Delanne and His Duo-Monoplanes
October 1950 Air Trails Hobbies for Young Men

October 1950 Air Trails

Table of Contents These pages from vintage modeling magazines like Flying Aces, Air Trails, American Modeler, American Aircraft Modeler, Young Men, Flying Models, Model Airplane News, R/C Modeler, captured the era. All copyrights acknowledged.

The October 1950 issue of Air Trails magazine did a duo-feature on Henri Delanne and his Duo-Monoplane designs. This article reports on the life and accomplishments of Delanne and his out-of-the-box concept of what an airplane should look like. While not quite canards, they did have the wing far back on the fuselage, and larger than usual horizontal stabilizer surfaces (essentially a second wing - almost a biplane with sever staggering) and dual vertical fins. Flying surfaces were so close to each other that airflow from the forward wing had to profoundly affect the rearward wing. Wind tunnels, pioneered by Wilbur and Orville Wright, were available for study of such configurations, but it would be very interesting to see on of Delannes Duo-Monoplanes modeled on a modern software simulator using computational fluid dynamics algorithms.

See also the "Duo-Mono" model airplane article and plans.

Delanne and His Duo-Monoplanes

By William S. Friedman

How a brilliant French designer kept from the Nazis the secret of· his sensational plane that may solve one of our most critical air problems today

In a quiet, cell-like room, below the level of New York's busy Park Avenue sits a studious engineer named Maurice Henri Delanne. His hair streaks from grey to dead white - characteristic irregularity for those whose hair turned color in a hurry. His neat beard is iron grey, and from a distance, he looks like a venerable savant, except for a pair of lively blue eyes that have a certain teenage sparkle to them. His face still carries the scars of great suffering, but his voice is gay, particularly when he talks about "my configuration." For these two words represent his prize possession - the possible solution to aviation's most pressing problem: landing speed and take-off distance.

The configuration is currently being merchandised as the Duo-Mono type. It is somewhat unconventional in general appearance. It resembles a highly stagger biplane in which the rear airfoil, located at the extreme rear of the fuselage, is somewhat smaller than its mate, and mounts on its trailing edge not only elevators but ailerons as well. End-plate fins and rudders are mounted on either side of the rear member.

The exact formula covering the relation between the wings in size, distance, angle of attack and the like was the prize in a neat yet terrible battle of wits and patience between Maurice Delanne and the agents of the Luftwaffe. Had the Nazis won, they might have had in their possession a system for giving their bombers and fighters faster take-off, greater range and cruising speed as well as better payloads and maneuverability. The end effect cannot be calculated at this point. However, the mathematical proof of the efficiency of this formula is so fantastic that it has taken since 1946 to convince some of our leading manufacturers that it was even possible.

Now, through a slow and scientific presentation of the facts, a number of leading plane builders are re-examining the Duo-Mono system. This time, they must. With the demand for higher cruising speeds for fighters and bombers, landing speeds and take-off distances are becoming impossible. The high-lift devices currently known are definitely limited, and jet-assisted take-off is not only expensive but has strict limitations for formation and rapid-sequence take-off. Something new has to be added. Delanne's Duo-Mono configuration may very well be it.

Those men who have had the opportunity to examine the Duo-Mono type's performance have great faith in its possibilities; but success or failure; it is the center of one of the most dramatic stories of our times, the story of a stubborn and courageous man who knew that he had something to offer mankind, and was bent on seeing it used for good purposes only.

Maurice Henri Delanne was born in the town of Diors in France early in 1901. He grew up in the golden age of French aviation, the age of Warman and Bleriot; of Fonck, Guynemer and Nunguesser. He received his degree at the famed Superior School of Aeronautical Engineering in Paris, in 1924. Having some funds of his own, he founded his own company, the "Société Anonyme de Recherches Aeronautique." In this era the biplane was still supreme. Surplus equipment from World War I was still available, so Delanne decided that what was needed was a high-performance, low-powered personal aircraft. He realized that most of the planes available at the time were overweight for their function; as a result, they had to use huge engines, with proportionately large fuel appetites.

Delanne's first design was a three-place low-wing monoplane powered by a 75 hp Anzani engine. This plane was the first semi-monocoque structure ever built in France. Its performance, at the time, was regarded as phenomenal. Even by today's standards, it would have been acceptable; a top speed in excess of 105 mph, The structural patents were considered so important that they were eventually acquired by the French Air Ministry.

During this period, Maurice Delanne learned 10 fly. By his own admission, he was not a very apt pupil. What disturbed him was the length of time it took to acquire the knack of flying well. It required at least two years for a man to become proficient in the full sense of the word, and a fairly constant degree of practice to "keep sharp." This was satisfactory for a professional pilot, but the number of serious amateurs who could devote that degree of time and effort to the art was, in Delanne's opinion, seriously limited.

