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RE: Mini-Blimps: One-Man Ultralight Airships
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crluf-@yahoo.co.uk
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Mar 17, 2009 08:46 PST
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Hello Ray,
I'm also sorry for you because I believe I stated things correctly. Similar to submarines in water, balloons and airships are buoyed up by the air they're immersed in (instead of water for subs) in accordance with Archimedes' principle, which states, "a body floating or submerged in a liquid is buoyed up by a force equal to the weight of the liquid displaced." The atmosphere (air) essentially behaves in a similar way to liquid in this respect. The main difference between air and liquid is that air is compressible compared to liquids, which are not. This affects the density of the atmosphere as one ascends and means that it's affected by temperature and pressure changes, which also affect the gas contained in the envelope.
It's a difficult concept to understand
because the
intuitive approach leads one to
think that the gas in the envelope provides the aerostatic lift. However, this is wrong! The gas is only there to support the envelope from collapsing against atmospheric pressure. When the gas' pressure is a little greater than the atmosphere's pressure the envelope experiences the resulting differential pressure across it, which tensions the membrane and enables its form to be maintained. Otherwise, it would just be a heap of fabric on the floor.
Then, since the gas also has weight, it must be deducted from the weight of air actually displaced by the envelope. Basic buoyancy is therefore: V(ρa - ρg), where V is the displaced volume, ρa is the density of the air and ρg is the density of the gas. There are other complications to consider (such as gas fill, gas purity, ballonet capacity, air and gas temperature, air and gas pressures, etc), but this is the basic principle.
If one could build a vessel strong enough to resist atmospheric
pressure applied on it without collapse, which they are prone to do due
to unstable compressive effects (with a vacuum within), then ρg would be zero and the resulting buoyancy consequently greater. However, the vessel then probably would be so heavy as to be unable to float due to vessel weight. That's why a light flexible membrane stabilised with internal pressure is used for blimp hulls. The gas that one uses therefore also must be of low density to minimise its weight and so the negative effect on buoyancy, but is the lesser evil compared with a vacuum vessel's weight (the falacy).
For the sub one should account in the same way for the air contained within it, for people to breath rather than to pressurise the hull. However, its density is so small compared to the density of water that it normally is neglected (not so for airships, where the gas density has a significant effect). Subs therefore behave like vacuum vessels and do implode when they go too deep, since the water pressure rises as it sinks. Tricky,
tricky!
Because buoyancy results from displacement of the air, changes in atmospheric conditions (temperature and pressure) do result in buoyancy change when the gas is unable to change at the same rate (there is always lag), which is difficult to deal with.
For exmple, this occurs when a cold front moves across the envelope where the air's reduced temperature increases its density, causing a rapid rise of aerostatic lift from increased weight of air displaced. To compensate pilots can adjust pitch in flight to balance the effect with negative aerodynamic lift or vent gas to reduce the displacement - when the ballonet then is inflated with more air to compensate (so less displacement). So you are right about the effect of dropping temperature and it is a problem to be managed.
Wrt hydrogen, you also need to think again. Its use does enable greater lift than would be the case for helium, but due to the small weight of the gas compared to air,
the benefit is small. If at a common reference height the density of air = 1.2 kg/m^3, helium = 0.18 kg/m^3 and hydrogen = 0.09 kg/m^3 then buoyancy for a 1 m^3 displacement with helium = 1(1.2 - 0.18) = 1.02 kg and buoyancy with hydrogen = 1(1.2 - 0.09) = 1.11 kg. Buoyancy with helium therefore is 1.02 x 100 / 1.11 =
92% as much as with
hydrogen, so not so bad.
--- On Tue, 17/3/09, Ray Waters <ray_wa-@hotmail.com> wrote:
From: Ray Waters <ray_wa-@hotmail.com>
Subject: RE: LB Mini-Blimps: One-Man Ultralight Airships
To: crluf-@yahoo.co.uk, LBli-@topica.com
Date: Tuesday, 17 March, 2009, 10:33 AM
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I'm sorry you'll have to explain-Lift is the weight of the volume of the atmosphere displaced. It seems to me, this statement can't be right; because you can increase the atmosphere volume weight just by dropping the temperature.
