Blade width, and/or number of blades cannot compensate for reduced

diameter

in the prop efficiency game. It only lets you absorb the engine

power at the

reduced diameter(also very important if your engine cannot make

power

you cannot turn it into thrust)\
Disk area is the 300 pound gorilla at low - ie STOL speeds
but the advantage of diameter decreases at higher speeds. At 200 mph

the

larger
diameter is still better, but that advantage narrows to about a

pencil

width.
Vance J.

Hi Vance
In the efficiency game we know that the blades near the hub, and out for

a

distance is usually flying in dirty air, more so for us pusher builders,

but what

causes the wider chord shorter blades to be less efficient than a

longer/more

narrow chord blade.
Anyone care to cover some prop theory/practical ideas on the pros/cons

of long

narrow blades, verses shorter wider chord blades? And maybe throw in

some thoughts

on blade count.
Unless it it too much off the subject of this newsletter.
Royce

As intimated above - the big driver for efficiency is the disk loading ie
the bigger the
diameter (until tip sonic effects rise and smite you) the better. But the
faster you
go, the increase from greater diameter becomes less of an issue. So long as
you have
the right amount of blade area for your power, the effects of multiplicity
of blades
and aspect ratio  tend to be rather small. using more blades to incrase the
blade
aspect ratio reduces local induced drag, but the interference between blade
wakes
pretty much uses up that gain. Some vibration reduction is often experienced
with an odd number of blades. Vance J.

Or for a non-engineering explanation/example, think of a 1000 lb helicoptor
being lifted straight up by a 160 hp engine.

Charlie England

Gee that sounds familar. Now where did I read that lately? :-)

Paul Lamar
 
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