It was the plane designer, Delanne decided, not the pilot, who must close the gap between the contemporary airplane and safe flying conditions. Conventional aircraft, it seemed, required too much skill of the pilot, a condition which would limit personal aviation to the very few who could afford the time to fly constantly. This would make aviation a very limited industry. Motor cars, Delanne observed, did not become common until their operation was simplified and professional chauffeurs were not needed.

In the late Twenties Maurice Delanne decided to alter the classic approach to designing airplanes: that of starting with the aerodynamics and powerplants, and hoping that the skill of the pilots would make up the difference. He began with the limited capabilities of the average man, and decided to tailor the aerodynamics to fit not the highly skilled pilot, but the Sunday-driving, somewhat inept average world citizen.

After considerable study of the subject, Delanne outlined certain basic requirements for his future design. He wanted a stable airplane; one that would take off rapidly, climb out of short fields well, land short and have no true stall; only a gradual reduction of lift. With power off and in landing position, the design would permit the plane to be "landed" if necessary, a hundred feet in the air, and then "mush" into the ground in perfect safety. These characteristics were to be accomplished without any complex and expensive high-lift devices, land with a cruising speed required to make it a practical air vehicle.

A tall order. In the early Thirties, the single-engined low-wing monoplane that Delanne had helped pioneer was achieving supremacy. He knew its shortcomings. The so-called tandem monoplane, the system of one wing ahead of the other showed great possibilities, despite the performance loss entailed by the interference between the two airfoils. Maurice Delanne sensed that there must be some ideal relationship between the wings in a tandem arrangement where the stability and stall resistance could be retained with. out sacrificing cruising speed.

In 1932, he initiated a test program to discover this ideal relationship. It was a long, slow process, involving over sixty sets of wind tunnel models, their tests and accompanying calculations. Out of this test series came a simple formula for the relation between two airfoils in space and position which resulted in certain marked advantages over the existing systems. In the final arrangement, the wings were so arranged .that at high angles of attack, the down wash effect from the front wing "fed into" the airflow of the rear airfoil.

This slot-like interaction compressed the air flowing over the rear so that even at high angles of attack, and at slow speeds a normal volume of airflow was directed over the rear airfoil. Since this surface contained both ailerons and elevators, it retained not only lift but control sensitivity as well. The "end-plate" effect of the twin rudders at the tips of the rear airfoil further contained the airflow, boxing in the tip losses, and retaining control sensitivity at very slow speeds.

The tests, certified by the French Air Ministry, showed that the Delanne configuration had a ratio between landing and top speed of better than 7:1. (3:1 is average, 4:1 is considered very good.) It also certified that at normal cruising levels, the fuselage drag appeared to vanish. (Thus far there is no complete explanation for this phenomenon. It stems either from some positive pressure, descending from the wing, impinging on the fuselage, or from some defect in the classic Prandl formula for calculating drag.)

The F.A.M. report also indicated that the slot-like action, as previously stated, made the ship stall-proof. Two other outstanding features had shown up in the tests; the design indicated that it could maintain longitudinal stability characteristics up to a center of gravity location of 67 percent of the mean aerodynamic chord. In practical terms, that meant that all of the fuselage was available for useful work, and that virtual coincidence of the center of weight and center of gravity was no longer necessary. To top it off, the configuration showed 35 percent more lift than a typical rectangular conventional wing of the same area and curve.

This was late 1936. The Air Ministry proceeded to give Delanne development contracts to build prototypes of his configuration. The first contract was for a two-place command fighter, a rather odd machine whose military purpose stemmed from a combat theory long since abandoned by air tacticians. Contemporary French tactical experts believed that the commander of a fighter squadron should fly a "winged command post" above his formation of fighters, and direct their actions by radio. To achieve this, a special two-place machine was designed in which the pilot-commander was freed from the task of defending his rearward arc by strong defensive armament. This called for a machine of varied characteristics.

Delanne's two-place command fighter was the only design submitted that satisfied the stringent requirements. The machine, known as the Type 10 C2 was a braced high-wing monoplane, powered by an 860 hp. Hispano engine. The use of the braced-gull wing was characteristic of French military demands at the time. Delanne wanted a straight cantilever structure, but the Air Ministry was adamant on the subject.

The ship carried two men, command pilot and gunner. It was armed with a 20-mm cannon, firing through the hub, two 12.7-mm machine guns in the wing, just free of the propeller arc, and an electric turret in the tail, carrying four rifle-caliber guns. Despite the load, the ship achieved a top speed of 360 mph, climbed at 40 feet per second, had a 17.6 feet per second rate of descent and landed at a bit under 50 mph. Like most of the French fighters of its time, its range was about 1,000 miles.

