Instructions for assembly and use of wooden propellers
BORN PROPELLER only uses local lumbers for the wooden propellers like ash, maple and beech. All lumbers are chosen according to strict regulations, dried and seasoned properly.
We cut out the best pieces from the boards only and manufacture these into propellers. If you get a propeller of a weight of 3 kg, we have already cut 45 kg wood for its manufacturing!
Nevertheless, your propeller may still show small imperfections, which however do not affect its function or even its reliability at all.
You help protecting the tropical rain forest, when using propellers made of local lumbers. Moreover tropical lumbers show some technical disadvantages like for example low bending fatigue strength due to too short wood fiber.
During manufacturing the geometry is controlled permanently like blade width, blade thickness, form of profile, track and balance.
The low density of the material (ca. 0.7 g/ cm³) allows for propeller weights, which are about 50 % of the actual metal propellers. The polar weight moment of inertia is significantly lower than that of metal propellers. That is why a wood composite propeller runs much more steadily.
Rotary speed restrictions are not necessary because of the high natural damping of the wood. Blade tip fatigue breakages occurring with metal propellers again and again are unknown.
In order to protect the wooden blade body against humidity and erosion thoroughly tested polyurethane varnishes are used. This special varnish is resistant against fuel, oil and other chemical products. This kind of varnish even offers an excellent flexibility. Because of the destroying effect of the ultraviolet rays on wood it is necessary to use colored varnish.
Scratches or dents should be covered with a layer of waterproof varnish on the occasion of the usual maintenance.
Please check the track. Maximum deviation are 3 mms, measured 10 cms from the blade tip at the trailing edge. If track is bigger, you have to locate the reason and check the contact surfaces. A conversion on the flange may be possible. Different fastening torques up to 3 Nms are tolerable. If all this does not help, please send back the propeller to the manufacturer.
Characteristics of wood and storage
Wood is a natural material. With changes of the temperature wood absorbs or loses humidity. A certain concentration of residual moisture is important for the preservation of good technical quality characteristics. Please keep in mind that wood might also warp on absorbing or losing humidity.
Wooden propellers never should be stored in heated rooms. Please never keep it with one blade downwards for any length of time, but preferably always horizontally at an air humidity of about 60 %. The storage temperature should be between 10° and 20°C, preferably closer to 10 °C.
Wrong storage often causes unbalances, which can only be adjusted at our workshop.
Damaged propellers
Any kind of damage of your propeller should be repaired immediately: As soon as for example the varnish coating is damaged there is the risk of humidity soaking into the propeller and making it unusable. Even the smallest damaged spot can develop into a total loss sooner or later. You know this effect from your car: small damages to the paintwork quickly lead to corrosion.
Any damages occurring within an radius of 400 mms around the hub usually are total losses, because in this area the material is strained most.
Of course you can call us in order to get help in estimating a damage. We also offer you our repair or exchange service.
Smaller damages to the paintwork up to 5 mms can easily be repaired with a water-resistant sealing varnish.
Assembly
Bolt fastening torques: M6 = 10-12 Nm
M8 = 17-22 Nm
Preferably the propeller bolts are fastened steadily by means of a torque wrench.
By the means of different fastening torques you are able to balance misalignments.
Performance
The actual flight performance of your aircraft depends on the following factors:
- engine power
- carburetor tuning
- gas-oil-mixture
- air temperature
- air humidity
- flying altitude
- age of the engine
- age and condition of the propeller
The power information you get on the purchase of a propeller always refers to standard conditions and may be about 20 % better or worse than the results you get.