Expert: Ray Wilkinson - 6/20/2006

Question
Ray, Thanks, here is a follow up:  The interest comes for experimental aircraft intentions.  Yes, I am a pilot and part of the EAA, but have no access to expertise at this time for this challenge.  The question: where can this design be found that you mentioned in your answer.  Sincerely, Oscar
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Followup To

Question -
My question is about aviation propellor technology.  We have seen the same basic airscrew prop design for years, but occasionally a variant is displayed such as the Unducted Fan.  My question: Has anyone developed a turbine-like propellor with 5 or more blades that can be mounted directly to a higher RPM automobile engines turning 5,500-6,500 RPMs?  I am envisioning the faster prop blast coming from this apparatus. (although smaller cross-sectional airbite)

Answer -
Oscar

Sorry, propellers are not really my field, but I'll try to help.

In fact, airscrew development has taken place, but is not especially visible. The trend is to use more blades of shorter span to try to improve efficiency, and the shape of blades changes gradually - compare the straight blades of the old C130 with the scimitar-bladed six-blade prop on the new J version.

The use of fans on automotive applications is quite different, because they are more interested in low cost and low noise than high efficiency. On an aircraft, all of the power is delivered through the prop so it's a crucial link in operating efficiency, and a tiny improvement can make a huge difference in an industry where an aircraft costs more in fuel through its life than it costs to buy. On a car, it's normally for cooling and  only consumes a fraction of the power generated.

The emphasis is on easy manufacture, without complex multi-part moulds. You would not normally run a fan at high speed, for several reasons - safety (blade shedding and the energy involved if body parts mix with a rotating fan), materials limitations (stress goes up as the square of rpm), noise (principally related to tip speed). Besides, it's easy to reduce the speed, as the fan is often driven by a belt, so you can change the size of the pulley.

I hope this answers your question.

Regards

Ray

Answer
Oscar

The C-130 can be seen in detail on the RAF Lyneham website, which shows both variants. Take a look at
http://www.lyneham.raf.mod.uk/html/hercules/gallery.htm

If you are interested in pursuing the use of an automotive engine for aircraft use (presumably GA or microlight), maybe you need to speak to us. We are always interested in potential student projects. However, you need to do this quickly, as we are approaching cutoff dates for next year's projects (starting in September). I'm fully committed myself, but could pass on your details to some of my colleagues if you wish.

Regards