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0 votes
asked by (44 points)
Ive done my best to work this out myself, but finally concluded I need help :)

I have a 3-screen Mac system - XP11 is amazing and works extremely well on screens #1, 2 & 3.

Now, I want to display instruments by themselves on screen #4.

I understand that you need separate instances of XP11 to do this ... XP11 runs one view per instance, so in order to have multiple views, you need multiple instances - that makes sense.

I can get this working by running separate instances of XP11 on separate Macs, and networking them together - it's easy to set up because each machine has a separate IP address. All good so far -> but I want to achieve this on one machine.

The XP11 Forum contains posts by Windows users who also want to run instruments on a separate display. They run multiple instances of XP on one machine, with one instance as a 'master', and the other as an external independent view.

The trick seems to relate to setting up the IP addresses and UDP ports. Unfortunately, the instructions posted in the forum were for XP9, and the settings screens on XP11 are quite different, so I couldn't figure it out.

I can easily run multiple instances of XP11 on one Mac - I can fly an F4 Phantom II on screen #1, a Stinson L5 on screen #2 and a Cirrus SF50 on #3 - or all 3 instances on one screen (albeit a bit noisy - it would be good if the sound muted when the window was deactivated), with hardly any degradation in frame rate.

So the question is ...

Given that each instance of XP11 is running on a single Mac with a single IP address, how can I set up the UDP ports (assuming this is what I need to do ) on one instance to run as a 'master' (eg cockpit view with HUD) and others as independent external views (eg instruments / external views) ???

Many thanks,


3 Answers

0 votes
answered by (44 points)
edited by

OK - I worked it out - it's actually REALLY easy.

You need to run 1 instance of XP11 to generate the simulation (the MASTER), and one instance to generate each external view (the Slave/s).

A. Set up the FIRST instance of XP11 as MASTER

     1. Launch XP11

     2. In Settings/Network, set 'This machine's role' = Master


          - enter the SAME IP address as the Master (THIS MACHINE'S IP ADDRESS)

          - set the UDP port to 49020

     4. Leave the UDP ports at the default values :-

          Port we receive on = 49000

          Port we send from = 49001

     5. Click DONE

     6. Start your flight, then PAUSE 

B. Set up the SECOND instance of XP11 as SLAVE

     1. Launch the second instance of XP11

          open terminal and type "open -n -a [pathname]", where [pathname] is the path for your XP11 app.

          It's actually easier to type "open -n -a ", then drag the X11 app onto the end of the text.

     2. When the app launches, immediately click the 'Settings' button and go to Networks.

     3. In Settings/Network, set 'This machine's role' = External Visuals

     4. For MASTER MACHINE, set the IP address to the same as the Master (THIS MACHINE'S IP ADDRESS)

          Leave the UDP port at 49000

     5. Set the UDP ports :-

          Port we receive on = 49020

          Port we send from = 49021

     6. Click DONE

     7. Click Resume Last Flight or New Flight - the MASTER will automatically set the aircraft and airport.

C. You will see the 2nd instance of XP11 is PAUSED, and the aircraft and airport are the same as the MASTER.

D. Set whichever views you like, then un-pause - and fly !




1. You can run as many instances of XP11 as you like - one for each view.

2. I had 3 instances running with different simulations - with virtually no degradation in frame rate.

3. You can use this little AppleScript to launch 1 instance of XP11 :-

     do shell script "open -n -a [pathname]

     A trick - if any segment of your pathname includes a space, then enclose in single quotes ... like this ...

     do shell script "open -n -a /Applications/'X-Plane 11'/"

     You can use this as many times as you like - just run it once for each instance.

5. Once you've tested the script, save it as an 'Application' - then just double-click to launch a new instance of XP11.



commented by (22 points)
Great!  Thanks for all that.

Now, XP11 is not released yet except as beta.  I'm designing a 6-view simulator but I don't really want to pay 6 times for XP11.  Not that the cost is an objection, but the maintenance effort of 6 different accounts certainly is.

Did you pay for two instances or just one?

Does your recipe also work with the trial version?
commented by (44 points)
edited by

Hi Rob,

Thanks ... I actually developed this solution on the trial version, and here's a pic of it running on my Mac (it's not upside-down - I'm flying inverted :)

If you go to this thread ...

