Helicopter Rotor Blades
Rotor blades are what define the helicopter. It was once said by BJ Schram that you built a helicopter around its rotor assemble, not a rotor assembly for a helicopter. This was how much importance he placed on the right marriage of the components it takes to build a successful helicopter. Rotor blades come in many different styles and materials, not all of which are suitable for the homebuilt helicopter.
Main Rotor Blade Options
Profiles: One of the most common helicopter blade profiles is the NACA 0012 symmetrical blade still popular to this day for its broad range of performance. Being symmetrical, it becomes the most practical to construct for the home builder. There are many different profiles now available including the trailing edge reflex design used at one stage on the Mosquito helicopters to the newer asymmetrical designs promoting different performance abilities in hover, and/or transitional flight. To add to this there are individual manufacturer specific trademark designs and additions that claim to improve flight performance for given situations.
Materials: Historically, helicopter rotorblades were made from laminated wood shaped to the profile required, with the addition of a balance weight for correct center of ballance. This later evolved to variations of wood core and ply style skin type blades with high tensile steel main spars. One of the downsides of the wooden blade was its suseptability to moisture causing imbalance between blades and on occasion, swelling of the wood which altered the airfoil shape. To counter this, high-tech coatings wrere applied including fibreglass type coverings for both strength and protection.
It wasn't long before metals were considered the most practical as the primary construction material. They offered a more consistent and uniform finish and while overcame the moisture absorbsion issue, were susceptable to corrosion and metal fatigue. Today, aluminum/aluminium is still the primary construction material for many commercial and homebuilt helicopters. It becomes the most practical choice for its price and availability. There are a few options on the market that come and go, for blade "kits" consisting of a lead edge spar of aircraft grade aluminum/aluminium along with the trailing edge skin and attaching rivets. It is imperitive that ALL MATERIALS are of aircraft grade, NOT commercial grade.
Finally it was the advances in composite technology that bought us to todays modern helicopter rotorblades. Composite rotor blades offer many advantages with increased fatigue life being the most significant. Molding processes keep a high degree of uniformity along with being able to manufacture complex shapes and airfoils never before possible. The flexibility of the composite blade allows for rigid fitting, in some cases, doing away with the need for complicated flapping and/or lead-lag hinges. Composite rotor blades are not only for the larger commercial helicopters, they can also be found on many of todays kit built production helicopters. There are also a few select manufacturers producing composite blades available to the public the expect to pay heavily for them.
Tail Rotor Blades
Tail rotor blades become slightly less critical in requirements allowing for more construction options. You can build or buy them in wood, sheet stainless folded over a metal spar, sheet aluminium/aluminum folded over a spar, shaped and formed solid aluminium/aluminum and many variations of kevlar, carbon fibre and other composites.
They generally stick to a simple symmetric airfoil that acts as a directional fan with equal pitch changes changing the deflection of the blades. The simplist is the two blade teetering type suitable for most performance requirements and ranging up to multi-blade and fenestron shrouded type tail rotor assembly offering quiter and safer blade operations.