And hydrogen would have more lift, not because it is half the size of helium; but more atoms of hydrogen can fit in the same volume as using helium. 2 to 1
my name is Ray Waters in Tucson Arizona I hope I'm not speaking out of turn.
To: LBli-@topica.com
From: crluf-@yahoo.co.uk
Subject: Re: LB Mini-Blimps: One-Man Ultralight Airships
Date: Tue, 17 Mar 2009 05:21:45 +0000
Sorry Reed, but I have to make a small
correction on this.
Aerostatic lift (buoyancy) is the weight of the volume of atmosphere
displaced minus the weight of the gas doing the
displacing and acts in the opposite direction (i.e, weight down, lift up).
Naturally, one then must consider the weight of the structure and its contents to determine the state of equilibrium between buoyancy and overall airship weight to be airborne and continue in balanced flight.
Lift also may be generated aerodynamically and this is a useful method to maintain or adjust overall lift.
Amen
PS I agree that Brad has many good ideas and should build models to determine how things work and whether they are practical.
--- On Tue, 17/3/09, Reed Gleason <ree-@comcast.net> wrote:
From: Reed Gleason <ree-@comcast.net>
Subject: Re: LB Mini-Blimps: One-Man Ultralight Airships
To: nimbl-@netzero.com, LBli-@topica.com
Cc:
ballandch-@yahoo.com, billg-@sbcglobal.net, bj1-@netins.net, caly-@aol.com, chg-@yahoo.com, cobb-@centurytel.net, Dar3r-@sbcglobal.net, dclar-@aol.com, Dee-@aol.com, geminis-@aol.com, gmel-@sbcglobal.net, jansfa-@yahoo.com, jud-@hotmail.com, Lacs-@aol.com, lat-@sbcglobal.net, lillie-@yahoo.com, NANCYD-@COX.NET, roll-@hotmail.com, sharon-@sbcglobal.net, sweet-@earthlink.net, woodl-@pacbell.net
Date: Tuesday, 17 March, 2009, 2:34 AM
Lots of good ideas Brad. Some have been described or tried before,
and sometimes something is tried and works, and is forgotten
anyway. Building models is very educational.
The lift of hydrogen is not twice that of helium, even though it weighs
half as much. Lift is the weight of the volume of atmosphere
displaced minus the weight of the structure doing the
displacing.
At 10:01 PM 3/15/2009, Brad Cobb wrote:
I've found the discussions of
"personal mini-blimp" one-person airships fruitful, fun and
eye-opening thus far; it's gotten the old Grey matter stirred up and
curiosity bump itching and scratching! <grin>
http://home.teleport.com/~reedg/whitedwarf.html
I must say: surprised that so small an envelope would have sufficient
lift!
Now as how to go faster whilst being more stable, and other "Little
Blimp" group goals?
HHHhhhuuuuuummmmmmmmm...!
How about considering a flattened, domed, saucer shape?
This ought to be somewhat immune to winds quartering, and smooth flight
in any direction, further allowing for ease in engine working through
whatever winds might exist, combining features for most efficiency
available in flight envelope.
Now as to reducing friction and increasing performance further....how
about getting rid of the gondola, and moving THAT drag up into the
balloon structure, so that the domed, flattened saucer shape will be able
to shield and smooth airstream around the now-enclosed pilot
position? Bit like going from sitting on the wing of a Curtis
pusher, to sitting in a cockpit of WW1 fighter, eh, what?
By making the lift envelope a flattened saucer shape with a pilot
observation dome, visibility ought to be high enough to observe out above
the domed saucer shaped top section.
To maintain stability, motors, lift bags, solar/heat collection stations
would have to be located so as taking into account center of gravity/lift
and other flight sharacteristics.
Keeping costs down; Why not consider providing for maximum visibility
utilizing 6 mil clear plastic sheeting (ultraviolet inhibitor within
plastic's chemistry), which could be fitted upon a framework of PVC
pipping (PVC attractive as being widely available, flexible; able to
withstand internal pressure <for increasing strength, frame would be
pressurized> as well about as cheap as anything you can buy!)?
This construction methodology works well for locals in building their
DIY, backyard homegrown greenhouse structures.
