Re: windmill blades.
On Mon, Jun 26, 2023 at 10:09:57AM +0100, Roger Whiteley via Discuss wrote:
Date: Mon, 26 Jun 2023 10:09:57 +0100
From: Roger Whiteley roger.whiteley@me.com
To: discuss@lists.openscad.org
Subject: [OpenSCAD] Re: windmill blades.
Try these.. https://hackaday.com/2020/08/14/quick-3d-printed-airfoils-with-these-openscad-helpers/
I already found this! I've implemented "twist" in the generated wing
already. That's useful for airplane wings: It improves the stall
characteristics. You balance the plane such that the center-of-lift
matches the center-of-gravity, but with a swept wing the inner part of
the wing will be generating lift in FRONT of the center of gravity. So
if the pitch there is higher than at the tip of the wing, you'll stall
there first, lose lift in front of the CG, keep some lift behind the
CG and the nose will drop and the plane starts picking up speed again.
It seems the big wind turbine blades have very little twist. A couple
of the realistic looking models have little to no twist in them.
Roger.
I especially like http://chaaawa.com/airfoils/index.cgi?o=name&n=50&p=2
Which produced this..
// Points from cr1.dat in the archive:
http://m-selig.ae.illinois.edu/ads/archives/coord_seligFmt.tar.gz
// Not necessarily in the same order as in:
http://m-selig.ae.illinois.edu/ads/coord/cr1.dat
cr1_points = [[1000,0.0173],[990,2.6651],[980,5.2997],[970,7.9079],[960,10.4761],[940,15.4453],[920,20.2277],[900,24.9688],[880,29.7881],[860,34.6645],[840,39.5362],[819.9999,44.3404],[800,49.0156],[780,53.5129],[760,57.8435],[740,62.0373],[720,66.1238],[700,70.1324],[680,74.083],[660,77.9406],[640,81.6511],[620,85.1617],[600,88.4199],[580,91.3811],[560,94.0411],[540,96.4112],[520,98.5024],[500,100.3252],[480,101.8894],[460,103.2027],[440,104.2715],[420,105.1022],[400,105.701],[380,106.0724],[360,106.2082],[340,106.0956],[320,105.7211],[300,105.0716],[280,104.1314],[260,102.8691],[240,101.2466],[220,99.2238],[200,96.7598],[180,93.8086],[160,90.3037],[140,86.1657],[120,81.1676],[100,74.8305],[80,66.7124],[60,57.1529],[50,51.5424],[40,44.9223],[30,37.219],[20,28.4739],[12,20.4608],[8,15.913],[4,10.4752],[2,6.9026],[1,4.5082],[0.5,2.8877],[0,0],[0.5,-4.9013],[1,-6.3669],[2,-8.4885],[4,-11.5467],[8,-15.8525],[12,-19.0076],[20,-23.277],[30,-26.5473],[40,-28.8161],[50,-30.386],[60,-31.4227],[80,-32.2357],[100,-31.904],[120,-31.0798],[140,-29.893],[160,-28.3204],[180,-26.4458],[200,-24.4737],[220,-22.5857],[240,-20.826],[260,-19.2004],[280,-17.7151],[300,-16.3755],[320,-15.1843],[340,-14.1278],[360,-13.1887],[380,-12.3493],[400,-11.5922],[420,-10.903],[440,-10.2799],[460,-9.7239],[480,-9.2366],[500,-8.8192],[520,-8.4708],[540,-8.1817],[560,-7.9399],[580,-7.7333],[600,-7.5498],[620,-7.3791],[640,-7.2182],[660,-7.0659],[680,-6.921],[700,-6.7822],[720,-6.6495],[740,-6.527],[760,-6.4199],[780,-6.3335],[800,-6.273],[819.9999,-6.2355],[840,-6.1851],[860,-6.0768],[880,-5.866],[900,-5.5081],[920,-4.9546],[940,-4.1417],[960,-3.0058],[970,-2.3222],[980,-1.5842],[990,-0.8099]];
linear_extrude(height=20)
scale([15, 15])
translate([0,0])
scale (0.001)
polygon(points=cr1_points);
--
** R.E.Wolff@BitWizard.nl ** https://www.BitWizard.nl/ ** +31-15-2049110 **
** Delftechpark 11 2628 XJ Delft, The Netherlands. KVK: 27239233 **
f equals m times a. When your f is steady, and your m is going down
your a is going up. -- Chris Hadfield about flying up the space shuttle.
I already found this! I've implemented "twist" in the generated wing
already. That's useful for airplane wings: It improves the stall
characteristics. You balance the plane such that the center-of-lift
matches the center-of-gravity, but with a swept wing the inner part of
the wing will be generating lift in FRONT of the center of gravity. So
if the pitch there is higher than at the tip of the wing, you'll stall
there first, lose lift in front of the CG, keep some lift behind the
CG and the nose will drop and the plane starts picking up speed again.
What you want in a normal aircraft wing is an elliptical load
distribution, as this gives you the least induced drag. This can be done
by keeping the profile constant and varying the size to be elliptical
(like the famous Spitfire), or by introducing twist. You are right that
this stall the center section first, which is a good thing because it
keeps the ailerons working and therefore the whole aircraft controllable.
Twist is also used in tailless aircraft in combination with swept wings,
as the wing tips then form the tail.
It seems the big wind turbine blades have very little twist. A couple
of the realistic looking models have little to no twist in them.
In wind turbines, the structural forces are more important, because of
the centripetal forces on the blades. Historical windmills do have twist
in the "blades", however.