Nobile's N.5

Umberto Nobile (1885-1978) was probably the leading proponent of the semi-rigid airship. The semi-rigid was sort of a cross between a blimp and a zeppelin. It had a rigid keel to which everything else was attached, including the gasbag which was usually divided into separate compartments.

The best-known of his designs was the N.1 "Norge" which was the first aircraft to reach the North Pole, flying from Spitsbergen to Alaska in 1926. Its sister ship N.4 was the "Italia", of Red Tent fame. Another sister ship N.3 was sold to Japan.

In 1925 Nobile, who was Director of the Italian Government Airship Construction Establishment, read a paper titled "The Trend of Airship Construction in Italy" at the Third International Air Congress in Brussels. Besides the N.1 (which hadn't yet made its historic flights), he described the N.2, which was somewhat smaller, and a much larger ship of 51,000 cubic metres volume, which was under construction. Details of this ship were published in the October 22, 1925 issue of FLIGHT.

The N.51000 or N.5 was never completed. Nobile fell out of favor with the Italian government (largely, I guess, because the "Italia" expedition didn't bring Italy the positive publicity that had been hoped for), and the project was literally scrapped (like the R100 after the R101 disaster!). Since the N.5 never flew there are no pictures. I realized that if I modelled it in Flight Simulator we could see it fly (sort of) and take pictures (screen captures) of it.


The N.5 would have been the largest semi-rigid airship ever built. To place it relative to the rigids, it was more than twice as long as the Zeppelin NT, and almost 75 percent as long as the Graf Zeppelin. The most distinctive feature of the N.5 was its cross-section. Unlike the Norge, which had a tear-drop shaped cross-section, the N.5 was nearly circular. As you can see in the drawing, the keel was 5-sided and wide. Multiple suspensions from the top helped to maintain the shape of the envelope. The wide keel made it easy to suspend the engines and support the horizontal tail. The side portions of the keel were occupied by the bottoms of the ballonets, so there was very little loss of volume. The ballonets were pressurized by air taken from an inlet on the nose of the hull.

There were six Maybach engines similar to those used on the N.1. Four of them were in separate engine cars or nacelles. The other two were located in a single aft car and drove a single larger-diameter propeller through reduction gears. Airships seldom used all their engines at once - only when maximum speed was required. The N.5 would not normally be moored to a mast; it sat on the ground. There were inflated rubber bumpers under the control car and the aft engine car. [You will appreciate that the engines had to be stopped, with the two-bladed propellers horizontal, before touch-down!] The four wing-cars had retractable radiators to reduce drag when those engines were not being used. There would be an engine-man in each car to look after such things, besides running the engine.

The propellers did not tilt. Takeoff required that the ship be light, if necessary by dropping water ballast. [I guess the handling crew wore raincoats!] When high enough to clear any obstacles, the engines were started. As speed increased, the elevators could be used to tilt the nose upward for a climb to cruise altitude. Ideally, landing was achieved by stopping the engines while the ship was coasting downward, low enough for the handling crew to catch the dangling ropes. If necessary, hydrogen was released to make the ship slightly heavy.

Airships did not have pilots. There was a captain or commander who made decisions and gave orders. There was a helmsman whose job was to operate the rudder wheel and maintain the heading. There was an elevator-man whose job was to operate the elevator wheel and maintain the specified altitude (or climb or descent). This could be a busy task, dealing with gusts, changes in buoyancy, etc. Also, if the ship hit the ground it was his fault! The picture above, reproduced from FLIGHT, shows the control car of the N.1. Visibility was very good!


For people not familiar with Microsoft Flight Simulator: this is a computer program in which any aircraft defined in a "model" file can be seen flying in any scenery defined in a "scenery" file, in real time, under the control of the "pilot" who is running the program. At any time, it is possible to "capture" the image that is being displayed on the monitor screen.

The following images are screen captures of my computer model of Nobile's N.5 flying in FlightSimulater98. Most of the images show the N.5 flying near the coliseum in Rome, as represented in the default FS98 scenery. The two end-on images were captured when I was flying the N.5 over Montreal, as represented in the Quebec 5.3 scenery from Quebec Virtual Pilots.

Click an image to enlarge Glenn Adams 2004

Copyright Glenn Adams 2004