Multiple instances with one digital download license? - General X-Plane Forum - X-Plane.Org Forum

it says that the XP license key authenticates one *computer* - and that multiple instances running on one machine at the same time are OK. AFAIU, its OK to run copies on *different* machines, but not at the same time.​

If you try out my solution, I'd be very interested to know whether it works for you.



commented by (22 points)
edited by
Hi Gary,

Thanks. I'll try your solution later (not enought itme right now), but just with one instance the fans of my macbook pro go to well over 5500 revs.

The whole licence key business is very confusing, and reading the forum threads is just mind-numbing I must say, but thanks for the link.

Yesterday I did put a trial version 11 on both my laptop and my wife's (identical machine) and they were easily linked up as master and slave to give two different views of the same flight.  But that's probably because there is no licence limit on the trial anyway.

In planned 6 screen simulator for the aeroclub all machines would permanently be disconnected from the net:  I don't want anyone to accidentally download anything, and I certainly don't want the OS to update its own software automatically(*).  I just want it built, then operate it, totally disconnected, for a long time.  Our old simulator has been running for 15 years, and the only reason it is now to be replaced is that the very nice controls have an RS232 interface for which I would have to write a hardware-level driver to interface them.

Staying off the internet will be impossible with the DD version.  With the DVD version it's probably easier: in versions 9 and 10 all I had to do was make a disk image of the first DVD, mount that before launching X-Plane, and it all works well.  No DVD player needed.

I don't mind paying 6 licence fees.  I worry about the complexity.  I don't want to end up with 6 machines and 6x10=60 DVDs.  I wonder if I can run two instances on a Mac Mini, high end.  Then I would just need three machines.  But I also need to think about how fragile such a complex setup is:  how well will another person be able to diagnose problems and fix them?  Will I be called in all the time to fix things?

Yet another item:  if I run multiple machines/instances with different views, will I need to start each machine/instance by hand and set parameters?  Or can I have just a single switch which powers all machines and then start-up sequences will make it all happen?  I don't think X-Plane has an Applescript interface.


(*)I had to do a very painful roll-back from Sierra to El Capitan on our home server because Sierra was incompatible with some software.  It would be rather a catastrophe if from one day to the next the simulator stopped working because Apple decided on some obscure change which it forced down our throats through the internet.
commented by (44 points)

Hi Rob,

Thanks for your speedy reply ...

Yes, the fans in my iMac were running pretty fast last night ... but its 37C here in Sydney, which doesn't help - I'm sure it would have been worse using a MBP :)

I'm using a 2012 quad-core i7 iMac with an average video card (NVIDIA GeForce GTX 680MX) - it was never set up for graphics-intensive apps, but it handles XP11 really well - with 3 instances in full simulation, I get about 30fps, which is adequate, even with mid-range settings for textures etc.

Re your setup ...

If you plan on having 6 screens, you don't need 6 views (or 6 copies of XP11). Presumably you'll run most of the screens as a 'wide view' - you only need ONE instance of XP11 for that - and set up multiple screens in the 'Graphics section'. I've done that with my 3-screen setup, it works really well - I only wanted additional views for instruments and maps.

Have you thought of a VR headset ? *much* better than multiple screens if your budget can manage it. Not available for Mac yet, but there are rumours that Apple is about to release one :)

Have you considered getting an RS232 <> USB converter for your old controls ... $30 at JayCar - more here - you can also use a converter like JoyToKey to manage the mapping if needed.

Regarding DD vs DVD ...

Once the software is installed, DVD or DD are the same - you only need to connect to the internet when loading new planes or scenery, or checking for updates etc, which you will need to do periodically. I suspect that XP11 will be DD-only or maybe also USB -  most developers have stopped shipping software on DVD.

Re OS updates (your *) ...

I've had an identical problem with updates killing old apps. OSX will never update itself without permission - but the best way to guarantee that it doesn't is to simply disable the network connection in preferences - which would be OK if you have a dedicated sim and don't need web access other than for XP11 maintenance & updates. You can easily lock the prefs so no-one can 'fiddle' the settings.

I've also been looking at a top-end MacMini for graphics work ... you can get a MM with a 3GHz Dual-Core i7 with a reasonable (Iris) graphics card. There are rumours that Apple is going to drop the MM range - but there are other rumours that a 'beefed up' MM with high-end graphics will be announced in March - more here. With SSD and 16BG RAM, it would be about USD 1,700 - expensive if you need 3+ units - a Mac Pro might be an alternative - I'm sure it could easily handle multiple instances.

BTW - if you get MMs, go for the SSD option - the HD in my MM died, and it was cheaper to get an external SSD than replace the drive - but it made the MM *MUCH* faster.

