Jump to content

Sign in to follow this  
GodAtum

Extracting the flight model

Recommended Posts

Thank you for your awesome answer Tabs, i really appreciate your post :) I could not pretend to know why a plane flies in real life lol but i find PMDGs realistic enough for me. Flying your planes in the sim has actually given me confidence to fly as a passenger in real life.

Share this post


Link to post
Share on other sites

Although I will never grasp any of the technobabble that goes into making this stuff work, I am in supreme awe of the work you guys do. Seriously, it's mind blowing.

  • Upvote 1

Jason Lee

Share this post


Link to post
Share on other sites

No, we're not doing this for multiple reasons:

 

1. We already do something quite similar - the NGX is already completely "fly by software" - we intercept the joystick prior to FSX and modify the inputs behind the scenes to produce things FSX can't normally do. Remember that the guy who programmed these algorithms here is an engineer with a PhD in computational fluid dynamics - I've seen people who appear to think we're just using FSX defaults or something and nothing could be further from the truth. This guy designs these types of mathematical physics models in real life industry. Simply put, using some other FDE would be pretty redundant here, Vangelis is already doing a ton of work of his own that's similar to this. It isn't just the flight modelling either - we do almost everything on its own outside the sim - fuel, pneumatics, autobrakes, electrical etc - it's all custom. Apparently we need to highlight this a bit more in the marketing we do, because a lot of people seem to be under the assumption that we aren't doing these things when in fact we were one of the pioneers of it going all the way back to the first NG we did in 2003.

 

2. The jet modeling in FSX is not nearly as bad as the free-rotating turboprop is. We can get very very close by tweaking/massaging the FSX model into doing what we need and it'll do 99% of the envelope right on the numbers from Boeing. Edge of the envelope is extremely difficult even in multimillion dollar full motion level D sims. I've personally seen level D sims completely "spazz out" and require reloading the situation if you get it into certain edge of the envelope states that it can't process. (it just starts flipping around unrealistically like crazy, it's pretty funny actually) Separated airflow/high AoA/stall physics is not something that is easy to model at all even for the best simulations in the world. Unless you are a Boeing test pilot, stalling a 737 or 777 is absolutely the last thing you'd ever want to do in the real airplane anyway.

As an aside on this - I've seen some people make claims in the past week to the effect that the NGX doesn't "feel" realistic. The idea that a large swept wing jet should fly in a similar manner to a smaller and much lighter straight wing turboprop is something that doesn't make a whole lot of sense. The weight and the way the wing of a larger jet works is going to smooth out a lot of that "loose" getting-thrown-around-by-the-airmass type feeling you get in a smaller plane. You can feel this difference as a passenger even - a couple months ago I got off a 757 straight onto an ERJ-145. There's a very pronounced difference there - the 757 feels very stable and has that almost "on rails" thing going on. It's a big airplane that's displacing a ton of air and you don't notice little bumps and gusts. The ERJ on the other hand is more like a turboprop - it's small, has a straighter wing, and you feel the airmass a lot more. We had a ton of real life pilots on the 737 test team (and even more on the 777 team), we got to fly the full flight simulators ourselves, Robert himself has an ATP and has flown large jets. etc. I don't think we're wrong about how they fly after all of that.

 

3. To do this sort of thing you have to run FSX in what amounts to slew mode where the external FDE is just positioning the plane where it wants it based on the algorithms - this breaks compatibility with a ton of addons and hardware that read information out of the FSX flight model, causes the aircraft to not respond to the FSX weather events like turbulence, and so on. We're definitely not willing to do that - we'd have a ton of complaints if we did with how big our market is.

