Flight Simulation Performance Analyzed

by Scott “Blade124” Gentile


The purpose of this article is to assist the flight sim community in understanding the basics of how a computer runs a modern flight simulation. Hopefully, this will help take some of the mystery out of your next pc upgrade. We’ve all seen enough Quake and Unreal video card tests to last a lifetime. This is for the flight simmer. We will review the three major hardware components of a computer system, and how they each affect flight simulation performance: CPU, video card, and memory (RAM).

We each perceive quality differently

Every flight simmer wants the best in image quality, and the best in framerates. Some will sacrifice framerates for image quality, or vise versa. I’m sure you’ve seen your share of framerate debates that start when someone says, “It runs as smooth as glass on my PIII system.” Believe it or not, some people consider 15fps (frames per second) smooth, while others consider 30fps choppy. It’s true. Don’t make the mistake of thinking what you see is the same as what someone else sees – “Framerate perception is in the eye of the beholder.”

In this article, I will consider 20fps as acceptable and 30fps as good, and strive to obtain the best picture quality somewhere in between those numbers.

Quick CPU / video card bottleneck test

CPU test:

To find your CPU bottleneck, simply run your favorite game at its lowest resolution and make a note of the framerate performance. This is a good indication of the CPU running that particular game as fast as it can, usually regardless of the video card. If it is choppy at the lowest resolution, chances are no video card will resurrect the CPU.

Video card:

Once you find your CPU bottleneck, increase the resolution and color depth (16bit / 32bit) incrementally until you start to notice a slowdown. This is your graphics card showing its limit. As a general rule, I find the best compromise between framerates and quality while sitting on the runway, and then back it off one. For example, if 1280 X 960 X 32bit color is the highest acceptable setting sitting on the runway, try running your simulation at 1024 X 768 X 32 because your computer may experience a serious slowdown when flying over busy target areas.

Video card comparison

System specs:

  • Intel 845 motherboard
  • Intel P4 2.4GHz / 533MHz
  • 1GB PC2700 (DDR333) Ram
  • Seagate 7200 RPM hard drives
  • Windows XP Pro SP1
  • DX9.0a

Video cards tested:

  • Nvidia GF3 Ti 200 with 42.68 drivers
  • Nvidia GF4 Ti 4200 with 42.68 drivers
  • ATI Radeon 9700 (NOT the PRO version) 3.2 drivers
  • Vsync – OFF
  • Monitor refresh – 85Mz

We used the generic framerate counter utility, FRAPS to test in-game framerate performance.

Note: In all tests, X2 and X4 stand for X2 / X4 FSAA (Full Scene Anti-Aliasing)

IL-2 Forgotten Battles (beta)

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All cards do well at 1280 X 960 resolution. Upgrading from a GF3 to a GF4 will allow you to run the same resolution with some FSAA, to improve picture quality. These tests were run under OpenGL, which was considerably faster than Direct X.

Microsoft Combat Simulator 3

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ATI could be THE card for CFS3, however, the GF4 will give its expected 50% improvement over the GF3.

Note: After these tests were completed, I loaded some experimental Omega GeForce drivers, which increased performance and helped closed the gap. Ed Note: Using beta or 3rd party drivers can cause serious issues with system stability. In addition, 3rd party drivers should never be used for comparison as features can be disabled or altered which can seriously affect performance and/or image quality.

Stuttering in CFS3:

This one is tricky. You can get a good framerate in CFS3 at a particularly high setting, but may notice stuttering increased as you approach what you think is an acceptable resolution. CFS3 also exhibited extreme stutters on the system with 128MB of RAM.

Another type of stutter encountered on every system was when the bullets from your aircraft struck another aircraft. One parameter in particular that makes a big difference in reducing stutter when attacking aircraft is the “aircraft quality slider”. Lowering this slider to “1” was the only fix when using a GF3 card, regardless of the resolution. On an ATI card, if I run it hard, I need to lower this setting too, but the ATI will run stutter free at high video quality across the board if the overall resolution is set very low.

Strike Fighters Project 1

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Strike Fighters and the ATI card have compatibility issues.

