P3D v4 Special projects class

[aSIMetric]

So as part of an inspirational educational project, we are looking to create a near future SSTO project, think Skylon with crew. One of the first challenges is to try to replicate rocket engines as close as possible. Be able to get the vehicle to 80,000ft at Mach 4.5 in its first stage. After that, we are looking at switching to TerraBuilder’s new ballistic model for orbit, with help from TerraBuilder. All work in progress.

I’ve been messing with the config file and air files for a while now (countless hours in truth) not making much progress. The SDK literature is mind-boggling, not really helping, as a newbie, I have yet to be able to see the matrix. I've looked at what others have done like the X15 models for P3D but I'm not able to find the magic numbers, is this a matter of scripting?

Can we have a conversation about rocket proxies? Can anyone offer any advice on how to tweak the system to best replicate rocket engines? Much appreciated.

 

[=rk=]

I'd say it's a matter of continuing to fiddle. I started with the .air file of an FSX X-15, but just kept adjusting until it felt right. It has an odd transitional area where it wants to roll inverted at about 750 kts, but after that it's smooth sailing to the invisible barrier.

 

[aSIMetric]

mmmm...maybe I just need to miniaturize? I can get the vehicle off the runway like a bullet, yet no matter what I seem to do by the time I'm at altitude iv lost two-thirds of my speed. Once I level out the speed remains static, and I'm not able to accelerate. What is the best source of information or explanation regarding the air.file? is the SDK it? I am assuming the magic lies somewhere within the N1/N2 vs Thrust/mack numbers with a little help from dropping the drag factors? Between 5-10,000ft it's Mach 4.5 without breaking a sweat, by 80,000ft you are at full thrust, down to 700-knots, and not able to move the dial any further. Maybe its size?

 

[=rk=]

Ya, I would not trust the metrics displayed from instruments. I would have to say that some component of velocity is measured relative to the user, because the only metric of motion that ceased at 249,999 feet elevation, was the rotation of the altimeter. So I would say, that at the edge of "simulated space," velocity is somewhat "inertial." You'd want to remember, that MSFS simulates otherwise impossible events, by running mathematics and algorithms. The algorithms themselves, are just another simulation. They get you close, but if calculations were sufficient, we would not need an Edwards Air Force base. Bottom line, when you are flying a flight simulator into outer space, things are likely to get weird.

As a virtual test pilot, I want to give myself enough thrust to power through the muddy math. When the algorithms collide, I want the deadlock to be broken by the shock wave of my nose cone. First, I gave myself gobs of power, I don't know if that was obvious in the video. The vehicle starts to roll while the compressors are still spooling up and by the time the actual rocket ignites, it's already in the air and I can barely keep from plowing into the runway again. I mean, it's so unreal I think it's funny, but it is what it took to get to higher speeds, vertical and still accelerating.

The physical model has nothing to do with flight characteristics, but it did allow me the excuse to cut mass to a minimum. Once I got the power where I wanted it, I next tweaked the control surfaces to provide useable maneuverability, without being stalled out and useless at higher speeds.

As to .AIR file mysteries, Jerry Beckwith is my preferred expert. His air file manager tool has the best functionality of air file tools, imo. The thing is, .bgl's and .air files were proprietary software and no documentation was ever released. Everything we know about these, has been reverse engineered. In this regard, we are all experimenting with black magic in the wizards workshop.

 

[aSIMetric]

I guess I'm not sure about the starting point. with a vehicle of the equivalent size of a 777, I guess the starting point is to take the air.file and config file from a 777 equivalent aircraft and start adjusting from there. Would that seem correct? Or start from a blank slate?

 

[Roy Holmes]

It is not true that no official air file documentation was released. If you look at the P3D SDK there is a section called "Flight Model" which has examples of the various air files by engine type. This section appeared around the time when MS was selling the sim to Lockheed Martin. As it happens, there was only one sub section of the released file which differed from the unofficial concepts, the remainder was exact.
There is no reason why you cannot create a very accurate air file using published typical aerodynamic coefficients. You can get the engine thrust within one percent across the envelope. No black magic required.

Now, doing that in MSFS is another story.
Roy

 

[=rk=]

It is not true that no official air file documentation was released.

I'm not going to belabor the point, but Microsoft Flight Simulator was developed by Bruce Artwick and when the Aces Studio closed, he took all his source code and developmental knowledge with him.

Aces Game Studio - Wikipedia

en.wikipedia.org

Everything we've learned about the core files has been reverse engineered and BAO never released AIR file documentation. I've seen the P3D SDK and to me it doesn't explain things any better than just seeing the values in AirWrench, but I'm kind of stubborn, or dumb, or both that way.

There is no reason why you cannot create a very accurate air file using published typical aerodynamic coefficients. You can get the engine thrust within one percent across the envelope. No black magic required.

Great to hear. If you've successfully developed an SSTO the size of a 777, maybe you could share the FDE.

I guess I'm not sure about the starting point.

This will depend on how you want to accomplish it. Have you tried an aircraft project from the sdk? It will give you a good idea of what to expect and what you can have control over. If you build a project in DevMode, you can open the aircraft in an interactive editor. Keep in mind that if you go this route, the editor already has your model, so control surface dimensions and flight profile has to pretty closely match what you have, it won't let you cheat, except with thrust and mass, to some extent.

