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

The program uses a table of lift and drag coeff for a
Clark Y , zero degree at flat bottom, Std rough, for
an aspect ratio 0f 6:1. This can be modified just by
putting new numbers in the table sections. Using the
bottom of a flat bottom foil Clark or RAF is the most
common method, but there ar as many methods as there
are prop designers, and they are all valid so long as
you know what they are doing.

The program totaly ignores everything inside of .2 R
since it is almost totally blocked and is only 4
precent of the area anyway - so hubs and spinners are
left out.

For a constant speed prop one would set the twist for
a compromise pitch, and accept the errors at other
pitch values (generally small). to evaluate this with
my program, I can force the angles at the selected
stations for runs at different speeds -(time
consuming)

The program computes for true helical geometry unless
you input the angles.
The engine curve I used was for an aircraft direct
drive engine (0360 Lyc 180hp) if this is a gear
reduced engine with max power at breathing limits, it
is a very different power curve shape - that is
actually benificial at the lower speed points.
I have a tendency to believe that your Lancair 320 is
not quite that clean, unless you have done an
outstanding job on gear doors and all gaps (and
whoever said that was like a Long EZ with fixed mains
is really optimistic) a quick check seems to indicate
that you need less than 1 sq ft of equiv flat plate to
do 240 on 180 hp. Vance

 
The Aircraft Rotary Engine Newsletter.              Powered by Linux.

http://home.earthlink.net/~rotaryeng/            http://www.linux.org