ProGlass Design 

The design pedigree of Bolly Injection moulded propellers is like no other. Firstly there are the years of experience making propellers for everything from rubber powered models through to 330 kph racing aircraft. Then making props from every material imaginable and from single blades to 5 blades. It was with this experience that we designed our first injection moulded propeller - for Taipan propellers.

Our Clubman Series propellers were the result of spending many months analysing and documenting everything we had learnt and converting it into a specially written design program from which in October 1995 we produced our first injection moulded propeller, the Clubman 10.5 x 7. It was a huge success, and remains so to this day. Even today we would change very little about that design.

The Clubman Series design algorithms have gone on the be modified for producing full size aviation propellers (Bolly Optima Series Propellers) with great success. It proves our core underlying design principles are correct.

Of course the World moves on, and now (2008), a whole new range of propellers are needed for electric, folding, ducted fan and slow fly applications. Those same core principles which underpinned the Clubman and Optima Series propellers are now producing the new Bolly ProGlass propellers.

Further, we have made improvements in the raw material and manufacturing technologies to produce an even better product - see our "Manufacture" section.

Bolly Injection Moulded Propellers have several unique design elements often not found in other props, and almost never found in other brands as the complete design package:

  1. High Aspect Ratio Blade (exceptions apply)
  2. Reynolds Number Correction
  3. Progressive Pitch
  4. Hub to Blade Integration
  5. Tip Silence
  6. Airfoil Accuracy
  7. High Strength Raw Material
  8. Excellent Balance

High Aspect Ratio Blade - If you are familiar with the design of high lift capacity aircraft, you'll note that they feature long, slim wings. Our "standard" design applies this design philosophy, which is why our "Gas" propellers have that extra half inch when compared to other prop sizes. Compared to a standard 10-7, the 10.5-7 will present a similar load to the engine, but generate more thrust as a result of this unique blade design.

However for smaller diameter and slower spinning propellers the above high aspect ratio ceases to work. Hence all our propellers have a Reynolds Number Correction factor applied. In essence this means the smaller and slower the propeller the wider the blade.

Progressive Pitch - Whilst many other manufactures advertise the use of constant pitch (i.e. using much the same pitch from root to tip), Bolly Propellers use a different design philosophy (some exceptions apply in our CF range). The pitch of the blade is progressively increases from root to tip, with perhaps a slight decrease at the tip to reduce noise. More information on our design philosophy can be found in the Bolly Book.

Hub to Blade Integration - This is the downfall of many other props. We've spent a tremendous amount of time and money using the latest software to produce the ideal hub to blade transition. Higher strength, lighter weight and a level of structural and aerodynamic integrity untouched by other props. The added bonus is that our propellers look like a propeller and not a warped stick.

Tip Silence -  Many, many hours were spent designing a prop tip that would be the most quiet, efficient, and resilient to damage. Testing has proven that ALL of these design goals were met!

Airfoil Accuracy and selection is of utmost importance. We have had written a custom design program to generate the airfoils for our props. The choice of airfoil is varied with prop size and application, and remains one of the secrets we will never reveal. All Bolly injection moulded propellers (and more recent CF propellers) use CAD design and CNC machined tooling primarily to guarantee airfoil accuracy.

Whilst the choice of Raw Material is not in itself a core design feature - we cannot optimise the design unless the material used is the correct choice. All Bolly injection moulded products are made from a long grain glass fibre reinforced polymer. Too much glass and the propeller is too heavy, too brittle, prone to voids and look like !@#$% - conversely, too little glass and the product is too flexible and poor performance. Perhaps just as important is to use good quality virgin material and properly designed moulds to ensure correct fibre orientation. This will become a full chapter in the 2009 Bolly Book.

There is little point in designing the best propeller to then sell a product that is out of Balance. Even the most perfect moulds and moulding equipment will produce variations; hence it's not practical to guarantee perfect balance on a propeller that costs just a few dollars. At Bolly we go to extra lengths to ensure our props are acceptably close to the perfect balance, hence it has become a design feature of our product range.

Continue the tour, see ProGlass   Manufacture   &   Testing


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