If you just want to edit test and build, you have more freedom. You'll want to be careful, if you decide to use pre published FDE. Older AIR files are just funky and some parameters won't change with available editors. You'll run the risk of putting a lot of time into a flight envelope and then encounter some brick wall somewhere, you'll not want to abandon it, but the flight characteristic you can't adjust, might force you to.

In my example, the AIR file was from an X-15 that was published for FSX, but in the editor I could see it had been written for FS2004. It means the Waverider will have quirks I might never find the proper, I don't know, purple magic to exorcise.

I think that if you took the SDK sample SimpleAircraft, or GaugeAircraft and dialed it up with all the stats you have, used a decent model and ran it through the DevMode editor, you'd get a good start.

 

[WarpD]

I can state that much of the sim's .air file content was completely undocumented. I asked L-M for details regarding sections like REC 1101 and they stated there was no documentation provided from Microsoft regarding any of the .air file entries, they were told there was none available to provide. While I can not confirm that Bruce Artwick walked away with any possible documentation, nor can I confirm that he walked away with any source code that would legally belong to Microsoft at the time of the studio closing.

 

[aSIMetric]

Thanks for the information guys, interesting back story. Well, I guess it's time to create a wonderful spreadsheet heaven and begin grinding away at the rough stone.

Have you tried an aircraft project from the sdk?

I've been working away at it. I have a basic model, animations, and texture (although there are some issues there). I have a functioning addon folder for the vehicle, it's just getting the flight model tuned to a point we can try to create the 'in sim' switch to the ballistic model and have a true runway to orbit experience. I will share updates.

 

[=rk=]

nor can I confirm that he walked away with any source code that would legally belong to Microsoft at the time of the studio closing.

Well put. We do know BAO created the software, the compilers and the source code, we know the split had been dramatic, we know we have access to the compilers and the software and beyond some really crafty reverse engineering, it's about all we know, for sure.

Thanks for the information guys, interesting back story. Well, I guess it's time to create a wonderful spreadsheet heaven and begin grinding away at the rough stone.

I've been working away at it. I have a basic model, animations, and texture (although there are some issues there).

Awesome. I'll probably apply for test pilot candidacy if you get that far.

 

[Roy Holmes]

As is often the case, there appears to be some confusion as to which simulator we are discussing. The original post is flagged P3DV4 and refers to configuration and air files which are in P3D.
RK appears to be working in MSFS. It has no air file as such. and is much more difficult to develop unless you are working on a simple prop plane.
As regards my post, there are sample air files in the SDK and I only did fast jets because that is what my flying was on.
Roy

 

[=rk=]

As is often the case, there appears to be some confusion as to which simulator we are discussing. The original post is flagged P3DV4 and refers to configuration and air files which are in P3D.

Good observation.

RK appears to be working in MSFS. It has no air file as such. and is much more difficult to develop unless you are working on a simple prop plane.

That's probably more a matter of opinion. While I started with the AIR file, as mentioned above, those values are easily transferred, imo, to the relevant .cfg files and I'll humbly defer the implied complement, with the sincere suggestion that you really ought to give it a try. Really, all I did, was replace the SimpleAircraft model and textures with my own, transcribed the relevant .cfg values and fiddled from there. Additionally, you get to use the inbuilt editor, if you keep it realistic ish.

Thanks for the information guys, interesting back story. Well, I guess it's time to create a wonderful spreadsheet heaven and begin grinding away at the rough stone.

As to the platform, I recommend the switch, sorry for the oversight, but I do have a FSX/P3D version of Waverider, you can use it's AIR file and aircraft.cfg for your development, if you'd like. In those sims it's performance is far less restricted, you really shouldn't need it, as those sims all us to get almost anything into orbit. I'd be glad to help with the conversion if you do develop to MSFS.

 

[WarpD]

I will point out that newer Prepar3D versions allow for totally custom flight dynamics that ignore everything to do with aircraft.cfg and .air file data.

 

[aSIMetric]

I will point out that newer Prepar3D versions allow for totally custom flight dynamics that ignore everything to do with aircraft.cfg and .air file data.

Are you talking about v5?

 

[WarpD]

Actually, I think it started in v3.

 

[aSIMetric]

I will point out that newer Prepar3D versions allow for totally custom flight dynamics that ignore everything to do with aircraft.cfg and .air file data.

Im not sure if that means outside the cfg of .sim file, or are we talking about scripting?

I'm able to launch the 416-ton vehicle off the runway to the international space station in less than a minute, literally like a rail gun round. Yet clearly that's not what we are looking for. Need a controlled positive acceleration climb, at least 10 degrees pitch to 80k feet. something a little more realistic, replicating something like Skylon's air-breathing SABRE engines. Right now it's messing with the N1 N2 vs thrust relationship in all kinds of ways. I'll get there.

 

[WarpD]

Take the time to read the SDK about the SimObject API in the ISimObjects category. Also look in the PDK Samples Overview under the category of ISimObject PDK Examples.

What you're trying to do steps outside the typical flight dynamics of the sim.

 

[aSIMetric]

AAhh yes the PDK. No matter how hard one tries to avoid coding in life, the attempt seems futile. One must learn to code or one must die.