If you need assistance, please send an email to forum at 4hv dot org. To ensure your email is not marked as spam, please include the phrase "4hv help" in the subject line. You can also find assistance via IRC, at irc.shadowworld.net, room #hvcomm.
Support 4hv.org!
Donate:
4hv.org is hosted on a dedicated server. Unfortunately, this server costs and we rely on the help of site members to keep 4hv.org running. Please consider donating. We will place your name on the thanks list and you'll be helping to keep 4hv.org alive and free for everyone. Members whose names appear in red bold have donated recently. Green bold denotes those who have recently donated to keep the server carbon neutral.
Special Thanks To:
Aaron Holmes
Aaron Wheeler
Adam Horden
Alan Scrimgeour
Andre
Andrew Haynes
Anonymous000
asabase
Austin Weil
barney
Barry
Bert Hickman
Bill Kukowski
Blitzorn
Brandon Paradelas
Bruce Bowling
BubeeMike
Byong Park
Cesiumsponge
Chris F.
Chris Hooper
Corey Worthington
Derek Woodroffe
Dalus
Dan Strother
Daniel Davis
Daniel Uhrenholt
datasheetarchive
Dave Billington
Dave Marshall
David F.
Dennis Rogers
drelectrix
Dr. John Gudenas
Dr. Spark
E.TexasTesla
eastvoltresearch
Eirik Taylor
Erik Dyakov
Erlend^SE
Finn Hammer
Firebug24k
GalliumMan
Gary Peterson
George Slade
GhostNull
Gordon Mcknight
Graham Armitage
Grant
GreySoul
Henry H
IamSmooth
In memory of Leo Powning
Jacob Cash
James Howells
James Pawson
Jeff Greenfield
Jeff Thomas
Jesse Frost
Jim Mitchell
jlr134
Joe Mastroianni
John Forcina
John Oberg
John Willcutt
Jon Newcomb
klugesmith
Leslie Wright
Lutz Hoffman
Mads Barnkob
Martin King
Mats Karlsson
Matt Gibson
Matthew Guidry
mbd
Michael D'Angelo
Mikkel
mileswaldron
mister_rf
Neil Foster
Nick de Smith
Nick Soroka
nicklenorp
Nik
Norman Stanley
Patrick Coleman
Paul Brodie
Paul Jordan
Paul Montgomery
Ped
Peter Krogen
Peter Terren
PhilGood
Richard Feldman
Robert Bush
Royce Bailey
Scott Fusare
Scott Newman
smiffy
Stella
Steven Busic
Steve Conner
Steve Jones
Steve Ward
Sulaiman
Thomas Coyle
Thomas A. Wallace
Thomas W
Timo
Torch
Ulf Jonsson
vasil
Vaxian
vladi mazzilli
wastehl
Weston
William Kim
William N.
William Stehl
Wesley Venis
The aforementioned have contributed financially to the continuing triumph of 4hv.org. They are deserving of my most heartfelt thanks.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Udo provided the maths here, Patrick. I can't do that. All I can do is provide the basic theory. As I said in an earlier thread, my experience is with marirne propellers. I've learn't a lot this evening, thanks to Udo.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
i have really important data captured. but i need to put it into excel or a table. but theres some important results revealed.
first below 4krpm these props are ultra low on thrust, but at 5krpm and above they really pick up fast. second as would be expected, most of the thrust comes from the outer sector of the radius swept.
third, the electric "E" 11x5.5 prop meant for fixed wing flight generates: 6.5g/W at 5,100 rpm (458g, 71W) 5.7g/W at 6,100 rpm (646g, 114W) 4.9g/W at 7,050 rpm (884g, 179W) (<- at 16.1 Amps and 140F, this is getting close to the max.)
which is important, now i can choose the operating point for the hover more for the grams per Watt value than just hope and guess. It does occur to me that at minimum thrust the efficiency is high, so many small props and motors would be advantageous, i guess we've talked that out before too.
so a 3-blade prop should generate more thrust from a given diameter.
The above wide fan induction blades intrest me, is there any practical way to get higher g/W values with out the diameter getting bigger and bigger? After 10" in diameter ducts get hard to support, there prone to wobble and flutter.
3 and 5 blades per prop may be needed if its the outer circumference where the effciency and force are trying to hide from me.
so what should a duct look like then Uspring? should it follow the pressure drop driven by the veolcity?
I was thinking of something like this: The duct should have a snug fit around the prop since there is a pressure jump from right before to behind the prop. Your thrust stand should be useful for some research.
Edit:The numbers you measured agree quite nicely with the equation
F = eff * (2 * rho * A * P^2)^(1/3)
F = thrust, rho = 1.225kg/m^3 (air density), A = prop area, P = motor power. eff is the props efficiency, which turns out to be about 0.5 for your measurement.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
FWIW, 50%-55% efficiency is about the best that super-cavitating, surface piercing props on offshore racing powerboats can achieve, although some large, slow turning props on ships can reach around 80% efficiency, if I remember correctly. It's a while since I was involved in this stuff. It's good to see you're making some progress, Patrick.
Patrick wrote ...
It does occur to me that at minimum thrust the efficiency is high, so many small props and motors would be advantageous, i guess we've talked that out before too.
Several small props close together (as in my heptacopter design) should approximate to one large prop, and the efficiency should rise further (meaning you can carry more batteries), although this is unproven theory, as yet, anyway.
Registered Member #2529
Joined: Thu Dec 10 2009, 02:43AM
Location:
Posts: 600
Uspring wrote ...
The physics for drag and propellers are similar. Both are based on acceleration of air masses.
More precisely, as the propeller (or any body) moves through the air, it deflects the air, and also creates drag on the air.
Both go, to a first approximation, as v^2 (where v is the speed of the rotor through the air, not the down-wash speed), and the two are related by the L/D ratio:
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Uspring wrote ...
so what should a duct look like then Uspring? should it follow the pressure drop driven by the veolcity?
I was thinking of something like this: The duct should have a snug fit around the prop since there is a pressure jump from right before to behind the prop. Your thrust stand should be useful for some research.
Edit:The numbers you measured agree quite nicely with the equation
F = eff * (2 * rho * A * P^2)^(1/3)
F = thrust, rho = 1.225kg/m^3 (air density), A = prop area, P = motor power. eff is the props efficiency, which turns out to be about 0.5 for your measurement.
it really looks like a tube around a prop or turbine, but those are heavy as i said, and difficult to attach. I was told by Embry-Riddel students to keep the the gap at 0.010 or so from tip the duct. but thats awful hard, in my first attempt you could hear the prop chattering the whole time.
in that pic are they using an electric turbine, Uspring? we cant really see the face.
if i could go from 0.5 to 0.7 eff id freak ouuut.... and consider this whole thing a sucess. im also wondering if i should mod the stator to carry more copper for the same number of turns.
This site is powered by e107, which is released under the GNU GPL License. All work on this site, except where otherwise noted, is licensed under a Creative Commons Attribution-ShareAlike 2.5 License. By submitting any information to this site, you agree that anything submitted will be so licensed. Please read our Disclaimer and Policies page for information on your rights and responsibilities regarding this site.
Novel flying machines
