ADVANCE
SUMMARY
for
TECHNICAL
INTELLIGENCE REPORTS
ANALYSIS
DIVISION
TSNTS-2
18 April 1946
Title:
The Horten Tailless
Aircraft
File No. R.A.E. Report No.
F.A. 259/1, Tech.
Note No. Aero 1703, October 1945
Royal Aircraft
Establishment, Farnborough
Author: Wilkinson,
B.Sc.D.I.C.
1. This report cover the
activities of the Brothers
Horten, at Bonn, Germany on the Horten Tailless
Aircraft. This flying
wing type had reached an advanced stage of development
with a high degree
of controllability and performance. The report
is both historical
and technical.
2. The collection of
material on this tailless
aircraft was brought about by an investigation of a
C.I.O.S. Team of the
Horten home at Bonn in March 1945. In May 1945
the Horten Brothers
were interrogated in England, and final interrogation
was carried out by
a team sponsored by the Tailless Advisory Committee in
September 1945.
Such information has been collated and presented in
this report.
3. The reports set forth
the career of the
Horten Brothers on tailless aircraft development from
their first glides
in 1927 to 1945. During that period the brothers
developed many models
of their craft, beginning with the H I and ending with
the H XIV.
These models ranged from single seat glider model to a
six-engine trans-Atlantic
transport. Models of the craft were driven by
engine-propeller units
and by jet propulsion. Also at various times
models of the craft
carried the pilot in seated and prone positions.
4. The Hortens started
their careers as
aircraft designers in a very practical way without
assistance from “highbrow”
theory. Early designs were based mainly on what
they found satisfactory
on a small-scale model. Wing sections were
designed from scratch
and were seldom tunnel tested.
5. From the first the
Horten Brothers have
been of the opinion that the flying wing is the most
efficient form of
aircraft, and all their efforts have been directed
towards achieving this
ideal.
6. Drawings and photographs
of most of the
models are included, together with design data, stress
analyses, equations,
charts and tables. Weight and performance
figures are given, flying
characteristics are described, and stability, stall
and recovery characteristics
are discussed. Spinning characteristics were
tested with different
center of gravity locations.
7. Many novel features are
shown, such as
waggle tip control, spoilers, elevons and drag
rudders. In the various
models wings have been given sweepbacks from 9.5° in
the conventional
type wing to 60° in the arrowhead type. Aspect
ratios have ranged
from 4 to 32.4.
Collection: Total pp. 75; text 48
pp. Including
tables, photographes 19 pp.; diagrams 14 pp.
Frank A. Cerruti, Analyst
Note: Agencies outside AMC
should submit
requests for documents within two weeks to C.G., AMC,
Wright Field, Ohio,
Attn: Air Documents Division (TSRPR-5)
Class number
629.13.014.48 (43)
Horten
R.A.E. Report No. P.A. 259/1
US Tech Note No. Aero 1703
October, 1945
ROYAL AIRCRAFT
ESTABLISHMENT, FARNBOROUGH
The Horten Tailless Aircraft
By
K.G. Wilkinson, B.Sc., D.I.C.
SUMMARY
In March
this year a
C.I.O.S. team visited the original home of Horten
Aircraft in Bonn, and
brought back information on the recent activities of
the brothers Horten
which revealed that their development of the flying
wing type had reached
an advanced stage. Several powered types of
great interest had been
built and flown, and a six-engined flying model of a
transport plane half
completed.
Later on
the Hortens
were interrogated in England and a party form R.A.E.
followed this up by
visiting the Horten factories and flight test center
in Germany in an attempt
to find and preserve some of the more useful
aircraft. The trip was
disappointing in that all the power aircraft except
the half completed
H VIII were found to be destroyed. One glider
was, however, brought
back.
Finally,
in September,
a party was sponsored by the Tailless Advisory
Committee to visit Germany
for further discussion with the Hortens and others
interested in tailless
problems. The following note is the result of a
collation of all
the interrogation reports on the Hortens and is an
attempt to present a
consistent and fairly complete account of their work.
Prof.
Hill
(Part
Time)
S/Ldr.
Kronfeld (A.F.R.E.)
Messrs.
Prower
(General Aircraft, Ltd.)
Watson
(Armstrong
Whitworth Ltd.)
