Incidently, the stated twist distribution for the LAEV blades is

very

strange, and I have not heard any response on the reason and

logic

of that decision - Vance J

As a guess Vance what speed would you say it is twisted for.
I think Bill made some assumptions as to the actual direction of

the in

flow

around the hub. I think he assumed a certain amount of external

diffusion

directly in front of the cowl as I recall. Is it the hub angles
of attack you are concerned with?

Paul Lamar

That's what I thought too Vance when I tried to figure out what

the

"pitch" of the blade was at various tip angles. All I could figure

was

Bill de-pitched it near the hub because he knew it was for a

tractor.

But I haven't asked him (yet).

--
Perry Mick

Vance W Jaqua wrote:

Here are a couple of plots of pitch distribution versus radial

portions

of the blade versus a bunch of tip angle settings. The first is a

simp;e

table, which I am sure a lot of the guys and gals have already
computed. The second is a graphic plotted against radius squared
which better shows the amount of disk area impacted by each radial
zone. The twist does not appear to be optimized for major areas of
true helical pitch. at any speed. In virtualy all settings, over 30

percent

of disk area
near the tip appears to be at least 20 percent under pitched ??
It will probably work reasonably well, since propellers are really
rather forgiving devices - but???
Vance J

Bill had some pretty good reasons for doing this at the time Vance.
As I recall we discussed this at length. If I get time I will look
up the pertinent messages.

>From memory I think the outer de pitching was to reduce the
transonic drag rise.

Paul Lamar

Here are a few of the charts Bill used as I recall.

I think this points up the desire to determine the twist distribution that
Tracy Saylor used on his 2 blade prop (if he is willing to share that
info). Failing that, measure the twist distribution on a factory
installation
for a fast plane. I have heard of fixed pitch makers relieving pitch
slightly
at the tip with the supposed reduction of sonic losses. However a well
designed prop at design point will be almost zero angle of attack
for about 0.3 t0 0.5 Cl, and it would not take too much reduction of angle
to get in a local reverse thrust situation. I would consider the back off of
pitch at the outer zone (much more than just the tip) to be a bit excessive
Vance

Could be Vance. Time will tell. Props are still more art than science.

Paul Lamar
 
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