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 #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141
If you look at elecric fans designed to move high volumes of air efficiently they use as much blade area as possible
Aircraft use thin blades for a couple of reasons; . engines are more efficient at higher rpm . gearboxes loose power . high speed airflow is required for high speed flight
the vertical airspeed of a 'copter is almost zero
I still think that you should try fan blades like those used in domestic free standing fans with ducting/cowling.
This would however require a gearbox to use high efficiency (power/weight) motors.
Side note; if the 'copter is meant to be used in hazardous areas it should itself not be a hazard, a tri-copter or even quad-copter will probably crash if one fan fails for any reason; a hex-copter can compensate for the loss of one fan.
So, I think that you need six or more large low speed ducted fans for this purpose. or two really large fans, somewhat like a heavy lift helicopter
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Sulaiman wrote ...
If you look at elecric fans designed to move high volumes of air efficiently they use as much blade area as possible
Aircraft use thin blades for a couple of reasons; . engines are more efficient at higher rpm . gearboxes loose power . high speed airflow is required for high speed flight
the vertical airspeed of a 'copter is almost zero
I still think that you should try fan blades like those used in domestic free standing fans with ducting/cowling.
This would however require a gearbox to use high efficiency (power/weight) motors.
Side note; if the 'copter is meant to be used in hazardous areas it should itself not be a hazard, a tri-copter or even quad-copter will probably crash if one fan fails for any reason; a hex-copter can compensate for the loss of one fan.
So, I think that you need six or more large low speed ducted fans for this purpose. or two really large fans, somewhat like a heavy lift helicopter
some of the ultra light or small quads use a reduction gear from motor to prop. I think for the reasons you site.
All the props, including those for supposed multirotors, seem to be mostly fast velocity fixed wing propellers slightly modified.
I wonder if the under-cambered props of small helos, would entrain more air at a lower velocity. Adding a wide blade chord, as c Sulaiman suggests, would all drive this new prop towards the ideal for hovering purposes.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062
Yup, MFCs would probably work if the efficiencies were a bit higher. Also why stop at methanol, simple methane would probably work at least somewhat and is easy enough to store as a liquid. -A
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
The questions regarding higher RPM and greater pitch are connected. Greater diameter, lower RPM and lower pitch is more efficient than smaller diameter, higher RPM and higher pitch.
We haver discussed this before, all the losses are at the interface of the fast moving, accelerated air and the 'static' air surrounding the craft.
EDIT: Also, one large prop is more efficient than six small ones. It's a 'surface area' divided by 'circumferance' thing.
Also, I don't think 'slip' is really a factor here, as it doesn't really contribute to efficiency. I can ellaborate if required. (Having said that, greater pitch is more 'lossy' than finer pitch, all other factors being equal)
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Don't underestimate the size and weight of the support equipment needed to make a fuel cell work. Pumps and the like.
Hydrogen has a poor energy density by volume, and compressed hydrogen has a poor energy density by weight when the weight of the pressure vessel is taken into account. The metal hydride storage tank is a recent invention that might be relevant: BMW briefly experimented with it as a fuel tank for hydrogen-powered cars.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Steve Conner wrote ...
Don't underestimate the size and weight of the support equipment needed to make a fuel cell work. Pumps and the like.
Hydrogen has a poor energy density by volume, and compressed hydrogen has a poor energy density by weight when the weight of the pressure vessel is taken into account. The metal hydride storage tank is a recent invention that might be relevant: BMW briefly experimented with it as a fuel tank for hydrogen-powered cars.
I looked at the hydride 3.2Mpa storage of H. It came out to 90g hydride for 15g of H.
As you said, tankage, valves and such add up. I wasn't surprised by re high mass low power of thy 1kw unit, but 18,000 dollars for a PEM fuel cell, was shocking. Even with platinum present, that's freaking high.
This is a 200w version note the graph, and note-the note "not for VTOL use" :
But all these companies and Darryl Hannah say it's so easy, just plug them in and it'll all work.
Once the solid oxide FCs get going in 15+ years, I think these PEM FC's will be doomed, for fixed locations.
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.
Need Help : Hydrogen Tank, Molar Quantity.
