Summary

My childhood just started at the end of the second world war and , to set the background, I have known the horse carriage of my grandparents that we used to take when going to the neighboring village during summer vacations ... In this days, there was not many toys so, very early, I got the need to invent my own world, made with garage, miniature cars, sail boats, etc... No need to say that also very early I knew the saw and the hammer (not the hammer and the sickle...) (ouch my fingers!). At the farm nearby, there was a small work-shop with a thick carpet of wood shavings that smelt good... I spent hours there. My oldest brothers had built up a sailing ship that made me dream a lot and originated many of my projects. My father that recognized in me a little talent encouraged me a lot while he got me in touch with the airplane model club of the town nearby. It's there that I learnt how to design my own gliders (I always preferred to "invent" rather than "copy") and to work out my first radio control transmitters and receivers with vacuum tubes (at this time the servos got similar mechanism to old clocks but driven by rubber motors...). Then I had to give up all that to carry on with my studies, family and business life kept me apart from those exciting activities. All that remained at stand by for a long time and finally lead me to a new approach when I realized that my youngest son, Chris, got high level psychomotor qualities : he might become a skilful pilot (all the opposite of me). We then started with cars and boats (offshore). To get him happy I made a training circuit covering most of the backyard... also a very small raft just enough to get back wild boats (helpless giggling...). And as all that was going on well, the helicopter of the closest shop was really the thing to do. It was a Mosquito, a very good machine that provided a lot of satisfaction but also some cooling problems at the beginning. Then came a Kalt GS Alpha with its 22cm3 gas engine that I turned into the "Ecureuil (Squirrel)" of Eurocopter (my best scale model). But it looked so beautiful to us that after some frightening attitudes, we no longer dare to fly this machine. It's better standing at home (scale models often turn this way...).

Summary

Whether in business life or in general life, energy savings were always one of my favorite topics. I just got out of my business life and I got a lot of time to dedicate to my first love : electric helicopters came just at the right moment , what an excellent topic : it's silent (it's the turbine of the poor), it starts at every moment from the transmitter, it's clean but unfortunately it doesn't fly long enough. So it's a good topic with a huge job to get progress in flight duration.  There it was born : the HBE project! This stands for Low Energy Helicopter (Hélicoptère Basse Energie).

Helicopters got something like magic (I'll never say that enough...) : I remember in the air army service to be taken in Alouette II and Chinhook (tandem rotor of course...) and taxiing to reach the runway : gliding gently at about 1.5m from ground is a fantastic feeling... In addition, for an amateur of techniques, helicopters bring a concentration of miscellaneous technologies at ultimate performances : mechanics materials, aerodynamics, flight control, etc...

The present time that we live in has nothing in common with the past decades through the technologies it brings today. It drives us into an ascending spiral that offers always more and more technologies (computers, materials, etc...). Many components, radio controls (receivers, servos, gyros...) have exploded usual standards of performances. PC's have become as exciting as exasperating but provided that you stroke it in the right way, it provides marvels in terms of computation and communication, drawing and photo/video, etc... What a tool box, let's take advantage of it !!! 

Summary

Coming to this famous project, it was required to begin by the beginning : learning how to work a rotor out. This was the reason why I started by a test bench providing measurement that could be compared and possibly matched to the computation (thank to Pierre). I had not too many tools at the beginning and it was at the shop of a friend of mine that I learnt to mill my first mechanical components for this bench. But the biggest task  was the interface unit between the computer (PC) and the mechanical bench. This was a big job of electronic design. Another important task was the specification and the edition of the software (thank to my son Vincent for the software). Back to the interface unit, I had to build it up and to run it (one cent of electronic circuits); I had to soldier all the cabling under magnification and when there are busses to cable (10 to 20 leads in parallel with many integrated circuits piping on it) it's hard. One of the most critical moments was to find how to program the computer to get the RS232 interface working as we wanted to (essential condition for the success of this operation; maybe simple for some professionals, but for an amateur...). Also many problems at the end because the current drawn by the motor interacted with the measurements and the PC crashed... When not equipped to deal with electromagnetic compatibility, it's all a mess and it's helpless to have completed a complex system, vital for the project, that might go right to the bin! I have tried many isolation devices to decouple power circuits from measurement circuits but actually nothing worked, not even opto couplers. With some tenacity, the luck has finally arrived and the success came with some ferrites wisely placed to stop the radiation from its source. What a great relief : the project could carry on.

