Agree with most of that.
Ultralight aircraft use reduction drives. For best performance at low speed
(and least noise) a large reduction is better. Therefore some good
ultralight propellers (Arplast for example) have blades with lots of pitch.
Below is the twist profile for an Arplast Ecoprop and VP prop wide blade
style as recommended for 912S and 914 Europas.
Pitch in degrees from 64" to 20" diameter in 4" steps
17.80
19.00
20.40
21.80
23.40
24.20
25.20
26.40
28.20
30.10
33.00
36.90
The blades are adjustable so the absolute pitch can be changed.
Pitch is measured on the back of the aerofoil so there is a small error as
the back of the blade is not the aerodynamic reference but its a good
indication.
I have an Excel spreadsheet that predicts pitch given aircraft speed, engine
speed and gear ratio. I mean to put it on my web site when I get a spare
moment.
The 912 blade has a little less pitch because the gearbox ratio is smaller
and angular velocity greater.
Jerry
LTS@avnet.co.uk
http://www.avnet.co.uk/touchdown
----- Original Message -----
From: Nic <tgynz@cts.com>
Subject: Blade twist
> Propeller blade twist is to provide somewhat of a constant aerodynamic
pitch
> (alpha) along as much of the blade as practical.
> Propeller blade twist is a function of desired RPM and desired aircraft
> speed, typically described as climb or cruise or race.
>
> A propeller for an ultralight is nearly twistless.
> A propeller for fast planes have quite a bit of twist.
>
> Some of this twist at the root can be for improved ground cooling.
> Controllable pitch propeller blades can have twist for climb or cruise.
>
> In an installation w/ low power, blades w/ twist for climb is 'better'.
> Then advancing the pitch at speed will get you some extra performance.
>
> In a high power to airframe type ratio installation, the extra performance
> is the improved launch and climb w/ finer pitch settings allowing the
engine
> to rev up and provide power.
>
> Check out the twist of the popular choices.
> I am currently researching these factors and might have a spreadsheet
soon.
>
> Nic - xs145
> :)
>
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