Aces High Bulletin Board
General Forums => The O' Club => Topic started by: Virage on July 23, 2003, 04:20:39 PM
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You know, the ones without the guns.
XPlane?
Fly2!?
MSFS?
Anyone tried these or others?
I'm finishing my PPL and want to practice all these pesky procedures my instructor keeps insisting on. Now there's one guy I wouldn't mind seeing go down in flames :).
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They all suck.
Sometimes I fire up MSFS2002 to check a few IFR things, but then it sucks so bad that I rather try it on a combat sim.
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MSFS 2004 I'd guess
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X-plane.
MSFS uses lookup tables to figure out how the plane should behave at different angles of attacks, speeds, and altitudes. X-Plane models the airflow and calculates the lift over the wing.
"So? If the lookup tables are good, then what's the problem with them?"
It's not so much of a problem as it is that the only planes you can fly in MSFS are ones that have been developed by huge teams of programmers. In X-plane, there are hundreds of planes you can download for free, as well as something like 30-40 different planes in the program itself. Why? Because X-Plane comes with a plane creator. You enter thrust, wing chords, shape the fuselage, landing gear, everything. You choose your NACA air foils, specify drag coefficients, it's an amazing amount of detail. Once you're done, the plane flies just like the real on in the sim (assuming you did everything correctly).
There are even companies that build aircraft that use X-Plane to simulate their designs while they are developing them. Carter Copter, Burt Rutan, and more.
Ask an MSFS user to simulate an X-15 flight, starting with dropping from the wing of a B-52, the flight to the edge of space, using reaction control thrusters to alter your planes attitude, then setting up a re-entry and the subsequent glide out to Edwards. Sometimes I like to set up the drop out in the Pacific and land my X-15 at LAX, it's a real challenge.
MSFS is prettier right now, and the ATC kicks butt, but X-plane is really a lot more versatile right now. Also, Squawkbox support is finally being added, so X-Plane pilots can now fly alongside MSFS pilots in the same online world.
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Choirboy, there are THOUSANDS of planes available for MSFS2K2 and you don't need large quantities of programers to make new planes, most are done by single individuals. X-Plane is ok, I own it, but I find it very lacking in too many areas to suit me. However, to each his own. Microsoft Flight Simulator would be the one I reccomend, the newest version due out on the 30th of this month. It's called a Century of Flight.
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Sure, but how accurately do they fly? I'm not trying to get into a religious debate about flight simulators, just informing someone that there's an alternative to MSFS for people interested in flight realism.
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I'd say FS2004 would be the answer for learning the procedures.
I don't think you'll need any extremely detailed flight models there... you aren't going to do stunts in the cessna types anyway.
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MS flightsim is lacking in some areas when aerobatics are involved, no argument there. I personaly fly mostly non aerobatic aircraft or limit myself to rolls and loops and the occasional hammerhead. Some of the models I have purchased actually do correct spins and other maneuvers. Most of this is based on who designed the flight model of that particular aircraft.
X-Plane is a good alternative to MSFlightsim Choirboy, I won't argue with that, however... and this is just my opinion, I feel more like I am "there" flying the MS product. Your mileage may vary of course :).
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definitely go for FS2k2, it sells at discount prices and it's good enough, plus it already has lots of addons developed.
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Originally posted by Chairboy
Sure, but how accurately do they fly? I'm not trying to get into a religious debate about flight simulators, just informing someone that there's an alternative to MSFS for people interested in flight realism.
Given the amount of processing power it takes someone like NASA to run a realtime computerised aerodynamic model I often wonder how accurate X-Plane can really be?
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it has to be very crude. accurate computational fluid dynamics simulations take weeks on PCs
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Originally posted by udet
definitely go for FS2k2, it sells at discount prices and it's good enough, plus it already has lots of addons developed.
Most, if not all, of those addons will work with FS2K4 also Udet :).
The really cool thing about the new one is a host of new aircraft depicting the Golden Years of flying. It includes a Jenny, The Winnea May, a DC-3 and a couple of others. It has new weather and new navigational aids and real time IFR communication with the tower.
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X-plane does laminar flow calculations by breaking each surface into 8 sections and calculating it for them. It's using a mathematical trick that's about a hundred years old and was used to calculate lift before computers, so it's not processor intensive.
It isn't nasa grade accurate, but it's a heck of a lot more accurate then programs like MSFS that don't do any calculations at all.
Again, there are companies that use X-Plane as the simulator when testing new designs. _Nobody_ uses MSFS when they are designing their planes.
Carter Copter uses X-plane extensively, and Burt Rutan uses it too. Remember the White Night x-prize space craft that Rutan unveiled a few months ago? Its simulator uses X-Plane.
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Originally posted by Chairboy
X-plane does laminar flow calculations by breaking each surface into 8 sections and calculating it for them. It's using a mathematical trick that's about a hundred years old and was used to calculate lift before computers, so it's not processor intensive.