The ATI clearly has issues with Strike Fighters Project 1. Notice the linear line that indicates that it never reached its bottleneck, which again bears out an inherent problem with the ATI and Strike Fighters Project 1. Explosions made dramatic slow-downs on the ATI. Going into the BIOS and lowering the AGP Aperture setting to 16MB gave the ATI a huge bump, but the other games did not like that change. Seeing that you have to reboot the computer to change the BIOS settings every time you want to either go from or to playing Strike Fighters, this is a bit of an inconvenient fix.

A note on the AGP aperture size:

In a nutshell, the AGP aperture size is the amount of main system memory (RAM) allocated for your video card to use as video memory. The original vision of AGP was video card manufacturers could utilize less expensive system memory as video memory, reducing the need to place large amounts of memory on the video card. Then the 3D video card arms race began. The AGP bus was unable to keep up with the GPU (graphics processing unit) memory demands, so the on-board video ram just kept growing. In fact, even the high-speed, expensive video memory has been the critical bottleneck for years. Recent compression standards have gone a long way in helping programs stay on the video card and out of the main system memory (RAM). The bottom line is if your video card ever needs to frequently throw large textures down that AGP bus, your game will turn in to a slide show. 128MB of video ram is quickly becoming the standard amount of memory needed on a video card these days.

Falcon 4 SP3

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If you have an ATI video card, and a fast CPU, viewing Falcon4 at 1600X1200 resolution with FSAA will produce some of the best landscape visuals, even when compared to the latest games. Falcon4 has no right to still look so good, but it does. People like “Snakeman” who are running the service pack projects are just one of the many heroes that have pushed this classic sim to new heights.

Jane’s F/A-18

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Jane’s F-18 is a strange beast, based on the very old but very good Jane’s F-15 engine. I’m not a programmer, but it almost seems that the framerates are governed by the sheer amount of fill-rate your card can handle. It is ironic that it takes a GeForce4 to deliver acceptable framerates on an aging title. Still, a classic simulation with a dedicated following.

CPU comparison

System 1

  • Aopen Via AX34 motherboard
  • Intel PIII 1.1GHz CPU
  • 512MB PC133 RAM
  • Seagate 7200RPM hard drives
  • GF3Ti200 43.65 drivers

System 2

  • Intel 845 motherboard
  • Intel P4 2.4GHz / 533MHz
  • 1GB PC2700 (DDR333) Ram
  • Seagate 7200 RPM hard drives
  • GF3Ti200 43.65 drivers

The higher you crank up the resolution, all systems end up at the same bottleneck – the video card. Note the CPU shows it’s muscle at the lower resolutions.

IL-2 Forgotten Battles (beta)

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You can barely get by with a PIII in IL-2 FB, as a 1.1GHz PIII can barely pass 20fps at the lowest resolution. A fast CPU can do very well with a GF3 card though.

Strike Fighters Project 1

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One word to describe what killed the PIII in this test…MIRRORS. Turning the mirrors off on the PIII increased framerates from 10fps to 19fps. External views slowed down considerably when viewing other aircraft. This isn’t necessarily a bad thing, because unlike the AI aircraft in IL-2 FB, Strike Fighter’s AI flight models behave incredibly close to the ones you fly.

Microsoft Combat Simulator 3

CFS3 is quite playable on a PIII with a GF3 card. It also shows you how much more efficient CFS3’s table lookup flight models are on the CPU (some would argue this is a weakness).

Memory (RAM)

If your system has less RAM than a simulation utilizes, you will probably notice significantly longer load times, screen transitions, and perhaps some stuttering during the game as your computer makes room on your hard drive to use a temporary place to use as RAM (referred to as a swap file or page file). Hard drives deliver typically less than 10% the performance of system RAM, so when your computer has to reach for the hard drive for RAM, get ready to wait and listen to a grinding hard drive (the little blinking activity light) trying to cough of more memory. Typically, low RAM will not seriously lower your systems framerate performance once the simulation loads (except, the system may experience in-game stutters and delays).

Look below to see how much RAM the following programs will use on your system:

Janes F-18 42MB (not a typo)
Falcon4 SP3 104MB
CFS3 228MB
SFP1 235MB
IL-2 FB 580MB!

