Vance Jaqua wrote:
Vance here - With a rigid fixed pitch prop and this
speed range you have a real problem. My prop size
program suggests for a 70 inch diameter prop a ptch of
about 97 t0 98 inches with blade widths at .9 R 3.25
in at .7R 4 inch at .5R 5 inch and .3R 6 inch. The
program adjusts blade widths for a uniform hp per sq
ft over the working range of the disk (.2 on out)
generally tip further narrowing is suggested in the
last 10 percent to reduce tip losses.
Using a typical
180 bhp aircraft engine power curve, you are, of
course, grossly stalled and bogged down at static to
about 1900 rpm where the hp is about 108, and thust is
about 306 lbs.
It gets even worse on the roll as
sections start unstalling and bog the engine down even
further at 60 mph 1800 rpm about 97 bhp and 304 lbs. At
100 it is not much better 1900 again and about 280
lbs. Even at 140 a little over 2100 rpm 130 hp 275
lbs, 180 just under 2400 160 hp 280 lbs, 220 a tad
over 2600 almost 180 hp 265 lbs, and at 240 slightly
over speed about 2750 190 hp 260 lbs.
The take off
roll would be long and the climb suffers. The good
news is that with more flexible props of proper blade
shape, like Klaus and others provide, the low end rpm
and power come up, and performance is improved. In
terms of airfoil, props do not benefit as much as
wings from fancy foils because of the low Reynolds
numbers. Vance
Hi Vance
Pine here - Thanks for the input. Its a bit discouraging to read and gave me
the idea that building a CS prop is the only way to go.
I have access to a ISEL CNC machine to manufacture the blades and allthough
Paul said I must hang-ten for their trail runs I'm burning up to get my
brother to cut a 1/4 scale of the blade so we can smooth over the
manufacturing process.
The numbers you run for me is for a fixed pitch prop. Would the blade twist
be radically different for a CS blade. (Stupid Question I suppose) let me
rephrase. Is the design parameters for a CS blade and for a fixed pitch
blade the same. Except for the fact that with a CS blade you have an x
amount of pitch change say 33deg.
Working through the theory of prop design there seam to be a lot of
confusing issues. But in practise theres only so much that can be changed.
The problem for me seems to be, knowing what changes gives what affects. And
then to know how to interpret the numbers thats given.
Does the software you use give a different solution path for CS blades?
You mention that it solves the chord lenght to give a uniform hp per sq ft,
how will this be affected where one want to use a more rounded crossection
at the blade root for machinical hub reasons.
Would it be possible for you run these numbers again as if it was going to
be a CS blade. ??
Could you also let me have the chord angle for the given stations and let me
know if its on the blade bottom (ClarkY) or on the blade chored.
Many Thanks
Pine Pienaar
pine@cpro.co.za
Lancair 360 #664
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