MIGNET'S HM-14: FIRST FLIGHTS
September 10 to November 8 1933:
Henri Mignet's life had been totally dedicated to Sport Aviation. In 1912 he built a glider inspired from a Lilienthal design. After WW1, between 1920 and 1927 he designed no less than 7 prototypes of various configurations.
In 1928, his first viable design, the HM-8, took off on its maiden flight.
The HM-8 was quite sturdy and safe for its time, and approximately 200 were built. However, Mignet wanted to take one further step toward designing and flying a totally safe amateur-built airplane, and he resumed his research.
Using a home made wind tunnel, he directed his research toward the interaction between two wings, in order to create a slot effect that would inhibit stalling. He considered the stall the most dangerous feature of the classical aircraft.
These studies eventually lead him in 1933 to the development of the HM-14, a tailless staggered wing biplane, in which a variable incidence front wing would govern pitch control. The HM-14 made its first flight on September 10, 1933.
The scene for this historic event was the now legendary "petit bois de bouleau", the little birch wood, a desolate place surrounded by marshland, about 70 miles Northeast of Paris. It is the same place where Mignet had camped over 450 nights in a span of three years, suffering torrid summers and harsh winters. The reader can refer to the article "The Little Birch Wood" published previously in the Pou-Renew for additional information.
Three years ago, 67 years after the event, I made a pilgrimage to this site. The autumnal country was silent. Suddenly, I heard the shrill noise of a motorcycle engine. My heart stopped beating for a second; was I back in the past? But it was just someone passing on the road nearby.
Let's look back upon what happened on September 10.
When we discuss the first flight of a newly built homebuilt light aircraft, the plane is typically built either from a kit or from plans of a well-known model that has already flown successfully. In this scenario, if the pilot is competent, the first flight is almost a routine operation. The situation was totally different for the Flying Flea. Henri Mignet was far from an excellent pilot and was totally ignorant of the machine’s behavior. He had no idea where the location of the center of gravity ought to be for this unique design. He did not even know if his strange machine was capable of flight. Only his faith in the new concept was pushing him to carry on with the experiments that lasted two months before the Flying Flea was properly adjusted.
Hereunder are some extracts from the diary of this courageous man.
The wind comes from the East. It is 91 degrees under the tent yet opened on both sides. I wait for the evening. I am scared.
7:00pm: Let's go! The engine is wonderful, running smoothly and powerful. Quick to accelerate, The machine is at once tail-up. I pull the stick. Still tail-up, I pull more. Easy take-off, but stick full aft. My flight is very jerky. I am very nervous and very brusque. Fortunately no one can see me. The machine bounces 10 or 15 feet high, touches down, bounces again. My piloting technique is awful. With regard to the machine, too much lift on the rear wing (both wings have the same span, 5.56 m). I am uneasy with the lateral stability. It should be OK theoretically. But it does not seem to be. Too much warp on the left wing. The engine torque seems too low.
Very bumpy taxi on the grass strip, a jog for 1600 feet. The ground reacts too much and my back not enough. I have to adjust the rear suspension. I passed over deep ruts. Terrible bounces, but the pivoting front wing reacts very well.
All in all, I am happy.
Nothing works. I do not understand what is happening. No stability in any direction. The sun has been in my face all day. The day is hot as in midsummer. The grass is high on the strip and the wind is blowing crossways. I am terribly thirsty and my mind is blank. I was so comfortable in Paris in my cool workshop!
I flew two straight lines, by leaps and bounds. I flew badly and landed badly. I taxied back to my tent, fed up of everything, and arrived to see that I have visitors.
I remove the rear wing fabric in the middle. I cut off 40" of spar and splice the 2 ends. I fit the fabric back and varnish it. That reduces the span 5 feet. The plane is better looking this way.
In the morning I put the rear wing back on the fuselage and tighten the tension cables.
In the evening, the wind drops. A friend coming from the North of France brings me luck. I make two nice 1500 feet flights, which he photographs. If I reduce the throttle brusquely before landing, the plane goes nose up, If I do it slowly, it is better. The front wing is too high. Not good looking and upward couple. Very long gliding before landing. I land in the dirt track at the end of my strip. I take off at 1,400 RPM and my engine can go as high as 1,600. Sounds good!
104 degrees in my tent. No air. I work with only my undergarments on.
I cut the cabane tubing to lower the front wing 5".
Gliding improves, but I keep throttling back too late. Landings are endless. I land several times in the ploughed field. Very hard to tow back to the strip.
