Trying to run this game on a Windows 10 64-bit installation with a GTX670 I was getting sub 10 FPS frame rates.
As I have found no solution to this problem around the internet I'm posting what worked for me in case some one else also has the same problem.

Simply running the main executable via DXWnd allows the game to run perfectly on my system.

https://sourceforge.net/projects/dxwnd/

Run DXWnd as administrator and drag aphavoc.exe from the games install directory into the window that opens up.

Right click on aphavoc.exe inside DXWnd and click modify and uncheck "Run in Window"

Double click on aphavoc.exe inside the DXWnd window to start the game.

The game should hopefully run fine. You will even be able to increase the resolution by pressing ctrl + F4 without the game crashing. Just don't expect the 2D hud to fit properly anymore.

Hopefully this helps someone. :)

I know it's been a while since this post, but for everyone else passing by: This did the trick for me as well. I haven't managed to run the game in fullscreen mode yet, but at least it works.

Reviving a old post again, this solved my sub 15 fps framerate and got it up to a 30ish fps which is somewhat stable but nowhere near as bad. Fullscreen works for me I did alot of testing trying to find the best settings in DXwind for Apache Vs. Havoc. I have Fullscreen, 30FPS, and it looks pretty good (Not as good as running the game in a super tiny window though lol, You can Increase the games resolution by pressing CTRL+F4 but anything over and sometimes at 720x480 crashed the game on my computer.

Im working on going through every option in DXwind to find which ones results in the best visual quality and performance balance. I just started this a little bit ago and will share my Notes from the notes Section in DXwind I used for recording changes so if I broke something I would know what to revert back to fix it. Here you go - this may not work for everyone. I am sure the FPS issue is related 100% to the game not anyone's hardware unless it is a really underpowered computer, I have a Custom Built by myself Gaming Rig (Its my hobby and my Job, I own my own computer repair and Custom Computer Building business Speedy Computer Repair) so computer parts compatibility with each other and performance is in my area of expertise. I know its the game because after messing with the game and DXwind I got a glitch where the view was messed up and the game ran super good high FPS and everything. I believe the CockPit textures or how its drawn is the issue. I think its a overlay and some of the methods they use or something to display it onscreen is broken by hardware changes/software code changes since the era PCs this game was originally run and optimized for.

heres my settings list for DXwind
Test #1
Enabling "Suppress Overlay Capability" Causes screen to show black outside of the cockpit. though I notice there is no lag, one of the textures must be causing the issue with low framerate.

Test #2
Disabled "Suppress Overlay Capability", test results now
-Outside of cockpit is still black, FPS was around 30. Not sure why its doing that I haven't changed any settings since it was showing the exterior.
NOT FIXED
Tes!#3
Set Z order to "Default" forgot I changed that setting and it was before I started using the notes section here. Attempting test now!
Did not work.

Test #4
Forgot I checked "Don't fix pixel format" befor eusing this notes section to record tests.. Unchecked it, now to test! Scren still black, it's like its not drawing or refreshing.
NOT FIXED

Test #5
Checked "Auto Primary Surface Blit", Checked "Recover Screen mode", Rechecked Aero Compatible Mode" & Optimize for Aero Mode", Set VSync to off",
Unchecked "Trim Texture Formats" forgot to record note when I checked it. Unchecked "Set 16BPP RGB565 encoding" Not sure what it does.
Checked "Enable Gamma Ramp Emulation" Still not working
NOT FIXED

Test #6
Rechecked "Set 16BPP RGB565 encoding" going to try it in windowed mode and see if it begins working!
NOT FIXED

TEST #7 GOING TO RE ADD THE GAME TO DXwind and see what settings I may have chnaged thats causing this! Standby
Checked "Flip Emulation" & "Emulate Win Maximize" Unchecled "Recover Screenmode
FIXED
My theory is that it is the "flip Emulation" that broke it whatever that means/does.

Test #8 Now going to work on changing settings to improve FPS!
Checked
Direct X - Checked "Auto Primary Surface Blit" "Compemsate Flip Emulation"
Direct 3D Set "Force Vertex Proc. / Execute Buffer" to
"Hardware Video"

YESS ITS RUNNING FAIRLY WELL GIVEN 30FPS and below sometimes, working on optimizations!

Test #8 Checked "Locked Sys colors" going to look for the file to delete that i read a while ago that fixed low FPS to try and increase the FPS and Stability more

I just want to finally play the game now it has a bearable FPS and works right, WHOO WHOO YEET!

There is solution for perfect APACHE HAVOC even in 4k in 60FPS on WIndows 10.

delete removethis from link below (it does not allow me to put links)

go here: http:removethis//dege.freeweb.hu/dgVoodoo2/dgVoodoo2/

1. download dgvoodo2
2. copy all extracted files and floders into aphavoc folder
3. copy all the files (4xdll files) from MS/x86 you downloaded into aphavoc folder (where aphavoc.exe is located)
4. start the aphavoc.exe (uncheck all the complatibilties options)
5. you can configure AA, aniso, resolution starting dgVoodooCpl.exe from aphavoc folder

you have perfdect gaming exp.

YOU WELCOME !!!

P.S. click image below to see how the folders should look after all steps are done:

Is there a solution to having the cockpit not shrink when increasing resolution in game, I have also tried to download and install "eech all mods" but installer is broken.

Yes, the cockpits in the game are drawn for 640x480 resolution so select that for the game and scale it up using the dgvoodoo app.

Sorry I've managed to get eech all mods to work but cant get the cockpit on the older version eeah to work, all of the external views are high res but cockpit detail is still low res, I've managed to get full screen 45fps stable but, cockpit detail low