HORTEN S P I R IT OF T H U R I N G IA The Horten All-Wing Jet Fighter Andrei Shepelev and Huib Ottens Reaching speeds approaching 800 kph in prototype form, the Horten Ho 229'Nurflügel' - 'all wing' - was one of the most enigmatic aircraft projects to emerge from World War Two and is redolent of today's 'stealth' concept. In terms of design, it is seen as a precursor to it. In this book, the authors, who have spent many years researching the Horten brothers and their remarkable designs, examine the Ho 229 in great detail with considerable emphasis on the build and structure of the aircraft, an area which has often been inaccurately and insufficiently portrayed. Developed from a series of tailless Horten glider designs, the Ho 229 was planned as the first of the 'next-generation' jet fighters for the Luftwaffe, following on from the Messerschmitt Me 262 and - ultimately - as a high-speed, cannon-equipped, all-weather fighter-bomber, heavy fighter, night fighter and reconnaissance aircraft with plans for airfield strike operations over England in late 1944/early 1945. Unlike the Me 262, the distinctive, bat-shaped Ho 229 was capable of operating from grass airfields and of carrying the same armament as the Messerschmitt jet, but also possessing a range comparable to that of the Arado Ar 234 jet bomber/reconnaissance aircraft. It was also to be fitted with the latest radar and radio systems and a pilot ejector seat. Later plans included long-range bomber designs capable of attacking the east coast of North America. With 250 fascinating photographs, plus the most extensive set of accurate scale drawings ever produced on this aircraft by internationally acclaimed draftsman, Arthur Bentley, and accompanied by computer-generated colour artwork, and cutaways by Andrei Shepelev, this book represents the most thorough technical study of the Ho 229 ever produced. S P I R IT OF T H U R I N G IA The Horten All-Wing Jet Fighter Dedicated to the all the 'Flying Brothers' who wrote their stories for the History of Aviation: The Montgolfier brothers The Wright brothers The Voisin brothers The Nieuport brothers The Farman brothers The Short brothers The Granville brothers The Horten brothers Iand sister) The Günter brothers (Heinkel Flugzeugbau) The Hütter brothers (Schempp-Hirth Segelflugzeugbau) The Loughead (Lockheed) brothers The Dittmar brothers The Hutan brothers The Schweizer brothers The Loening brothers The Miles brothers and many others... Andrei Shepelev and Huib Ottens An imprint of lan Allan Publishing Andrei Shepelev has been interested in aviation, especially in unconventional and lesser-known designs, since an early age, and as an aircraft modeller. He is a former student of the Kuibyshev Aviation Institution, specialising in spacecraft and rocket technology and has worked for a number of publishing organisations as an editor and designer. He is married and has a son and two daughters and lives in Russia. Huib Ottens first became interested in aviation when he read Biggies stories as a boy. He has a particular interest in the history of the Luftwaffe and has been researching the history of the Horten Brothers and their flying wing designs for some 20 years. He lives with his partner and their two children in Holland and works as a systems designer and developer for the IT department of a large Dutch bank. Acknowledgements The authors wish to acknowledge the following individuals for their kind help in the preparation of this work: In Germany: Manfred Boehme, Hartmut Küper, Prof. Dr. Karl Nickel, Gunilde Nickel-Horten, Winfried Römer, Peter F. Seiinger, Reinhold Stadler, Ewald Uden, Gerd Zipper In the USA: Albion H. Bowers, Mark Cowan, Richard T. Eger, Kenneth Kik, Richard Kik Jr., Russell E. Lee, David Myhra, Geoff Steele In Belgium: Eric du Trieu de Terdonck In Great Britain: Arthur Bentley, Robert Forsyth, Eddie J. Creek In Australia: Alan Scheckenbach In Spain: Raul Escapa First published 2006 ISBN (10)1 903223 66 0 ISBN (13) 978 1 903223 66 6 All rights reserved. No part of this book may be reproduced or transmitted in any form or by any means, electronic or mechanical including photocopying or by any information storage and retrieval system without permission from the Publisher in writing. Produced by Chevron Publishing Limited Project Editors: Robert Forsyth and Chevron Publishing Limited Cover and book design: Mark Nelson © Colour artwork: Andrei Shepelev © Technical drawings: Arthur Bentley The line drawings produced in this book by Arthur Bentley as well as his other extensive aviation line art can be ordered from www.albentley-drawings.com An imprint of lan Allan Publishing Ltd, Hersham, Surrey KT12 4RG. Printed in England by lan Allan Printing Ltd, Hersham, Surrey KT12 4RG. Visit lan Allan Publishing at www.ianallanpublishing.com C O N T E N TS Foreword by Karl Nickel Introduction by Albion H Bowers Introduction Chapter One Fledged in the Third Reich 11 Chapter Two Nurflügel goes to War 26 Chapter Three A Bomber for England 40 Chapter Four A Batwing from Gotha City 59 Chapter Five The Last Stronghold in Thuringia 74 Chapter Six Reaching Enemy Soil 82 Epilogue Invisible Legacy 113 Appendices 121 Endnotes 124 Bibliography & Sources 127 Index 128 Foreword by When looking at the designs of aircraft since the end of the Second World War one finds many extremely interesting new designs and developments. Karl Nickel If one restricts oneself to the area of military fighters one finds that this region is especially interesting. But of all the fighter-bombers which have been designed and built during the last 65 years there is, however, one model which is quite outstanding in every respect. This is the Horten HIX, also known as the Ho 229. No other aircraft exists which can be compared with it. Even an unbiased observer sees immediately by looking at pictures of this bird the qualities of elegance, simplicity, avoidance of all superfluous parts and of any unnecessary drag, clear lines and a certain streamlined beauty. I am quite happy to see that Andrei Shepelev and Huib Ottens pay tribute to this aerodynamic marvel and bring it to the public eye. I enjoy this fact even more because part of my own life is interwoven with this wonder of technology and with the two Horten brothers. It has namely been my own duty between the years of 1943 and 1945 to make extensive calculations for the H IX with respect to dimensioning of the spars and the shell by computing the stress and strain, ensuring stability and finally to evaluate and to predict performance. This book contains much information for both the expert and the interested layman. Therefore I wish it the success which it deserves! Freiburg i.Br. Germany T HE history of aviation is full of great ideas. solution was published by Prandtl in 1918. The optimum shape of the spanload is elliptical. This solution is so compelling that even today most Some of the ideas from the early pioneers have textbooks refer to the elliptical spanwise load for the survived to this day; others have been passed by wing as the optimum, without stating what it is the as too difficult to create with current technology, optimum for. This optimum is the minimum drag for and some have just proven to be outright wrong. a wing of a given span and a given lift. But Prandtl But in the Pantheon of truly great revolutionary did not stop there. In 1933, he published a little ideas, there are few. known paper in German, the title of which is Over one hundred years ago, two brothers translated as 'The Minimum Induced Drag of decided to create practical flight. Their innovations Wings' Why would Prandtl rescind his earlier and approach survive to this day. These two optimum elliptical spanload for a different new one? An Introduction brothers, Orville and Wilbur Wright, and their ideas, This new spanload considered a different case. are generally recognized by history and by nearly all Prandtl asked himself, given an elliptical spanload by scientists and engineers as being the first truly as optimum for a given span, is there a different practical approach to flight. The Wrights created spanload which would give the same bending Albion H Bowers flight by breaking the necessary components of moment at the root of the wing as the elliptical flight down to their respective parts. They solved the spanload and have the same lift, that would create problems of structure, propulsion, stability, control, less induced drag? The wing root bending moment and performance. To do this, they started with the is the primary consideration given to the size of the fundamentals they observed from the flight of birds. "When was structure required to hold the wing together, the One of the great leaps forward the Wrights made wing spar. With Prandtl's lifting line theory, this was when they shook off the illusion of mechanical could be investigated. The new optimum spanload, the last time you flight as being simply an extension considering the wing root bending moment, was not of two-dimensional travel, namely railroad elliptical but was bell-shaped. The results of saw a bird technology. They saw the problem of flight as being Prandtl's analysis showed that for the same lift and one of banking the aircraft to turn it. In so doing, it the same wing root bending moment, a 22 per cent with a was necessary to invent the vertical tail and three- increase in span resulted in an 11 per cent decrease axis control. This is the same thing most in induced drag. Prandtl's paper was not given much vertical tail?" aeronautical engineers do today to design aircraft. recognition (not even today), but the implications But with the Wrights doing this, the flight of birds are vast and far reaching, and even Prandtl did not was left behind as the ideal model for flight. This realize it. was how the Wrights flew, for the first time, at Kitty In 1932, there were two other brothers who Hawk, North Carolina in 1903. began to investigate the possibilities of flight. These One of the discoveries the Wrights made was brothers were Reimar and Walter Horten. Their first that with roll control there is a dramatic tendency for aircraft, a small sailplane, was an all flying wing, the roll to cause a yaw motion in the direction with no vertical surfaces at all. This first Horten opposite to the turn. This is called adverse yaw, and sailplane did not use Prandtl's new bell-shaped it is the primary