I test the stability by rocking the stick sideways. I make extreme control movements. Pushing the stick too much forward, I dive from 15 or 20 feet up. The bottom of the fuselage knocks on the ground, the bungees being at their full length. (The propeller cuts) propeller cuts 2 grooves in the ground. I bounce. I do not know how high - 25 or 30 feet in the air. The engine vibrates. I stop it. I shake the stick, then flare, touch down correctly. The prop tips are smashed into pieces. I have the prop wrench in the plane. I remove the broken prop, walk back to my campsite and come back with a spare prop. Its pitch is too small, but I fix the prop on the hub and restart the engine. Meanwhile, night has fallen. I come back to the camp full throttle, scaring off a flock of partridges. My honor is saved!
So, then what? Well, everything is fine. Pitch stability totally perfect, roll control very effective, even at low speed, but even when I tilt it, this damned machine does not turn. Too stable!
Thinking about my accident the day before yesterday. I had the same accident last year and broke the HM-12. This time, being more sturdy, I withstood the shock. What did I do exactly? In both cases, I pushed the stick too much forward. Why? You idiot, I maneuver too abruptly. I have to calm down and be gentler on the controls.
In the morning, I purchase two beech beams, which I roughly shape at a local carpenter in Vailly. In the evening, I carve propeller # 20, except for the hub hole.
Tonight, prop # 20 is varnished and installed on the plane.
At night, I fly with the new prop. The pitch is a little too high. (55") Long time to accelerate. Light crosswind. To run straight, I have to give a lot of rudder to prevent the weather cock effect. I let the plane gain speed by getting the tail up. I give a sharp pull to the stick to take off. And it really goes sideways because of the drift. The machine is very stable and refuses to sideslip in flight. I make very correct straight lines but still do not know what I will have to do to turn. The sporting way would be to climb to 1,000 feet in 3 miles and to try turning. Daredevil method! It works, or…
I am scared to death. I will never do it!
After 4 days of drizzle, at last a clear evening. Several 2,000 or 2,500 foot-long flights. The machine is too sensitive. Delicate to pilot. I must be centered too much to the rear.
When I push the stick to accelerate it pulls too much in my hand. I have to slow down half power and fly nose high. If it were a classical aircraft, I would spin.
Back to the camp, taxiing on the dirt path, a large rut combined with a stone makes me topple to the front. The propeller sticks into the ground and the engine stalls. A blade is broken clear through.
I spend the afternoon at the carpenter's. In 5 hours I carve prop # 21. Pitch 51".
Landing on a "private hunting ground" signpost, I break two ribs of the rear wing. I repair them in two hours.
At night, I make a nice flight. I switch off the engine before landing at 50 feet high. First time I do it.
I remove the fabric of the front wing trailing edge and raise the trailing edge. The glue is slow to dry, as the air is very humid. Difficult to varnish too. The varnish comes milky.
I remove the rudder and add a counterbalance front part to it. I move the rear wing backward and tighten the cables. It is raining and the rudder is drying in the car.
The machine is ready, Stormy weather.
Excellent flight. The reaction of the stick in a dive is perfect. The balance is OK. My happiness knows no bounds.
I change the struts cables to 3/16" They carry the load of the plane. It is not necessary, but puts my mind at rest.
I fly a few straight lines. By mistake, I am on the right side of the strip. I gently push the stick to the left. The machine banks, I let it go where it wants and I make a good landing. That means that I turned!
Interesting! Let’s do it again. I push the stick to the left. The landscape slips to the right. The machine banks and turns left. That means that the plane turns correctly. Lifting the tail of the ribs ¾" made the difference. A small change for a big success! I could not turn because I was flying nose up and near stall. I feel that from now on the experiments will progress faster. Now, I have to study how the machine climbs.
Altitude record! I climb to 100 feet. I fly over the birch wood and my camp. I dare not yet turn and come back to my starting point. The plain, 1 ½ mile wide and 2 miles long, is not large enough.
A storm nearly blows down my tent.
The engine is overhauled. I am ready for the next flight, which should be the real first flight. The machine is stable in pitch and roll. I can turn with a large radius. The climbing is fast. I remind myself to fix the altimeter on the instrument panel.
This day, I sent a cable to my wife: "My first turn lasted 20 minutes. Altitude, 1300 feet. Behavior much safer than conventional aircraft."
A mild wind blows from the East. I wait nervously for the evening. I am going to make a real flight! I cannot stay here endlessly. The cold season is coming and I will have to leave. Let's take the chance! It climbs, it turns, it is stable, etc.
I ruminate over these thoughts all day long. I take a walk to warm up my body and my ideas. When I am cold, I am good for nothing. What a chicken!
At 3:30 pm I make a last check and handprop the engine. Am I going to make a flight test?
I move off to the East, take off correctly and pull the stick. I am 50 feet high. There is still time to land if I want to. No, let’s go!
The rest of the story was published in issue #3 of Pou-Renew (Third quarter 2001) "On the Flying-Flea's trail"
Translated by Paul Pontois