Horten Ho V
The H V was designed form the outset as a powered aircraft using two Hirth H.M. 60 R motors driving oppositely rotating propellers through extension shafts. It has a span of 52.5 feet, aspect ratio of 6:1, and a quarter chord sweepback of 32 degrees. Engines were completely buried and drove propellers on extension shafts raised relative to the engine crankshaft and driven through a reduction gear. The undercarriage was of fixed tricycle type with castoring nose wheel and trousered main wheels. The nose wheel actually too 55% of the static weight when on level ground.
Three examples were built. The first, built at Ostheim in 1936 was constructed of plastic material with riveted sheet plastic covering. Pilot and passenger were contained entirely in the wing contour and the nose wheel was retractable. This aircraft crashed on its first flight, due mainly to its unorthodox waggle-tip control. The second version used more normal control methods and conventional construction, it was started in 1937 and flew successfully. In 1941 it was completely rebuilt & as a single-seater, but retained the same control system.
In its original form the H V was fitted with waggle tip control in which the fore and aft sweep of the wing tips was geared to the stick, producing incidence change by a skew hinge arrangement. The aircraft crashed on it first flight due to the control taking charge after a bounce during landing. The reason for the accident was obscured by a failure of one engine but the control system was not regarded as satisfactory by the Hortens who later developed the idea further on an H III. They considered that damping is necessary to prevent the tips oscillating under suddenly applied acceleration (as occur during take off and landing).
The second aircraft in both its forms had a two stage elevon control rather similar to the H III. Maximum control deflections were as follows:
The outer control flaps had a 20% Frise nose and assymmetrically geared tabe to compensate the non linear moment characteristics of the nose balance. The inner flap pair had round noses.
Split trailing edge flaps were fitted to the center section, the flap between the engines lowering to 60 degrees and the part outboard to 45 degrees. The inner elevon flaps dropped to 30° when the center section flaps were lowered and still operated as elevons about this new zero position. The idea of using graded flap deflections originated from a hunch of the Hortens that the sudden discontinuity and greater spanwise flow with ungraded flaps might cause stability and control troubles. They later found that this fear was unfounded and gave up the graded deflection principle.
Rudder control on the second two aircraft was by split nose flaps on the H III pattern.
A great deal of flying was done on the second and third H V’s, including about twenty flights on the latter in 1943 by Prof. Stuper of A.V.A. Gottingen. The Hortens themselves had lost interest in the H V because later designs incorporated many improvements. Stuper has also flown the H IIId with Walter Mikron engine.
Tests at A.V.A. were undertaken at the request of D.V.L. who wanted information on single engine characteristics and an unbiased comparison between tailless and conventional handling qualities. Stuper’s comments were as follows:
Longitudinal dynamic stability was good and no fundamental different from a conventional aircraft could be noticed. In rough air he thought it had a more abrupt pitch response than normal, which was only a disadvantage if gun platform steadiness was needed. (Walter Horten thought this effect might be due to the low wing loading (6 lb/sq.ft.) on the H V and Stuper agreed that this might be so).
Lateral stability appeared satisfactory. No tendency to “dutch roll” instability was found and no arratic changes of heading due to low Nv and Yv were noticeable. Stuper was in fact expecting trouble from this source but failed completely to find any. He added that his impressions were purely qualitative as they had no time to instrument the aircraft.
Controls were light and effective, with the exception of the rudder, which was heavy and not effective enough. Aileron was heavier than the elevator “in the ratio 4:3”. With the stick back, aileron movement was restricted, which Stuper thought a bad point since plenty of aileron was useful in an approach in gusty weather. The aircraft was in trim virtually over the whole speed range without movement of the elevator trimmer. When flaps were lowered there was a slight nose heavy tendency which could easily be held.
Summing up, Stuper said that aileron and elevator control were quite normal but rudder control needed improvement.
Behavior at the stall (flaps down) was very satisfactory, the nose dropped gently and the aircraft gained speed. Wing dropping could be induced if the aircraft was stalled in a yawed attitude but normally the wings remained level and ailerons still effective, thought restricted in movement. The stall was reached with the stick not quite fully back; only one CG position was tested. Stalling speed was about 70 kph.
Flight on one engine was possible, without rudder, at 120 kph by flying with 10 degrees of bank and 80% aileron. Rudders were not used much because they were so heavy, although Walter Horten claimed that at 130 kph single engine flight could be maintained on rudder only (engine nearly at full power) if the pilot was strong enough.
Ground maneuvering was easy using throttles and wheel brakes. During take-off the aircraft could quite easily be kept straight until the drag rudders became effective, and flew itself off the ground without assistance from the pilot - in fact it made very little difference what the pilot did with the controls during take-off. There was no tendency to bounce during the ground run. R.L.M. require that for normal tricycles, it should be possible to left the nose wheel before take-off speed is reached; Walter Horten thought this was unnecessary if the aircraft would fly itself off. Landing was quite straightforward and normally the aircraft settled down on all wheels at once. Stuper thought it was not possible to land on the main wheels first because the ground incidence was too high.
Stuper had done some tests of take-off performance with flaps down, which resulted in his flying into a hanger and terminating the A.V.A.test programme. Apparently he landed and immediately (Walter Horten said not immediately) opened up to take-off again - after 530 meters he was 8 meters high and at that point entered the hanger. The airborne distance was about 150 meters.
Although the split flaps in front of the propellers caused poor thrust, there were apparently no vibration problems.
Summarizing his impressions on the H V, Stuper said that it was hardly fair to compare it with conventional aircraft with many years more development behind them but it was nevertheless, a good example of tailless design and a perfectly practical aeroplane - if anyone wanted tailless aeroplanes. His main suggestion for improvement was in the rudder control.
Wingspan: 16 m / 52 ft 6 in
Max. speed: 260 km/h / 162 mph