Blade Element Theory.
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Originally posted by Chairboy
It isn't nasa grade accurate, but it's a heck of a lot more accurate then programs like MSFS that don't do any calculations at all.
Carter Copter uses X-plane extensively, and Burt Rutan uses it too. Remember the White Night x-prize space craft that Rutan unveiled a few months ago? Its simulator uses X-Plane.
Saying MSFS doesn't do any calculations is extremely misleading. Its quite possible to build extensive lookup tables far more complex than Xplane (who knows if they do or not). I'm sorry but I just don't have huge faith in a PCs CPU to do complex realtime areodynamic calculations. First its simplified, second what calculations or complex factors are left out?
Whats the difference between pre-tablising data and simplifying a complex surface into 8 components? Sounds like 6 of 1/half a dozen of the other to me.
And what do they use it for? A general 'here have a fly' sim, or a design sim. If they use it for design I'll wait a few rounds before I take a ride ;)
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They use 'em as part of their design process. Go to x-plane.com and see for yourself. Also, as good as lookup tables can be, you still end up either needing to develop one for each plane or risk having a general one that doesn't accurately reflect the performance of the plane.
BTW, it doesn't really matter if you believe it or not. The FAA says you can use X-plane towards a commercial pilot certification, plane manufacturers use it to test their designs, and your skepticism isn't really important because smarter people then you or I have decided that X-Plane is the right tool for the job.
(edit: Changed FCC to FAA, whoops!)
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kids kids.. lets chill
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Interesting reading:
http://www.popsci.com/popsci/aviation/article/0,12543,463052,00.html
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The ELITE system, with the hardware.
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The Federal Communications Commission is telling people they can use X-Plane for a commercial pilot's license?
I'm pretty sure that at some point, X-Plane uses a lookup table to reproduce some effects.
Even with the simplified airfoil model, there are so many other forces acting on a plane, it would bring any home PC to it's knees.
-SW
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Once again, you could clear your misconceptions up if you just visited x-plane.com. I know it is fun to speculate, but when the actual answer is just a click or two away, it's kind of silly.
If you don't want to find the answer on the x-plane site, then I suggest this article from popular science. It is easier to digest:
http://www.popsci.com/popsci/aviation/article/0,12543,463052,00.html
(fixed URL)
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That link isn't complete.
Of course, I'm not speculating that there are either a) extremely simplified forces beyond just the airfoil, or b) using look up tables to relieve some stress on the CPU.
It's not misconception that any home PC could not simulate flight without a lot of short cuts, beyond just the airfoil, and therefore use a look up table for several of the parts of flight.
Il2/Forgotten Battles lays claim to one of those "new-fangled physics engines" to simulate flight, what many people don't realise is that it's still using look up tables to derive much of the input into those equations.
Boeing simulators, the ones for the passenger jets, have a whole load of computers to compute the flight model. Reducing the airfoil to just 8 sections won't relieve that much of the CPU's stresses, since there are so many other factors that go into replicating flight. Therefore, more short cuts must be had to get the process to run at acceptable speeds on home PCs.
-SW
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For more information about using X-Plane as credited training for FAA (whoops on the FCC part, my bad!), click here:
http://x-plane.com/FTD.html
You'll find that X-Plane can be used towards instrument rating as well as Commercial Certificate and Airline Transport Certificate.
Elite is cool, btw, but can only be used towards instrument rating.
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Here's some info from X-Plane about how their engine 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?
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Originally posted by Chairboy
They use 'em as part of their design process. Go to x-plane.com and see for yourself. Also, as good as lookup tables can be, you still end up either needing to develop one for each plane or risk having a general one that doesn't accurately reflect the performance of the plane.
BTW, it doesn't really matter if you believe it or not. The FAA says you can use X-plane towards a commercial pilot certification, plane manufacturers use it to test their designs, and your skepticism isn't really important because smarter people then you or I have decided that X-Plane is the right tool for the job.
(edit: Changed FCC to FAA, whoops!)
PC memory could allow for fairly large lookup tables. So precalculation is not that bad and could be fairly complex. Precalculation can add in many aerodymanic factors a PC could not handle.
I believe MSFS is allowed for use towards instrument rating is allowed as well (and has been for some time)?
I'm know aerodynamic genius but I do know what real (big) flight sims require for horse power and what a PC has for horse power. X-Plane fanbois are like the boy-racers (I believe yanks call em ricers?) of the sim world :)
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Originally posted by Vulcan
PC memory could allow for fairly large lookup tables. So precalculation is not that bad and could be fairly complex. Precalculation can add in many aerodymanic factors a PC could not handle.
I believe MSFS is allowed for use towards instrument rating is allowed as well (and has been for some time)?
I'm know aerodynamic genius but I do know what real (big) flight sims require for horse power and what a PC has for horse power. X-Plane fanbois are like the boy-racers (I believe yanks call em ricers?) of the sim world :)
Theres alot more to designing an aircraft than just using lookup tables to see if the airframe will fly or not.