Lec
(Handley
Page Ltd.)
Wilkinson
(R.A.E.)
LIST OF CONTENTS
1. Introduction
2. Brief Historical Survey
3. Brief Description of the Horten
Aircraft
3.1 General Lines of Development
3.2 Horten I
3.3 Horten II
3.4 Horten III
3.5 Horten IV
3.6 Horten IVb
3.7 Horten V
3.8 Horten VI
3.9 Horten VII
3.10 Horten VIII
3.11 Horten IX
3.12 Horten X
3.13 Horten XI
3.14 Horten XII
3.15 Horten XIII
3.16 Horten XIV
3.17 Parabola
3.18 Projected Jet
Bomber
4. How the Hortens Design
Their Aircraft
4.1 Wing Section
Design
4.2 Calculation of
Aerodynamic Centers
4.3 Fixing the Layout
4.4 Control Design
4.5 Flight Stability
4.6 Undercarriage
Design
4.7 Stressing
5. Comments on Some
Aerodynamic Aspects
of the Horten Designs
5.1 Stability and
Control in Unstalled
Flight
5.2 Behavior at the
Stall and Recovery
from the Spin
5.3 Tests on Laminar
Flow
5.4 CLmax
5.5 Waggle Tip
Control
LIST OF APPENDICES
Centers of Horten Activity
Flight Test Report on the H II
LIST OF TABLES
Data Sheet for Horten Aircraft
Wing Sections from the H IV
Wing Sections from the H IVb
LIST OF ILLUSTRATIONS
General Arrangement of H I and H
II
General Arrangement of H III
Pictures of H III and Parabola
Pictures of Powered H III
General Arrangement of H IV
Pictures of H IV
Pictures of Drag Rudders
Pictures of Control Balance
Wing Sections of H IV
Wing Sections of H IVb
Control Mechanism
General Arrangement of H V
Pictures of H V
General Arrangement of H VI
General Arrangement of H VII
Pictures of H VII
Pictures of Drag Rudders
General Arrangement of H VIII
General Arrangement of H IX
Pictures of H IX V.1
Pictures of H IX V.2
Pictures of H IX Center Section
General Arrangement of Parabola
Pictures of H XIII
Sketch of H X
Diagrams of Waggle Tips
Pictures of Waggle Tip
Mechanism of H IX Spoiler
1. INTRODUCTION
The
activities of the
Horten Brothers in the design of tailless aircraft
have been reported at
various times in the German journal “Flugsport” and
translations have been
published by R.F.E. during the war. Their more
serious efforts based
on early experience with gliders were not well known
until a C.I.O.S. team
investigated the Horten home at Bonn (March 1945) and
interviewed Herr
Berger who who supplied information of many of their
later projects.
After the
cessation
of hostilities, the Horten Brothers were interrogated
in England (May 1945)
and in the first two weeks of June 1945 the writer
visited Germany, with
the Hortens, and investigated their center of
activity. Final interrogation
was carried out by a team sponsored by the Tailless
Advisory Committee
in September. The material from these
investigations has been collated
and a fairly complete picture of the Horten
development is presented in
the following report. The complete series of
aircraft is described
in some detail and the design methods used are
summarized. Results
from flight tests on performance and handling are
given where possible,
but no written evidence in the way of reports or
calculations were found
by an of the investigators. This feature is
unfortunate since many
of the figures quoted for performance, etc., are
dependent on the accuracy
of Reimar Horten’s memory.
Only one
aircraft (the
H IV sailplane) was discovered in the British sector
in Germany in a condition
suitable for transport to England for test
flying. Other gliders
were found in the American and French sectors but all
the power aircraft
were so badly damaged as to be useless.
Illustrations for the
report have been prepared from general arrangement
drawings of the early
gliders (I, II and III) published in the German
technical press together
with drawings of the later aircraft found in
Germany. Photographs
were supplied by Reimar Horten or taken by the author.
2. BRIEF HISTORICAL
SURVEY
Walter
and Reimar Horten
commenced their experiments on tailless aircraft at
the ages of 11 and
10, respectively, by building and flying small
models. In 1927 they
started gliding and in the following years helped the
Bonn group at the
Wasserbuppe. By 1932 Walter had his C glider
license and an A2 power
license, and Reimar had his C glider license and had
started power flying.
