Author Topic: FLIGHT modeling =)  (Read 1522 times)

Offline Gunslayer

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FLIGHT modeling =)
« Reply #15 on: April 30, 2001, 10:39:00 PM »
Well Mako, I hate to break this too ya but.... computers are pretty fast these days.   Basically , x-plane breaks the plane down into its component surfaces, it doesn't simulate every nook and cranny. But it comes quite close. Its kinda like a Jpeg is a compressed picture image. A modern computer can easily handle this info. I do have one question though, if the aces flight model is spot on, explane the Niki  

P.S. you decided to get technical so here is a rip from the X-plane website. I don't understand all this, but this is how x-plane's FM works.

How it Works:

X-Plane reads in the geometric shape of any aircraft and then figures out how that aircraft will fly. It does this by an engineering process called "blade element theory", which involves breaking the aircraft down into many small elements and then finding the forces on each little element many times per second. These forces are then converted into accelerations which are then integrated to velocities and positions... of course, all of this technical theory is completely transparent to you... you just fly! It's fun!


X-Plane goes through the following steps to propagate the flight:

1: Element Break-Down
Done only once during initialization, X-Plane breaks the wing(s), horizontal stabilizer, vertical stabilizer(s), and propeller(s) (if equipped) down into a finite number of elements. The number of elements is decided by the user in Plane-Maker. Eight elements is the maximum, and studies have shown that this provides roll rates and accelerations that are very close to the values that would be found with a much larger number of elements.

2: Velocity Determination
This is done twice per cycle. The aircraft linear and angular velocities, along with the longitudinal, lateral, and vertical arms of each element are considered to find the velocity vector of each element. Downwash, propwash, and induced angle of attack from lift-augmentation devices are all considered when finding the velocity vector of each element.
Propwash is found by looking at the area of each propeller disk, and the thrust of each propeller. Using local air density, X-Plane determines the propwash required for momentum to be conserved.
Downwash is found by looking at the aspect ratio, taper ratio, and sweep of the wing, and the horizontal and vertical distance of the "washed surface" (normally the horizontal stabilizer) from the "washing surface" (normally the wing), and then going to an empirical look-up table to get the degrees of downwash generated per coefficient of lift.

3: Coefficient Determination
The airfoil data entered in Part-Maker is 2-dimensional, so X-Plane applies finite wing lift-slope reduction, finite-wing CLmax reduction, finite-wing induced drag, and finite-wing moment reduction appropriate to the aspect ratio, taper ratio, and sweep of the wing, horizontal stabilizer, vertical stabilizer, or propeller blade in question. Compressible flow effects are considered using Prandtl-Glauert, but transonic effects are not simulated other than an empirical mach-divergent drag increase. In supersonic flight, the airfoil is considered to be a diamond shape with the appropriate thickness ratio... pressures behind the shock waves are found on each of the plates in the diamond-shaped airfoil and summed to give the total pressures on the foil element.

4: Force Build-Up
Using the coefficients just determined in step 3, areas determined during step 1, and dynamic pressures (determined separately for each element based on aircraft speed, altitude, temperature, propwash and wing sweep), the forces are found and summed for the entire aircraft. Forces are then divided by the aircraft mass for linear accelerations, and moments of inertia for angular accelerations.

5: Get Back to Work
Go back to step 2 and do the whole thing over again at least 15 times per second. Aren't computers great?

funked

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FLIGHT modeling =)
« Reply #16 on: April 30, 2001, 10:46:00 PM »
Deez you have been sold a bill of goods.  AH (and WB and any other modern flight sim) does most of that stuff already.

Offline Thorns

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FLIGHT modeling =)
« Reply #17 on: April 30, 2001, 11:13:00 PM »
Does X-plane have a cup holder like my Pony does?  My Pony has a 8-track tape player too... it was a NACA experiment in 1945....The "Redtails" were groovin' on those long bomber flights... :-P

If the flight models are calculated "close", and are the same for everyone flying in the sim....have fun!