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Also, MSFS cannot be used towards instrument rating. The FAA does not allow it because the flight behavior is not representative.
Out of curiousity, how does pointing out a mistaken assumption (Namely, that MSFS has a more realistic flight model than X-P) make me analogous to a 'ricer' or fan boy?
I think I'd be a fan boy if I was posting 'MS Flight Sim sucks!' and 'you loozers are lame for using microsoft krap, x-p rulz!', but I'm not. I like MSFS, it has a better interface and prettier graphics, but it is apparent that X-Plane has better realism. The FAA, plane manufacturers, and a bunch of commercial pilots agree.
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earlier versions of x-plane had problems simulating stall. From what you guys said iy sounds like they are doing a very crude numerical modelling. I'd rather have tables.
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Originally posted by Chairboy
Also, MSFS cannot be used towards instrument rating. The FAA does not allow it because the flight behavior is not representative.
Out of curiousity, how does pointing out a mistaken assumption (Namely, that MSFS has a more realistic flight model than X-P) make me analogous to a 'ricer' or fan boy?
I think I'd be a fan boy if I was posting 'MS Flight Sim sucks!' and 'you loozers are lame for using microsoft krap, x-p rulz!', but I'm not. I like MSFS, it has a better interface and prettier graphics, but it is apparent that X-Plane has better realism. The FAA, plane manufacturers, and a bunch of commercial pilots agree.
I was comparing X-Plane to real aerodynamic sims, ie big uns like NASA uses, not an MSFS-XPlane comparison, as the ricer comparison.
As far as the intrument rating goes, I remember this from years and years ago. I'm not an MSFS fan (in fact I haven't touched it for years).
All I'm pointing out is that a simplyfied aerodynamic blade model is not necessarily more accurate than a table based model. And (mrcoffee) that neither compares to the larger supercomputer based simulations as far as design goes (ie I wouldn't set foot on an aircraft designed in MSFS :D )
The disadvantage of Xplane is it HAS to be simplified AND exclude certain aerodynamic forces.
For example from your own posting:
"then going to an empirical look-up table"
"but transonic effects are not simulated "
"In supersonic flight, the airfoil is considered to be a diamond shape"
The advantage of a lookup table is that the generating engine can be extremely complex and add nuances or unusual characteristics (such as changes in shape to the wing) without having to sacrifice accuracy to be realtime.
And, as we can see above, X-Plane uses lookup tables which to me is an admission that these are still superior on lower powered computer systems (ie not mainframes).
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Your selective quoting is misleading. Regarding the lookup table, here's the rest of the sentence:
"empirical look-up table to get the degrees of downwash generated per coefficient of lift"
Eg, it uses a table to get the downwash based on a certain lift coefficient, NOT as the flight model. MSFS uses lookup tables for every aspect of flight, and the realism suffers greatly.
It doesn't model transonic flight, but then again, neither does MSFS.
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Originally posted by Chairboy
blah blah blah it uses a table blah blah blah
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While I have never done any programming of flight sims I have worked on large scale physics simulations. Since the computing resources capable of running these simlutions were limted (we had to share time with other users) we had needed to limit the total load on the system. In order to do this standard prctice is to work out what parts of the calculations need to be done live and what parts can be calculated before hand. For the stuff we could do before hand we ran a "physics render": essential we ran the calculations with all the relevant data ranges and stored the data in lookup tables. This data was then used by the simulation in real time (or in actual fact scaled-up time). As long as you are are dilligent and make sure that the physics render produces results of the accuracy and granularity required then there is no reason why the results should not be as accurate doing the whole set of calculations live. In fact you may be able to make it more accurate because you can do the render more accurately as you don't need to worry about resources as much: i.e. you can devote more horsepower to the calculations.
Until we have quantum computers that can simulate the real world down to the actual molecules and atomic forces "look-up" tables are likely to be more efficient in making simulations.
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HT had something very interesting to say about look up tables vs real time calulating, do a search.
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For something like Aces High, lookup tables are great! Users are not creating their own planes, so it's logical to do all the calculations on the back end.
It's apples & oranges, the real time calculating is cool in X-Plane because you can accurately model the flight characteristics of almost every plane built just by entering the numbers (air foils, wing sizes, chords, pitches, drag coefficients, etc). There's no 'tweaking' required.
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If you do a search on X-Plane and Hitech you find some very interesting comments, many of which indicate tweaking IS required acheive accurate modelling.
But like you said, Apples and Oranges, and from the informed comments I read it sounds like tables are good for historical models (like AH) and X-Plane is good for experimenting with designs and is as accurate as you could get with a PC for new untested unbenchmarked designs.
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Thnx for the responses,
MSFS2004 or X-plane, hmm.
Which does VFR Cross country the best?
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MSFlightsim 2004 :)
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MSFS.