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Light Electric Rotorcraft



 
 
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  #11  
Old October 3rd 05, 01:16 AM
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Well, some research group is claiming to have come up with a new way to
store hydrogen, which may make it more feasible as a vehicular fuel:

http://www.sciencedaily.com/releases...0907102549.htm

http://denmark.dk/portal/page?_pagei..._schema=PORTAL

http://www.amminex.com/

http://www.thewatt.com/modules.php?n...rticle&sid=763

http://www.investindk.com/visNyhed.asp?artikelID=13670

But admittedly, it's very new and as yet untried in the marketplace.

  #12  
Old October 3rd 05, 02:47 AM
Frank van der Hulst
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Richard Riley wrote:
On Mon, 03 Oct 2005 10:52:49 +1300, Frank van der Hulst
wrote:

wrote:
: And hydrogen is a lightweight fuel too, for lower fuel load.
: But suppose you want some extra juice sometimes, for more
: maneuvering/lifting power.
:
:Hydrogen is only a lightweight fuel in its uncompressed, gaseous form.
:In fact, in terms of energy per Kg, hydrogen is not a good fuel. Storing
:hydrogen in sufficient density to be useful requires strong (read heavy)
:tanks.

Liquid hydrogen has the most energy per pound of any chemical fuel.
It has 39,000 Wh/kg, gasoline only has 12,200 Wh/kg.

Unfortunately it is also not very dense - even in it's liquid form.
Liquid hydrogen has a density of 0.07 grams per cubic centimeter,
whereas water has a density of 1.0 g/cc and gasoline about 0.75 g/cc.


Oops, yes, you're right. It was in terms of energy/volume that hydrogen
is poor, NOT energy/mass.

Therefore the container to hold your liquid hydrogen needs to be large.
It also needs to be strong, and therefore heavy.

Therefore, as Richard said, hydrogen won't be a practical aircraft fuel
unless the storage issue can be solved.
  #13  
Old October 3rd 05, 03:11 AM
Morgans
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"Frank van der Hulst" wrote

It *might* be possible that diesel-electric system would be lighter than
pure electric or pure diesel.


I'm from Oklahoma. Show me!

A small diesel could be optimised to run continuously at its most
economical RPM,


It would already have to have a gearbox for a heli, so it can run whatever
RPM you want. An electric motor would also have a gearbox. Yes I know,
there are low speed electric motors, but they are huge and heavy.

producing only a little more electricity than needed to
drive the rotor in level flight.


There will always be losses, driving a generator, then a motor. You will
have to have at least 10% more power output by the diesel motor, just to
break even, and more than that to charge batteries.

So lets see, we have to have a gearbox both ways, no change in weight
between the two. We will have to have a bigger diesel to take care of
losses, so penalty goes to electric. We would have to have batteries for
electric, so more penalty for electric. Since our electric has gotten
heavier, we will have to have a bigger engine, and more fuel, so BIG penalty
for electric.

For additional power, electricity from the battery would also drive the

rotor. When descending, the battery gets charged faster.

What you are talking about is like an autorotation. The blades in an
autorotation have to go to negative pitch, just to make the blades maintain
RPM, and to get more power to generate electricity than a plain
autorotation, they would have to be at even more negative pitch. You would
have to descend so fast to get the rotor to produce electricity, your
passengers would freak!
--
Jim in NC

  #14  
Old October 3rd 05, 03:16 AM
Frank van der Hulst
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Morgans wrote:
"Frank van der Hulst" wrote
A small diesel could be optimised to run continuously at its most
economical RPM,



It would already have to have a gearbox for a heli, so it can run whatever
RPM you want. An electric motor would also have a gearbox. Yes I know,
there are low speed electric motors, but they are huge and heavy.


The whole point of these wheelmotors is that they are smaller than
equivalent DC motors, and turn at low speeds. The numbers I've seen are
110-150rpm. See http://www.smartmotor.no/products/quiet_traction/ --
this talks about wheelmotors in relation to wheelchairs, and claims
twice the efficiency over traditional DC+gearbox systems.

You could think of the generator/motor combination as an electrical
rather than mechanical gearbox.

Another interesting site is http://www.killacycle.com/ -- an
electrically powered drag bike that gets 9.450 seconds @152.07 mph over
the 1/4 mile. Still a long way from the 5.895 @ 238.22 nitro powered
world record though.

producing only a little more electricity than needed to
drive the rotor in level flight.



There will always be losses, driving a generator, then a motor. You will
have to have at least 10% more power output by the diesel motor, just to
break even, and more than that to charge batteries.

So lets see, we have to have a gearbox both ways, no change in weight
between the two. We will have to have a bigger diesel to take care of
losses, so penalty goes to electric. We would have to have batteries for
electric, so more penalty for electric. Since our electric has gotten
heavier, we will have to have a bigger engine, and more fuel, so BIG penalty
for electric.


But the diesel only ever runs at one speed... it's most economical. I'm
assuming that there will be significant weight savings in that. I may be
wrong in that assumption.

I do know that having a car petrol engine which can potentially deliver
a lot more horsepower means that it uses more fuel at lower horsepower
output. Maybe this relationship doesn't apply to diesels.

For additional power, electricity from the battery would also drive the


rotor. When descending, the battery gets charged faster.

What you are talking about is like an autorotation.