Thorns

Offline StSanta

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FLIGHT modeling =)
« Reply #18 on: April 30, 2001, 11:34:00 PM »
Deez, I said it in the MA, and I'll say it here:

WE HEARD YOU THE FIRST TIME

It's very rude of you to keep pushing this down our throats.

If you continue being rude, I'll start being so too.

:/

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"If you return from a mission with a victory, but without your Rottenflieger, you have lost your battle."
- D. Hrabak, JG 54 "Grünherz"

Hammer Head

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FLIGHT modeling =)
« Reply #19 on: April 30, 2001, 11:57:00 PM »
 
Quote
Originally posted by Gunslayer:
Well Mako, I hate to break this too ya but.... computers are pretty fast these days.     Basically , x-plane breaks the plane down into its component surfaces, it doesn't simulate every nook and cranny. But it comes quite close. Its kinda like a Jpeg is a compressed picture image. A modern computer can easily handle this info. I do have one question though, if the aces flight model is spot on, explane the Niki    

hehe this is good

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"That was some of the best flying I've seen yet, right up until the point where you got killed."

[This message has been edited by Hammer Head (edited 04-30-2001).]

Offline Blue Mako

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« Reply #20 on: May 01, 2001, 12:00:00 AM »
Gun,

Thanks for your reply and for posting the X-plane stuff.  Basically the write up from X-plane agrees with my reply.  They say there that they make assumptions about the aircraft shape in order to calculate the behaviour of the air around the various surfaces.  This is the sort of stuff I did while studying aerodynamics and mechanics of flight.  It works well for approximations, but the number of panels needed to give a true result is virtually infinite.  Thus the processing time required to model this becomes infinite as well.  The problem with finite element analysis is that a good model is dependent on a large number of elements and the processing time goes up exponentially with the number of elements.

Basically it is impossible to represent an aircraft completely faultlessly, every method has it's limitations.

Btw, every computer model is only as good as the information fed into it.  That's why UFO's can still exist (eg. Niki according to some sources)

P.S. notice what X-plane said "...then going to an empirical look-up table to get the degrees of downwash generated per coefficient of lift"  Even X-plane uses tabulated data to produce it's flight model.  


Offline DeeZCamp

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FLIGHT modeling =)
« Reply #21 on: May 01, 2001, 12:37:00 AM »
To start off, I would like to thank those who have not only agreed with what I have suggested, but also thank those Who have not been quick to try and flame me away even though some having disagreements to what I have posted.
     
     I would like to thank gunslayer for posting the Technical (in laymans terms) process of blade element theory application from the X-plane website. Most of all the Questions that may arise are actually answered within the excerpts from the x-plane page/gunslayers post. The questions that cannot be answered from this post(try x-plane's wwII aircraft)  
   
     At no point am I/or was I trying to give the Impression that one should GO and look to X-plane for ITS combat role.  Simply because it has NONE.. (wardog   ) but would highly encourage those to see the difference in flight characteristics and to see what one is able to accomplish with an Aircraft that is from the Current Aces High plane set.  

    As Blue Mako posted earlier the propellers are the only thing that would be calcualted for blade element theory please read gunslayers post  

    St santa im sorry that this disturbs you, im not trying to change the world, or hurt anything as far as aces high goes, im actually trying to improve upon its already great simulated aircraft in such a way that could eliminate predetermined  "flight models". I may not have all the Specific Knowledge as far as being a programmer and what is/isnt able to be updated within the Aces High Code, but then again this Entire post is a suggesstion.

 Also At no time have you ever provided anything positive in response to this issue.
You have done nothing to inquire about whether or not blade theory was higher fidelity than what is currently used within Aces. As far as being rude im sorry that you feel this way, I feel that I have acted in a professional manner.
   
    Hitech I really do love how this ever evolving program is comming along. I dont even want to really call it a game anymore becuase it is Becomeing a Very good WWII multi - War simulation.  So dont ever think that I am by anymeans putting Aces down  

okay this is getting lenghty, So ill end it.
Salute to all   Even the ones who flame me  

Ps citabra it was a T-43 Navy Trainer =) Full Acro ride  nice  

MrSiD

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« Reply #22 on: May 01, 2001, 03:47:00 AM »
Never mind the flight models..