Now look how much faster these programs load with more RAM. System tested: PIII 1.1GHz, Seagate 7200RPM Hard Drive, 128MB 512MB Improvement

  128MB 512MB Improvement
SFP1 75 sec. 25 sec. 300%
CFS3 84 sec. 36 sec. 233%

Note: IL-2 FB Beta took a whopping 88 seconds to load with 512MB of RAM. I didn’t even want to try it with 128MB. This is no jab at IL-2; it just shows how many good things are loading up under the hood.

Notice how a P4, 2.4GHz with 1GB of RAM doesn’t improve load times all that much over a PIII with ½ the RAM. 512MB seems to be the sweet spot (law of diminishing returns).

  PIII 512MB PIV 1GB Improvement
SFP1 25 sec. 20 sec. 25%
CFS3 36 sec. 27 sec. 33%

Basically, plenty of RAM and a fast hard drive are the two key components to a fast loading (and exiting) flight sim. It also makes entering and quitting missions much faster. In some cases, changing views will even speed up with more RAM.

Final recommendations

To make this as simple as possible, there are two fictitious people who I am making recommendations to:

  1. Sam is someone who needs smooth framerates at all times. He is happy with 1024X768X32 (color) resolution with no fsaa, as long as he is always over 30fps.

  2. Pete prefers a really nice picture (HATES jaggies), at the cost of framerates and doesn’t mind if his sim dips well below 20fps.


IL-2 Forgotten Battles (beta)

If either Sam or Pete are running this one a PIII, they will both long for a P4 or a fast AMD. Sam will find a P4 with a GF3 card fine, while Pete must have a P4 with a GF4 4200 (NOT an MX) at the minimum. Pete will appreciate an upgrade to an ATI 9700 or 9800.

Given a standard CPU , the following resolutions are recommended:

Card Sam Pete
ATI. 9700 1280 X 960 X 2fsaa 1280 X 960 X 2fsaa+
GF4 Ti 4200 1280 X 960 1024 X 768 X 2fsaa
GF3 Ti 200 1024 X 768 800 X 600 X 2fsaa

Microsoft Combat Simulator 3

Sam is happy running CFS3 on a PIII with a GF3 card. Pete will be happy with a PIII with a GF4 4200 card, but will certainly appreciate and ATI 9700.

Regardless of CPU, the following resolutions are recommended:

Card Sam Pete
ATI. 9700 1280 X 960 X 2 1280 X 960 X 4fsaa+
GF4 Ti 4200 1024 X 768 1024 X 768 X 2fsaa
GF3 Ti 200 800 X 600 800 X 600 X 2fsaa

Strike Fighters: Project 1

The first thing both Sam and Pete must do is make sure their mirrors are turned off, or else they will not be the least bit happy with a PIII. Either way, Strike Fighters demands a P4 to be seen in its full glory. Sam can survive with his PIII GF3, but Pete’s only option is a P4 / fast AMD with a GF4 card, since the ATI and Strike Fighters have problems together. In fact, I would recommend that Pete buy the fastest GF card (due to compatibility issues with the ATI) he can afford.

Regardless of CPU, the following resolutions are recommended:

Card Sam Pete
ATI. 9700 1280 X 960 X 2 1280 X 960 X 4fsaa+
GF4 Ti 4200 1024 X 768 1024 X 768 X 2fsaa
GF3 Ti 200 800 X 600 800 X 600 X 2fsaa

The ATI is not recommended, but if you have one, these would be the settings I would go with. If it is going to be choppy, it may as well look good.

Falcon 4 SP3

You can’t lose. Both Sam and Pete will enjoy their PIII with a GF3 card. More is better however, especially when taking into account higher resolutions and more image quality. It’s an old adage that still applies to computers regardless of the game!

Jane’s F/A-18

What killed this sim out of the box for me was the terrible framerates. Only just recently, after buying the ATI and GF4, have I flown this sim with acceptable framerates. Ironically, Sam and Pete must have a GF4 or ATI regardless of the CPU. Jane’s F-18 needs a fast video card.

I hope this article has been informative.


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