Sack AS-7 "Flying Pancake"

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Have you ever wondered how a pancake feels when you swing it in a pan full of hot oil? Well, fly this plane and you'll find out ...

This plane never existed in reality, but it is based on a real one. When I was a teenager, I had a book about UFOs which included some pictures of human-made flying disks. One of them was a circular-winged German propeller plane prototype which immediately fascinated me. As far as I remember, they called it the "flying pancake" in that book.

Many years later, when X-Plane came into my life, I remembered that plane and tried to find more information. I found it here on the Luft '46 web site.

The Sack AS-6 (see photo on the left) was the first and only manned aircraft built by Arthur Sack, a German farmer and aircraft enthusiast who dreamt of a circular-winged plane. It was completed in 1944. However, it never flew successfully, it just achieved some brief hops. One problem was that the horizontal stabilizer was too close to the vacuum area behind the wing disk, another problem was the big propeller torque effect due to the small wingspan. According to other sources I found, the plane was also nicknamed the "flying beertray". There's nothing left of it today.

Since the AS-6 was not a success, I decided to build a (fictional) improved successor model, the AS-7. My first prototypes were designed as pure flying disks without a horizontal stabilizer, but with elevators integrated into the wing disk. However, these models were about as successful as the AS-6... So I added a separate horizontal stabilizer like the AS-6 had, but positioned on top of the vertical stabilizer to avoid the vacuum zone (though I don't know whether X-Plane simulates that at all). This greatly enhanced the plane's stability in the air (I guess that's why they call it a stabilizer ...).

The plane required a lot of tweaking until I achieved
a really stable flight. One trick was to move the center of gravity quite far to the front and compensate the noseheaviness by tilting the back of the horizontal stabilizer slightly upwards. This sacrifices some speed, but keeps the plane from flipping over (due to its large wing area) when you pull up the nose.

Speaking of speed: The original AS-6 had only a 240 hp engine ... I decided to equip the AS-7 with a real WW II engine of 1700 hp (similar to the one used e.g. in the Focke Wulf 190). With this monster, the plane reaches up to 600 km/h in level flight.

The propeller torque problem of the AS-6 is also noticeable with the AS-7 at low speeds, though you can compensate it if you are prepared. Taking off is a little tricky in any case, especially if you want to take advantage of the STOL capabilities of the AS-7 (low aspect ratio designs generally need shorter runways than conventional planes, which was the main reason why the Luftwaffe encouraged Arthur Sack to continue with his experiments).

I also built a two-propeller version to avoid the torque problem and to achieve even higher speeds. You can find it here.