Can anyone explain to me why the majority of folks writing here can't spell?

Let's resolve that one first and then dig into the more demanding stuff.  

G10Whore

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FLIGHT modeling =)
« Reply #23 on: May 01, 2001, 05:40:00 AM »
how much are they paying you to advertise like that, deez?

Offline SirLoin

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« Reply #24 on: May 01, 2001, 06:12:00 AM »
Just add spin/stalls and buffeting and AH would be 10/10.Gameplay is the #1 priority and AH has it in spades,but FM could be more challenging.<not more realistic,but more challenging>Lets discuss and not throw buttered shrimps on the barbie..
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Offline moose

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« Reply #25 on: May 01, 2001, 06:36:00 AM »
wait, beef

youd rather have something that is more challenging then realistic?

I'd think most people prefer a FM which is exact?
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Offline miko2d

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« Reply #26 on: May 01, 2001, 10:11:00 AM »
 
Quote
Originally posted by moose:
wait, beef

youd rather have something that is more challenging then realistic?

I'd think most people prefer a FM which is exact?

 But since they wouldn't know exact if it bit them on the prettythang, they try to judge exactness by a method's name - as if it has anything to do with accuracy of the result.  

 Who said that results produced by a table would differ in any way from results produced by realtime calculation? Computers are faster - fine. That allows to store bigger and more detailed tables.

 miko


[This message has been edited by miko2d (edited 05-01-2001).]

Offline SB

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« Reply #27 on: May 01, 2001, 03:11:00 PM »
=====================================
The fact is Aces is a constantly evolving and improving product, and that is one of the reasons I like it. But I feel that we the Aces High customers have every right to make well thought out (not just flight model _____ is porked) suggestions to Hitech and and have them considered without being ridiculed. Like Deezcamp says Aces High is an excellent game as a whole , but there are other games out there they may do certain things a little better. No one doubts Hitech's expertise in this field, he has been doing airplane simulations for years, but I think if Hitech could occasionally put his ego aside he may just get some good suggestions from the community.
==========================================

Hmm and where do you think the majority of the suggestions that have been implemented into Aces High have come from? Could it be the user community? *gasp*!!

I did not see HiTech ridicule the suggestion, only point out that there is more than one way to accomplish the same task. I believe you read a bit too much into a short post that said exactly what he meant it to say.

SB

Offline LePaul

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« Reply #28 on: May 01, 2001, 03:24:00 PM »
I haven't flown any WW2 airplanes in real life, so I'll accept the Flight Models as being as accurate as can be duplicated on the PC, and credit HTC for doing the best they can with the data they have.

I HAVE flown a DeHavilland Vampire, a very early jet fighter and can tell you, the arado reminds me a lot of it.  Takes quite a while to slow down and speed up.  Those traits are definetly consistent with all the early jets  



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Offline Gunslayer

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« Reply #29 on: May 01, 2001, 04:45:00 PM »
SB - I think that you are reading something into my post. I never said that Hitech "ridiculed" Deezcamp's suggestion. I basically said that Hitech shrugged it off as tripe, as I have seen him do to many poeple's suggestions. I have seen Hitech get offended by certain suggestion, and it seems the FM is the quickest way to do it. I guess I would just like to see a little more friendly relationship between the customers and Hitech.

As far as tables being able to model flight as well as real time calculation, the proof is in the planes, if you will. Planes like the niki are hard proof of the failing of the tables model. With a real time model, a plane like the Niki would perform according to its shape, weight, and power, not some table that says "At X alt pulling Y amount of Gs , Fly this speed."

I kinda feel like the people here don't even wan't to try anything else to see if there is a difference. Only a couple poeple here have even tried it. Most seem content to thow out their theory then stick their head in the ground. Just try it for goodness sakes. Watch the way the planes move. Try a hammerhead and tell me that the planes momentum doesn't seem more realistic. But don't just slam deez for making suggestions.