 

4. Running more processes like this on top of what FSX is already doing is not going to improve framerates. I suspect their FPS are higher largely because their VC has a lot less clickspots, animations, draw calls and texture resolution than then NGX does, not because the flight modelling is somehow granting it a ton more frames. As well done as their simulation is, it's also a fact that a Q400 is a much simpler airplane (in real life) than a 737 or 777. Full geometric path VNAV that takes into account both altitude and speed with all manner of soft and hard constraints, variable target descent speeds and limits, autothrottle logic etc is very heavy math. (There's all kinds of calculus and differential equations involved in doing it) Look at what our LNAV is doing too - all the turn prediction curve drawing etc - those aren't static things that get drawn once, they're dynamically generated based on the current flight situation and get recalculated with every "tick" of the aircraft's system timers. Again, very heavy math that the Q400's route line drawing doesn't have to do.

 

To sum up - I do really like what Majestic's done - I've been flying it a lot since it came out, but this kind of flight model thing as it's implemented in the Q400 is not something we're going to be pursuing for all the reasons listed above.

Hello, i am really interested in this stuff about flight dynamics and the effects of having an external one. You said that an external flight dynamics engine makes the aircraft incompatible with the weather engine of the sim, so how does the majestic dash q400 can perfectly handle the weather used in p3d? it also have a functinal weather radar.

 

This thread is two years old, maybe you can give us some updated info about how pdmg is working with the flight modeling nowadays, do you have any plans to introduce a new tecnology??

 

 

Thanks

Ricardo Muelle

Share this post


Link to post
Share on other sites

 

 


You said that an external flight dynamics engine makes the aircraft incompatible with the weather engine of the sim, so how does the majestic dash q400 can perfectly handle the weather used in p3d?

 

Quite easy, the Q400 is not designed to be as sensitive to environmental changes as the PMDG products. More to the point, and something you're missing, is the absolutely unrealistic behavior of winds, pressure and temperatures in the MSFS wx engine; if that engine were more realistic then PMDG products would work very well. Right now, ASN does a pretty good job of doing the stuff outside the box with weather with same strategy as used by PMDG with aerodynamics.  But even with ASN the turbulence scales need dialed back to about the 25% range.


Dan Downs KCRP

Share this post


Link to post
Share on other sites

I was lucky enough to fly a full motion 737-800 sim at alaska airlines training center and one thing I noticed was that at low airspeeds, the aircraft would (very slowly, and exponentially decreasing in speed) continue to bank if you initiated a bank and returned the yoke to neutral aileron. A very lethargic feel as expected at 160 knots. That's the only real difference I noticed. Love what you guys do! :D


Aidan Hutchison

Share this post


Link to post
Share on other sites

I actually push the sliders of turbulence in ASN to 100%, because otherwise it's unrealitically mild when significant weather conditions are being reported :-)


Flight Simulation is the Virtual Materialization of a Dream...

 

Share this post


Link to post
Share on other sites

No, we're not doing this for multiple reasons:

 

1. We already do something quite similar - the NGX is already completely "fly by software" - we intercept the joystick prior to FSX and modify the inputs behind the scenes to produce things FSX can't normally do. Remember that the guy who programmed these algorithms here is an engineer with a PhD in computational fluid dynamics - I've seen people who appear to think we're just using FSX defaults or something and nothing could be further from the truth. This guy designs these types of mathematical physics models in real life industry. Simply put, using some other FDE would be pretty redundant here, Vangelis is already doing a ton of work of his own that's similar to this. It isn't just the flight modelling either - we do almost everything on its own outside the sim - fuel, pneumatics, autobrakes, electrical etc - it's all custom. Apparently we need to highlight this a bit more in the marketing we do, because a lot of people seem to be under the assumption that we aren't doing these things when in fact we were one of the pioneers of it going all the way back to the first NG we did in 2003.

 

2. The jet modeling in FSX is not nearly as bad as the free-rotating turboprop is. We can get very very close by tweaking/massaging the FSX model into doing what we need and it'll do 99% of the envelope right on the numbers from Boeing. Edge of the envelope is extremely difficult even in multimillion dollar full motion level D sims. I've personally seen level D sims completely "spazz out" and require reloading the situation if you get it into certain edge of the envelope states that it can't process. (it just starts flipping around unrealistically like crazy, it's pretty funny actually) Separated airflow/high AoA/stall physics is not something that is easy to model at all even for the best simulations in the world. Unless you are a Boeing test pilot, stalling a 737 or 777 is absolutely the last thing you'd ever want to do in the real airplane anyway.

