HO IX

This is some info on one of my favourite airplanes, the first "stealth" airplane, from 1944. The sources are various, and I can not guarantee the rightness of it all, but here is the story anyway:

Horten IXor the
Gota go 229

In 1943, Richsmarsalk Goering held a speech to representatives of the Aircraft Industry and announced that a contract would be issued to the manufacturers who could build an aircraft that could carry 1000 kg of bombs 1000 km at a speed of 1,000 km/h.

Fighter divisions also requested that the plane should be armed with 30 mm cannons.

Horten, led by the brothers Reimar and Walter, began construction without obtaining any contract. Their design was a shell structure of wood. From the outset the intention was that the plane would have wet wings. But Horten could not find an existing fuel-resistant adhesive, thus the fuel load had to be reduced with the result that the operating radius decreased to 800 km.

This meant, however, that the bomb load could be doubled. This proposal was accepted by the German authorities, provided that the plane could be flight ready in six months!

Since there were no engines available it was decided that the first aircraft would be a glider. There were several good reasons to choose wood as a construction material. At the end of WW2, it was great energy shortage in Germany and the wood was much less energy intensive to produce. Aluminium required more than 3000 kWh, while wood was less than 3 kWh. In addition, the wood was less labuor intensive to process, 200 hours per ton compared to 5,000 hours per ton of dural.

For example, a nose frame was produced by a triangular piece of pine that was glued between two plywood boards. Production time: ten minutes. When the glue had dried the frame were stretched out along a template and in were ready in less than 5 minutes. The entire wing was built in the same simple way.

Rudder Cables, electrical and hydraulic lines were inside the wing spar, a box construction, so that the rest of the wing could be used as a fuel tank when a fuel resistant glue was available.

The adhesive was also supposed to be able to attach to already glued surfaces, in order to simplify production.

The skin plywood on the prototypes were very thick, 17 mm, three times as much as was needed. On the production aircraft it would be replaced by a sandwich material consisting of two 1.5 mm thick plywood boards with a 12 mm spacer material containing of mixed sawdust, charcoal and glue. This material was not only much lighter, it also worked as a Radar Absorbent Material and thereby reducing the radar cross section.

Moreover, the sandwich material should be more resistant to battle damage than a conventional stressed skin structure.

The wings angle of attack varied between nil at the root to minus 3 degrees geometric and 1.5 degrees aerodynamic at the tip, all to give the desired bell shape of the lift distribution over the wing. The elevons were initially of the Frise-type but proved to be inadequate, so blunt nosed rudder was used instead.

Since the aerodynamics were rather unproven, ant no engines were yet available, the first prototypes were built as gliders to test stability and different configurations, mainly of the rudder and elevators.

First flight were on the first of march 1944, but the tow plane, a He 45 were too small, and it could only tow it in ground effect. Five days later an He 111 were assigned as a tower, and it easily towed the plane in to the air. At 12000 ft the pilot, Scheid Hauer, released the cable and made an uneventful flight back to the airstrip. Unfortunately the brake parachute did not deploy at landing, so he retracted the nose gear to stop the airplane. Despite this, the damages to the airplane were small.

The second aircraft were to fly three months later but the engines which would come in March were late. It took several weeks and when the engines finally arrived, they were too big. They had added an extra section to the motor housing, thereby increasing the diameter 60-80 cm without informing Horten.

Since the engine would go through the wing box, where the hole was only 60 cm, it was obvious that it would not work. In addition, they were only six weeks away from the promised first flight.

If one were to maintain the shape of the aircraft Horten would be forced to increase the span from 16 to 21.3 m and the wing area from 42 to 75 m2.

This would make it impossible to achieve the promised performance, although the engine were more powerful than promised. The only possibility left were to modify the basic form.

An additional frame was installed 40 cm outside the original, thus the centre section became 80 cm wider. The outer wing remained unchanged. The new centre section airfoil was 13% thicker than the old one. The greater thickness of the middle section made to the critical Mach number decreased to 0.75, giving a maximum speed of 920 km / h.

The rudder, which consisted of small air brakes on the wings, was supplemented by larger air brakes, which dropped out as soon as the small was fully extended. To save time, several parts were taken from existing aircraft. Nose wheel was the tail wheel from a He 177, They could even use parts of retract mechanism!

Horten worked hard to get the plane ready by the end of the 1944. According to Horten the first flight was around December 18, but the pilot is Lt. Erwin Ziller wrote in his logbook that the first flight was the second February 1945.

It was probably not only his first flight in this airplane, but also his first flight in a jet.

Air Ministry were satisfied with the tests, and ordered Gota Wagonfactory to build 40 aircraft under the designation 8 -229.

H IX V-2 flew probably three or four times before the accident on February 18.

There are many versions of what happened, and they do not have much in common.

The weather was marginal for the test flight and the ground was soft and muddy. But Lt. Ziller started, retracted the landing gear and climbed through the clouds. According to a report one engine stopped, and Ziller diverted against Oranineburg for an emergency landing.

Since it was a low cloud base he made a flat approach to the airfield. The hydraulic pump was on the dead engine, so the landing gear and flaps were extended with the emergency system. This meant that they could not be retracted again.

To maintain the rate of descent, despite the extra drag, Lt. Ziller opened the throttle, but the asymmetrical thrust made the plane yaw. He found that he could not maintain the course, despite giving full rudder. To maintain control of the aircraft he throttled back on the remaining engine and decided to do a minus landing instead. He landed the plane in a field, it slid into a barrier flipped over and crushed the pilot.

The American third army corps took Gota factory April 14. They found the H IX V-3 intact and almost complete. In addition, they found the V-4, V 5 and V-6 in various stages of completion. The ninth armoured corps found H IX V-1 in good condition, near Leipzig.

What happened next to this plane is unknown.

V-3 was shipped later to the U.S.