In 1933
they started
work on their first man carrying glider which they
built in the family
home in Bonn. Trials began with bungee catapult
launches on level
ground; auto and winch launches were tried without
much success and finally
it was aero towed. About two hours flying were
done up to March 1934
and later that year it won a prize at the Rhön gliding
competitions
as an original design. Longitudinal stability
seemed to have been
fairly good but lateral control was unsatisfactory
(due mainly apparently
to adverse yawing moments from the ailerons), and
longitudinal control
became very ineffective at low speeds.
After the
1934 Rhön
contest the first aircraft was scrapped and work
started on the Horten
II, which incorporated lessons learned on the previous
H I. This
was finished in May 1935 but could not be entered for
the Rhon, so a 80
hp engine was fitted (Fig. 1)
and extensive
test flying carried out.
At this
stage the brothers
were called up for military service, but continued to
work on their tailless
designs and during 1936 schemed the H III and IV
(gliders) and the twin
engined H V. Two more H II’s were built and
entered by the Luftwaffe
for the 1937 Rhön contests. No great success was
achieved because
the brothers were out of practice. General Udet
(sp.) was interested
in the Horten’s work and asked Hanna Reitsch to test a
H II, in December
1938, and give an independent assessment. Her
report (Appendix II)
showed that considerable development was necessary in
control design but
that the aircraft had some very good features, in
particular the behavior
at the stall was good and the longitudinal damping
satisfactory.
Mail troubles were with lateral and directional
control.
Whilst
studying at the
Bonn Technical High School in 1938 and 1939 the
brothers organized the
construction of a number of H III’s which were paid
for by the Ministry
of Education. Two of the type were entered for
the 1938 Rhön
contests flown by Bloch and Scheidhauer (later their
chief test pilot).
Remarkable performances were put up by both
aircraft. On August 6th
Bloch climbed to 26,000’ in a cumulo-nimbus
cloud. He had to abandon
his aircraft (probably due to icing troubles) and was
unfortunately hit
by it and killed on the way down. He had a
special fixed auxiliary
front aerofoil fitted to his H III to assist in
performing tight circles.
Scheidhauer also iced up in the same cloud and had to
take to his parachute.
During this period the H VII, a development of the H V
(which had been
built to the Horten designs and was already flying)
was projected but could
not be built. Discussion took place with Heinkel
and Messerschmitt
with a view to engaging Reimar on tailless projects
but nothing came of
the negotiations.
From 1939
to 1942 the
brothers were again in the Luftwaffe and Walter, by
devious means managed
to get an H IV (a new high aspect ratio sailplane)
build at Konigsberg
where he was stationed. This clandestine
construction was discovered
by his commander and Walter was sacked.
In 1942
Nortrhop’s work
in America attracted attention in Germany and Walter
was ordered to restart
development. Luftwaffe Sonder Kommando 9 was set
up with 200 men,
factory premises and government grants to the tune of
L500,000 for getting
machinery. Headquarters were at Gottingen and
the Peschke works at
Minden was used to build Hrten designs. (This
was a furniture factory
which turned over to aircraft components during the
war years.) Many
other dispersed workshops and test and design groups
were organized.
Construction of the VII was authorized and it was
flown successfully in
1943.
Official
enthusiasm
waned again in 1943 when the quantity order for the
VII was cut, but they
continued to work without authority and started the H
IX as a private venture.
Official interest revived when it was half completed
and Goring ordered
them to finish it quickly. It flew as a glider
in 1944 and design
work was started on the H VIII which they succeeded in
selling to
R.L.M. Their high performance glider H VI also
flew in 1944.
The
powered H IX flew
in January 1945 at Oranienberg. It was
demonstrated to Goring in
March and the Gotha concern got an order to
productionize the desgn and
build 20. On March 12th a conference was called
at Carinhall at which
Goring presided and it was decided that the Chief of
the Air Equipment
Branch should consider immediate inclusion of Horten
development and production
work into the Fuhrers’ emergency programs. The
meeting put on record
that it considered the flying wings produced by the
Hortens to point the
way for future development of all aircraft (presumably
excluding rotary
aircraft). The State Research Council was
ordered to organize a group
of specialists to cooperate with the Hortens in future
development work,
and give the brothers all possible support.
