F – A – Q
by Paul Pontois
I would like to build a HM-14. Where can I find plans ?
A very simple question, which does not have an easy answer!
For many flying-flea lovers, the
HM-14 is still the archetype of the Flying-Flea, even though they know that
many newer models exist, they still feel attracted by the vintage design of the
small aircraft Henri Mignet flew for the first time in September 1934 from the
legendary Little Birch Wood .
He never issued any plan of the HM-14, but wrote a book where he explains his philosophy of flight and also indicates with precise sketches how an average amateur can build and fly a HM-14.
This 1934 book was partly translated to English and you can find this translation on:
But, when fatal accidents occurred, mainly because of a wrongly moved back center of gravity, Henri Mignet realized that his prototype had not enough safety margin and changed the design of his HM-14 for a more foolproof version. After extensive flight tests with the new prototype, he made in 1936 a new edition of his book, which has never been translated to English but was several times republished and may be purchased easily on Amazon, Alapage or ebay, from the French printer, Imprimerie Gatignol et fils, 14 Ave Maryse Bastié, 17200 ROYAN (France) email@example.com
or from ULM Technologie (France)
With the English text of the first edition and the measurements of the second edition HM-14, an English speaking builder can easily build a safe vintage HM-14.
But, after the 1936 HM-14, Henri Mignet continued improving his formula (new wing airfoils, folding wings, etc). He designed several new models, one of them is the HM-360.
His son Pierre confided to several amateurs that he had in mind, after the Saintonge project, to redesign the HM-14. Would it have been a simple adaptation of the original plan, or a model totally redesigned, as Volkswagen made for the New Beetle? We will unfortunately never know.
Bernard Domont, one of the most talented Flying-Fleas builders, thought of matching the HM-360 wings with the HM-14 fuselage to keep the vintage look of the HM-14 and benefit from the modern technology and aerodynamics of the HM-360 wings.
Several builders were interested in this solution and at least 5 or 6 of them are currently flying with what I will call a HM-14/360.
This solution is technically very satisfactory, but the size of the fuselage is sometimes a problem for the 2010 tall and well fed pilots and several persons find it difficult to insert their legs and knees under the instrument panel.
I have been asked several times to recommend new dimensions for a modern HM-14 fuselage.
As I am not going to build myself a fuselage of HM-14/360, all I could do was to gather information, make some experiments and give the results.
First, I noticed the difference of length between the 1934 fuselage and the 1936 fuselage.
Obviously, the rear of the fuselage is much longer on the 1936 model.
The reason for this difference is that, on the 1936 model, Mignet increased the gap between the 2 wings (which were overlapping in 1934) and made the rear wing moveable.
As, with the HM-360 set of wings and airfoil, the moveable rear wing is not necessary anymore and as the chord of a HM-360 wing is only 1,300 mm vs 1,400 mm for a HM-14, I realized that I will be able to recuperate at the rear of the fuselage the extra length I will have to add to the front. That will also make the W & B easier as the modern engines are generally light. Nevertheless, some pilots may prefer a slightly longer fuselage (Norbert Mosson and J-J Legrand, for instance). This choice would give some more weight to the rear, but would give more room for a seatback tank and would allow the pilot to sit on the fuselage top while entering the cockpit.
I chose also to use on my project the HM-360 rudder, slightly rounded at the bottom part to follow the bottom line of the fuselage, but if a builder wants, as Thibaut Cammermans suggested, to be closer to the original 1934 design, he can be inspired by the 1934 plan and make a rounder rudder.
To make the rear wing incidence (6°) easier to set, I slopped the upper longerons of the rear fuselage. That was my choice, but if a builder prefers, like Norbert Mosson, having a horizontal fuselage and adding spacers between fuse and wing, it is also a possibility.
To conclude with the rear of the fuselage, I gave it the exact width of a HM-360 fuselage. Why change something perfect ?
