This is exactly what the rotary should be used for.
https://en.wikipedia.org/wiki/Turbomeca_Astafan

Dan Gorsline

Ducted fans are very inefficient in this speed range.
Many have tried before.

Paul Lamar


My father worked in engineering at Aero Commander, starting in the fall of 1951. He knew all the guys who started it up and hand-built the first prototype in Culver City, after WWII; at that time dad was working at the Santa Monica Douglas plant, which is where that original team formed. The manufacturing went to Oklahoma City. My dad was there when the first production aircraft made its first flight. We knew Ted Smith, the visionary engineer who was the inspiration behind it; he later started up the Aerostar. Don't know if the ducted fan would make the aircraft better, but it was interesting to see the pictures.

There is also a very real family resemblance between the Aero Commanders (particularly the earlier ones) and the Douglas A-26. Same wing plan, same tail plan. No coincidence; they were designed by the same people. Look at both of them in the plan view.

BTW, the subject of my Master's thesis was to design and build an air-cushion vehicle -- hovercraft. Don't ask why, long story. But for forward propulsion I build a ducted fan that used a McCulloch go-kart engine of about five horsepower driving a cooling fan from a Fiat 850. I made the duct from fiberglass with a male mold; it looked like a very big carburetor venturi. I did this on the advice of someone who should have known better. It didn't work worth a damn and I think the reason is that the fan was far too small to utilize the engine's power, so it just screamed away at about a million revs, made a lot of noise, blew some air, but wouldn't move the damn thing. In retrospect the possible speed of the vehicle was likely way, way removed from any reasonably usable speed of the fan. All this was a long time ago. Best part was that I did get the Master's. Second-best part was that I donated the whole shebang to the college, got a receipt and took it off my taxes for a couple of years and got it out of the garage.

I also learned that, in those days (early 1970s) the expected life span of a Craftsman hand-operated pop rivet tool was about 500 rivets before the jaws wore out and it wouldn't pull the rivets tight. I just took them back to Sears and got a new one. Lost count on how many.

Don Fuller

Gee Don I did not know you had a masters degree.

Paul Lamar


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