function of the rudder to overcome spanload (it would not be called bell-shaped until the adverse yaw. Every student pilot has adverse years later, and then it was only called this by yaw drilled into their heads and soon kicking the Reimar Horten), and it did not fly well. But the rudder, with aileron roll input, becomes automatic. Hortens, particularly Reimar, were persistent and This is more prevalent in aircraft with large or long solved the problems of flying wings one at a time. wings and small or short tails (sailplanes exhibit this The optimum bell-shaped spanload later solved the tendency more than most other kinds of aircraft for problems of directional stability, and helped to exactly this reason). What is happening is that the minimize the structure needed for their long wing wing creates more lift to move up and creates more sailplanes. The problem of adverse yaw would drag, and so is moved aft. This idea of roll control is plague their aircraft all through their years together exactly what the Wrights patented, the idea of bank- in Germany, through World War Two, followed to-turn, not the idea of the propeller aircraft. Reimar through his PhD, and even to his move to Now ask yourself, when was the last time you Argentina after the war. Reimar continued to design saw a bird with a vertical tail? What is it that birds and build sailplanes. The final solution came to Dr. Ludwig Prandtl. know that we do not? Reimar while he was in Argentina, the solution to Enter one of the great minds, if not the greatest the adverse yaw problem. There were a handful of mind, of all aeronautics - this is the true father of designs from Horten in Argentina that solved all the modern design theory for aircraft: Dr. Ludwig great problems of the all flying wing aircraft (even Prandtl. Prandtl invented the lifting line theory to sailplanes) and required no vertical tail. explain and model how wings create lift. With a working theory of how wings worked, Prandtl then The solution lay in how the wingtip vortices are theorized and obtained the optimum wing load treated. With the bell-shaped spanload, the vortices distribution across the span to minimize the drag act on the wingtips more strongly than in the created by the lift of the wing. This drag is seen as elliptical spanload case. The result is that the lift at wingtip vortices and is called induced drag. The the wingtips is influenced by the wingtip vortices, energy left in these vortices is energy taken from the and the lift is rotated far more forward than in the wing as it passes through the air. The optimum case of the elliptical spanload. Now, instead of flight by reducing the flight of birds to their creating more drag with more lift, because the lift is component parts and solving each problem rotated forward from the effect of the wingtip individually. The Hortens reintegrated the flight of vortices, the greater lift overcomes the greater drag birds into a single holistic unit that is optimal in all and the wing that moves up creates induced thrust ways. Just as birds are. forward. Roll is coupled to yaw in a proverse way, This great revolutionary idea is one whose time not adverse; and the vertical tail is rendered has come. It is not recognized, even by some of superfluous. But this proverse yaw can only happen today's foremost authorities in aeronautical if the part of the wing creating the greater lift is at engineering. the very tips of the wings: all the roll control must The story presented in this book is a snapshot of reside near the very ends of the wingtips while using the creation during World War Two of one of the the bell-shaped spanload. Dr. Reimar Horten had Hortens' most ambitious and beautiful aircraft, the used Dr. Ludwig Prandtl's bell-shaped spanload to Ho 229. It did not incorporate all the pieces optimize the drag, minimize the structure, solve the necessary to solve the problems of the flight of problem for minimum control surfaces and birds. Yet the story is both compelling and beautiful, eliminate the vertical tail. drawing us into the thoughts and ideas of the Again, when was the last time you saw a bird Hortens. Our thanks to Andrei Shepelev and Huib with a vertical tail? Ottens in weaving this tale together for us to enjoy, For birds to survive, they too must be optimal in a tale of one of the truly beautiful, great and all these same ways. For a bird to carry unnecessary revolutionary ideas. body parts means the design of such a bird is not optimal to fit into its ecological niche. Such an animal would become extinct quickly. The chest muscles of the bird can only carry so much load, analogous to the wing root bending moment and spar size problem. Further, the feathers of birds cannot carry heavy loads near the tip as demanded by elliptical spanloads, but a bell-shaped spanload has very light loads near the tip. And if the roll Albion H. Bowers control of the bird is near the tips, the bird would not Deputy Director of Research have adverse yaw. All of these solutions for the NASA Dryden Flight Research Center Hortens can be solved the same way as with birds. Edwards, California The result of this is to see that the Wrights created 31 March 2006