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The Canadian HM-8 Replica
Project --Page 2
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NEW PLANS FOR A VINTAGE AIRCRAFT.
Why did we have to redraw the plans?
In the beginning, it was André Létourneau's request. He is from a family of organ builders and is accustomed to working with detailed plans that do not leave anything to the builder's initiative. The Osprey 2 and the Cubs he built also had detailed plans. The broad-brush approach Mignet had of building with long written explanations and artistic sketches, in his view, gave the builder too much initiative. He did not feel familiar enough with Mignet's spirit to interpret the drawings.
The second reason the plans were re-drawn was that, after long discussions with the HMS staff, we decided to build a HM-8 that could be displayed in flight. It is not really much more complicated to build a flying model than a static display replica; it is more rewarding for the builder and more interesting for the visitor. We have the examples of Old Rhinebeck in the United States and La-Ferté-Allais in France that clearly illustrate this point.
But, as we had to fly it, we had to make sure that the aircraft would be as safe as possible. Some details needed to be updated, which is not unusual for a 70-year-old design. The proper choice of wing airfoil is an important safety factor, and Henri Mignet left several possibilities to the builder.
Most of the original HM-8s had utilized sharp-nosed ribs, which is no longer considered an optimal solution. Mignet may have already had this feeling, as he mentions the possibility of using a round nose airfoil. We decided to use a Riblet airfoil, derived from a Göttingen airfoil contemporary to the HM-8 and very close to the airfoil that was used by Lérin, one of the most talented HM-8 builders. This airfoil is currently used on several light aircraft with excellent results.
Another example of the original design requiring updating: the ailerons. At the time, ailerons were very often activated by a single cable that was kept under tension by some kind of spring (Mignet speaks of a piece of saw blade). We could obviously not take the risk of using this method, even though it could work quite well. So we decided to use a very classical device with standard bellcranks. A differential control would eliminate the risk of adverse yaw.
Mignet also gave three possibilities of wing shapes, rectangular, rectangular with round tips and elliptic. He obviously had a preference for this third version, as most of the artistic drawings he made depicted elliptical wings. His preference pointed us the proper direction.
ANOTHER HM-8.
Looking one day at the American Flying-Flea web page, on the chapter dedicated to the HM-8, I was extremely surprised to discover that the HM-8 drawings, which I had so often looked at without really seeing them, were different from the classical HM-8 plans shown in Mignet's book. I could not believe my eyes and enlarged the drawings. No confusion was possible. The drawing figured the HM-8 D, a late and apparently unknown version which was not shown on the book.
I asked the web page editor where these sketches (and the corresponding text) were coming from and he referred me to one of the booklet published by Raymond Buckland, who for years worked tirelessly to spread the good word about the Mignet formula. That gave me a perfect opportunity to renew contact with Buck and I was pleased to hear that he was OK and busier than ever with his writing. Buck informed me that he had picked up the text and drawings from an old issue of the EAA Experimenter. With his usual cheerful kindness, he mailed a copy to me.
The text was a translation of a French magazine dated 1932 "L'Almanach de l'Aviation" and it became more and more obvious to me that the HM-8D was the missing link between the conventional HM-8 and the first Flying-Flea, the triplane HM-11. The front part of the fuselage and the shape of the wingtips were already very close to what Mignet designed for the Pou-du-Ciel.
I told Pierre Mignet about my conclusion and I must say that he was very surprised, as he did not remember anything about a last version of the HM-8. He suspected some kind of fraud and when I asked him if we should build a replica of the HM-8D, he persuaded us not to do it. We were quite sure that he was wrong and that the drawings were authentic, but, after discussion, we decided that we could not go against his advice and we started working on the classical HM-8, as per the book.
Nevertheless, I continued my investigation and called M. Ravel, the director of the Angers aviation museum. There is a HM-8 on display in this museum and I thought that M. Ravel could give me more information. M. Ravel stated that he knew only of the conventional HM-8, but he suggested me to call Daniel Château, a builder and collector very interested in the Mignet designs and who had built a web site about the HM-8:
Daniel was very interested in my research. To the best of his recollection, there was no HM-8 D version. However, he started to pore through his documentation and finally unburied the original article published in the "Almanach de l'aviation". He selected the principal drawings and published them in our behalf in a new web page:
That was the proof we needed to convince Pierre Mignet.
I printed this page and mailed it to Pierre.
His reply was immediate: "I was wrong" he said, "the HM-8D really existed. I am now convinced and it is the model you have to build!" Meanwhile, Daniel told me to get in touch with another collector, Maurice Garsault, who confirmed the existence of the HM-8D. He sent me more info, in particular an article by Henri Mignet in the Magazine "Les Ailes" that pointed out that about 50 HM-8 D had been built. By the way, he also gave me previously completely unknown information about the first flights of the HM-11 Flying-Flea, opening new horizons of wisdom.
Unfortunately, for the HM-8D, it was too late for us, as a part of the ribs of the standard HM-8 had already been built by André Létourneau, and as Paul Fournier was already well advanced in the his drawing efforts. We consoled ourselves by reasoning that the model we were going to build was the one built most widely, nearly 200 aircraft. And the elliptical wing is so beautiful!
I have decided to build a scaled replica of the model D, which does not deserve to sink into oblivion. My friend Chris Frank, from New York , another Flea-builder, has volunteered to help me build this model. It will be on display near the classical HM-8 we are building.
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