 

As an aside on this - I've seen some people make claims in the past week to the effect that the NGX doesn't "feel" realistic. The idea that a large swept wing jet should fly in a similar manner to a smaller and much lighter straight wing turboprop is something that doesn't make a whole lot of sense. The weight and the way the wing of a larger jet works is going to smooth out a lot of that "loose" getting-thrown-around-by-the-airmass type feeling you get in a smaller plane. You can feel this difference as a passenger even - a couple months ago I got off a 757 straight onto an ERJ-145. There's a very pronounced difference there - the 757 feels very stable and has that almost "on rails" thing going on.  It's a big airplane that's displacing a ton of air and you don't notice little bumps and gusts. The ERJ on the other hand is more like a turboprop - it's small, has a straighter wing, and you feel the airmass a lot more. We had a ton of real life pilots on the 737 test team (and even more on the 777 team), we got to fly the full flight simulators ourselves, Robert himself has an ATP and has flown large jets. etc. I don't think we're wrong about how they fly after all of that.

 

3. To do this sort of thing you have to run FSX in what amounts to slew mode where the external FDE is just positioning the plane where it wants it based on the algorithms - this breaks compatibility with a ton of addons and hardware that read information out of the FSX flight model, causes the aircraft to not respond to the FSX weather events like turbulence, and so on. We're definitely not willing to do that - we'd have a ton of complaints if we did with how big our market is.

 

4. Running more processes like this on top of what FSX is already doing is not going to improve framerates. I suspect their FPS are higher largely because their VC has a lot less clickspots, animations, draw calls and texture resolution than then NGX does, not because the flight modelling is somehow granting it a ton more frames. As well done as their simulation is, it's also a fact that a Q400 is a much simpler airplane (in real life) than a 737 or 777. Full geometric path VNAV that takes into account both altitude and speed with all manner of soft and hard constraints, variable target descent speeds and limits, autothrottle logic etc is very heavy math. (There's all kinds of calculus and differential equations involved in doing it) Look at what our LNAV is doing too - all the turn prediction curve drawing etc - those aren't static things that get drawn once, they're dynamically generated based on the current flight situation and get recalculated with every "tick" of the aircraft's system timers. Again, very heavy math that the Q400's route line drawing doesn't have to do.

 

To sum up - I do really like what Majestic's done - I've been flying it a lot since it came out, but this kind of flight model thing as it's implemented in the Q400 is not something we're going to be pursuing for all the reasons listed above.

 

Does the PMDG 737 realistically model the Short Period Oscillation when you have your own flight model and FDE modeled? It would be very interesting to me to learn more about that, as I want to use PMDG as basis for my 737 simulator

Share this post


Link to post
Share on other sites

Does the 777 have a realistic brake temp simulation when using autobrakes or is it bugged like with the 737 due to the flawed ground friction in FSX/P3D?

 

How will it be on the 747? 

 

I hope you can find a way to work on it!  :smile:

 

P.S. 

That slew mode thingy on the Majestic is really annoying as you said Tabs!


Fabrizio Barbierato

CLX319_zps10aeywtl.pngECN0550.png

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

  • Tom Allensworth,
    Founder of AVSIM Online


  • Flight Simulation's Premier Resource!

    AVSIM is a free service to the flight simulation community. AVSIM is staffed completely by volunteers and all funds donated to AVSIM go directly back to supporting the community. Your donation here helps to pay our bandwidth costs, emergency funding, and other general costs that crop up from time to time. Thank you for your support!

    Click here for more information and to see all donations year to date.
  • Donation Goals

    AVSIM's 2020 Fundraising Goal

    Donate to our annual general fundraising goal. This donation keeps our doors open and providing you service 24 x 7 x 365. Your donation here helps to pay our bandwidth costs, emergency funding, and other general costs that crop up from time to time. We reset this goal every new year for the following year's goal.


    2%
    $680.00 of $25,000.00 Donate Now
×
×
  • Create New...