Saturday, July 21, 2012

Adventures in Unconventional Propeller Flight

The Austrian D-Dalus design is meant to be the "hummingbird" of this class of unconventional rotor designs. Think of how maneuverable a hummingbird can fly, while still achieving a very high top speed.

The D-Dalus has the potential to be the "special ops" platform of choice for rapid insertions, extractions, and quick stealthy near ground-level attacks.
A flying machine with no airfoil, rotor or jet propulsion can travel where most cannot: in very tight spaces and through terrible weather.


The craft’s four rotors spin at 2,200 rpm, and six blades attached to carbon-fiber disks create directional thrust. The blades act as mini airfoils, their angle of attack constantly shifting in relation to rotation. For vertical lift, a blade’s leading edge rises away from the center of the disk at the top of its rotation and toward the center of the disk at the bottom [pictured], creating a pressure differential.


Existing bearings were unable to withstand 1,000 Gs of force between the carbon-fiber disks and their blades and still deliver some degree of maneuverability. Engineers at IAT21 developed their own bearings, shaped like metal barrels, that hold up to the force better than spheres (think: arches) but can still roll enough for the blades to move. _Popsci

The Fanwing, seen below, is more of a slow semi-hovering craft, meant to linger overhead for extended periods of observational time. Fanwing is more of a recon aircraft.

Fanwing Simulation

The cycloidal drive propeller below was taken from an earlier marine drive -- used for tugboats and other highly maneuverable water craft.

When applied to a flying craft, the cycloidal drive has the potential to function as either a helicopter replacement, or as a drive for a larger airship or "blimp."

Cycloidal Drive Simulation

The Voith Schneider propeller (VSP), also known as a cycloidal drive (CD) is a specialized marine propulsion system (MPS). It is highly maneuverable, being able to change the direction of its thrust almost instantaneously. It is widely used on tugs and ferries.

From a circular plate, rotating around a vertical axis, a circular array of vertical blades (in the shape of hydrofoils) protrude out of the bottom of the ship. Each blade can rotate itself around a vertical axis. The internal gear changes the angle of attack of the blades in sync with the rotation of the plate, so that each blade can provide thrust in any direction, very similar to the collective and cyclic of helicopter flight controls. _ngcraft


Wednesday, July 11, 2012

From Hypersonics to Space Planes: A New Era

The US Defense Department's DARPA is resuming efforts to develop a hypersonic "X-plane (HX). DARPA's plans are ambitious, and will require very rapid innovation and development in order to meet its schedule -- achieving a rocket launched hypersonic craft by the year 2016.
The hypersonic X-plane (HX) will launch using a disposable rocket stack, unlike previous models which have used space launch rockets, then begin its hypersonic glide. The plan is for the "highly manoeuvrable" vehicle to be recoverable, meaning it will either return to Earth with the help of a parachute, or possibly land on a runway.

Darpa is reigniting the hypersonic flight research with the intention of launching future missions ranging from "space access to survivable, time-critical transport [troop deployment] to conventional prompt global strike." _Wired

Development of the Skylon spaceplane has passed a critical milestone following tests on the key component for its Sabre engine.

The engine, being developed by Reaction Engines Ltd, looks set to revolutionise not only space travel but also air transport around the world.

It promises to allow a new generation of aircraft to fly from one side of the Earth to the other, e.g. the UK to Australia, in just four hours instead of the 22 or so needed nowadays.

But it will also provide sufficient boost to send the Skylon spaceplane into orbit where it could deliver satellites or link up with the International Space Station.

What makes Sabre different from other aircraft engines is a revolutionary ability to switch from an air-breathing mode to that of a rocket engine.

This hybrid function will allow it to power aircraft at up to five times the speed of sound within the atmosphere or directly into Earth orbit at 25 times the speed of sound. _Wired
Hybrid engines of this type may provide a crucial weight savings in the early stages of the development of workable hypersonic craft. Engineers need to be cautious in avoiding excessive complexity in this new type of engine. KISS (Keep it simple, stupid!) is the key, as far as it is possible.
The type of craft pictured above has been discussed by Brian Wang in multiple articles. It is powered in multiple ways: by chemical rocket, air-breathing propulsion, by MHD, and by dense plasma focus fusion -- all of which should combine to allow it to travel at very high velocities. It will require significant development of several components, including the focus fusion module, before it becomes practical.

The Stratolaunch air launch system pictured above allows for a very versatile approach to orbital insertions. The huge carrier craft serves as the "first stage" of the launch system, carrying the launch craft to altitude and providing a wider range of opportunistic launch attitudes than is conveniently possible for fixed launch sites.

Ideally, all components of the system would be reusable, to save on costs. There are several tradeoffs to be made in terms of launch platforms, launch attitudes, propulsion strategies: pure vs. hybrid vs multiple etc., numbers of propulsion stages, orbital vs sub-orbital flight, method of terrestrial return, and so on.

Hypersonic flight inside the Earth's atmosphere is very punishing, physically. Better types of outer covering materials are needed to provide greater durability for multiple flights. Alternatively, inexpensive spray-on outer skins may be applied prior to each flight, which will naturally ablate in the course of the flight.

An earlier Al Fin article on this topic


Sunday, July 01, 2012

Using Nuclear "Waste" to Provide Thousands of Years of Electrical Power and Industrial Process Heat

This article was previously published on the Al Fin Energy blog

Scientists at Argonne National Labs are developing ways of utilising 95% of the energy in Uranium fuel rods -- rather than the mere 4% or so currently being extracted. They are developing new techniques of chemical separation of waste from fuel, and more efficient ways of burning the recycled fuel after being separated from the waste.
When used fuel comes out of a light-water reactor, it’s in a hard ceramic form, and almost all of it is still just uranium – about 95 percent, along with one percent other long-lived radioactive elements, called actinides. Both of these can be recycled as fuel. The remaining four percent are fission products, which are truly unusable.

Pyroprocessing begins by chopping the ceramic fuel into little pieces and converting it into metal. Then it’s submerged in a vat of molten salts, and an electric current separates out uranium and other reusable elements, which can be shaped back into fuel rods.

The truly useless fission products stay behind to be removed from the electrorefiner and cast into stable glass discs. These leftovers do have to be put into permanent storage, but they revert back to the radioactivity of naturally occurring uranium in a few hundred years – far less than the thousands of years that untreated used fuel needs to be stored. _PO

One of the reasons why so little uranium is used is that almost every commercial reactor today is a type called a light-water reactor, or LWR. While LWRs are good at many things, they aren’t designed to wring every last watt of energy out of fuel. But LWRs aren’t the only type of reactor. Another class, called fast reactors, boasts the ability to “recycle” used fuel to get much more energy out of it. The main difference between the types of reactors is what cools the core. LWRs use ordinary water. Fast reactors use a different coolant, such as sodium or lead. This coolant doesn’t slow the neutrons as much, and consequently, the reactor can fission a host of different isotopes. This means that fast reactors can get electricity out of many kinds of fuel, including all of that leftover used fuel from LWRs. (LWRs can burn recycled fuel too, with some modification, but they aren’t as good at it.) _PO

More on pyroprocessing used nuclear fuel (PDF)

Extracting 30 times more energy from the same amount of nuclear fuel will help to make the same amount of fuel go much further. While we are being more efficient at using the nuclear fuel (and nuclear wastes) that we already have, we can learn many more ways to generate energy from mass.

The limits are in our heads.


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