the concept wood ? building



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the mosquito zero is our first prototype. Ideally we want it to be light, safe, fast, reliable, simple, small, versatile, low maintenance, sexy and... silent. To make it real, we have decided to spent a few years just laying down the design. You can have a look down the wood?tech talk section for informations.
we had the opportunity to source some french spruce, which is not as stiff and resistant as the sitka spruce or the douglas fir. The lower mechanical properties and strength to weight ratio have been compensated by increasing the beam sections. Our main goal being to build the prototype, and the project being late, we decided to go for a quick route and to use the spruce.

 

conventionnal turning and milling is used to fabricate all the aluminium fittings and various brackets/mounts. all parts are then anodised for corrosion protection. Sulfuric anodising is one of the only surface metal treatment and finish that is eco-friendly.

carbon fibre work: the main rear spar is an opened beam in order to ease the air flow circulation behind the back of the cyclist. Because of this severe requirement from a structural point, the sides of the beam have to be stiffenened. This is achieved with a triaxial carbon fibre reinforcement.

To keep the carbon fibre reinforcement compatible with its woody partner, the plies have to be extremely thin (0.2mm). Other areas were there is little room for pure wood beams had to be locally stiffened without introducing stress riser, mostly between the crank bracket and the front wheel.

in total, carbon fibre composites count for less than 10% of the frame weight

With the mosquito, we give ourselves the opportunity to test ideas and concepts we have had years ago.

other carbon parts include the 2 struts of the 4-bars linkage.
the pre-stressed thin walled tube is bonded to the anodised aluminium 7075T651 fittings. For added safety it is also secured with monel rivets. Titanium foil is used to make sure the bearing strength of the composite is never reached.
by pre-stressing or pressurising the tube we can save the need for a stabilising core or ribs. Plus it sounded cool just to experiment this rarely seen option. We are very proud of this critical part. Moulded around a metalic mandrel, the 1mm walls are within a tight 0.1mm tolerance. This part can withstand bending and torsionnal loads the same magnitude as those on a bicycle race frame.

CAD model of the main frame
Finite Element Analysis model of the main frame. It has yet to be "adjusted" by comparaison with the real mosquito. By corrrecting the overall stiffness of the model we can make sure the predicted stress is very close to the reality.

FEA post process

and the real work...the main front spar has to be within very close tolerances compare with the model. Murphy's law has been yet again experimented of course, leading to more delays and more overweight. But that's the fate of any prototype.

 

 

 

 




 
the wood core brackets connecting the rear wheels: the experience learned by building the front gave us the possibility to mould those 2 brackets, in total 8 x3 plies of birch and 6plies of poplar, laid at 0/90/+45/-45deg. Ideally, the plies have to be as thin as possible to make those 2 parts as strong as the theory can predict.

 

bonding jig for the rear spar. All our toolings are designed, made and controlled to make sure everything is built within the tightest margins.

JAR-VLA 685 control system details (extracts according to relevance)
(a) Each detail of each control system must be designed and installed to prevent jamming, chafing, and interference from cargo, passengers, loose objects, or the freezing of moisture.
(c) There must be means to prevent the slapping of cables or tubes against other parts.
JAR-VLA 689 Cable systems
(a) Each cable, cable fitting, turnbuckle, splice and pulleys used must meet approved specifications. In addition -
--(2) Each cable system must be designed so that there will be no hazardous change in cable tension throughout the range of travel under operating conditions and temperature variations;
--(3) there must be means for visual inspection at each fairlead, pulley, end-fitting and turnbuckle.
(b) Each kind of size of pulleys must correspond to the cable with which it is used. Each pulley must have closeley fitted guards to prevent the cable from being misplaced or fouled, even when slack. Each pulley must lie in the plane passing through the cable so that the cable does not rub against the pulley flange.
(c) Fairleads must be installed so that they do not cause a change in cable direction of more than 3°.
(d) Clevis pins subject to load or motion and retained only by split-pins may not be used in the control system.
(e) Turnbuckles must be attached to parts having angular motion in a manner that will positively prevent binding throughout the range of travel.

 
 
 
... to be continued with the building of the streamlined shell