Production for training
purposes was ordered to recommence.
There the
story of the
Horten’s tailless work finishes; a remarkable record
of progress made in
spite of obstacle. In the early stages work was
only kept going by
a genius for getting people to work for nothing and in
the end continuity
had to be achieved in spite of fluctuating
official support.
In addition to running a very complex and dispersed
organization, the brothers,
with assistance on calculations from their sister, had
to grapple with
aerodynamic and engineering problems on a bewildering
variety of aircraft.
This side of the work was run mainly by Reimar who
remained independent
and original in his thought throughout and got little
help from outside.
Apart
from the design
and production of the VII, VIII and IX, which
represented an ambitious
series, time and resources were found to pursue the
old interest of glider
design. By 1945 serious production of the III
and IVb had been organized,
amount to about four a month and two new gliders were
constructed – the
aerobatic H XI and the mass production H XIV sports
sailplane, designed
to the Olympic Games specification.
Concurrently with this
work a new two-seater private owners aircraft with a
100 hp engine was
designed, and one built and flown as a glider.
Serious thought was
also being given to supersonic aircraft and tentative
steps in this direction
were taken with the research designs H XIII and H X.
In
reviewing the Horten
achievements one cannot help being impressed with the
speed of their work
and the utter irrelevance of much of it to the German
war effort.
Prototype gliders were knocked up with astonishing
speed with the very
minimum of drawings. Although the basic design
and general arrangement
were soundly worked out by Reimar, detail work was
largely settled by the
workmen on the job with occasional interference from
Horten. Perchke
was reduced to despair by the Hortens on many
occasions because they were
always altering details as the design progressed and
he could never get
the production drawings tidy.
There is
no doubt that
much of the work on sailplanes was a dead loss to
Germany – for example
the HVI, H IX and H XIV and the motor sailplane IIId
had no connection
with military or civil designs and taught no useful
lessons. Much
of the work was without R.L.M.’s consent, and Reimar
commented that an
advantage of dispersal was the R.L.M. could not find
out what was going
on, or how their money was being spent. An
extreme example was the
second glider H VI, which was started at Bonn, moved
to Hersfled when the
Allies threatened Bonn and finished just before the
Armistice. It
was then hidden in a barn where we found it in June
1945. The construction
took about 8000 man hours. Reimar said that he
preferred building
sailplanes because he could do the complete design
himself. He resented
time spent in supervising staff on his larger
projects.
3. BRIEF DESCRIPTION
OF THE HORTEN AIRCRAFT.
3.1 GENERAL LINES
OF DEVELOPMENT
From the
first the Horten
brothers have been of the opinion that a pure flying
wing is the most efficient
form of aircraft and all their efforts have been
directed towards achieving
this ideal. They have steadfastly refused to
compromise on this issue
by fitting fins of any sort, although some of their
undercarriage trousers
must contribute substantially to the sideforce
derivative yv and so give
some of the benefits of a fin. Their later power
aircraft have dispensed
even with this partial fin. On aircraft with
narrow chord wings they
have approached the pure wing as closely as possible
by putting the pilot
in the prone position.
The
development of aerodynamic
ideas has been almost entirely through flight
experiment. No wing
tunnel tests have been made on complete models,
although they have bad
access to basic wind tunnel data and research work,
for example, on the
delay of shock stall on highly swept back wings and
tunnel tests on low
drag sections. Their general attitude seems to
be that tunnel tests
take too long and give too little information. A
certain amount of
their flight testing has been done with
instrumentation but they have done
nothing as thorough as the current instrumented flight
research here and
in the U.S.A. The most complete investigation
seems to have been
on the glider version of the H IX, which was
instrumented by D.F.B. for
lateral stability test to determine its suitability as
a gun platform.
Many of the gliders were performance tested to measure
drag polars and
CLmax and tuft tests to show stall development were
carried out on three
aircraft.
Apart
from this, the
majority of flight research seems to have relied on
test pilots reports.
The
following paragraphs
give a brief description of each aircraft. A
more general discussion
of some of the aerodynamic feature common to several
designs is given later.
General arrangement drawings and photographs are given
in Figures 1-26
and dimension and weight data in Table I. (ed.
- Some of these
figures and tables will be included as this goes
along, if they can be
reproduced.)
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