During this period of development, Delanne built some conventional ships in his plant in order to meet operational expenses. One was the Model 60-E-1, a single-place aerobatic training glider. Nessler, the noted French glider pilot, kept one of these machines aloft for 28 hours. Two hundred of them were ordered by the French government in 1938. Three-quarters of the lot were delivered before the invasion of France. On the basis of the single-seater's success, a two-place machine was ordered. The prototype was test flown, but the invasion cut short its production.

Even though the conventional gliders were his bread-and-butter contracts, Maurice Delanne's heart was in the Duo-Monoplane. When the fighter contract was launched, a requirement for an aerobatic trainer was posted by the French Air Ministry. This, too, was a job in which, a Duo-Mono design could have performed well. The Air Ministry awarded Delanne a study contract, but Delanne, impatient of delay and confident of an ultimate contract, proceeded to build the trainer as a four-fifth scale model of the fighter. The little ship, the 20T-02, was finished before the fighter, in March of 1938. The delay in the fighter stemmed from certain confusions in French prewar industry that delayed parts for prototype aircraft.

The little trainer was given a two-month workout in the full-scale wind-tunnel at Chailais-Meudon, and was delivered to the Air Ministry late in the spring of 1939. The trainer was powered by a 180 hp Regnier engine. It spanned 25.8 feet, weighed 2145 lbs., and had a top speed of 195 mph. The machine climbed at 1740 feet per minute, descended at 17.6 feet per second and landed at 37.5 mph.

The official reports on the trainer make very good reading. For example, one of the tests required the plane to clear a 65-foot hurdle from a dead start, 1,970 feet away. Classical type 1939 airplanes just about cleared it. The Delanne trainer cleared it with 108 feet to spare. M. Lane, Delanne's test pilot, popped the eyes of the observing F.A.F. officers when he cut the throttle over the hurdle and with his prop idling, flaps retracted and still all the way back, landed the plane from an altitude of over 170 feet. At 56 mph airspeed, he contacted the ground at only 17.23 feet per second, On the second try around, Lane tried it with full flaps, and the contact speed, at 37.3 mph indicated air speed was only 17.7 feet per second. The average man sitting down on a chair makes contact at just about that velocity.

Despite the pressure of other established manufacturers, the French Air Ministry showed definite signs of interest in the Delanne plane. He was given contracts to do design studies on a bomber and on a glide bomb, as well as to design and prepare to build a giant troop glider.

In the meantime, he was in the process of perfecting the prototype fighter and trainer, preparatory to production, when France fell.

The offices of Delanne's company were in Paris. The prototypes were at the Villacoublay airport on the outskirts. When the capitulation occurred, collaborationists were in command of the airport, and they sealed it off from anyone they thought could not be trusted.

Maurice Delanne joined the father of the French Resistance units, Mouvement Vengeance, and became not only an operative but a recruiting contact. In the meantime, the Resistance movements developed central command, and instructions came down the line for Delanne to start working from inside the enemy camp. He was to pretend to collaborate, and to use his position to gather information about the action of the enemy.

The Germans were in need of a ground-attack design for use on the Russian front. The Delanne fighter, with its heavy rearward turret, looked as if it had possibilities. The Vichy government ordered Delanne to complete his test program, and to turn the prototypes and data over to the Germans. Delanne sought instructions from the Resistance headquarters. Their answer was, "Stall as long as you can!"

Delanne and his crew were a valuable asset. In addition to the inside dope they were able to gather on German technical progress, they were able to hide a couple of small cameras in the aircraft, and the pictures they took of factories and airfields in the Paris area were priceless to the Allies.

Finally, the Germans indicated that they were not waiting for Delanne any longer: They were moving in. Delanne had, in the meantime, "corrected" his technical data so that it was worthless. The two prototypes however, could have formed the basis for the rediscovery of the subtle Delanne formula, so they had to be destroyed. The Vichy guards had been instructed to keep the French pilots away from the machines, but Delanne was permitted to work on them. Maurice chose a daylight raid on the airport as the time to act. Feigning great worry and confusion, he hopped into the trainer on the pretense of taxiing it to safety, and being an "excitable individual and a poor pilot," he managed to ram the fighter, destroying it. As a matter of fact, he hit it so badly that the two wrecks started burning, and the designer barely escaped with his skin.

The Germans accepted his explanation with very poor grace. They sentenced Delanne to five years in the fortress of Siegburg, near Bonn. For the time being, they had solved their contour fighter problem with the conversion of the Seibel trainer, so the temperamental designer who flew so badly, went off to prison.