No. I'm saying that when descending, less power from the
engine/generator goes to the rotor, leaving more to go to the battery.
  #15  
Old October 3rd 05, 03:17 AM
red
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manofsan,
Differential rotor speeds -will- rotate the aircraft, but will that turn
the aircraft, in level flight, or just rotate the aircraft in yaw? The
hard part about differential rotor speeds is not in yawing the aircraft.
The hard part is NOT yawing the aircraft, constantly. Gyros might do the
job of balancing rotor speeds for you (with *more* expense and complexity),
but you would still lose the safety advantages of simplicity, and
maintaining control if one motor fails. The spider gears and one motor
might not maintain altitude, but you could still move forward and steer as
you descend slowly, to select a good place for the BRS deployment. In a
deployment situation, one motor could still be used for a last-minute burst
of power, to soften the parachute landing.
Recovering energy by auto-rotation would mean a lot of weight and
complexity for very small gains. Aircraft are like boats, always fighting
drag, and if aircraft could get anything back on descent, they would have
to expend a lot more energy to do the climb, first. You can never win
against drag, so at best, we just try to cut our losses, up front.
I hear Boeing is working on a single-engine plane using a fuel cell and an
electric motor to provide propellor thrust, so that technology seems
realistic. New hydrogen storage systems can derive their hydrogen "fuel"
from other liquids, rather than highly pressurized hydrogen gas, which
would need strong and heavy tanks.
The WaveCrest motor idea looks good, too.
--
(Replies *will* bounce, unless you delete
the letter A from my email address)
Cheers,
Red

wrote:

Hi red, thanks for the great ideas.

Hmm, I read about how a coax design can use differential rotation speed
between the 2 rotors for the purpose of turning the aircraft. That'd be
pretty easy to do with a wheelmotor for each rotor.

Here's a link to a new kind of wheelmotor which is attracting
attention:

http://www.wavecrestlabs.com

The company is headed by General Wesley Clark, former NATO commander.
Regarding portable fuel cell for propulsion, here's another link:

http://www.intelligent-energy.com/in...6&artID=3 709

And hydrogen is a lightweight fuel too, for lower fuel load.
But suppose you want some extra juice sometimes, for more
maneuvering/lifting power. Then use the new Toshiba battery:

http://www.dpreview.com/news/0503/05...sh1minbatt.asp

It can apparently discharge and absorb energy at a very high rate. This
might be useful for using regenerative braking to recover energy from
your rotor when you're reducing airspeed/altitude, since a wheelmotor
can convert torque/rpm back into electricity. Once you've landed,
regenerative braking would allow you to quickly bring the rotors to a
stop while recovering energy from them.

I'd also imagine the electric motors would be quieter too, so your
eardrums don't take a beating.

  #16  
Old October 3rd 05, 05:56 AM
Flyingmonk
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Richard Riley wrote:
So you build your aircraft engine so it's best fuel economy is at full
throttle. If it's not getting it's best economy during decent and
landing, that's fine, it's at idle anyway.


You must be thinking of fixed-wings Richard. A helo's engine only goes
to idle during and auto not during decent nor landing. Actually during
landing a helo uses a whole lot of power, more than while flying (due
to loss of translational lift).

Bryan "The Monk" Chaisone

  #17  
Old October 3rd 05, 06:06 PM
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Richard Riley wrote:


Believe me, I've been doing the trade studies for the last 3 years.
You can't buy a COTS fuel cell, and the volume required to store H2
(not to mention the handling difficulties) mean it won't be used as a
fuel for anything but very high end, special purpose machines for a
very long time to come.


How does liquified methane (at high pressure, ambient temperature) look
to power a conventional internal combustion engine, or perhaps even a
methane fuel cell?

I think that methane requires somewhere around 3700 psi to compress it
into a liquid at normal temperature, surely there's got to be some
carbon-fibre reinforced, aluminum polyester-lined composite tank
technology available nowadays that can handle the pressures necessary
to handle non-cryo liquified methane, without being prohibitively heavy
for an aircraft. Methane has a motor octane rating of around 130 in a
piston engine too, and you certainly won't be needing a fuel pump, just
a good strong pressure regulator / phase change heat
exchanger/gassifier at the tank's output valve to feed a direct fuel
injection metering system for the engine. You could probably employ the
phase change heat exchanger as a clever way to air-condition the cabin
too! (just make damn sure of no leaks)

  #18  
Old October 4th 05, 02:59 AM
Flyingmonk
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Richard Riley wrote:
What percentage of a helicopter's flying lifecycle is spent at or near
it's rated power output, and what percentage is spent at a small
fraction of that rated power output?


About 100% of the time Richard, more power to fly higher, less to fly
lower. It only goes into idle while NOT flying.

Bryan "The Monk" Chaisone

  #19  
Old October 4th 05, 04:39 AM
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Here is yet another interesting design from that same website:

http://www.gizmag.com/go/3107/

I wonder if this could be converted into a gyroplane? Here's how I
imagine it.

sorry, my ascii art isn't good enough to reproduce the chassis, so I
just drew the tires (which of course have the electric wheelmotors in
them):


==========
|
|

( o----------------+ ========

|
|
===========

Note that the "o-------------+" is supposed to be the rotor mast folded
back along the longitudinal axis of the craft. Okay, I guess that would
require the craft to have some kind of upper fuselage canopy for the
mast to attach to. The "o" is the base of the mast which attaches to
the upper fuselage canopy, while the "+" is where the rotor head would
be.
But the rotor mast wouldn't have to be very long, since it doesn't need
much height for its rotors to clear the rest of the craft. The rotors
themselves would be bent forward in V-shape from the rotorhead, with
their tips clipped to the sides of the fuselage/chassis.

So the wheelmotors roll the craft along the ground until it picks up
lots of speed. Then the rotor mast pops upright, the rotors are freed
and start spinning overhead. The craft then takes off like a gyroplane,
and once airborn the front tires swivel to face frontwards to act as
fan-props:

||
||____
|| |
|| |


( + =======


|| |
||___|__
||
||


Heh, very James Bond-ish, huh? ;P

 




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