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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