Back to the main point of discussion, the measures of the front fuselage.
The pointed shape of the HM-14 front is almost unique and, obviously, the problem was not only to give some extra room for the legs of the pilot.
After making some unsatisfactory drawings, I realized that I had to take a more scientific approach.
I found in an American book, concerning light aircraft construction, some indications about making articulated cardboard puppets for various pilot sizes.
I decided to choose scale 1/10 for my fuselage drawings and for my puppets.
After a few trial and error experiments, I thought that I was close enough to the solution to go to step 2, a full size mock-up, higher and longer than the 1936 model.
With the active participation of my Beloeil colleagues Claude Martin, Paul Fournier and André Létourneau (a few years ago we already committed a HM-8 together), joined by Réjean Samson, the new owner of my HM-293 and some scrap pieces of plywood and cardboard glued and nailed, I built an adjustable HM-14 seat, engine stand and instrument panel.
That gave the strange mock-up illustrated below:
Every pilot passing through our workshop and intrigued by this atypical construction was invited to sit down in the cockpit and to give his feeling,
From the smallest and lightest to the tallest and heaviest:
Paul : 5pi 6po (1m,68) – 161 lbs (73 kg)
Claude: 5pi 8po (1m,72) – 140 lbs (63,500 kg)
Réjean : 5pi 10po ½ (1m,79) – 180 lbs (82 kg)
Jean-Pierre : 5pi 11po (1m,80) – 240 lbs (109 kg)
Alain : 6pi (1m,83) – 160 lbs (72,500 kg)
Jean: 6pi 2po (1m,88) – 140 lbs (63,500 kg):
These experiments allowed me to put the finishing touch to my first drawing, which mainly meant:
-Keeping the length of the cockpit opening, but reducing the height of the fuselage.
-Leaning the seat backward to prevent abrasion of the calf on the front of the floor which is one of the most uncomfortable features of the original design.
-For the same reason, reducing the height of the wheel axle box and planning making adjustable footrests.
-Adjusting the width of the fuselage to fit the largest pilots without going to extremes.
I sent my handmade drawing to Charlie Crawley who was kind enough to make a CAD version of it. (As he did for all the other sketches of this text. Charlie had already made all the difficult work of replacing the French text with the English one on the HM-360/380 plans)
a PDF version of this file click here
As a matter of interest, the reader can compare the outline of this suggested fuselage with the outline of the 1934 and 1936 versions previously shown.(for a side comparison, click here)
I believe that this drawing will continue the interesting study made a few years ago by Bruno Corbeau on the same subject and I hope that it will be of some help for the future builders of HM-14/360.
The following drawing of the new fuselage traced on a HM-360 plan shows that, in fact, the suggested HM-14 is nothing but a HM-360 with a new fuselage.
I draw the attention of the builders to the following points:
-For the tailwheel, I suggest the HM-293 latest tailwheel as designed by Rodolphe Grunberg (Plan# 10bis)
-W e realized that adding (or not) cushions on request on the seat bottom and seat back, and making a footrest adjusted to the length of the pilot’s legs makes this fuselage very easy to fit to very different heights of pilots.
-Norbert Mosson was kind enough to send me photos of the cabane and wings fixation brackets of his HM-14/360. These photographs are precise and sharp and I suggest the builders to draw their inspiration from them and from the HM-360 plans.
Please find here under a few photographs of some HM-14/360 currently flying.
I would be pleased to add other HM-14/360 to this photo gallery. I could not get in touch with everyone and I may have lost some photos. Do not hesitate to call me.
Thank you to Charlie Crawley, Norbert Mosson, Thibaut Cammermans, Bruno Corbeau, Jean-Jacques Legrand, Claude Martin, André Létourneau, Réjean Samson, Émile Gomez, Étienne Bouvier and to all those who helped me with this project.
Your comments will be welcome.
Ph: 819 228 3159 (evenings and week-ends)