Continuing concerning design concepts inside described pressurized
framework, this being covered with 6 mil plastic, and internally
sectioned into separate airbag compartments for increased safety and
control. <Life rafts use sections as described for
safety/reliability>
1. Not politically correct, and probably have to investigate
legalities (here in California when smog exceeds limits, breathing
becomes illegal), BUT much easier to produce (IE: Joe Cell, Hydroxy
boost, et al) being MUCH cheaper: hydrogen(!) VS helium.
Hydrogen has twice the lift as helium, allowing for a much smaller
centralized lift bag, permitting further safety layers of protection
using additional bags enclosing the hydrogen bag.
For further safety, venting any leaking hydrogen gas, one could follow
"HelioStat's" example using the sun's rays with solar
collection/heating of surrounding airbags to manipulate lift, allowing
heated exhaust air with venting to aid thrust and maneuvering
motors.
There are sold hot-air solar-powered heat engines (Popular Mechanics ran
articles how-to build your own large versions-Ya gotta roll up yer
sleeves and LOOK in local library-I haven't the plans or time to find
them for you!) which could be fed the heated exhaust air for the lift
bags/solar collector.
The focusing collector capability of the saucer disc shape could (with
cheap "Space-blanket" reflective material) be controlled to
provide the heat collection for both lifting, and powering the heat
engines for thrust and control.
Somebody out there with a lot more engineering savvy than I would be
capable to design a computer chip to control and keep energies maximized,
interpreting commands via a pilot's video-game sort of joystick (again
cheap and plentiful-engineering brains not so much).
Another innovation taken from current large airship design which ought
apply well for our purposes, being drive motors fully directional,
pivoting all directions and rotating with enclosing shrouds (prop safety
and thrust improvement) having props feather; reversing; allows for
greater maneuverability and control, providing for thrust to be directed
as benefits VTOL.
Taken altogether, these above mentioned design features could lessen need
for ground crew, one 'Little Blimp's" groups admirable goal.
Goodyear came up with a semi-rigid design in it's inflatable airplanes,
which could serve purpose of light weight and strength anywhere needed in
the saucer-blimp design. There is an answer to maintaining strength
and eliminating weight though lessening need for additional weighty
reinforcing structure.
Not exactly sure what the diameter of envisioned "Flying Saucer
Blimp" would be, but a compromise in keeping circumference to a
minimum would include allowing more volume on the topside of the saucer,
IE: dome with pilot "bubble" atop. Calculations anyone
(doubtless these would be applied for helium lift gas)? Guesses,
maybe Professors?
Using directional alignment motors (a la Sunstat solar powered balloon)
would allow for smaller amount of expensive lift gas, while reducing need
for ballast.
Computer (or even solar cells driving axis-rotational motors, being set
such as sunlight falling on solar cells to power props only when off
maximum solar exposure orientation) control could be engineered to keep
disc-shaped solar collector always facing sun) provided to maximize solar
collection/lift, as provided by and interpreting pilot commands <via
joystick, for example>
Not to forgo or forget the concepts of adding high voltage static
electric pulses (NOT to hydrogen lift gasses, of course!!!) at high
frequencies to envelope, to experimentally increase lift (a la
lifters).
If the pilot's position was centralized in the bubble atop saucer dome,
the pilot could swivel his chair to keep properly oriented to direction
of flight, as desired-and with today's electronic revolution, wireless
video could also provide visual inputs, along with GPS.
If desirable, doubtless a computer could be arranged to allow parts of
the internal working to rotate (as in Frisbee, and as static electric
generator) for further stability/lift enhancement (ala Searl disc) whilst
keeping the pilot station stationary, directed however
preferred.
Yummy food for thought! <grin> :-D
Now as to making all concepts relative come together and work as cohesive
whole, check out some links as to those who have pioneered and are as
doin":
http://www.treehugger.com/files/2009/02/cool-earth-solars-cool-headed-apprach-to-saving-the-world.php?daylife=1&dcitc=daylife-article
http://pagesperso-orange.fr/ballonsolaire/en-presentation.htm
http://www.nott.com/Pages/records.php
http://www.24en.com/day/images/data/20070911.jpg
http://jnaudin.free.fr/lifters/main.htm
http://en.wikipedia.org/w/index.php?title=Ionocraft&printable=yes
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