BUT ...

One issue with multiple instances on the same machine relates to settings... AFAIK, there's no straightforward way to store separate XP11 settings for each instance - you have to set the parameters for each instance when you launch it.

You can write a script to launch as many instances as you need on one machine (just duplicate the line in the script in my post), but I havent looked into how to pre-set the preferences / settings for each instance - I'm sure it's reasonably straightforward. If you run more than 1 instance on any of your machines, then you will have to manage this issue.

Everything needs to launch in a coherent way if you have a power outage or reboot - IMHO it would be worth writing a little script to launch the instances and set the modes and UDP ports.

The only other solution is 1 machine per instance - with one license each \:o}

I hope that helps :)


commented by (22 points)
Gary - Glenn:


Hi Glenn,  I'll have to study the plugins page you sent; it mentions an Elite HW interface, and Elite is the hardware we currently have! Very solid, and would be a real shame to have to throw it away.  So I'll look at that in depth.  The end result will run on Windows I'm pretty sure, so that's not a problem.

Hi Gary, (-7C here near Geneva)

Some points:

No, the 6 screens will each have their view.  Maybe the two front ones may display a single view, but the side ones will have views along a different line of sight, otherwise the perspective is horribly wrong.  So I need at least 5 instances.  Those may be instances on the same machine, or one machine for each, or whatever other combination.

As the current Elite simulator now runs on a PC, yes, I had to find an RS232-USB adapter, I did and it works fine.  But it runs only from the Elite software, which is not capable of multiple views.

As to processors, I'll probably go for low-cost PCs, or even better: there is a shop in Geneva specialising in custom-built machines and they may have a way to put several motherboards into a single box.  Macs (I had my first one in 1984… and personally only ran Macs since) are simply far too expensive and unflexible for this kind of job. MMs may do it but are expensive (I do have one as a home server though and hope Apple will continue the line; they are just so cute for that type of application)

If I end up with multiple machines, as is very likely, I'll have to learn to write scripts for Windows  :-(

The problem of the Instructor's screen is solved:  the iPad app to do that works beautifully, and makes it also easier for the instructor to sit next to the student.

The instrument panel should be solved by getting enough real hardware panels from Saitek.


commented by (10 points)
I tried following these steps on a PC and I still get the UDP error when launching the second copy of X-Plane 11.

The only portion of the steps I didn't replicate exactly is the bit about starting copy 2 from the terminal window as I'm not sure what it's doing exactly so I can find the Win10 equivalent.

Can you explain what the -n and -a attributes are doing exactly?

commented by (44 points)

Hi ...

This procedure describes how to run multiple instances of X-Plane on Mac OS. In Mac OS, you can't normally run multiple instances of the same app, like you can in Windows.

The 'open -n -a' terminal command is to launch additional instances of X-Plane.

[-n] tells Mac OS to pen a new instance of the application, even if one is already running.

[-a application] specifies the application to use - in this case, 'X-Plane 11'

If you're using Windows, you don't need to do this because Win can run multiple instances of X-Plane without the need for a terminal command.

I hope that helps :)


commented by (10 points)
Thank you for the explanation.  This method did work for me after trying it a second time.  Appreciate the original post!
commented by (17 points)

Hi Robert,

Did you manage to write a hardware-level driver to interface the Elite controls. If so I'll be very interested in it.

Since I saw this for Xplane 11 I thought it might be possible: If you have flight instruments or other hardware you plug into a serial port, you can send datarefs from X‑Plane to the serial port to drive them. To do this, first go to the Data Output section of Settings and click on Dataref Read/Write. Check the box next to A COM port, then select the com-port number and enter the baud rate in the lower-right.

Best regards, Caesar

commented by (22 points)
Hi Caesar:

Unfortunately no, and I did not even try.  It's a complex job requiring expertise in very low-level programming.  I have not done that since 1976, more than forty years ago…  Plus I have no detailed documentation about the Elite hardware.

It would be much simpler to connect the Elite hardware with a few levers and linkages to Saitek hardware (or joysticks) and I have actually thought about looking into that. Easier to debug too!  :-)
commented by (17 points)
I'll keep the Elite hardware running with FSX and I'll use X-Plane 11 with a joystick then, I wished I could switch completely to X-Plane. Anyhow, thanks for the input!

0 votes
answered by (5.3k points)

Hi Garry and Robert,

Why don't you have a look at Panel Builder which can be found at   in the USA or   in the UK instead of trying to run additional copies of X-Plane.



commented by (44 points)
Hi Glenn,

Many thanks for that suggestion ...

