The Horten Tailless Aircraft
by K.G. Wilkinson, B.Sc. D.I.C.
Horten V, VI, and VII
V was designed form the outset as a powered aircraft using two Hirth
H.M. 60 R motors driving oppositely rotating propellers. 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.
In its original form
the H V was fitted with waggle tip control (Fig.
26) in which the fore and aft sweep of the wing tips was geared to
the stick, producing incidence change by a skew hinge arrangement similar
to the illustrated in Figs. 26 & 27.
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).
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.
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. We questioned
him extensively about his impressions of the aircraft (Sept. 21, 1945),
because it was the most recent Horten product he had flown. 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
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
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.
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.
Single Engine Flight
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.
Landing and Take-off
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.
3.8 Horten VI
In general layout of
this aircraft was very similar to the H IV.
The span was increased to 24 m (78.7’) accompanied by a decrease of 5%
in wing area, giving an aspect ratio of 32.4.
3.9 Horten VII
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.
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
This followed normal
Horten practice, the center section being of welded tube construction and
the wings of single spar wooden construction with ply covering.
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).
The following performance data were quoted by Reimar Horten from memory:
Flying weight (minimum)
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”.