This dumps enough fuel into the engine, even at IDLE throttle, to keep the flame from going out.

If this knob is about halfway back, then you are at GROUND idle. This is a lower idle speed, designed for the taxi-only operations, where a flame-out would not be catastrophic.

If this knob is all the way back, then you are at CUT-OFF: All fuel to the engine is cut, with predictable results.

The Blue Knob: Prop RPM

This knob does not control fuel to the engine, but instead commands the RPM that the prop WANTS to turn.

If the prop is turning SLOWER than the RPM commanded by the blue knob, then the prop will FLATTEN.

If the prop is turning FASTER than the RPM commanded by the blue knob, then the prop will INCREASE its pitch to slow down.

As long as there is enough power and/or airspeed through the prop disc, then the RPM that you have commanded with the blue knob will be followed by the prop.

Now, if the blue knob is all the way FORWARD, then the prop will adjust pitch to try to hold REDLINE RPM (maximum rpm for take-off or fast cruise). As you drag the blue knob AFT, you get progressively less and less commanded RPM, until you get the blue knob all the way aft, at which point the prop will FEATHER (if this is a feather-able prop–some are, some aren’t), where it goes to the feathered pitch of the prop, which will result in basically zero rpm.

The Black Knob: Throttle

And now, finally, the BLACK KNOB, which we commonly refer to as the ‘throttle’, but will also control the prop in certain cases, as we will show below.

When you are doing regular flying, you have the throttle at or forward of the idle stop. As long as the throttle is at or forwards of the idle stop, the propeller is in what is called ALPHA mode.

In ALPHA MODE, the propeller acts as described above, adjusting pitch to try to hold the RPM commanded by the blue knob (redline when all the way forward, minimum or feathered when all the way back). This means that it tries to hold the RPM commanded by the BLUE KNOB, and it does this by adjusting prop pitch as needed to hold that commanded RPM. This is how you taxi and fly.

Now, sometimes, as you taxi in a PT-6 turboprop, your taxi speed starts to build up too high for comfort even with the engine at IDLE!

This, perhaps, is not surprising when you have an engine of about 1,000 horsepower on a light airplane, and being a turbine, it even idles fast to keep the desired airflow running through the engine. (This is needed, interestingly, to keep the engine from overheating! If a PT-6 were to idle too slowly, then the blanket of air that isolates the flame of combustion from the engine wall would deteriorate, allowing the flame to touch the engine wall and melt the engine! So we actually have to idle fast in a PT-6 to keep the combustion flame from reaching the engine wall and destroying it!)

When taxiing, we have a hugely powerful engine running at a high idle, so even at ground idle, the taxi speed might be too fast for comfort.

In that case, you lift the black knob aft of the idle stop and drag it back.

As you do so, the engine stays at idle, and the farther you drag the handle aft, the more the prop pitch moves from flat pitch to beta pitch. This is beta.

If you keep moving the throttle back even FARTHER, then the prop pitch moves from BETA pitch to REVERSE pitch, and the throttle starts coming up as well! This is reverse.

NOTE: Beta and reverse only work if the blue knob is all the way forwards. For whatever reason, Pratt and Whitney just designed the system this way.

Here is a table diagram:
(NOTE: all transitions between the states should be smooth and continuous. There is no sudden jump anywhere.)

Setting up Plane Maker

Now, on to Plane-Maker, which you can set up to perfectly match the PT-6 described above.

Go to the ENGINE tab in Plane-Maker.

For the critical altitude upper-left, enter the maximum altitude at which that maximum power is actually available.

PT-6’s are typically flat-rated, so you can enter some altitude above 0 here… most PT-6’s continue to give full power as they climb until they hit a temp-limit and then they lose power as they climb above that point. Whatever point you first have to drop below max torque at max RPM due to hitting a temp-limit–that is the critical altitude: The highest you can fly and still get full power.

Below that you see the box for the FADEC. Check it if you have it–some PT-6’s have that, some don’t.

Throttle available at max lever is the throttle available when the throttle is all the way forwards. This is usually 1.00, but if your Ng (called N1 in X-Plane) goes over 100% in the real plane, then enter a slightly higher number here.

Below that, you see your low and high idle adjustments: Simply adjust these ‘idle screws’ up or down a bit as needed to idle at just the right Ng, or torque, when you are at low or high idle.

Now, below that, you see “Go to BETA PITCH below this throttle lever position”. This is the position shown in line 2 in the throttle position map up above.
If you are dragging the throttle with the mouse or have a hardware throttle, then below this value for that device, we start going into BETA.

Now, below that, you see “Go to REVERSE below this throttle lever position”. This is the position shown in line 3 in the throttle position list up above.

If you are dragging the throttle with the mouse or have a hardware throttle, then below this value for that device, we start going into REVERSE, and the throttle starts coming up as well!

Now, below that, you see “throttle available at max reverse lever position”. This is simply the percentage of maximum throttle that is available when you pull the lever all the way back to the aft stop. It is the throttle available from the engine in line 4 above.

Now, here is something interesting: If you want your physical throttle handle to be set up like the throttle in a real KingAir or Evolution or the like, then you will use the values above to scale the throttle accordingly.

But here is where it gets bogus: In the REAL airplane, there is a GATE at the idle stop of the throttle that keeps you from going into beta by mistake: You have to lift a trigger to get over the gate and into beta to keep you from going into beta by mistake in flight. But you probably don’t have that gate on your physical throttle quadrant, or want to mess with trying to find that exact point when moving the throttle, or even operating the throttle with the mouse on the monitor. You probably want to just drag your throttle all the way back to go to idle, since that is the way any normal person would want to descend! So, in Plane-Maker, you could easily enter ZERO for the “Go to BETA PITCH below this throttle lever position” and “Go to REVERSE below this throttle lever position,” so X-Plane NEVER goes into beta or reverse when you drag the throttle all the way aft! This way, you can just slap the throttle back to the aft stop to go to idle. This is the way anyone would want to fly the airplane.

Then, to go into beta, hit the / key. To go into reverse, hit the ? key. (And hit again to toggle out). And, while in reverse, you can run the throttle right back up again to go farther into reverse! This way the ergonomics are not like the real airplane, but you can really control what is going on. If you want the ergonomics to be the same as the real plane, then enter the throttle positions as mentioned above… but you better not drag the throttle all the way back in flight, or you will go into beta and then reverse in flight! The REAL plane has a gate at the idle stop to stop this from happening!

In the main screen at right, for the maximum power box, enter the maximum continuous power allowed by the engine. This is the maximum power allowable at sea level (not maximum thermodynamic, which you would never use or you would wreck your gear-box!).

For the prop pitch numbers, the top is the feathered pitch of the blade, as you get with the blue knob all the way back… maybe 60 degrees.

Then the coarse pitch is the maximum the prop can open up in alpha mode… maybe 45 degrees.

The fine pitch is the flattest the prop can go in alpha mode… maybe 10 degrees.

The beta pitch is the flattest the prop can go in beta mode… maybe 0 degrees.

The reverse pitch is the flattest the prop can go in reverse mode… maybe -45 degrees.

So, that is how a real PT-6 works, and how to set it up in X-Plane.