Delanne's adventures in Siegburg would make a novel in themselves. He was placed in solitary confinement for his noncooperation. After a while, he was let out for interrogation and for labor, but was made to spend all off-duty hours alone in his cell. Over a period of time, he was able to accumulate enough scraps and pieces to allow him to build a simple radio receiver, which he hid in an abandoned chimney in his cell. Thus he was able to receive the BBC broadcasts. The contents of these were circulated among the other inmates of the fortress by means of a little handwritten newspaper, Le Petit Menteur, or the Little Liar.

One of the things that kept many a patriotic Frenchman in forced labor of the Nazis was the fact that, with some ingenuity, he could always find some way to sabotage the Nazi war effort. One of Delanne's first jobs was that of knitting wool socks. They used hand-operated knitting machines. After due study, Maurice "redesigned" the system of tying of the yarn at the toes so that, after a little use, they would come apart at the heel and toe.

Later, he was assigned to a group making hand grenades. He managed to re-rig the system so that the greater part of that unit's output would either fail to detonate or would fire prematurely, in the German soldier's hand.

Another job was that of overhauling German automotive equipment. Delanne discovered ways of hiding emery powder, salvaged from around the fixed grinding wheels in the shop, in those places in the engines where it would come loose after several hundred miles of running. This usually brought the breakdown somewhere in the fighting zone, where it would do the greatest harm.

Late in 1944 the Germans again looked up Maurice Delanne. They had a problem with their interceptor fighters. While the Me 262 jet fighter was adequate for most purposes, it needed two engines. Furthermore, it was a big airplane, tough to produce. The Germans were seeking an easy-to-fly single-jet design with take-off characteristics good enough to get it off of short fields. Someone remembered a design that had once been termed by a Nazi researcher as the most valuable thing the Reich got from France.

They located Delanne at Siegburg. They offered him his freedom, a plant to work in and "the good life," if he would cooperate. They underestimated the mild-mannered Delanne. The "convincing" process wasn't pretty. It reduced Maurice Delanne to a taut-skinned skeleton weighing barely 80 pounds. He had to be carried out of Siegburg when the fortress was finally delivered by troops from the 15th Army under Major Donald S. Scarborough of Coxackie, New York.

One has to examine the situation in Germany, late in the war, to discover the real effect of Delanne's heroism on the final stages. Had the Germans been able to get an easy-to-fly jet fighter in time, they might have turned their air war into a stalemate. The time they wasted "convincing" Delanne can be subtracted from the so-called Volksjaeger program. In desperation, the Luftwaffe ordered large numbers of the Heinkel 162-A fighters, the little single-jet mass-production job. Luckily for the Allies, it proved a tough and unstable plane to fly, and vital weeks were wasted improving it.

Had Delanne given up his formula easily, the Luftwaffe might have had an easy-to-fly single-engined jet in time for a last-stage fight for their inner citadel. While it might not have changed the ultimate result of battle, it might have dragged the conclusion out by many months.

It took Maurice Delanne over a year to regain the salvageable part of his health. His plant was gone, his resources were scattered. France, trying to reconstruct her economy, had to re-build her major airplane plants first, so there was no room for the heroic, quiet man. On the invitation of one of our major airplane builders, Maurice Delanne came to the U. S. His arrival here was ill-timed, for the nation, confident in her victory, was cutting back on defense appropriations. Here too, the major problem was keeping the heart of the industry alive, and newcomers with new ideas had a difficult time.

Selling airplane companies on a new configuration, no matter how promising, is a difficult problem. Even primary explorations are expensive. Certain government agencies had shown and demonstrated some interest in the system, but their work cannot be discussed in print.

There are definite signs of interest on the part of two or three of the nation's leading companies. The demand for a workable military liaison plane that can perform the wide range of jobs that are being piled on the "jeeps of the sky" point to an immediate task for the Delanne Duo-Mono. The needs of certain personal and agricultural types are similar, and plane builders, seeking better designs for the flying farmers vehicle, are examining the design with a much more sympathetic eye than four years ago. There are also a number of military uses possible and being explored that were not even considered a few months ago.

In the meantime, Maurice Delanne sits over his drawing board with his dreams and a formula that reads like magic. He has ideas about a fighter that can outrun sound and land just a little faster than a trainer; a heavy bomber that can take off and land from the length of a fighter strip. But best of all, he has in mind a sweetheart of a four-place job that the tyro pilot can fly safely, and as Maurice Delanne puts it: "A sheep I can fly even wan I am ze great grandfatheire .... !"

Posted September 18, 2021