oneiron:
at the risk of being argumentative...
my point boils down to this,
you will never get close to the betz limit with a home built machine, or for that matter
with a factory machine either, most especially in the 10ft class doing battery charging duty in the typical install location seen by most people...
further,
it is doubtful that most folks will ever get close to half the betz limit under such conditions...
your point in re to crowd sourcing fails to account for the collective cost of both time and money, and the problems associated with any project that is done by many folks, in many locations, under many differing conditions, materials and capabilities. just ask boeing about their experience when it comes to this problem.
all i am saying is this, start with an accepted number from someone that ought to know, such as paul gipe, hugh piggot, the dan's book, flux, and numerous others here and find a range, then pick a realistic number to accept as a baseline, then...
as you work on your unit, be very careful to document everything, triple check every test, and be "very, very, very" suspect if your results are much more than a percentage point or more over that of the accepted baseline number as established earlier.
doing this sort of work requires all sorts of stuff most folks either don't have access too or have little interest in doing in the first place. things like 2 or 3 separate volt meters to cross check even the accuracy of the voltage output can sometimes explain errors in your findings.
don't get me wrong, i have no problem with your interest in testing and improving efficiencies, however just remember it is overall efficiency that counts. be prepared to run back to back testing over and over again to determine if your gains in efficiency are truly gains and not some other factor that is skewing your results.
also it makes me little difference whether you are an amateur or an electrical engineer, i have seen faulty numbers from both, just as i have seen good numbers from either. the point being results from an engineer are just as suspect to me as those from jon doe out in his garage.
i will close with this assertion,
it is doubtful after 150 years of generator development, over 100 years of airfoil development, and over a half century of work from everyone between jacobs to boeing, from hugh to flux, from you, me and everyone else that dabbles in this stuff that there will be some radical improvement in the basic machine as is typically built by folks here. raising the efficiency of a typical 10ft class of machine by more than a couple percentage points is going to be a very costly endeavor in my opinion.
but don't let me stop you, you might well be smarter or luckier than others, and come up with a real game changer, however doubtful i think it might be.
i write this not to be rude or to pour cold water on you or anyone that wants to do what you are proposing, i just want you to be aware of the true costs of development. i have been in the research and development game myself for the last 4-5 years with micro cogeneration, and i can tell you this...
i have more time and money invested in the test cell than most folks will ever have in their home built cogenerator or windgenerator for that matter. i have seen changes in efficiency come in with a 5 point gain, only to find out later that it can be explained by a fault somewhere in measurement or calculations. these faults are much easier to find in an engine driven generator than one driven by wind where windspeed can be so variable that getting accurate numbers can be very tricky.
also be aware that it will likely be something less than 1% of all the folks that build windgenerators that will be committed to this level of testing, research and development.
that makes crowdsourceing a very small group indeed.
good luck.
bob g
ps. my comment in re to alternator efficiency coming in at 50% or so is as applied, that is you may well build an alternator that tests on the bench to be 70 or more percent efficient, but how efficient it is when applied to battery charging is where the rubber meets the road. who cares if a car has a 400 hp motor if it only gets 200 hp to the tires and to the road? who cares if it makes 400hp at 8k rpm if it is a grocery getter and will be driven at an average rpm of 2k rpm?
this is my problem with claimed efficiency numbers, i can tweak any single component to give me any number i want, however it is the overall efficiency doing what the unit is designed to do, under the conditions it will be used under that is of the only importance.
at least that is how i see it.