johnbr

Horten_H_V11_0

Horten Ho226 The H VII was projected in 1938 and the first of the type was built by Peschke at Minden in 1943. It bears a general resemblance to the modified H V in layout and control design and used the same outer wing panels: the span was the same (16m) the sweepback slightly greater (34 degrees) and aspect ratio 5.8 instead of 6.1. Its function seems to have been that of a high speed two-seater commun- ications aeroplane and trainer for tailless pilots. Engines were Argus AS 10 C of 240 hp. Fig. 15 shows the general arrangement and Fig 16 (ed. - not reproducible) gives some pictures of it on the ground and in flight. Altogether two were completed and flown and a third was nearing completion at Minden when the district was occupied by the Allies. Two aircraft were damaged beyond repair and the third fell into Russian hands at Eilenburg. Controls Single stage elevon control was used on the H VII with 25% Frise nose and geared tab. Inboard of the elevons was a plain flap and in the middle trailing edge split flaps extending for the full width of the center section. Initially the graded flap angle principle was used, the part between the engines opening to 60 degrees, between the engine and the outer wing panels to 45 degrees, and the plain flap on the wing lowering to 20 degrees. When R.L.M. ordered the design in quantity however they asked for it to be simplified and for landing speed to be raised to give pilots more realistic training for high speed aircraft. The plain flap was accordingly locked up on the second aircraft and omitted altogether on the series production model. Plug spoiler drag rudders of the H IV type (Fig. 7, ed. - not reproducible) were used on the first aircraft. These tended to suck open and had to be held closed by springs. They were not very satisfactory from the point of view of control forces and feel, and after about 10 flights they were scrapped and replaced by a new “trafficator” design. This was simply a bar which projected 40 cm in a spanwise direction from the wing tip when rudder was applied and retracted flush with the wing surface when not in use. Fig 17 (ed. - not reproducible) shows the rudder in open and closed positions but without the vent holes, which were cut to adjust aerodynamic balance. The vent holes allowed flow through the bar and deflected the flow sideways to generate a self-closing aerodynamic force. This was supplemented by a spring loading and the two components adjusted to give satisfactory feel on the rudder bar. This type of rudder was claimed to be cheap and easy to make and generally more satisfactory then previous designs. Structure This followed normal Horten practice, the center section being of welded tube construction and the wings of single spar wooden construction with ply covering. The undercarriage was a completely retractable four-wheel layout, the front wheel pair taking about 50% of the total weight when resting on level ground. The constant speed airscrews were driven through extension shafts with a thrust ball bearing and rubber flexible coupling at the engine end and a self aligning ball bearing at the airscrew end mounted on a cantilever form the main structure. Aerodynamic Design Outer wing panels were of the same aerodynamic shape as those of the H V. At the center line the section was 16% thick with 1.8% camber (zero Cmo) graded to 8% symmetrical tip sections. Wing twist was 5 degrees; 2 degrees linearly and 3 degrees parabolically distributed. The aircraft trimmed with elevons neutral at 260 kph (CL = 0.16). Performance The following performance data were quoted by Reimar Horten from memory: Flying weight (minimum) 2,900 kg Flying weight with full equipment 3,200 kg Engines 2 x 240 hp Argus AS 10 C (normally aspirated) Sea level (crusing speed (180-200 hp per engine) 310 kph Sea level (top speed) 340 kph Normal take-off speed 110 kph Ground run 250 meters Sea level rate of climb at 180 kph (full power) 7 m/sec. Ceiling 6,500 meters CLmax = 1.2 no flaps = 1.6 with all flaps Delta CL due to plain flap was 0.1 Handling Characteristics Reimar Horten told us that prior to the first flights b Scheidhauer on the H VII, his brother Walter had supervised the CG’ing of the aircraft ad mistakenly put ballast in the nose because the measurements were made with a steel tape with 10 cm missing from the end. Scheidhauer’s comments to us were that the aircraft had to be brought in at a minimum speed of 120 kph, with the stick nearly right back, if the nose was to be lifted for the hold off; the aircraft then floated (stick fully back) util 90 kph before touching down. Normal take-off procedure was to accelerate to 120 kph and then pull the stick back when the aircraft immediately took off and climbed away. Apparently it could be unstuck at 90 kph by pulling back hard but would not climb until 120 kph had been reached. It was impossible to stall the aircraft with the CG in this position; the general behavior was said to be “good natured”. Walter flew the H VII (with the CG in its correct position) on 30-40 occasions, a total flying time of about 18 hours. (Scheidhauer’s time was also about 18 hours). Apparently the change in CG brought the approach speed down to about 100 kph and the aircraft could be touched down on the rear wheels. It was not certain that a complete stall could be produced in steady flight. With the stick fully back the aircraft sank on an even keel with fair lateral control. Lateral control was pleasant, the 25% Frise balance eliminated adverse yaw and virtually enabled flying on two controls. Tests with the “trafficator” drag rudder showed that single engine flight could be maintained with half rudder and a little sideslip; turns could be made in level flight against the dead engine. On one test the pilot was carrying out a single engine approach when he realized that he had stopped the engine supplying the undercarriage hydraulics and could not lower the wheels. He was able to climb away, start the dead engine and made a normal landing.

Horten_H_V11_0
johnbr, Mar 24, 2011
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