Summary

For us, testing a tandem rotor was something really new (for the anecdote, I am still ashamed to to recall that I was wrong of 90 degrees with the swash plate phasing). I had planned to begin ground testing step by step up to the take off limit to measure rotor speed and power consumption. Then to test the dynamic behavior we were rather fearful. We had imagined a three axis balance, a sort of big frame bearing the machine and allowing only rotation motion in pitching, rolling and yaw. The trials were done in a small garage generating a great deal of turbulences. In this conditions, the machine got violent reactions very difficult to manage. Testing in open air improved a lot but finally this method was rather disappointing. In fact we should have modified the balance and damped the three axis motions with sensors to measure the torques and compare with the computation Pierre made but it would have been a lot of work and not very efficient.

In front of the difficulties to overcome we decided to carry on the trials outdoor on the green that I had done in my garden. Unexpectedly the things become quite easy. We started power feeding the machine with car batteries. Except for the power cable the machine was free end piloting in calm air was not difficult. The conclusion of all that is that any hindrance to movements leads to unexpected behavior (even the presence of the power feeding cable is experienced while piloting). So we'd better take the plunge and start the new machine with a hoop, it's more careful.

At the beginning HBE_00 was equipped with rigid rotor heads and one gyro for pitching : it hovered well without wind. Once my son Christian as pilot encountered a small gust and could not steer off a little bank and this was the first crash... but it was not that critical. The biggest job : remake the four aluminum blades that were severely bent. At this occasion I noticed that the aluminum foil was pelable, yielding the epoxy core with a good surface quality. This was how came up to me the idea to make composite blades injected in a pelable mold (a single use mold unfortunately).

Summary

To improve the tandem rotor, Jacques prompted me to work out new rotor heads and when Jacques prompts somebody, it's difficult to oppose to him because he'll prompt all day long... As it happens currently, we had a brain storming session that, after hard talks, led to positive outcomes; when we're not in agreement it's because we didn't discuss enough and didn't share our point of views. He is Mister "Reliability" and I am rather Mister "Just enough at the right place" (supporter of "lace" and perimetric framework; 1gr is 1gr...); in these conditions, it's not surprising to meet some points of frictions, all advices being good to consider and it's when points of view are promoted that we improve the know how. Coming back to the rotor heads, we wanted to design a flapping rotor head and get rid of ball bearings that burden their mass and their cost. Finally we succeeded to find and attractive solution that provided satisfaction after some modifications (at the beginning our rotor heads didn't provide enough angular travel and got a non symmetrical flexibility  in flapping). How nice was it for the pilot to get free blades, at last (we'll never insist to much on this point) !!!

All that we learnt with this prototype was forwarded to the followings : HBE_E et HBE_T.

Summary

We have been a little long to get aware (we used to fly in the garden protected from winds) that stability of our tandem rotors was a major problem and even a key problem! This has nothing to do with tandem rotors but stands on the fact that they are ultra light models (a feather in the wind, is not it, Jacques?).

The investigations we made are that close to the ground, winds act generally as rolls, coming to "bite" the surface swept by the rotors from any side, any angle. This generates locally ascending or descending flows. It is then easy to imagine that it tend to topple the machine. In addition the reaction of our models is about ten times faster than our poor reflexes of pilot, producing a situation impossible to stand : get rid of your Bell bar and your yaw gyro and tell us if you're ready  to try again (if your helicopter is still alive!). It was then required to link a gyro with each axis (pitching, roll and yaw) to compensate what the pilot cannot manage to do. Due to speed problems of the flight controls (electronic mixers + servos) we have spent a lot of energy to analyze the problems and find satisfactory solutions.

Summary

For a record attempt it's better to get some help and to be lucky. Reported as a feedback, not only the rainy weather vanished at the right moment, but just after landing, the belt fastening of Jacques' transmitter broke out... (imagine the situation during flight !!!). in addition one of the three gyros got free from its support... and I don't mention my Peak Infinity charger that broke down when charging just before the attempt... (fortunately I had another one, this is more secure). We never had before such an addition of critical events; let's take it as a lesson !!!

Summary

Such a project can be successfully driven only by the contribution of numerous people. I think to the test bench software (my son, Vincent), to the encouragements and the organization provided by our club president (Denis Genty), to the efficient action of the leaders of our federation (FFAM).

I would never insist too much about the essential contributions brought by my two friends Pierre and Jacques to make this record attempt successful. I focused too much on mechanical design so that I would never be able to start the project without them. Having met them in this field made me aware that I was going to live a unique experience.

Jacques was not only the only one that knew how to pilot but also the partner able to share his estimates and analysis about flight behavior. He originated numerous initiatives and specially on the technique involved in the rotor heads and the general optimization (about 4 stroke motors, PC and RC software, gyros and mixers...).

The part of Pierre was absolutely essential in computation not only about rotor aerodynamic but also on rotor distortion and stability behavior. Without him it would have been impossible to make the right choices. He explained and re explained many times in good humor the analysis that we could hardly follow. Go and see his impressive literature and don't hesitate to request explanations that seems inexplicable... (technical articles : don't forget to contact him).