Yes, I've looked at SimPlugIns - they look great, but are for PCs, not Macs {:/

Multiple views is also very useful for displaying maps, and keeping an eye on the surrounding terrain - its actually really easy to do - and free !
commented by (5.3k points)
Hi Gary,

Thought this may help.  Good luck in solving the dilemma.

PS.  Seems as though we both live downunder.  Temps for us have been high 30s with anticipated temps in the mid 40s for the next few days (or weeks).

0 votes
answered by (22 points)
Do you know how the computational load is distributed over the CPU and GPU?

Presumably the CPU is tasked with simulating the plane's behaviour and the GPU with painting the scenery.

And presumably the master instance simulates the plane while the other instances only paint additional views.

If that is true, then I need a powerful machine for the master instance but only moderate machines for the other instances although they need a good graphics card.
commented by (44 points)

Hi Robert

Today we are 47*C apart :)

Based on my understanding of your 6-screen setup, IMHO you don't actually need to run multiple instances or use multiple machines ... if all you want to do is display different perspectives of the same view, then XP11 can do that for you with only 1 instance.

I suggest you look at XP11's multi-monitor modes in Settings/Graphics ... this allows you to set each of your monitors to display a different perspective of the same view.

For example, you could set the 2 left monitors to look out the left window and over the left wing, the front 2 monitors to look out the left/right front screens, and the 2 right monitors to look out the right window and over the right wing - all within one instance of the app.

Here's what I mean - sorry for the poor pic, it only took a minute to set this up for you, I haven't adjusted the offsets etc to compensate for the bezel width.

Contrast this with a SINGLE perspective stretched across 3 monitors - it looks flat, and (as you mentioned) the perspective is all wrong - although it does give a good effect with very little effort and no setup.

I suggest you set up XP11 with several monitors attached, and experiment with the settings in Settings/Graphics - you will see one setup panel there for each monitor connected.

This method requires only one instance to run the simulation, which reduces the load on your processor, and generate one view for each screen - XP11 will do all that for you.

I hope that helps ...


commented by (22 points)

Hi Gary,

Temp. has gone up here to -1.5; view from the kitchen window:

(the mountains in the background are the Jura, as in Jurassic).

However, when I try to follow your suggestion I get: 

monitor panel

i.e. I seem to be able to do something with the second monitor OR with the main one, but not both…  But this is perhaps because the lid of my MacBook is closed, as it sits behind what I think of as my "main monitor".  There is a Cinema (2560x1600) attached and an Acer (1920x1080).  So I'll experiment some more.

However, your answer indicates once again that we —and X-Plane— urgently need a terminology to describe these issues in unambiguous terms.

I'm off to a meeting, let you know as soon as I can.


commented by (44 points)
Hi Robert,

Thanks for the pic - very beautiful view, we could do with a bit of snow here now, its 9pm and still 24*C after a very hot day.

Looking at your screen ... your Mac has definitely 'seen' at least 2 monitors - that's why you have 2 settings panels (and there may be a 3rd off to the right).

Interestingly, the size of the monitor settings panels in Settings/Graphics is in proportion to monitor resolutions - so it looks like your 'Monitor 1' is very low res, and Main Monitor is MUCH higher. Try setting them to about the same resolution to get started.

Try clicking the 'Unused' drop-down and it *should* give you some view settings. Or try setting Monitor 1 to 'Unused' and then try the Main Monitor again.

Your MacBook display will almost certainly go offline when you close the MacBook- try opening that and you should see 3 settings panels (I hope :).


commented by (22 points)

OK, just before heading to bed (22:32 here):  I followed your suggestions and it seems to do exactly what I want from a single machine and a single instance.

However, I had a long struggle with graphic setup before I realised that the monitors panel in X-Plane mimics the arrangement panel in the System Preferences.  That made for some scrollling before I could get to the offset fields.

Now I will have to do this with a PC and Windows, no way out of that.

So, if I get that fabulous card that handles 6 screens, the card may make it look like a 3x2 array, something like this:

Therefore the next thing to check is whether I can put any view on any of these screens, e.g. if 1 and 2 make up the main forward view, can 3 be the view to the left of 1, 4 that to the right of 2 etc.  I think so, but I'll have to put the question to a PC salesman.  So back to the 1000Ordi shop in the next few days.

Ultimately there will be nothing like trying it out on a real configuration, but that costs a lot of money if it does not work out.