Simanaitis Says

On cars, old, new and future; science & technology; vintage airplanes, computer flight simulation of them; Sherlockiana; our English language; travel; and other stuff


SO THERE I WAS, just like SAAB engineers with their 21A fighter: They wanted to convert it to jet power. For details, see “Saab 21—Where’s My Prop?” here at SimanaitisSays.

Above, the real Saab 21A; below, its jet-powered 21R sibling. This and other images from The Saab 21 A & R, Profile Publication No. 138.

A Miscalculation.  Bo Widfeldt recounted in Saab 21 A and R, Profile Publications Limited, 1966, “When the detailed plans for the conversion were studied, it was calculated that the necessary airframe alternations would be of the order of 20 percent. In fact, when the 21R was finally ready for construction, it differed from the original 21A by more than 50 percent.

Swapping a V-12 piston engine’s spinning prop for the Goblin 3’s turbine thrust worked out to be more complicated than engineers envisioned. 

GMax/Fltsim Fooling. By contrast, my project would be much simpler: I had a GMax Saab 21A for my Microsoft Flight Simulator FS9, and all I needed was to delete the prop, put in a couple of scoops and wing tanks, and change a few entries in the aircraft’s Fltsim .cfg file defining its performance.

This and other images are of my GMax 21A and 21R, but not without some fun and games.

Adieu, Windows XP. In the midst of this easy-peasy project, my GMax/Fltsim world had a meltdown of its iMac 27’s Windows XP partition (which had worked just fine thank you for some 10 years). 

Fortunately, files were backed up on the computer’s Bootcamp, part of the partitioning process. And I had a perfectly nice Dell laptop PC sitting largely idle (except for watching Metropolitan Opera On Demand on its cool 2-in-1 easel).

True, there’d be plenty of file swapping, but the GMax Saab 21R jet was no more than a 20-percent modification of my 21A prop version. 

Wait. Where have I heard that 20-percent jazz before? 

Here are tidbits of the GMax 21A to 21R conversion. All in good fun.

From Prop to Jet. The 21A is powered by an inverted Daimler-Benz V-12. I had already devised GMax animation of its engine hatches, along with necessary ingress/egress of its pilot.

By the way, at first I pondered the pilot’s means of access until the Profile Publications documentation arrived. A photo of a lineup of 21A’s showed a retracting ladder, dropped side window, and pivoting canopy section. 

This and other images from The Saab 21 A & R, Profile Publication No. 138.

DB 605 vs Goblin 3. Engines are good fun to model, especially in deciding how wacko to go with details. Spark plugs and fuel injectors on each bank of the DB V-12 were just about my limit.

The Saab 21A under the skin.

By contrast, the Goblin 3 was basically a bunch of nestled tubes. I had fun with a couple of spinning compressors which are buried inside (one of them is visible until the engine is up to speed; then it’s replaced by a red disc rotating in the exhaust). Talk about wacko; sorta like artisans sculpting gargoyles high up cathedral spires.

Above, the Goblin 3. Below, before and after lightoff. 

Minor Details. Fabricating the Goblin 3’s sizable air inlets necessitated redesign and reanimation of the hatches. And a new instrument panel was called for: Flight instrumentation is identical. But, of course, power monitoring is completely different.

The 21A’s panel. The right portion of the 21R’s panel is cribbed from another jet in my collection, as are its flight dynamics.

There were other workarounds, perhaps related to the Windows XP crash or laptop limitations; I won’t know until I opt for a big-screen PC one of these days. In the meantime, I’ll remember the Saab engineers’ optimism…. ds 

© Dennis Simanaitis,, 2022  


  1. Bob Storck
    December 8, 2022

    I suggest that you check out the Vultee XP-54 and the Kyūshū J7W Shinden, both period pushers that were considered for conversion to jets. One that made the conversion was the XB-42 which became the XB-43, and was our first flying jet bomber.

  2. sabresoftware
    December 8, 2022

    Instead of buying a large screen PC, you could try Parallels software ( on your 27″ iMac, which allows you to create a number of Virtual machines.

    Currently I have 5 virtual machines, a Win 10, Win 11, MacOS X El Capitan, Ubuntu Linux, and FreeDOS.

    I have the MacOS X El Capitan (10.11.6) virtual machine because my current Mac OS Ventura (13.0.1) will not run some older Mac software (stuff that isn’t 64-bit compatible), or even read some older CDs/DVDs, but with the virtual machine I can still access this older stuff. I even have an emulator (that won’t run under 13.0.1) that allows me to even run some really old stuff by emulating a Motorola 68000 series Mac.

    My Win 10 machine isn’t running very well right now, but with Win 11 I have access to running most PC software that I occasionally need, and so I will probably just let the Win 10 box die. And the FreeDOS machine lets me run some really old DOS software.

    All you need is the disks for your software to install a new virtual machine.

    You can run these virtual machines either in a window, or full screen.

    The really neat thing is that you can “Suspend” any of these machines when you don’t need them, and resume at a later date/time without having to reboot them. And you can share data/files across all the machines, including copying something on one machine, and pasting on another machine, including the Mac itself under its current OS version.

    • simanaitissays
      December 9, 2022

      Hi, Sabre,
      How does this compare with my partitioning operation (done successfully on my two iMac 27s, until the older machine packed in its Windows XP after years).

      • sabresoftware
        December 9, 2022

        I don’t have any experience with Bootcamp as I have been using Parallels since before Bootcamp came out.

        I’m not sure about performance (virtual machine versus Bootcamp partition), but the following web page has a comparison of the two.

      • simanaitissays
        December 9, 2022

        Thanks for the comparo link. Given that my usage is specific, either fooling with GMax/Fltsim (in Windows) or my website (all set up on Apple side of the partition), the Parallels benefit of cross usage is irrelevant.
        What I should do is try reinstalling Windows XP on my “second” i.e. Wife Dottie’s iMac 27. It worked there flawlessly for ten years.
        There’s zero cost in this. Only time.
        Thanks for providing the useful info, in any case.

      • sabresoftware
        December 10, 2022

        My pleasure

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.

%d bloggers like this: