ROYAL AIRCRAFT ESTABLISHMENT
Farnborough Hants
THE HORTEN TAILLESS AIRCRAFT
By
K.G. Wilkinson, B.Sc. D.I.C.
Technical Note. Aero 1703
October 1945


The information presented below was provided by Al Bowers and David Lednicer from their archives.  The material was a copy of a copy, etc., taken from microfiche so the quality wasn't good enough to scan much other than the line drawings, although I have tried to include what at least is discernibile.  I have tried to recreate as much as possible, but there are a lot of pages and it will take time.  SO, I am putting it out here a little at a time as I get it transcribed.  This way I can share it with you now while building on it over time until the almost complete work is is available.  Come back to this page from time to time to see what is new.  I have provided a dated directory to aid you in going to the newest piece.  I hope everyone enjoys this historic perspective of the Hortens.


DIRECTORY

SECTION TITLE
DATE ADDED
TOTAL FILE SIZE
..Summary and Introduction ....February 25, 2001 (Revised) ..Presented below
..H I, H II and H III ....March 8, 2001 (Revised) ..130 kb including pictures
..H IV and H IVb ....March 8, 2001 (Revised) ..220 kb including pictures
..H V, H VI and H VII ....March  8, 2001 (Revised) ..135 kb including pictures
..H VIII and H IX ....March  8, 2001 (Revised) ..120 kb including pictures
..H X, H XI, H XII, H XIII, H XIV, Parabola, Jet Bomber ....March 9, 2001 ..140 kb including pictures
..How the Hortens Design Their Aircraft .....March 11, 2001 ......79 kb including pictures
..Comments on Some Aerodynamic Aspects of the Horten Designs .....March 11, 2001 ...102 kb including pictures
..Appendix I,...Table 1,..Table 2..Table 3 .....March 16, 2001 .......1 kb each


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.)

..NEXT SECTION

...3/16/01
DIRECTORY
Back Home...