Wartime Notes On The Ho IX
In a speech before representatives of the aircraft industry, Reichsmarshall Goering had announced that no new contracts would be given, unless the proposed aircraft could carry 1000 kg bombs, fly 1000 km /h, and have a penetration depth of 1000 km; penetration depth being defined as the total range.
The Fighter Division requested that the aircraft also be fitted with 30 mm machine guns, something that would lessen the machine's efficiency as a bomber.
"We started drawing and calculating without a contract. Our plan was to build two full size prototypes. The initial penetration depth would only be 800 km, since the fuel proof glue necessary for the full wet wing, was not yet available. On the other hand, the smaller fuel load allowed a doubling of the bomb load, so we went ahead and submitted our proposal.
A contract was awarded with the demand that the first flight be made in six months! Since the jet engine was not yet ready, the first machine would be a glider. The previously deactivated Air Force Command IX was reactivated, and ordered to proceed with the project. Fortunately, the preliminary work that we did without a contract, put us sufficiently ahead, so the six month deadline locked feasible.
There were several reasons for choosing wood as the building material. Duraluminum required more energy to produce; over 3000 KWH, versus less than 3 KWH for wood per ton. The required labor for aluminum production was also much higher; 5000 hr/ton against 200 hr/ton for wood. In addition, aural was difficult to find, and skilled sheet metal workers in short supply. Unskilled workers could easier be trained to work with wood.
Typically, a nose rib was built from a triangular piece of spruce, sandwiched between two plywood sheets, all scrap wood. Production time: 10 minutes. After the glue dried, the rib was simply roused out along a master template in less that 5 minutes. The rest of the wing was built in a similar crude fashion, to pave the way for mass production by unskilled workers.
The main box spar contained all cables and control rods, to free the remaining space in the wing for fuel. That, we planned to pump right into the wing itself, without tanks or bladders. To do this, we needed the fuel-proof glue, that could be used to coat the inside surfaces as well. The glue allowed additional gluing to dissolve and adhere to already coated surfaces, which greatly simplified construction.
The skin was very thick: 17 mm, all plywood; three times the necessary strength. On the production aircraft, this would be replaced by two 1.5 mm plywood sheets, with a 12 mm layer of sawdust, charcoal and glue mix, sandwiched in between. The charcoal in this much lighter skin would diffuse radar beams, and make the aircraft "invisible" on radar (STEALTH Technology -ed).
Finally, should a 20 mm shell explode inside the wing, a relatively harmless hole would result, whereas a metal wing would balloon out and lose its lift.
The H IX wing was designed with 3 geometric and 1.5 aerodynamic twist, to give it the desired bell shaped lift distribution with all controls neutral. The Frise-nose on the elevons had proven to be unsatisfactory, so we decided to use blunt nose elevons instead. The sharply enlarged wing root chord served mainly to eliminate the middle-effect. The maximum thickness line (T-4 line) therefore made a sharp bend in the middle, which resulted in the characteristic pointed tail. As this would affect stability, a test aircraft with large aspect ratio, that had the control surface far outside the test area, was needed. The H Vl would serve this purpose, while other preliminary tests were made with a H II and a H III.
The H IX V-1 took off right on schedule on March 1, 1944 in Gottingen. The small He 45 towplane barely got off the ground, so test pilot Scheidhauer released, and landed straight ahead, after only a short hop. Five days later, he was off again on a snow covered runway behind an infinitely more powerful He 111. He released at 12000 feet, made an uneventful glide back to the airport, then faced problems during landing when the drag chute did not function. As the end of the runway approached, he retracted the nose wheel, and skidded to a stop with only minor damage.
The second aircraft, scheduled to fly three months later, was awaiting its engines, promised in March. Several weeks passed, and then... Disaster!
The engines arrived with an accessory section added to the case, making the cross section oval, and the diameter 20 cm greater! No one had bothered to inform us! Now, just six weeks before the first flight, we were faced with the problem of fitting an 80 cm engine into an aircraft with a 60 cm hole in the spar! It meant that the wing would have to be made thicker.
To maintain the aerodynamic qualities of our design, we would have to increase the span from 16 to 21.3 meters, and the wing area from 42 m2 to 75 m2. Such an aircraft would never reach the targeted performance, even with higher engine thrust. We choose instead to do the best we could with patchwork modifications. The wings remained the same. Another root rib was added 40 cm outside the original, making the center section 0.8 m wider. The new airfoil was 13% thicker than before, and the bend in the T-4 line became much larger. The thicker center section lowered the critical Mach number to 0.75, or a maximum speed of 920 km/in.
The ratio of movement between the control column and the elevons could be reduced to by the pilot for high speed flight. A small high speed drag rudder was supplemented by a larger one that deployed after the smaller was fully extended. Many parts were scrounged from other aircraft left at the test facility in Gottingen. The nose wheel, for instance, came from the tail wheel of a He 177 heavy bomber. We were even able to use the strut and retract cylinder!
The men of Air Force Command IX did their utmost to complete the aircraft before the end of 1944, sometimes working more than 90 hours per week.
I remember that Lt. Erwin Ziller made the first flight about December 18th, 1944, but his log book indicates that the first flight occurred on February 2nd., 1945. I am quite sure the first flight of the H IX was also his first in a jet. Our leaders had little concern for such risks.
Satisfied with the initial flight, the Air ministry ordered 40 aircraft to be built by the Goetha Waggonfabrik under the designation Ho-229.
It appears that the H IX V-2 had flown three or four times before tragedy struck on February 18th. The many versions of the story have a few things in common. The weather was overcast, the ground soft and muddy. The visibility marginal for a test flight, as Lt. Ziller took off, retracted the gear and disappeared. We received a report that one engine had failed, and that the H IX was returning to Oranienburg. Due to the low ceiling, a shallow approach to the airport was initiated. Since the hydraulic pump was on the dead engine, gear and flaps were extended by the emergency compressed air system. Once down, they could no. be retracted. To maintain his glide slope, Lt. Ziller added power. to overcome the extra drag, and found to his horror that he could "no longer maintain directional control; the fully developed drag rudder unable to overcome the asymmetrical thrust. Rather than lose control, he retarded the throttle to land short of the runway. The aircraft touched down in a field, slid into an embankment and flipped over, crushing its pilot.
The US Third US Army Corps reached the Goetha plant on April 14th 1945. Here they found the H IX V-3 intact and nearly completed, and also the V-4, V-5 and V-6 in various stages of completion. The Ninth US Armored Division found the H IX V-1 in good condition near Leipzig. Its fate is unknown.
The H IX V-3 was later shipped to USA, and is now in the Smithsonian collection, awaiting restoration.
More amazing pictures of the Ho IX